tailieunhanh - Image and Videl Comoression P14

In this chapter, we introduce the fundamentals of digital video coding which include digital video representation, rate distortion theory, and digital video formats. Also, we give a brief overview of image and video coding standards which will be discussed in the subsequent chapters. DIGITAL VIDEO REPRESENTATION As we discussed in previous chapters, a digital image is obtained by quantizing a continuous image both spatially and in amplitude. Digitization of the spatial coordinates is called image sampling, while digitization of the amplitude is called gray-level quantization. Suppose that a continuous image is denoted by g(x, y), where the amplitude or value of. | Section IV Video Compression 2000 by CRC Press LLC 15 Fundamentals of Digital Video Coding In this chapter we introduce the fundamentals of digital video coding which include digital video representation rate distortion theory and digital video formats. Also we give a brief overview of image and video coding standards which will be discussed in the subsequent chapters. DIGITAL VIDEO REPRESENTATION As we discussed in previous chapters a digital image is obtained by quantizing a continuous image both spatially and in amplitude. Digitization of the spatial coordinates is called image sampling while digitization of the amplitude is called gray-level quantization. Suppose that a continuous image is denoted by g x y where the amplitude or value of g at the point x y is the intensity or brightness of an image at that point. The transformation of a conntinuous image to a digital image can then be expressed as f m n g g x0 mAx y0 nAy where Q is a quantization operator xo and yo are the origin of image plane m and n are the discrete values 0 1 2 . and Dx and Dy are the sampling intervals in the horizontal and vertical directions respectively. If the sampling process is extended to a third temporal direction or the original signal in the temporal direction is a discrete format a sequence f m n t is obtained as introduced in Chapter 10 f m n t g g x0 mAx y0 n Ay t0 1 At where t is the values 0 1 2 . and D t is the time interval. Each point of the image or each basic element of the image is called as a pixel or pel. Each individual image is called a frame. According to the sampling theorem the original continuous signal can be recovered exactly from its samples if the sampling frequency is higher than twice the bandwidth of the original signal Oppenheim and Schafer 1989 . The frames are normally presented at a regular time interval so that the eye can perceive fluid motion. For example the NTSC National Television Systems Committee specified a temporal sampling .