Pixel types for Rust

Operating on pixels as weakly-typed vectors of u8 is error-prone and inconvenient. It's better to use vectors and slices of pixel structs, like &[Rgb<u8>].

However, Rust is so strongly typed that your Rgb struct is not compatible with my Rgb struct. This crate provides common structs to share between crates.

Features

• It's a shared type used in many crates, which allows you to seamlessly and reliably share pixel data between them.

• Compiles quickly and has low overhead. The dependencies are only for interoperability with the broader ecosystem, and are all optional.

• Implements standard Rust traits, and has convenience methods for operating on all channels of the pixels. Saves you from having to copy-paste the same lines for r, g, and b.

• It's unopinionated about color management, which lets it prepresent most RGB-related pixels without interfering. If you need more advanced conversions and non-RGB color spaces, use the palette crate instead.

Basic Usage

use rgb::{Rgb, Rgba, Argb, Bgr, Bgra, Abgr, Grb}; // and more
use rgb::prelude::*; // traits with convenience methods

let rgb_pixel = Rgb { r: 0u8, g: 100, b: 255 };
let wider_pixel = rgb_pixel.map(u16::from);

println!("{rgb_pixel}"); // prints rgb(0, 100, 255)
println!("{rgb_pixel:X}"); // prints #0064FF

assert_eq!(rgb_pixel.to_color_array(), [0, 100, 255]);
assert_eq!(rgb_pixel.with_alpha(128), Rgba::new(0, 100, 255, 128));

Conversions from/to other types

We defer to the bytemuck crate to have safe zero-cost conversions between types. See bytemuck::cast_slice() and cast_vec().

let pixels: Vec<u8> = vec![0u8; 3 * size];
let rgb_pixels: Vec<Rgb<u8>> = rgb::bytemuck::allocation::cast_vec(pixels);

for rgb_pixel in &rgb_pixels {
}

If you'd like to work with 2D slices of pixels, see the imgvec crate.

Stable and testing versions

The version 0.8 is stable, and we plan to support it for a long time. You can use it, and rely on it.

[dependencies]
rgb = "0.8.50"

We want to release a proper v1.0.0 eventually. We plan to have it backwards-compatible with crates using v0.8, except some deprecated cruft removed/fixed. We hope the migration will be seamless for most users. Please help us test it!

# This is required due to how version unification works in Cargo
[patch.crates-io]
rgb.git = "https://github.com/kornelski/rust-rgb"

[dependencies]
rgb = "0.8.90"

• Are the names of the traits and their methods good?
• Are there any standard library traits you'd like implemented on the pixel types?
• Is the split between Pixel, HetPixel, HasAlpha sensible? (pixels support a different type for the alpha channel, and there's Rgbw without alpha).

Please open issues in the repo with the feedback or message @[email protected].

Usage

use rgb::{Rgb, Rgba, Argb, Bgr, Bgra, Abgr, Grb, Gray_v09 as Gray, GrayA};

let rgb = Rgb {r: 0, g: 0, b: 0};
let rbga = Rgba {r: 0, g: 0, b: 0, a: 0};
let argb = Argb {a: 0, r: 0, g: 0, b: 0};

let bgr = Bgr {b: 0, g: 0, r: 0};
let bgra = Bgra {b: 0, g: 0, r: 0, a: 0};
let abgr = Abgr {r: 0, g: 0, b: 0, a: 0};

let grb = Grb {g: 0, b: 0, r: 0};

let gray = Gray {v: 0};
let gray_a = GrayA {v: 0, a: 0};

If you have a pixel type you would like to use that is not currently implemented, please open an issue to request your pixel type.

The pixel types with an alpha component such as Rgba have two generic type parameters:

struct Rgba<T, A = T> {
    r: T,
    g: T,
    b: T,
    a: A,
}

This makes them more flexible for more use-cases, for example if you needed more precision for you color components than your alpha component you could create an Rgba<f32, u8>. However, in most use-cases the alpha component type will be the same as the color component type.

A pixel with separate types for the color and alpha components is called a heterogeneous pixel (HetPixel), whereas a pixel with a single type for both color and alpha components is called a homogeneous pixel (Pixel).

Pixel Traits

All functionality for the pixel types is implemented via traits. This means that none of the pixel types, like Rgb<u8>, have any inherent methods. This makes it easy to choose which methods you'd like to be in scope at any given time unlike inherent methods which are always within scope.

