Justere lysstyrken i et billede

Hej!

Kan man justere lysstyrken på billedet i denne kode - eller i det hele taget generelt?

<?php

// Set the content-type
header("Content-type: image/jpeg");

$sourcepic = $_GET[image];

// Create the image
$im = imagecreatefromjpeg($sourcepic);

// Create some colors
$txtcolor = imagecolorallocate($im, 255, 255, 255);

// The text to draw
$text = $_GET[text];
// Replace path by your own font path
$font = 'tahomabold.ttf';

// Add the text
imagettftext($im, 20, 0, 10, 120, $txtcolor, $font, $text);

// Using imagepng() results in clearer text compared with imagejpeg()
imagepng($im, '', 100);
imagedestroy($im);
?>