---
title: "How to add a duotone with Claude (tested prompt and ffmpeg command)"
description: "Every color drains out and the shot is repainted in just two: the dark dropper cap and bottle edges turn deep indigo while the bright backdrop glows coral. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/duotone
---

# How to add a duotone with Claude

Every color drains out and the shot is repainted in just two: the dark dropper cap and bottle edges turn deep indigo while the bright backdrop glows coral.

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 duotone to input.mp4
   Shadow color (indigo): 35, 20, 95
   Highlight color (coral): 255, 140, 105
   ```

## 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 duotone 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                                                                     |
| --------------------------- | --------------- | -------------------------------------------------------------------------------- |
| `DARK_R, DARK_G, DARK_B`    | `35, 20, 95`    | Shadow color (indigo).                                                           |
| `LIGHT_R, LIGHT_G, LIGHT_B` | `255, 140, 105` | Highlight color (coral).                                                         |
| `BLACK`                     | `50`            | Input brightness that becomes the pure shadow color. Raise it for more indigo.   |
| `WHITE`                     | `240`           | Input brightness that becomes the pure highlight color. Lower it for more coral. |

## Without the skill

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

```
Give input.mp4 a duotone look for its whole length: turn each frame to grayscale, stretch brightness 50 to 240 to the full range (clip anything outside), then map that brightness onto a straight blend between two colors, indigo (35, 20, 95) for the darkest pixels and coral (255, 140, 105) for the brightest. No other colors should be left in the picture. Keep the size, 30fps and the audio, use ffmpeg, and save it as output.mp4.
```

## Run it without Claude

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

```
sh duotone.sh input.mp4 output.mp4
```

```
#!/bin/sh
# Duotone: map the picture's brightness onto two colors, deep indigo in the shadows and coral in the highlights.
# Usage: sh duotone.sh input.mp4 output.mp4
# Needs ffmpeg.
set -e
IN="$1"; OUT="$2"
DARK_R=35;   DARK_G=20;  DARK_B=95   # shadow color (indigo)
LIGHT_R=255; LIGHT_G=140; LIGHT_B=105 # highlight color (coral)
BLACK=50     # input brightness that becomes the pure shadow color
WHITE=240    # input brightness that becomes the pure highlight color

# brightness from 0 (shadow color) to 1 (highlight color), after stretching BLACK..WHITE to the full range
TONE="clip((val-$BLACK)/($WHITE-$BLACK),0,1)"
ffmpeg -y -i "$IN" -vf "format=gray,format=gbrp,lutrgb=r='$DARK_R+($LIGHT_R-$DARK_R)*$TONE':g='$DARK_G+($LIGHT_G-$DARK_G)*$TONE':b='$DARK_B+($LIGHT_B-$DARK_B)*$TONE',format=yuv420p" \
  -r 30 -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)