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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<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;
}
}
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