Background Information and Techniques - Computer Animation: Algorithms and Techniques - page 493

The common 1/2 00 video formats are VHS and S-VHS. S-VHS is a format in which the Y and C
signals are kept separate when played back, thus avoiding the problems created when the signals
are superimposed. All video equipment actually records signals this way, but S-VHS allows the Y signal
(luminance) to be recorded at a higher resolution than color. The color information is recorded with the
same fidelity as on VHS. In addition, the sound is encoded differently than on regular VHS, also result-
ing in greater fidelity. The advantages of S-VHS are especially pronounced when it is played back on an
S-VHS-compatible television.

B.10.2 In the digital world
Full-color (24 bits per pixel), video resolution (640 480), video rate (30 fps) animation requires

approximately 1.6 gigabytes of information per minute of animation when stored as uncompressed
RGB images. The problem is how to store and play back the animation. Various trade-offs must be
considered when choosing a format, including the amount of compression, the time it takes for the
compression/decompression, and the color and spatial resolution supported. The objective here is to
provide an overview of the terminology, the important issues, and the most popular standards in record-
ing animation. The discussion is at the level of consumer-grade technology and is not intended for
professionals involved in the production of high-quality digital material.
Digital video sometimes refers specifically to digital versions of video to be broadcast for reception
by television sets. In some literature this is also referred to as digital TV (DTV), which is the term used
here. On the other hand, digital video (DV) is also used in the sense of computer-generated moving
images intended to be played back on an RGB computer monitor. DV is used here to specifically denote
material intended to be displayed by a computer. These two categories of digital representations, DTV
and DV, have much in common. One of the most important common issues is the use of compression/
decompression (codec) technology described in the following paragraphs.
Standards related to DTV have two additional concerns. First, the standards are concerned with
images that will be encoded for broadcast. As a result, they rarely deal directly with RGB images. When
destined for television, digital images are at least partially encoded in a format related to the broadcast
video standard (NTSC) soon after they leave the camera (e.g., YUV). DTV has the advantage of encod-
ing a better image (480p) in less bandwidth than its analog counterpart. As a result, DTV can broadcast
additional information in the bandwidth given a channel.
Digital images synthesized for playback on a computer are typically generated as RGB images,
compressed for storage and transmission, and then decompressed for playback on RGB monitors. Sec-
ond, DTV standards are concerned with an associated recording format of the images and audio on
tape; tape is the common storage medium for broadcast video studios. Because images for computer
playback are typically stored digitally on a hard disk or removable disk, DV standards do not cover tape
formats. However, there are DV standards for file formats and for digital movies. Digital movie formats
organize the image and audio data into tracks with associated timing information.

Compression/decompression
The recent explosion in multimedia applications, especially as a result of the Web, has led to the devel-
opment of a variety of compression/decompression schemes [ 25 ] . After the frames of an animation are
computed, they are compressed and stored on a hard disk or CD-ROM. When playback of the animation
is requested, the compressed animation is sent to the compute box, using disk I/O or over the Web, where
the frames are decompressed and displayed. The decompression and playback can take place in real time