Very slow and very messy floodfill animation

floodfill.py

import os
from statistics import mean

from PIL import Image
from tqdm import tqdm

# render frames with
# ffmpeg -framerate 60 -pattern_type glob -i '*.png' -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" -c:v libx264 -pix_fmt yuv420p out.mp4

source_img = 'tfoust10.jpg'
dest_dir = "frames"
threshold = 160 # out of 255
start_x, start_y = (574, 527)

# animation specification
fps = 60
desired_secs = 30
last_frame_hold_secs = 7

frame_i = 0
skip = -1
# skip_interval is auto-calculated below
def save_frame(im):
    global frame_i
    global skip

    skip += 1
    if skip % skip_interval != 0:
        return

    fname = f'frame_{frame_i:04d}.png'
    tqdm.write(f'Saving {fname}')
    im.save(os.path.join(dest_dir, fname), compress_level=1)
    frame_i += 1

def visit(x, y, width, height, pixels, orig_pixels, im, to_visit, to_fade, visited, start_avg):
    global skip_interval

    tqdm.write(f'visiting {x}, {y}')
    if x < 0 or y < 0 or x >= width or y >= height:
        return False

    # drop white pixels
    avg = mean(orig_pixels[x,y])
    if abs(start_avg - avg) > threshold:
        # restore original colour
        pixels[x,y] = orig_pixels[x,y]
        return False

    # list so we can pass-by-ref later
    to_fade[(x,y)] = [256 * skip_interval * 2]

    for dx, dy in ((-1,0), (0, -1), (1, 0), (0, 1)):
        new_x = x + dx
        new_y = y + dy
        if (new_x, new_y) not in visited:
            visited.add((new_x,new_y))
            to_visit.append((new_x, new_y))

    return True

def update_fade(pixels, to_fade):
    global skip_interval

    to_drop = []
    for (x,y), val in to_fade.items():
        # pass-by-ref for python
        if val[0] > 0:
            val[0] -= 32
            v = val[0] // skip_interval
            if v > 255:
                v //= 2
                pixels[x, y] = (255-v, 255, 0)
            else:
                pixels[x, y] = (255, v, 0)
        else:
            to_drop.append((x,y))

    for drop in to_drop:
        to_fade.pop(drop)

if not os.path.isdir(dest_dir):
    os.mkdir(dest_dir)

im = Image.open(source_img)

orig_im = im.copy()

width, height = im.size
pixels = im.load()
orig_pixels = orig_im.load()

start_colour = pixels[start_x, start_y]
start_avg = mean(start_colour)

total_frames = 0
tqdm.write('Determining frame count')
for x in tqdm(range(width)):
    for y in range(height):
        if abs(start_avg - mean(pixels[x,y])) < threshold:
            total_frames += 1

desired_frames = fps*desired_secs
skip_interval = total_frames // desired_frames if total_frames > desired_frames else total_frames

visited = set((start_x, start_y))
to_visit = list()
to_fade = dict()
visit(start_x, start_y, width, height, pixels, orig_pixels, im, to_visit, to_fade, visited, start_avg)

with tqdm(total=total_frames) as progress:
    while True:
        try:
            update_fade(pixels, to_fade)

            next_x, next_y = to_visit.pop(0)
            if visit(next_x, next_y, width, height, pixels, orig_pixels, im, to_visit, to_fade, visited, start_avg):
                save_frame(im)
                progress.update()
        except IndexError:
            break

# don't make people wait a ton of time and then blueball them on the final result
last_frame_duplicate = last_frame_hold_secs * fps * skip_interval
for _ in tqdm(range(last_frame_duplicate), desc='Duplicating final frame'):
    update_fade(pixels, to_fade)
    save_frame(im)