# Prisma - The Rust Color Library

## Overview:

Prisma is a rust library aimed to be a comprehensive set of color representations, manipulations, conversions and algorithms that are easy to use for projects of all levels. Prisma follows a model of "opt-in" complexity, meaning that if you just want a library to convert from Rgb to Hsv and back, prisma will let you do it with minimal knowledge of color science. If you need to access the CIE spaces or do color space conversions however, prisma also provides that functionality with wrappers to use the type system to enforce validity.

Prisma aims to be the go-to source for color conversions and color science in rust. It is currently a work in progress, and any contributions or feature requests are appreciated.

### Color Models:

Currently prisma supports the following color models:

#### Device Dependent:

• Rgb - The standard color model for displays
• Rgi - A chromaticity model constructed from Rgb that decouples chromaticity and lightness
• Hsv - Hue, saturation, value: a more intuitive polar Rgb model
• Hsl - Hue, saturation, lightness: an alternate to Hsv fulfilling similar roles
• Hsi - Hue, saturation, intensity: a hue-based model without distortion
• eHsi - An extension to Hsi that rescaled saturation to avoid going out of gamut in Rgb
• Hwb - Hue, whiteness, blackness: a hue-based model made to be easy for users to select colors in
• YCbCr - A representation of the various YUV and YIQ models used in display and broadcast

#### Device Independent:

Prisma also supports these color spaces with an alpha channel via the Alpha type.

### Why Prisma?

Currently, there are two main color libraries for rust:

• color -- color is a very old library that hasn't been updated in several years. While it works for conversion through a few color spaces, and is easy to use, it has a very minimal set of features.

• palette -- palette has significantly more features and can go into a few of the CIE spaces, but requiring all computations to be done in linear encoding is a serious drawback, as if you just want a nice looking gradient in a game, linear Hsv will not get you that. It also is built on predefined models and doesn't support dynamic configuration. prisma supports considerably more color spaces, as well as multiple encodings and spaces which can be built at runtime. prisma also does not require you to specify a color space, as most applications don't really care and use the device color space or sRgb.

Prisma aims to support all the features of the above libraries, while making it up to the user how much complexity they need.

### A Tour by Example:

##### Converting from Rgb to Hsv, manipulating hue, and converting back
#[macro_use] extern crate approx;
extern crate angular_units as angle;

use prisma::{Rgb, Hsv, FromColor};
use angle::Deg;

let rgb = Rgb::new(0.5, 0.75, 1.0);
let mut hsv = Hsv::from_color(&rgb);
hsv.set_hue(Deg(180.0));
let rgb = Rgb::from_color(&hsv);
assert_relative_eq!(rgb, Rgb::new(0.5, 1.0, 1.0), epsilon=1e-6);
##### Interpolating between two colors in Hsl.
#[macro_use] extern crate approx;
extern crate angular_units as angle;

use prisma::{Rgb, Hsl, FromColor, Lerp};
use angle::Deg;

let rgb1 = Rgb::new(0.8, 0.25, 0.0f32);
let rgb2 = Rgb::new(0.5, 0.66, 1.0);
// Specify the hue channel should use degrees
let hsl1: Hsl<_, Deg<f32>> = Hsl::from_color(&rgb1);
let hsl2 = Hsl::from_color(&rgb2);
// Note that hue channels will interpolate in the shortest direction. This is usually
// the expected behavior, but you can always go forward with lerp_flat.
let rgb_out = Rgb::from_color(&hsl1.lerp(&hsl2, 0.35));
assert_relative_eq!(rgb_out, Rgb::new(1.0, 0.045, 0.62648), epsilon=1e-4);
##### Converting from Rgb to Rgb
#[macro_use] extern crate approx;

use prisma::Rgb;

let rgb_in = Rgb::new(100, 200, 255u8);
let rgb_out: Rgb<f32> = rgb_in.color_cast();
assert_relative_eq!(rgb_out, Rgb::new(0.39216, 0.78431, 1.0), epsilon=1e-4);
##### Convert from sRgb encoded to linear encoded Rgb
#[macro_use] extern crate approx;

use prisma::Rgb;
use prisma::encoding::{EncodableColor, TranscodableColor, SrgbEncoding};

// This returns a EncodedColor<Rgb<f32>, SrgbEncoding>
// Note: no encodind is done. srgb_encoded says that this value is already in sRgb encoding.
let rgb_srgb = Rgb::new(0.5, 1.0, 0.25f32).srgb_encoded();
// Decode goes from an encoding to linear.
let rgb_linear = rgb_srgb.clone().decode();
assert_relative_eq!(rgb_linear, Rgb::new(0.21404, 1.0, 0.05088).linear(), epsilon=1e-4);
// We can then go back with encode
let rgb_out = rgb_linear.encode(SrgbEncoding);
assert_relative_eq!(rgb_out, rgb_srgb, epsilon=1e-6);
##### Going to XYZ
#[macro_use] extern crate approx;

use prisma::{Rgb, Xyz};
use prisma::encoding::{EncodableColor, TranscodableColor};
use prisma::color_space::{ColorSpace, EncodedColorSpace, ConvertToXyz};
use prisma::color_space::named::SRgb;

let rgb = Rgb::new(0.25, 0.5, 0.75f32).srgb_encoded();
let color_space = SRgb::new();
// In this case, since rgb and color_space know their own encodings, the conversion to linear
// is automatic.
let xyz = color_space.convert_to_xyz(&rgb);
assert_relative_eq!(xyz, Xyz::new(0.191803, 0.201605, 0.523050), epsilon=1e-5);

## Modules

 channel Provides helper scalar and channel types used internally by the color types allowing them to be used generically over the underlying types. color_space Traits and structures to define color spaces and convert from device-dependent to device-independent spaces encoding Traits and structs for dealing with and changing a color's encoding lms The LMS cone response device-independent color space tags Unit structs for identifying the various color models in generic contexts white_point Defines the named standard illuminants for both 2 and 10 degree observers ycbcr A module for encoded values in the YUV and YIQ family of device-dependent color models.

## Structs

 Alpha A wrapper around a color with an alpha channel ChromaticityCoordinates A pair of chromaticity coordinates $\alpha$ and $\beta$ Hsi The HSI device-dependent polar color space Hsl The HSL device-dependent polar color model Hsv The HSV device-dependent polar color model Hwb The HWB device-dependent polar color model Lab The CIELAB perceptually uniform device-independent color space Lchab The $\textrm{Lch}_{(\textrm{ab})}$ device-independent polar color space Lchuv The $\textrm{Lch}_{(\textrm{uv})}$ device-independent polar color space Luv The CIELUV perceptually uniform device-independent color space Matrix3 A 3x3 matrix used for linear color transformations Rgb The Rgb device-dependent cartesian color model. Rgi The rgI device-dependent chromaticity color model XyY The xyY device-independent chromaticity space Xyz The CIE XYZ device-independent color space eHsi The eHSI device-dependent polar color model

## Enums

 HsiOutOfGamutMode Defines methods for handling out-of-gamut transformations from Hsi to Rgb

## Traits

 Bounded A value that is constrained between a minimum and maximum in its "normal" form Broadcast A color that can have all of its channels set from a single value Color The base color trait, representing any color Color3 A color with three channels Color4 A color with four channels DeviceDependentColor A color which must have a space specified in order to uniquely represent a color Flatten A color that can be represented as a slice without any conversion FromColor Infallibly convert between two color models FromHsi Convert from Hsi to another color model FromTuple A trait for colors that can be constructed from a tuple of channels FromYCbCr Convert from YCbCr to another color model HomogeneousColor A color only having one type of channel Invert A value that can be inverted Lerp A value that can be linearly interpolated between two values PolarColor A color that has a angular hue channel

## Type Definitions

 Hsia An Hsi value with an alpha channel Hsla An Hsl value with an alpha channel Hsva An Hsv value with an alpha channel Hwba An Hwb value with an alpha channel Laba An Lab value with an alpha channel Lchaba An Lchab value with an alpha channel Lchauv An Lchuv value with an alpha channel Lmsa An Lmsa value with an alpha channel Luva An Luv value with an alpha channel Rgba An Rgb value with an alpha channel Rgia An Rgi value with an alpha channel XyYa An XyY value with an alpha channel Xyza An Xyz value with an alpha channel YCbCra An YCbCr value with an alpha channel eHsia An eHsi value with an alpha channel