Graduate admissions are handled by the School of Computing. If you are interested in computer graphics, you can indicate it in the application form. It would be a good idea to include images and videos (as links to video sites like youtube or vimeo) from your prior graphics-related work and copies of papers you published or submitted (if any) with your application. Note that, for PhD applications, the graduate admissions committee would be particularly interested in knowing your desire and ability to participate in research activities.