How to add an anime style with Claude

Give input.mp4 (540x960) an anime cartoon look from 1.0 seconds to the end; before 1.0 seconds leave every frame untouched. For each frame from 1.0 s: shrink it to half size (270x480, box filter) and run a 5x5 median filter on it (Pillow's MedianFilter(5)) to flatten texture into smooth areas of color. Color: scale that back up to 540x960 (bicubic), convert to HSV, cut V into 4 flat bands (v becomes (floor(v*4/256)+0.5)*64, so 32, 96, 160 or 224), multiply S by 2.2 (capped at 255), keep H, and convert back to RGB. Outlines: on the half-size smoothed frame's grayscale, take the brightness difference between the pixels on either side horizontally and vertically (central differences), and mark every pixel where the length of that gradient is above 15. Scale the mask up to 540x960, thicken it with a 3x3 max filter, soften it with a 0.6 pixel Gaussian blur and use it to paint dark ink (25, 15, 40) over the color image. Use Python with numpy and Pillow for the frames and ffmpeg to read and write the video (don't use ffmpeg's drawtext if you add any text), keep the size, 30fps, the 6 second length and the audio, and save it as output.mp4.

#!/usr/bin/env python3
"""Anime style: at one second the shot is redrawn as a cel-shaded cartoon with dark ink outlines and vivid flat color.

Usage: python3 anime-style.py input.mp4 output.mp4
Needs ffmpeg, Pillow and numpy (pip install pillow numpy).
"""
import json
import subprocess
import sys

import numpy as np
from PIL import Image, ImageFilter

START = 1.0              # second the picture turns into a cartoon
SMOOTH = 5               # median filter size (at half resolution) that irons out texture into flat areas of color
SHADES = 4               # flat brightness bands (cel shading); fewer gives a bolder, more graphic look
SATURATION = 2.2         # color boost; 1 keeps the original colors
EDGE = 15                # brightness step (0-255, across 2 half-size pixels) that gets an outline; lower draws more lines
LINE = 3                 # outline thickness in pixels (odd)
INK = (25, 15, 40)       # outline color


def anime(img):
    """Redraw one frame as a cartoon: flatten it, band its brightness, boost its color and ink its edges."""
    half = img.resize((img.width // 2, img.height // 2), Image.BOX)        # half size: faster, and smooths grain
    flat = half.filter(ImageFilter.MedianFilter(SMOOTH))
    h, s, v = [np.asarray(c, np.float32) for c in flat.resize(img.size, Image.BICUBIC).convert("HSV").split()]
    v = (np.floor(v / 256 * SHADES) + 0.5) * 256 / SHADES                 # flat cel-shading bands
    s = np.clip(s * SATURATION, 0, 255)
    hsv = Image.merge("HSV", [Image.fromarray(c.astype(np.uint8)) for c in (h, s, v)])
    color = np.asarray(hsv.convert("RGB"), np.float32)

    gray = np.asarray(flat.convert("L"), np.float32)
    gx, gy = np.zeros_like(gray), np.zeros_like(gray)
    gx[:, 1:-1] = gray[:, 2:] - gray[:, :-2]
    gy[1:-1] = gray[2:] - gray[:-2]
    edges = Image.fromarray((np.hypot(gx, gy) > EDGE).astype(np.uint8) * 255)
    edges = edges.resize(img.size, Image.BILINEAR).filter(ImageFilter.MaxFilter(LINE)).filter(ImageFilter.GaussianBlur(0.6))
    ink = (np.asarray(edges, np.float32) / 255)[..., None]
    return color * (1 - ink) + np.array(INK, np.float32) * ink


def probe(path):
    info = json.loads(subprocess.check_output(["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_entries",
                                               "stream=width,height,r_frame_rate", "-of", "json", path]))
    s = info["streams"][0]
    num, den = s["r_frame_rate"].split("/")
    return s["width"], s["height"], s["r_frame_rate"], float(num) / float(den)


src, out = sys.argv[1:3]
w, h, rate, fps = probe(src)
reader = subprocess.Popen(["ffmpeg", "-v", "error", "-i", src, "-f", "rawvideo", "-pix_fmt", "rgb24", "-"],
                          stdout=subprocess.PIPE)
writer = subprocess.Popen(["ffmpeg", "-y", "-v", "error", "-f", "rawvideo", "-pix_fmt", "rgb24", "-s", f"{w}x{h}",
                           "-r", rate, "-i", "-", "-i", src, "-map", "0:v", "-map", "1:a?",
                           "-c:v", "libx264", "-crf", "18", "-pix_fmt", "yuv420p", "-c:a", "copy", "-shortest", out],
                          stdin=subprocess.PIPE)
i = 0
while raw := reader.stdout.read(w * h * 3):
    if i / fps >= START:
        img = anime(Image.frombytes("RGB", (w, h), raw))
        raw = np.clip(img, 0, 255).astype(np.uint8).tobytes()
    writer.stdin.write(raw)
    i += 1
writer.stdin.close()
if reader.wait() or writer.wait():
    sys.exit("ffmpeg failed")