基本思想：
直方图图均衡化是图像处理中的常用图像增强手段，直方图均衡化的主要优点是
可以降低图像噪声，提升图像的局部显示。对于常见的RGB图像，直方图均衡化
可以分别在三个颜色通道上处理，基本的直方图均衡化的公式为：
其中nj表示灰度级为Rk的像素的个数，L为图像中灰度总数，对于RGB来说L的
取值范围为[0~255]总灰度级为256个。而R表示输入图像的直方图数据。根据输
出的灰度值Sk计算出输出像素的每个像素值，完成直方图均衡化之后的像素处理
程序效果：
源代码：
- package com.gloomyfish.filter.study;
- import java.awt.image.BufferedImage;
- public class HistogramEFilter extends AbstractBufferedImageOp{
- @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[][] rgbhis = new int[3][256]; // RGB
- int[][] newrgbhis = new int[3][256]; // after HE
- for(int i=0; i<3; i++) {
- for(int j=0; j<256; j++) {
- rgbhis[i][j] = 0;
- newrgbhis[i][j] = 0;
- }
- }
- int index = 0;
- int totalPixelNumber = height * width;
- 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 = (inPixels[index] >> 24) & 0xff;
- tr = (inPixels[index] >> 16) & 0xff;
- tg = (inPixels[index] >> 8) & 0xff;
- tb = inPixels[index] & 0xff;
- // generate original source image RGB histogram
- rgbhis[0][tr]++;
- rgbhis[1][tg]++;
- rgbhis[2][tb]++;
- }
- }
- // generate original source image RGB histogram
- generateHEData(newrgbhis, rgbhis, totalPixelNumber, 256);
- 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 = (inPixels[index] >> 24) & 0xff;
- tr = (inPixels[index] >> 16) & 0xff;
- tg = (inPixels[index] >> 8) & 0xff;
- tb = inPixels[index] & 0xff;
- // get output pixel now...
- tr = newrgbhis[0][tr];
- tg = newrgbhis[1][tg];
- tb = newrgbhis[2][tb];
- outPixels[index] = (ta << 24) | (tr << 16) | (tg << 8) | tb;
- }
- }
- setRGB( dest, 0, 0, width, height, outPixels );
- return dest;
- }
- /**
- *
- * @param newrgbhis
- * @param rgbhis
- * @param totalPixelNumber
- * @param grayLevel [0 ~ 255]
- */
- private void generateHEData(int[][] newrgbhis, int[][] rgbhis, int totalPixelNumber, int grayLevel) {
- for(int i=0; i<grayLevel; i++) {
- newrgbhis[0][i] = getNewintensityRate(rgbhis[0], totalPixelNumber, i);
- newrgbhis[1][i] = getNewintensityRate(rgbhis[1], totalPixelNumber, i);
- newrgbhis[2][i] = getNewintensityRate(rgbhis[2], totalPixelNumber, i);
- }
- }
- private int getNewintensityRate(int[] grayHis, double totalPixelNumber, int index) {
- double sum = 0;
- for(int i=0; i<=index; i++) {
- sum += ((double)grayHis[i])/totalPixelNumber;
- }
- return (int)(sum * 255.0);
- }
- }
