banks. We also discuss a number of topics, such as compactly supported wavelets,
biorthogonal wavelets, and wavelet lifting schemes, because they are useful in
applications. The concepts are first introduced in the context of one-dimensional
(1-D) signals and then extended to two-dimensional (2-D) signals and images.
7.1.1 Linear Transformations
Linear system theory plays an important role in wavelet theory. A signal or
function f (x) can often be better described, analyzed, or compressed if it is
transformed into another domain using a linear transform such as the Fourier
transform or a wavelet transform [3]. A signal f (x) can be expressed as a linear
combination of a set of basis functions:
f (x) ¼
X
j
c
j
c
j
(x)(7:1)
where j is an integer index, c
j
are