collagegen.py

from math import floor, ceil

from PIL import Image, ImageOps
import os
import random


collage_filename = "__collage.png"
path = "your_imagefolder_path_here"

def best_ratio(width, height):
    ratio = width / height
    best = 100
    bestx = 0
    besty = 0

    for x in range(1, 20):
        for y in range(1, 20):
            if x * y > num_pics:
                diff = min(best, abs(ratio - (x / y)))
                if best > diff:
                    best = diff
                    bestx, besty = x, y

    return bestx, besty

os.chdir(path)

list = os.listdir(".")
if list.count(collage_filename) > 0:
    list.remove(collage_filename)

random.shuffle(list)

width = 1920*2
height = 1080*2 - 20
# init as black
collage = Image.new("RGBA", [width, height], "#000000ff")

num_pics = len(list)

rows, cols = best_ratio(width, height)
imgw = ceil(width / rows)
imgh = ceil(height / cols)

x, y, i = 0, 0, 0

empty_rows = floor((rows * cols - num_pics) / cols)
padding_y = int(empty_rows * (imgh / 2))

for file in list:
    x, y = (i % rows), floor(i / rows)
    img = Image.open(file)
    img = ImageOps.fit(img, [imgw, imgh], Image.BICUBIC)
    collage.paste(img, [x * imgw, y * imgh + padding_y, (x+1) * imgw, (y+1) * imgh+ padding_y])

    i += 1

collage.save(collage_filename, "PNG")
print(f"saved to file {path}/{collage_filename}")