How to add a HDR look with Claude

Give input.mp4 a fake HDR look for the whole clip, from the first frame to the last: lift the shadows, bring the highlights down and crunch the local contrast, like an HDR photo app. Do it per frame in Python with OpenCV and numpy: convert the frame to Lab (8-bit, cv2.COLOR_RGB2LAB) and work on L as float. Get the broad light by shrinking L to half size (INTER_AREA), running cv2.bilateralFilter(small, 0, 25, 10) on it (sigmaColor 25, sigmaSpace 10, which is 20 pixels at full size) and scaling it back up (INTER_LINEAR); the edge-preserving filter keeps halos off the bottle's outline. Then new L = 128 + (broad - 128) * 0.55 + (L - broad) * 2.5, so the broad light keeps 55% of its spread around mid gray and the detail on top of it is 2.5 times stronger. Multiply a and b's distance from 128 by 1.35 for richer color, clip to 0-255 and convert back to RGB. The black dropper cap, around brightness 38, should come out around 72 (about 1.9 times brighter); the pale backdrop, around 205, should come out around 163 (about 20% darker); the whole frame should average about 157 out of 255 instead of 193, and fine detail (Laplacian variance) should be about 3 to 4 times the input's. Don't crop, zoom or add anything else, and don't add any text (if you ever do, draw it with Pillow, not ffmpeg's drawtext). Read and write the frames through ffmpeg pipes, keep the 540x960 size, 30fps, the 6 second length and the audio, encode H.264 yuv420p and save it as output.mp4.

#!/usr/bin/env python3
"""HDR look: shadows lift, highlights come down and local contrast crunches, for a hyper-detailed, gritty picture.

Usage: python3 hdr-look.py input.mp4 output.mp4
Needs ffmpeg and Python 3 with OpenCV and numpy (pip install opencv-python-headless numpy).
It's a fake tone map, as HDR photo apps do it: each frame's brightness is split into the broad light (smoothed with
an edge-preserving bilateral filter, so outlines don't glow) and the detail on top of it; the broad light is
squeezed toward mid gray and the detail is amplified.
"""
import json
import subprocess
import sys

import cv2
import numpy as np

MID = 128            # brightness (0-255) the broad light is squeezed toward
COMPRESS = 0.55      # how much of the broad light's spread is kept: lower lifts shadows and darkens highlights more
RADIUS = 20          # size in pixels of the broad light: bigger lets wider shapes count as detail
EDGE = 25            # brightness step (0-255) the smoothing won't cross, which keeps halos off outlines
DETAIL = 2.5         # detail gain: 1 leaves textures as they are, higher crunches them
SATURATION = 1.35    # color gain, so the colors hold up against the extra contrast


def broad_light(light):
    """The light with its detail smoothed away but its edges kept (worked out at half size, for speed)."""
    h, w = light.shape
    small = cv2.resize(light, (w // 2, h // 2), interpolation=cv2.INTER_AREA)
    return cv2.resize(cv2.bilateralFilter(small, 0, EDGE, RADIUS / 2), (w, h), interpolation=cv2.INTER_LINEAR)


def tone_map(frame):
    lab = cv2.cvtColor(frame, cv2.COLOR_RGB2LAB).astype(np.float32)
    light = lab[:, :, 0]
    base = broad_light(light)
    lab[:, :, 0] = MID + (base - MID) * COMPRESS + (light - base) * DETAIL
    lab[:, :, 1:] = 128 + (lab[:, :, 1:] - 128) * SATURATION
    return cv2.cvtColor(np.clip(lab, 0, 255).astype(np.uint8), cv2.COLOR_LAB2RGB)


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


src, out = sys.argv[1:3]
w, h = probe(src)
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", out], stdin=subprocess.PIPE)
size = w * h * 3
while raw := reader.stdout.read(size):
    if len(raw) < size:
        break
    writer.stdin.write(tone_map(np.frombuffer(raw, np.uint8).reshape(h, w, 3)).tobytes())
writer.stdin.close()
if reader.wait() or writer.wait():
    sys.exit("ffmpeg failed")