Photoshop图像处理算法—色阶调整

前言：之前在公司做项目的用到photoshop颜色空间的一些相关方法，在此总结一下。下面原理部分是从我的总结文档里截取来的。需要复制的童鞋自己手写一下~

2、程序部分

1）Matlab实验程序。

clc;clear;close all;
Image=imread('Fotor_LomoOrg.bmp');
figure(1);
imshow(Image);

R=double(Image(:,:,1));
G=double(Image(:,:,2));
B=double(Image(:,:,3));

%调整参数
HighLight=238;
Shadow=159;
Midtones=0.51;

Diff=HighLight-Shadow;
rDiff=R-Shadow;
gDiff=G-Shadow;
bDiff=B-Shadow;

rDiff(rDiff<0)=0;  
gDiff(gDiff<0)=0;  
bDiff(bDiff<0)=0;  

R=(rDiff/Diff).^(1/Midtones)*255;
G=(gDiff/Diff).^(1/Midtones)*255;
B=(bDiff/Diff).^(1/Midtones)*255;

R(R>255)=255;
G(G>255)=255;
B(B>255)=255;

img(:,:,1)=uint8(R);
img(:,:,2)=uint8(G);
img(:,:,3)=uint8(B);
figure(2);
imshow(img);

2）C程序

void LevelAdjustRGB(unsigned char *pSrc, unsigned char *pDest, int nWidth, int nHeight,int nShadow,int nHighLight,double dMidtone)
{
       //局部变量声明
	int i = 0; 
	int nLength  = nWidth * nHeight;
	double dDiff = nHighLight-nShadow;
	int *nRgbDiff = new int[3 * nLength];

	for(i = 0;i < 3 * nLength; i++)
	{
		nRgbDiff[i] = pSrc[i] - nShadow;
		if(nRgbDiff[i] < 0)
		{
			nRgbDiff[i] = 0;
		}

		//此处必须用int作为中间变量 不能用char  会有数据截断
		int nTemp = static_cast(pow((nRgbDiff[i] / dDiff),1 / dMidtone) * 255);
		pDest[i] = CLIP8(nTemp);
	}
	//释放空间
	if(!nRgbDiff)
	{
		delete []nRgbDiff;
		nRgbDiff = NULL;
	}
}

其中

#define  CLIP8(a)  (((a) & 0xFFFFFF00) ? (((a) < 0) ? 0 : 255 ) : (a))      ///<判断8位数据范围

3、实验结果，同photoshop处理结果

图1  原图

图2 nShadow=159  nHighLight=238  dMidtone=0.51结果