How do I make a lighter version of a colour using PHP?

Question

Hello fellow earthlings. A quesion about RGB color and its usefulness in a simple tiny php code:

Imagine I have variable $colorA containning a valid six char color. say B1B100, a greenish natural color. Now If I would like to make a new color from that, which is, say, ten steps lighter thatn that original color, roughly.

$colorA = B1B100 // original color
php code with little color engine lightening stuff up goes here
$colorB = ?????? // original color lightened up

Is there a php ready function that KNOWS rgb colors something like

php function RGB ( input color, what to do, output color) Where what to do could be +/- 255 values of brightness etc etc.

Is something like this already possible or am I day dreaming?

rgb-hsl($colorA, +10, $colorB);

If this does not exist, what would be the shortest code for doing this? Suggestions, code or ideas are all answers to me. Thanks.

Answer 1

This SO question has a full-blown PHP script that can convert a RGB to a HSL colour, and increase its H component of a HSL colour - it should be trivial to change to increase L instead.

Answer 2

In general if you want a lighter shade of a particular colour, the most accurate process is to convert from RGB to HSL (or HSV), change the 'L' (or 'V') value which represents lightness, and then convert back to RGB.

This will preserve the "hue", which represents where the colour sits on the spectrum, but change the "tint" (if lightening) or "shade" (if darkening) of that colour.

See http://en.wikipedia.org/wiki/HSL_and_HSV for more information.

Answer 3

On this website: http://www.sitepoint.com/forums/showthread.php?t=586223 they are talking about this code which is originally made by opensource Drupal. Seems to work fine in PHP!?

Now, how do I now indermingle myself with this code and change the lightness of an HSL value, before its outputted as RGB again?

<?php
### RGB >> HSL
function _color_rgb2hsl($rgb) {
  $r = $rgb[0]; $g = $rgb[1]; $b = $rgb[2];
  $min = min($r, min($g, $b)); $max = max($r, max($g, $b));
  $delta = $max - $min; $l = ($min + $max) / 2; $s = 0;
  if ($l > 0 && $l < 1) {
    $s = $delta / ($l < 0.5 ? (2 * $l) : (2 - 2 * $l));
  }
  $h = 0;
  if ($delta > 0) {
    if ($max == $r && $max != $g) $h += ($g - $b) / $delta;
    if ($max == $g && $max != $b) $h += (2 + ($b - $r) / $delta);
    if ($max == $b && $max != $r) $h += (4 + ($r - $g) / $delta);
    $h /= 6;
  } return array($h, $s, $l);
}

### HSL >> RGB
function _color_hsl2rgb($hsl) {
  $h = $hsl[0]; $s = $hsl[1]; $l = $hsl[2];
  $m2 = ($l <= 0.5) ? $l * ($s + 1) : $l + $s - $l*$s;
  $m1 = $l * 2 - $m2;
  return array(_color_hue2rgb($m1, $m2, $h + 0.33333),
               _color_hue2rgb($m1, $m2, $h),
               _color_hue2rgb($m1, $m2, $h - 0.33333));
}

### Helper function for _color_hsl2rgb().
function _color_hue2rgb($m1, $m2, $h) {
  $h = ($h < 0) ? $h + 1 : (($h > 1) ? $h - 1 : $h);
  if ($h * 6 < 1) return $m1 + ($m2 - $m1) * $h * 6;
  if ($h * 2 < 1) return $m2;
  if ($h * 3 < 2) return $m1 + ($m2 - $m1) * (0.66666 - $h) * 6;
  return $m1;
}

### Convert a hex color into an RGB triplet.
function _color_unpack($hex, $normalize = false) {
  if (strlen($hex) == 4) {
    $hex = $hex[1] . $hex[1] . $hex[2] . $hex[2] . $hex[3] . $hex[3];
  } $c = hexdec($hex);
  for ($i = 16; $i >= 0; $i -= 8) {
    $out[] = (($c >> $i) & 0xFF) / ($normalize ? 255 : 1);
  } return $out;
}

### Convert an RGB triplet to a hex color.
function _color_pack($rgb, $normalize = false) {
  foreach ($rgb as $k => $v) {
    $out |= (($v * ($normalize ? 255 : 1)) << (16 - $k * 8));
  }return '#'. str_pad(dechex($out), 6, 0, STR_PAD_LEFT);
}

/* $testrgb = array(0.2,0.75,0.4); //RGB to start with
print_r($testrgb); */
      print "Hex: ";

  $testhex = "#b7b700";
      print $testhex;

  $testhex2rgb = _color_unpack($testhex,true); 
      print "<br />RGB: ";

  var_dump($testhex2rgb);
      print "<br />HSL color module: ";

  $testrgb2hsl = _color_rgb2hsl($testhex2rgb); //Converteren naar HSL

  var_dump($testrgb2hsl);
      print "<br />RGB: ";

  $testhsl2rgb = _color_hsl2rgb($testrgb2hsl); // En weer terug naar RGB    
  var_dump($testhsl2rgb); 
      print "<br />Hex: ";

  $testrgb2hex = _color_pack($testhsl2rgb,true);
  var_dump($testrgb2hex);

?>

Answer 4

PHP does have a couple image manipulation libraries. Either GD or Imagemagick

EDIT: I jumped the gun, these libraries do not have direct PHP color manipulation functions - I honestly assumed they did of a sort after seeing a lot of the things they can do with images via PHP. They do accomplish a lot of cool things. Here's one guy's example.