Wacton.Unicolour 4.3.0

Unicolour

Unicolour is a .NET library written in C# for working with colour:

• Colour space conversion
• Colour mixing / colour interpolation
• Colour difference / colour distance
• Colour gamut mapping
• Colour chromaticity
• Colour temperature
• Wavelength attributes

Targets .NET Standard 2.0 for use in .NET 5.0+, .NET Core 2.0+ and .NET Framework 4.6.1+ applications.

Contents

1. 🧭 Overview
2. 🔆 Installation
3. ⚡ Quickstart
4. 🌈 Features
5. 💡 Configuration
6. ✨ Examples
7. 🔮 Datasets

🧭 Overview

A Unicolour encapsulates a single colour and its representation across 30+ colour spaces. It can be used to mix and compare colours, as well as other useful tools for working with colour.

Supported colour spaces

RGB · Linear RGB · HSB / HSV · HSL · HWB · CIEXYZ · CIExyY · CIELAB · CIELChab · CIELUV · CIELChuv · HSLuv · HPLuv · YPbPr · YCbCr / YUV (digital) · YCgCo · YUV (PAL) · YIQ (NTSC) · YDbDr (SECAM) · IPT · ICTCP · Jzazbz · JzCzhz · Oklab · Oklch · Okhsv · Okhsl · Okhwb · CIECAM02 · CAM16 · HCT · CMYK ?

Unicolour pink = new("#FF1493");
Console.WriteLine(pink.Oklab); // 0.65 +0.26 -0.01

This library was initially written for personal projects since existing libraries had complex APIs, missing features, or inaccurate conversions. The goal of this library is to be accurate, intuitive, and easy to use. Although performance is not a priority, conversions are only calculated once; when first evaluated (either on access or as part of an intermediate conversion step) the result is stored for future use.

Unicolour is extensively tested, including verification of roundtrip conversions, validation using known colour values, and 100% line coverage and branch coverage.

🔆 Installation

1. Install the package from NuGet

dotnet add package Wacton.Unicolour

2. Import the package

using Wacton.Unicolour;

3. Use the package

Unicolour colour = new(ColourSpace.Rgb255, 192, 255, 238);

⚡ Quickstart

The simplest way to get started is to make a Unicolour and use it to see how the colour is represented in a different colour space.

var cyan = new Unicolour("#00FFFF");
Console.WriteLine(cyan.Hsl); // 180.0° 100.0% 50.0%

var yellow = new Unicolour(ColourSpace.Rgb255, 255, 255, 0);
Console.WriteLine(yellow.Hex); // #FFFF00

Colours can be mixed or interpolated using any colour space.

var red = new Unicolour(ColourSpace.Rgb, 1.0, 0.0, 0.0);
var blue = new Unicolour(ColourSpace.Hsb, 240, 1.0, 1.0);

/* RGB: [1, 0, 0] ⟶ [0, 0, 1] = [0.5, 0, 0.5] */
var purple = red.Mix(blue, ColourSpace.Rgb);
Console.WriteLine(purple.Rgb); // 0.50 0.00 0.50
Console.WriteLine(purple.Hex); // #800080

/* HSL: [0, 1, 0.5] ⟶ [240, 1, 0.5] = [300, 1, 0.5] */
var magenta = red.Mix(blue, ColourSpace.Hsl); 
Console.WriteLine(magenta.Rgb); // 1.00 0.00 1.00
Console.WriteLine(magenta.Hex); // #FF00FF

The difference or distance between colours can be calculated using any delta E metric.

var white = new Unicolour(ColourSpace.Oklab, 1.0, 0.0, 0.0);
var black = new Unicolour(ColourSpace.Oklab, 0.0, 0.0, 0.0);
var difference = white.Difference(black, DeltaE.Ciede2000);
Console.WriteLine(difference); // 100.0000

Other useful colour information is available, such as chromaticity coordinates, temperature, and dominant wavelength.

var equalTristimulus = new Unicolour(ColourSpace.Xyz, 0.5, 0.5, 0.5);
Console.WriteLine(equalTristimulus.Chromaticity.Xy); // (0.3333, 0.3333)
Console.WriteLine(equalTristimulus.Chromaticity.Uv); // (0.2105, 0.3158)
Console.WriteLine(equalTristimulus.Temperature); // 5455.5 K (Δuv -0.00442)
Console.WriteLine(equalTristimulus.DominantWavelength); // 596.1

Reference white points (e.g. D65) and the RGB model (e.g. sRGB) can be configured.

