Computer Animation 451-113 Introduction to Computer Graphics and Systems
Principles of Animation • The real world is continuous and analogue • We perceive movement through changing scale and differential parallax • In order to reproduce this we need to ‘sample’ the real world, and to exploit properties of the human viewing system
The Human Eye • Our retina retains a latent image for about 1/15 second • If we can view a series of images faster than this, we will perceive this as fluid movement • A lesser frequency (or frame rate) and will will see this as jerky
Background • Humankind has used illustrations and movement to explain stories for millennia • shadows on cave walls • wayang puppets • lines in the sand
The Industrial Revolution • Science and technology facilitated the reproduction of movement • Before photography, artists drew sequences of images and we observed then through a device to simulate movement • After the 1830s, photography took over this role from artists
Edweard Muybridge • Often credited with being the inventor of motion pictures • Studied the gait of humans and animals using a camera and a moving stage
Movie Animation • Walt Disney set the standard for cartoon animation of characters, Steamboat Willie released in 1928 • Once again artists drew key frames, and cheaper labour filled in the missing frames (inbetweening, a term we still use)
Information Revolution • Mechanical and manual methods of animation are replaced by computer systems • Computer graphics packages are now used to create rendered frames, artists still supply creative input
Animation Methods • Animated GIFs • Flythoughs • Keyframes • Parametric • Motion Capture
Animated GIFs • Basically the same approach as a flip book • A series of GIF images are played sequentially • The basis of Web animation • small, fast
Software Systems • MicroStation permits flythroughs and keyframing, with some script control • Better systems use all methods • It is a very involved process if it is to appear realistic
Flythrough Animation • For a flythrough, only the camera is moved • All other elements remain stationery, including the objects, lighting, materials and so on • Generally, a camera path is determined, the number of frames decided, and the rendering method set
Keyframe Animation • In this case the key frames are determined • this includes materials, lights, objects, camera position • The number of frames between the keyframes are determined • The system then generated the in between frames (inbetweening!)
Parametric Animation • A set of behaviours are determined for each object to be animated • These are then used to generate the animations • Good for repeated sequences • a flock of birds, water, rain drops… • often achieved by the use of ‘plugins’ (3DMax)
Video Systems • There are 3 common video systems used in the world, SECAN, NTSC and PAL • In Australia we use PAL • 760x576± resolution, 25 frames per second • We need to use this if our animations are written to video tape • If not, anything goes!
Codecs • Short for compressors/decompressors • Used to reduce the final file size • full frame video at 25Hz = 30Mb/s±! • very few graphics cards can reproduce this • the Internet certainly cannot • Common ones include MicroSoft Video (for AVI), MPEG, Quicktime, Real Video...
Web Delivery • Prerecorded video can be delivered across the Internet only if it is compressed • ‘Streaming’ is possible with some formats but not with MPEG • Another approach to deliver animation is to produce VRML files • gives interactivity and movement
Virtual Reality Modelling Language (VRML) • Delivers 3d geometry over the Internet, as well as animations • Gives the user a degree of interactivity • Support in the industry varies • SGI Cosmoplayer now defunct • Cortona VRML a new release • see example
Summary • Good computer animation is difficult • However modern computers give people a viable outlet for their creative bent • A flythrough of a block of cheese is just the beginning!