Slow image processing with Python and PIL
from PIL import Image

source = Image.open("source.jpg")
colors = source.getcolors(source.size[0] * source.size[1]) #maxcolor value =256, get   all colors with source.size[0] * source.size[1]
pixels = []
for i, color in colors:
    pixels.extend(i * [color])
    pixels.sort()
    new = Image.new('RGB', source.size)
    new.putdata(pixels)
    new.save("new.png")

from PIL import Image

source = Image.open("source.jpg")
colors = source.getcolors(source.size[0] * source.size[1]) #maxcolor value =256, get   all colors with source.size[0] * source.size[1]
pixels = []
for i, color in colors:
    pixels.extend(i * [color])
pixels.sort()
new = Image.new('RGB', source.size)
new.putdata(pixels)
new.save("new.png")

colors = source.getcolors(source.size[0] * source.size[1])
colors.sort(key=lambda pair: pair[1])