🌈 Features

Convert between colour spaces

Unicolour calculates all transformations required to convert from one colour space to any other, so there is no need to manually chain multiple functions and removes the risk of rounding errors.

Unicolour colour = new(ColourSpace.Rgb255, 192, 255, 238);
var (l, c, h) = colour.Oklch.Triplet;

Colour space	Enum	Property
RGB (0–255)	ColourSpace.Rgb255	.Rgb.Byte255
RGB	ColourSpace.Rgb	.Rgb
Linear RGB	ColourSpace.RgbLinear	.RgbLinear
HSB / HSV	ColourSpace.Hsb	.Hsb
HSL	ColourSpace.Hsl	.Hsl
HWB	ColourSpace.Hwb	.Hwb
CIEXYZ	ColourSpace.Xyz	.Xyz
CIExyY	ColourSpace.Xyy	.Xyy
CIELAB	ColourSpace.Lab	.Lab
CIELChab	ColourSpace.Lchab	.Lchab
CIELUV	ColourSpace.Luv	.Luv
CIELChuv	ColourSpace.Lchuv	.Lchuv
HSLuv	ColourSpace.Hsluv	.Hsluv
HPLuv	ColourSpace.Hpluv	.Hpluv
YPbPr	ColourSpace.Ypbpr	.Ypbpr
YCbCr / YUV (digital)	ColourSpace.Ycbcr	.Ycbcr
YCgCo	ColourSpace.Ycgco	.Ycgco
YUV (PAL)	ColourSpace.Yuv	.Yuv
YIQ (NTSC)	ColourSpace.Yiq	.Yiq
YDbDr (SECAM)	ColourSpace.Ydbdr	.Ydbdr
IPT	ColourSpace.Ipt	.Ipt
ICTCP	ColourSpace.Ictcp	.Ictcp
Jzazbz	ColourSpace.Jzazbz	.Jzazbz
JzCzhz	ColourSpace.Jzczhz	.Jzczhz
Oklab	ColourSpace.Oklab	.Oklab
Oklch	ColourSpace.Oklch	.Oklch
Okhsv	ColourSpace.Okhsv	.Okhsv
Okhsl	ColourSpace.Okhsl	.Okhsl
Okhwb	ColourSpace.Okhwb	.Okhwb
CIECAM02	ColourSpace.Cam02	.Cam02
CAM16	ColourSpace.Cam16	.Cam16
HCT	ColourSpace.Hct	.Hct
CMYK ?	-	-

Mix colours

Two colours can be mixed by interpolating between them in any colour space, taking into account cyclic hue, interpolation distance, and alpha premultiplication.

var red = new Unicolour(ColourSpace.Rgb, 1.0, 0.0, 0.0);
var blue = new Unicolour(ColourSpace.Hsb, 240, 1.0, 1.0);
var magenta = red.Mix(blue, ColourSpace.Hsl, 0.5, HueSpan.Decreasing); 
var green = red.Mix(blue, ColourSpace.Hsl, 0.5, HueSpan.Increasing); 

Hue span	Enum
Shorter 👈 default	HueSpan.Shorter
Longer	HueSpan.Longer
Increasing	HueSpan.Increasing
Decreasing	HueSpan.Decreasing

Compare colours

Two methods of comparing colours are available: contrast and difference. Difference is calculated according to a specific delta E (ΔE) metric.

var red = new Unicolour(ColourSpace.Rgb, 1.0, 0.0, 0.0);
var blue = new Unicolour(ColourSpace.Hsb, 240, 1.0, 1.0);
var contrast = red.Contrast(blue);
var difference = red.Difference(blue, DeltaE.Cie76);

