A problem of remove_noise_with_hsv

[zlhaa23]

The current procedure of remove_noise_with_hsv is as follows.

1. Find the 2nd most frequent color (the standard color), (std_h, std_s, std_v)
2. For each pixel in the original CAPTCHA image, calculate its deviation from the standard color, (delta_h, delta_s, delta_v)
3. If delta_h <= h_tol && delta_s <= s_tol && delta_v <= v_tol, set the new grayscale value to be 1 - delta_v, or 0 otherwise.

   Problem

This method may produce very different thicknesses for some CAPTCHA images.

Case A

Case B

The original chars appear to have almost identical thicknesses; after this procedure, the char in Case A is ~2x as thick as in Case B.

If this is fixed...

• Better performance of char partitioning (less wrong partitions)
• More hint on char partitioning
• Better performance of the MLP