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Fix occuring artifacts in fillPoly#23076

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alalek merged 1 commit intoopencv:3.4from
inayd:22012-bugfixFillPoly
Jan 28, 2023
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Fix occuring artifacts in fillPoly#23076
alalek merged 1 commit intoopencv:3.4from
inayd:22012-bugfixFillPoly

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@inayd inayd commented Jan 2, 2023 •
edited by alalek
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Fixes #22012
Fixing the bug described in #22012

The artifacts can occur when corners of a polygon are outside of the image. To be more precise, the outline of the polygon is being drawn using clipped endpoints of an edge, while the borders of the area to be filled are determined using unclipped points of an edge. This can introduce a small offset between the outline and the filled area in polygons which have corner points outside of the image.

The issue is fixed by correcting the edges when lines are clipped.

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  • I agree to contribute to the project under Apache 2 License.
  • To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
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alalek
alalek reviewed Jan 2, 2023
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@inayd inayd marked this pull request as draft January 4, 2023 16:21
@inayd inayd marked this pull request as ready for review January 4, 2023 16:21
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inayd commented Jan 18, 2023

I adjusted the code after the review. Could you take another look? 🙂

@inayd inayd requested a review from alalek January 25, 2023 19:52
alalek
alalek approved these changes Jan 28, 2023
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LGTM 👍 Thank you for contribution!

@alalek alalek merged commit c67d4fc into opencv:3.4 Jan 28, 2023
This was referenced Jan 28, 2023
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@asmorkalov asmorkalov mentioned this pull request May 31, 2023
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dan-masek commented Sep 6, 2024

Today I ran across this question: https://stackoverflow.com/questions/78955298/python-opencv-draws-polygons-outside-of-lines

Looks like it started to appear between 4.7 and 4.8 which leads me to believe it's related to this patch.

import cv2
import numpy as np
    
points = np.array([[[44, 27], [7, 37], [7, 19],[38, 19]]], np.int32).reshape((-1, 1, 2))
img = np.zeros((50, 50, 3), dtype=np.uint8)

cv2.fillPoly(img, [pts], (0, 0, 255))
cv2.polylines(img, [pts], True, (255, 0, 0), 1)

cv2.imwrite("output_v" + str(cv2.__version__) + ".png", img)

In 4.7 and older:
output_v4 7 0

In 4.8 and younger:
output_v4 8 0

Is that expected?

@dan-masek dan-masek mentioned this pull request Sep 9, 2024
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@inayd inayd mentioned this pull request Sep 26, 2024
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