Library of color conversion tools in PHP

color.lib.php

<?php
/*
	Color lib by Yosko (http://www.yosko.net/)
	Licence: WTFPL except for the following
	source for HSL algorithm: http://www.easyrgb.com/index.php?X=MATH
*/

//returns a clean 6 digit hex number as a string
function cleanHexColor($hex) {
    $hex = strtolower($hex);
    //remove the leading "#"
    if(strlen($hex) == 7 || strlen($hex) == 4)
        $hex = substr($hex, -(strlen($hex)-1));
    
    // $hex like "1a7"
    if(preg_match('/^[a-f0-9]{6}$/i', $hex))
        return $hex;
    // $hex like "162a7b"
    elseif(preg_match('/^[a-f0-9]{3}$/i', $hex))
        return $hex[0].$hex[0].$hex[1].$hex[1].$hex[2].$hex[2];
    //any other format
    else
        return "000000";
}

//returns an array of 3 [0-255] int
function hex2rgb($hex) {
    return array(
        hexdec(substr($hex, 0, 2)),
        hexdec(substr($hex, 2, 2)),
        hexdec(substr($hex, 4, 2)),
    );
}

//returns a 6 digit hex number as a string
function rgb2hex($rgb) {
    return ""
        .substr("00".dechex(ceil($rgb[0])), -2)
        .substr("00".dechex(ceil($rgb[1])), -2)
        .substr("00".dechex(ceil($rgb[2])), -2)
    ;
}

//returns a 2 dimensional array of subarrays (HSL: 3 values [0-1] floats)
function variationAround($hsl, $stepSize = 0.2,  $constant = "hue") {
    if($constant == "hue") {
        $i = 1; $j = 2;
    } elseif($constant == "sat") {
        $i = 0; $j = 2;
    }if($constant == "lum") {
        $i = 0; $j = 1;
    }
    
    $variations = array();  //resulting variations
    $hslTemp = array();     //stores current variation
    $mod = array();         //stores modulos for h, s & l
    
    $mod[0] = (float)(($hsl[0]*100) % ($stepSize * 100)) / 100;
    $mod[1] = (float)(($hsl[1]*100) % ($stepSize * 100)) / 100;
    $mod[2] = (float)(($hsl[2]*100) % ($stepSize * 100)) / 100;
    
    $hslTemp = $hsl;
    $hslTemp[$i] = $mod[$i];
    while($hslTemp[$i] <= 1) {
        $row = array();
        $hslTemp[$j] = $mod[$j];
        while($hslTemp[$j] <= 1) {
            $row[(string)$hslTemp[$j]] = array($hslTemp[0], $hslTemp[1], $hslTemp[2]);
            $hslTemp[$j] = (float)($hslTemp[$j] + $stepSize);
        }
        $variations[(string)$hslTemp[$i]] = $row;
        $hslTemp[$i] = (float)($hslTemp[$i] + $stepSize);
    }
    
    return $variations;
}

function rgb2hsl($rgb) {
    //work with range [0-1] for RGB values
    $r = $rgb[0] / 255;
    $g = $rgb[1] / 255;
    $b = $rgb[2] / 255;
    
    //get min and max from RGB
    $min = min($r, $g, $b);
    $max = max($r, $g, $b);
    $delta = $max-$min;
    
    //luminance
    $l = ($max + $min) / 2;
    
    //saturation & hue
    if($min == $max) {
        //grayscale
        $s = 0;
        $h = 0;
    } else {
        //saturation
        if($l < 0.5)    $s = $delta/($max+$min);
        else            $s = $delta/(2-$max-$min);
        
        //hue
        if($r == $max)      $h = ($g-$b)/(6*$delta);
        elseif($g == $max)  $h = 1/3 + ($b-$r)/(6*$delta);
        elseif($b == $max)  $h = 2/3 + ($r-$g)/(6*$delta);
        
        //keep hue in the range [0,1]
        if ($h < 0) $h++;
        if ($h > 1) $h--;
    }
    
    return array($h, $s, $l);
}

function hsl2rgb($hsl) {
    $h = $hsl[0];
    $s = $hsl[1];
    $l = $hsl[2];
    
    //no saturation: grayscale
    if($s == 0) {
        $r = $g = $b = round($l * 255);
    } else {
        if($l < 0.5)    $var2 = $l * (1 + $s);
        else            $var2 = ($l + $s) - ($s * $l);
        
        $var1 = 2 * $l - $var2;
        
        $r = 255 * hue2rgb($var1, $var2, $h + 1/3);
        $g = 255 * hue2rgb($var1, $var2, $h);
        $b = 255 * hue2rgb($var1, $var2, $h - 1/3);
    }
    
    return array($r, $g, $b);
}

function hue2rgb($v1, $v2, $vH)
{
   if ( $vH < 0 ) $vH += 1;
   if ( $vH > 1 ) $vH -= 1;
   if ( $vH < 1/6 ) return $v1 + ( $v2 - $v1 ) * 6 * $vH;
   elseif ( $vH < 1/2 ) return $v2;
   elseif ( $vH < 2/3 ) return $v1 + ( $v2 - $v1 ) * ( 2/3 - $vH ) * 6;
   else return ( $v1 );
}