Delta E	Enum
ΔE76 (CIE76)	DeltaE.Cie76
ΔE94 (CIE94) - graphic arts	DeltaE.Cie94
ΔE94 (CIE94) - textiles	DeltaE.Cie94Textiles
ΔE00 (CIEDE2000)	DeltaE.Ciede2000
ΔECMC (CMC l:c) - 2:1 acceptability	DeltaE.CmcAcceptability
ΔECMC (CMC l:c) - 1:1 perceptibility	DeltaE.CmcPerceptibility
ΔEITP	DeltaE.Itp
ΔEz	DeltaE.Z
ΔEHyAB	DeltaE.Hyab
ΔEOK	DeltaE.Ok
ΔECAM02	DeltaE.Cam02
ΔECAM16	DeltaE.Cam16

Map colour into display gamut

Colours that cannot be displayed with the configured RGB model can be mapped to the closest in-gamut colour. The gamut mapping algorithm conforms to CSS specifications.

var outOfGamut = new Unicolour(ColourSpace.Rgb, -0.51, 1.02, -0.31);
var inGamut = outOfGamut.MapToGamut();

Convert between colour and temperature

Correlated colour temperature (CCT) and delta UV (∆uv) can be obtained from a colour, and can be used to create a colour. CCT from 500 K to 1,000,000,000 K is supported but only CCT from 1,000 K to 20,000 K is guaranteed to have high accuracy.

var chromaticity = new Chromaticity(0.3457, 0.3585);
var d50 = new Unicolour(chromaticity);
var (cct, duv) = d50.Temperature;

var temperature = new Temperature(6504, 0.0032);
var d65 = new Unicolour(temperature);
var (x, y) = d65.Chromaticity;

Create colour from spectral power distribution

A spectral power distribution (SPD) can be used to create a colour. Wavelengths should be provided in either 1 nm or 5 nm intervals, and omitted wavelengths are assumed to have zero spectral power.

var spd = new Spd
{
    { 575, 0.5 }, 
    { 580, 1.0 }, 
    { 585, 0.5 }
};
        
var intenseYellow = new Unicolour(spd);

Get wavelength attributes

The dominant wavelength and excitation purity of a colour can be derived using the spectral locus. Wavelengths from 360 nm to 700 nm are supported.

var chromaticity = new Chromaticity(0.1, 0.8);
var hyperGreen = new Unicolour(chromaticity);
var dominantWavelength = hyperGreen.DominantWavelength;
var excitationPurity = hyperGreen.ExcitationPurity;

Detect imaginary colours

Whether or not a colour is imaginary — one that cannot be produced by the eye — can be determined using the spectral locus. They are the colours that lie outside of the horseshoe-shaped curve of the CIE xy chromaticity diagram.

var chromaticity = new Chromaticity(0.05, 0.05);
var impossibleBlue = new Unicolour(chromaticity);
var isImaginary = impossibleBlue.IsImaginary;

Simulate colour vision deficiency

A new Unicolour can be generated that simulates how a colour appears to someone with a particular colour vision deficiency (CVD) or colour blindness.

var colour = new Unicolour(ColourSpace.Rgb255, 192, 255, 238);
var noRed = colour.SimulateProtanopia();

Colour vision deficiency	Method
Protanopia (no red perception)	SimulateProtanopia()
Deuteranopia (no green perception)	SimulateDeuteranopia()
Tritanopia (no blue perception)	SimulateTritanopia()
Achromatopsia (no colour perception)	SimulateAchromatopsia()

Handle invalid values

It is possible for invalid or unreasonable values to be used in calculations, either because conversion formulas have limitations or because a user passes them as arguments. Although these values don't make sense to use, they should propagate safely and avoid triggering exceptions.

var bad1 = new Unicolour(ColourSpace.Oklab, double.NegativeInfinity, double.NaN, double.Epsilon);
var bad2 = new Unicolour(ColourSpace.Cam16, double.NaN, double.MaxValue, double.MinValue);
var bad3 = bad1.Mix(bad2, ColourSpace.Hct, amount: double.PositiveInfinity);

Sensible defaults, highly configurable

Unicolour uses sRGB as the default RGB model and standard illuminant D65 (2° observer) as the default white point of all colour spaces, ensuring consistency and a suitable starting point for simple applications. These can be overridden using the Configuration parameter, and common configurations have been predefined.

var defaultConfig = new Configuration(RgbConfiguration.StandardRgb, XyzConfiguration.D65);
var colour = new Unicolour(defaultConfig, ColourSpace.Rgb255, 192, 255, 238);

💡 Configuration

The Configuration parameter can be used to customise how colour is processed.

