16位图片转换成8位图，并进行灰度值的范围调节

注：主要是通过调整upper_limit这个参数

cv::Mat float16touint8(cv::Mat image, float lower_limit, float upper_limit)
{
	clock_t s = clock();
	if (image.empty())
		return cv::Mat();

	int width = image.cols;//图片宽度
	int height = image.rows;//图片高度
	Mat dst = Mat::zeros(height, width, CV_8UC1);//先生成空的目标图片
	double minv = 0.0, maxv = 0.0;
	double* minp = &minv;
	double* maxp = &maxv;
	minMaxIdx(image, minp, maxp);  //取得像素值最大值和最小值
	maxv = min((int)maxv, 26000);
	maxv *= upper_limit / 255.0;
	
	//用指针访问像素，速度更快
	ushort* p_img;
	uchar* p_dst;
	double val;
	width *= height;
	height = 1;
	for (int i = 0; i < height; i++)
	{
		p_img = image.ptr<ushort>(i);//获取每行首地址
		p_dst = dst.ptr<uchar>(i);
		for (int j = 0; j < width; ++j)
		{
			val = (p_img[j] - minv) / (maxv - minv) * 255;
			if (val > 255)
				val = 255;
			else if (val < 0)
				val = 0;
			p_dst[j] = val;
		}
	}

	return dst;
}