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Chessboard black square is NOT detected via contour?

asked 2020-08-26 21:26:43 -0500

Hi, I'm testing some chessboard images using cv2.findContours(), using cnts = cv2.findContours(otsu, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE) .

I obtained the binary image via otsu binarization, and did some cv2.HoughLinesP experiments. So far, what I can obtain are as follows:

image description image description image description

My question is: why ONLY the white squares/rectangles have been successfully detected, but those BLACK ones failed to be detected ?

Any possibilities?

Thank you ...

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answered 2020-08-27 04:50:36 -0500

berak gravatar image

findContours expects white foreground and black background.

if you want it the other way round (detect black things) -- invert the image

img = ~img
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Asked: 2020-08-26 21:26:43 -0500

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Last updated: Aug 27 '20