图像处理之Hessian矩阵提取关键点

一：大致的算法流程

1. 对每个像素点计算图像在X方向Y方向的二阶偏导数，计算图像的XY方向的导数

2. 根据第一步的计算结果，有Hessian Matrix计算D(h) = Ixx*Iyy - Ixy*Ixy

其中Ixx表示X方向的二阶偏导数

Iyy表示Y方向的二阶偏导数

Ixy表XY方向的二阶导数

3. 根据第二步计算出来的值使用3×3窗口实现非最大信号压制，

我的做法， 直接给了threshold值，这个其实不很对，真的懒，不想弄啦！

二：导数计算实现

关于一阶与二阶高斯偏导数计算请看这里：

http://blog.csdn.net/jia20003/article/details/16369143

三：程序效果

四：算法代码

package com.gloomyfish.image.harris.corner;import java.awt.image.BufferedImage;import java.util.ArrayList;import java.util.List;import com.gloomyfish.filter.study.AbstractBufferedImageOp;public class HessianFeatureDetector extends AbstractBufferedImageOp {private GaussianDerivativeFilter gdFilter;private double minRejectThreshold = 4.1; // (r+1)^2/rprivate List<HessianMatrix> pixelMatrixList;public HessianFeatureDetector(){gdFilter = new GaussianDerivativeFilter();pixelMatrixList = new ArrayList<HessianMatrix>();}@Overridepublic BufferedImage filter(BufferedImage src, BufferedImage dest) {int width = src.getWidth();        int height = src.getHeight();        initSettings(height, width);        if ( dest == null )            dest = createCompatibleDestImage( src, null );        int[] inPixels = new int[width*height];        gdFilter.setDirectionType(GaussianDerivativeFilter.XX_DIRECTION);        BufferedImage bixx = gdFilter.filter(src, null);        getRGB( bixx, 0, 0, width, height, inPixels );        extractPixelData(inPixels, GaussianDerivativeFilter.XX_DIRECTION, height, width);                // YY Direction        gdFilter.setDirectionType(GaussianDerivativeFilter.YY_DIRECTION);        BufferedImage biyy = gdFilter.filter(src, null);        getRGB( biyy, 0, 0, width, height, inPixels );        extractPixelData(inPixels, GaussianDerivativeFilter.YY_DIRECTION, height, width);                // XY Direction        gdFilter.setDirectionType(GaussianDerivativeFilter.XY_DIRECTION);        BufferedImage bixy = gdFilter.filter(src, null);        getRGB( bixy, 0, 0, width, height, inPixels );        extractPixelData(inPixels, GaussianDerivativeFilter.XY_DIRECTION, height, width);                int[] outPixels = new int[width*height];        int index = 0;        for(int row=0; row<height; row++) {        int ta = 0, tr = 0, tg = 0, tb = 0;        for(int col=0; col<width; col++) {        index = row * width + col;        ta = 255;        HessianMatrix hm = pixelMatrixList.get(index);        double[] t = hm.getThreshold();        if(t[0] > minRejectThreshold)        {        tr = 127;        }        else        {        tr = 0;        }        if(t[1] > minRejectThreshold)        {        tg = 127;        }        else        {        tg = 0;        }        if(t[2] > minRejectThreshold)        {        tb = 127;        }        else        {        tb = 0;        }                outPixels[index] = (ta << 24) | (tr << 16) | (tg << 8) | tb;        }        }        setRGB( dest, 0, 0, width, height, outPixels );        return dest;}private void initSettings(int height, int width){        int index = 0;        for(int row=0; row<height; row++) {        for(int col=0; col<width; col++) {        index = row * width + col;                HessianMatrix matrix = new HessianMatrix();                pixelMatrixList.add(index, matrix);        }        }}private void extractPixelData(int[] pixels, int type, int height, int width){        int index = 0;        for(int row=0; row<height; row++) {        int ta = 0, tr = 0, tg = 0, tb = 0;        for(int col=0; col<width; col++) {        index = row * width + col;        ta = (pixels[index] >> 24) & 0xff;                tr = (pixels[index] >> 16) & 0xff;                tg = (pixels[index] >> 8) & 0xff;                tb = pixels[index] & 0xff;                HessianMatrix matrix = pixelMatrixList.get(index);                if(type == GaussianDerivativeFilter.XX_DIRECTION)                {                matrix.setXx(new double[]{tr, tg, tb});                }                if(type == GaussianDerivativeFilter.YY_DIRECTION)                {                matrix.setYy(new double[]{tr, tg, tb});                }                if(type == GaussianDerivativeFilter.XY_DIRECTION)                {                matrix.setXy(new double[]{tr, tg, tb});                }        }        }}}

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