OpenCV中imread函數如下所示：
C++: Mat imread(const string& filename, int flags=1 )
其中flags可以爲：
flags –
Flags specifying the color type of a loaded image:
- CV_LOAD_IMAGE_ANYDEPTH - If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.
- CV_LOAD_IMAGE_COLOR - If set, always convert image to the color one
- CV_LOAD_IMAGE_GRAYSCALE - If set, always convert image to the grayscale one
-
- >0 Return a 3-channel color image.
-
Note
In the current implementation the alpha channel, if any, is stripped from the output image. Use negative value if you need the alpha channel.
- =0 Return a grayscale image.
- <0 Return the loaded image as is (with alpha channel).
注意的是如果是讀入RGB的三色圖像，其channel的排列如下：
Note
In the case of color images, the decoded images will have the channels stored in B G R order.
即：
flowu = nocGTFlow.at<Vec3s>(i,j)[0]; B通道
flowv = nocGTFlow.at<Vec3s>(i,j)[1]; G通道
valid = nocGTFlow.at<Vec3s>(i,j)[2]; R通道
