图像处理之调整亮度与对比度

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
        	int ta = 0, tr = 0, tg = 0, tb = 0;
        	for(int col=0; 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
        	int ta = 0, tr = 0, tg = 0, tb = 0;
        	for(int col=0; 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;
	}
 
}