Video Coding: An Introduction to Standard Codecs
From the ground up, this guide explains video coding algorithms to video compression systems, and more.
TABLE OF CONTENTS Video Coding: An Introduction to Standard Codecs
9.7: Coding of Still Images
9.7 Coding of Still Images
MPEG-4 also supports coding of still images with a high coding efficiency as well as spatial and SNR scalability. This coding method is compatible with the new method of coding of still images under the JPEG-2000 [14].
The coding principle is based on the discrete wavelet transform, which is a sub-class of sub-band coding. The lowest sub-band after quantisation is coded with a differential pulse code modulation (DPCM) and the higher bands with a novel technique, called zero-tree coding [15]. The quantised DPCM and zero-tree data are then entropy coded with an arithmetic encoder. Figure 9.21 shows a block diagram of the still image encoder.
Figure 9.21: Block Diagram of a Wavelet-Based Still Image Encoder
In the following sections each part of the encoder is described.
9.7.1 Discrete Wavelet Transform
Discrete wavelet transform, under the generic name of sub-band coding, was first introduced by Crochiere et al. in 1976 [16], and has since proved to be a simple and powerful technique for speech and image compression. The basic principle is the partitioning of the signal spectrum into several frequency bands, then coding and transmitting each band separately. This is particularly suited to image coding. Firstly, natural images tend to have a non-uniform frequency spectrum, with most of the energy being concentrated in the lower frequency band. Secondly, according to the human visual system, noise visibility tends to fall off at both high and low frequencies and this enables the designer to adjust...
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