Example configuration with predefined Rec. 2020 RGB & illuminant D50 (2° observer) XYZ:

Configuration config = new(RgbConfiguration.Rec2020, XyzConfiguration.D50);
Unicolour colour = new(config, ColourSpace.Rgb255, 204, 64, 132);

Example configuration with manually defined wide-gamut RGB & illuminant C (10° observer) XYZ:

var rgbConfig = new RgbConfiguration(
    chromaticityR: new(0.7347, 0.2653),
    chromaticityG: new(0.1152, 0.8264),
    chromaticityB: new(0.1566, 0.0177),
    whitePoint: Illuminant.D50.GetWhitePoint(Observer.Degree2),
    fromLinear: value => Math.Pow(value, 1 / 2.19921875),
    toLinear: value => Math.Pow(value, 2.19921875)
);

var xyzConfig = new XyzConfiguration(Illuminant.C, Observer.Degree10);

var config = new Configuration(rgbConfig, xyzConfig);
var colour = new Unicolour(config, ColourSpace.Rgb255, 202, 97, 143);

A Configuration is composed of sub-configurations. Each sub-configuration is optional and will fall back to a sensible default if not provided.

RgbConfiguration

Defines the RGB model, often used to specify a wider gamut than standard RGB (sRGB).

Predefined	Property
sRGB 👈 default	.StandardRgb
Display P3	.DisplayP3
Rec. 2020	.Rec2020
A98	.A98
ProPhoto	.ProPhoto
ACES 2065-1	.Aces20651
ACEScg	.Acescg
ACEScct	.Acescct
ACEScc	.Acescc
Rec. 601 (625-line)	.Rec601Line625
Rec. 601 (525-line)	.Rec601Line525
Rec. 709	.Rec709
xvYCC	.XvYcc
PAL (Rec. 470)	.Pal
PAL-M (Rec. 470)	.PalM
PAL 625 (Rec. 1700)	.Pal625
PAL 525 (Rec. 1700)	.Pal525
NTSC (Rec. 470)	.Ntsc
NTSC (SMPTE-C)	.NtscSmpteC
NTSC 525 (Rec. 1700)	.Ntsc525
SECAM (Rec. 470)	.Secam
SECAM 625 (Rec. 1700)	.Secam625

• Parameters
  • Red, green, and blue chromaticity coordinates
  • Reference white point
  • Companding functions to and from linear values

XyzConfiguration

Defines the XYZ white point (which is also inherited by colour spaces that do not need a specific configuration), as well as the observer to use for temperature calculations.

Predefined	Property
D65 (2° observer) 👈 default	.D65
D50 (2° observer)	.D50

• Parameters
  • Reference white point or illuminant
  • Observer

YbrConfiguration

Defines the constants, scaling, and offsets required to convert to YPbPr and YCbCr.

Predefined	Property
Rec. 601 👈 default	.Rec601
Rec. 709	.Rec709
Rec. 2020	.Rec2020
JPEG	.Jpeg

• Parameters
  • Luma constants for component video separation
  • Mapping ranges for digital encoding

CamConfiguration

Defines the viewing conditions for CAM02 and CAM16, which take into account the surrounding environment to determine how a colour is perceived.

Predefined	Property
sRGB 👈 default	.StandardRgb
HCT	.Hct

The predefined sRGB configuration refers to an ambient illumination of 64 lux under a grey world assumption.

• Parameters
  • Reference white point
  • Adapting luminance
  • Background luminance

IctcpScalar & JzazbzScalar

There is ambiguity and no clear consensus about how XYZ values should be scaled before calculating ICTCP and Jzazbz. These scalars can be changed to match the behaviour of other implementations if needed.

White points

All colour spaces are impacted by the reference white point. Unicolour applies different reference white points to different sets of colour spaces, as shown in the table below. When a conversion to or from XYZ space involves a change in white point, a chromatic adaptation transform (CAT) is performed using the Bradford method.

