Techniques for Frame Buffer Animation

Frame buffer animation creates the illusion of limited real-time animation with static pic­ tures stored in the image memory of a digital frame buffer. Hardware features in the output video chain such as the video controller, the crossbar switch, and the colour tables allow tech­ niques like zoom-pan-scroll animation, crossbar animation, three forms of colour table animation, and various combinations. These techniques, the hardware required to implement them, their application to low-cost systems such as Telidon, and future hardware and software enhancements are discussed. In tro d u c tio n l Animation is a technique for creating the illusion of motion with a series of static “images” . The motivation for using animation is suggested by a secondary definition for “animation": imparting interest or zest and the enlivening of images [8], Throughout this essay we will think of animation not as an alternative to live action filming, but as a means for improving an other­ wise static presentation. Traditional forms of animation such as cel animation and three dimensional model anima­ tion are highly labour intensive tasks and thus very expensive. The use of computers to reduce the effort in the creation of in-between frames, in inking cels, and in the manipulation and simula­ tion of three dimensional models is the subject of much current research. Various surveys, (16], [9] and (5], provide a more complete description of traditional and computer animation. We will restrict attention to the specific goal of using digital frame buffers to achieve real-time playback of an animation sequence. Ron Baecker has already championed the proposition that dynamic graphics is no longer the sole domain of calligraphic systems, but he observed that “current frame buffers are unsuited to dynamic imagery” because of the requirement, inherent in frame buffer architecture, that changes to the image require explicit modification of pixels in memory (3, p. 54). The amount of compu­ tation required for major changes, coupled with the need to synchronize those changes with video generation, have precluded full real-time animation. The term frame buffer animation refers to a class of animation techniques that make use of digital frame buffers to enhance static images through the illusion of real-time motion. The trick is that the image stored in the memory of the frame buffer remains entirely unchanged once created. Dynamics are added by modifying the pattern in which pixels are read from memory and the way in which their bits are interpreted. Frame buffer animation provides some degree of interactive control over the playback of an animated sequence because an intermediate medium, such as film or video tape, is not necessary. As well, frame buffer animation is cheaper than performing “real” animation, not because the