Chapter 2. Video formats and quality
Video coding is the process of compressing and decompressing a digital video signal. This chapter examines the structure and characteristics of digital images and video signals and introduces concepts such as sampling formats and quality metrics. Digital video is a representation of a natural or real-world visual scene, sampled spatially and temporally. A scene is typically sampled at a point in time to produce a frame, which represents the complete visual scene at that point in time, or a field, which typically consists of odd- or even-numbered lines of spatial samples. Sampling is repeated at intervals (e.g. 1/25 or 1/30 second intervals) to produce a moving video signal. Three components or sets of samples are typically required to represent a scene in colour. Popular formats for representing video in digital form include the ITU-R 601 standard, High Definition formats and a set of 'intermediate formats'. The accuracy of a reproduction of a visual scene must be measured to determine the performance of a visual communication system, a notoriously difficult and inexact process. Subjective measurements are time consuming and prone to variations in the response of human viewers. Objective or automatic measurements are easier to implement but as yet do not accurately match the behaviour of a human observer.
Natural video scenes
A 'real world' or natural video scene is typically composed of multiple objects each with their own characteristic ...