<!–?php
/**
 * pjlColour
 *
 * Set and return colours in different formats: RGB, HSL and css
 *
 * @package pjlColour
 *
 * @version 1.0
 * @copyright Peter Lux
 * @author Peter Lux
 * @link http://www.plux.co.uk/php-colour-format-conversion/
 * @license GPL http://www.opensource.org/licenses/gpl-license.html
 *
 * HSL format is Hue(0-360), Saturation (0-100), Luminance (0-100%)
 * RGB, CMY, CMYK have colour values of 0-255
 *
 *
 */

/**
 *  Set and return colours in different formats: RGB, HSL and css
 *
 */
class pjlColour {

    const RED = 0;
    const GREEN = 1;
    const BLUE = 2;

    const HUE = 0;
    const SATURATION = 1;
    const LUMINANCE = 2;

    protected $rgb = array(0,0,0);

    /**
    * Constructor.
    * @param int $r Red intensity 0 to 255.
    * @param int $g Green intensity 0 to 255.
    * @param int $b Blue intensity 0 to 255.
    *
    * @return void.
    */
    function __construct($r=0,$g=0,$b=0) {
        $this-&gt;rgb[self::RED] = $r;
        $this-&gt;rgb[self::GREEN] = $g;
        $this-&gt;rgb[self::BLUE] = $b;
    }

    /**
    * setRGB.
    *
    * sets the colour using RGB values
    *
    * @param int $r Red intensity 0 to 255.
    * @param int $g Green intensity 0 to 255.
    * @param int $b Blue intensity 0 to 255.
    *
    * @return void.
    */
    function setRGB($r,$g,$b) {
        $this-&gt;rgb[self::RED] = $r;
        $this-&gt;rgb[self::GREEN] = $g;
        $this-&gt;rgb[self::BLUE] = $b;
    }
    /**
    * getRGB.
    *
    * @return array (red, green, blue).
    */
    function getRGB() {
        return ($this-&gt;rgb);
    }

    /**
    * getHexDigit($hex).
    * @param int $hex digit to convert.
    *
    * @return string the hexidecimal representation of the digit with leading zero.
    */
    private function getHexDigit($hex) {
        $hexDigit = dechex($hex);

        // Add a leading zero if necessary
        if(strlen($hexDigit) == 1) {
            $hexDigit = "0" . $hexDigit;
        }
        return $hexDigit;
    }

    /**
    * setHex($hex).
    * @param int $hex string in css hexidecimal with leading #.
    *
    * @return true.
    */
    public function setHex($hex) {
        if (substr($hex,0,1) != ‘#’)
            throw new Exception (‘"’.$hex.‘" is not a valid hex colour’);
        $hex = substr($hex,1);

        $d = ‘[a-fA-F0-9]’;

        // Make sure $hex is valid
        if (preg_match("/^($d$d)($d$d)($d$d)\$/", $hex, $rgb)) {
            $this-&gt;rgb[self::RED] = hexdec($rgb[1]);
            $this-&gt;rgb[self::GREEN] = hexdec($rgb[2]);
            $this-&gt;rgb[self::BLUE] = hexdec($rgb[3]);
        } else if (preg_match("/^($d)($d)($d)$/", $hex, $rgb)) {
            $this-&gt;rgb[self::RED] = hexdec($rgb[1] . $rgb[1]);
            $this-&gt;rgb[self::GREEN] = hexdec($rgb[2] . $rgb[2]);
            $this-&gt;rgb[self::BLUE] = hexdec($rgb[3] . $rgb[3]);
        } else {
            throw new Exception ("cannot convert hex ‘$hex‘ to RGB");
        }
        return(true);
    }

    /**
    * getHex().
    * @param void.
    *
    * @return string current colour in css hexidecimal notation.
    */
    function getHex() {
        return ‘#’.$this-&gt;getHexDigit($this-&gt;rgb[self::RED]).$this-&gt;getHexDigit($this-&gt;rgb[self::GREEN]).$this-&gt;getHexDigit($this-&gt;rgb[self::BLUE]);
    }

