Merge pull request #25808 from DmitryYurov:bug-25806-checkerboard-marker-black-tile

Enable checkerboard detection with a central / corner marker on a black tile #25808

This pull request closes the issue #25806.

The issue doesn't require any documentation - it's quite intuitive that the detection result shouldn't depend on the color of the marker's tile.

### Pull Request Readiness Checklist

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
- [x] 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/chessboard.cpp

@@ -1625,8 +1625,6 @@ bool Chessboard::Board::normalizeMarkerOrientation()
             if(!current_cell->marker || !current_cell->right || !current_cell->right->marker)
                 continue;
 
-            if(current_cell->black)
-            {
             if(current_cell->right->top && current_cell->right->top->marker)
             {
                 rotateLeft();
@@ -1640,9 +1638,6 @@ bool Chessboard::Board::normalizeMarkerOrientation()
                 pcell = current_cell->right;
                 break;
             }
-            }
-            else
-            {
             if(current_cell->top && current_cell->top->marker)
             {
                 rotateRight();
@@ -1657,7 +1652,6 @@ bool Chessboard::Board::normalizeMarkerOrientation()
             }
         }
     }
-    }
     if(pcell)
     {
         //check for ambiguity

modules/calib3d/test/test_chesscorners.cpp

@@ -679,6 +679,26 @@ TEST(Calib3d_AsymmetricCirclesPatternDetector, accuracy) { CV_ChessboardDetector
 TEST(Calib3d_AsymmetricCirclesPatternDetectorWithClustering, accuracy) { CV_ChessboardDetectorTest test( ASYMMETRIC_CIRCLES_GRID, CALIB_CB_CLUSTERING ); test.safe_run(); }
 #endif
 
+TEST(Calib3d_ChessboardWithMarkers, regression_25806_white)
+{
+    const cv::String dataDir = string(TS::ptr()->get_data_path()) + "cv/cameracalibration/";
+    const cv::Mat image = cv::imread(dataDir + "checkerboard_marker_white.png");
+
+    std::vector<Point2f> corners;
+    const bool success = cv::findChessboardCornersSB(image, Size(9, 14), corners, CALIB_CB_MARKER);
+    ASSERT_TRUE(success);
+}
+
+TEST(Calib3d_ChessboardWithMarkers, regression_25806_black)
+{
+    const cv::String dataDir = string(TS::ptr()->get_data_path()) + "cv/cameracalibration/";
+    const cv::Mat image = cv::imread(dataDir + "checkerboard_marker_black.png");
+
+    std::vector<Point2f> corners;
+    const bool success = cv::findChessboardCornersSB(image, Size(9, 14), corners, CALIB_CB_MARKER);
+    ASSERT_TRUE(success);
+}
+
 TEST(Calib3d_CirclesPatternDetectorWithClustering, accuracy)
 {
     cv::String dataDir = string(TS::ptr()->get_data_path()) + "cv/cameracalibration/circles/";