window fourier and wavelet transforms. properties and applications of the wavelets. a.s. yakovlev
TRANSCRIPT
Window Fourier and wavelet transforms.
Properties and applications of the wavelets.
A.S. Yakovlev
Contents
1. Fourier Transform2. Introduction To Wavelets3. Wavelet Transform4. Types Of Wavelets5. Applications
Window Fourier TransformOrdinary Fourier Transform
Contains no information about time localization
Window Fourier Transform
Where g(t) - window functionIn discrete form
1( ) ( )
2i tFf f t e dt
win ( , ) ( ) ( ) i tT f s f t g t s e dt
win, 0( ) ( ) i t
m nT f f t g t ns e dt
Window Fourier Transform
Window Fourier TransformExamples of window functions
Hat function
Gauss function
Gabor function 0
0 22
( )1( ) exp ( ) exp
22
t tg t i t t i
2
0
2 2)(
exp2
1)(
tt
tg
1,0
]1,0[,1
0,0
xg
xg
xg
Window Fourier TransformExamples of window functions
Gabor function
Fourier Transform
Window Fourier Transform
Window Fourier TransformDisadvantage
Multi Resolution Analysis MRA is a sequence of spaces {Vj} with
the following properties:1. 2. 3. 4. If 5. If 6. Set of functions where
defines basis in Vj
1 jj VV
Zj j RLV
2
Zj jV
0
1)2()( jj VtfVtf
jj VktfVtf )()(
kj ,)2(2 2/
, ktjjkj
Multi Resolution Analysis
Multi Resolution Analysis Definitions
Father function basis in V Wavelet function basis in WScaling equationDilation equationFilter coefficients hi , gi
)2(2 2/, ktjjkj
( ) (2 )ii Z
x h x i
1
( ) 2 (2 )
( 1)
ii Z
ii L i
x g x i
g h
Zi
Continuous Wavelet Transform (CWT)
wave 1/ 2( , ) | | ( )t b
T f s a f t dta
wave( ) ( , )t b
f t T f s d dsa
Direct transform
Inverse transform
Discrete Wavelet DecompositionFunction f(x)
Decomposition
We want
In orthonormal case
2 1
, ,0
( ) ( )j
j k j k jk
f t s t V
1 2 1 2 1
, , , ,0 0
( ) ( ) ( )j LJ
j k j k L k L kj L k k
f t w t s t
, ,
, ,
( ) ( )
( ) ( )
j k j k
j k j k
s f t t dt
w f t t dt
Discrete Wavelet Decomposition
0321
0121
WWWW
VVVVV
nnn
nnn
Fast Wavelet Transform (FWT) Formalism
In the same way
, , 2 1,
2 , 2 1,
( ) ( ) ( ) ( )
( ) ( )
j k j k l k j ll Z
l k j k l k j ll Z l Z
w f t t dt f t g t
g f t t dt g s
, 2 1,j k l k j ll Z
s h s
Fast Wavelet Transform (FWT)
1,0 0,0
1,1 0,1
1,2 0,2 0,0 0,0
1,3 0,3 0,1 0,1
1,4 0,0 0,2 0,2
1,5 0,1 0,3 0,3
1,6 0,2
1,7 0,3
s s
s s
s s s w
s s s wT
s w s w
s w s w
s w
s w
Fast Wavelet Transform (FWT) Matrix notation
0 1 2 3
0 1 2 3
0 1 2 3
0 1 2 3
2 3 0 12
0 1 2 3
0 1 2 3
0 1 2 3
0 1 2 3
2 0 0 1
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
D
h h h h
h h h h
h h h h
h h h h
h h h hT
g g g g
g g g g
g g g g
g g g g
g g g g
Fast Wavelet Transform (FWT) Matrix notation
0 2 0 2
1 3 1 3
2 0 2 0
3 1 3 1
2 0 2 02 2
3 1 3 1
2 0 2 0
3 1 3 1
2 0 2 0
3 1 3 1
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
rev tD D
h h g g
h h g g
h h g g
h h g g
h h g gT T
h h g g
h h g g
h h g g
h h g g
h h g g
Fast Wavelet Transform (FWT) Note
FWT is an orthogonal transform
It has linear complexity
1
*
rev t
rev
T T T
T T I
Conditions on wavelets
1. Orthogonality:
2. Zero moments of father function and wavelet function:
2 , k k l lk Z
h h l Z
( ) 0,
( ) 0.
ii
ii
M t t dt
t t dt
Conditions on wavelets
3. Compact support:Theorem: if wavelet has nonzero coefficients with only indexes from n to n+m the father function support is [n,n+m].
