An orthonormal wavelet basis is an orthonormal basis of the form
B=
2j2ψ2jt−k
j∈Z and k∈Z
B
2
j
2
ψ
2
j
t
k
j
k
(1)
The function
ψt
ψ
t
is called the
wavelet.
The problem is how to find a function
ψt
ψ
t
so that the set BB is an
orthonormal set.
The Haar basis
(described by Haar in 1910) is an orthonormal
basis with wavelet
ψt
ψ
t
ψt={1 if 0≤t≤1/2-1 if 1/2≤t≤10 otherwise
ψ
t
1
0
t
12
-1
12
t
1
0
(2)
For the Haar wavelet, it is easy to verify that the set
BB is an orthonormal set (
Figure 1).
Notation:
ψ
j
,
k
t=2j2ψ2jt−k
ψ
j
,
k
t
2
j
2
ψ
2
j
t
k
where jj is an index of
scale and kk
is an index of location.
If BB is an orthonormal set then
we have the wavelet series.
xt=∑j=−∞∞∑k=−∞∞djk
ψ
j
,
k
t
x
t
j
k
d
j
k
ψ
j
,
k
t
(3)
djk=∫−∞∞xt
ψ
j
,
k
tdt
d
j
k
t
x
t
ψ
j
,
k
t