Java Colour library

The library provides classes to easily handle colours in Java by being able to accept several colour codifications and conversions between them.

Index

• Description
• How it works?
  • Some ColourCode examples
  • Convert a ColourCode to another
  • Using Colour
  • Dealing with transparency
• Notes

Description

The library provides classes to handle colours in Java. It works with several colour codifications like RGB, HSL, CMYK... and it provides conversion algorithms that convert any colour code to another. The basics are:

• ColourCode: representation of a colour in a specific codification, e.g., RGB or HSV.
• ColourCodeConversion: algorithm that converts a colour from codification A to B directly.
• ColourCodeConverter: after specifying the available conversion algorithm list (ColourCodeConversion), it can convert a colour from one codification to another directly or by using some middle steps.
• Colour: it can be created from any ColourCode and it's the representation of a color as a concept. It means that two Colours are equal iff they represent the same colour, no matter what codification they use.

How it works?

Some ColourCode examples

Each ColourCode has some constructor that allow creating them easily.

RgbCode redRgb = new RgbCode(255, 0, 0);
HexCode greenHex = new HexCode("#00FF00");
HslCode blueHsl = new HslCode(240, 100, 50);
CmykCode greyCmyk = new CmykCode(0, 0, 0, 50);

All implemented AcceptedByCssColourCode have also a constructor that receives the colour's CSS representation.

RgbCode rgbFromCss = new RgbCode("rgba(63, 127, 88, 0.18)");
HslCode hslFromCss = new HslCode("hsl(3, 9%, 88%)");

Convert a ColourCode to another

It's possible to convert one colour code to another by using directly the ColourCodeConversion needed:

ColourCodeConversion<RgbCode, HexCode> rgb2Hex = new RgbToHexCodeConversion();

RgbCode redRgb = new RgbCode(255, 0, 0);
HexCode redHex = rgb2Hex.convert(redRgb);

But this isn't the best way to achieve it. Instead of instantiate the ColourCodeConversion, it's better to use a ColourCodeConverter.

ColourCodeConverter converter = new ColourCodeConverter();

RgbCode redRgb = new RgbCode(255, 0, 0);
HexCode redHex = converter.convert(redRgb, HexCode.class); // Converts RGB to Hex
CmykCode redCmyk = converter.convert(redHex, CmykCode.class); // Converts Hex to CMYK
HslCode redHsl = converter.convert(redCmyk, HslCode.class); // Converts CMYK to HSL

The default converter doesn't offer a specific conversion algorithm between each pair of colour code. But if it has a ColourCodeConversion that converts A to B, and another that converts B to C, it will be able to convert a colour codified in A to C.

In any case, you can always create your own conversion algorithm A to C and add it to the available conversions of the ColourCodeConverter, that way you can speed up the conversion you need.

The default converter deals with all defined colour codes in this library.

Using Colour

You can instantiate a Colour from any ColourCode implementation.

// Instantiate a new Colour by passing its codification
RgbCode redRgb = new RgbCode(255, 0, 0);
Colour redFromRgb = new Colour(redRgb);

// Create it directly using ColourCode.toColour()
Colour redFromHex = new HexCode("FF0000").toColour();

Once you have a Colour, you can get its representation in any ColourCode. (It's another way to convert colour codifications)

HexCode redHex = redFromRgb.as(HexCode.class);

When a Colour is created, it will reference a default ColourCodeConverter, thanks to it is possible to get different codifications of one colour. You can always create it passing your custom converter.

To work with codifications extracted directly from CSS, you create a Colour passing the String codification directly to a WebColour.

String css = "#FF0AFB";
// Assertion is unnecessary, but call WebColour.from() with a not valid css code will throw an IllegalArgumentException
if(WebColour.isCssColourCode(css)) {
    Colour colour = WebColour.from(css);
}

Dealing with transparency

Colours used in web has transparency. If transparency isn't explicitly indicated, it will act as full opacity. E.g.: rgba(0, 0, 0, 50%) represents a black colour with 50% opacity.

The library supports this characteristic too. And conversions between colours will transfer opacity, but only and only if both work with opacity.

Notes

• New ColourCode will be added in the future: HWB, NCol, HTML named colours and PMS (for the moment).
• At this moment, the CSS constructor of the implemented AcceptedByCssColourCode will throw an exception with some codifications supported by CSS. E.g.: it's not possible to use rad or deg hsl(150deg 30% 60%)