这是我的创建缩略图代码。缩略图宽度/高度较小 (400)。但文件大小更大（111KB），旧文件大小（95KB）
为什么？如何压缩和缩小文件大小？
create_thumbnail( 'http://upload.wikimedia.org/wikipedia/en/2/2e/Doraemon_first_appearance.jpg', './test.jpg', 400,'w','jpg' );
function create_thumbnail( $source_file, $destination_file, $max_dimension, $one_dimension=false,$source_file_type=false)
{
list($img_width,$img_height) = getimagesize($source_file); // Get the original dimentions
$aspect_ratio = $img_width / $img_height;
// If either dimension is too big...
if ( ($img_width > $max_dimension) || ($img_height > $max_dimension) )
{
if ( $img_width > $img_height ) // For wide images...
{
if($one_dimension=='h')
{
$new_width = $img_width * $max_dimension / $img_height;
$new_height = $max_dimension;
}
else
{
$new_width = $max_dimension;
$new_height = $new_width / $aspect_ratio;
}
}
elseif ( $img_width < $img_height ) // For tall images...
{
if($one_dimension=='w')
{
$new_width = $max_dimension;
$new_height = $img_height * $max_dimension / $img_width;
}
else
{
$new_height = $max_dimension;
$new_width = $new_height * $aspect_ratio;
}
}
elseif ( $img_width == $img_height ) // For square images...
{
$new_width = $max_dimension;
$new_height = $max_dimension;
}
else { echo "Error reading image size."; return FALSE; }
// Make sure these are integers.
$new_width = intval($new_width);
$new_height = intval($new_height);
$thumbnail = imagecreatetruecolor($new_width,$new_height); // Creates a new image in memory.
// The following block retrieves the source file. It assumes the filename extensions match the file's format.
if(!$source_file_type) $source_file_type = get_file_ext($source_file,true);
if ( $source_file_type=="gif" ) { $img_source = ImageCreateFromGIF($source_file); }
elseif ( ($source_file_type=="jpg") || ($source_file_type=="jpeg") || ($source_file_type=="pjpeg") ) { $img_source = imagecreatefromjpeg($source_file); }
elseif ( $source_file_type=="bmp" ) { $img_source = imagecreatefromwbmp($source_file); }
elseif ( $source_file_type=="png" ) { $img_source = imagecreatefrompng($source_file); }
// Here we resample and create the new jpeg.
imagecopyresampled($thumbnail, $img_source, 0, 0, 0, 0, $new_width, $new_height, $img_width, $img_height);
imagejpeg( $thumbnail, $destination_file, 100 );
// Finally, we destroy the two images in memory.
imagedestroy($img_source);
imagedestroy($thumbnail);
}
// If it's already smaller, don't change the size.
else {
copy($source_file, $destination_file);
}
}