CODEWITHSUNDEEP
copencvcomputer-visioncontourfeature-detection
Wojtek
Wojtek

Reputation: 2524

OpenCV cvFindContours finds only one contour

I'm continuing my work with openCV, my first adventures I described here. It goes on quite well, but I've stumbled upon another tricky thing. I want to find contours on the image I've applied adaptive threshold to:

enter image description here

So the cvFindContours seems to work quite nice and here's the result:

enter image description here

The problem is, when I try to iterate over the found countours, it says there's only one contour (contours->total in the following code equals 1). Here's the code:

IplImage* img;
if((img = cvLoadImage( "photos/img-000012.ppm", 1)) == 0 )
{
    perror("cvLoadImage");
    return 1;
}
cvNamedWindow( "Image view", 1 );
cvShowImage( "Image view", img );

IplImage* gray = cvCreateImage( cvGetSize(img), 8, 1 ); // allocate a 1 channel byte image
cvCvtColor( img, gray, CV_BGR2GRAY );
cvShowImage( "Image view", gray );
cvWaitKey(0);

cvAdaptiveThreshold(gray, gray,
        255,    //  Non-zero value assigned to the pixels for which the condition is satisfied
        CV_ADAPTIVE_THRESH_MEAN_C, // adaptiveMethod
        CV_THRESH_BINARY_INV,   // thresholdType
        11, // blockSize
        5); // Constant subtracted from the mean or weighted mean
cvShowImage( "Image view", gray );
cvWaitKey(0);

IplConvKernel *se = cvCreateStructuringElementEx(3, 3, 1,  1,  CV_SHAPE_RECT, NULL);
cvErode(gray, gray, se, 1);
cvShowImage( "Image view", gray );
cvWaitKey(0);

IplImage *canny_out = cvCreateImage(cvGetSize(gray), 8, 1);
cvCanny(gray, canny_out, 50, 100, 3);
cvShowImage( "Image view", canny_out );
cvWaitKey(0);

CvMemStorage *storage = cvCreateMemStorage(0);
CvSeq *contours = cvCreateSeq(0, sizeof(CvSeq), sizeof(CvPoint), storage);
cvFindContours(gray, storage, &contours, sizeof(CvContour), CV_RETR_LIST,
        CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));
printf("contours->total = %d\n", contours->total);

cvDrawContours(img, contours, CV_RGB(0,255,0), CV_RGB(0,0,255),
        2, 1, 8, cvPoint(0, 0));
cvShowImage( "Image view", img );
cvWaitKey(0);

Should it be this way, that there's only one contour? Maybe I don't understand the openCV's definition of a contour? I'd appreciate your help.

Upvotes: 0

Views: 6407

Answers (2)

srgb
srgb

Reputation: 1

  1. you don't need to cvCreateSeq() before cvFindContours()

  2. instead of contours->total, iterate through them.

    for (; contours != 0; contours = contours->h_next)

Upvotes: 0

ArtemStorozhuk
ArtemStorozhuk

Reputation: 8725

Actually cvFindContours returns number of founded contours (I tested your picture and it returned >1). See docs. But I don't know why total equals one.

Upvotes: 2

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