用GD库生成高质量的缩略图片

$FILENAME="image_name";   
  
// 生成图片的宽度   
$RESIZEWIDTH=400;   
  
// 生成图片的高度   
$RESIZEHEIGHT=400;   
  
  
function ResizeImage($im,$maxwidth,$maxheight,$name){   
    $width = imagesx($im);   
    $height = imagesy($im);   
    if(($maxwidth && $width > $maxwidth) || ($maxheight && $height > $maxheight)){   
        if($maxwidth && $width > $maxwidth){   
            $widthratio = $maxwidth/$width;   
            $RESIZEWIDTH=true;   
        }   
        if($maxheight && $height > $maxheight){   
            $heightratio = $maxheight/$height;   
            $RESIZEHEIGHT=true;   
        }   
        if($RESIZEWIDTH && $RESIZEHEIGHT){   
            if($widthratio < $heightratio){   
                $ratio = $widthratio;   
            }else{   
                $ratio = $heightratio;   
            }   
        }elseif($RESIZEWIDTH){   
            $ratio = $widthratio;   
        }elseif($RESIZEHEIGHT){   
            $ratio = $heightratio;   
        }   
        $newwidth = $width * $ratio;   
        $newheight = $height * $ratio;   
        if(function_exists("imagecopyresampled")){   
              $newim = imagecreatetruecolor($newwidth, $newheight);   
              imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);   
        }else{   
            $newim = imagecreate($newwidth, $newheight);   
              imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);   
        }   
        ImageJpeg ($newim,$name . ".jpg");   
        ImageDestroy ($newim);   
    }else{   
        ImageJpeg ($im,$name . ".jpg");   
    }   
}   
  
  
if($_FILES['image']['size']){   
    if($_FILES['image']['type'] == "image/pjpeg"){   
        $im = imagecreatefromjpeg($_FILES['image']['tmp_name']);   
    }elseif($_FILES['image']['type'] == "image/x-png"){   
        $im = imagecreatefrompng($_FILES['image']['tmp_name']);   
    }elseif($_FILES['image']['type'] == "image/gif"){   
        $im = imagecreatefromgif($_FILES['image']['tmp_name']);   
    }   
    if($im){   
        if(file_exists("$FILENAME.jpg")){   
            unlink("$FILENAME.jpg");   
        }   
        ResizeImage($im,$RESIZEWIDTH,$RESIZEHEIGHT,$FILENAME);   
        ImageDestroy ($im);   
    }   
}   
  
?>   
  
<img src="<? echo($FILENAME.".jpg?reload=".rand(0,999999)); ?>"><br/><br/>   
  
<form enctype="multipart/form-data" method="post">   
<br/>   
<input type="file" name="image" size="50" value="浏览"><p>   
<input type="submit" value="上传图片">   
</form>    
  
</body>   
</html>