Question

I’m planning to try contours on some image. Lets say I have three object after binarized. Does it mean I have three contours? If yes, how can I process every each of the contours?

Thank you.

Updated: I need to process blobs #1 first. FYI, the blobs are not exactly like a quadrilateral. If tried using cvSetImageROI but blob #2 and part of blob #3 might appear in the cropped image. I was thinking if contours can extract only blob #1 without having blob #2 and #3. Is it clear with the explanation? (using C API not C++ API).

Answer 1

Each contour is array (std::vector) of Points. When you call findContours it returns array of contours in your binary image. Here’s simple example:

vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
Mat src;

findContours(src, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);

for(size_t i = 0; i<contours.size(); i++)
{
    //process contours[i]
    for (size_t j=0; j<contours[i].size(); j++)
    {
        int x = contours[i][j].x;
        int y = contours[i][j].y;
        // process point j in contour i
    }
}

Here’s official OpenCV manual.