Given an image file, splits into N bitmaps of identical dimensions, one each for each unique color in the input file.

split_by_color.py

#!/usr/bin/env python3

# Given an image file, splits into N bitmaps of identical dimensions, one each 
# for each unique color in the input file.
# via https://stackoverflow.com/a/65392173

# Requirements
# pip3 install opencv-python

import cv2
import numpy as np
import argparse

# Handle input
parser = argparse.ArgumentParser(description='Split an image by color into bitmap layers.')
parser.add_argument('inputfile', metavar='F', type=str, nargs=1,
                    help='Filename of image to be split into bitmap layers.')
args = parser.parse_args()
f = args.inputfile[0]
print(f'Opening image {f}...')

# Load image
im = cv2.imread(f)

# Reshape into a tall column of pixels, each with 3 RGB pixels and get unique rows (colors)
colors  = np.unique(im.reshape(-1,3), axis=0)

# Iterate over the colors we found
for i,color in enumerate(colors):
    print(f'Exporting color {i}: {color[::-1]}') # print in RGB order
    res = np.where((im==color).all(axis=-1),255,0)
    cv2.imwrite(f'color-{i}.png', res)