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fix getUndistortRectangles() to ignore corners #27374

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fix getUndistortRectangles() to ignore corners #27374

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daishironishida
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@daishironishida daishironishida commented May 28, 2025 •
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getUndistortRectangles() generates points along the image border, and uses the mapping of these points to determine the inscribed/circumscribed rectangles. However undistortPoints() is likely to fail in the image corners, and when it fails, it returns the input point. As a result, the inscribed rectangle cannot be greater than the input image size. This means that the result of getOptimalNewCameraMatrix() for alpha=0 has a smaller FOV than ideal.

Below image plots the points along the image border (Source Points) for a 1280x720 image, and the results of undistortPoints() for an AXIS M2035-LE camera.

Plot

I have edited getUndistortRectangles() to skip the image corners.
It is preferable to only ignore points where undistortPoints() failed, but that requires quite a bit of refactoring.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

  • 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
  • The PR is proposed to the proper branch
  • There is a reference to the original bug report and related work
  • There is accuracy test, performance test and test data in opencv_extra repository, if applicable
    Patch to opencv_extra has the same branch name.
  • The feature is well documented and sample code can be built with the project CMake

@asmorkalov
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Related PR: #24927

@daishironishida
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Looks like test_videoio in Linux x64 Debug timed out. Can I run again?

command timed out: 600 seconds without output running buildenv python ../4.x/opencv/modules/ts/misc/run.py --configuration=Debug --test_tag_skip=size_hd --gtest_output=xml:results_test_videoio.xml -t videoio -a --test_threads=2, attempting to kill
process killed by signal 15
program finished with exit code -1
elapsedTime=668.744162


commands lock was released

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Please ignore it.

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