losing quality after adding watermark to the picture - image

Question

I'm working on a website wich i haven't create/developed
Anyway users can upload image and when they do that , there's a function that create a duplicate of that image with a watermark
But the copy with the watermark has low quality and also it's size is much smaller than original image
I dont see anything lowering the quality , maybe it's how CI watermark works ?!
without watermark
http://img.akstube.ir/images/2013/05/DSC_0168_69_70_tonemapped.jpg
with watermark
http://img.akstube.ir/images/2013/05/irwm_DSC_0168_69_70_tonemapped.jpg
here is the function
function ir_watermark($file,$name='',$rebuild=FALSE)
{
$ci = &get_instance();
$pathinfo = pathinfo($file);
$filename = $pathinfo['basename'];
$path = $pathinfo['dirname'];
$new_image = $path . '/irwm_'. $filename;
$path_to_img = base_url(str_replace(base_path(),'',$new_image));
if ($rebuild == FALSE)
if (file_exists($new_image))
{
if ($ci->uri->segment(1) == 'test')
echo "<img src='{$path_to_img}' />";
return $path_to_img;
}
$config['source_image'] = $file;
$config['new_image'] = $new_image;
$config['wm_type'] = 'overlay';
$config['wm_overlay_path'] = base_path('/files/transparent_bar.png');
$config['wm_font_path'] = base_path('application/assets/view/tahomabd.ttf');
$config['wm_font_size'] = '8';
$config['wm_font_color'] = 'ffffff';
$config['wm_vrt_alignment'] = 'bottom';
$config['wm_hor_alignment'] = 'left';
$config['wm_hor_offset'] = '0';
$config['wm_vrt_offset'] = '0';
$ci->image_lib->initialize($config);
$ci->image_lib->watermark();
$config['new_image'] = $config['new_image'];
$config['source_image'] = $config['new_image'];
$config['wm_hor_offset'] = '10';
$config['wm_vrt_offset'] = '2';
$config['wm_overlay_path'] = base_path('/files/akstube_logo6.png');
$ci->image_lib->initialize($config);
$ci->image_lib->watermark();
$config['wm_type'] = 'text';
$config['wm_vrt_offset'] = '-3';
$config['wm_text'] = 'Photo : ' . $name;
$config['wm_text'] = strtoupper($config['wm_text']);
$config['wm_hor_alignment'] = 'right';
$config['wm_hor_offset'] = '-50%';
$ci->image_lib->initialize($config);
$ci->image_lib->watermark();
if ($ci->uri->segment(1) == 'test')
echo "<img src='{$path_to_img}' />";
return $path_to_img;
}
WATERMARK IMAGE
http://akstube.ir/files/akstube_logo6.png
http://akstube.ir//files/transparent_bar.png