wavelets: theory and applications - central university of...
TRANSCRIPT
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Wavelets: Theory and Applications
Somdatt Sharma
Department of Mathematics,Central University of Jammu,Jammu and Kashmir, India
Email:[email protected]
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Contents I
1 Representation of Functions
2 Fourier AnalysisFourier TransformBasic properties of Fourier transform
3 Gabor AnalysisLimitations of STFT
4 Wavelet AnalysisExamplesContinuous Wavelet transform
5 References
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
The simplest method to represent a function is to use point sampling. Inthe one dimensional case a real function of one-variable f : I ⊂ R→ R isdiscretized by taking a partition t1 < t2 < · · · < tn of the domain intervalI. The representation is given by the vector
fn =(f(t1), f(t2), . . . , f(tn)
)∈ Rn
.In this way, the space of real functions defined on the interval I isrepresented by the Euclidean space Rn.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Fourier series
A Fourier series may be defined as an expansion of a 2π-periodic functionf in series by sines and cosines and is given by
f(x) = a0 +
∞∑k=1
(ak cos kx+ bk sin kx)
where
ak =1
π
∫ π
−πf(x) cos kxdx k = 0, 1, . . .
and
bk =1
π
∫ π
−πf(x) sin kxdx k = 0, 1, . . .
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Example 1
Let f(x) = x, x ∈ [−π, π]. Then the Fourier series of the given functionis given by
f(x) = 2
[sinx− sin
2x
2+ sin
3x
3− · · ·
]S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Example 2
Let f(x) = x2, x ∈ [−π, π]. Then the Fourier series of the given functionis given by
f(x) = 2
[π2
3+ 4
∞∑n=1
(−1)n
n2cosnx
]S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Fourier transform
The Fourier transform of any function f(x) ∈ L2(R) is given by
F(ξ) = f(ξ) =
∫ ∞−∞
f(t)e−iξtdt
and its Inverse Fourier transform is
f(t) =1
2π
∫ ∞−∞
f(ξ)eiξtdξ.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Example(Characteristic function)
Consider the function
f(t) =
1 |t| ≤ a
0 |t| > a, a > 0.
Then the Fourier transform f(ξ) of f(t) is given by
f(ξ) =
∫ ∞−∞
f(t)e−iξtdt =2 sin aξ
ξ.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Characteristic function and its Fourier transform
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Gaussian function and its Fourier transform
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Let f, g ∈ L1(R) and α, β be any two complex constants. Then thefollowing properties of Fourier transform hold:
1 Linearity:
F [αf(t) + βg(t)] = F [αf(t)] + F [βg(t)] = αf(ξ) + βg(ξ).
2 Time shift → frequency modulation:
F [Taf(t)] = F [f(t− a)] = e−iaξ f(ξ) =M−af(ξ).
3 Scaling: For a 6= 0,
F
D1
a
f(t)
= Daf(ξ) =1√af
(ξ
a
).
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Let f, g ∈ L1(R) and α, β be any two complex constants. Then thefollowing properties of Fourier transform hold:
1 Linearity:
F [αf(t) + βg(t)] = F [αf(t)] + F [βg(t)] = αf(ξ) + βg(ξ).
2 Time shift → frequency modulation:
F [Taf(t)] = F [f(t− a)] = e−iaξ f(ξ) =M−af(ξ).
3 Scaling: For a 6= 0,
F
D1
a
f(t)
= Daf(ξ) =1√af
(ξ
a
).
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Let f, g ∈ L1(R) and α, β be any two complex constants. Then thefollowing properties of Fourier transform hold:
1 Linearity:
F [αf(t) + βg(t)] = F [αf(t)] + F [βg(t)] = αf(ξ) + βg(ξ).
2 Time shift → frequency modulation:
F [Taf(t)] = F [f(t− a)] = e−iaξ f(ξ) =M−af(ξ).
3 Scaling: For a 6= 0,
F
D1
a
f(t)
= Daf(ξ) =1√af
(ξ
a
).
S. D. Sharma Wavelets: Theory and Applications
![Page 14: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/14.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Properties Contd...
4. Exponential modulation → frequency shift:
F [Maf(t)] = F [eiatf(t)] = f(ξ − a) = Taf(ξ).
5. Change of roof: ∫ ∞−∞
f(t)g(t)dt =
∫ ∞−∞
f(t)g(t)dt.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Properties Contd...
4. Exponential modulation → frequency shift:
F [Maf(t)] = F [eiatf(t)] = f(ξ − a) = Taf(ξ).
