图像处理之图像梯度效果（转载）

转载自：http://blog.csdn.net/jia20003/article/details/7664777

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);
    }

}