快速方差计算方法

int DetImgDev(unsigned char* img, int ImgH, int ImgW)
{
	int i, sum1, sum2, size, n;
	int ImgAvg, ImgDev;
	n = sum1 = sum2 = 0;
	size = ImgH*ImgW;
	for (i = 0; i < size; i++) {
	sum1 += img[i];
		sum2 += img[i] * img[i];
	}
	ImgAvg = sum1 / size;
	ImgDev = (sum2 - (((sum1 >> 1)*ImgAvg) << 1)) / size;

	return ImgDev;
}