    /**
    * getHSL().
    * @param void.
    *
    * @return array(hue, saturation, Luminance).
    *
    * algorithum based on
    * http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
    *
    */
    function getHSL() {
        $Saturation = 0;
        $Luminance = 0;
        $Hue = 0;

        $r = $this-&gt;rgb[self::RED]/255;
        $g = $this-&gt;rgb[self::GREEN]/255;
        $b = $this-&gt;rgb[self::BLUE]/255;

        $min = min($r,$g,$b);
        $max = max($r,$g,$b);

        $Luminance = ($min + $max)/2;
        if ($min != $max) {
            if ($Luminance &lt; 0.5) {
                $Saturation = ($max–$min)/($max+$min);
            } else {
                $Saturation = ( $max–$min)/(2.0–$max–$min);
            }
            if ($max == $r) {
                $Hue = ($g–$b)/($max–$min);
            } else if ($max == $g) {
                $Hue = 2.0 + ($b–$r)/($max–$min);
            } else {
                $Hue = 4.0 + ($r–$g)/($max–$min);
            }
        }
        $Hue = $Hue * 60;
        if ($Hue &lt; 0) {
            $Hue = $Hue + 360;
        }

        return(array(round($Hue,2),round($Saturation*100,2),round($Luminance*100,2)));
    }

    /**
    * setHSL($h,$s,$l).
    * @param float Hue 0-360.
    * @param float Saturation 0 – 100%
    * @param float Luminance 0 – 100%
    *
    * @return void.
    *
    * algorithum based on
    * http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
    *
    */
    function setHSL($h,$s,$l) {
        // convert values to fractions
        $h = $h /360;
        $s = $s / 100;
        $l = $l / 100;

        // if there is no saturation then it is greyscale
        if ($s == 0) {
            $this-&gt;rgb[self::RED] = $l * 255;
            $this-&gt;rgb[self::GREEN] = $this-&gt;rgb[self::RED];
            $this-&gt;rgb[self::BLUE] = $this-&gt;rgb[self::RED];
        } else {
            if ($l &lt; 0.5) {
                $temporary_1 = $l * (1 + $s);
            } else {
                $temporary_1 = $l + $s – $l * $s;
            }

            $temporary_2 = 2 * $l – $temporary_1;

            // $temporary is $h + 0.333 for red, $h for green and $h – 0.333 for blue. Therefore I multiply
            // 0.333 by (1-$i) which is 1,0,-1
            for ($i=0 ; $i&lt;3 ; $i++) {
                $temporary = $h + (1–$i)*0.333;
                if ($temporary &gt; 1)
                    $temporary = $temporary – 1;
                else if ($temporary &lt; 0 )
                    $temporary += 1;

                if (6 * $temporary &lt; 1) {
                    $this-&gt;rgb[$i] = intval(($temporary_2 + ($temporary_1 – $temporary_2) * 6 * $temporary) * 255);
                } else if (2 * $temporary &lt; 1) {
                    $this-&gt;rgb[$i] = intval($temporary_1 * 255);
                } else if (3 * $temporary &lt; 2) {
                    $this-&gt;rgb[$i] = intval(($temporary_2 + ($temporary_1 – $temporary_2) * (0.666 – $temporary) * 6) * 255);
                } else {
                    $this-&gt;rgb[$i] = intval($temporary_2 * 255);
                }
            }
        }
    }

    /**
    * function setCMY($c,$m,$y).
    * @param int cyan intensity (0-255)
    * @param int Magenta intensity (0-255)
    * @param int Yellow intensity (0-255)
    *
    * @return void.
    *
    */
    public function setCMY($c, $m, $y) {
        setRGB(255–$c, 255–$m, 255–$y);
    }

