Since the progress of animation industry, background layers are now replaced by CGI which also applies to 2D animation. Conventional 2D techniques are still used to create the main characters, but the film's backgrounds, such as buildings and trees, are modeled using 3D CGI. Since the film Mulan (1998), CGI has been used for crowd scenes and backgrounds and has been increasingly used to produce mainstream cartoons to this day. The advantage of this technique is that it made it easier to locate and adjust the camera during a shot, while the "multi-plane" system causes perspective distortion from the camera's tracking and zoom shots. Thus, CGI offers more freedom than the "old" system because the background is redrawn to fit the perspective of each frame (Mitchell, 2002)