White point configuration	Affected colour spaces
RgbConfiguration	RGB · Linear RGB · HSB / HSV · HSL · HWB · YPbPr · YCbCr / YUV (digital) · YCgCo · YUV (PAL) · YIQ (NTSC) · YDbDr (SECAM)
XyzConfiguration	CIEXYZ · CIExyY · CIELAB · CIELChab · CIELUV · CIELChuv · HSLuv · HPLuv
CamConfiguration	CIECAM02 · CAM16
None (always D65/2°)	IPT · ICTCP · Jzazbz · JzCzhz · Okhsv · Okhsl · Okhwb · HCT

Convert between configurations

A Unicolour can be converted to a different configuration, in turn enabling conversions between different RGB models, XYZ white points, CAM viewing conditions, etc.

/* pure sRGB green */
var srgbConfig = new Configuration(RgbConfiguration.StandardRgb);
var srgbColour = new Unicolour(srgbConfig, ColourSpace.Rgb, 0, 1, 0);                         
Console.WriteLine(srgbColour.Rgb); // 0.00 1.00 0.00

/* ⟶ Display P3 */
var displayP3Config = new Configuration(RgbConfiguration.DisplayP3);
var displayP3Colour = srgbColour.ConvertToConfiguration(displayP3Config); 
Console.WriteLine(displayP3Colour.Rgb); // 0.46 0.99 0.30

/* ⟶ Rec. 2020 */
var rec2020Config = new Configuration(RgbConfiguration.Rec2020);
var rec2020Colour = displayP3Colour.ConvertToConfiguration(rec2020Config);
Console.WriteLine(rec2020Colour.Rgb); // 0.57 0.96 0.27

✨ Examples

This repository contains projects showing how Unicolour can be used to create:

1. Gradient images
2. Heatmaps of luminance
3. Diagrams of colour data
4. A colourful console application
5. 3D visualisation of colour spaces in Unity

Gradients

Example code to create gradient images using 📷 SixLabors.ImageSharp can be seen in the Example.Gradients project.

Gradients generated through each colour space

Visualisation of temperature from 1,000 K to 13,000 K

Colour spectrum rendered with different colour vision deficiencies

Demonstration of interpolating from red to transparent to blue, with and without premultiplied alpha

Perceptually uniform colourmaps from Unicolour.Datasets

Heatmaps

Example code to create heatmaps of luminance using 📷 SixLabors.ImageSharp with images from 🚀 NASA can be seen in the Example.Heatmaps project.

Heatmap of the ☀️ sun using perceptually uniform colourmaps from Unicolour.Datasets

Heatmap of the 🌕 moon using perceptually uniform colourmaps from Unicolour.Datasets

Diagrams

Example code to create diagrams of colour data using 📈 ScottPlot can be seen in the Example.Diagrams project.

CIE xy chromaticity diagram with sRGB gamut

CIE xy chromaticity diagram with Planckian or blackbody locus

CIE xy chromaticity diagram with spectral locus plotted at 1 nm intervals

CIE 1960 colour space

CIE 1960 colour space with Planckian or blackbody locus

Console

Example code to create a colourful console application using ⌨️ Spectre.Console can be seen in the Example.Console project.

Console application displaying colour information from a hex value

Unity

Example code to create 3D visualisations of colour spaces using 🎮 Unity can be seen in the Example.Unity project.

Try it out online in Unity Play!

3D visualisation of colour spaces in Unity

3D movement through colour spaces in Unity

🔮 Datasets

Some colour datasets have been compiled for convenience and are available as a NuGet package.

Commonly used sets of colours:

• CSS specification named colours
• xkcd colour survey results
• Macbeth ColorChecker colour rendition chart

Perceptually uniform colourmaps / palettes:

• Viridis, Plasma, Inferno & Magma (sequential)
• Cividis (sequential)
• Mako, Rocket, Crest & Flare (sequential)
• Vlag & Icefire (diverging)
• Twilight & Twilight Shifted (cyclic)
• Turbo (rainbow)
• Cubehelix (sequential)

Colour data used in academic literature:

• Hung-Berns constant hue loci data
• Ebner-Fairchild constant perceived-hue data

Example usage:

1. Install the package from NuGet

dotnet add package Wacton.Unicolour.Datasets

2. Import the package

using Wacton.Unicolour.Datasets;

3. Reference the predefined Unicolour

var pink = Css.DeepPink;
var green = Xkcd.NastyGreen;
var mapped = Colourmaps.Viridis.Map(0.5);

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Wacton.Unicolour is licensed under the MIT License, copyright © 2022-2024 William Acton.