上一篇讲拉普拉斯锐化,不能提供精细的调整,在photoshop中采用USM(Unsharp mask)可以进一步优化。目的是:
for(j = 0; j < height; j++)
{
for(i = 0; i < width; i++)
{
pMask[0] = abs(pSrc[0] - pDst[0]) < threshold ? 0 : 128;
pMask[1] = abs(pSrc[1] - pDst[1]) < threshold ? 0 : 128;
pMask[2] = abs(pSrc[2] - pDst[2]) < threshold ? 0 : 128;
pDst += 4;
pSrc += 4;
pMask += 4;
}
pDst += offset;
pSrc += offset;
pMask += offset;
}
for(j = 0; j < height; j++)
{
for(i = 0; i < width; i++)
{
// 计算像素差
b = pSrc[0] - pDst[0];
g = pSrc[1] - pDst[1];
r = pSrc[2] - pDst[2];
// 原值 + 像素差 * 系数 (amount >> 7 == [0, 128]/128 == [0, 1.0])
// 即得到 rgb = 原值 + 像素差 * [0, 1]
b = (pSrc[0] + ((b * amount) >> 7));
g = (pSrc[1] + ((g * amount) >> 7));
r = (pSrc[2] + ((r * amount) >> 7));
b = (b * pMask[0] + pSrc[0] * (128 - pMask[0])) >> 7;
g = (g * pMask[1] + pSrc[1] * (128 - pMask[1])) >> 7;
r = (r * pMask[2] + pSrc[2] * (128 - pMask[2])) >> 7;
pSrc[0] = CLIP3(b, 0, 255);
pSrc[1] = CLIP3(g, 0, 255);
pSrc[2] = CLIP3(r, 0, 255);
pSrc += 4;
pDst += 4;
pMask += 4;
}
pSrc += offset;
pDst += offset;
pMask += offset;
}
完整代码:
#include"f_USM.h"
#include"f_GaussFilter.h"
#include<stdlib.h>
#include<math.h>
#include<string.h>
#include<stdio.h>
#include"Commen.h"
int f_USM(unsigned char* srcData,int width, int height,int stride,int radius, int amount, int threshold)
{
int ret = 0;
if(radius == 0)
return ret;
radius = CLIP3(radius, 0, 100);
amount = CLIP3(amount, 0,500);
threshold = CLIP3(threshold, 0,255);
unsigned char* gaussData = (unsigned char*)malloc(sizeof(unsigned char) * height * stride);
memcpy(gaussData, srcData, sizeof(unsigned char) * height * stride);
f_FastGaussFilter(gaussData, width, height, stride, radius);
int i, j, r, g, b, offset;
offset = stride - width * 4;
// 将 amount 均匀到[0, 128] 的范围内,如果输入值是[0, 100]
// 128有什么特殊的含义呢?128 = 256 / 2,即RGB色值的一半
// 一半是锐化的临界点
amount = amount * 128 / 100;
unsigned char* pSrc = srcData;
unsigned char* pDst = gaussData;
unsigned char* maskData = (unsigned char*)malloc(sizeof(unsigned char) * height * stride);
unsigned char* pMask = maskData;
for(j = 0; j < height; j++)
{
for(i = 0; i < width; i++)
{
pMask[0] = abs(pSrc[0] - pDst[0]) < threshold ? 0 : 128;
pMask[1] = abs(pSrc[1] - pDst[1]) < threshold ? 0 : 128;
pMask[2] = abs(pSrc[2] - pDst[2]) < threshold ? 0 : 128;
pDst += 4;
pSrc += 4;
pMask += 4;
}
pDst += offset;
pSrc += offset;
pMask += offset;
}
pDst = gaussData;
pSrc = srcData;
pMask = maskData;
f_FastGaussFilter(maskData, width, height, stride, radius);
for(j = 0; j < height; j++)
{
for(i = 0; i < width; i++)
{
// 计算像素差
b = pSrc[0] - pDst[0];
g = pSrc[1] - pDst[1];
r = pSrc[2] - pDst[2];
// 原值 + 像素差 * 系数 (amount >> 7 == [0, 128]/128 == [0, 1.0])
// 即得到 rgb = 原值 + 像素差 * [0, 1]
b = (pSrc[0] + ((b * amount) >> 7));
g = (pSrc[1] + ((g * amount) >> 7));
r = (pSrc[2] + ((r * amount) >> 7));
b = (b * pMask[0] + pSrc[0] * (128 - pMask[0])) >> 7;
g = (g * pMask[1] + pSrc[1] * (128 - pMask[1])) >> 7;
r = (r * pMask[2] + pSrc[2] * (128 - pMask[2])) >> 7;
pSrc[0] = CLIP3(b, 0, 255);
pSrc[1] = CLIP3(g, 0, 255);
pSrc[2] = CLIP3(r, 0, 255);
pSrc += 4;
pDst += 4;
pMask += 4;
}
pSrc += offset;
pDst += offset;
pMask += offset;
}
free(gaussData);
free(maskData);
return ret;
};
参考:https://baijiahao.baidu.com/s?id=1651538317157891526&wfr=spider&for=pc