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Fix hue-based interpolation
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‎README.md‎

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@@ -20,6 +20,7 @@ These [can be overridden](#advanced-configuration-) using the `Configuration` pa
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This library was initially written for personal projects since existing libraries had complex APIs or missing features.
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The goal of this library is to be intuitive and easy to use; performance is not a priority.
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It is also [extensively tested](Unicolour.Tests) against known colour values and other .NET libraries.
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More functionality will be added over time.
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@@ -31,7 +32,7 @@ Targets .NET Standard 2.0 for use in .NET 5.0+, .NET Core 2.0+ and .NET Framewor
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dotnet add package Wacton.Unicolour
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```
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2. Create a `Unicolour` from RGB or HSB/HSV values:
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2. Create a `Unicolour`:
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```c#
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using Wacton.Unicolour;
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...
@@ -64,6 +65,8 @@ var contrast = unicolour1.Contrast(unicolour2);
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var difference = unicolour1.DeltaE76(unicolour2);
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```
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See also the [example code](Unicolour.Example/Program.cs), which uses `Unicolour` to generate gradients through different colour spaces.
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## Advanced configuration 💡
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A `Configuration` parameter can be used to change the RGB model (e.g. Adobe RGB, wide-gamut RGB)
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and the white point of the XYZ colour space (e.g. D50 reference white used by ICC profiles).

‎Unicolour.Example/Inconsolata-Regular.ttf‎

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‎Unicolour.Example/OFL.txt‎

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Copyright 2006 The Inconsolata Project Authors
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This Font Software is licensed under the SIL Open Font License, Version 1.1.
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This license is copied below, and is also available with a FAQ at:
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http://scripts.sil.org/OFL
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-----------------------------------------------------------
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SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
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-----------------------------------------------------------
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PREAMBLE
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The goals of the Open Font License (OFL) are to stimulate worldwide
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development of collaborative font projects, to support the font creation
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efforts of academic and linguistic communities, and to provide a free and
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open framework in which fonts may be shared and improved in partnership
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with others.
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The OFL allows the licensed fonts to be used, studied, modified and
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redistributed freely as long as they are not sold by themselves. The
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fonts, including any derivative works, can be bundled, embedded,
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redistributed and/or sold with any software provided that any reserved
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names are not used by derivative works. The fonts and derivatives,
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however, cannot be released under any other type of license. The
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requirement for fonts to remain under this license does not apply
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to any document created using the fonts or their derivatives.
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DEFINITIONS
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"Font Software" refers to the set of files released by the Copyright
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Holder(s) under this license and clearly marked as such. This may
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include source files, build scripts and documentation.
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"Reserved Font Name" refers to any names specified as such after the
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copyright statement(s).
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"Original Version" refers to the collection of Font Software components as
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distributed by the Copyright Holder(s).
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"Modified Version" refers to any derivative made by adding to, deleting,
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or substituting -- in part or in whole -- any of the components of the
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Original Version, by changing formats or by porting the Font Software to a
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new environment.
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"Author" refers to any designer, engineer, programmer, technical
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writer or other person who contributed to the Font Software.
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PERMISSION & CONDITIONS
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of the Font Software, to use, study, copy, merge, embed, modify,
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redistribute, and sell modified and unmodified copies of the Font
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Software, subject to the following conditions:
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1) Neither the Font Software nor any of its individual components,
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in Original or Modified Versions, may be sold by itself.
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2) Original or Modified Versions of the Font Software may be bundled,
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redistributed and/or sold with any software, provided that each copy
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contains the above copyright notice and this license. These can be
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included either as stand-alone text files, human-readable headers or
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in the appropriate machine-readable metadata fields within text or
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binary files as long as those fields can be easily viewed by the user.
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3) No Modified Version of the Font Software may use the Reserved Font
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Name(s) unless explicit written permission is granted by the corresponding
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Copyright Holder. This restriction only applies to the primary font name as
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presented to the users.
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4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
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Software shall not be used to promote, endorse or advertise any
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Modified Version, except to acknowledge the contribution(s) of the
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Copyright Holder(s) and the Author(s) or with their explicit written
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permission.
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5) The Font Software, modified or unmodified, in part or in whole,
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must be distributed entirely under this license, and must not be
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distributed under any other license. The requirement for fonts to
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remain under this license does not apply to any document created
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using the Font Software.
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TERMINATION
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This license becomes null and void if any of the above conditions are
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not met.
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DISCLAIMER
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THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
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OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
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COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
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DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
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OTHER DEALINGS IN THE FONT SOFTWARE.