This crate offers the following traits:

HetPixel

The most foundational pixel trait implemented by every pixel type.

use rgb::{Rgba, HetPixel};

let mut rgba: Rgba<u8> = Rgba::try_from_colors_alpha([0, 0, 0], 0).unwrap();

*rgba.each_color_mut()[2] = u8::MAX;
assert_eq!(rgba.to_color_array(), [0, 0, 255]);

*rgba.alpha_opt_mut().unwrap() = 50;
assert_eq!(rgba.alpha_opt(), Some(50));

let rgba = rgba.map_colors(u16::from);
let rgba = rgba.map_colors_same(|c| c * 2);
let rgba = rgba.map_alpha(f32::from);
let rgba = rgba.map_alpha_same(|a| a * 2.0);

assert_eq!(rgba, Rgba::<u16, f32> {r: 0, g: 0, b: 510, a: 100.0});

Pixel

A stricter form of HetPixel where the two component types, color and alpha, are the same.

use rgb::{Rgba, Pixel};

let mut rgba: Rgba<u8> = Rgba::try_from_components([0, 0, 0, 0]).unwrap();

*rgba.each_mut()[2] = u8::MAX;
assert_eq!(rgba.to_array(), [0, 0, 255, 0]);

let rgba = rgba.map(u16::from);
let rgba = rgba.map_same(|c| c * 2);

assert_eq!(rgba, Rgba::<u16> {r: 0, g: 0, b: 510, a: 0});

GainAlpha

A way to add alpha to a pixel type in various ways.

use rgb::{Rgb, Rgba, GainAlpha};

let expected: Rgba<u8> = Rgba {r: 0, g: 0, b: 0, a: 255};

assert_eq!(Rgb {r: 0, g: 0, b: 0}.with_default_alpha(255), expected);
assert_eq!(Rgb {r: 0, g: 0, b: 0}.with_alpha(255), expected);
assert_eq!(Rgba {r: 0, g: 0, b: 0, a: 0}.with_alpha(255), expected);

HasAlpha

A trait only implemented on pixels that have an alpha component.

Due to a naming conflict with several now-deprecated inherent functions with the same name (such as Rgb::alpha()) the HasAlpha::alpha() method requires fully qualified syntax for disambiguation. The deprecated functions are due to be removed in a future release which will solve this issue.

use rgb::{Rgba, HasAlpha};

let mut rgba: Rgba<u8> = Rgba {r: 0, g: 0, b: 0, a: 255};

*rgba.alpha_mut() -= 50;

assert_eq!(HasAlpha::alpha(&rgba), 205);

Crate Features

• num-traits: Enables various num_traits traits impls for the pixel types such as CheckedAdd.
• defmt-03 = Enables the Format trait impls from defmt v0.3 for the pixel types
• serde = Enables Serializable and Deserializable trait impls from serde for the pixel types
• bytemuck = Enables Pod and Zeroable trait impls from bytemuck for the pixel types

The following crate features are only kept for backwards compatibility, and will be removed in the next major version:

# These are no longer used
argb = []
grb = []
checked_fns = []
as-bytes = ["bytemuck"]

Color-Space Agnostic

This crate is purposefully a basic lowest-common-denominator, and it does not dictate what color spaces the pixel types are supposed to use. For example, Gray<u8> could be either linear lightness or gamma-corrected luma, however you wish to use it. Correct color management is a complex problem, and this crate doesn't want to impose any specific solutions.

If you need strongly-typed color spaces, you can use newtypes as component types for Rgb<T> and Rgba<T, AlphaType>, e.g.:

# use rgb::Rgb;
struct LinearLight(u16);
type LinearRGB = Rgb<LinearLight>;

Roadmap to 1.0

The plan is to provide easy migration to v1.0. There will be a transitional v0.9 version released that will be mostly backwards-compatible with 0.8, and forwards-compatible with 1.0.

The changes:

• Types were renamed to follow Rust's naming convention: RGBA → Rgba. Type aliases with an 8 or 16 suffix (RGBA8) were kept as-is.
• The grayscale types have changed from being tuple structs with .0/.1 to structs with named fields .v (value) and .a (alpha).
• GrayAlpha has been renamed to GrayA.
• bytemuck::Pod (conversions from/to raw bytes) require color and alpha components to be the same type (i.e. it works with Rgba<u8>, but not Rgba<Newtype, DifferentType>).
• Most inherent methods were moved to a new Pixel trait.

Migrating away from deprecated items

Some items in this crate have become deprecated in preparation for a future release which removes them. Here is a checklist of things you may need to do.

1. Update to the latest version of 0.8, and fix all deprecation warnings.
   • rename .alpha() to .with_alpha()
   • rename .map_c() to .map_colors()
2. Change field access on GrayAlpha from .0 and .1 to .v and .a where possible.
3. Use the bytemuck crate for conversions from/to bytes instead of ComponentBytes trait. Disable the as-bytes feature if possible.
4. Use the num-traits crate for .checked_add(), don't enable checked_fns feature.
5. Don't enable gbr and argb features. All pixel types are enabled by default.
6. AsRef<[T]> implementations have changed to AsRef<[T; N]>. In most cases .as_ref()/.as_mut() calls should coerce to a slice anyway.
7. Instead of pixel.as_slice() use pixel.as_ref().
8. Stop using the rgb::Gray/rgb::GrayAlpha types and switch to rgb::Gray_v09 as Gray/rgb::GrayA instead respectively.
9. In generic code operating on pixels, add Copy + 'static bounds to the pixel types and their components.