cording to the Nyquist frequency criteria is 30 Hz in and design of digital signal processing systems. the case of television broadcast. Therefore any rapid Two-dimensional or spatial sampling is a simple intensity change (caused for instance by a moving edge) extension of the one-dimensional case. The Nyquist between two successive frames will cause aliasing criteria has to be obeyed in both dimensions, i.e., the because the harmonic frequency content of such a step- sampling rate in the horizontal direction must be two like function exceeds the Nyquist frequency. Temporal times greater than the upper frequency bound in the aliasing of this kind can be greatly mitigated in CCDs by horizontal direction, and the sampling rate in the vertical the use of low pass temporal filtering to remove the high direction must be two times greater than the upper frequency content. Photoconductor storage tubes are used frequency bound in the vertical direction. In practice, for recording broadcast television signals. They are analog spatial sampling grids are square SO that an equal number scanning devices whose electrical characteristics filter the of samples per unit length in each direction are collected. high frequency temporal content and minimize temporal Charge coupled devices (CCDs) are typically used to aliasing. Indeed, motion picture film also introduces low spatially sample analog imagery and video. The sampling pass filtering when capturing image frames. The exposure grid spacing of these devices is more than sufficient to speed and the response speed of the photo chemical film CHAPTER 7.. Video compression (a) Magnitude of Fourier Spectrum for input -3/2fs 1/2 fs -fB fB 1/2 fs (b) Magnitude of Fourier Spectrum for sampled input Is, with -3/2fs 3/2 fs (c) Magnitude of Fourier Spectrum for sampled input ls, with <2fB Figure 7.4-2 Nyquist sampling theorem. combine to mitigate high frequency content and 7.4.4.2 Digital video formats temporal aliasing. These factors cannot completely stop temporal aliasing, SO intellige