‎Unicolour.Example/Program.cs‎

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using SixLabors.Fonts;
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using SixLabors.ImageSharp;
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using SixLabors.ImageSharp.Drawing.Processing;
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using SixLabors.ImageSharp.PixelFormats;
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using SixLabors.ImageSharp.Processing;
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using Wacton.Unicolour;
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var startColour = Unicolour.FromHsb(260, 1.0, 0.33);
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var endColour = Unicolour.FromHsb(30, 0.66, 1.0);
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var backgroundRgba32 = AsRgba32(Unicolour.FromHex("#404046"));
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var textRgba32 = AsRgba32(Unicolour.FromHex("#E8E8FF"));
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FontCollection collection = new();
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var fontFamily = collection.Add("Inconsolata-Regular.ttf");
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var font = fontFamily.CreateFont(32);
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var gradientWidth = 1000;
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var gradientHeight = 200;
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var image = new Image<Rgba32>(gradientWidth, gradientHeight * 3);
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image.Mutate(x => x.BackgroundColor(backgroundRgba32));
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for (var x = 0; x < gradientWidth; x++)
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{
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var distance = x / (double)(gradientWidth - 1);
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var interpolatedRgb = startColour.InterpolateRgb(endColour, distance);
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var interpolatedHsb = startColour.InterpolateHsb(endColour, distance);
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var interpolatedHsl = startColour.InterpolateHsl(endColour, distance);
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SetPixels(x, interpolatedRgb, interpolatedHsb, interpolatedHsl);
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}
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image.Save("gradients.png");
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void SetPixels(int x, Unicolour viaRgb, Unicolour viaHsb, Unicolour viaHsl)
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{
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for (var y = 0; y < gradientHeight; y++)
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{
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image[x, y] = AsRgba32(viaRgb);
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image[x, y + 200] = AsRgba32(viaHsb);
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image[x, y + 400] = AsRgba32(viaHsl);
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}
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PointF TextLocation(float targetY) => new(24, targetY + 24);
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image.Mutate(context => context.DrawText("RGB", font, textRgba32, TextLocation(0)));
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image.Mutate(context => context.DrawText("HSB", font, textRgba32, TextLocation(200)));
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image.Mutate(context => context.DrawText("HSL", font, textRgba32, TextLocation(400)));
47+
}
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Rgba32 AsRgba32(Unicolour unicolour)
50+
{
51+
var rgb = unicolour.Rgb;
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return new Rgba32((byte) rgb.R255, (byte) rgb.G255, (byte) rgb.B255);
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}
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‎Unicolour.Example/Unicolour.Example.csproj‎

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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<ImplicitUsings>enable</ImplicitUsings>
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<Nullable>enable</Nullable>
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<IsPackable>false</IsPackable>
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<AssemblyName>Wacton.Unicolour.Example</AssemblyName>
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<RootNamespace>Wacton.Unicolour.Example</RootNamespace>
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<Authors>William Acton</Authors>
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</PropertyGroup>
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<ItemGroup>
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<PackageReference Include="SixLabors.ImageSharp" Version="2.1.0" />
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<PackageReference Include="SixLabors.ImageSharp.Drawing" Version="1.0.0-beta14" />
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</ItemGroup>
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<ItemGroup>
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<ProjectReference Include="..\Unicolour\Unicolour.csproj" />
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</ItemGroup>
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<ItemGroup>
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<None Update="Inconsolata-Regular.ttf">
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<CopyToOutputDirectory>Always</CopyToOutputDirectory>
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</None>
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</ItemGroup>
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</Project>

