Build a color palette from image URL

Question

I am trying to create an API which takes an image URL as input and returns back a color palette in JSON format as output.

It should work something like this: http://lokeshdhakar.com/projects/color-thief/

But should be in Python. I have looked into PIL (Python Image Library) but didn't get what I want. Can someone point me in the right direction?

Input: Image URL
Output: List of Colors as a palette

Answer 1

import numpy as np
import Image

def palette(img):
    """
    Return palette in descending order of frequency
    """
    arr = np.asarray(img)
    palette, index = np.unique(asvoid(arr).ravel(), return_inverse=True)
    palette = palette.view(arr.dtype).reshape(-1, arr.shape[-1])
    count = np.bincount(index)
    order = np.argsort(count)
    return palette[order[::-1]]

def asvoid(arr):
    """View the array as dtype np.void (bytes)
    This collapses ND-arrays to 1D-arrays, so you can perform 1D operations on them.
    http://stackoverflow.com/a/16216866/190597 (Jaime)
    http://stackoverflow.com/a/16840350/190597 (Jaime)
    Warning:
    >>> asvoid([-0.]) == asvoid([0.])
    array([False], dtype=bool)
    """
    arr = np.ascontiguousarray(arr)
    return arr.view(np.dtype((np.void, arr.dtype.itemsize * arr.shape[-1])))


img = Image.open(FILENAME, 'r').convert('RGB')
print(palette(img))

palette(img) returns a numpy array. Each row can be interpreted as a color:

[[255 255 255]
 [  0   0   0]
 [254 254 254]
 ..., 
 [213 213 167]
 [213 213 169]
 [199 131  43]]

To get the top ten colors:

palette(img)[:10]

Answer 2

The color-thief library is also available in python: https://github.com/fengsp/color-thief-py

Example implementation :

pip install colorthief

# -*- coding: utf-8 -*-

import sys

if sys.version_info < (3, 0):
    from urllib2 import urlopen
else:
    from urllib.request import urlopen

import io

from colorthief import ColorThief


fd = urlopen('http://lokeshdhakar.com/projects/color-thief/img/photo1.jpg')
f = io.BytesIO(fd.read())
color_thief = ColorThief(f)
print(color_thief.get_color(quality=1))
print(color_thief.get_palette(quality=1))