Remove stamp from bill python

Question

Any ideas on how to remove the stamp from this bill prior to OCR processing?

Answer 1

Here is one way to do that in Python/OpenCV.

• Read input
• Threshold on yellow
• Dilate to fill out rectangle
• Get largest contour
• Draw a white filled contour on the input image
• Save the results

Input:

import cv2
import numpy as np

# read image
img = cv2.imread('form_with_label.jpg')

# threshold on yellow
lower=(0,200,200)
upper=(100,255,255)
thresh = cv2.inRange(img, lower, upper)

# apply dilate morphology
kernel = np.ones((9,9), np.uint8)
mask = cv2.morphologyEx(thresh, cv2.MORPH_DILATE, kernel)

# get largest contour
contours = cv2.findContours(mask, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
contours = contours[0] if len(contours) == 2 else contours[1]
big_contour = max(contours, key=cv2.contourArea)
x,y,w,h = cv2.boundingRect(big_contour)

# draw filled white contour on input 
result = img.copy()
cv2.drawContours(result,[big_contour],0,(255,255,255),-1)

# save cropped image
cv2.imwrite('form_with_label_thresh.png',thresh)
cv2.imwrite('form_with_label_mask.png',mask)
cv2.imwrite('form_with_label_removed.png',result)

# show the images
cv2.imshow("THRESH", thresh)
cv2.imshow("MASK", mask)
cv2.imshow("RESULT", result)
cv2.waitKey(0)
cv2.destroyAllWindows()

Thresholded Image:

Morphology Dilated Image:

Result: