Generates a RGB histogram of an image.

colorhistogram.py

import sys
from PIL import Image, ImageDraw


def scale(r, g, b):
    return ((r // 10000) * 2,
            (g // 10000) * 2,
            (b // 10000) * 2)

im = sys.argv[1]
histogram = Image.open(im).histogram()

red = histogram[:256]
green = histogram[256:512]
blue = histogram[512:]

assert(len(red) == len(green) == len(blue))

color_values = list(map(lambda i: scale(red[i], green[i], blue[i]),
                        range(256)))

h_im = Image.new('RGB', (256, 256), color=(255, 255, 255))
dr = ImageDraw.Draw(h_im)

for x in range(256):
    r, g, b = color_values[x]
    for y in range(255, -1, -1):
        color = ((255 if r > (255-y) else 0),
                 (255 if g > (255-y) else 0),
                 (255 if b > (255-y) else 0))
        dr.point((x, y), fill=color)

h_im.save('{}-histogram.png'.format(im))