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OpenCV-Python教程（9）（10）（11）：使用霍夫变换检测直线直方图均衡化轮廓检测

2018-01-05 20:17 691 查看

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<h1><a name="t0"></a>OpenCV-Python教程（9、使用霍夫变换检测直线）</h1>





相比C++而言，<a title="Python知识库" class="replace_word" style="color:rgb(223,52,52); text-decoration:none; font-weight:bold" href="http://lib.csdn.net/base/11" target="_blank">Python</a>适合做原型。本系列的文章介绍如何在Python中用OpenCV图形库，以及与C++调用相应OpenCV函数的不同之处。这篇文章介绍在Python中使用OpenCV的霍夫变换检测直线。 





提示： 



<ul style="color:rgb(51,51,51); font-family:Arial; font-size:14px; line-height:26px">

<li>转载请详细注明原作者及出处，谢谢！ 

</li><li>本文介绍在OpenCV-Python中使用霍夫变换检测直线的方法。</li><li>本文不介详细的理论知识，读者可从其他资料中获取相应的背景知识。笔者推荐清华大学出版社的《<a style="color:rgb(51,102,153); text-decoration:none" href="http://www.amazon.cn/%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86%E4%B8%8E%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%A7%86%E8%A7%89%E7%AE%97%E6%B3%95%E5%8F%8A%E5%BA%94%E7%94%A8-%E5%B8%95%E7%A7%91%E5%B0%94/dp/B0083PY050/ref=sr_1_1?ie=UTF8&qid=1373614562&sr=8-1&keywords=%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86%E4%B8%8E%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%A7%86%E8%A7%89%E7%AE%97%E6%B3%95%E5%8F%8A%E5%BA%94%E7%94%A8%28%E7%AC%AC2%E7%89%88%29"
target="_blank">图像处理与计算机视觉算法及应用(第2版)</a> 》。</li></ul>

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t1"></a>

<a name="t0" style="color:rgb(51,102,153)" target="_blank"></a>霍夫变换 

</h2>



Hough变换是经典的检测直线的算法。其最初用来检测图像中的直线，同时也可以将其扩展，以用来检测图像中简单的结构。 





OpenCV提供了两种用于直线检测的Hough变换形式。其中基本的版本是cv2.HoughLines。其输入一幅含有点集的二值图（由非0像素表示），其中一些点互相联系组成直线。通常这是通过如Canny算子获得的一幅边缘图像。cv2.HoughLines函数输出的是[float, float]形式的ndarray，其中每个值表示检测到的线(ρ , θ)中浮点点值的参数。下面的例子首先使用Canny算子获得图像边缘，然后使用Hough变换检测直线。其中HoughLines函数的参数3和4对应直线搜索的步长。在本例中，函数将通过步长为1的半径和步长为π/180的角来搜索所有可能的直线。最后一个参数是经过某一点曲线的数量的阈值，超过这个阈值，就表示这个交点所代表的参数对(rho,

theta)在原图像中为一条直线。具体理论可参考<a style="color:rgb(51,102,153); text-decoration:none" href="http://www.opencv.org.cn/opencvdoc/2.3.2/html/doc/tutorials/imgproc/imgtrans/hough_lines/hough_lines.html" target="_blank">这篇文章</a>。

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#coding=utf-8 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-lea
4000
ding-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

import cv2 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

import numpy as np </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

img = cv2.imread("/home/sunny/workspace/images/road.jpg", 0) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

img = cv2.GaussianBlur(img,(3,3),0) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

edges = cv2.Canny(img, 50, 150, apertureSize = 3) </li><li class="alt" style="border-left-width:3px; border-style:none
none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

lines = cv2.HoughLines(edges,1,np.pi/180,118) #这里对最后一个参数使用了经验型的值 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

result = img.copy() </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

for line in lines[0]: </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 rho = line[0] #第一个元素是距离rho </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 theta= line[1] #第二个元素是角度theta </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 print rho </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 print theta </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 if (theta < (np.pi/4. )) or (theta > (3.*np.pi/4.0)): #垂直直线 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important">

 #该直线与第一行的交点 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 pt1 = (int(rho/np.cos(theta)),0) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 #该直线与最后一行的焦点 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 pt2 = (int((rho-result.shape[0]*np.sin(theta))/np.cos(theta)),result.shape[0]) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

 #绘制一条白线 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 cv2.line( result, pt1, pt2, (255)) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 else: #水平直线 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px
0px 10px!important; background-color:rgb(248,248,248)">

 # 该直线与第一列的交点 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 pt1 = (0,int(rho/np.sin(theta))) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 #该直线与最后一列的交点 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 pt2 = (result.shape[1], int((rho-result.shape[1]*np.cos(theta))/np.sin(theta))) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 #绘制一条直线 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 cv2.line(result, pt1, pt2, (255), 1) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow('Canny', edges ) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.imshow('Result', result) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.waitKey(0) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.destroyAllWindows() </li></ol>

