Glossary

Palettized textures
A form of texture compression. Used to reduce the size of a texture when the texture does not have many unique colors. 4-bit palletized textures can have 16 (2^4) different colors. 8-bit palletized textures can have 256 (2^8) different colors.

PAL format
Phase Alternation Line; the European standard color television system, except for France. PAL's image format is 4:3, 625 lines, 50 Hz and 4-MHz video bandwidth with a total 8 MHz of video channel width. PAL uses YUV. See also NTSC, SECAM.

Parallel Port
A parallel interface for connecting an external device such as a printer. Also known as a Centronics Port which was developed by the Centronics Corporation, However the Parallel Ports as they are today was enhanced by Epson Corp. Most personal computers have both a parallel port and at least one serial port. On PCs, the parallel port uses a 25-pin connector (type DB-25) and is used to connect printers, computers and other devices that need relatively high bandwidth. A newer type of parallel port, which supports the same connectors as the Centronics interface, is the EPP (Enhanced Parallel Port) or ECP (Extended Capabilities Port). Both of these parallel ports support bi-directional communication and transfer rates ten times as fast as the Centronics port. Macintoshes have a SCSI port, which is parallel, but more flexible.

Parameter
A variable that may take one of many values. See also flag.

Past reference picture
A reference picture that occurs at an earlier time than the current picture in display order.

PCI
Acronym for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. Many analysts, however, believe that PCI will eventually replace ISA entirely. PCI is also used on newer versions of the Macintosh computer.

PCI is a 64-bit bus, though it is usually implemented as a 32-bit bus. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps. Although, it was developed by Intel, PCI is not tied to any particular family of microprocessors.

Pel aspect ratio
The ratio of a pel's nominal vertical height to its nominal horizontal width.

Pel
Picture element.

Perspective correction
A technique that is used to give the proper illusion of depth when pictures are texture mapped onto polygons. Without perspective correction, warping will occur and the resulting image will not look realistic.

PhotoYCC color space
For Kodak's PhotoCDtm, similar to YCbCr.

Picture
Source, coded, or reconstructed image data. A source or reconstructed picture consists of three rectangular matrices of 8-bit numbers representing luminance and two chrominance signals. For progressive video, a picture is identical to a frame, while for interlaced video, a picture can refer to a frame, a top field, or a bottom field depending on the context.

Pixel
An abbreviation of picture element; the minimum raster display element, represented as a point with a specified color or intensity level. One way to measure picture resolution is by the number of pixels used to create images.

Post-production
The stage in the preparation of a film or video program after the original footage has been shot. Can include editing, encoding, computer program authoring, etc.

P-Picture (Predictive-coded picture)
A picture that is coded using motion compensated prediction from past reference pictures. See also motion compensation.

Prediction
The process of estimating the pel value or data element currently being decoded using a predictor.

Prediction error
The difference between the actual value of a pel or data element and its predictor.

Predictor
A linear combination of previously decoded pel values or data elements.

Pre-production
All design tasks (flow-charting, story-boarding, script-writing, software design, etc.) that lead up to the actual shooting of material on video or film, or up to the authoring of multimedia software.

Production
In video terms, the period when video or film footage is actually shot. See also pre-production, post-production.

Profile
A defined subset of a specification's syntax.