[WeChat QR] Fixing issue that Hybrid Binarizer not working due to integral calculation.

[ninh-huynh]

This should fixes #3156 #3008

The size of block array blocks_ is subWidth * subHeight but the block integral size is width * height. I believe something wrong when calculating the blockIntegral with that size.

opencv_contrib/modules/wechat_qrcode/src/zxing/common/binarizer/hybrid_binarizer.cpp

Line 41 in 508c8db

blocks_ = getBlockArray(subWidth * subHeight);

opencv_contrib/modules/wechat_qrcode/src/zxing/common/binarizer/hybrid_binarizer.cpp

Line 58 in 508c8db

blockIntegral_ = new Array<int>(width * height);

I suggest change it size to (subWidth + 1) * (subHeight + 1) (These extra row and column is just for padding 0 arroud). Also update the precalculation of the blockIntegral, calculate sum base on that blockIntegral

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

force_builders=linux,docs

[ninh-huynh]

Tested with these two samples:
https://github.com/opencv/opencv_extra/blob/4.x/testdata/cv/qrcode/link_ocv.jpg
https://github.com/opencv/opencv_extra/blob/4.x/testdata/cv/qrcode/link_wiki_cv.jpg

[ninh-huynh]

Waiting for Maintainers to trigger CI manually.

[ninh-huynh]

/cc @dddzg

[dddzg]

There are some test cases failed in Win64,Mac and Win32.
https://pullrequest.opencv.org/buildbot/builders/precommit-contrib_windows64/builds/15419

[ninh-huynh]

There are some test cases failed in Win64,Mac and Win32. https://pullrequest.opencv.org/buildbot/builders/precommit-contrib_windows64/builds/15419

Got it. Already fix those test cases in new commit.

[dddzg]

@alalek

[alalek]

I don't see code changes related to reading of blockIntegral_ with new layout. I see changes in "generator" only.

[ninh-huynh]

It took me a while to understand the logic in here due to unclear meaning of left, top, offset1, offset2

opencv_contrib/modules/wechat_qrcode/src/zxing/common/binarizer/hybrid_binarizer.cpp

Lines 198 to 210 in 7a35d3d

	int left = cap(x, THRES_BLOCKSIZE, subWidth - THRES_BLOCKSIZE - 1);
	int top = cap(y, THRES_BLOCKSIZE, subHeight - THRES_BLOCKSIZE - 1);
	int sum = 0;
	// int sum2 = 0;
	int offset1 = (top - THRES_BLOCKSIZE) * (subWidth + 1) + left - THRES_BLOCKSIZE;
	int offset2 = (top + THRES_BLOCKSIZE + 1) * (subWidth + 1) + left - THRES_BLOCKSIZE;
	int blocksize = THRES_BLOCKSIZE * 2 + 1;
	sum = blockIntegral[offset1] - blockIntegral[offset1 + blocksize] -
	blockIntegral[offset2] + blockIntegral[offset2 + blocksize];

As my understanding, the left, top correspond to centerX, centerY of 5 x 5 block square. And offset1, offset2 are A, C in

A - - B
|        |
C - - D

The blockIntegral is already used with new layout so we don't need to modify anything in there.

[ninh-huynh]

For more clear, we could change subWidth + 1 to blockIntegralWidth in here

opencv_contrib/modules/wechat_qrcode/src/zxing/common/binarizer/hybrid_binarizer.cpp

Lines 204 to 205 in 7a35d3d

	int offset1 = (top - THRES_BLOCKSIZE) * (subWidth + 1) + left - THRES_BLOCKSIZE;
	int offset2 = (top + THRES_BLOCKSIZE + 1) * (subWidth + 1) + left - THRES_BLOCKSIZE;

[alalek]

LGTM 👍
Thank you for contribution!