User Guide

Glossary 323

open GOP Group of pictures whose B- and P-pictures can reference pictures from another

GOP. MPEG streams with open GOPs cannot be edited. Compare with closed GOP.

P-picture (Predictively Coded Picture). MPEG video picture that contains only the

information that is different from previous frames or ﬁelds. Each P-picture provides a

reference point for B-pictures and subsequent P-pictures in a GOP. See also B-picture, GOP,

I-picture.

PAL (Phase Alternate Line) Television standard used in Europe and most of the rest of the

world. PAL television uses 625 scan lines (576 are used for picture information) transmitted

at 25 frames (50 ﬁelds) per second. Compare with NTSC.

pan and scan Method for displaying widescreen (16:9) video on a standard (4:3) television

screen. The widescreen image is cropped to ﬁt the 4:3 aspect ratio. Compare with letterbox.

PCM (Pulse Code Modulation) Uncompressed digital audio format. The quality of PCM audio

depends both on the sample rate (a 48 kHz sample rate is better than 44.1 kHz) and on the

sample size (16-bits per sample is better than 8-bits).

PICT Graphics ﬁle format developed by Apple Computer, Inc.

pixel One of the dots that makes up a digital image. The resolution of an image is measured

in pixels (width x height).

pixel aspect ratio Ratio between a single pixel’s width and its height. This is usually

expressed as a decimal number.

Pixels on a computer monitor are square and have a pixel aspect ratio of 1. Pixels on a

television screen are rectangular: on a standard NTSC television, each pixel is slightly taller

than it is wide, with an aspect ratio of 0.9; on a standard PAL television, each pixel is slightly

wider than it is tall, for a pixel aspect ratio of 1.0666. This is why standard NTSC and PAL

televisions have the same 4:3 aspect ratio even though they use a different number of scan

lines.

For widescreen (16:9) televisions, the pixel aspect ratios are 1.2 for NTSC and 1.4222 for

PAL.

PNG (Portable Network Graphic) Lossless compressed bitmap graphics format. Files have

the extension .png.