</div>



结果如下：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130712153232796?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 









注意：



在C++中，HoughLines函数得到的结果是一个向量lines，其中的元素是由两个元素组成的子向量(rho, theta)，所以lines的访问方式类似二维数组。因此，可以以类似：

<div class="dp-highlighter bg_cpp" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[cpp] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/9253823#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/9253823#" target="_blank">copy</a><div style="left: 470px; top: 2115px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_2" width="18" height="18" align="middle"
id="ZeroClipboardMovie_2" pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" type="application/x-shockwave-flash" wmode="transparent" flashvars="id=2&width=18&height=18"
allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:563px; top:2302px; width:18px; height:18px; z-index:99">

</div>

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</div>

<ol class="dp-cpp" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

std::vector<cv::Vec2f>::const_iterator it= lines.begin(); </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

float rho= (*it)[0]; </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

float theta= (*it)[1]; </li></ol>

</div>







这样的方式访问rho和theta。



而在Python中，返回的是一个三维的np.ndarray！。可通过检验HoughLines返回的lines的ndim属性得到。如：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/9253823#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/9253823#" target="_blank">copy</a><div style="left: 487px; top: 2290px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_3" width="18" height="18" align="middle"
id="ZeroClipboardMovie_3" pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" type="application/x-shockwave-flash" wmode="transparent" flashvars="id=3&width=18&height=18"
allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:2491px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

lines = cv2.HoughLines(edges,1,np.pi/180,118) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

print lines.ndim </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#将得到3 </li></ol>

</div>

至于为什么是三维的，这和NumPy中ndarray的属性有关（关于NumPy的相关内容，请移步至<a style="color:rgb(51,102,153); text-decoration:none; font-family:Arial; font-size:14px; line-height:26px" href="http://blog.csdn.net/sunny2038/article/details/9002531"
target="_blank">NumPy简明教程</a>），如果将HoughLines检测到的的结果输出，就一目了然了：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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<div style="position:absolute; left:587px; top:2666px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#上面例子中检测到的lines的数据 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

3 #lines.ndim属性 </li><li style="border-left-width:3px;
border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

(1, 5, 2) #lines.shape属性 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

#lines[0] </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

[[ 4.20000000e+01 2.14675498e+00] </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 [ 4.50000000e+01 2.14675498e+00] </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 [ 3.50000000e+01 2.16420817e+00] </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 [ 1.49000000e+02 1.60570288e+00] </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 [ 2.24000000e+02 1.74532920e-01]] </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

=============== </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#lines本身 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px
0px 10px!important; background-color:rgb(248,248,248)">

[[[ 4.20000000e+01 2.14675498e+00] </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 [ 4.50000000e+01 2.14675498e+00] </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 [ 3.50000000e+01 2.16420817e+00] </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 [ 1.49000000e+02 1.60570288e+00] </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 [ 2.24000000e+02 1.74532920e-01]]] </li></ol>

</div>

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t2"></a>

<a name="t1" style="color:rgb(51,102,153)" target="_blank"></a>概率霍夫变换</h2>







观察前面的例子得到的结果图片，其中Hough变换看起来就像在图像中查找对齐的边界像素点集合。但这样会在一些情况下导致虚假检测，如像素偶然对齐或多条直线穿过同样的对齐像素造成的多重检测。



要避免这样的问题，并检测图像中分段的直线（而不是贯穿整个图像的直线），就诞生了Hough变化的改进版，即概率Hough变换（Probabilistic Hough）。在OpenCV中用函数cv::HoughLinesP 实现。如下：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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<div style="position:absolute; left:587px; top:3217px; width:18px; height:18px; z-index:99">

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<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#coding=utf-8 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

import cv2 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

import numpy as np </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

img = cv2.imread("/home/sunny/workspace/images/road.jpg") </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

img = cv2.GaussianBlur(img,(3,3),0) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

edges = cv2.Canny(img, 50, 150, apertureSize = 3) </li><li class="alt" style="border-left-width:3px; border-style:none
none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

lines = cv2.HoughLines(edges,1,np.pi/180,118) </li><li style="border-left-width:3px; border-style:none none none solid;
border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

result = img.copy() </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

#经验参数 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important">

minLineLength = 200 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px
0px 10px!important; background-color:rgb(248,248,248)">

maxLineGap = 15 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important">

lines = cv2.HoughLinesP(edges,1,np.pi/180,80,minLineLength,maxLineGap) </li><li style="border-left-width:3px; border-style:none
none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

for x1,y1,x2,y2 in lines[0]: </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 cv2.line(img,(x1,y1),(x2,y2),(0,255,0),2) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow('Result', img) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.waitKey(0) </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.destroyAllWindows() </li></ol>

</div>

结果如下：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130712153437515?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast">



未完待续。。。

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t3"></a>

<a name="t2" style="color:rgb(51,102,153)" target="_blank"></a>参考资料：</h2>



1、《Opencv2 Computer Vision Application Programming Cookbook》



2、《OpenCV References Manule》

 

 



 



<h1><a name="t4"></a>OpenCV-Python教程（10、直方图均衡化）</h1>





相比C++而言，<a title="Python知识库" class="replace_word" style="color:rgb(223,52,52); text-decoration:none; font-weight:bold" href="http://lib.csdn.net/base/11" target="_blank">Python</a>适合做原型。本系列的文章介绍如何在Python中用OpenCV图形库，以及与C++调用相应OpenCV函数的不同之处。这篇文章介绍在Python中使用OpenCV和NumPy对直方图进行均衡化处理。 





提示： 



<ul style="color:rgb(51,51,51); font-family:Arial; font-size:14px; line-height:26px">

<li>转载请详细注明原作者及出处，谢谢！ 

</li><li>本文不介详细的理论知识，读者可从其他资料中获取相应的背景知识。笔者推荐清华大学出版社的《<a style="color:rgb(51,102,153); text-decoration:none" href="http://www.amazon.cn/%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86%E4%B8%8E%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%A7%86%E8%A7%89%E7%AE%97%E6%B3%95%E5%8F%8A%E5%BA%94%E7%94%A8-%E5%B8%95%E7%A7%91%E5%B0%94/dp/B0083PY050/ref=sr_1_1?ie=UTF8&qid=1373614562&sr=8-1&keywords=%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86%E4%B8%8E%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%A7%86%E8%A7%89%E7%AE%97%E6%B3%95%E5%8F%8A%E5%BA%94%E7%94%A8%28%E7%AC%AC2%E7%89%88%29"
target="_blank">图像处理与计算机视觉算法及应用(第2版)</a> 》，对于本节的内容，建议直接参考<a style="color:rgb(51,102,153); text-decoration:none" href="http://zh.wikipedia.org/zh-cn/%E7%9B%B4%E6%96%B9%E5%9B%BE%E5%9D%87%E8%A1%A1%E5%8C%96"
target="_blank">维基百科直方图均衡化</a>，只需看下页面最后的两幅图就能懂了。</li></ul>



本文内容： 



<ul style="color:rgb(51,51,51); font-family:Arial; font-size:14px; line-height:26px">

<li>使用查找表拉伸直方图</li><li>使用OpenCV和NumPy的函数以不同的方式进行直方图均衡化 

</li></ul>



在某些情况下，一副图像中大部分像素的强度都集中在某一区域，而质量较高的图像中，像素的强度应该均衡的分布。为此，可将表示像素强度的直方图进行拉伸，将其平坦化。如下：



<img style="border:none; max-width:100%" alt="" src="http://upload.wikimedia.org/wikipedia/commons/7/71/Histogrammspreizung.png"> 

图来自维基百科

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t5"></a>

<a name="t0" style="color:rgb(51,102,153)" target="_blank"></a>实验数据</h2>



本节的实验数据来自维基百科，原图如下：



<img style="border:none; max-width:100%" alt="" src="http://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Unequalized_Hawkes_Bay_NZ.jpg/800px-Unequalized_Hawkes_Bay_NZ.jpg">



其直方图为：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130724201943453?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 



<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t6"></a>

<a name="t1" style="color:rgb(51,102,153)" target="_blank"></a>使用查找表来拉伸直方图 

</h2>



在图像处理中，直方图均衡化一般用来均衡图像的强度，或增加图像的对比度。在介绍使用直方图均衡化来拉伸图像的直方图之前，先介绍使用查询表的方法。 





观察上图中原始图像的直方图，很容易发现大部分强度值范围都没有用到。因此先检测图像非0的最低（imin）强度值和最高（imax）强度值。将最低值imin设为0，最高值imax设为255。中间的按255.0*(i-imin)/(imax-imin)+0.5)的形式设置。



实现的任务主要集中在查询表的创建中，代码如下：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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</div>

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</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

minBinNo, maxBinNo = 0, 255 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#计算从左起第一个不为0的直方图位置 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

for binNo, binValue in enumerate(hist): </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 if binValue != 0: </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px
3px 0px 10px!important; background-color:rgb(248,248,248)">

 minBinNo = binNo </li><li class="alt" style="border-left-width:3px; border-style:none none
none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 break </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

