Trouble with image resize library.

[eluser]JasonS[/eluser]

Code:

$config['image_library'] = 'GD';
$config['source_image'] = $upload_dir.'portfolio/'.$this->upload->file_name;
$config['create_thumb'] = TRUE;
$config['maintain_ratio'] = TRUE;
$config['width'] = 75;
$config['height'] = 50;
$this->load->library('image_lib', $config);
            
$this->image_lib->resize();

I am trying to create a resized image which will be called imagename_thumb.ext

When I run the above code. Nothing happens, there is no error and certainly no image is created.

Am I missing something here?