Buying Image Magik GD Quality Fix

I'm using this code for image magic gd.php file, which works, but I'd like to improve quality. Here's my code. Let me know if you can quickly modify the code to improve quality.

<?
$image_magick_exists=true;
$DOCUMENT_ROOT=$_SERVER['DOCUMENT_ROOT']."";//"/home/aegeanmx/public_html/";
$mp="/usr/bin/";
//$mp="/usr/local/bin/";
/* ==================== */
$maxw=$_GET['maxw'];
$maxh=$_GET['maxh'];
$back=$GET['b'];
$w=$_GET['w'];
$h=$_GET['h'];
$pic=$_GET['pic'];

$mode=$_GET['mode'];
$type=$_GET['type'];
$quality=$_GET['q']==''?100:$_GET['q'];
if($pic=='')Exit();
$enlarge=$_GET['enlarge']; //yes/no/ - enlarge smaller images
if(!(($enlarge=="yes") or ($enlarge=="no"))) $enlarge="yes";
$fill=$_GET['fill']; //yes/no - fill whole image or not
if(!(($fill=="yes") or ($fill=="no"))) $fill="yes";
$always_create=($_GET['refresh']=="yes");
//***********************************Load and create image*******************************************
while(substr($pic,0,1)=="/"){$pic=substr($pic,1);}
if(!file_exists($pic)) $pic="images/cross.gif";
$img_info=IMgetimagesize($pic);
$img_w=$img_info[0];
$img_h=$img_info[1];
if($img_w==0 and $img_h==0) $image_magick_exists=false;//return original
if(!$image_magick_exists)
{
	header("Content-Length: ".filesize($pic));
	$fh=fopen($pic, "rb");
	$s=fread ($fh, filesize ($pic));
	fclose($fh);
	echo $s;
	exit();
}
if($h=="")
{
	$h=ceil(($w*$img_h)/$img_w);
}
elseif($w=="")
{
	$w=ceil(($img_w*$h)/$img_h);
}
$path_parts = pathinfo($pic);
$dir=$path_parts["dirname"];
$extension=".".$path_parts["extension"];
$fnm=basename($pic, $extension);

$thumb_dir = $dir.'/thumbs';

if(!is_dir($thumb_dir."/")) {
	if(!mkdir($thumb_dir,0777)) die("Can't make thumbs dir");
}
else
{
}

$rfn=$thumb_dir."/".$fnm."-".$w."x".$h."-".($fill=="yes"?"filled":"not_filled")."-".($enlarge=="yes"?"enlarged":"not_enlarged").$extension;
if(($enlarge=='no') and ($img_w<$w and $img_h<$h)) 
{
	copy ($pic, $rfn);
}
	if(file_exists($rfn)and (!$always_create))// and filemtime($pic)==filemtime($rfn))
	{
		header("Content-Length: ".filesize($rfn));
		$fh=fopen($rfn, "rb");
		$s=fread ($fh, filesize ($rfn));
		fclose($fh);
		echo $s;
		exit();
	}


if($fill=="yes")
{
	$r1=$w/$h;
	$r2=$img_w/$img_h;

	if($r1>=$r2)
	{

		$new_w=$w;
		$new_h=ceil($new_w*$img_h/$img_w);
		$off_y=0;
		$off_x=ceil(($new_h-$h)/2);
		$g=$w;
	}
	else
	{
		$new_h=$h;
		$g="x".$w;
		$new_w=ceil($img_w*$new_h/$img_h);
		$off_y=ceil(($new_w-$w)/2);
		$off_x=0;
	}
}
else
{
	if($img_w>$img_h)
	{
		$new_w=$w;
		$new_h=ceil($new_w*$img_h/$img_w);
	}
	else
	{
		$new_h=$h;
		$new_w=ceil($img_w*$new_h/$img_h);
	}
	$off_x=0;
	$off_y=0;
}
//***********************************Get new size aspects***************************************************

if($b=="") $b="#ffffff";
$s=$mp."convert -resize  ".$new_w."x".$new_h."! \"".$pic."\" \"".$rfn."\"";
exec($s);
$s=$mp."convert -crop ".$w."x".$h."+".$off_y."+".$off_x." \"".$rfn."\" \"".$rfn."\"";
exec($s);
$time=time();
$fh=fopen($rfn, "rb");
$s=fread($fh, filesize ($rfn));
fclose($fh);
echo $s;
exit();
function IMgetimagesize($filename)
{
	global $mp, $image_magick_exists;
	$x=$mp."identify -format \"%wx%hx%m\" \"".$filename."\"";
	exec($x, $ans);
	$ans=join("",$ans);
	$ans=explode("x",$ans);
	return $ans;
}
?>

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