Very useful to build a pseudo-sphere with a color gradient...
<?php
 $width = 300;
 $center = $width / 2;
 $colordivs = 255 / $center;
 $im = @imagecreate($width, $width);
 $back_color = imagecolorallocate($im, 20, 30, 40);
 imagefill($im, 0, 0, $back_color); 
 for ($i = 0; $i <= $center; $i++)
 {
     $diametre = $width - 2 * $i;
    $el_color = imagecolorallocate($im, $i * $colordivs, 0, 0);
    imagearc($im, $center, $center, $diametre, $diametre, 0, 360, $el_color);
    imagefilltoborder($im, $center, $center, $el_color, $el_color);
 }
 imagepng($im);
?>
Dark Skull Software
http://www.darkskull.net 
     