Pixel types for Rust

Operating on pixels as weakly-typed vectors of u8 is error-prone and inconvenient. It's better to use vectors of pixel structs. However, Rust is so strongly typed that your Rgb pixel struct is not compatible with my Rgb pixel struct. So let's all use mine :P

v0.8.90 is a transitional/preview release

The RGB crate is getting a major update, which will eventually be stablized as v1.0.0.

For testing, use:

[dependencies]
rgb = "0.8.90"

# this is required, because v0.8.90 is not on crates.io
[patch.crates-io]
rgb.git = "https://github.com/kornelski/rust-rgb"

We welcome your feedback about the crate!

• 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 @kornel@mastodon.social.

Installation

If you want to run a stable, compatible version, run cargo add rgb@0.8.47. If you want to try unstable experimental version, run cargo add rgb@0.8.90-alpha.1 or add this to your Cargo.toml:

[dependencies]
rgb = "0.8.90-alpha.1" # unstable experimental version
# rgb = "0.8.47" # older, stable

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.color_array_mut()[2] = u8::MAX;
assert_eq!(rgba.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);

Bytemuck

If you have a &[u8] or Vec<u8> type and you want a &[Rgb<u8>] or Vec<Rgb<u8>> type then you can safely achieve these type-casts via the bytemuck crate (see cast_slice() and cast_vec()).

You will need to enable the bytemuck crate feature in order to use functions from the bytemuck library on the pixel types in this crate.

Crate Features

• default: The default feature which does nothing.
• 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

Legacy Features

The following crate features are only exposed for compatibility with the v0.8 release so as to be non-breaking, however, once migrated to v0.9 you should no longer be using any of these features. They are going to be removed in the next major release after v0.9.

argb = []
grb = []
checked_fns = []
as-bytes = ["bytemuck"]

Color-Space Agnostic

This crate is purposefully agnostic about the color-spaces of the pixel types. For example, Gray<u8> could be either linear lightness or gamma-corrected luma, etc.

Correct color management is a complex problem, and this crate aims to be the lowest common denominator, so it's intentionally agnostic about it.

However, this library supports any subpixel type for RGB<T>, and RGBA<RGBType, AlphaType>, so you can use them with a newtype, 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.

Planned changes:

• Types will be renamed to follow Rust's naming convention: RGBA → Rgba. The names with an 8 or 16 suffix (RGBA8) will continue to work.
• The Gray and GrayAlpha types will change from tuple structs with .0 to structs with named fields .v (value) and .a (alpha). Through a Deref trick both field names will work, but .0 is going to be deprecated.
• bytemuck::Pod (conversions from/to raw bytes) will require color and alpha components to be the same type (i.e. it will work with Rgba<u8>, but not Rgba<Newtype, DifferentType>). Currently it's unsound if the alpha has a different size than color components.
• Many inherent methods will be moved to a new Pixel trait.

Migrating away from deprecated items

Many 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()
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.
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.