Enum image_canvas::color::Color

#[non_exhaustive]
pub enum Color {
    Rgb {
        primary: Primaries,
        transfer: Transfer,
        whitepoint: Whitepoint,
        luminance: Luminance,
    },
    Yuv {
        primary: Primaries,
        whitepoint: Whitepoint,
        transfer: Transfer,
        luminance: Luminance,
        differencing: Differencing,
    },
    Oklab,
    Scalars {
        transfer: Transfer,
    },
    SrLab2 {
        whitepoint: Whitepoint,
    },
}

Identifies a color representation.

This names the model by which the numbers in the channels relate to a physical model. How exactly depends on the variant as presented below. Some of them can be customized further with parameters.

Notably, there are NOT the numbers which we will use in image operations. Generally, we will use an associated linear representation of those colors instead. The choice here depends on the color and is documented for each variants. It is chosen to provide models for faithful linear operations on these colors such as mixing etc.

TODO: colors describe paths to linear display, so we should somehow implement direction conversions such as “BT.2087 : Colour conversion from Recommendation ITU-R BT.709 to Recommendation ITU-R BT.2020” in a separate manner.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Rgb

Fields

primary: Primaries

transfer: Transfer

whitepoint: Whitepoint

luminance: Luminance

An rgb-ish, additive model based on the CIE 1931 XYZ observers.

The linear representation is the screen space linear RGB, which depends on primaries, whitepoint and reference luminance. It is derived from the encoded form through the transfer function.

Yuv

Fields

primary: Primaries

whitepoint: Whitepoint

transfer: Transfer

luminance: Luminance

differencing: Differencing

A lightness, chroma difference scheme.

Oklab

The simple but perceptual space Oklab by Björn Ottoson.

The linear representation of this color is Lab but its quantized components are may be either Lab or LCh.

It’s based on a combination of two linear transforms and one non-linear power-function between them. Coefficients of these transforms are based on optimization against matching pairs in the detailed CAM16 model, trying to predict the parameters in those pairs as precisely as possible. For details see the post’s derivation.

Reference: https://bottosson.github.io/posts/oklab/

Scalars

Fields

transfer: Transfer

The transfer to use for points, as if they are RGB-ish colors. You can simply use Linear if you do not want to encode and rgb texel.

A group of scalar values, with no assigned relation to physical quantities.

The purpose of this color is to simplify the process of creating color ramps and sampling functions, which do not have any interpretation themselves but are just coefficients to be used somewhere else.

The only SampleParts that are allowed to be paired with this are XYZ.

Additionally, you might use the images created with this color as an input or an intermediate step of a transmute to create images with chosen values in the linear representation without the need to manually calculate their texel encoding.

SrLab2

Fields

whitepoint: Whitepoint

A LAB space based on contemporary perceptual understanding.

The newly defined SRLAB2 color model is a compromise between the simplicity of CIELAB and the correctness of CIECAM02.

By combining whitepoint adaption in the (more) precise model of CIECAM02 while performing the transfer function in the cone response space, this achieves a good uniformity by simply modelling the human perception properly. It just leaves out the surround luminance model in the vastly more complex CIECAM02.

This is lacking for HDR. This is because its based on L*ab which is inherently optimized for the small gamut of SDR. It’s not constant luminance at exceedingly bright colors where ICtCp might provide a better estimate (compare ΔEITP, ITU-R Rec. BT.2124).

Reference: https://www.magnetkern.de/srlab2.html

Implementations

impl Color

pub const SRGB: Color = Color::Rgb { luminance: Luminance::Sdr, primary: Primaries::Bt709, transfer: Transfer::Srgb, whitepoint: Whitepoint::D65, }

pub const BT709_RGB: Color = Color::Rgb { luminance: Luminance::Sdr, primary: Primaries::Bt709, transfer: Transfer::Bt709, whitepoint: Whitepoint::D65, }

pub const BT709: Color = Color::Yuv { luminance: Luminance::Sdr, primary: Primaries::Bt709, transfer: Transfer::Bt709, whitepoint: Whitepoint::D65, differencing: Differencing::Bt709, }

pub fn model(&self) -> Option<ColorChannelModel>

Trait Implementations

impl Clone for Color

fn clone(&self) -> Color

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Color

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq<Color> for Color

fn eq(&self, other: &Color) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Color) -> bool

This method tests for !=.

impl Eq for Color

impl StructuralEq for Color

impl StructuralPartialEq for Color