OpenCV for OCR: How to compute thresholding levels for gray image OCR

Question

I\'m trying to prepare images for OCR, and so far here is what I\'ve done using info from Extracting text OpenCV

From the resulting image I use the contours that hav

Answer 1

I've tried to maximize the distance between the minimum and the maximum color of one channel and then inverted the colors. (See Code)

img1 = cv2.imread('img.png')
img_reverted = img1.copy()

for i in range(3):
  tmp = (img1[:, :, i] - img1[:, :, i].min()) / img1[:, :, i].max()
  tmp = tmp * 255
  tmp = -1 * tmp + 255
  img_reverted[:, :, i] = tmp.astype('uint8');

The results are quite good. (See images)

Original image:

Reverted image: