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。
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);
- }
- }
