Using drawContours OpenCV function in python

Question

I have installed OpenCV 2.2 and when I try to use drawContours I get the following error:

cv.drawContours(frame, contours, 0, cv.RGB(255, 0, 0))
TypeError: <unknown> is not a numpy array

The code related to this error is the following:

storage = cv.CreateMemStorage(0)
contours = cv.FindContours (color_mask, storage, method = cv.CV_CHAIN_APPROX_SIMPLE)
cv.drawContours(frame, contours, 0, cv.RGB(255, 0, 0))

The python documentation does not correspond with the correct order of parameters (I know the correct order thank to IDLE) and the C++ documentation for this function does not help me very much

Here is the full code (relevant code):

    cv.NamedWindow("MyWindow", 1)
    capture = cv.CaptureFromCAM(0)

    while 1:
        frame = cv.QueryFrame(capture)

        color_mask = cv.CreateImage(cv.GetSize(frame), 8, 1)

        cv.InRangeS(frame, cv.Scalar(*min_color), cv.Scalar(*max_color), color_mask)

        cv.CvtColor(frame, frame, cv.CV_BGR2HSV)

        storage = cv.CreateMemStorage(0)
        contours = cv.FindContours (color_mask, storage, method = cv.CV_CHAIN_APPROX_SIMPLE)
        cv.drawContours(image = frame, contours = contours, contourIdx = 0, color = cv.RGB(255, 0, 0))

        cv.ShowImage("MyWindow", frame)

Thanks in advance

Answer 1

You should be aware that drawContours and DrawContours are two different functions. They actually do the same thing, but they accept different parameters. I believe the first one only accepts numpy arrays instead of CvMat or other arrays from openCV.