Get a quanity of pixels with specific color at image. Python, opencv

I have small image. enter image description here
b g r, not gray.

original = cv2.imread('im/auto5.png')
print(original.shape) # 27,30,3
print(original[13,29]) # [254 254 254]


As you can see, there is white pic (digit 14) in my image, mostly black. On the right corner (coordinates [13,29]) I get [254 254 254] - white color.

I want to calculate number of pixels with that specific color. I need it to further comparing such images with different numbers inside. There are different backgrounds on these squares, and I consider exactly white color.

[13,29]

(254,254,254)

[13,29]

(8,7,6)

2 Answers
2

I would do that with numpy which is vectorised and much faster than using for loops:

numpy

for

#!/usr/local/bin/python3
import numpy as np
from PIL import Image

# Open image and make into numpy array
im=np.array(Image.open("p.png").convert('RGB'))

# Work out what we are looking for
sought = [254,254,254]

# Find all pixels where the 3 RGB values match "sought", and count them
result = np.count_nonzero(np.all(im==sought,axis=2))
print(result)


Sample Output

35


It will work just the same with OpenCV's imread():

imread()

#!/usr/local/bin/python3
import numpy as np
import cv2

# Open image and make into numpy array
im=cv2.imread('p.png')

# Work out what we are looking for
sought = [254,254,254]

# Find all pixels where the 3 RGB values match "sought", and count
result = np.count_nonzero(np.all(im==sought,axis=2))
print(result)


numpy

for

axis=1

axis=2

axis=3

np.all(im==sought,axis=2)

sought

Image in cv2 is an iterable object. So you can just iterate through all pixels to count the pixels you are looking for.

import os
import cv2
main_dir = os.path.split(os.path.abspath(__file__))[0]
file_name = 'im/auto5.png'
color_to_seek = (254, 254, 254)

original = cv2.imread(os.path.join(main_dir, file_name))

amount = 0
for x in range(original.shape[0]):
for y in range(original.shape[1]):
b, g, r = original[x, y]
if (b, g, r) == color_to_seek:
amount += 1

print(amount)


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