get mask from contour with OpenCV

Question

I would like to get an image mask from the contour (it exists only 1 contour) I have computed thanks to cv.findContours.

However, while my contour variable is not empty, I do not manage to retrieve an image mask using cv.drawContours, my destination image being always empty.

Here is my code:

img = mosaicImage[:,:,0].astype('uint8')
contours, _ = cv.findContours(img.copy(), cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)
mask = np.zeros(img.shape, np.uint8)
cv.drawContours(mask, contours, -1, (0,255,0),1)

I hope you could help!

Thanks

mask is single channel. you try to set channel 2... try cv.drawContours(mask, contours, -1, (255),1) — Micka
If you're creating a mask, would you want to fill in the contours? You can do that by changing the last parameter to drawContours from 1 to -1 — jjinking

Micka Micka · Accepted Answer · 2015-09-04T18:09:02

you are setting color (0,255,0) to the mask, but the mask is single channel so you draw the contour in color 0.

try

 cv.drawContours(mask, contours, -1, (255),1)

or

 cv.drawContours(mask, contours, -1, (255,255,255),1)

get mask from contour with OpenCV

1 Answers