how can create thumbnail in php

how can create thumbnail in php

<?php

$imagefolder='.';
$thumbsfolder='.';
$pics=directory($imagefolder,"jpg,JPG,JPEG,jpeg,png,PNG");
$pics=ditchtn($pics,"tn_");
if ($pics[0]!="")
{
foreach ($pics as $p)
{
createthumb($p,"tn_".$p,150,150);
}
}

/*
Function ditchtn($arr,$thumbname)
filters out thumbnails
*/
function ditchtn($arr,$thumbname)
{
foreach ($arr as $item)
{
if (!preg_match("/^".$thumbname."/",$item)){$tmparr[]=$item;}
}
return $tmparr;
}

/*
Function createthumb($name,$filename,$new_w,$new_h)
creates a resized image
variables:
$name Original filename
$filename Filename of the resized image
$new_w width of resized image
$new_h height of resized image
*/
function createthumb($name,$filename,$new_w,$new_h)
{
$system=explode(".",$name);
if (preg_match("/jpg|jpeg/",$system[1])){$src_img=imagecreatefromjpeg($name);}
if (preg_match("/png/",$system[1])){$src_img=imagecreatefrompng($name);}
$old_x=imageSX($src_img);
$old_y=imageSY($src_img);
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);
} else {
imagejpeg($dst_img,$filename);
}
imagedestroy($dst_img);
imagedestroy($src_img);
}

/*
        Function directory($directory,$filters)
        reads the content of $directory, takes the files that apply to $filter
and returns an array of the filenames.
        You can specify which files to read, for example
        $files = directory(".","jpg,gif");
                gets all jpg and gif files in this directory.
        $files = directory(".","all");
                gets all files.
*/
function directory($dir,$filters)
{
$handle=opendir($dir);
$files=array();
if ($filters == "all"){while(($file = readdir($handle))!==false){$files[] = $file;}}
if ($filters != "all")
{
$filters=explode(",",$filters);
while (($file = readdir($handle))!==false)
{
for ($f=0;$f<sizeof($filters);$f++):
$system=explode(".",$file);
if ($system[1] == $filters[$f]){$files[] = $file;}
endfor;
}
}
closedir($handle);
return $files;
}
?>