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opencvfilterdetection

OpenCV squares: filtering output

Here is the out put of square-detection example my problem is filter this squares

http://ozsulastik.com/ocvsquares.png

  • first problem is its drawing one than more lines for same area;
  • second one is i just need to detect object not all image.

The other problem is i have to take just biggest object except all image.

http://ozsulastik.com/ocvsquares2.png

Here is a code for detection:

static void findSquares( const Mat& image, vector >& squares ){

squares.clear();

Mat pyr, timg, gray0(image.size(), CV_8U), gray;

// down-scale and upscale the image to filter out the noise
pyrDown(image, pyr, Size(image.cols/2, image.rows/2));
pyrUp(pyr, timg, image.size());
vector<vector<Point> > contours;

// find squares in every color plane of the image
for( int c = 0; c < 3; c++ )
{
    int ch[] = {c, 0};
    mixChannels(&timg, 1, &gray0, 1, ch, 1);

    // try several threshold levels
    for( int l = 0; l < N; l++ )
    {
        // hack: use Canny instead of zero threshold level.
        // Canny helps to catch squares with gradient shading
        if( l == 0 )
        {
            // apply Canny. Take the upper threshold from slider
            // and set the lower to 0 (which forces edges merging)
            Canny(gray0, gray, 0, thresh, 5);
            // dilate canny output to remove potential
            // holes between edge segments
            dilate(gray, gray, Mat(), Point(-1,-1));
        }
        else
        {
            // apply threshold if l!=0:
            gray = gray0 >= (l+1)*255/N;
        }

        // find contours and store them all as a list
        findContours(gray, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);

        vector<Point> approx;

        // test each contour
        for( size_t i = 0; i < contours.size(); i++ )
        {
            approxPolyDP(Mat(contours[i]), approx, arcLength(Mat(contours[i]), true)*0.02, true);

            if( approx.size() == 4 &&
                fabs(contourArea(Mat(approx))) > 1000 &&
                isContourConvex(Mat(approx)) )
            {
                double maxCosine = 0;

                for( int j = 2; j < 5; j++ )
                {
                    // find the maximum cosine of the angle between joint edges
                    double cosine = fabs(angle(approx[j%4], approx[j-2], approx[j-1]));
                    maxCosine = MAX(maxCosine, cosine);
                }

                if( maxCosine < 0.3 )
                    squares.push_back(approx);
            }
        }
    }
}

}

Solution

  • You need to take a look at the flags for findContours(). You can set a flag called CV_RETR_EXTERNAL which will return only the outer-most contour (all contours inside of it are thrown away). This will probably return the entire frame, so you'll need to narrow down the search so that it doesnt check your frame boundaries. Use the function copyMakeBorder() to accomplish this. I would also recommend removing your dilate function as it is probably causing duplicate contours on either side of a line (you might not even need the border if you remove the dilate). Here is my output: enter image description here