图像处理的简单优化-02：算法设计
灰度计算
虽然是最简单的灰度算法，但也不能使用颜色平均之类太阳春的东西。标准点的应该是：0.21 * R + 0.71 * G + 0.07 * B。当然，浮点计算是绝对要避免的，所以要转换成定点计算，写成宏就是：
#define R_FACTOR (int)(0.21 * 256) #define G_FACTOR (int)(0.71 * 256) #define B_FACTOR (int)(0.07 * 256) #define RGB2GRAY(r, g, b) ((((r) * R_FACTOR) + ((g) * G_FACTOR) + ((b) * B_FACTOR)) >> 8)
像素处理
假设unsigned char* ptr为图像数据指针，对像素进行灰度化的处理为：
ptr++; // skip Alpha int r = *ptr, g = *(ptr + 1), b = *(ptr + 2); int gray = RGB2GRAY(r, g, b); *ptr++ = gray; *ptr++ = gray; *ptr++ = gray;
写成宏就是：
#define GRAY_PIXEL(ptr, gray) \
{ \
ptr++; \
int r = *ptr, g = *(ptr + 1), b = *(ptr + 2); \
gray = RGB2GRAY(r, g, b); \
*ptr++ = gray; \
*ptr++ = gray; \
*ptr++ = gray; \
}
逐点处理算法
int gray;
for(unsigned int h = 0; h < height; h++)
{
for(unsigned int w = 0; w < width; w ++)
{
GRAY_PIXEL(buffer, gray);
}
}
return true;
测试
现在找个图片进行测试，以4536*2404尺寸的图像为例,其Release性能为：
Done. 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 17, 17, 17, 17, 17, 17, 17, 18, 17, 18, 18, 17, 17, 17, 17, 17, 18, 17, 17, 17, 17, 17, 17, 17, 17, 18, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 982, 17, 17, 17, 17, 18, 17, 17, 17, 17, 17, 17, 18, 17, 17, 17, 18, 17, 18, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 17, 17, 19, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 17, 17, 18, 17, 17, 17, 17, 17, 18, 17, 17, 17, 17, 982, 17, 17, 17, 18, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 17, 18, 17, 17, Average:17 ms Max:19 Min:17 ms (Max + Min)/2=18 ms
注：在运行过程中，会偶尔出现一个很大的运行时间值，估计为受系统影响，故意将其舍去。