Changing black color to white but not white color to black with Python openCV PIL

Question

Im trying to change black pixels to white with opencv in python using cv2 or PIL.

Original picture:

Here is my code:

import cv2
import numpy as np

frame = cv2.imread("numptest/captcha.png")
cv2.imshow('frame',frame)

lower_black = np.array([0,0,0])
upper_black = np.array([1,1,1])
black_mask = cv2.inRange(frame, lower_black, upper_black)
cv2.imshow('mask0',black_mask)
cv2.waitKey()

The result looks like this:

while I would like it to look like this:

I have tried also this code, which does preserve what is inside those rectangles, but works only for exactly RGB 255 255 255, while i need it to work for wider range of RGB.

from PIL import Image
import numpy as np

im = Image.open('numptest/captcha.png')
im = im.convert('RGBA')
data = np.array(im)   
black_areas = (red == 0) & (blue == 0) & (green == 0)
data[..., :-1][black_areas.T] = (255, 255, 255)

im2 = Image.fromarray(data)
im2.show()'

Here is result of second code:

So I dont know, maybe best would be some combination of these codes, I just dont really understand how to use inRange in second code, that would probably solve my problem.

If it is a greyscale image why not use it as a greyscale image and and change everything below, lets say 10 (almost black) to 255 (white). With in range, you have to define which colors are in valid range using a lower bound and upper bound, then use this as a mask and color that area white. In this tutorial they show you how to filter by color, by upperr bound I would use something close to black (10,10,10) and lower bound just black (0,0,0) since black is not always pure — api55

user3281831 user3281831 · Accepted Answer · 2017-07-17T15:47:13

Actauly I found answer to my own question while writing the question. I just altered the second code.

this line:

       black_areas = (red == 0) & (blue == 0) & (green == 0)

with this line:

    black_areas = (red < 70) & (blue < 70) & (green < 70)

This is the result:

Changing black color to white but not white color to black with Python openCV PIL

1 Answers