pixa 🖼️

English | 日本語

A fast Rust image processing CLI — optimize AI-generated images for the web in one command, split sprite/expression sheets into individual avatars, generate favicon sets from a logo, remove Gemini AI watermarks, and more.

Features

Command	Description
`compress`	Compress, resize, and convert formats (MozJPEG / OxiPNG / WebP)
`convert`	Convert between JPEG ↔ PNG ↔ WebP ↔ BMP ↔ GIF ↔ TIFF
`info`	Show dimensions, color, EXIF, SHA-256, and other metadata
`favicon`	Generate a web-ready icon set (ICO + PNGs) from any image
`split`	Auto-detect and crop individual objects from a sheet image
`remove-watermark`	Remove the Gemini AI watermark via Reverse Alpha Blending
`detect`	Score whether a Gemini watermark is present in an image
`install`	Install the Claude Code skill so coding agents can use pixa

compress, convert, and remove-watermark accept either a file or a directory — pass -r/--recursive to walk into subdirectories.

The watermark removal algorithm is adapted from GeminiWatermarkTool by Allen Kuo (MIT License).

Use from AI coding agents

Claude Code, GitHub Copilot, and other coding agents can call pixa automatically once you install the Skill file:

pixa install --skills

This drops a Skill at ~/.claude/skills/pixa/SKILL.md so the agent knows when and how to use pixa for image-related requests. Re-run with --force to update.

Quick start

Web-optimize an AI-generated image (one command)

# 4K PNG → 1920px WebP (resize + format convert + compress)
pixa compress hero-4k.png -o hero.webp --max 1920
# 6.8 MB → 82.7 KB (-98.8%)

--max is the longest edge in pixels. Aspect ratio is preserved, and the same flag works for both landscape and portrait inputs.

Compress

pixa compress photo.jpg                          # → photo.min.jpg
pixa compress photo.jpg -o smaller.jpg           # explicit output
pixa compress ./photos -r                        # → ./photos.min/ (mirrored)
pixa compress logo.png -o logo.webp              # PNG → WebP via extension
pixa compress big.png -o thumb.webp --max 400    # thumbnail

When -o is omitted, pixa writes to <input>.min.<ext> (file) or <input>.min/ (directory) — it never overwrites the original. If the optimizer would make a file larger (already-minified assets), the original bytes are written to the destination instead.

Split a sheet image into individual files

pixa split hayate-expressions.png -o ./avatars \
  --names neutral,happy,thinking,surprised,sad

Background color is auto-detected from corner samples
Each object's bounding box is detected; text labels printed below characters are excluded automatically
All output PNGs are uniformly sized — smaller crops are centered on a max-sized canvas filled with the detected background color
When --names provides a count, the algorithm re-splits the widest blob if the initial detection finds fewer objects than expected (handles near-touching or variable-width characters)

Useful flags:

--preview writes <basename>-preview.png showing the detection
--preview-style detected|output|both controls what the preview draws
--padding 10 adds extra breathing room around each object

Generate a favicon set

pixa favicon logo.png -o ./public/favicon

Outputs:

favicon.ico (multi-resolution: 16×16, 32×32, 48×48)
favicon-16x16.png, favicon-32x32.png
apple-touch-icon.png (180×180)
android-chrome-192x192.png, android-chrome-512x512.png
HTML <link> snippet to paste into <head>

Convert format only

pixa convert photo.png photo.webp                # single file
pixa convert ./photos ./out -r --format webp     # directory recursive

For most cases, prefer compress -o foo.webp since that also re-encodes the output for size.

Inspect image

pixa info photo.jpg                              # human-readable
pixa info photo.jpg --json                       # machine-readable

Remove or detect Gemini watermark

pixa remove-watermark image.jpg -o clean.jpg
pixa remove-watermark ./photos -r -o ./cleaned --if-detected
pixa detect image.jpg

--if-detected skips images that don't actually contain a watermark.

Installation

From source

Requirements:

Rust 1.87+
CMake, NASM, pkg-config (needed by mozjpeg)

# Ubuntu / Debian
sudo apt install cmake nasm pkg-config libclang-dev

# macOS
brew install cmake nasm pkg-config

# Build
cargo build --release

The binary lands at target/release/pixa. Put it on your $PATH:

cp target/release/pixa ~/.local/bin/   # or anywhere on PATH

Project layout

pixa/
├── Cargo.toml
├── assets/
│   ├── watermark_48x48.png       # embedded chromakey alpha maps
│   ├── watermark_96x96.png
│   └── skills/pixa/SKILL.md      # bundled into the binary by `install`
└── src/
    ├── main.rs                   # CLI entry point
    ├── lib.rs                    # public library API
    ├── compress.rs               # JPEG / PNG / WebP encode + resize
    ├── convert.rs                # format conversion
    ├── favicon.rs                # favicon set generation
    ├── info.rs                   # metadata extraction
    ├── split.rs                  # sheet auto-cropping
    ├── watermark.rs              # Reverse Alpha Blending
    └── commands/                 # one file per subcommand
        ├── mod.rs                # shared utilities (walk, format, mirror)
        ├── style.rs              # ANSI color / symbol helpers
        ├── compress.rs
        ├── convert.rs
        ├── detect.rs
        ├── favicon.rs
        ├── info.rs
        ├── install.rs
        ├── remove_watermark.rs
        └── split.rs

How watermark removal works

Gemini composites its visible watermark using:

watermarked = α × logo + (1 - α) × original

pixa solves for the original pixel values:

original = (watermarked - α × logo) / (1 - α)

Pre-calibrated 48×48 / 96×96 alpha maps (embedded in the binary) are used directly, so no AI inference is required. Detection runs in three stages: Spatial NCC + Gradient NCC + Variance Analysis.

License

MIT

pixa 0.1.0