gd2 image resizing library in codeigniter

1How to resize image in php codeigniter
2
3    // Configuration.
4    $config['image_library'] = 'gd2';
5    $config['source_image'] = './img/images/uploaded/'.$ imgName.". jpeg";
6    $config['new_image'] = './img/images/uploaded/'.$ imgName." _new.jpeg";
7    $config['create_thumb'] = TRUE;
8    $config['maintain_ratio'] = TRUE;
9    $config['width'] = 50;
10    $config['height'] = 50;