#计算从右起第一个不为0的直方图位置 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

for binNo, binValue in enumerate(reversed(hist)): </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 if binValue != 0: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important">

 maxBinNo = 255-binNo </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 break </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print minBinNo, maxBinNo </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#生成查找表，方法来自参考文献1第四章第2节 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

for i,v in enumerate(lut): </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

 print i </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 if i < minBinNo: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 lut[i] = 0 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 elif i > maxBinNo: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 lut[i] = 255 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 else: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 lut[i] = int(255.0*(i-minBinNo)/(maxBinNo-minBinNo)+0.5) </li></ol>

</div>

查询表创建完成后，就直接调用相应的OpenCV函数即可，这里调用的是cv2.LUT函数：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:2975px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#计算 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px
0px 10px!important; background-color:rgb(248,248,248)">

result = cv2.LUT(image, lut) </li></ol>

</div>







cv2.LUT函数只有两个参数，分别为输入图像和查找表，其返回处理的结果，完整代码如下：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/9403059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:3106px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#coding=utf-8 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

import cv2 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

import numpy as np </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

image = cv2.imread("D:/test/unequ.jpg", 0) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

lut = np.zeros(256, dtype = image.dtype )#创建空的查找表 </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

hist= cv2.calcHist([image], #计算图像的直方图 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 [0], #使用的通道 </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 None, #没有使用mask </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 [256], #it is a 1D histogram </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 [0.0,255.0]) </li><li style="border-left-width:3px;
border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

minBinNo, maxBinNo = 0, 255 </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#计算从左起第一个不为0的直方图柱的位置 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

for binNo, binValue in enumerate(hist): </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 if binValue != 0: </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px
3px 0px 10px!important; background-color:rgb(248,248,248)">

 minBinNo = binNo </li><li class="alt" style="border-left-width:3px; border-style:none none
none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 break </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

#计算从右起第一个不为0的直方图柱的位置 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

for binNo, binValue in enumerate(reversed(hist)): </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 if binValue != 0: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important">

 maxBinNo = 255-binNo </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 break </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print minBinNo, maxBinNo </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#生成查找表，方法来自参考文献1第四章第2节 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

for i,v in enumerate(lut): </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

 print i </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 if i < minBinNo: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 lut[i] = 0 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 elif i > maxBinNo: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 lut[i] = 255 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 else: </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 lut[i] = int(255.0*(i-minBinNo)/(maxBinNo-minBinNo)+0.5) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px
3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#计算 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px
0px 10px!important; background-color:rgb(248,248,248)">

result = cv2.LUT(image, lut) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow("Result", result) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.imwrite("LutImage.jpg", result) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.waitKey(0) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.destroyAllWindows() </li></ol>

</div>

直方图结果如下，可以看到原来占的区域很小的直方图尖峰被移动了：







<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130724210808843?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 





处理结果为：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130724210833078?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 





关于直方图的绘制，请参考<a style="color:rgb(51,102,153); text-decoration:none" href="http://blog.csdn.net/sunny2038/article/details/9097989" target="_blank">这篇文章</a>。

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t7"></a>

<a name="t2" style="color:rgb(51,102,153)" target="_blank"></a>直方图均衡化</h2>

<h3 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t8"></a>

<a name="t3" style="color:rgb(51,102,153)" target="_blank"></a>介绍 

</h3>

有时图像的视觉上的缺陷并不在强度值集中在很窄的范围内。而是某些强度值的使用频率很大。比如第一幅图中，灰度图中间值的占了很大的比例。



在完美均衡的直方图中，每个柱的值都应该相等。即50%的像素值应该小于128，25%的像素值应该小于64。总结出的经验可定义为：在标准的直方图中p%的像素拥有的强度值一定小于或等于255×p%。将该规律用于均衡直方图中：强度i的灰度值应该在对应的像素强度值低于i的百分比的强度中。因此，所需的查询表可以由下面的式子建立：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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<div style="position:absolute; left:587px; top:5097px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

lut[i] = int(255.0 *p[i]) #p[i]是是强度值小于或等于i的像素的数目。 </li></ol>

</div>

p[i]即直方图累积值，这是包含小于给点强度值的像素的直方图，以代替包含指定强度值像素的数目。比如第一幅图像的累计直方图如下图中的蓝线：







<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130724220021500?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 





而完美均衡的直方图，其累积直方图应为一条斜线，如上图中均衡化之后的红线。



更专业一点，这种累积直方图应称为累积分布（cumulative distribition）。在NumPy中有一个专门的函数来计算。这在NumPy实现直方图均衡化一节中介绍。



通过上面的介绍，应该可以明白，直方图均衡化就是对图像使用一种特殊的查询表。在第三个例子中可以看到使用查询表来获得直方图均衡化的效果。通常来说，直方图均衡化大大增加了图像的表象。但根据图像可视内容的不同，不同图像的直方图均衡化产生的效果不尽相同。 



<h3 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t9"></a>

<a name="t4" style="color:rgb(51,102,153)" target="_blank"></a>直方图均衡化之OpenCV函数实现</h3>



