OpenCV Error:assertion failed (SCN ==3 | | scn==4) in Cv::cvtcolor

In the traversal of the file picture in turn, the face detection, but every time there is an exception, very puzzled, the program is written without problems, the Internet to check a bit.

my problem is because it is empty when I pass in the mat image, so there is no way to do it when cvtcolor.

Why?? Why is it empty??

Look up the face library look at the naming order only to find that there are some missing data in the middle. Such as:

Less image_0010.png this image.

So it would be nice to add an if (!img.empty ()) condition.

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OpenCV Error:assertion failed (SCN ==3 | | scn==4) in Cv::cvtcolor