iqa

iqa provides a single, ergonomic API over the patchwork of visual quality assessment metrics available in the Rust ecosystem. It wraps existing crates where they exist and fills in the gaps where they don't, so you can compute PSNR, SSIMULACRA2, and friends without juggling a different type, color space, and pixel format for each one.

Installation

cargo add iqa

This pulls in every metric. Some (such as ssimulacra2) compile vendored C/C++ and therefore need a C++ toolchain and the system lcms2 library — see Cargo features for the details. For a pure-Rust build with no system dependencies, disable the defaults and take just the metrics you need:

[dependencies]
iqa = { version = "0.1", default-features = false, features = ["psnr"] }

Quick start

iqa consumes a tightly packed, row-major sample buffer and deliberately leaves image decoding to you (here, the image crate):

use iqa::{Image, PsnrOptions};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Decode however you like, then hand iqa the raw samples.
    let reference = image::open("reference.png")?.to_rgb8();
    let distorted = image::open("distorted.jpg")?.to_rgb8();

    let (w, h) = reference.dimensions();
    let reference = Image::srgb8(w, h, reference.into_raw())?;
    let (w, h) = distorted.dimensions();
    let distorted = Image::srgb8(w, h, distorted.into_raw())?;

    // PSNR — pure Rust, always available.
    let psnr = iqa::psnr(&reference, &distorted, PsnrOptions::default())?;
    println!("PSNR:        {psnr:.3} dB");

    // SSIMULACRA2 — requires the `ssimulacra2` feature; 100 = identical.
    let ssimulacra2 = iqa::ssimulacra2(&reference, &distorted)?;
    println!("SSIMULACRA2: {ssimulacra2:.3}");

    Ok(())
}

Both inputs must share one pixel format, so a color-space, channel, or bit-depth mismatch is a compile error rather than a meaningless score. See examples/compare.rs for the full pipeline — run it with cargo run --release --example compare -- reference.png distorted.jpg.

Metrics

The table below tracks the planned metric set — the nine-metric full-reference core that covers essentially every published JXL/AVIF codec comparison from the last two years, plus LPIPS as a learned reference metric.

The Implementation column points at the implementation iqa is built on. We prefer porting or binding the upstream source implementation over reusing a Rust-specific reimplementation: cross-compilation is a requirement, but portability beyond that is not, so staying close to the reference keeps results faithful.

*: LPIPS is Python implementation only.

Status legend:

• Planned — selected for implementation, not yet started.
• Require testing — implemented, but not yet validated against reference outputs.
• Stable and tested — implemented and verified against the reference implementation.

Cargo features

Each metric is gated behind its own Cargo feature:

Every metric is enabled by default for convenience — cargo add iqa gets you the full set. Some metrics (such as ssimulacra2) bind native C/C++ code and therefore need a C++ toolchain and system libraries to build.

For leaner builds, disable the default features and opt into exactly the metrics you need:

[dependencies]
# Pure-Rust subset only — no C/C++ toolchain required.
iqa = { version = "0.1", default-features = false, features = ["psnr"] }

Building with ssimulacra2

SSIMULACRA2 is bound via FFI to the original C++ reference rather than reimplemented, so enabling it (including via the default feature set) needs a native build environment:

1. A C++ toolchain. build.rs compiles the reference with the cc crate, which uses c++ by default (override with the CXX environment variable).

2. lcms2. libjxl's color management needs the system lcms2 library, located via pkg-config:

   sudo apt install liblcms2-dev   # Debian / Ubuntu
   brew install little-cms2        # macOS / Homebrew
   

When you depend on iqa from crates.io that is all you need — the vendored C++ sources are packaged inside the published crate, so there are no submodules to fetch.

Building from a git checkout (contributors) additionally needs those sources, which live under third_party/ as git submodules:

git submodule update --init --recursive

Either way, build or test with the feature enabled:

cargo test --features ssimulacra2

Development

It is important that development velocity is maintained regardless of project complexity. Unit tests for all contributions are expected, especially for platform-specific behaviours!

Setup

Install lefthook and activate the pre-commit and pre-push hooks:

# macOS / Homebrew
brew install lefthook

# Linux (Homebrew on Linux)
brew install lefthook

# via cargo
cargo install lefthook

# then install the hooks
lefthook install

The pre-commit hook runs cargo fmt --check and cargo clippy. The pre-push hook runs the full test suite.

Releasing

Releases are automated with release-plz and driven by Conventional Commits: the commit messages landed on master decide the next version number and fill in CHANGELOG.md.

To cut a release:

1. Land changes on master with Conventional Commit messages (feat:, fix:, refactor!:, ...).
2. release-plz maintains an open release PR that bumps the version in Cargo.toml, updates CHANGELOG.md, and refreshes Cargo.lock. Review it as you would any other PR.
3. Merge the release PR. Merging it is the whole release: release-plz publishes the crate to crates.io, pushes a vX.Y.Z git tag, and creates the matching GitHub release.

Publishing authenticates with crates.io trusted publishing over OIDC, so no registry token is stored in the repository. The workflow lives in .github/workflows/release-plz.yml.

0.1.0 was published by hand to bootstrap the crate — trusted publishing can only be configured once a crate already exists on crates.io. Every release after it is fully automated by merging the release PR.