用OpenCV实现直方图均衡化很简单，只需调用一个函数即可：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
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<div style="position:absolute; left:587px; top:5993px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

img = cv2.imread('图像路径',0) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

equ = cv2.equalizeHist(img) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow('equ',equ) </li></ol>

</div>

这样图像就均衡化了。可以通过<a style="color:rgb(51,102,153); text-decoration:none; font-family:Arial; font-size:14px; line-height:26px" href="http://blog.csdn.net/sunny2038/article/details/9097989"
target="_blank">直方图的计算与显示</a>这篇文章中介绍的方法将结果绘制出来。





<h3 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t10"></a>

<a name="t5" style="color:rgb(51,102,153)" target="_blank"></a>直方图均衡化之NumPy函数实现</h3>



通过前面的介绍，可以明白直方图均衡化就是用一种特殊的查找表来实现的。所以这里用NumPy函数，以查找表的方式手动实现图像直方图的均衡化：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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<div style="position:absolute; left:587px; top:6248px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#coding=utf-8 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

import cv2 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

import numpy as np </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

image = cv2.imread("D:/test/unequ.jpg", 0) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

lut = np.zeros(256, dtype = image.dtype )#创建空的查找表 </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

hist,bins = np.histogram(image.flatten(),256,[0,256]) </li><li style="border-left-width:3px; border-style:none none none
solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cdf = hist.cumsum() #计算累积直方图 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cdf_m = np.ma.masked_equal(cdf,0) #除去直方图中的0值 </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cdf_m = (cdf_m - cdf_m.min())*255/(cdf_m.max()-cdf_m.min())#等同于前面介绍的lut[i] = int(255.0 *p[i])公式 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cdf = np.ma.filled(cdf_m,0).astype('uint8') #将掩模处理掉的元素补为0 </li><li style="border-left-width:3px;
border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

#计算 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px
0px 10px!important; background-color:rgb(248,248,248)">

result2 = cdf[image] </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

result = cv2.LUT(image, cdf) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow("OpenCVLUT", result) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important;
padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.imshow("NumPyLUT", result2) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.waitKey(0) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.destroyAllWindows() </li></ol>

</div>

最终结果







<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130724225038937?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 



<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t11"></a>

<a name="t6" style="color:rgb(51,102,153)" target="_blank"></a>验证</h2>



比较查找表和OpenCV直方图均衡化生成的直方图：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20130724224352546?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 



可以看出，总体上来看是吻合的，但OpenCV中函数的实现可能还有一些细微的差别（有空去翻下源码，不过今天就先到这里了）。 

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t12"></a>

<a name="t7" style="color:rgb(51,102,153)" target="_blank"></a>参考资料：</h2>



1、《Opencv2 Computer Vision Application Programming Cookbook》



2、《OpenCV References Manule》



3、<a style="color:rgb(51,102,153); text-decoration:none" href="http://opencvpython.blogspot.com/2013/03/histograms-2-histogram-equalization.html" target="_blank">http://opencvpython.blogspot.com/2013/03/histograms-2-histogram-equalization.html</a>

 

 



 



<h1><a name="t13"></a>OpenCV-Python教程（11、轮廓检测）</h1>

 







相比C++而言，<a title="Python知识库" class="replace_word" style="color:rgb(223,52,52); text-decoration:none; font-weight:bold" href="http://lib.csdn.net/base/11" target="_blank">Python</a>适合做原型。本系列的文章介绍如何在Python中用OpenCV图形库，以及与C++调用相应OpenCV函数的不同之处。这篇文章介绍在Python中使用OpenCV检测并绘制轮廓。 





提示： 



<ul style="color:rgb(51,51,51); font-family:Arial; font-size:14px; line-height:26px">

<li>转载请详细注明原作者及出处，谢谢！ 

</li><li>本文介绍在OpenCV-Python中检测并绘制轮廓的方法。</li><li>本文不介详细的理论知识，读者可从其他资料中获取相应的背景知识。笔者推荐清华大学出版社的《<a style="color:rgb(51,102,153); text-decoration:none" href="http://www.amazon.cn/%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86%E4%B8%8E%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%A7%86%E8%A7%89%E7%AE%97%E6%B3%95%E5%8F%8A%E5%BA%94%E7%94%A8-%E5%B8%95%E7%A7%91%E5%B0%94/dp/B0083PY050/ref=sr_1_1?ie=UTF8&qid=1373614562&sr=8-1&keywords=%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86%E4%B8%8E%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%A7%86%E8%A7%89%E7%AE%97%E6%B3%95%E5%8F%8A%E5%BA%94%E7%94%A8%28%E7%AC%AC2%E7%89%88%29"
target="_blank">图像处理与计算机视觉算法及应用(第2版)</a> 》。</li></ul>

<h1 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t14"></a>

<a name="t0" style="color:rgb(51,102,153)" target="_blank"></a>轮廓检测</h1>



轮廓检测也是图像处理中经常用到的。OpenCV-Python接口中使用cv2.findContours()函数来查找检测物体的轮廓。

<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t15"></a>

<a name="t1" style="color:rgb(51,102,153)" target="_blank"></a>实现</h2>



使用方式如下：





<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">copy</a><div style="left: 487px; top: 11096px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_12" width="18" height="18" align="middle"
id="ZeroClipboardMovie_12" pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" type="application/x-shockwave-flash" wmode="transparent" flashvars="id=12&width=18&height=18"
allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:967px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

import cv2 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

img = cv2.imread('D:\\test\\contour.jpg') </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

ret, binary = cv2.threshold(gray,127,255,cv2.THRESH_BINARY) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

contours, hierarchy = cv2.findContours(binary,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE) </li><li style="border-left-width:3px; border-style:none
none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.drawContours(img,contours,-1,(0,0,255),3) </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.imshow("img", img) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.waitKey(0) </li></ol>

</div>

 

需要注意的是cv2.findContours()函数接受的参数为二值图，即黑白的（不是灰度图），所以读取的图像要先转成灰度的，再转成二值图，参见4、5两行。第六行是检测轮廓，第七行是绘制轮廓。





<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t16"></a>

<a name="t2" style="color:rgb(51,102,153)" target="_blank"></a>结果 

</h2>



原图如下：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20131030153346984?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast">



检测结果如下：



<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20131030153441656?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast">



注意，findcontours函数会“原地”修改输入的图像。这一点可通过下面的语句验证： 



<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">copy</a><div style="left: 487px; top: 12664px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_13" width="18" height="18" align="middle"
id="ZeroClipboardMovie_13" pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" type="application/x-shockwave-flash" wmode="transparent" flashvars="id=13&width=18&height=18"
allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:2409px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow("binary", binary) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108);
list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

contours, hierarchy = cv2.findContours(binary,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE) </li><li class="alt" style="border-left-width:3px;
border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.imshow("binary2", binary) </li></ol>

</div>

执行这些语句后会发现原图被修改了。 





<h1 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t17"></a>

<a name="t3" style="color:rgb(51,102,153)" target="_blank"></a>cv2.findContours()函数</h1>



函数的原型为





<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">copy</a><div style="left: 487px; top: 12865px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_14" width="18" height="18" align="middle"
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allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:2638px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.findContours(image, mode, method[, contours[, hierarchy[, offset ]]]) </li></ol>

</div>

返回两个值：contours：hierarchy。 





<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t18"></a>

<a name="t4" style="color:rgb(51,102,153)" target="_blank"></a>参数</h2>



第一个参数是寻找轮廓的图像；



第二个参数表示轮廓的检索模式，有四种（本文介绍的都是新的cv2接口）： 

 cv2.RETR_EXTERNAL表示只检测外轮廓 

 cv2.RETR_LIST检测的轮廓不建立等级关系 

 cv2.RETR_CCOMP建立两个等级的轮廓，上面的一层为外边界，里面的一层为内孔的边界信息。如果内孔内还有一个连通物体，这个物体的边界也在顶层。 

 cv2.RETR_TREE建立一个等级树结构的轮廓。



第三个参数method为轮廓的近似办法 

 cv2.CHAIN_APPROX_NONE存储所有的轮廓点，相邻的两个点的像素位置差不超过1，即max（abs（x1-x2），abs（y2-y1））==1 

 cv2.CHAIN_APPROX_SIMPLE压缩水平方向，垂直方向，对角线方向的元素，只保留该方向的终点坐标，例如一个矩形轮廓只需4个点来保存轮廓信息 

 cv2.CHAIN_APPROX_TC89_L1，CV_CHAIN_APPROX_TC89_KCOS使用teh-Chinl chain 近似算法 



<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t19"></a>

<a name="t5" style="color:rgb(51,102,153)" target="_blank"></a>返回值</h2>



cv2.findContours()函数返回两个值，一个是轮廓本身，还有一个是每条轮廓对应的属性。 







<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t20"></a>

<a name="t6" style="color:rgb(51,102,153)" target="_blank"></a>contour返回值</h2>

cv2.findContours()函数首先返回一个list，list中每个元素都是图像中的一个轮廓，用numpy中的ndarray表示。这个概念非常重要。在下面drawContours中会看见。通过 

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">copy</a><div style="left: 487px; top: 13446px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_15" width="18" height="18" align="middle"
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allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:3343px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print (type(contours)) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

print (type(contours[0])) </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print (len(contours)) </li></ol>

