Merge pull request #7516 from sovrasov:find_contours_fix

modules/calib3d/test/test_chesscorners.cpp

@@ -373,8 +373,6 @@ bool CV_ChessboardDetectorTest::checkByGenerator()
 {
     bool res = true;
 
-// for some reason, this test sometimes fails on Ubuntu
-#if (defined __APPLE__ && defined __x86_64__) || defined _MSC_VER
     //theRNG() = 0x58e6e895b9913160;
     //cv::DefaultRngAuto dra;
     //theRNG() = *ts->get_rng();
@@ -473,7 +471,6 @@ bool CV_ChessboardDetectorTest::checkByGenerator()
 
         cv::drawChessboardCorners(cb, cbg.cornersSize(), Mat(corners_found), found);
     }
-#endif
 
     return res;
 }

modules/imgproc/include/opencv2/imgproc.hpp

@@ -3732,21 +3732,17 @@ CV_EXPORTS_W int connectedComponentsWithStats(InputArray image, OutputArray labe
 /** @brief Finds contours in a binary image.
 
 The function retrieves contours from the binary image using the algorithm @cite Suzuki85 . The contours
-are a useful tool for shape analysis and object detection and recognition. See squares.c in the
+are a useful tool for shape analysis and object detection and recognition. See squares.cpp in the
 OpenCV sample directory.
 
-@note Source image is modified by this function. Also, the function does not take into account
-1-pixel border of the image (it's filled with 0's and used for neighbor analysis in the algorithm),
-therefore the contours touching the image border will be clipped.
-
 @param image Source, an 8-bit single-channel image. Non-zero pixels are treated as 1's. Zero
-pixels remain 0's, so the image is treated as binary . You can use compare , inRange , threshold ,
-adaptiveThreshold , Canny , and others to create a binary image out of a grayscale or color one.
-The function modifies the image while extracting the contours. If mode equals to RETR_CCOMP
-or RETR_FLOODFILL, the input can also be a 32-bit integer image of labels (CV_32SC1).
-@param contours Detected contours. Each contour is stored as a vector of points.
-@param hierarchy Optional output vector, containing information about the image topology. It has
-as many elements as the number of contours. For each i-th contour contours[i] , the elements
+pixels remain 0's, so the image is treated as binary . You can use cv::compare, cv::inRange, cv::threshold ,
+cv::adaptiveThreshold, cv::Canny, and others to create a binary image out of a grayscale or color one.
+If mode equals to cv::RETR_CCOMP or cv::RETR_FLOODFILL, the input can also be a 32-bit integer image of labels (CV_32SC1).
+@param contours Detected contours. Each contour is stored as a vector of points (e.g.
+std::vector<std::vector<cv::Point> >).
+@param hierarchy Optional output vector (e.g. std::vector<cv::Vec4i>), containing information about the image topology. It has
+as many elements as the number of contours. For each i-th contour contours[i], the elements
 hierarchy[i][0] , hiearchy[i][1] , hiearchy[i][2] , and hiearchy[i][3] are set to 0-based indices
 in contours of the next and previous contours at the same hierarchical level, the first child
 contour and the parent contour, respectively. If for the contour i there are no next, previous,

modules/imgproc/src/contours.cpp

@@ -199,10 +199,10 @@ _CvContourScanner;
    Initializes scanner structure.
    Prepare image for scanning ( clear borders and convert all pixels to 0-1.
 */
-CV_IMPL CvContourScanner
-cvStartFindContours( void* _img, CvMemStorage* storage,
+static CvContourScanner
+cvStartFindContours_Impl( void* _img, CvMemStorage* storage,
                      int  header_size, int mode,
-                     int  method, CvPoint offset )
+                     int  method, CvPoint offset, int needFillBorder )
 {
     if( !storage )
         CV_Error( CV_StsNullPtr, "" );
@@ -310,15 +310,18 @@ cvStartFindContours( void* _img, CvMemStorage* storage,
     CV_Assert(size.height >= 1);
 
     /* make zero borders */
-    int esz = CV_ELEM_SIZE(mat->type);
-    memset( img, 0, size.width*esz );
-    memset( img + static_cast<size_t>(step) * (size.height - 1), 0, size.width*esz );
-
-    img += step;
-    for( int y = 1; y < size.height - 1; y++, img += step )
+    if(needFillBorder)
     {
-        for( int k = 0; k < esz; k++ )
-            img[k] = img[(size.width - 1)*esz + k] = (schar)0;
+        int esz = CV_ELEM_SIZE(mat->type);
+        memset( img, 0, size.width*esz );
+        memset( img + static_cast<size_t>(step) * (size.height - 1), 0, size.width*esz );
+
+        img += step;
+        for( int y = 1; y < size.height - 1; y++, img += step )
+        {
+            for( int k = 0; k < esz; k++ )
+                img[k] = img[(size.width - 1)*esz + k] = (schar)0;
+        }
     }
 
     /* converts all pixels to 0 or 1 */
@@ -328,6 +331,14 @@ cvStartFindContours( void* _img, CvMemStorage* storage,
     return scanner;
 }
 
+CV_IMPL CvContourScanner
+cvStartFindContours( void* _img, CvMemStorage* storage,
+                     int  header_size, int mode,
+                     int  method, CvPoint offset )
+{
+    return cvStartFindContours_Impl(_img, storage, header_size, mode, method, offset, 1);
+}
+
 /*
    Final stage of contour processing.
    Three variants possible:
@@ -1796,33 +1807,11 @@ icvFindContoursInInterval( const CvArr* src,
     return count;
 }
 
