not getting exact width and height in thumb image

[eluser]ratna[/eluser]
i have following code. i have here width and height 50 each. but in thumb image i didn't get the same width and height. it is always lesser than the 50. i want thumb to have exact 50 width and height. please suggest.

$config['image_library'] = 'gd2';
$config2['source_image'] = './uploads1/plane.jpg';
$config2['create_thumb'] = TRUE;
$config2['maintain_ratio'] = TRUE;

$config2['width'] = 50;

$config2['height'] = 50;

$this->load->library('image_lib', $config2);

$this->image_lib->resize();