Creating image thumbnails using PHP

Sometimes restricting images size is required. Following function is very useful to create images of certain sizes on the fly

function createThumbs($source, $dest, $requiredWidth, $requiredHeight, $fileType='')
{
    $size = getimagesize($source);
    $givenWidth = $size[0];
    $givenHeight = $size[1];
   
    if ($givenWidth > 800)
    {
        $requiredRatio = $requiredWidth / $requiredHeight;
        $middleWidth = ceil($givenHeight * $requiredRatio);
        if($middleWidth>$givenWidth){
            $requiredRatio = $requiredHeight / $requiredWidth;
            $middleHeight = ceil($givenWidth * $requiredRatio);
            $middleWidth = $givenWidth;
            $y = ceil(($givenHeight - $middleHeight)/2);
        }
        else{
            $middleHeight = $givenHeight;
            $middleWidth = ceil($givenHeight * $requiredRatio);
            $x = ceil(($givenWidth - $middleWidth)/2);
        }
       
        $new_im = imagecreatetruecolor($requiredWidth,$requiredHeight);
   
        $extention = strtolower(substr($source, strlen($source)-3, strlen($source)));
        if ($extention == "jpg" || $extention == "jpeg") { $im = imagecreatefromjpeg($source); }
        elseif ($extention == "gif") { $im = imagecreatefromgif($source); }
        elseif ($extention == "png") { $im = imagecreatefrompng($source); }
        else
        {
            //echo("ERROR: Unknown image source file format");
            return;
        }
   
        imagecopyresampled($new_im,$im,0,0,$x,$y,$requiredWidth,$requiredHeight,$middleWidth,$middleHeight);
        imagejpeg($new_im,$dest,85);
    }
}