</div>

可以验证上述信息。会看到本例中有两条轮廓，一个是五角星的，一个是矩形的。每个轮廓是一个ndarray，每个ndarray是轮廓上的点的集合。







由于我们知道返回的轮廓有两个，因此可通过 



<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.drawContours(img,contours,0,(0,0,255),3) </li></ol>

</div>

和

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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<div style="position:absolute; left:587px; top:3671px; width:18px; height:18px; z-index:99">

</div>

</div>

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<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.drawContours(img,contours,1,(0,255,0),3) </li></ol>

</div>

分别绘制两个轮廓，关于该参数可参见下面一节的内容。同时通过 

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<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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<div style="position:absolute; left:587px; top:3784px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print (len(contours[0])) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

print (len(contours[1])) </li></ol>

</div>

输出两个轮廓中存储的点的个数，可以看到，第一个轮廓中只有4个元素，这是因为轮廓中并不是存储轮廓上所有的点，而是只存储可以用直线描述轮廓的点的个数，比如一个“正立”的矩形，只需4个顶点就能描述轮廓了。 





<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t21"></a>

<a name="t7" style="color:rgb(51,102,153)" target="_blank"></a>hierarchy返回值</h2>



此外，该函数还可返回一个可选的hiararchy结果，这是一个ndarray，其中的元素个数和轮廓个数相同，每个轮廓contours[i]对应4个hierarchy元素hierarchy[i][0] ~hierarchy[i][3]，分别表示后一个轮廓、前一个轮廓、父轮廓、内嵌轮廓的索引编号，如果没有对应项，则该值为负数。 





通过 



<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

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<div style="position:absolute; left:587px; top:4113px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print (type(hierarchy)) </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

print (hierarchy.ndim) </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

print (hierarchy[0].ndim) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

print (hierarchy.shape) </li></ol>

</div>

得到 

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

<div class="bar" style="padding-left:45px">

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<div style="position:absolute; left:587px; top:4280px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

3 </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

2 </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

(1, 2, 4) </li></ol>

</div>

可以看出，hierarchy本身包含两个ndarray，每个ndarray对应一个轮廓，每个轮廓有四个属性。 





<h1 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t22"></a>

<a name="t8" style="color:rgb(51,102,153)" target="_blank"></a>轮廓的绘制</h1>



OpenCV中通过cv2.drawContours在图像上绘制轮廓。 



<h2 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t23"></a>

<a name="t9" style="color:rgb(51,102,153)" target="_blank"></a>cv2.drawContours()函数</h2>





<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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<div style="position:absolute; left:587px; top:4549px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.drawContours(image, contours, contourIdx, color[, thickness[, lineType[, hierarchy[, maxLevel[, offset ]]]]]) </li></ol>

</div>





<ul style="color:rgb(51,51,51); font-family:Arial; font-size:14px; line-height:26px">

<li>第一个参数是指明在哪幅图像上绘制轮廓；</li><li>第二个参数是轮廓本身，在Python中是一个list。</li><li>第三个参数指定绘制轮廓list中的哪条轮廓，如果是-1，则绘制其中的所有轮廓。后面的参数很简单。其中thickness表明轮廓线的宽度，如果是-1（cv2.FILLED），则为填充模式。绘制参数将在以后独立详细介绍。</li></ul>

<h1 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t24"></a>

<a name="t10" style="color:rgb(51,102,153)" target="_blank"></a>补充：</h1>



写着写着发现一篇文章介绍不完，所以这里先作为入门的。更多关于轮廓的信息有机会再开一篇文章介绍。 

 

但有朋友提出计算轮廓的极值点。可用下面的方式计算得到，如下

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<div class="bar" style="padding-left:45px">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
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<div style="position:absolute; left:587px; top:4889px; width:18px; height:18px; z-index:99">

</div>

</div>

</div>

<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

pentagram = contours[1] #第二条轮廓是五角星 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px;
margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

 </li><li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero
outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

leftmost = tuple(pentagram[:,0][pentagram[:,:,0].argmin()]) </li><li
style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

rightmost = tuple(pentagram[:,0][pentagram[:,:,0].argmin()]) </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

 </li><li style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside;
line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)">

cv2.circle(img, leftmost, 2, (0,255,0),3) </li><li
class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

cv2.circle(img, rightmost, 2, (0,0,255),3) </li></ol>

</div>

 







注意！假设轮廓有100个点，OpenCV返回的ndarray的维数是(100, 1, 2)！！！而不是我们认为的(100, 2)。切记！！！人民邮电出版社出版了一本《NumPy攻略：Python科学计算与数据分析》，推荐去看一下。



更新：关于pentagram[:,0]的意思



在numpy的数组中，用逗号分隔的是轴的索引。举个例子，假设有如下的数组：

<div class="dp-highlighter bg_python" style="font-family:Consolas,'Courier New',Courier,mono,serif; width:700.906px; overflow:auto; padding-top:1px; color:rgb(51,51,51); line-height:26px; margin:18px 0px!important; background-color:rgb(231,229,220)">

