Colourful .NET

Open source .NET library for working with color spaces.

The library is written in C# and released with an MIT license, so feel free to fork or use commercially.

Any feedback is appreciated, please visit the issues page or send me an e-mail.

Download

Binaries of the last build can be downloaded on the AppVeyor CI page of the project.

The library is also published on NuGet.org, install using:

PM> Install-Package Colourful

^{Colourful is CLS Compliant (to allow use in VB.NET etc.) and is built for .NET v4.5, .NET Standard 1.1 and .NET Standard 1.6. For .NET v4.0 see version 1 of the library.}

Usage

Color conversion

RGBColor input = new RGBColor(1, 0, 0);

var converter = new ColourfulConverter { WhitePoint = Illuminants.D65 };

XYZColor output = converter.ToXYZ(input);

The ColourfulConverter facade can convert from any of the supported color spaces to any other color space.

It always performs the chromatic adaptation if the input and output color space white points are different.

Chromatic adaptation

The adaptation can be also performed alone (e.g. from CIELAB D50 to CIELAB D65).

LabColor input = new LabColor(10, 20, 30, Illuminants.D50);

var converter = new ColourfulConverter { TargetLabWhitePoint = Illuminants.D65 };

LabColor output = converter.Adapt(input);

Conversion between RGB working spaces

Adaptation can also convert from one RGB working space to another (e.g. from sRGB to Adobe RGB).

RGBColor input = new RGBColor(Color.Yellow, RGBWorkingSpaces.sRGB);

var converter = new ColourfulConverter { TargetRGBWorkingSpace = RGBWorkingSpaces.AdobeRGB1998 };

RGBColor output = converter.Adapt(input);

Converter can be configured to arbitrary chromatic adaptation method, several are supported.

CCT approximation

Colourful also supports computing correlated color temperature (CCT) from chromaticity and computing chromaticity from CCT. Although these are just approximations with low precision.

var converter = new CCTConverter();

ChromaticityCoordinates chromaticity = converter.GetChromaticityOfCCT(5454); // x=0.33, y=0.34

double cct = converter.GetCCTOfChromaticity(new ChromaticityCoordinates(0.31271, 0.32902)); // cca 6500 K 

To obtain chromaticity of a color in any color space, use conversion to CIE xyY color space. To obtain color from chromaticity (xy), just add the luminance Y and the result is xyY.

Color difference

Colourful has several formulas for computing ΔE (difference between colors). The usage is trivial:

var color1 = new LabColor(l1, a1, b1);
var color2 = new LabColor(l2, a2, b2);

double deltaE = new CIEDE2000ColorDifference().ComputeDifference(color1, color2);

For more details, see the detailed XML documentation (generated during build), or the unit tests.

Macbeth ColorChecker

Colourful contains definition of all 24 Macbeth ColorChecker colors in sRGB, which are useful for color calibration. Access them this way:

RGBColor[] testColors = MacbethColorChecker.Colors; // array of 24 colors

RGBColor testColor = MacbethColorChecker.DarkSkin; // individual colors

What is supported

Color spaces

Colourful currently supports following color spaces (and conversions between each other):

• RGB (see working spaces below)
• linear RGB ^*
• CIE XYZ (1931)
• CIE xyY (derived from XYZ)
• CIE L*a*b* (1976) (CIELAB)
• CIE L*C*h°_ab (CIELCH)
• CIE L*u*v* (1976) (CIELUV)
• CIE L*C*h°_uv (CIELCH)
• Hunter Lab
• LMS (cone response)

^{* for more information, see: http://stackoverflow.com/questions/12524623/what-are-the-practical-differences-when-working-with-colors-in-a-linear-vs-a-no}

All of these color spaces (including RGB) have double precision. Conversion to System.Drawing.Color, which is 8-bit, is supported from RGBColor through implicit type-conversion operator to make integration seamless.

RGB working spaces

• sRGB
• Simplified sRGB
• ECI RGB v2
• Adobe RGB (1998)
• Apple sRGB
• Best RGB
• Beta RGB
• Bruce RGB
• CIE RGB
• ColorMatch RGB
• Don RGB 4
• Ekta Space PS5
• NTSC RGB
• PAL/SECAM RGB
• ProPhoto RGB
• SMPTE-C RGB
• Wide Gamut RGB
• Rec. 709 (ITU-R Recommendation BT.709 – HDTV)
• Rec. 2020 (ITU-R Recommendation BT.2020 – UHDTV)
• (custom RGB working spaces)

Illuminants — white points

• A (Incandescent / Tungsten)
• B (Direct sunlight at noon (obsolete))
• C (Average / North sky Daylight (obsolete))
• D50 (Horizon Light. ICC profile PCS)
• D55 (Mid-morning / Mid-afternoon Daylight)
• D65 (Noon Daylight: Television, sRGB color space)
• D75 (North sky Daylight)
• E (Equal energy)
• F2 (Cool White Fluorescent)
• F7 (D65 simulator, Daylight simulator)
• F11 (Philips TL84, Ultralume 40)
• (custom white points)

Chromatic adaptation

Right now there is only one chromatic adaptation method, the von Kries chromatic adaptation method. Custom used-defined chromatic adaptation methods are also supported. The von Kries chromatic adaptation method can be parametrized using LMS transformation matrix. These LMS transformation matrices are available:

• Bradford (default)
• Von Kries (Hunt-Pointer-Estevez adjusted for D65)
• Von Kries (Hunt-Pointer-Estevez for equal energy)
• XYZ scaling
• Spectral-sharpened Bradford
• CMCCAT2000
• CAT02
• (custom chromatic adaptation)

Color difference formulas (ΔE)

• CIE Delta-E 1976
• CMC l:c (1984)
• CIE Delta-E 1994
• CIE Delta-E 2000