How to make a grayscale or faded copy of an image?

[Mastra6]

Hi guys,

I've written a script that makes thumbnails of the images I upload (making a gallery script for my dad's web site) and it works very well. My code for the thumbnail bit is as follows:

$filename = "images/".$file;
list($width, $height) = getimagesize($filename);
$new_height = 100;
$new_width = ($new_height / $height) * $width;
$image_p = imagecreatetruecolor($new_width, $new_height);
$image = imagecreatefromjpeg($filename);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
imagejpeg($image_p, 'images/thumbs/".$file.".jpg', 100);

What I want to be able to do is change this to be the rollover image (I'll just add _over before the .jpg when creating the file) and then to have another image which will be the one that shows up when the mouse isn't over it that will either be faded out or grayscale or something. I've looked on the PHP manual but can't find anything that would help me to do this. Any ideas?

Thanks
Mastra6

[kitchin]

There is an example here, with corrections:
http://www.php.net/manual/en/function.imagecolorsforindex.php

I don't know how good it is, so I'll quote the resulting function here and people can comment:

function imagegreyscale(&$img, $dither=1) {   

  if (!($t = imagecolorstotal($img))) {
    imagetruecolortopalette($img, $dither, 256);   

    $t = imagecolorstotal($img);
  }
  for ($c = 0; $c < $t; $c++) {   

    $col = imagecolorsforindex($img, $c);
    $min = min($col['red'],$col['green'],$col['blue']);
    $max = max($col['red'],$col['green'],$col['blue']);
    $r= $g= $b= ($max+$min)/2;
    imagecolorset($img, $c, $r, $g, $b);
  }
}

I have not tried to CCIR method mentioned there.