ink_limit.py

from PIL import Image
import numpy as np
import sys

def main():
    # taking command line args
    input_path = sys.argv[1]
    output_path = sys.argv[2]
    ink_limit = int(sys.argv[3])

    # TODO check arguments

    img = Image.open(input_path, 'r')
    arr = np.asarray(img)

    # Apply ink limiting function to all points in image
    output_arr = limit_image(arr.copy(), ink_limit)

    # Create output image in .tiff format
    output_img = Image.fromarray(output_arr, mode='CMYK')
    output_img.save(output_path, compression='tiff_deflate')


# Apply ink limiting function to all points in image
def limit_image(img_arr, ink_limit):
    # TODO vectorize limit_point function instead of for loops
    for i in range(len(img_arr)):
        for j in range(len(img_arr[0])):
            img_arr[i, j] = limit_point(img_arr[i, j], ink_limit)

    return img_arr


# Limit ink for an individual point
def limit_point(point, ink_limit):
    cmy_range = [0,1,2]
    percent_point = map_np(convert_to_percent, point, np.float32)

    # If ink limit is not exceeded, just return
    if sum(percent_point) <= ink_limit:
        return point

    # First combine CMY values into black
    min_cmy = min(percent_point[0:3])

    for i in cmy_range:
        percent_point[i] -= min_cmy
    percent_point[3] = min(100, percent_point[3]+min_cmy)

    # If ink limit is not exceeded, return modified point
    if sum(percent_point) <= ink_limit:
        return map_np(convert_from_percent, percent_point, np.uint8)

    else:
        extra_ink = ink_limit/sum(percent_point)
        for i in range(4):
            percent_point[i] *= extra_ink

        return map_np(convert_from_percent, percent_point, np.uint8)

# Map function over all ink values of a point and return np array
def map_np(func, point, type):
    return np.fromiter(map(func, point),dtype=type)

# Convert number in range [0, 255] to [0, 100]
def convert_to_percent(integer):
    return 100*integer/255

# Convert number in range [0, 100] to [0, 255]
def convert_from_percent(percent):
    return np.uint8(255*percent/100)

if __name__ == "__main__":
    main()