很多时候，一张图像被过度曝光显得很白，或者光线不足显得很暗，有时候背景跟图像人物
也观察不清楚，这个时候可以通过调节图像的两个基本属性-亮度与对比度来获得整体效果
的提升，从而得到质量更高的图片。
基本原理：
图像亮度本质上图像中每个像素的亮度，每个像素的亮度本质上RGB值的大小，RGB值为0
是像素点为黑色，RGB都为255时像素点最亮，为白色。对比度则是不同像素点之间的差值，
差值越大，对比度越明显。从直方图分析的观点来看，对比度越好的图片，直方图曲线会越
明显，分布也越显得均匀。
算法流程：
调整图像亮度与对比度算法主要由以下几个步骤组成：
1. 计算图像的RGB像素均值– M
2. 对图像的每个像素点Remove平均值-M
3. 对去掉平均值以后的像素点 P乘以对比度系数
4. 对步骤上处理以后的像素P加上 M乘以亮度系统
5. 对像素点RGB值完成重新赋值
算法系数
对比度 contrast的最佳取值范围在[0 ~ 4],
亮度 brightness的最佳取值范围在[0~ 2]之间
算法的源程序代码见最后源代码部分
程序效果：
调整亮度与对比度的滤镜源代码如下：
- package com.process.blur.study;
- import java.awt.image.BufferedImage;
- /**
- * this filter illustrate the brightness and contrast of the image
- * and demo how to change the both attribute of the image.
- *
- * @author gloomy fish
- *
- */
- public class ConBriFilter extends AbstractBufferedImageOp {
- private float contrast = 1.5f; // default value;
- private float brightness = 1.0f; // default value;
- public ConBriFilter() {
- // do stuff here if you need......
- }
- @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];
- src.getRGB( 0, 0, width, height, inPixels, 0, width );
- // calculate RED, GREEN, BLUE means of pixel
- int index = 0;
- int[] rgbmeans = new int[3];
- double redSum = 0, greenSum = 0, blueSum = 0;
- double total = 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;
- redSum += tr;
- greenSum += tg;
- blueSum +=tb;
- }
- }
- rgbmeans[0] = (int)(redSum / total);
- rgbmeans[1] = (int)(greenSum / total);
- rgbmeans[2] = (int)(blueSum / total);
- // adjust contrast and brightness algorithm, here
- 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;
- // remove means
- tr -=rgbmeans[0];
- tg -=rgbmeans[1];
- tb -=rgbmeans[2];
- // adjust contrast now !!!
- tr = (int)(tr * getContrast());
- tg = (int)(tg * getContrast());
- tb = (int)(tb * getContrast());
- // adjust brightness
- tr += (int)(rgbmeans[0] * getBrightness());
- tg += (int)(rgbmeans[1] * getBrightness());
- tb += (int)(rgbmeans[2] * getBrightness());
- outPixels[index] = (ta << 24) | (clamp(tr) << 16) | (clamp(tg) << 8) | clamp(tb);
- }
- }
- setRGB( dest, 0, 0, width, height, outPixels );
- return dest;
- }
- public int clamp(int value) {
- return value > 255 ? 255 :(value < 0 ? 0 : value);
- }
- public float getContrast() {
- return contrast;
- }
- public void setContrast(float contrast) {
- this.contrast = contrast;
- }
- public float getBrightness() {
- return brightness;
- }
- public void setBrightness(float brightness) {
- this.brightness = brightness;
- }
- }