5. Change of roof: ∫ ∞−∞
f(t)g(t)dt =
∫ ∞−∞
f(t)g(t)dt.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Drawbacks of Fourier transform
It is suitable only for stationary signals.
It measures the frequency content of a signal globally, i.e.,throughout the entire domain R.
It does not give any information regarding to measure the positionand momentum of particle simultaneously at a particular point.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Drawbacks of Fourier transform
It is suitable only for stationary signals.
It measures the frequency content of a signal globally, i.e.,throughout the entire domain R.
It does not give any information regarding to measure the positionand momentum of particle simultaneously at a particular point.
S. D. Sharma Wavelets: Theory and Applications
![Page 18: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/18.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Fourier TransformBasic properties of Fourier transform
Drawbacks of Fourier transform
It is suitable only for stationary signals.
It measures the frequency content of a signal globally, i.e.,throughout the entire domain R.
It does not give any information regarding to measure the positionand momentum of particle simultaneously at a particular point.
S. D. Sharma Wavelets: Theory and Applications
![Page 19: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/19.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
A Walk in The Physical Universe
Our purpose is to obtain a transform that enables us to perform a localcomputation of the frequency density. The inspiration for this transformis to analyze the audio analysis performed by our auditory system.Consider for this an audio signal represented by a real function f of onevariable (time).
Real time analysis: The audio information we receive occurssimultaneously on time and frequency. This means that the signal fis transformed by the auditory system in a signal f(t, ω) thatdepends on the time and the frequency.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
A Walk in The Physical Universe
Our purpose is to obtain a transform that enables us to perform a localcomputation of the frequency density. The inspiration for this transformis to analyze the audio analysis performed by our auditory system.Consider for this an audio signal represented by a real function f of onevariable (time).
Real time analysis: The audio information we receive occurssimultaneously on time and frequency. This means that the signal fis transformed by the auditory system in a signal f(t, ω) thatdepends on the time and the frequency.
S. D. Sharma Wavelets: Theory and Applications
![Page 21: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/21.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Future sounds are not analyzed: This means that only values off(t) for t ≤ t1 can be analyzed when computing the transformf(t, ω).
The auditory system has finite memory: That is, sounds that wehave heard some time ago do not influence the sounds that we hearin a certain instant of time. This means that there exists a realnumber t0 > 0 such that the computation of the transform f(t, ω)depends only on the values of t on the interval [t− t0, t].
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Future sounds are not analyzed: This means that only values off(t) for t ≤ t1 can be analyzed when computing the transformf(t, ω).
The auditory system has finite memory: That is, sounds that wehave heard some time ago do not influence the sounds that we hearin a certain instant of time. This means that there exists a realnumber t0 > 0 such that the computation of the transform f(t, ω)depends only on the values of t on the interval [t− t0, t].
S. D. Sharma Wavelets: Theory and Applications
![Page 23: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/23.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Mathematically, the last two properties show that the modulatingfunction used to detect frequencies in the computation of the transformf(t, ω) must have its values concentrated in a neighborhood of t. We saythat it is localized in time. D. Gabor, was the first to propose a transformwith the above properties.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Window function
A non-trivial function g(x) ∈ L2(R) is called a window function iftg(t) ∈ L2(R). An example of such a window function is the Haarfunction.
f(t) =
1, 0 ≤ t < 1/2
−1, 1/2 ≤ t < 1
0, otherwise
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Window function(Haar function)
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Windowed Fourier transform
We define the Windowed Fourier transform of a function f ∈ L2(R) withrespect to a windowed function g evaluated at a location (b, ω) in thetime-frequency plane as
Ggf(b, ω) =
∫ ∞−∞
f(t)g(t− b)e−iwtdt
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Advantage over Fourier transform
Unlike the case of Fourier transform in which the function f must beknown for the entire time axis before its spectral component at any singlefrequency can be computed,short-time Fourier transform(STFT) orwindowed Fourier transform needs to know f(t) only in the interval inwhich g(t− b) is non zero.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Time-frequency window for STFT
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Unfortunately there is a limit to the localization precision in thetime-frequency domain.
This limitation comes from a general principle that governs the timefrequency transforms. This is the uncertainty principle. In simpleterms the statement of this principle is: We can not obtain preciselocalization simultaneously in the time and frequency domains.
The intuition behind this principle is simple: To measure frequencieswe must observe the signal for some period of time.
The more precision we need in the frequency measurements thelarger the time interval we have to observe.
S. D. Sharma Wavelets: Theory and Applications
![Page 30: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/30.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Unfortunately there is a limit to the localization precision in thetime-frequency domain.
