"Running out of colors" error when creating black masks for images-CodePudding

I'm trying to create a distractor set and I'm doing that with this for loop:

for mask in input_images:
    img = Image.open(path   mask)
    print(mask)

    width = img.size[0]
    height = img.size[1]

    for i in range(0, width):  # process all pixels
        for j in range(0, height):
            data = img.getpixel((i, j))
            img.putpixel((i, j), (0, 0, 0))

    img.save(masks_path   '/'   mask[:-4]   '.png')
    print(masks_path   '/'   mask[:-4]   '.png saved!')

It basically takes every image, converts the pixel of every image to black, and makes a copy of it. But this is the error it's throwing after a while:

Traceback (most recent call last):
  File "/home/onur/PycharmProjects/masking-image/main.py", line 24, in <module>
    img.putpixel((i, j), (0, 0, 0))
  File "/home/onur/PycharmProjects/masking-image/venv/lib/python3.9/site-packages/PIL/Image.py", line 1794, in putpixel
    value = self.palette.getcolor(value, self)
  File "/home/onur/PycharmProjects/masking-image/venv/lib/python3.9/site-packages/PIL/ImagePalette.py", line 143, in getcolor
    raise ValueError("cannot allocate more than 256 colors") from e
ValueError: cannot allocate more than 256 colors

I don't understand why I'm getting this. I am only referencing one color, which is black. Is there a quicker way to make purely black copies of images?

CodePudding user response：

I have no idea why you would want to fill an image with black, but here's a way to do it:

from PIL import Image

# Load original image and convert to greyscale to save space
im = Image.open('input.png').convert('L')

# Fill with black
im.paste(0, box=(0,0,*im.size))

Another way to do it is with a point processing function that makes each pixel zero:

# Make greyscale and set all pixels equal to zero
im = im.convert('L').point(lambda i: 0)