How to check whether a jpeg image is color or gray scale using only Python stdlib

Question

I have to write a test case in python to check whether a jpg image is in color or grayscale. Can anyone please let me know if there is any way to do it with out installing e

Answer 1

I faced a similar situation, where I tried the following approaches:

1. Reading using IMREAD_UNCHANGEDand checking for image.shape
2. Splitting B,G,R channels and checking if they are equal

Both of these approaches got me only like 53% accuracy in my dataset. I had to relax the condition for checking pixels in different channels and create a ratio to classify it as grey or color. With this approach, I was able to get 87.3% accuracy on my dataset.

Here is the logic which worked for me:

import cv2
import numpy as np

###test image
img=cv2.imread('test.jpg')

### splitting b,g,r channels
b,g,r=cv2.split(img)

### getting differences between (b,g), (r,g), (b,r) channel pixels
r_g=np.count_nonzero(abs(r-g))
r_b=np.count_nonzero(abs(r-b))
g_b=np.count_nonzero(abs(g-b))

### sum of differences
diff_sum=float(r_g+r_b+g_b)

### finding ratio of diff_sum with respect to size of image
ratio=diff_sum/img.size

if ratio>0.005:
    print("image is color")
else:
    print("image is greyscale")