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[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">copy</a><div style="left: 487px; top: 15155px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_23" width="18" height="18" align="middle"
id="ZeroClipboardMovie_23" pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" type="application/x-shockwave-flash" wmode="transparent" flashvars="id=23&width=18&height=18"
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<div style="position:absolute; left:587px; top:5257px; width:18px; height:18px; z-index:99">

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<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

a = np.array([[[3,4]], [[1,2]],[[5,7]],[[3,7]],[[1,8]]]) </li></ol>

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其shape是(5, 1, 2)。与我们的轮廓是相同的。那么a[:,0]的结果就是：

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<div class="bar" style="padding-left:45px">

<div class="tools" style="padding:3px 8px 10px 10px; font-size:9px; line-height:normal; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(108,226,108); background-color:rgb(248,248,248)">

[python] <a title="view plain" class="ViewSource" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px;
background-color:inherit" href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">view

plain</a> <a title="copy" class="CopyToClipboard" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:1px; margin:0px 10px 0px 0px; font-size:9px; display:inline-block; width:16px; height:16px; text-indent:-2000px; background-color:inherit"
href="http://blog.csdn.net/sunny2038/article/details/12889059#" target="_blank">copy</a><div style="left: 487px; top: 15268px; width: 18px; height: 18px; position: absolute; z-index: 99;"><embed name="ZeroClipboardMovie_24" width="18" height="18" align="middle"
id="ZeroClipboardMovie_24" pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" type="application/x-shockwave-flash" wmode="transparent" flashvars="id=24&width=18&height=18"
allowfullscreen="false" allowscriptaccess="always" bgcolor="#ffffff" quality="best" menu="false" loop="false"></div>

<div style="position:absolute; left:587px; top:5370px; width:18px; height:18px; z-index:99">

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<ol class="dp-py" style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)" start="1">

<li class="alt" style="border-left-width:3px; border-style:none none none solid; border-left-color:rgb(108,226,108); list-style:decimal-leading-zero outside; color:inherit; line-height:18px; margin:0px!important; padding:0px 3px 0px 10px!important">

[3,4], [1,2], [5,7], [3,7], [1,8] </li></ol>

</div>

这里a[:,0]的意思就是a[0:5,0]，也就是a[0:5,0:0:2]，这三者是等价的。







回头看一下，a的shape是(5,1,2)，表明是三个轴的。在numpy的数组中，轴的索引是通过逗号分隔的。同时冒号索引“:”表示的是该轴的所有元素。因此a[:, 0]表示的是第一个轴的所有元素和第二个轴的第一个元素。在这里既等价于a[0:5, 0]。



再者，若给出的索引数少于数组中总索引数，则将已给出的索引树默认按顺序指派到轴上。比如a[0:5,0]只给出了两个轴的索引，则第一个索引就是第一个轴的，第二个索引是第二个轴的，而第三个索引没有，则默认为[:]，即该轴的所有内容。因此a[0:5,0]也等价于a[0:5,0:0:2]。



再详细一点，a的全体内容为：[[[3,4]], [[1,2]],[[5,7]],[[3,7]],[[1,8]]]。去掉第一层方括号，其中有五个元素，每个元素为[[3,4]]这样的，所以第一个索引的范围为[0:5]。注意OpenCV函数返回的多维数组和常见的numpy数组的不同之处！



观察[[3,4]]，我们发现其中只有一个元素，即[3, 4]，第二个索引为[0:1]。



再去掉一层方括号，我们面对的是[3,4]，有两个元素，所以第三个索引的范围为[0:2]。



再次强调一下OpenCVPython接口函数返回的NumPy数组和普通的NumPy数组在组织上的不同之处。



PS：OpenCV-Python讨论群——219962286，欢迎大家加入互相探讨学习。 









得到的结果为如下： 

 

<img style="border:none; max-width:100%" alt="" src="https://img-blog.csdn.net/20131030171817578?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc3VubnkyMDM4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"> 



<h1 style="margin:0px; padding:0px; color:rgb(51,51,51); font-family:Arial; line-height:26px"><a name="t25"></a>

<a name="t11" style="color:rgb(51,102,153)" target="_blank"></a>参考资料：</h1>



1、《Opencv2 Computer Vision Application Programming Cookbook》



2、《OpenCV References Manule》



3、<a style="color:rgb(51,102,153); text-decoration:none" href="http://blog.csdn.net/sunny2038/article/details/12889059" target="_blank">OpenCV官方文档Contour部分</a>

 

 



 



from: http://blog.csdn.net/sunny2038/article/category/904451 


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标签： opencv python 图像处理霍夫变换检测

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