Replace colors in a given PDF file. The original goal was to print a PDF paper using a printer with no black cartridge!

pdf_color_replacement.py

import concurrent.futures
import itertools
import math

import pdf2image  # $ brew install poppler
from tqdm import tqdm

BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)

RGB = [RED, GREEN, BLUE]

THRESHOLD = 100
DPI = 1200  # Larger file size in exchange for higher print quality


def color_distance(color1, color2):
    r1, g1, b1 = color1
    r2, g2, b2 = color2
    distance = math.sqrt((r2 - r1) ** 2 + (g2 - g1) ** 2 + (b2 - b1) ** 2)
    return distance


def is_color_close(color1, color2, threshold=THRESHOLD):
    distance = color_distance(color1, color2)
    return distance < threshold


def is_gray_shade(color):
    r, g, b = color
    return r == g == b and (r, g, b) != (255, 255, 255)


def replace_color(image, source_color, destination_color):
    pixels = image.load()  # reference to the original Image object pixels
    for i, j in itertools.product(range(image.size[0]),
                                  range(image.size[1])):
        rgb = pixels[i, j]
        if is_gray_shade(rgb):
            pixels[i, j] = destination_color


def replace_iteratively(images):
    for i, image in tqdm(enumerate(images), total=len(images)):
        replace_color(image, BLACK, RGB[i % 3])
        # image.show()
    return images


def replace_worker(args):
    index, image = args
    replace_color(image, BLACK, RGB[index % 3])
    return image


def replace_concurrently(images):
    with concurrent.futures.ProcessPoolExecutor() as executor:
        images = list(tqdm(
            iterable=executor.map(replace_worker, enumerate(images)),
            total=len(images)
        ))
    return images


def main():
    images = pdf2image.convert_from_path('Input.pdf', dpi=DPI)
    images = replace_concurrently(images)
    images[0].save('Output.pdf', save_all=True, append_images=images[1:])