Merge pull request #24710 from MaximSmolskiy:do-not-dilate-binary-images-on-first-iteration-in-findChessboardCorners

Do not dilate binary images on first iteration in findChessboardCorners

modules/calib3d/src/calibinit.cpp

@@ -531,14 +531,14 @@ bool findChessboardCorners(InputArray image_, Size pattern_size,
     const int min_dilations = 0;
     const int max_dilations = is_plain ? 0 : 7;
 
-    // Try our standard "1" dilation, but if the pattern is not found, iterate the whole procedure with higher dilations.
-    // This is necessary because some squares simply do not separate properly with a single dilation.  However,
+    // Try our standard "0" and "1" dilations, but if the pattern is not found, iterate the whole procedure with higher dilations.
+    // This is necessary because some squares simply do not separate properly without and with a single dilations. However,
     // we want to use the minimum number of dilations possible since dilations cause the squares to become smaller,
     // making it difficult to detect smaller squares.
     for (int dilations = min_dilations; dilations <= max_dilations; dilations++)
     {
         //USE BINARY IMAGE COMPUTED USING icvBinarizationHistogramBased METHOD
-        if(!is_plain)
+        if(!is_plain && dilations > 0)
             dilate( thresh_img_new, thresh_img_new, Mat(), Point(-1, -1), 1 );
 
         // So we can find rectangles that go to the edge, we draw a white line around the image edge.
@@ -596,13 +596,13 @@ bool findChessboardCorners(InputArray image_, Size pattern_size,
                     block_size = block_size | 1;
                     // convert to binary
                     adaptiveThreshold( img, thresh_img, 255, ADAPTIVE_THRESH_MEAN_C, THRESH_BINARY, block_size, (k/2)*5 );
-                    if (dilations > 0)
-                        dilate( thresh_img, thresh_img, Mat(), Point(-1, -1), dilations-1 );
+                    dilate( thresh_img, thresh_img, Mat(), Point(-1, -1), dilations );
 
                 }
                 else
                 {
-                    dilate( thresh_img, thresh_img, Mat(), Point(-1, -1), 1 );
+                    if (dilations > 0)
+                        dilate( thresh_img, thresh_img, Mat(), Point(-1, -1), 1 );
                 }
                 SHOW("Old binarization", thresh_img);