PAL (Phase Alternating Line)

European video standard with image format 4:3, 625 lines, 50 Hz and 4 Mhz video bandwidth with a total 8 Mhz of video channel width. PAL uses YUV.

Parameter

A variable which may take one of a large range of values. A variable which can take one of only two values is a flag and not a parameter.

Past reference picture

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

PCM (Pulse Code Modulation)

Coding where input signal is represented by a given number of fixed-width samples per second. Often used for the coding employed in the telephone network.

Pel aspect ratio

The ratio of the nominal vertical height of pel on the display to its nominal horizontal width.

Pel

Picture element.

Picture

Source, coded or reconstructed image data. A source or reconstructed picture consists of three rectangular matrices of 8-bit numbers representing the 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, the top field or the bottom field of the frame depending on the context.

Prediction

The use of a predictor to provide an estimate of the pel value or data element currently being decoded.

P-Picture (Predictive-coded picture)

A picture that is coded using motion compensated prediction from past reference pictures.

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.

Profile

A defined sub-set of the syntax of a specification.