How to count number of white and black pixels in color picture in python? How to count total pixels using numpy

Question

I want to calculate persentage of black pixels and white pixels for the picture, its colorful one

import numpy as np
import matplotlib.pyplot as plt

image = cv2.imread("image.png")

cropped_image = image[183:779,0:1907,:]

Answer 1

You don't want to run for loops over images - it is dog slow - no disrespect to dogs. Use Numpy.

#!/usr/bin/env python3

import numpy as np
import random

# Generate a random image 640x150 with many colours but no black or white
im = np.random.randint(1,255,(150,640,3), dtype=np.uint8)

# Draw a white rectangle 100x100
im[10:110,10:110] = [255,255,255]

# Draw a black rectangle 10x10
im[120:130,200:210] = [0,0,0]

# Count white pixels
sought = [255,255,255]
white  = np.count_nonzero(np.all(im==sought,axis=2))
print(f"white: {white}")

# Count black pixels
sought = [0,0,0]
black  = np.count_nonzero(np.all(im==sought,axis=2))
print(f"black: {black}")

Output

white: 10000
black: 100

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If you mean you want the tally of pixels that are either black or white, you can either add the two numbers above together, or test for both in one go like this:

blackorwhite = np.count_nonzero(np.all(im==[255,255,255],axis=2) | np.all(im==[0,0,0],axis=2)) 

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If you want the percentage, bear mind that the total number of pixels is easily calculated with:

total = im.shape[0] * im.shape[1]

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As regards testing, it is the same as any software development - get used to generating test data and using it :-)