
Exercises 157
multiplication of the column vector f
⊤
with the matrix
W =
h
0
h
1
h
2
h
3
0 0 0 0
h
3
−h
2
h
1
−h
0
0 0 0 0
0 0 h
0
h
1
h
2
h
3
0 0
0 0 h
3
−h
2
h
1
−h
0
0 0
0 0 0 0 h
0
h
1
h
2
h
3
0 0 0 0 h
3
−h
2
h
1
−h
0
h
2
h
3
0 0 0 0 h
0
h
1
h
1
−h
0
0 0 0 0 h
3
−h
2
.
(a) Prove that W is an orthonormal matrix (its inverse is equal to its
transpose).
(b) In the transformed vector W f
⊤
, the components of f
1
= Hf and
d
1
= Gf are interleaved. They can be sorted to give the vector (f
1
, d
1
).
When the matrix
W
1
=
h
0
h
1
h
2
h
3
h
3
−h
2
h
1
−h
0
h
2
h
3
h
0
h
1
h
1
−h
0
h
3
−h
2
is then applied to the smoothed vector (f
1
)
⊤
and the result again sorted,
we obtain the complete discrete wavelet transformation of f , namely
(f
2
, d
2