How to add a synthwave look with Claude

Give all of input.mp4 a synthwave grade, on every frame from start to end. For each pixel (RGB, 0-255): take its brightness Y = 0.299R + 0.587G + 0.114B and work out a tone t = max(Y - 60, 0) / (225 - 60). Then tilt it by height so the top is graded darker and the bottom brighter: subtract a value that runs in a straight line from +0.45 on the top row to -0.45 on the bottom row, and clip t to 0-1. Map t through a three-color gradient: violet (40, 10, 90) at t = 0, hot pink (235, 40, 150) at t = 0.8 and cyan (30, 205, 240) at t = 1, blending linearly between them. Then add a neon glow: multiply the graded frame by t, blur it with a Gaussian blur of radius 12 pixels (Pillow's GaussianBlur), and add 0.3 times that blur back onto the graded frame, clipping to 0-255. The top 12% of the frame should come out violet-magenta around RGB (170, 30, 140), the band from 30% to 50% down hot pink around (225, 60, 180), and the bottom 15% glowing cyan around (40, 255, 255), with none of the original pale blue-white backdrop (around 193, 203, 214) left. Do it in Python with numpy and Pillow, piping raw frames from and back to ffmpeg. Add no text (any text you do add should be drawn with Pillow, not ffmpeg's drawtext). Keep the size, 30fps frame rate, 6 second length and audio the same, encode H.264 yuv420p and save it as output.mp4.

#!/usr/bin/env python3
"""Synthwave look: dark tones turn deep violet, midtones hot pink and highlights neon cyan, with a soft glow.

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

import numpy as np
from PIL import Image, ImageFilter

VIOLET = (40, 10, 90)       # the color the darkest tones turn
PINK = (235, 40, 150)       # the color the midtones turn
CYAN = (30, 205, 240)       # the color the brightest tones turn
BLACK_POINT = 60            # brightness (0-255) at and below which a pixel is all violet
WHITE_POINT = 225           # brightness at and above which a pixel is all cyan
PINK_AT = 0.8               # where pink sits between violet (0) and cyan (1)
HORIZON = 0.9               # how much darker the top of the frame is graded than the bottom: violet sky, cyan floor
GLOW = 0.3                  # strength of the soft neon glow added around bright areas
GLOW_RADIUS = 12            # blur radius of that glow, in pixels

src, dst = sys.argv[1], sys.argv[2]
w, h = map(int, subprocess.check_output(
    ["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_entries", "stream=width,height",
     "-of", "csv=p=0", src], text=True).strip().split(","))

LUMA = np.array([0.299, 0.587, 0.114], np.float32)
violet, pink, cyan = (np.array(c, np.float32) for c in (VIOLET, PINK, CYAN))
# upper rows lean toward violet and pink, lower rows toward cyan
tilt = np.linspace(HORIZON / 2, -HORIZON / 2, h, dtype=np.float32)[:, None, None]


def grade(rgb):
    tone = np.clip((rgb @ LUMA)[..., None] - BLACK_POINT, 0, None) / (WHITE_POINT - BLACK_POINT)
    tone = np.clip(tone - tilt, 0, 1)
    low = violet + (pink - violet) * np.clip(tone / PINK_AT, 0, 1)
    out = low + (cyan - low) * np.clip((tone - PINK_AT) / (1 - PINK_AT), 0, 1)
    glow = Image.fromarray(np.clip(out * tone, 0, 255).astype(np.uint8)).filter(ImageFilter.GaussianBlur(GLOW_RADIUS))
    out += GLOW * np.asarray(glow, np.float32)
    return np.clip(out, 0, 255).astype(np.uint8)


reader = subprocess.Popen(["ffmpeg", "-v", "error", "-i", src, "-vf", "fps=30", "-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", "30",
                           "-i", "-", "-i", src, "-map", "0:v", "-map", "1:a?", "-c:v", "libx264", "-crf", "18",
                           "-pix_fmt", "yuv420p", "-c:a", "copy", "-shortest", dst], stdin=subprocess.PIPE)
size = w * h * 3
while True:
    buf = reader.stdout.read(size)
    if len(buf) < size:
        break
    frame = np.frombuffer(buf, np.uint8).reshape(h, w, 3).astype(np.float32)
    writer.stdin.write(grade(frame).tobytes())
writer.stdin.close()
sys.exit(reader.wait() or writer.wait())