?>

example.php

<?php
/*
	Color lib by Yosko (http://www.yosko.net/)
	Licence: WTFPL except for the following
	source for HSL algorithm: http://www.easyrgb.com/index.php?X=MATH
*/

require_once ('color.lib.php');

//step size between 0 and 1
define("STEP_SIZE", (float)0.2);

if(isset($_GET['color'])) {
    $sourceColor = $_GET['color'];
} else {
    $sourceColor = "b7ff00";
}

$color = cleanHexColor($sourceColor);

$rgb = hex2rgb($color);
$hsl = rgb2hsl($rgb);

$samplesConstHue = variationAround($hsl, STEP_SIZE, "hue");
$samplesConstSat = variationAround($hsl, STEP_SIZE, "sat");
$samplesConstLum = variationAround($hsl, STEP_SIZE, "lum");

?><!DOCTYPE html>
<html lang="fr">
<head>
    <meta charset="utf-8">
    <title>HSL Color Sampler</title>
    <style>
    table { border-collapse: collapse; border: 2px solid black; text-align:center; }
    td, .preview { width:70px; height:50px; }
    th { border: 1px solid black; }
    .preview { display:table-cell; vertical-align:middle; text-align:center; color:#fff; font-weight: bold; }
    </style>
</head>
<body>
    <h1>HSL Color Sampler</h1>
    
    <h2>Source color</h2>
    <form method="get">
        <input type="text" name="color" value="<?php echo $sourceColor; ?>">
        <button type="send">
            Sample
        </button>
    </form>
    <div>6 digit hexadecimal number</div>
    <div>Configuration: <?php echo STEP_SIZE; ?> step variations</div>
    <div>Interpreted color : <span class="preview" style="background:#<?php echo $color; ?>;">#<?php echo $color; ?></span></div>
    <div>
        Note: the chosen color is supposed to appear in each (white text), but due to some rounded numbers, it may slightly differ (ex: 162417 instead of 162517).
    </div>
    
    <h2>Saturation/Luminance variation for a constant Hue</h2>
    <div>Hue : <?php echo round($hsl[0],2); ?></div>
    <table><?php
    $firsRow = array_keys(array_shift(array_values($samplesConstHue)));
    echo "<tr><th>sat \ lum</th>";
    for($i = 0; $i < count($firsRow); $i++) {
        echo "<th>".$firsRow[$i]."</th>";
    }
    echo "</tr>";
    foreach($samplesConstHue as $sat => $row) {
        $thisRow = (round($hsl[1],1) == round($sat,1));
        echo "\n\t\t<tr><th>".$sat."</th>";
        foreach($row as $lum => $value) {
            $thisLine = (round($hsl[2],1) == round($lum,1));
            $rgb = hsl2rgb($value);
            $html = "#".rgb2hex($rgb);
            if($thisRow && $thisLine)
                echo "<td class=\"preview\" style=\"background:".$html.";\">".$html."</td>";
            else
                echo "<td style=\"background:".$html.";\">".$html."</td>";
        }
        echo "</tr>";
    }
    ?>
    
    </table>
    
    <h2>Hue/Luminance variation for a constant Saturation</h2>
    <div>Saturation : <?php echo round($hsl[1],2); ?></div>
    <table><?php
    $firsRow = array_keys(array_shift(array_values($samplesConstSat)));
    echo "<tr><th>sat \ lum</th>";
    for($i = 0; $i < count($firsRow); $i++) {
        echo "<th>".$firsRow[$i]."</th>";
    }
    echo "</tr>";
    foreach($samplesConstSat as $hue => $row) {
        $thisRow = (round($hsl[0],1) == round($hue,1));
        echo "\n\t\t<tr><th>".$hue."</th>";
        foreach($row as $lum => $value) {
            $thisLine = (round($hsl[2],1) == round($lum,1));
            $rgb = hsl2rgb($value);
            $html = "#".rgb2hex($rgb);
            if($thisRow && $thisLine)
                echo "<td class=\"preview\" style=\"background:".$html.";\">".$html."</td>";
            else
                echo "<td style=\"background:".$html.";\">".$html."</td>";
        }
        echo "</tr>";
    }
    ?>
    
    </table>
    
    <h2>Hue/Saturation variation for a constant Luminance</h2>
    <div>Luminance : <?php echo round($hsl[2],2); ?></div>
    <table><?php
    $firsRow = array_keys(array_shift(array_values($samplesConstLum)));
    echo "<tr><th>sat \ lum</th>";
    for($i = 0; $i < count($firsRow); $i++) {
        echo "<th>".$firsRow[$i]."</th>";
    }
    echo "</tr>";
    foreach($samplesConstLum as $hue => $row) {
        $thisRow = (round($hsl[0],1) == round($hue,1));
        echo "\n\t\t<tr><th>".$hue."</th>";
        foreach($row as $sat => $value) {
            $thisLine = (round($hsl[1],1) == round($sat,1));
            $rgb = hsl2rgb($value);
            $html = "#".rgb2hex($rgb);
            if($thisRow && $thisLine)
                echo "<td class=\"preview\" style=\"background:".$html.";\">".$html."</td>";
            else
                echo "<td style=\"background:".$html.";\">".$html."</td>";
        }
        echo "</tr>";
    }
    ?>
    
    </table>
</body>