openCV: Sobel edge detection gives me assertion error

Question

I am using python-openCV. When using the Sobel edge detection I get the following assertion error:

src.size() == dst.size() && src.channels() == dst.channels() && ((src.depth() == CV_8U && (dst.depth() == CV_16S || dst.depth() == CV_32F)) || (src.depth() == CV_32F && dst.depth() == CV_32F))

I create the dest using CreateImage() and it has same size and channels as src. Also the depth of both src and dest is IPL_DEPTH_8U. I also tried loading image using LoadImageM() so that the constants are of kind CV_* but that didn't help.

I also happen to find out that IPL_DEPTH_8U == CV_8U is false.

Answer 1

I found the solution a bit tricky for novices to openCV:

src = cv.LoadImageM('src.png', cv.CV_LOAD_IMAGE_GRAYSCALE)
dest = cv.CreateMat(src.height, src.width, cv.CV_16S)
cv.Sobel(src, dest, 1, 1)

The important thing to note is that the image formats required for operations are not clearly documented in API references and one should pay very careful attention to errors generated.