---
title: "How to add a contrast boost with Claude (tested prompt and ffmpeg command)"
description: "The purple glass deepens and the dropper cap sinks toward black while the brightest streaks in the holographic backdrop flare to near white, and the cream label stays exactly as bright. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/contrast-boost
---

# How to add a contrast boost with Claude

The purple glass deepens and the dropper cap sinks toward black while the brightest streaks in the holographic backdrop flare to near white, and the cream label stays exactly as bright.

Made by the command on this page, from our own test clip.

## Get this effect

1. ### Switch to Code in your [Claude Desktop App](https://claude.com/download)

2. ### Install the skill (once)

   ```
   Install the Recharm video effects skill: download https://recharm-growth-staging.s3.us-east-2.amazonaws.com/website/downloads/recharm-video-effects.zip and unzip it into ~/.claude/skills
   ```

3. ### Ask for the effect

   ```
   Add a contrast boost to input.mp4
   Input/output point for the darks: 0.35/0.2
   The tone that doesn't move: 0.75/0.75
   ```

## Several videos, several effects, one ask

Put your clips in the folder, mention them with @, and ask for everything at once. Claude runs one tested script after another on each clip, then joins them.

Add a contrast boost to **@clip1.mp4**, put a sale badge on **@clip2.mp4**, give **@clip3.mp4** a VHS look, then join all three with crossfades.

## Settings you can change

Ask Claude to change any of these, or edit them at the top of the command.

| Setting     | Default     | What it does                                                                                                                              |
| ----------- | ----------- | ----------------------------------------------------------------------------------------------------------------------------------------- |
| `SHADOW`    | `0.35/0.2`  | Input/output point for the darks. A lower second number sinks the shadows harder.                                                         |
| `PIVOT`     | `0.75/0.75` | The tone that doesn't move. Set it near the shot's average brightness: about 0.5 for normal footage, higher for bright footage like this. |
| `HIGHLIGHT` | `0.9/0.98`  | Input/output point for the brights. A higher second number lifts the highlights closer to white.                                          |

## Without the skill

Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the command itself.

```
Boost the contrast of input.mp4 for the whole clip, from the first frame to the last, with an S-curve on all three color channels (ffmpeg: curves=all='0/0 0.35/0.2 0.75/0.75 0.9/0.98 1/1'). Black and white stay where they are; a 0.35 gray comes out at 0.2 so the darks sink, 0.75 (about the cream label's brightness, RGB 191) stays put, and 0.9 comes out at 0.98 so the brightest backdrop streaks rise to near white (RGB 240 to 250). The purple bottle glass should come out about 20% darker and more saturated, the label and the overall brightness unchanged. Don't add any text (if you ever do, draw it with Pillow, not ffmpeg's drawtext). Keep the size, 30fps, the 6 second length and the audio. Use ffmpeg, encode H.264 yuv420p and save it as output.mp4.
```

## Run it without Claude

This is the exact command we tested. Save it as `contrast-boost.sh` and run:

```
sh contrast-boost.sh input.mp4 output.mp4
```

```
#!/bin/sh
# Contrast boost: an S-curve that sinks the darks and lifts the brights, so a flat shot looks punchier.
# Usage: sh contrast-boost.sh input.mp4 output.mp4
# Needs ffmpeg.
set -e
IN="$1"; OUT="$2"
SHADOW="0.35/0.2"     # input/output point for the darks: 0.35 gray comes out at 0.2, so shadows sink
PIVOT="0.75/0.75"     # the tone that stays put; set it near the shot's average (bright footage sits high)
HIGHLIGHT="0.9/0.98"  # the brights: 0.9 comes out at 0.98, so the brightest streaks rise to near white

# black and white stay pinned at 0 and 1; the curve bends every tone between them away from the pivot,
# on all three color channels, so colors deepen with the contrast instead of going gray
ffmpeg -y -v error -i "$IN" -vf "curves=all='0/0 $SHADOW $PIVOT $HIGHLIGHT 1/1',fps=30,format=yuv420p" \
  -c:v libx264 -crf 18 -c:a copy "$OUT"
```

## More color looks

- [Apply a LUT **Apply a LUT**](https://www.recharm.com/effects/apply-a-lut)
- [Black and white **Black and white**](https://www.recharm.com/effects/black-and-white)
- [Bleach bypass **Bleach bypass**](https://www.recharm.com/effects/bleach-bypass)
- [Cinematic color grade **Cinematic color grade**](https://www.recharm.com/effects/cinematic-color-grade)
- [Color match **Color match**](https://www.recharm.com/effects/color-match)

## Find 3x _winning ads_

Recharm cuts your ad footage into tagged, searchable clips: hooks, testimonials, product shots. Find the shots that win, add the effect with Claude, and ship 3x more ad edits.

[Start 14-day free trial](https://www.recharm.com/get-started)