Databases Reference
In-Depth Information
Lossless Image Compression
7.1 Overview
In this chapter, we examine a number of schemes used for lossless compression
of images. We will look at schemes for compression of grayscale and color
images as well as schemes for compression of binary images. Among these
schemes are several that are a part of international standards.
7.2 Introduction
To this point in the topic, we have focused on compression techniques. Although some of them
may apply to some preferred applications, the focus has been on the technique rather than on
the application. However, there are certain techniques for which it is impossible to separate
the technique from the application. This is because the techniques rely upon the properties or
characteristics of the application. Therefore, we have several chapters in this topic that focus
on particular applications. In this chapter, we will examine techniques specifically geared
toward lossless image compression. Later chapters will examine speech, audio, and video
compression.
In earlier chapters, we observed that a more skewed set of probabilities for the message
being encoded results in better compression. In Chapter 6, we saw how the use of context
to obtain a skewed set of probabilities can be especially effective when encoding text. We
can also transform the sequence (in an invertible fashion) into another sequence that has the
desired property in other ways. For example, consider the following sequence:
