Cleaning up captcha image

Question

I\'m trying to clean up the image above I\'ve tried several different methods using open cv, I either erode the original image too much to the point where parts of the

Answer 1

Take a closer look to your captcha. most of the dust in that image has a different grayscale value than the text.

The text is in 140 and the dust is in 112.

A simple grayscale filtering will help a lot here.

from scipy.misc import imread, imsave
import numpy as np

infile = "A1nO4.png"
outfile = "A1nO4_out.png"

im = imread(infile, True)
out_im = np.ones(im.shape) * 255

out_im[im == 140] = 0

imsave(outfile, out_im)

Now use cv2.dilate (cv2.erode on a white on black text) to get rid of the remaining dust.