Find all images that are over 50% black - Python

I am trying to write code that will iterate over a directory of images and tell me which images are over 50% black - so I can get rid of those. This is what I have, but it isn't returning any results:

from PIL import Image
import glob
images = glob.glob('/content/drive/MyDrive/cropped_images/*.png') #find all filenames specified by pattern
for image in images:
    with open(image, 'rb') as file:
        img = Image.open(file)
        pixels = list(img.getdata())            # get the pixels as a flattened sequence
        black_thresh = (50,50,50)
        nblack = 0
        for pixel in pixels:
            if pixel < black_thresh:
                nblack += 1
            n = len(pixels)
        if (nblack / float(n)) > 0.5:
          print(file)

Hannah, tuple comparison in python might not be what you expect: https://stackoverflow.com/questions/5292303/how-does-tuple-comparison-work-in-python . It is element by element, only for tiebreaking. Perhaps your definition of over 50% black is not what you have mapped to code?

I ran the above code on a dark image and my file printed just fine. Example png: https://www.nasa.gov/mission_pages/chandra/news/black-hole-image-makes-history .

Recommendations: define over 50% black to something you can put in code, pull the n out of the for loop, add files to a list when they satisfy your criteria.