Merge pull request #25090 from MaximSmolskiy:compensate-edge-length-in-ChessBoardDetector-generateQuads-attempt-2

Compensate edge length in ChessBoardDetector::generateQuads (attempt 2) #25090

### Pull Request Readiness Checklist

New attempt for #24833, which was reverted as #25036.

Locally I fixed `Calib3d_StereoCalibrate_CPP.regression` test by corners refinement using `cornerSubPix` function

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

- [x] I agree to contribute to the project under Apache 2 License.
- [x] 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
- [x] The PR is proposed to the proper branch
- [x] 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

modules/calib3d/src/calibinit.cpp

@@ -234,7 +234,7 @@ public:
         all_quads_count = 0;
     }
 
-    void generateQuads(const cv::Mat& image_, int flags);
+    void generateQuads(const cv::Mat& image_, int flags, int dilations);
 
     bool processQuads(std::vector<cv::Point2f>& out_corners, int &prev_sqr_size);
 
@@ -547,7 +547,7 @@ bool findChessboardCorners(InputArray image_, Size pattern_size,
         rectangle( thresh_img_new, Point(0,0), Point(thresh_img_new.cols-1, thresh_img_new.rows-1), Scalar(255,255,255), 3, LINE_8);
 
         detector.reset();
-        detector.generateQuads(thresh_img_new, flags);
+        detector.generateQuads(thresh_img_new, flags, dilations);
         DPRINTF("Quad count: %d/%d", detector.all_quads_count, (pattern_size.width/2+1)*(pattern_size.height/2+1));
         SHOW_QUADS("New quads", thresh_img_new, &detector.all_quads[0], detector.all_quads_count);
         if (detector.processQuads(out_corners, prev_sqr_size))
@@ -612,7 +612,7 @@ bool findChessboardCorners(InputArray image_, Size pattern_size,
                 rectangle( thresh_img, Point(0,0), Point(thresh_img.cols-1, thresh_img.rows-1), Scalar(255,255,255), 3, LINE_8);
 
                 detector.reset();
-                detector.generateQuads(thresh_img, flags);
+                detector.generateQuads(thresh_img, flags, dilations);
                 DPRINTF("Quad count: %d/%d", detector.all_quads_count, (pattern_size.width/2+1)*(pattern_size.height/2+1));
                 SHOW_QUADS("Old quads", thresh_img, &detector.all_quads[0], detector.all_quads_count);
                 if (detector.processQuads(out_corners, prev_sqr_size))
@@ -1755,7 +1755,7 @@ void ChessBoardDetector::findQuadNeighbors()
 // returns corners in clockwise order
 // corners don't necessarily start at same position on quad (e.g.,
 //   top left corner)
-void ChessBoardDetector::generateQuads(const cv::Mat& image_, int flags)
+void ChessBoardDetector::generateQuads(const cv::Mat& image_, int flags, int dilations)
 {
     binarized_image = image_;  // save for debug purposes
 
@@ -1880,6 +1880,9 @@ void ChessBoardDetector::generateQuads(const cv::Mat& image_, int flags)
             float d = normL2Sqr<float>(q.corners[i]->pt - q.corners[(i+1)&3]->pt);
             q.edge_len = std::min(q.edge_len, d);
         }
+
+        const int edge_len_compensation = 2 * dilations;
+        q.edge_len += 2 * sqrt(q.edge_len) * edge_len_compensation + edge_len_compensation * edge_len_compensation;
     }
 
     all_quads_count = quad_count;

modules/calib3d/test/test_cameracalibration.cpp

@@ -1388,8 +1388,8 @@ void CV_StereoCalibrationTest::run( int )
 
         for( int i = 0; i < nframes; i++ )
         {
-            Mat left = imread(imglist[i*2]);
+            Mat left = imread(imglist[i*2], IMREAD_GRAYSCALE);
-            Mat right = imread(imglist[i*2+1]);
+            Mat right = imread(imglist[i*2+1], IMREAD_GRAYSCALE);
             if(left.empty() || right.empty())
             {
                 ts->printf( cvtest::TS::LOG, "Can not load images %s and %s, testcase %d\n",
@@ -1400,6 +1400,8 @@ void CV_StereoCalibrationTest::run( int )
             imgsize = left.size();
             bool found1 = findChessboardCorners(left, patternSize, imgpt1[i]);
             bool found2 = findChessboardCorners(right, patternSize, imgpt2[i]);
+            cornerSubPix(left, imgpt1[i], Size(5, 5), Size(-1, -1), TermCriteria(TermCriteria::EPS | TermCriteria::MAX_ITER, 30, 0.1));
+            cornerSubPix(right, imgpt2[i], Size(5, 5), Size(-1, -1), TermCriteria(TermCriteria::EPS | TermCriteria::MAX_ITER, 30, 0.1));
             if(!found1 || !found2)
             {
                 ts->printf( cvtest::TS::LOG, "The function could not detect boards (%d x %d) on the images %s and %s, testcase %d\n",