‎Unicolour.Tests/InterpolateHsbTests.cs‎

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@@ -22,7 +22,7 @@ public void SameColour()
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}
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[Test]
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public void EquidistantForward()
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public void Equidistant()
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{
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var unicolour1 = Unicolour.FromHsb(0, 0, 0, 0);
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var unicolour2 = Unicolour.FromHsb(180, 1, 1);
@@ -34,7 +34,7 @@ public void EquidistantForward()
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}
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[Test]
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public void EquidistantBackward()
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public void EquidistantViaRed()
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{
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var unicolour1 = Unicolour.FromHsb(0, 0, 0, 0);
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var unicolour2 = Unicolour.FromHsb(340, 0.5, 0.8, 0.2);
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AssertHsba(interpolated2, (45, 0.75, 0.25, 0.875));
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}
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[Test]
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public void CloserToEndColourViaRed()
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{
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var unicolour1 = Unicolour.FromHsb(300, 1, 0);
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var unicolour2 = Unicolour.FromHsb(60, 0, 1, 0.5);
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var interpolated1 = unicolour1.InterpolateHsb(unicolour2, 0.75);
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var interpolated2 = unicolour2.InterpolateHsb(unicolour1, 0.75);
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AssertHsba(interpolated1, (30, 0.25, 0.75, 0.625));
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AssertHsba(interpolated2, (330, 0.75, 0.25, 0.875));
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}
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[Test]
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public void CloserToStartColour()
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{
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AssertHsba(interpolated2, (135, 0.25, 0.75, 0.625));
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}
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[Test]
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public void CloserToStartColourViaRed()
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{
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var unicolour1 = Unicolour.FromHsb(300, 1, 0);
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var unicolour2 = Unicolour.FromHsb(60, 0, 1, 0.5);
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var interpolated1 = unicolour1.InterpolateHsb(unicolour2, 0.25);
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var interpolated2 = unicolour2.InterpolateHsb(unicolour1, 0.25);
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AssertHsba(interpolated1, (330, 0.75, 0.25, 0.875));
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AssertHsba(interpolated2, (30, 0.25, 0.75, 0.625));
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}
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[Test]
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public void BeyondEndColour()
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{

‎Unicolour.Tests/InterpolateHslTests.cs‎

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}
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[Test]
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public void EquidistantForward()
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public void Equidistant()
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{
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var unicolour1 = Unicolour.FromHsl(0, 0, 0, 0);
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var unicolour2 = Unicolour.FromHsl(180, 1, 1);
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}
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[Test]
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public void EquidistantBackward()
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public void EquidistantViaRed()
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{
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var unicolour1 = Unicolour.FromHsl(0, 0, 0, 0);
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var unicolour2 = Unicolour.FromHsl(340, 0.5, 0.8, 0.2);
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AssertHsla(interpolated2, (45, 0.75, 0.25, 0.875));
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}
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[Test]
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public void CloserToEndColourViaRed()
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{
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var unicolour1 = Unicolour.FromHsl(300, 1, 0);
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var unicolour2 = Unicolour.FromHsl(60, 0, 1, 0.5);
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var interpolated1 = unicolour1.InterpolateHsl(unicolour2, 0.75);
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var interpolated2 = unicolour2.InterpolateHsl(unicolour1, 0.75);
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AssertHsla(interpolated1, (30, 0.25, 0.75, 0.625));
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AssertHsla(interpolated2, (330, 0.75, 0.25, 0.875));
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}
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[Test]
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public void CloserToStartColour()
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{
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AssertHsla(interpolated2, (135, 0.25, 0.75, 0.625));
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}
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[Test]
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public void CloserToStartColourViaRed()
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{
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var unicolour1 = Unicolour.FromHsl(300, 1, 0);
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var unicolour2 = Unicolour.FromHsl(60, 0, 1, 0.5);
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var interpolated1 = unicolour1.InterpolateHsl(unicolour2, 0.25);
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var interpolated2 = unicolour2.InterpolateHsl(unicolour1, 0.25);
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AssertHsla(interpolated1, (330, 0.75, 0.25, 0.875));
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AssertHsla(interpolated2, (30, 0.25, 0.75, 0.625));
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}
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[Test]
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public void BeyondEndColour()
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{