-
-
-/*F///////////////////////////////////////////////////////////////////////////////////////
-//    Name: cvFindContours
-//    Purpose:
-//      Finds all the contours on the bi-level image.
-//    Context:
-//    Parameters:
-//      img  - source image.
-//             Non-zero pixels are considered as 1-pixels
-//             and zero pixels as 0-pixels.
-//      step - full width of source image in bytes.
-//      size - width and height of the image in pixels
-//      storage - pointer to storage where will the output contours be placed.
-//      header_size - header size of resulting contours
-//      mode - mode of contour retrieval.
-//      method - method of approximation that is applied to contours
-//      first_contour - pointer to first contour pointer
-//    Returns:
-//      CV_OK or error code
-//    Notes:
-//F*/
-CV_IMPL int
-cvFindContours( void*  img,  CvMemStorage*  storage,
+static int
+cvFindContours_Impl( void*  img,  CvMemStorage*  storage,
                 CvSeq**  firstContour, int  cntHeaderSize,
                 int  mode,
-                int  method, CvPoint offset )
+                int  method, CvPoint offset, int needFillBorder )
 {
     CvContourScanner scanner = 0;
     CvSeq *contour = 0;
@@ -1845,7 +1834,8 @@ cvFindContours( void*  img,  CvMemStorage*  storage,
     {
         try
         {
-            scanner = cvStartFindContours( img, storage, cntHeaderSize, mode, method, offset );
+            scanner = cvStartFindContours_Impl( img, storage, cntHeaderSize, mode, method, offset,
+                                            needFillBorder);
 
             do
             {
@@ -1867,6 +1857,35 @@ cvFindContours( void*  img,  CvMemStorage*  storage,
     return count;
 }
 
+/*F///////////////////////////////////////////////////////////////////////////////////////
+//    Name: cvFindContours
+//    Purpose:
+//      Finds all the contours on the bi-level image.
+//    Context:
+//    Parameters:
+//      img  - source image.
+//             Non-zero pixels are considered as 1-pixels
+//             and zero pixels as 0-pixels.
+//      step - full width of source image in bytes.
+//      size - width and height of the image in pixels
+//      storage - pointer to storage where will the output contours be placed.
+//      header_size - header size of resulting contours
+//      mode - mode of contour retrieval.
+//      method - method of approximation that is applied to contours
+//      first_contour - pointer to first contour pointer
+//    Returns:
+//      CV_OK or error code
+//    Notes:
+//F*/
+CV_IMPL int
+cvFindContours( void*  img,  CvMemStorage*  storage,
+                CvSeq**  firstContour, int  cntHeaderSize,
+                int  mode,
+                int  method, CvPoint offset )
+{
+    return cvFindContours_Impl(img, storage, firstContour, cntHeaderSize, mode, method, offset, 1);
+}
+
 void cv::findContours( InputOutputArray _image, OutputArrayOfArrays _contours,
                    OutputArray _hierarchy, int mode, int method, Point offset )
 {
@@ -1878,13 +1897,14 @@ void cv::findContours( InputOutputArray _image, OutputArrayOfArrays _contours,
 
     CV_Assert(_contours.empty() || (_contours.channels() == 2 && _contours.depth() == CV_32S));
 
-    Mat image = _image.getMat();
+    Mat image;
+    copyMakeBorder(_image, image, 1, 1, 1, 1, BORDER_CONSTANT, Scalar(0));
     MemStorage storage(cvCreateMemStorage());
     CvMat _cimage = image;
     CvSeq* _ccontours = 0;
     if( _hierarchy.needed() )
         _hierarchy.clear();
-    cvFindContours(&_cimage, storage, &_ccontours, sizeof(CvContour), mode, method, offset);
+    cvFindContours_Impl(&_cimage, storage, &_ccontours, sizeof(CvContour), mode, method, offset + Point(-1, -1), 0);
     if( !_ccontours )
     {
         _contours.clear();

modules/imgproc/test/test_contours.cpp

@@ -483,10 +483,26 @@ TEST(Imgproc_FindContours, hilbert)
     img.setTo(Scalar::all(0));
 
     drawContours(img, contours, 0, Scalar::all(255), 1);
-    //imshow("hilbert", img);
-    //waitKey();
+
     ASSERT_EQ(1, (int)contours.size());
     ASSERT_EQ(9832, (int)contours[0].size());
 }
 
+TEST(Imgproc_FindContours, border)
+{
+    Mat img;
+    copyMakeBorder(Mat::zeros(8, 10, CV_8U), img, 1, 1, 1, 1, BORDER_CONSTANT, Scalar(1));
+
+    std::vector<std::vector<cv::Point> > contours;
+    findContours(img, contours, RETR_LIST, CHAIN_APPROX_NONE);
+
+    Mat img_draw_contours = Mat::zeros(img.size(), CV_8U);
+    for (size_t cpt = 0; cpt < contours.size(); cpt++)
+    {
+      drawContours(img_draw_contours, contours, static_cast<int>(cpt), cv::Scalar(255));
+    }
+
+    ASSERT_TRUE(norm(img - img_draw_contours, NORM_INF) == 0.0);
+}
+
 /* End of file. */