[FIXED] OpenCV Python how to keep one color as is converting an image to Grayscale

Issue

How do I make it so everything in the image is in gray-scale except the orange cone. Using opencv python.

Solution

You can achieve your goal by using bitwise_and() function and thresholding. Steps:

• generate mask for the required region.(here thresholding is used but other methods can also be used)
• extract required regions using bitwise_and (image & mask).
• Add masked regions to get output.

Here's sample code:

import cv2
import numpy as np

img = cv2.imread('input.jpg')

# creating mask using thresholding over `red` channel (use better use histogram to get threshoding value)
# I have used 200 as thershoding value it can be different for different images
ret, mask = cv2.threshold(img[:, :,2], 200, 255, cv2.THRESH_BINARY)

mask3 = np.zeros_like(img)
mask3[:, :, 0] = mask
mask3[:, :, 1] = mask
mask3[:, :, 2] = mask

# extracting `orange` region using `biteise_and`
orange = cv2.bitwise_and(img, mask3)

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
img  = cv2.cvtColor(gray, cv2.COLOR_GRAY2BGR)

# extracting non-orange region
gray = cv2.bitwise_and(img, 255 - mask3)

# orange masked output
out = gray + orange

cv2.imwrite('orange.png', orange)
cv2.imwrite('gray.png', gray)
cv2.imwrite("output.png", out)

Results:

masked orange image

masked gray image

output image

Answered By - Girish Dattatray Hegde