input.png

rainbowizer.py

# makes a gif (or png sequence) from input.png where all instances of #ff00ff are rainbowified
# gif (`png = False`) doesn't support semi-transparency and makes gradients look ugly
# you might need to run `pip install numpy pillow` in admin command prompt first
# i don't think this is copyrightable even but just in case: cc0 unlicense 0bsd wtfpl

import math
import numpy
from PIL import Image

framecount = 360
framedelay = 50   # (for gif) in milliseconds, can't be lower than 20 (= 50 fps) i think?
saturation = 0.8
value = 0.8         # basically brightness
png = False

# https://gist.github.com/mathebox/e0805f72e7db3269ec22
def hsv_to_rgb(h, s, v):
    i = math.floor(h*6)
    f = h*6 - i
    p = v * (1-s)
    q = v * (1-f*s)
    t = v * (1-(1-f)*s)

    r, g, b = [
        (v, t, p),
        (q, v, p),
        (p, v, t),
        (p, q, v),
        (t, p, v),
        (v, p, q),
    ][int(i%6)]

    return r, g, b
	
frames = []

name = "input.png"
img = numpy.array(Image.open(name).convert("RGBA"))
red, green, blue, alpha = img[:,:,0], img[:,:,1], img[:,:,2], img[:,:,3]
mask = (red == 255) & (green == 0) & (blue == 255)

for i in range(framecount):
    img2 = numpy.copy(img)
    img2[:,:,:3][mask] = tuple((i * 255 for i in hsv_to_rgb(i / framecount, saturation, value)))
    frames.append(Image.fromarray(img2))

if png:
    for i in range(framecount):
        frames[i].save(f"rainbow_{i}.png")
else:
    frames[0].save("rainbow.gif", save_all=True, append_images=frames[1:], optimize=0, duration=framedelay, loop=0, transparency=255)