In an image, there are two nested rectangles, and they share two sides. How to use opencv to identify the two rectangles

Question

Sorry, the original image cannot be uploaded due to some security reasons. The following is a schematic diagram:

original image：

original image

my goal：

my goal

Current situation：

Current situation

now I use findContours function to to complete the goal，The code currently used is（use Python 3 and OpenCV）:

edges = cv2.Canny(mask, 10, 150)
contours, _ = cv2.findContours(edges, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
cv2.drawContours(ima, [contour], -1, (0, 0, 255), 5)

I also used the following function parameters：

cv2.RETR_EXTERNAL，cv2.RETR_LIST，cv2.RETR_CCOMP，cv2.CHAIN_APPROX_NONE,cv2.CHAIN_APPROX_TC89_L1，cv2.CHAIN_APPROX_TC89_KCOS

fact original image：

Asked By: Hasegaawa Haruka

||

Source

Answer 1

Bounding-box of each white regions can be used to judge the simple rectangular "nested" relation.

Using connectedComponentsWithStats, AABB(axis-aligned bounding boxes) can be obtained.

(Following code is C++.)

//Judge the rectangular nested relation
bool Is_A_Including_B( const cv::Rect &A, const cv::Rect &B, int Margin )
{
    int Left = A.x - Margin;
    int Right = Left + A.width + 2*Margin - 1;
    int Top = A.y - Margin;
    int Bottom = Top + A.height + 2*Margin - 1;
    
    auto B_br = B.br();
    return ( Left<=B.x  &&  B_br.x<=Right  &&  Top<=B.y  &&  B_br.y<=Bottom );
}

//main
int main()
{
    //Load Image and Binalize
    cv::Mat SrcImg = cv::imread( "Regs.png", cv::IMREAD_GRAYSCALE );
    if( SrcImg.empty() )return 0;

    cv::Mat BinImg;
    cv::threshold( SrcImg, BinImg, 128, 255, cv::THRESH_BINARY );

    //Find Bounding Boxes of white regions
    std::vector< cv::Rect > BBs;
    {
        cv::Mat Labels, Stats, Centroids;
        int N = cv::connectedComponentsWithStats( BinImg, Labels, Stats, Centroids );

        BBs.reserve( N-1 );
        for( int i=1; i<N; ++i )
        {
            BBs.emplace_back(
                Stats.at<int>( i, cv::CC_STAT_LEFT ),
                Stats.at<int>( i, cv::CC_STAT_TOP ),
                Stats.at<int>( i, cv::CC_STAT_WIDTH ),
                Stats.at<int>( i, cv::CC_STAT_HEIGHT )
            );
        }
    }

    //Find nested region
    std::vector< cv::Rect > Found;
    for( auto i=BBs.begin(); i!=BBs.end(); ++i )
    {
        for( auto j=BBs.begin(); j!=BBs.end(); ++j )
        {
            if( i == j )continue;
            if( Is_A_Including_B( *i, *j, 5 ) )
            {   Found.push_back( *j );  }
        }
    }

    //Visualize
    cv::Mat ShowImg;
    cv::cvtColor( BinImg, ShowImg, cv::COLOR_GRAY2BGR );
    ShowImg *= 0.5;
    for( const auto &Rect : Found )
    {
        cv::rectangle( ShowImg, Rect, cv::Scalar(0,0,255), 4 );
    }
    cv::imshow( "Result", ShowImg );
    cv::waitKey();
    return 0;
}

Result:

Answered By: fana

In an image, there are two nested rectangles, and they share two sides. How to use opencv to identify the two rectangles

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