opencv imread 函数读取CV_16UC1的png图片

opencv 2.4.11中imread读取图片有三种方式：

CV_LOAD_IMAGE_UNCHANGED (<0) loads the image as is (including the alpha channel if present)
CV_LOAD_IMAGE_GRAYSCALE ( 0) loads the image as an intensity one
CV_LOAD_IMAGE_COLOR (>0) loads the image in the RGB format

如果待读取的png图片是灰度图，而且是16位的，那么应该选用CV_LOAD_IMAGE_UNCHANGED，用Mat类型保存。

例如：

Mat img = imread("depth.png",CV_LOAD_IMAGE_UNCHANGED);

那么img就是一个CV_16UC1类型的数据，访问像素(i,j)

img.at<ushort>(i,j)即可。