information is generated by sampling the formance capabilities are changing at a rapid pace intensity of the original continuous analog video signal and the choice of the best solution requires careful I(x, y, t) in three dimensions. The spatial component of analysis of the all possible system and encoder the video signal is sampled in the horizontal and vertical alternatives. dimensions (x, y), and the temporal component is sam- Rate-distortion requirements - The rate-distortion pled in the time dimension (t). This generates a series of requirement is a basic consideration in the selection digital images or image sequence 1(i, j, k). Video signals of the video encoder. The video encoder must be that contain color information are usually decomposed able to provide the bit rate(s) and video fidelity (or into three parameters (YCCb, YUV, RGB, etc.) whose range of video fidelity) required by the application. intensities are likewise sampled in three dimensions. The Otherwise, any aspect of the system may not meet sampling process inherently quantizes the video signal specifications. For example, if the bit rate specifica- due to the digital word precision used to represent the tion is exceeded in order to support a lower MSE, intensity values. Therefore the original analog signal can a larger than expected transmission error rate may never be reproduced exactly, but for all intents and cause a catastrophic system failure. purposes, a high-quality digital video representation can Standards requirements - Video encoder compati- be reproduced with arbitrary closeness to the original bility with existing and future standards is an analog video signal. important consideration if the digital video system is An important result of sampling theory is the Nyquist required to inter-operate with existing and/or future sampling theorem. This theorem defines the conditions systems. A good example is that of a desktop video- under which sampled analog signals can be "perfectly" conferencing application supporting a number of reco