Repalette

Repalette is an image colorizer written in C. It is available as both a CLI utility and a web application.

Features

• Recolor images using nearest neighbor search.
• Optional dithering for smoother results.

Web-version:

• WASM-powered web application (mostly for mobile usage)
• Fetch color schemes from Gosh
• Support for both text-based and color-picker-based palette editing
• Responsive layout and adaptive light/dark theme

Benchmark

• Processor: Intel® Core™ i5-8300H Processor
• Input: 7680x4320 JPEG image
• Color palette: Nord
• Average of 10 runs

Dithering algorithm	Mean (s)	%slower
No dithering	2.001	0
Floyd-Steinberg	3.514	75
Atkinson	3.489	74
Jarvis, Judice, and Ninke	4.367	118
Burkes	3.891	94
Sierra	4.337	116
Sierra lite	3.191	59

To run the benchmark yourself:

• Install hyperfine
• Build the CLI version
• Put an image with the name input.jpg in the same directory as benchmark.sh
• Run ./benchmark.sh

Building

You need:

• For native build: Any C compiler that supports C99.
• For WASM build: Clang, LLVM, and LLD.
• GNU make.

Build everything with Clang

make

Only build the native version with GCC

make repalette CC=gcc

Note:

Repalette uses stb_image and stb_image_write for working with images. They're automatically downloaded as make dependencies using curl.

Usage

CLI version

USAGE:
  repalette -h | --help
  repalette <input file> <output file> [options]
OPTIONS:
-p, --palette COLOR[,COLOR...]
-d, --dither  none | floyd-steinberg | atkinson | jjn | burkes | sierra | sierra-lite

• The default color palette is 000000,ffffff (black and white)
• The default dithering algorithm is floyd-steinberg

Example:

repalette input.jpg output-no-dither.png -p 000000,ff0000,ffffff --dither none
repalette input.jpg output-burkes.png -p 000000,ff0000,ffffff --dither burkes

input.jpg	output-no-dither.png	output-burkes.png

Web version

Host the website with any server or go to https://ziap.github.io/repalette.

The user interface:

License

This project is licensed under the AGPL-3.0 license.