图像处理之图像梯度效果

图像处理之图像梯度效果

基本思想：

利用X方向与Y方向分别实现一阶微分，求取振幅，实现图像梯度效果。关于如何计算图像

一阶微分参见这里：http://blog.csdn.net/jia20003/article/details/7562092

使用的两种微分算子分别为Prewitt与Sobel，其中Soble在X, Y两个方向算子分别为：



Prewitt在X, Y方向上梯度算子分别为：



二：程序思路及实现

梯度滤镜提供了两个参数：

– 方向，用来要决定图像完成X方向梯度计算， Y方向梯度计算，或者是振幅计算

– 算子类型，用来决定是使用sobel算子或者是prewitt算子。

计算振幅的公式可以参见以前《图像处理之一阶微分应用》的文章

三：运行效果

原图像如下：



基于Prewitt与sobel算子的XY方向振幅效果如下：





该滤镜的源代码如下：

package com.process.blur.study;

import java.awt.image.BufferedImage;
/**
*
* @author gloomy-fish
* @date 2012-06-11
*
* prewitt operator
* X-direction
* -1, 0, 1
* -1, 0, 1
* -1, 0, 1
*
* Y-direction
* -1, -1, -1
*  0,  0,  0
*  1,  1,  1
*
* sobel operator
* X-direction
* -1, 0, 1
* -2, 0, 2
* -1, 0, 1
*
* Y-direction
* -1, -2, -1
*  0,  0,  0
*  1,  2,  1
*
*/
public class GradientFilter extends AbstractBufferedImageOp {

// prewitt operator
public final static int[][] PREWITT_X = new int[][]{{-1, 0, 1}, {-1, 0, 1}, {-1, 0, 1}};
public final static int[][] PREWITT_Y = new int[][]{{-1, -1, -1}, {0,  0,  0}, {1,  1,  1}};

// sobel operator
public final static int[][] SOBEL_X = new int[][]{{-1, 0, 1}, {-2, 0, 2}, {-1, 0, 1}};
public final static int[][] SOBEL_Y = new int[][]{{-1, -2, -1}, {0,  0,  0}, {1,  2,  1}};

// direction parameter
public final static int X_DIRECTION = 0;
public final static int Y_DIRECTION = 2;
public final static int XY_DIRECTION = 4;
private int direction;
private boolean isSobel;

public GradientFilter() {
direction = XY_DIRECTION;
isSobel = true;
}

public void setSoble(boolean sobel) {
this.isSobel = sobel;
}

public int getDirection() {
return direction;
}

public void setDirection(int direction) {
this.direction = direction;
}

@Override
public BufferedImage filter(BufferedImage src, BufferedImage dest) {
int width = src.getWidth();
int height = src.getHeight();

if (dest == null )
dest = createCompatibleDestImage( src, null );

int[] inPixels = new int[width*height];
int[] outPixels = new int[width*height];
getRGB( src, 0, 0, width, height, inPixels );
int index = 0, index2 = 0;
double xred = 0, xgreen = 0, xblue = 0;
double yred = 0, ygreen = 0, yblue = 0;
int newRow, newCol;
for(int row=0; row<height; row++) {
int ta = 255, tr = 0, tg = 0, tb = 0;
for(int col=0; col<width; col++) {
index = row * width + col;
for(int subrow = -1; subrow <= 1; subrow++) {
for(int subcol = -1; subcol <= 1; subcol++) {
newRow = row + subrow;
newCol = col + subcol;
if(newRow < 0 || newRow >= height) {
newRow = row;
}
if(newCol < 0 || newCol >= width) {
newCol = col;
}
index2 = newRow * width + newCol;
tr = (inPixels[index2] >> 16) & 0xff;
tg = (inPixels[index2] >> 8) & 0xff;
tb = inPixels[index2] & 0xff;

if(isSobel) {
xred += (SOBEL_X[subrow + 1][subcol + 1] * tr);
xgreen +=(SOBEL_X[subrow + 1][subcol + 1] * tg);
xblue +=(SOBEL_X[subrow + 1][subcol + 1] * tb);

yred += (SOBEL_Y[subrow + 1][subcol + 1] * tr);
ygreen +=(SOBEL_Y[subrow + 1][subcol + 1] * tg);
yblue +=(SOBEL_Y[subrow + 1][subcol + 1] * tb);
} else {
xred += (PREWITT_X[subrow + 1][subcol + 1] * tr);
xgreen +=(PREWITT_X[subrow + 1][subcol + 1] * tg);
xblue +=(PREWITT_X[subrow + 1][subcol + 1] * tb);

yred += (PREWITT_Y[subrow + 1][subcol + 1] * tr);
ygreen +=(PREWITT_Y[subrow + 1][subcol + 1] * tg);
yblue +=(PREWITT_Y[subrow + 1][subcol + 1] * tb);
}
}
}

double mred = Math.sqrt(xred * xred + yred * yred);
double mgreen = Math.sqrt(xgreen * xgreen + ygreen * ygreen);
double mblue = Math.sqrt(xblue * xblue + yblue * yblue);
if(XY_DIRECTION == direction)
{
outPixels[index] = (ta << 24) | (clamp((int)mred) << 16) | (clamp((int)mgreen) << 8) | clamp((int)mblue);
}
else if(X_DIRECTION == direction)
{
outPixels[index] = (ta << 24) | (clamp((int)yred) << 16) | (clamp((int)ygreen) << 8) | clamp((int)yblue);
}
else if(Y_DIRECTION == direction)
{
outPixels[index] = (ta << 24) | (clamp((int)xred) << 16) | (clamp((int)xgreen) << 8) | clamp((int)xblue);
}
else
{
// as default, always XY gradient
outPixels[index] = (ta << 24) | (clamp((int)mred) << 16) | (clamp((int)mgreen) << 8) | clamp((int)mblue);
}

// cleanup for next loop
newRow = newCol = 0;
xred = xgreen = xblue = 0;
yred = ygreen = yblue = 0;

}
}
setRGB(dest, 0, 0, width, height, outPixels );
return dest;
}

public static int clamp(int value) {
return value < 0 ? 0 : (value > 255 ? 255 : value);
}

}

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