How to add an apply a LUT with Claude

Make a 3D LUT and apply it to all of input.mp4. First write a .cube file called golden-hour.cube: a 33x33x33 grid (LUT_3D_SIZE 33, red index changing fastest, then green, then blue). For each grid point with r, g, b from 0 to 1, the output is r^0.8, g^1.05 and 0.85 x b^1.1; then push saturation to 1.25 around its brightness Y = 0.299R + 0.587G + 0.114B (new = Y + 1.25 x (color - Y)), clipped to 0-1, written with 6 decimals. Then apply it with ffmpeg's lut3d filter (interp=tetrahedral) on every frame from start to end. The pale blue backdrop, around RGB (187, 197, 208), should end up warm cream-gold, around RGB (200, 194, 167); the cream label turns a toasted beige around RGB (208, 186, 138) and the purple bottle a rosy orchid around RGB (167, 99, 139). Use Python with numpy to write the .cube file and ffmpeg for the video. Keep the size, 30fps frame rate, length and audio the same, encode H.264 yuv420p and save it as output.mp4.

"""Apply a LUT: recolor every frame of a video through a .cube color preset with ffmpeg's lut3d filter.

Usage: python3 apply-a-lut.py input.mp4 output.mp4 [look.cube]
Needs ffmpeg and Python 3 with numpy. Pass your own .cube file as the third argument; without one, the
recipe writes a sample "golden hour" LUT (warm highlights, rosy purples) next to the output and uses that.
"""
import subprocess
import sys
from pathlib import Path

import numpy as np

# The sample LUT: each color channel gets a curve, then saturation is pushed
LUT_SIZE = 33                    # grid points per axis in the .cube file (33 is the common size)
GAMMA = (0.8, 1.05, 1.1)         # per-channel gamma: below 1 lifts a channel, above 1 pulls it down
GAIN = (1.0, 1.0, 0.85)          # per-channel multiplier after the gamma; less blue makes it warm
SATURATION = 1.25                # 1 keeps the color strength, higher makes it richer


def write_sample_lut(path):
    """Write a .cube file: one output RGB per grid point, red changing fastest."""
    steps = np.linspace(0, 1, LUT_SIZE)
    b, g, r = np.meshgrid(steps, steps, steps, indexing="ij")
    rgb = np.stack([r, g, b], axis=-1).reshape(-1, 3)
    rgb = np.array(GAIN) * rgb ** np.array(GAMMA)
    luma = rgb @ np.array([0.299, 0.587, 0.114])
    rgb = np.clip(luma[:, None] + (rgb - luma[:, None]) * SATURATION, 0, 1)
    lines = ['TITLE "golden hour"', f"LUT_3D_SIZE {LUT_SIZE}"] + [f"{r:.6f} {g:.6f} {b:.6f}" for r, g, b in rgb]
    Path(path).write_text("\n".join(lines) + "\n")


src, out = sys.argv[1], sys.argv[2]
if len(sys.argv) > 3:
    lut = sys.argv[3]
else:
    lut = str(Path(out).with_name("golden-hour.cube"))
    write_sample_lut(lut)

subprocess.run(["ffmpeg", "-y", "-v", "error", "-i", src, "-vf", f"lut3d=file='{lut}':interp=tetrahedral",
                "-r", "30", "-c:v", "libx264", "-crf", "18", "-pix_fmt", "yuv420p", "-c:a", "copy", out], check=True)