Merge pull request #16625 from D-Alex:findChessboard

diff --cc modules/calib3d/include/opencv2/calib3d.hpp
Simple merge

diff --cc modules/calib3d/src/chessboard.cpp
index 99a8045,04a3bbe..8716e9c
--- 1/modules/calib3d/src/chessboard.cpp
--- 2/modules/calib3d/src/chessboard.cpp
+++ b/modules/calib3d/src/chessboard.cpp
@@@ -3004,10 -3647,10 +3647,10 @@@ Chessboard::Board Chessboard::detectImp
      std::vector<KeyPoint> keypoints_seed;
      std::vector<std::vector<float> > angles;
      findKeyPoints(gray,keypoints_seed,feature_maps,angles,mask);
-     if(keypoints_seed.empty())
+     if(int(keypoints_seed.size()) < parameters.chessboard_size.width * parameters.chessboard_size.height)
          return Chessboard::Board();
  
 -    // check how many points are likely a checkerbord corner
 +    // check how many points are likely a checkerboard corner
      float response = fabs(keypoints_seed.front().response*MIN_RESPONSE_RATIO);
      std::vector<KeyPoint>::const_iterator seed_iter = keypoints_seed.begin();
      int count = 0;

diff --cc modules/calib3d/src/chessboard.hpp
Simple merge