    /**
    * getCMY().
    * @param void.
    *
    * @return array(cyan, magenta, yellow).
    *
    */
    public function getCMY() {
        return(array(255–$this-&gt;rgb[self::RED],255–$this-&gt;rgb[self::GREEN],255–$this-&gt;rgb[self::BLUE]));
    }

    /**
    * function setCMYK($c,$m,$y).
    * @param int cyan intensity (0-255)
    * @param int Magenta intensity (0-255)
    * @param int Yellow intensity (0-255)
    *
    * @return void.
    *
    */
    public function setCMYK($c, $m, $y, $k) {
        setRGB((255–$c)*(255–$k), (255–$m)*(255–$k), (255–$y)*(255–$k));
    }

    /**
    * getCMYK().
    * @param void.
    *
    * @return array(cyan, magenta, yellow).
    *
    */
    public function getCMYK() {
        $k = 255 – max($this-&gt;rgb);
        return(array(round(255*((255–$this-&gt;rgb[self::RED]–$k)/(255–$k)),0),
                     round(255*((255–$this-&gt;rgb[self::GREEN]–$k)/(255–$k)),0),
                     round(255*((255–$this-&gt;rgb[self::BLUE]–$k)/(255–$k)),0),
                     $k));
    }

    /**
    * function increaseLuminance($increase).
    * @param float % increase in Luminance (use negative $increase to decrease).
    *
    * @return void.
    *
    * if luminance is not in range 0-100 it corrects to 0 or 100
    */
    public function increaseLuminance($increase) {
        $hsl = $this-&gt;getHSL();
        $l = $hsl[2] + $increase;
        if ($l &gt; 100) $l = 100;
        if ($l &lt; 0) $l = 0;
        $this-&gt;setHSL($hsl[self::HUE], $hsl[self::SATURATION], $l);
    }

    /**
    * function increaseSaturation($increase).
    * @param float % increase in Saturation (use negative $increase to decrease).
    *
    * @return void.
    *
    * if saturation is not in range 0-100 it corrects to 0 or 100
    */
    public function increaseSaturation($increase) {
        $hsl = $this-&gt;getHSL();
        $s = $hsl[1] + $increase;
        if ($s &gt; 100) $s = 100;
        if ($s &lt; 0) $s = 0;
        $this-&gt;setHSL($hsl[self::HUE], $s, $hsl[self::LUMINANCE]);
    }

    /**
    * function increaseSaturation($increase).
    * @param float degree increase in Hue (use negative $increase to decrease).
    *
    * @return void.
    *
    * Will wrap round if $hue is out of 0-360 range
    * this can be used to set complimenary colour by calling -&gt;increaseHue(180)
    */
    public function increaseHue($increase) {
        $increase = $increase % 360;
        $hsl = $this-&gt;getHSL();
        $h = $hsl[self::HUE] + $increase;
        if ($h &gt; 360) $h = $h – 360;
        if ($h &lt; 0) $h = $h + 360;
        $this-&gt;setHSL($h, $hsl[self::SATURATION], $hsl[self::LUMINANCE]);
    }
}
?–>

$colour = new pjlColour(140,80,120); // create new colour with R,G,B values
$colour-&gt;getHex();  // get hex value i.e. #8c5078
$colour-&gt;getHSL();  // returns an array containing HSL values (0-360, 0-100, 0-100)
$colour-&gt;getCMY();  // returns an array of the CMY values (0-255)
$colour-&gt;getCMYK(); // returns an array of the CMYK values (0-255)
$colour-&gt;setHSL(200,50,50); // set HSL value hue:200 with 50% saturation and luminance
$colour-&gt;setCMYK(0,127,127,50); // set CMYK values
$colour2 = clone $colour;  // get a copy of the colour
$colour2-&gt;increaseHue(180); // increase Hue by 180 degrees – wraps round after 360
$colour2-&gt;increaseSaturation(10) // increase the saturation by 10%
$colour2-&gt;increaseLuminance(–20) // decrease the Luminance by 20%