Determine if a point is inside or outside of a shape with opencv

Question

I have images with white background and simple shapes in them (each image has one shape). I want to determine if a certain point (x,y) is inside the shape or not. How can I

Answer 1

if you want to access all the points inside the convex hull, you can do masking

I solve this by first painting my convex hull white colour with cv2.fillPoly() on a black frame

1. First create black frame that follows your frame's shape
   black_frame = np.zeros_like(your_frame).astype(np.uint8)
2. Paint the convex hull with white
   cv2.fillPoly(black_frame , [hull], (255, 255, 255))
3. Create a mask by using numpy boolean indexing, it will produce a mask with True/False values inside, it will be True is the pixel value is white
   mask = black_frame == 255
4. You can access your pixel values by getting the product between your frame and mask, if False, value will
   targetROI = your_frame * mask
5. Access your pixels by using the mask.

black_frame = np.zeros_like(your_frame).astype(np.uint8)
cv2.fillPoly(black_frame , [hull], (255, 255, 255))
mask = black_frame == 255
targetROI = your_frame * mask