This limitation comes from a general principle that governs the timefrequency transforms. This is the uncertainty principle. In simpleterms the statement of this principle is: We can not obtain preciselocalization simultaneously in the time and frequency domains.
The intuition behind this principle is simple: To measure frequencieswe must observe the signal for some period of time.
The more precision we need in the frequency measurements thelarger the time interval we have to observe.
S. D. Sharma Wavelets: Theory and Applications
![Page 31: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/31.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Unfortunately there is a limit to the localization precision in thetime-frequency domain.
This limitation comes from a general principle that governs the timefrequency transforms. This is the uncertainty principle. In simpleterms the statement of this principle is: We can not obtain preciselocalization simultaneously in the time and frequency domains.
The intuition behind this principle is simple: To measure frequencieswe must observe the signal for some period of time.
The more precision we need in the frequency measurements thelarger the time interval we have to observe.
S. D. Sharma Wavelets: Theory and Applications
![Page 32: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/32.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
Unfortunately there is a limit to the localization precision in thetime-frequency domain.
This limitation comes from a general principle that governs the timefrequency transforms. This is the uncertainty principle. In simpleterms the statement of this principle is: We can not obtain preciselocalization simultaneously in the time and frequency domains.
The intuition behind this principle is simple: To measure frequencieswe must observe the signal for some period of time.
The more precision we need in the frequency measurements thelarger the time interval we have to observe.
S. D. Sharma Wavelets: Theory and Applications
![Page 33: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/33.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
The windowed Fourier transform introduces a scale (the width of thewindow), and analyzes the signal from the point of view of that scale. Ifthe signal has important frequency details outside of the scale, we willhave problems in the signal analysis:
If the signal details are much smaller than the width of the window,we will have a problem similar to the one we faced with the Fouriertransform: The details will be detected but the transform will notlocalize them.
If the signal details are larger than the width of the window, theywill not be detected properly.
S. D. Sharma Wavelets: Theory and Applications
![Page 34: Wavelets: Theory and Applications - Central University of Jammucujammu.ac.in/5090/5090_media/PPT/WAVELETS THEORY AND... · 2016-02-15 · Representation of Functions Fourier Analysis](https://reader030.vdocuments.us/reader030/viewer/2022040502/5e267a38a34ece1fa44b5195/html5/thumbnails/34.jpg)
Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
Limitations of STFT
The windowed Fourier transform introduces a scale (the width of thewindow), and analyzes the signal from the point of view of that scale. Ifthe signal has important frequency details outside of the scale, we willhave problems in the signal analysis:
If the signal details are much smaller than the width of the window,we will have a problem similar to the one we faced with the Fouriertransform: The details will be detected but the transform will notlocalize them.
If the signal details are larger than the width of the window, theywill not be detected properly.
S. D. Sharma Wavelets: Theory and Applications
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Limitations of STFT
The windowed Fourier transform introduces a scale (the width of thewindow), and analyzes the signal from the point of view of that scale. Ifthe signal has important frequency details outside of the scale, we willhave problems in the signal analysis:
If the signal details are much smaller than the width of the window,we will have a problem similar to the one we faced with the Fouriertransform: The details will be detected but the transform will notlocalize them.
If the signal details are larger than the width of the window, theywill not be detected properly.
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Limitations of STFT
To solve this problem when we analyze a signal using the windowedFourier transform, we must define a transform which is independent ofscale. This transform should not use a fixed scale, but a variable one.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Where doWavelets Fit?
In order to understand the role of the wavelets in the scenario ofcomputational mathematics, even without understanding what a waveletis, we must remember that our major concern is the description,representation, and reconstruction of functions. The different uses ofwavelets in computationalmathematics, and in particular in computergraphics, are related with two facts:
Representation and reconstruction of functions;
Multiresolution representation, a problem that consists inrepresenting the graphics object in different resolutions.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Where doWavelets Fit?
In order to understand the role of the wavelets in the scenario ofcomputational mathematics, even without understanding what a waveletis, we must remember that our major concern is the description,representation, and reconstruction of functions. The different uses ofwavelets in computationalmathematics, and in particular in computergraphics, are related with two facts:
Representation and reconstruction of functions;
Multiresolution representation, a problem that consists inrepresenting the graphics object in different resolutions.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Where doWavelets Fit?
In order to understand the role of the wavelets in the scenario ofcomputational mathematics, even without understanding what a waveletis, we must remember that our major concern is the description,representation, and reconstruction of functions. The different uses ofwavelets in computationalmathematics, and in particular in computergraphics, are related with two facts:
Representation and reconstruction of functions;
Multiresolution representation, a problem that consists inrepresenting the graphics object in different resolutions.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
To solve this problem when we analyze a signal using the windowedFourier transform, we must define a transform which is independentof scale. This transform should not use a fixed scale, but a variableone.
