NumPy/OpenCV 2: how do I crop non-rectangular region?

Question

I have a set of points that make a shape (closed polyline). Now I want to copy/crop all pixels from some image inside this shape, leaving t

Answer 1

The following code would be helpful for cropping the images and get them in a white background.

import cv2
import numpy as np

# load the image
image_path = 'input image path'
image = cv2.imread(image_path)

# create a mask with white pixels
mask = np.ones(image.shape, dtype=np.uint8)
mask.fill(255)

# points to be cropped
roi_corners = np.array([[(0, 300), (1880, 300), (1880, 400), (0, 400)]], dtype=np.int32)
# fill the ROI into the mask
cv2.fillPoly(mask, roi_corners, 0)

# The mask image
cv2.imwrite('image_masked.png', mask)

# applying th mask to original image
masked_image = cv2.bitwise_or(image, mask)

# The resultant image
cv2.imwrite('new_masked_image.png', masked_image)

Input Image:

Mask Image:

Resultant output image: