Glen Keane originally wanted the film to be animated using a traditional 2D animation process. However, Disney executives David Stainton and Dick Cook announced that they would only approve the film for production if it were created using the 3D computer graphics. In response to that demand, Glen Keane held a seminar called ""The Best of Both Worlds"", where he, with 50 Disney CGI artists and traditional artists, focused on the pros and cons of each style. After the meeting, it was decided that the film would be made in 3D CG animation, but in a way as to become an extension of the traditional 2D Disney "aesthetic", a term which referred to the naturalistic animation that conforms to the fundamental principles of animation as documented by Frank Thomas and Ollie Johnston in the book "The Illusion of Life: Disney Animation".