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liftfilt

Apply elementary lifting steps on filters

Since R2021b

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    Syntax

    [LoDN,HiDN,LoRN,HiRN] = liftfilt(LoD,LoR,LiftingSteps=ELS)
    [LoDN,HiDN,LoRN,HiRN] = liftfilt(LoD,LoR,NormalizationFactor=NF)
    liftfilt(___)

    Description

    [LoDN,HiDN,LoRN,HiRN] = liftfilt(LoD,LoR,LiftingSteps=ELS) returns the four filters obtained by adding an array of elementary lifting steps (ELS) starting from the two filters LoD and LoR.

    example

    [LoDN,HiDN,LoRN,HiRN] = liftfilt(LoD,LoR,NormalizationFactor=NF) scales the filters by the normalization factor NF.

    liftfilt(___) with no output arguments plots the successive biorthogonal pairs. A scaling function and a wavelet comprise each pair.

    Examples

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    Open Live Script

    This example shows how to obtain the bior1.3 wavelet filters using Haar filters and elementary lifting steps.

    Obtain the Haar lowpass decomposition and reconstruction filters.

    [LoD,~,LoR,~] = wfilters("haar");

    Use liftingStep to create two elementary lifting steps of type update. Create an array consisting of the two steps.

    els1 = liftingStep(Type="update",...
    Coefficients=[0.125 -0.125],MaxOrder=0);
els2 = liftingStep(Type="update",...
    Coefficients=[0.125 -0.125],MaxOrder=1);
elsBoth = [els1;els2];

    Apply the lifting steps to the Haar filters to obtain new filters.

    [LoDN,HiDN,LoRN,HiRN] = liftfilt(LoD,LoR,LiftingSteps=elsBoth);

    Obtain the bior1.3 wavelet filters. Confirm that up to a sign change, the wavelet filters are equal to the filters liftfilt returns.

    [LoDw,HiDw,LoRw,HiRw] = wfilters("bior1.3");
samewavelet = ... 
isequal([LoDw,HiDw,LoRw,HiRw],[LoDN,-HiDN,LoRN,HiRN])
    samewavelet = logical
   1

    Use liftfilt to plot the successive biorthogonal pairs of scaling functions and wavelets.

    liftfilt(LoD,LoR,LiftingSteps=elsBoth)

    Figure contains 4 axes objects. Axes object 1 with title Analysis scaling function (phiA) contains an object of type line. Axes object 2 with title Analysis wavelet function (psiA) contains an object of type line. Axes object 3 with title Synthesis scaling function (phiS) contains an object of type line. Axes object 4 with title Synthesis wavelet function (psiS) contains an object of type line.

    Input Arguments

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    Lowpass filters associated with a wavelet, specified as real-valued vectors. LoD is the lowpass decomposition filter. LoR is the lowpass reconstruction filters.

    Example: For [LoD,~,LoR,~] = wfilters("db4"), liftfilt(LoD,LoR,LiftingSteps=lsteps) applies the elementary lifting steps specified in lsteps to the db4 filters.

    Data Types: double

    Lifting steps, specified as a structure array consisting of elementary lifting steps.

    • If liftingStep.Type="update", LoR and HiD are unchanged, where HiD is the associated highpass decomposition filter.

    • If liftingStep.Type="predict", LoD and HiR are unchanged, where HiR is the associated highpass decomposition filter.

    Example: liftfilt(LoD,LoR,LiftingSteps=ELS) applies the elementary lifting steps specified in lsteps to the filters LoD and LoR.

    Data Types: struct

    Normalization factor, specified as a nonzero scalar.

    Example: [LoDN,HiDN,LoRN,HiRN] = liftfilt(LoD,LoR,NF=2) scales the filters by 2.

    Data Types: double

    Output Arguments

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    Decomposition filters, returned as a pair of real-valued vectors. LoDN and HiDN correspond to the lowpass and highpass filters, respectively.

    Data Types: double

    Reconstruction filters, returned as a pair of real-valued vectors. LoRN and HiRN correspond to the lowpass and highpass filters, respectively.

    Data Types: double

    Extended Capabilities

    Version History

    Introduced in R2021b

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    See Also

    Functions

    Objects