slimg

A fast image optimization CLI. Convert, compress, and resize images using modern codecs.

한국어

Supported Formats

Installation

Cargo (crates.io)

cargo install slimg

Homebrew (macOS / Linux)

brew install clroot/tap/slimg

Pre-built binaries

Download from GitHub Releases:

From source

git clone https://github.com/clroot/slimg.git
cd slimg
cargo install --path cli

Build requirements

• Rust 1.85+ (edition 2024)
• C compiler (cc)
• nasm (for MozJPEG / rav1e assembly optimizations)
• meson + ninja (for building dav1d AVIF decoder from source)
• Set SYSTEM_DEPS_DAV1D_BUILD_INTERNAL=always to build dav1d from source

Usage

convert

Convert an image to a different format.

# Convert a JPEG to WebP at quality 80 (default)
slimg convert photo.jpg --format webp

# Convert to AVIF at quality 60
slimg convert photo.png --format avif --quality 60

# Convert all images in a directory
slimg convert ./images --format webp --output ./output --recursive

# Limit to 4 parallel jobs
slimg convert ./images --format webp --recursive --jobs 4

optimize

Re-encode an image in the same format to reduce file size.

# Optimize a JPEG at quality 80
slimg optimize photo.jpg

# Optimize in-place (overwrite original)
slimg optimize photo.jpg --overwrite

# Optimize a directory of images
slimg optimize ./images --quality 70 --recursive

# Limit to 2 parallel jobs (useful for large images)
slimg optimize ./images --recursive --jobs 2

resize

Resize an image with optional format conversion.

# Resize by width (preserves aspect ratio)
slimg resize photo.jpg --width 800

# Resize by height
slimg resize photo.jpg --height 600

# Fit within bounds (preserves aspect ratio)
slimg resize photo.jpg --width 800 --height 600

# Scale by factor
slimg resize photo.jpg --scale 0.5

# Resize and convert format
slimg resize photo.jpg --width 400 --format webp --output thumb.webp

Batch Processing

When processing directories with --recursive, slimg uses all available CPU cores via rayon. Use --jobs to limit parallelism (useful for large images or memory-constrained environments).

# Use 4 threads instead of all cores
slimg convert ./images --format webp --recursive --jobs 4

Error handling — If a file fails to process, slimg skips it and continues with the rest. A summary of failed files is printed at the end.

Safe overwrite — When using --overwrite, slimg writes to a temporary file first and renames it on success. If encoding fails, the original file is preserved.

Benchmarks

See docs/benchmarks.md for detailed performance measurements across all codecs and pipeline operations.

Language Bindings

Library

The core functionality is available as a library crate (slimg-core):

use slimg_core::*;

// Decode an image file
let (image, format) = decode_file(Path::new("photo.jpg"))?;

// Convert to WebP
let result = convert(&image, &PipelineOptions {
    format: Format::WebP,
    quality: 80,
    resize: None,
})?;

// Save the result
result.save(Path::new("photo.webp"))?;

License

MIT OR Apache-2.0