获取图像中具有特定颜色的像素数量。 Python, opencv

Question

I have small image. enter image description here bg 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.

Answer 1

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

#!/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() :

#!/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 NoTE ** BGR not RGB  values match "sought", and count
result = np.count_nonzero(np.all(im==sought,axis=2))
print(result)

Answer 2

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)

Answer 3

Try this:

import cv2
import numpy as np
img = cv2.imread("im/auto5.png")
color = [48,75,105] # set color to looking for
im = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
result = np.count_nonzero(np.all(im==color,axis=2))
print("Total pixels " + str(result))