This is a function I used once for an image upload script. It works really well, the only thing I don't know how to do is how to preserve transparency (in gifs and pngs) when generating the thumbnail.
Code:
function createthumb($name,$filename,$new_w,$new_h){
$system=explode('.',$name);
if (preg_match('/jpg|jpeg|JPG/',$system[1])){
$src_img=imagecreatefromjpeg($name);
}
if (preg_match('/png|PNG/',$system[1])){
$src_img=imagecreatefrompng($name);
}
if (preg_match('/gif|GIF/',$system[1])){
$src_img=imagecreatefromgif($name);
}
$old_x=imageSX($src_img);
$old_y=imageSY($src_img);
If($old_x <= $new_w && $old_y <= $new_h){
$dst_img=ImageCreateTrueColor($old_x,$old_y);
imagecopyresampled($dst_img,$src_img,0,0,0,0,$old_x,$old_y,$old_x,$old_y);
if (preg_match("/png/",$system[1]))
{
imagepng($dst_img,$filename);
}
if (preg_match("/gif/",$system[1]))
{
imagegif($dst_img,$filename);
}
else {
imagejpeg($dst_img,$filename);
}
}else {
if ($old_x > $old_y) {
$thumb_w=$new_w;
$thumb_h=$old_y*($new_h/$old_x);
}
if ($old_x < $old_y) {
$thumb_w=$old_x*($new_w/$old_y);
$thumb_h=$new_h;
}
if ($old_x == $old_y) {
$thumb_w=$new_w;
$thumb_h=$new_h;
}
$dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);
imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);
if (preg_match("/png/",$system[1]))
{
imagepng($dst_img,$filename);
}
if (preg_match("/gif/",$system[1]))
{
imagegif($dst_img,$filename);
}
else {
imagejpeg($dst_img,$filename);
}
imagedestroy($dst_img);
imagedestroy($src_img);
}
}
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