Little CMS wrapper for Rust

Convert and apply color profiles with a safe abstraction layer for the LCMS library. LCMS2 is a mature, fully-featured color management engine. These bindings have been stable for years, and used in production at scale.

See the API reference for the Rust functions, and the LCMS2 documentation in HTML/or the original PDF for more background information about the functions.

use lcms2::*;

fn example() -> Result<(), std::io::Error> {
    let icc_file = include_bytes!("custom_profile.icc"); // You can use Profile::new_file("path"), too
    let custom_profile = Profile::new_icc(icc_file)?;

    let srgb_profile = Profile::new_srgb();

    let t = Transform::new(&custom_profile, PixelFormat::RGB_8, &srgb_profile, PixelFormat::RGB_8, Intent::Perceptual);

    // Pixel struct must have layout compatible with PixelFormat specified in new()
    let source_pixels: &[rgb::RGB<u8>] = …;
    t.transform_pixels(source_pixels, destination_pixels);

    // If input and output pixel formats are the same, you can overwrite them instead of copying
    t.transform_in_place(source_and_dest_pixels);

    Ok(())
}

To apply an ICC profile from a JPEG:

if b"ICC_PROFILE\0" == &app2_marker_data[0..12] {
   let icc = &app2_marker_data[14..]; // Lazy assumption that the profile is smaller than 64KB
   let profile = Profile::new_icc(icc)?;
   let t = Transform::new(&profile, PixelFormat::RGB_8,
       &Profile::new_srgb(), PixelFormat::RGB_8, Intent::Perceptual);
   t.transform_in_place(&mut rgb);
}

There's more in the examples directory.

This crate requires Rust 1.64 or later. It's up to date with LCMS 2.15, and should work with a wide range of versions.

Threads

In LCMS all functions are in 2 flavors: global and *THR() functions. In this crate this is represented by having functions with GlobalContext and ThreadContext. Create profiles, transforms, etc. using *_context() constructors to give them their private context, which makes them sendable between threads (i.e. they're Send).

By default Transform does not implement Sync, because LCMS2 has a thread-unsafe cache in the transform. You can set Flags::NO_CACHE to make it safe (this is checked at compile time).

Upgrading from v5

If you're using a custom RGB type with Transform, implement bytemuck::Pod and Zeroable for it. Make sure you use arrays or #[repr(C)] struct types for pixels. Rust tuples have a technically undefined layout, and can't be used as as a pixel format.

unsafe impl Pod for RGB {}
unsafe impl Zeroable for RGB {}

You don't need to do this if you use the rgb crate.