【OpenCV】绘制图像的直方图

#include "stdafx.h"

#include <cv.h>
#include <highgui.h>
#include <cxcore.h>
#include <vector>
#include <cmath>

using namespace std;
using namespace cv;

void FillWhite(IplImage *pImage)
{
cvRectangle(pImage, cvPoint(0, 0), cvPoint(pImage->width, pImage->height), CV_RGB(255, 255, 255), CV_FILLED);
}
// 创建灰度图像的直方图
CvHistogram* CreateGrayImageHist(IplImage **ppImage)
{
int nHistSize = 256;
float fRange[] = {0, 255};  //灰度级的范围
float *pfRanges[] = {fRange};
CvHistogram *pcvHistogram = cvCreateHist(1, &nHistSize, CV_HIST_ARRAY, pfRanges);
cvCalcHist(ppImage, pcvHistogram);
return pcvHistogram;
}
// 根据直方图创建直方图图像
IplImage* CreateHisogramImage(int nImageWidth, int nScale, int nImageHeight, CvHistogram *pcvHistogram)
{
IplImage *pHistImage = cvCreateImage(cvSize(nImageWidth * nScale, nImageHeight), IPL_DEPTH_8U, 1);
FillWhite(pHistImage);

//统计直方图中的最大直方块
float fMaxHistValue = 0;
cvGetMinMaxHistValue(pcvHistogram, NULL, &fMaxHistValue, NULL, NULL);

//分别将每个直方块的值绘制到图中
int i;
for(i = 0; i < nImageWidth; i++)
{
float fHistValue = cvQueryHistValue_1D(pcvHistogram, i); //像素为i的直方块大小
int nRealHeight = cvRound((fHistValue / fMaxHistValue) * nImageHeight);  //要绘制的高度
cvRectangle(pHistImage,
cvPoint(i * nScale, nImageHeight - 1),
cvPoint((i + 1) * nScale - 1, nImageHeight - nRealHeight),
cvScalar(i, 0, 0, 0),
CV_FILLED
);
}
return pHistImage;
}

int main( int argc, char** argv )
{
const char *pstrWindowsSrcTitle = "原图";
const char *pstrWindowsGrayTitle = "灰度图";
const char *pstrWindowsHistTitle = "直方图";

// 从文件中加载原图
IplImage *pSrcImage = cvLoadImage("5.jpg", CV_LOAD_IMAGE_UNCHANGED);
IplImage *pGrayImage = cvCreateImage(cvGetSize(pSrcImage), IPL_DEPTH_8U, 1);
// 灰度图
cvCvtColor(pSrcImage, pGrayImage, CV_BGR2GRAY);

// 灰度直方图
CvHistogram *pcvHistogram = CreateGrayImageHist(&pGrayImage);

// 创建直方图图像
int nHistImageWidth = 255;
int nHistImageHeight = 150;  //直方图图像高度
int nScale = 2;
IplImage *pHistImage = CreateHisogramImage(nHistImageWidth, nScale, nHistImageHeight, pcvHistogram);

// 显示
cvNamedWindow(pstrWindowsSrcTitle, CV_WINDOW_AUTOSIZE);
cvNamedWindow(pstrWindowsGrayTitle, CV_WINDOW_AUTOSIZE);
cvNamedWindow(pstrWindowsHistTitle, CV_WINDOW_AUTOSIZE);
cvShowImage(pstrWindowsSrcTitle, pSrcImage);
cvShowImage(pstrWindowsGrayTitle, pGrayImage);
cvShowImage(pstrWindowsHistTitle, pHistImage);

cvWaitKey(0);

cvReleaseHist(&pcvHistogram);

cvReleaseImage(&pSrcImage);
cvReleaseImage(&pGrayImage);
cvReleaseImage(&pHistImage);                                                                                                                                                                                                                                                                                        cvDestroyAllWindows(); 
return 0;
}