lwtcoef2

Extract 2-D LWT wavelet coefficients and orthogonal projections

Since R2021b

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    Syntax

    y = lwtcoef2(ll,lh,hl,hh)
    y = lwtcoef2(ll,lh,hl,hh,Name=Value)

    Description

    y = lwtcoef2(ll,lh,hl,hh) returns the level 1 reconstructed approximation coefficients that correspond to the approximation coefficients ll and the horizontal (lh), vertical (hl), and diagonal (hh) wavelet coefficients. The coefficients in ll, lh, hl, and hh are the outputs of lwt2 using default values.

    y = lwtcoef2(ll,lh,hl,hh,Name=Value) specifies options using one or more name-value arguments. For example, lwtcoef2(ll,lh,hl,hh,Type="detail",OutputType="projection") returns the projection of the detail coefficients at the finest scale using the db1 wavelet.

    example

    Examples

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    Open Live Script

    Load and plot a grayscale image.

    load gatlin
figure
image(X)
colormap(map)
title("1964 Gatlinburg Conference on Numerical Algebra",...
    "Wilkinson, Givens, Forsythe, Householder, Henrici, and Bauer")

    Figure contains an axes object. The axes object with title 1964 Gatlinburg Conference on Numerical Algebra contains an object of type image.

    Create a lifting scheme associated with the bior3.7 wavelet. Use the lifting scheme to obtain the wavelet decomposition of the image to the maximum level.

    lscheme = liftingScheme(Wavelet="bior3.7");
[ll,lh,hl,hh] = lwt2(X,LiftingScheme=lscheme);

    Extract and display the approximation coefficients at level 2. Confirm the row and column dimensions are one-quarter the size of those of the original image.

    approxCF = lwtcoef2(ll,lh,hl,hh,...
    LiftingScheme=lscheme,OutputType="coefficients",Level=2);
figure
image(approxCF)
colormap(map)

    Figure contains an axes object. The axes object contains an object of type image.

    size(X)./size(approxCF)
    ans = 1×2

     4     4

    Obtain the orthogonal projection of the level 1 approximation coefficients. Also obtain the orthogonal projections of the detail coefficients at level 1. Display the projections corresponding to the LH and HL detail coefficients. Observe that the prominent features in the LH- and HL-derived images correspond to the horizontal, and vertical features, respectively, of the original image.

    approx = lwtcoef2(ll,lh,hl,hh,...
    LiftingScheme=lscheme,OutputType="projection",Level=1);
dLH = lwtcoef2(ll,lh,hl,hh,...
    LiftingScheme=lscheme,OutputType="projection",Level=1,Type="LH");
dHL = lwtcoef2(ll,lh,hl,hh,...
    LiftingScheme=lscheme,OutputType="projection",Level=1,Type="HL");
dHH = lwtcoef2(ll,lh,hl,hh,...
    LiftingScheme=lscheme,OutputType="projection",Level=1,Type="HH");
subplot(1,2,1)
imagesc(dLH)
title("LH - Horizontal")
subplot(1,2,2)
imagesc(dHL)
title("HL - Vertical")

    Figure contains 2 axes objects. Axes object 1 with title LH - Horizontal contains an object of type image. Axes object 2 with title HL - Vertical contains an object of type image.

    Confirm the sum of the four projections equals the original image.

    max(max(abs(X-(approx+dLH+dHL+dHH))))
    ans = 
2.3448e-13

    Input Arguments

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    Approximation coefficients at the coarsest scale, specified as a scalar, vector, or matrix. The coefficients are the output of lwt2.

    Data Types: single | double
    Complex Number Support: Yes

    Horizontal detail coefficients by level, specified as a LEV-by-1 cell array, where LEV is the level of the decomposition. The elements of lh are in order of decreasing resolution. The coefficients are the output of lwt2.

    Data Types: single | double
    Complex Number Support: Yes

    Vertical detail coefficients by level, specified as a LEV-by-1 cell array, where LEV is the level of the decomposition. The elements of hl are in order of decreasing resolution. The coefficients are the output of lwt2.

    Data Types: single | double
    Complex Number Support: Yes

    Diagonal detail coefficients by level, specified as a LEV-by-1 cell array, where LEV is the level of the decomposition. The elements of hh are in order of decreasing resolution. The coefficients are the output of lwt2.

    Data Types: single | double
    Complex Number Support: Yes

    Name-Value Arguments

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    Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

    Example: y = lwtcoef2(ll,lh,hl,hh,OutputType="projection",LiftingScheme=lscheme)

    Orthogonal or biorthogonal wavelet, specified as a character vector or string scalar. See the Wavelet property of liftingScheme for the list of supported wavelets. The specified wavelet must match the value that you used to obtain the coefficients ll, lh, hl, and hh.

    You cannot specify Wavelet and LiftingScheme at the same time.

    Example: y = lwtcoef2(ll,lh,hl,hh,Wavelet="bior3.5") uses the bior3.5 biorthogonal wavelet.

    Data Types: char | string

    Lifting scheme, specified as a liftingScheme object. The specified lifting scheme must be the same lifting scheme that you used to obtain the coefficients ll, lh, hl, and hh.

    You cannot specify LiftingScheme and Wavelet at the same time.

    Example: y = lwtcoef2(ll,lh,hl,hh,LiftingScheme=lScheme) uses the lScheme lifting scheme.

    Output type, specified as one of these:

    • "coefficients" — Extract the approximation or details coefficients

    • "projection" — Return the projection (reconstruction) of the approximation or details coefficients

    Example: y = lwtcoef2(ll,lh,hl,hh,OutputType="projection",Type="detail") returns the projection corresponding to the detail coefficients at the finest scale.

    Type of coefficients to extract or reconstruct, specified as one of these:

    • "ll" — Approximation coefficients

    • "lh" — Horizontal coefficients

    • "hl" — Vertical coefficients

    • "hh" — Diagonal coefficients

    Example: y = lwtcoef2(ll,lh,hl,hh,Type="hh") extracts the diagonal coefficients at the finest scale.

    Level of coefficients to extract or reconstruct, specified as a positive integer less than or equal to length(hh).

    Example: y = lwtcoef2(ll,lh,hl,hh,LiftingScheme=lsc,Level=3) uses the lifting scheme lsc to extract the approximation coefficients at level 3.

    Data Types: double

    Extension mode to use to extract or reconstruct the coefficients, specified as one of these:

    • "periodic" — Periodized extension

    • "zeropad" — Zero padding

    • "symmetric" — Symmetric extension

    This argument specifies how to extend the signal at the boundaries. The extension mode must match the value you used to generate ll, lh, hl, and hh.

    Example: y = lwtcoef2(ll,lh,hl,hh,Extension="zeropad") specifies zero padding.

    Handling integer-valued data, specified as one of these:

    • 1 (true) — Preserve integer-valued data

    • 0 (false) — Do not preserve integer-valued data

    Int2Int must match the value you used to generate ll, lh, hl, and hh.

    Example: y = lwtcoef2(ll,lh,hl,hh,Int2Int=true) preserves integer-valued data.

    Output Arguments

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    Extracted coefficients or projection, returns as a matrix. y has the same dimensionality as the input used by the lwt2 function to generate the approximation and details coefficients.

    Data Types: single | double

    Extended Capabilities

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    C/C++ Code Generation
    Generate C and C++ code using MATLAB® Coder™.

    Version History

    Introduced in R2021b

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    See Also

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