php resize image

1// resize on upload
2$maxDim = 800;
3$file_name = $_FILES['myFile']['tmp_name'];
4list($width, $height, $type, $attr) = getimagesize( $file_name );
5if ( $width > $maxDim || $height > $maxDim ) {
6    $target_filename = $file_name;
7    $ratio = $width/$height;
8    if( $ratio > 1) {
9        $new_width = $maxDim;
10        $new_height = $maxDim/$ratio;
11    } else {
12        $new_width = $maxDim*$ratio;
13        $new_height = $maxDim;
14    }
15    $src = imagecreatefromstring( file_get_contents( $file_name ) );
16    $dst = imagecreatetruecolor( $new_width, $new_height );
17    imagecopyresampled( $dst, $src, 0, 0, 0, 0, $new_width, $new_height, $width, $height );
18    imagedestroy( $src );
19    imagepng( $dst, $target_filename ); // adjust format as needed
20    imagedestroy( $dst );
21}