Filling contour won't work using drawContours() thickness=-1

Question

I am trying to fill a contour which was obtained by separately thresholding 3 color channels.

image_original = cv2.imread(original_image_path)
image_contours = np.zeros((image_original.shape[0], image_original.shape[1], 1), dtype=np.uint8)
image_contour = np.zeros((image_original.shape[0], image_original.shape[1], 1), dtype=np.uint8)
image_binary = np.zeros((image_original.shape[0], image_original.shape[1], 1), dtype=np.uint8)
image_area = image_original.shape[0] * image_original.shape[1]
for channel in range(image_original.shape[2]):
    ret, image_thresh = cv2.threshold(image_original[:, :, channel], 120, 255, cv2.THRESH_OTSU)
    _, contours, hierarchy = cv2.findContours(image_thresh, 1, 1)
    for index, contour in enumerate(contours):
        if( cv2.contourArea( contour )  > image_area * background_remove_offset ):
            del contours[index]
    cv2.drawContours(image_contours, contours, -1, (255,255,255), 3)
_, contours, hierarchy = cv2.findContours(image_contours,  cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)
cv2.drawContours(image_contour, max(contours, key = cv2.contourArea), -1, (255, 255, 255), 1)
cv2.imwrite(output_contour_image_path, image_contour)
cv2.drawContours(image_binary, max(contours, key = cv2.contourArea), -1, (255, 255, 255), thickness=-1)
cv2.imwrite(output_binary_image_path, image_binary)
cv2.imshow("binary", image_binary)

which is supposed to work by setting the thickness=-1 but it only draws up the contour with 1 thickness same as that of thickness=1 specifically in the following line.

cv2.drawContours(image_binary, max(contours, key = cv2.contourArea), -1, (255, 255, 255), thickness=-1)

Results are as follows,

Which should come up with a binary filled image other than a one just with a contour of thickness=1

Asked By: Ishara Abeykoon

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Source

Answer 1

well, solved it it seems the cv2.drawContours() function need contours as list type, just changing the line

cv2.drawContours(image_binary, max(contours, key = cv2.contourArea), -1, 255, thickness=-1)

to

cv2.drawContours(image_binary, [max(contours, key = cv2.contourArea)], -1, 255, thickness=-1)

Solves it.

Answered By: Ishara Abeykoon

Filling contour won't work using drawContours() thickness=-1

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