使用 OpenCV 从图像中删除不均匀的白色边框

Question

I'm trying to remove uneven white borders from different set of pictures. They all look like these:

What I'm doing right now is just drawing a rectangle around the picture in hope that it covers the white area:

h, w = img.shape
cv2.rectangle(img, (0,0), (w,h), (0,0,0), 2)

Depending on the picture it might work or not. As there are a variety number of pictures which are in similar situation I'm looking for a more logical solution which is applicable to all pictures with this kind of issue.

Answer 1

I think your way is right, but it's unaware whether it overlays figures (you may increase the thickness if you know there won't be figures with that margin) and the desired thickness is unknown.

You may use findContour. Find the "thick" figures (if you expect particular metrics as in the picture). Sort their extreme coordinates, add some margin and that would set the max depth of the border.

However then not a rectangle, but a line would be better drawn per each side, in case there are figures very close to the border.

Another scenario: first draw concentrating black rectangles (or lines per side) in order to clear the unevenness, then draw the white lines/rectangle with the desired thickness.