The scale is defined by the width of the modulation function.Therefore we must use a modulation function which does not have afixed width.Moreover the function must have good time localization.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
To solve this problem when we analyze a signal using the windowedFourier transform, we must define a transform which is independentof scale. This transform should not use a fixed scale, but a variableone.
The scale is defined by the width of the modulation function.Therefore we must use a modulation function which does not have afixed width.Moreover the function must have good time localization.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Wavelet
A function ψ ∈ L2(R) is called a basic wavelet or mother wavelet if thefollowing condition ∫ ∞
−∞
|ψ(ξ)|2
|ξ|<∞
is satisfied where ψ(ξ) is the Fourier transform of ψ(t). This condition isknown as the admissibility condition.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Wavelets are mathematical functions which are generated by the dyadicdilations and integer shifts a single function called a mother wavelet andare defined by
ψa,b(t) =1√aψ
(t− ba
), a, b ∈ R, a 6= 0
where a is called a scaling parameter which measures the degree ofcompression or scale, and b is a translation parameter which determinesthe time location of the wavelet.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Wavelets are mathematical functions which are generated by the dyadicdilations and integer shifts a single function called a mother wavelet andare defined by
ψa,b(t) =1√aψ
(t− ba
), a, b ∈ R, a 6= 0
where a is called a scaling parameter which measures the degree ofcompression or scale, and b is a translation parameter which determinesthe time location of the wavelet.
S. D. Sharma Wavelets: Theory and Applications
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Haar Wavelet and its Fourier transform
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Mexican hat Wavelet and its Fourier transform
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
The continuous wavelet transform Wψ of a function f ∈ L2(R) withrespect to wavelet ψ is defined as
Wψf(a, b) = 〈f, ψa,b〉 =∫ ∞−∞
f(t)ψa,b(t)dt,
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Time-frequency window for continuous wavelet transform
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
ExamplesContinuous Wavelet transform
Inverse wavelet transform
The inverse wavelet transform is given by
f(t) =1
Cψ
∫ ∞−∞
∫ ∞−∞
Wψf(a, b)ψa,b(t)dadb
a2,
where
Cψ = 2π
∫ ∞−∞
|ψ(ξ)|2
|ξ|<∞
is known as admissibility condition.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
N. Bi, X. Dai and Q. Sun, Construction of compactly supportedM -band wavelets, Appl. Comput. Harmon. Anal. 6 (1999) 113-131.
A. Chai and Z. Shen, Deconvolution: a wavelet frame approach,Numer. Math. 106 (2007) 529-587.
I. Daubechies, B. Han, A. Ron and Z. Shen, Framelets: MRA-basedconstructions of wavelet frames, Appl. Comput. Harmon. Anal.14(2003) 1-46.
L. Debnath and F. A. Shah, Wavelet Transforms and TheirApplications, Birkhauser, Boston, 2015.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
B. Han, Wavelets and framelets within the framework ofnon-homogeneous wavelet systems, In Approximation Theory XIII.Neamtu, M., Schumaker, L., Eds.; Springer, 2012., pp. 121-161.
J. C. Han and Z. Cheng, The construction of M -band tight waveletframes, In Proceedings of the Third Intemational Conference onMachine Learning and Cybemetics. Shanghai. 2004, pp. 26-29.
T. Lin, S. Xu, Q. Shi and P. Hao, An algebraic construction oforthonormal M -band wavelets with perfect reconstruction, Appl.Comput. Harmon. Anal. 172 (2006) 717-730.
A. P. Petukhov, Explicit construction of framelets, Appl. Comput.Harmon. Anal. 11 (2001) 313-327.
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Representation of FunctionsFourier AnalysisGabor Analysis
Wavelet AnalysisReferences
A. Rakotomamonjy and S. Canu, Frames, reproducing kernels,regularization and learning, J. Mach. Learn. Res. 6 (2005)1485-1515.
A. Ron and Z. Shen, Affine systems in L2(Rd): the analysis of theanalysis operator, J. Funct. Anal. 148 (1997) 408-447.
F. A. Shah and L. Debnath, Explicit construction of M -band tightframelet packets, Analysis. 32 (2012) 281-294.
P. Steffen, P. N. Heller, R. A. Gopinath and C. S. Burrus, Theory ofregular M -band wavelet bases, IEEE Trans. Sig. Proces. 41 (12)(1993) 3497-3510.
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THANKS!!
S. D. Sharma Wavelets: Theory and Applications