4. Rational coefficients.5. Symmetry of coefficients.
Types Of WaveletsHaar Wavelets
1. Orthogonal in L2
2. Compact Support3. Scaling function is symmetric
Wavelet function is antisymmetric
4. Infinite support in frequency domain
Types Of WaveletsHaar WaveletsSet of equation to calculate coefficients:
First equation corresponds to orthonormality in
L2, Second is required to satisfy dilation
equation.
Obviously the solution is
2 20 1
0 1
1
2
h h
h h
0 1
1
2h h
Types Of WaveletsHaar Wavelets
Theorem: The only orthogonal basis with the symmetric, compactly supported father-function is the Haar basis.
Proof:Orthogonality:For l=2n this is For l=2n-2 this is
1 0 0 1[..., ,..., , , , ,..., ,...]n nh a a a a a a
2 0, if 0.k k lk Z
h h l
1 1 0,n n n na a a a
3 1 2 2 1 3 0.n n n n n n n na a a a a a a a
Types Of WaveletsHaar WaveletsAnd so on. The only possible sequences are:
Among these possibilities only the Haar filterleads to convergence in the solution of
dilationequation.End of proof.
1 1[...,0,0, ,0,0,0,0,0,0, ,0,0,...]
2 2
Types Of WaveletsHaar WaveletsHaar a)Father function and B)Wavelet
function
a) b)
Types Of WaveletsShannon Wavelet
Father function
Wavelet functionx
xxx
)sin(
)(sinc)(
xxx
)sin()2sin(
Types Of WaveletsShannon Wavelet
Fourier transform of father function
Types Of WaveletsShannon Wavelet
1. Orthogonal2. Localized in frequency domain3. Easy to calculate4. Infinite support and slow decay
Types Of WaveletsShannon Wavelet
Shannon a)Father function and b)Wavelet function
a) b)
Types Of WaveletsMeyer Wavelets
Fourier transform of father function
Types Of WaveletsDaubishes Wavelets
1. Orthogonal in L2
2. Compact support3. Zero moments of father-function
( ) 0iiM x x dx
Types Of WaveletsDaubechies Wavelets
First two equation correspond to orthonormality
In L2, Third equation to satisfy dilation
equation, Fourth one – moment of the father-function
2 2 2 20 1 2 3
0 2 1 3
0 1 2 3
1 2 3
1
0
2
2 3 0
h h h h
h h h h
h h h h
h h h
Types Of WaveletsDaubechies Wavelets
Note: Daubechhies D1 wavelet is Haar Wavelet
Types Of WaveletsDaubechies Wavelets
Daubechhies D2 a)Father function and b)Wavelet function
a) b)
Types Of WaveletsDaubechies Wavelets
Daubechhies D3 a)Father function and b)Wavelet function
a) b)
Types Of WaveletsDaubechhies Symmlets
(for reference only)Symmlets are not symmetric!They are just more symmetric than
ordinary Daubechhies wavelets
Types Of WaveletsDaubechies Symmlets
Symmlet a)Father function and b)Wavelet function
a) b)
Types Of WaveletsCoifmann Wavelets (Coiflets)
1. Orthogonal in L2
2. Compact support
3. Zero moments of father-function
4. Zero moments of wavelet function
( ) 0iiM x x dx
( ) 0ii x x dx
Types Of WaveletsCoifmann Wavelets (Coiflets)
Set of equations to calculate coefficients2 2 2 2
2 1 0 1 2 3
2 0 1 1 0 2 1 3
2 2 1 3
2 1 0 1 2 3
2 1 1 2 3
2 1 1 2 3
1
0
0
2
2 2 3 0
2 2 3 0
h h h h h h
h h h h h h h h
h h h h
h h h h h h
h h h h h
h h h h h
Types Of WaveletsCoifmann Wavelets (Coiflets)
Coiflet K1 a)Father function and b)Wavelet function
a) b)
Types Of WaveletsCoifmann Wavelets (Coiflets)
Coiflet K2 a)Father function and b)Wavelet function
a) b)
How to plot a function
Using the equation ( ) (2 )ii Z
x h x i
How to plot a function
Applications of the wavelets
1. Data processing2. Data compression3. Solution of differential equations
“Digital” signal
Suppose we have a signal:
“Digital” signalFourier method
Fourier spectrum Reconstruction
“Digital” signalWavelet Method
8th Level Coefficients Reconstruction
“Analog” signal
Suppose we have a signal:
“Analog” signalFourier Method
Fourier Spectrum
“Analog” signalFourier Method
Reconstruction
“Analog” signalWavelet Method
9th level coefficients
“Analog” signalWavelet Method
Reconstruction
Short living stateSignal
Short living stateGabor transform
Short living stateWavelet transform
Conclusion
Stationary signal – Fourier analysisStationary signal with singularities –
Window Fourier analysisNonstationary signal – Wavelet
analysis
Acknowledgements
1. Prof. Andrey Vladimirovich Tsiganov
2. Prof. Serguei Yurievich Slavyanov