‎Unicolour.sln‎

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EndProject
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Unicolour.Tests", "Unicolour.Tests\Unicolour.Tests.csproj", "{43CC17D1-2A95-4554-9900-D97FA9CEA2D0}"
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EndProject
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Unicolour.Example", "Unicolour.Example\Unicolour.Example.csproj", "{DA851ED7-FCE5-4A17-818A-ED80BE673EBB}"
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EndProject
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Global
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GlobalSection(SolutionConfigurationPlatforms) = preSolution
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Debug|Any CPU = Debug|Any CPU
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{43CC17D1-2A95-4554-9900-D97FA9CEA2D0}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{43CC17D1-2A95-4554-9900-D97FA9CEA2D0}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{43CC17D1-2A95-4554-9900-D97FA9CEA2D0}.Release|Any CPU.Build.0 = Release|Any CPU
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{DA851ED7-FCE5-4A17-818A-ED80BE673EBB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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{DA851ED7-FCE5-4A17-818A-ED80BE673EBB}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{DA851ED7-FCE5-4A17-818A-ED80BE673EBB}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{DA851ED7-FCE5-4A17-818A-ED80BE673EBB}.Release|Any CPU.Build.0 = Release|Any CPU
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EndGlobalSection
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EndGlobal

‎Unicolour/Interpolation.cs‎

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var a = Interpolate(startAlpha.A, endAlpha.A, distance);
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return Unicolour.FromHsl(startColour.Config, h.Modulo(360), s, l, a);
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}
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private static (double startHue, double endHue) GetHuePoints((bool hasHue, double hueValue) start, (bool hasHue, double hueValue) end)
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{
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// don't use hue if one colour is monochrome (e.g. black n/a° to green 120° should always stay at hue 120°)
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var noHue = !start.hasHue && !end.hasHue;
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var startHue = noHue || start.hasHue ? start.hueValue : end.hueValue;
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var endHue = noHue || end.hasHue ? end.hueValue : start.hueValue;
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var forwardStart = startHue;
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var forwardEnd = endHue;
72-
var backwardStart = Math.Min(startHue, endHue) + 360;
73-
var backwardEnd = Math.Max(startHue, endHue);
74-
75-
var interpolateForward = Math.Abs(forwardStart - forwardEnd) <= Math.Abs(backwardStart - backwardEnd);
76-
startHue = interpolateForward ? forwardStart : backwardStart;
77-
endHue = interpolateForward ? forwardEnd : backwardEnd;
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70+
if (startHue > endHue)
71+
{
72+
var endViaRed = endHue + 360;
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var interpolateViaRed = Math.Abs(startHue - endViaRed) < Math.Abs(startHue - endHue);
74+
return (startHue, interpolateViaRed ? endViaRed : endHue);
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}
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if (endHue > startHue)
78+
{
79+
var startViaRed = startHue + 360;
80+
var interpolateViaRed = Math.Abs(endHue - startViaRed) < Math.Abs(endHue - startHue);
81+
return (interpolateViaRed ? startViaRed : startHue, endHue);
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}
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return (startHue, endHue);
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}
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‎Unicolour/Unicolour.csproj‎

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<TargetFramework>netstandard2.0</TargetFramework>
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<GeneratePackageOnBuild>True</GeneratePackageOnBuild>
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<PackageIcon>Resources\Unicolour.png</PackageIcon>
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<PackageVersion>1.1.0</PackageVersion>
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<PackageVersion>1.1.1</PackageVersion>
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<PackageTags>colour color converter RGB HSB HSV HSL LAB XYZ color-spaces colour-spaces interpolation comparison contrast luminance deltaE</PackageTags>
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<PackageReleaseNotes>Add HSL support</PackageReleaseNotes>
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<PackageReleaseNotes>Fix hue-based interpolation</PackageReleaseNotes>
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<ApplicationIcon>Resources\Unicolour.ico</ApplicationIcon>
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<PackageLicenseFile>LICENSE</PackageLicenseFile>
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</PropertyGroup>

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