Python - find out how much of an image is black

Question

I am downloading satellite pictures like this
_{(source: u0553130 at home.chpc.utah.edu)}

Since some images are mostly black, like this one, I don't want to save it.

How can I use python to check if the image is more than 50% black?

Answer 1

You're dealing with gifs which are mostly grayscale by the look of your example image, so you might expect most of the RGB components to be equal.

Using PIL:

from PIL import Image
im = Image.open('im.gif')
pixels = im.getdata()          # get the pixels as a flattened sequence
black_thresh = 50
nblack = 0
for pixel in pixels:
    if pixel < black_thresh:
        nblack += 1
n = len(pixels)

if (nblack / float(n)) > 0.5:
    print("mostly black")

Adjust your threshold for "black" between 0 (pitch black) and 255 (bright white) as appropriate).