Sophisticated representation of color

Iridescence implements several algorithms for working with colors represented in different forms.

• represents colors using a variety of different color models
• work with colors in RGB, HSV, CMY, CMYK, HSL, CIELAB and XYZ
• convert between any colors
• utilize color profiles (where necessary)
• provides a standard palette of named colors
• print colors as CSS, Hex or ANSI
• brighten, lighten, darken and blend colors
• calculate perceptual deltas between colors

Iridescence has not yet been published. The medium-term plan is to build Iridescence with Fury and to publish it as a source build on Vent. This will enable ordinary users to write and build software which depends on Iridescence.

Subsequently, Iridescence will also be made available as a binary in the Maven Central repository. This will enable users of other build tools to use it.

For the overeager, curious and impatient, see building.

Iridescence provides seven different ways of representing colors:

• Srgb: sRGB,
• Xyz: CIE 1931 XYZ
• Cielab: Lab* or CIELAB
• Cmy: CMY
• Cmyk: CMKY
• Hsl: HSL
• Hsv: HSV

Each color model uses either three or four continuous coordinates, all represented in Iridescence as Doubles in the unit interval (0 ≤ c ≤ 1), to describe an apparently full spectrum of colors perceived by the human eye.

Given the complex nature of sight and color, different models make different tradeoffs in their representations of different colors. While sRGB is the most direct representation of the colored light emitted by a computer monitor, and indeed the most common representation for computers, CMY and CMYK are more common in printing.

Meanwhile, the HSL and HSV representations representations use the natural qualititative properties of hue, saturation, lightness and brightness, and the XYZ and CIELAB color spaces are derived empirically. CIELAB attempts to maintain the property that the Euclidean distance between two colors is proportional to the perceptual difference between those colors, as determined by experimentation.

The particular color model should be chosen according to the requirements of the particular task.

import iridescence.*

given profile = profiles.Ultralume50

val pink: Cielab = colors.Ivory.cielab.mix(colors.DarkMagenta.cielab)
val palePink: Srgb = pink.srgb.hsv.tint(0.5).srgb
println(s"${color.ansiFg24}Hello World!")

Iridescence provides case classes to immutably represent each of the seven color models, above. Colors in one representation can be directly converted into many of the other representations, and the remaining conversions can be performed indirectly.

In general, every color representation provides the Color#srgb method to convert it to an Srgb value. Conversely, the Srgb type provides the methods cmy, cmyk, cielab, xyz, hsv and hsl to convert to these alternative representations.

While it would be possible to provide an n×n set of methods for converting between any pair of representations, conversions which rely on an unspecified intermediate representation (for example converting between HSL and CMYK) are generally not provided unless the intermediate representation is a necessary step in the calculation. This is to make it clear when conversions are happening.

For example, the methods Hsl#srgb and Srgb#xyz both exist, but Hsl#xyz is not implemented. However, Srgb#cielab is provided, even though the conversion is made via an intermediate XYZ value.

Here are some examples:

val DeepPink: Srgb = Srgb(1, 0.078, 0.576)
val Gold: Hsv = Srgb(1, 0.843, 0).hsv
val Gold2: Cmyk = Gold.srgb.cmyk

The colors object provides a standard palette of about 140 named colors defined in sRGB space.

Certain color representations rely on additional information that characterizes the conditions under which the colors are encoded, and this information is necessary for conversions between certain color spaces.

For example, to convert from Srgb to Cielab requires a profile. Profiles are provided through the Profile type, and several are provided in the profiles object. These should be specified, implicitly or explicitly with each conversion, like so:

val color = DeepPink.cielab(using profiles.MidMorningDaylight)

or,

given Profile = profiles.CoolFluorescent
val color = LawnGreen.xyz

For generality, conversions to Srgb always require a profile to be given (even for conversions where it is not used). This restriction may be lifted later. A good default profile to use is the Daylight profile.

given Profile = profiles.Daylight

Additional methods are provided on certain color types for producing new colors from old. In general, these methods are particular to the color model being used.

For example, the methods saturate, desaturate, pure and rotate (for changing the hue) are provided on Hsl and Hsv types, while Hsv additionally provides shade, tint and tone methods. These latter methods take black and/or white parameters to specify the amount of shading, tinting or toning to be applied.

Cielab provides a delta method for comparing two colors (returning a Double in the unit interval), and the mix method for combining two colors. Cielab#mix takes another Cielab color as its first parameter, and a mix ratio (again, in the unit interval) as an optional second parameter. If left unspecified, it defaults to the midpoint between the two colors.

Use of these methods might typically involve converting a color to the model which defines them, then applying them as necessary, before converting back. For example,

colors.IndianRed.hsv.tone(0.2, 0.4).srgb

Different formats, languages and protocols will represent colors as strings in a number of different ways. Iridescence provides serialization methods to the following formats:

• 24-bit ANSI foreground and background escape codes,
• RGB CSS, in the form rgb(100, 78, 12),
• HSL CSS, in the form hsl(310, 12%, 84%),
• 12-bit and 24-bit hexadecimal, e.g. #afc or #ffed00

These are available on the Srgb type, with the exception of Hsl#css.

There is no support for transparency.

Iridescence is classified as maturescent. For reference, Soundness projects are categorized into one of the following five stability levels:

• embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
• fledgling: of proven utility, seeking contributions, but liable to significant redesigns
• maturescent: major design decisions broady settled, seeking probatory adoption and refinement
• dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version 1.0.0 or later
• adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated

Projects at any stability level, even embryonic projects, can still be used, as long as caution is taken to avoid a mismatch between the project's stability level and the required stability and maintainability of your own project.

Iridescence is designed to be small. Its entire source code currently consists of 489 lines of code.

Iridescence will ultimately be built by Fury, when it is published. In the meantime, two possibilities are offered, however they are acknowledged to be fragile, inadequately tested, and unsuitable for anything more than experimentation. They are provided only for the necessity of providing some answer to the question, "how can I try Iridescence?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Iridescence's build structure, dependencies and source location; the file format should be short and quite intuitive. Copy the sources into a source directory in your own project, then repeat (recursively) for each of the dependencies.

   The sources are compiled against the latest nightly release of Scala 3. There should be no problem to compile the project together with all of its dependencies in a single compilation.

2. Build with Wrath

   Wrath is a bootstrapping script for building Iridescence and other projects in the absence of a fully-featured build tool. It is designed to read the fury file in the project directory, and produce a collection of JAR files which can be added to a classpath, by compiling the project and all of its dependencies, including the Scala compiler itself.

   Download the latest version of wrath, make it executable, and add it to your path, for example by copying it to /usr/local/bin/.

   Clone this repository inside an empty directory, so that the build can safely make clones of repositories it depends on as peers of iridescence. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Iridescence's dependencies.

   If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributors to Iridescence are welcome and encouraged. New contributors may like to look for issues marked beginner.

We suggest that all contributors read the Contributing Guide to make the process of contributing to Iridescence easier.

Please do not contact project maintainers privately with questions unless there is a good reason to keep them private. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.

Iridescence was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

The word iridescent, defined as "having a play of changeable colors", also describes the functionality of Iridescence.

In general, Soundness project names are always chosen with some rationale, however it is usually frivolous. Each name is chosen for more for its uniqueness and intrigue than its concision or catchiness, and there is no bias towards names with positive or "nice" meanings—since many of the libraries perform some quite unpleasant tasks.

Names should be English words, though many are obscure or archaic, and it should be noted how willingly English adopts foreign words. Names are generally of Greek or Latin origin, and have often arrived in English via a romance language.

The logo illustrates a color wheel.

Iridescence is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.