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idualtree2

Kingsbury Q-shift 2-D inverse dual-tree complex wavelet transform

Description

imrec = idualtree2(A,D) returns the inverse 2-D complex dual-tree transform of the final-level approximation coefficients, A, and cell array of wavelet coefficients, D. A and D are outputs of dualtree2. For the reconstruction, idualtree2 uses two sets of filters:

  • Orthogonal Q-shift filter of length 10

  • Near-symmetric biorthogonal filter pair with lengths 7 (scaling synthesis filter) and 5 (wavelet synthesis filter)

example

imrec = idualtree2(___,Name,Value) specifies additional options using name-value pair arguments. For example, 'LowpassGain',0.1 applies a gain of 0.1 to the final-level approximation coefficients.

Examples

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This example shows how to reconstruct an approximation based on a subset of the wavelet subbands.

Load a 128-by-128 grayscale image.

load xbox
imagesc(xbox)
colormap gray

Obtain the dual-tree wavelet transform of the image down to level 2

lev = 2;
[a,d] = dualtree2(xbox,'Level',lev);

Since there are six wavelet subbands in each level of the decomposition, create a 2-by-6 matrix of zeros.

dgains = zeros(lev,6);

To reconstruct an approximation based on the 2nd and 5th wavelet subbands, set the second and fifth rows of dgains equal to 1. The 2nd and 5th wavelet subbands correspond to the highpass filtering of the rows and columns of the image.

dgains(:,[2 5]) = 1;

Obtain two reconstructions using the specified wavelet subbands. Include the scaling (lowpass) coefficients only in the first reconstruction.

imrec = idualtree2(a,d,'DetailGain',dgains);
imrec2 = idualtree2(a,d,'DetailGain',dgains,'LowpassGain',0);
figure
subplot(2,1,1)
imagesc(imrec)
title('With Lowpass Coefficients')
subplot(2,1,2)
imagesc(imrec2)
title('Without Lowpass Coefficients')
colormap gray

Input Arguments

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Final-level approximation coefficients, specified as a real-valued array. The approximation coefficients are the output of dualtree2.

Data Types: double | single

Approximation coefficients, specified as a cell array. The wavelet coefficients are the output of dualtree2.

Data Types: double | single

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'LevelOneFilter','antonini','LowpassGain',0.5

Biorthogonal filter to use in the first-level synthesis, specified by one of the values listed here. For perfect reconstruction, the first-level synthesis filters must match the first-level analysis filters used in dualtree2.

  • 'legall' — LeGall 5/3 filter

  • 'nearsym13_19' — (13,19)-tap near-orthogonal filter

  • 'nearsym5_7' — (5,7)-tap near-orthogonal filter

  • 'antonini' — (9,7)-tap Antonini filter

Orthogonal Hilbert Q-shift synthesis filter pair length to use for levels 2 and higher, specified as one of the listed values. For perfect reconstruction, the filter length must match the filter length used in dualtree2.

Wavelet coefficients subband gains, specified as a real-valued matrix with a row dimension of L, where L is the number of elements in D. There are six columns in DetailGain for each of the six wavelet subbands. The elements of DetailGain are real numbers in the interval [0, 1]. The kth column elements of DetailGain are the gains (weightings) applied to the kth wavelet subband. By default, DetailGain is a L-by-6 matrix of ones.

Gain to apply to final-level approximation (lowpass, scaling) coefficients, specified as a real number in the interval [0, 1].

References

[1] Antonini, M., M. Barlaud, P. Mathieu, and I. Daubechies. “Image Coding Using Wavelet Transform.” IEEE Transactions on Image Processing 1, no. 2 (April 1992): 205–20. https://doi.org/10.1109/83.136597.

[2] Kingsbury, Nick. “Complex Wavelets for Shift Invariant Analysis and Filtering of Signals.” Applied and Computational Harmonic Analysis 10, no. 3 (May 2001): 234–53. https://doi.org/10.1006/acha.2000.0343.

[3] Le Gall, D., and A. Tabatabai. “Sub-Band Coding of Digital Images Using Symmetric Short Kernel Filters and Arithmetic Coding Techniques.” In ICASSP-88., International Conference on Acoustics, Speech, and Signal Processing, 761–64. New York, NY, USA: IEEE, 1988. https://doi.org/10.1109/ICASSP.1988.196696.

Extended Capabilities

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

Introduced in R2020a