RGB and HSV conversion in PHP

rgb-hsv-conversion.php

<?php
// note: some of these are written with $this so they work inside classes. 
// you could easily rewrite this to be a general function outside a class.
// sorry for the inconsistent tabs
// adapted from: http://www.actionscript.org/forums/showthread.php3?t=50746 via http://stackoverflow.com/questions/1773698/rgb-to-hsv-in-php
class MyClass
{

    // usage: $this->hexColorMod("#aa00ff", -0.2); // darker by 20%
    // returns: #8700cc

    private function hexColorMod($hex, $diff) {
        $rgbhex = str_split(trim($hex, '# '), 2);
        $rgbdec = array_map("hexdec", $rgbhex);
        $hsv = $this->RGB_TO_HSV($rgbdec[0], $rgbdec[1], $rgbdec[2]);

        $hsv['V'] = max(0, min(1, $hsv['V'] + $diff)); 

        $rgbdark = $this->HSV_TO_RGB($hsv['H'], $hsv['S'], $hsv['V']);
        $output = array_map("dechex", $rgbdark);
        $output = array_map(array($this,"zeropad2"), $output); // gotta zero-pad single-digit hex
        return '#'.implode($output);
    }

    private function zeropad2($num)
    {
        $limit = 2;
        return (strlen($num) >= $limit) ? $num : $this->zeropad2("0" . $num);
    }

    private function RGB_TO_HSV ($R, $G, $B)  // RGB Values:Number 0-255 
    {                                 // HSV Results:Number 0-1 
       $HSL = array(); 

       $var_R = ($R / 255); 
       $var_G = ($G / 255); 
       $var_B = ($B / 255); 

       $var_Min = min($var_R, $var_G, $var_B); 
       $var_Max = max($var_R, $var_G, $var_B); 
       $del_Max = $var_Max - $var_Min; 

       $V = $var_Max; 

       if ($del_Max == 0) 
       { 
          $H = 0; 
          $S = 0; 
       } 
       else 
       { 
          $S = $del_Max / $var_Max; 

          $del_R = ( ( ( $var_Max - $var_R ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max; 
          $del_G = ( ( ( $var_Max - $var_G ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max; 
          $del_B = ( ( ( $var_Max - $var_B ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max; 

          if      ($var_R == $var_Max) $H = $del_B - $del_G; 
          else if ($var_G == $var_Max) $H = ( 1 / 3 ) + $del_R - $del_B; 
          else if ($var_B == $var_Max) $H = ( 2 / 3 ) + $del_G - $del_R; 

          if ($H<0) $H++; 
          if ($H>1) $H--; 
       } 

       $HSL['H'] = $H; 
       $HSL['S'] = $S; 
       $HSL['V'] = $V; 

       return $HSL; 
    } 

    function HSV_TO_RGB ($H, $S, $V)  // HSV Values:Number 0-1 
    {                                 // RGB Results:Number 0-255 
        $RGB = array(); 

        if($S == 0) 
        { 
            $R = $G = $B = $V * 255; 
        } 
        else 
        { 
            $var_H = $H * 6; 
            $var_i = floor( $var_H ); 
            $var_1 = $V * ( 1 - $S ); 
            $var_2 = $V * ( 1 - $S * ( $var_H - $var_i ) ); 
            $var_3 = $V * ( 1 - $S * (1 - ( $var_H - $var_i ) ) ); 

            if       ($var_i == 0) { $var_R = $V     ; $var_G = $var_3  ; $var_B = $var_1 ; } 
            else if  ($var_i == 1) { $var_R = $var_2 ; $var_G = $V      ; $var_B = $var_1 ; } 
            else if  ($var_i == 2) { $var_R = $var_1 ; $var_G = $V      ; $var_B = $var_3 ; } 
            else if  ($var_i == 3) { $var_R = $var_1 ; $var_G = $var_2  ; $var_B = $V     ; } 
            else if  ($var_i == 4) { $var_R = $var_3 ; $var_G = $var_1  ; $var_B = $V     ; } 
            else                   { $var_R = $V     ; $var_G = $var_1  ; $var_B = $var_2 ; } 

            $R = $var_R * 255; 
            $G = $var_G * 255; 
            $B = $var_B * 255; 
        } 

        $RGB['R'] = $R; 
        $RGB['G'] = $G; 
        $RGB['B'] = $B; 

        return $RGB; 
    } 
}

Thanks for the class and code. This works only to darken a color.
I modified the following part, so you can adjust the new color to be lighter or darker.

change #17
$hsv['V'] = $hsv['V'] + $diff;

top:
$hsv['V'] = max(0, min(1, $hsv['V'] + $diff));

@despecial thanks, changed!