遍历所有像素以检查哪些像素为白色，哪些像素为黑色

Question

I'm trying to iterate over an image with only black and white pixels. For every black pixel I want to decrease a score, while for each white pixel I would like to increase a score. However upon testing the following code I get this error:

ValueError: The truth value of an array with more than one element is ambiguous.

It has something to do with the img[i, j] statement. How can there be multiple pixels in that aray? Am I not specifically calling one pixel by using img[i,j] ? Does someone know how I could fix this, or if there is another working method for accessing 1 specific pixel?

def score(img):
    score = 0

    height, width, _ = img.shape
    for i in range(height):
        for j in range(width):
            if img[i, j] == [255,255,255]:
                score = score + 1
            else:
                score = score - 1
    print(score)

The image was read using the openCV library. The original image is then filtered for a specific color, with which a mask is created. This mask only has black and white pixels, as mentioned before.

img = cv2.imread("images/test.jpg")
mask = cv2.inRange(img, lower_bound, upper_bound)

Answer 1

This happens because img[i, j] gives an array with the RGB values

img[i, j] = [0, 0, 0] # for black

img[i, j] = [255, 255, 255] # for white

And these arrays are not associated to True or False . You need to change your condition.

>>> img[0,0] == [0,0,0]
array([ True,  True,  True])
>>> all(img[0,0] == [0,0,0])
True

Your condition needs an all() .

Answer 2

It means that your array has got 3 dimension. You can print img[i,j] to see how it looks like. The value you want is probably often at the same position so calling img[i,j,0] or img[i,j,1] should work

Answer 3

Here you go =^..^=

from PIL import Image

# load image
img = Image.open('BlackWhite.gif').convert('RGB')
pixel = img.load()

# calculate the score
score = 0
w=img.size[0]
h=img.size[1]
for i in range(w):
  for j in range(h):
      if pixel[i, j] == (255, 255, 255):
          score += 1
      elif pixel[i, j] == (0, 0, 0):
          score -= 1