Quality loss in resized image

<?  
 /* 
#  * usage: 
#  * resize.php [destination_width] [destination_height] 
#  * 
#  * destination_width and destination_height are optional 
#  * parameters for destination resize geometry 
#  * 
#  * resize.php will create output directory to save resized 
#  * images leaving originals intact 
#  * 
#  * This script uses "identify" and "convert" utilities which 
#  * are members of the ImageMagick suite of tools 
#  * 
#  */  
   
# // input arguments for destination image size  
 $w2 = $argv[1]; // image width  
 $h2 = $argv[2]; // image height  
#   
# // both values should be numeric or use default size 800x600  
 if (!is_numeric($w2) || !is_numeric($h2)){  
   $w2 = 150; // default image width  
   $h2 = 190; // default image height  
 }  
   
# // prepare directory name for saving resized images  
# // directory name will look like "_800x600"  
 $dir = "Image";  
#   
# // create directory (inside current directory) for saving  
# // resized images (@ means to be quiet - don't display  
# // warning if directory alredy exists)  
 @mkdir($dir); 
 
#   
# // read files inside current directory  
 $files = scandir('.');  
#   
# // open loop for all fetched files in current directory  
 foreach ($files as $file){  
#   // convert file name to lower case  
   $file_lowercase = strtolower($file);  
#   // if file extension is jpg then process image  
   if (substr($file_lowercase, -3) == 'jpg'){  
#     // describe image format and image characteristics  
     $identify = shell_exec("identify $file");  
#     // read image geometry  
     preg_match('/(\d+)x(\d+)/', $identify, $matches);  
     $g1 = $matches[0]; // image geometry  
     $w1 = $matches[1]; // image width  
     $h1 = $matches[2]; // image height  
#     // prepare destination image geometry  
     if ($w1 < $h1) $g2 = $h2 .'x' .$w2;  
     else           $g2 = $w2 .'x' .$h2;  
#     // print current image status  
     print "$file ($g1) -> $dir/$file_lowercase ($g2)\n";  
#     // resize image and save to destination directory  
     system("convert -size $g1 $file -resize $g2 $dir/$file_lowercase");  
   }  
 }  
# ?>

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