|| Hervé Locteau on 2012-05-16 15:16
|| Priority: Normal
|| Affected: None
|| Category: imgproc, video
|| Tracker: Bug
|| Difficulty: None
|| PR: None
|| Platform: None / None

The findContours function may deliver bad structural information on the attached image.
The call leads to this sub hierarchy (id of parent ; id of first child ; id of next ; id of previous) :

* contour 139 : -1 ; 140 ; 138 ; 149
* contour 140 : 139 ; 141 ; -1 ; 146
* contour 141 : 140 ; -1 ; -1 ; 142
* contour 142 : 140 ; -1 ; 141 ; 143
* contour 143 : 140 ; -1 ; 142 ; 144
* contour 144 : 140 ; -1 ; 143 ; 145
* contour 145 : 140 ; -1 ; 144 ; -1

while we may expect :
* contour 139 has no child
* contours 142, 143, 144 and 145 have no parent

Notes
# the contour 140 is a hole touching the outer boundary of the connected component's outer contour (139).
# removing any connected component in the image leads to a correct hierarchy
@
cv::Mat img = cv::imread ( "debug_e.png", 0) ;
std::vector< std::vector< cv::Point > > edges_cc ;
std::vector< cv::Vec4i > tree_cc ;
cv::findContours( img, edges_cc, tree_cc, CV_RETR_TREE, CV_CHAIN_APPROX_NONE ) </pre>
@

My configuration file is :
<pre>
General configuration for OpenCV 2.4.0 =====================================
Version control:                 svn:8318
  Platform:
    Host:                        Linux 3.0.0-19-generic x86_64
    CMake:                       2.8.5
    CMake generator:             Unix Makefiles
    CMake build tool:            /usr/bin/make
    Configuration:               Release
  C/C++:
    Built as dynamic libs?:      YES
    C++ Compiler:                /usr/bin/c++ (ver 4.6.1)
    C++ flags (Release):         -Wall -Wno-long-long -pthread -fomit-frame-pointer -msse -msse2 -ffunction-sections -O3 -DNDEBUG   -DNDEBUG
    C++ flags (Debug):           -Wall -Wno-long-long -pthread -fomit-frame-pointer -msse -msse2 -ffunction-sections -g  -O0 -DDEBUG -D_DEBUG -ggdb3
    C Compiler:                  /usr/bin/gcc
    C flags (Release):           -Wall -Wno-long-long -pthread -fomit-frame-pointer -msse -msse2 -ffunction-sections -O3 -DNDEBUG  -DNDEBUG
    C flags (Debug):             -Wall -Wno-long-long -pthread -fomit-frame-pointer -msse -msse2 -ffunction-sections -g  -O0 -DDEBUG -D_DEBUG -ggdb3
  Media I/O:
    ZLib:                        /usr/lib/x86_64-linux-gnu/libz.so (ver 1.2.3.4)
    JPEG:                        /usr/lib/x86_64-linux-gnu/libjpeg.so (ver 62)
    PNG:                         /usr/lib/x86_64-linux-gnu/libpng.so (ver 1.2.46)
    TIFF:                        /usr/lib/x86_64-linux-gnu/libtiff.so (ver 42)
    JPEG 2000:                   /usr/lib/x86_64-linux-gnu/libjasper.so (ver 1.900.1)
    OpenEXR:                     NO
    OpenNI:                      NO
    OpenNI PrimeSensor Modules:  NO
  Other third-party libraries:
    Use IPP:                     NO
    Use TBB:                     NO
    Use Cuda:                    NO
    Use Eigen:                   NO
    Use Clp:                     NO
</pre>

-   Target version deleted (2.4.1)