Keep only red colors in an image python

Question

I am trying to refine an image through removing the noise. The image has a red color as dominant so I am trying to remove any other color except the red .. Here's an example of the image

I have found this code but couldn't use it properly. Please if you will put an answer consider me as very newbie and take it step by step as I need to learn not only to solve a problem

import cv2
import numpy as np

# Load image
im = cv2.imread('Output.png')

# Make all perfectly green pixels white
im[np.all(im == (193, 47, 47), axis=-1)] = (0,0,0)

# Save result
cv2.imwrite('result1.png',im)

I need to keep only the red color and the white as a background color.

I would like to refine the image so as to be able to extract numbers from it using such a code

def getCaptcha(img):
    pytesseract.pytesseract.tesseract_cmd=r'C:\\Program Files\\Tesseract-OCR\\tesseract.exe'
    img=Image.open(img)
    text=pytesseract.image_to_string(img, lang='eng',config='--psm 10 --oem 3 -c tessedit_char_whitelist=0123456789')
    return text

print(getCaptcha('red_numerals_thresh.jpg'))
print(getCaptcha('red_numerals_result.jpg'))

Answer 1

Here is one way to do that in Python OpenCV using cv2.inRange().

Input:

import cv2
import numpy as np

# Read image
img = cv2.imread('red_numerals.jpg')

# threshold red
lower = np.array([0, 0, 0])
upper = np.array([40, 40, 255])
thresh = cv2.inRange(img, lower, upper)
    
# Change non-red to white
result = img.copy()
result[thresh != 255] = (255,255,255)

# save results
cv2.imwrite('red_numerals_thresh.jpg', thresh)
cv2.imwrite('red_numerals_result.jpg', result)

cv2.imshow('thresh', thresh)
cv2.imshow('result', result)
cv2.waitKey(0)
cv2.destroyAllWindows()

Threshold image:

Result: