dddtree2
Dual-tree and double-density 2-D wavelet transform
Syntax
Description
returns the wt
= dddtree2(typetree
,x
,level
,fdf
,df
)typetree
discrete wavelet transform of the 2-D input image,
x
, down to level, level
. The wavelet transform
uses the decomposition (analysis) filters, fdf
, for the first level and
the analysis filters, df
, for subsequent levels. Supported wavelet
transforms are the critically sampled DWT, double-density, real oriented dual-tree, complex
oriented dual-tree, real oriented dual-tree double-density, and complex oriented dual-tree
double-density wavelet transform. The critically sampled DWT is a filter bank decomposition
in an orthogonal or biorthogonal basis (nonredundant). The other wavelet transforms are
oversampled filter banks with differing degrees of directional selectivity.
uses the filters specified in wt
= dddtree2(typetree
,x
,level
,fname1
,fname2
)fname1
for the first stage of the
dual-tree wavelet transform and the filters specified in fname2
for
subsequent stages of the dual-tree wavelet transform. Specifying different filters for stage
1 is valid and necessary only when typetree
is
'realdt'
, 'cplxdt'
, 'realdddt'
,
or 'cplxdddt'
.
Examples
Real Oriented Dual-Tree Wavelets
Visualize the six directional wavelets of the real oriented dual-tree wavelet transform.
Create the first-stage Farras analysis filters for the two trees.
Faf{1} = [0 0 -0.0884 -0.0112 0.0884 0.0112 0.6959 0.0884 0.6959 0.0884 0.0884 -0.6959 -0.0884 0.6959 0.0112 -0.0884 0.0112 -0.0884 0 0]; Faf{2} = [ 0.0112 0 0.0112 0 -0.0884 -0.0884 0.0884 -0.0884 0.6959 0.6959 0.6959 -0.6959 0.0884 0.0884 -0.0884 0.0884 0 0.0112 0 -0.0112];
Create the 6-tap Kingsbury Q-shift analysis filters for subsequent stages of the multiresolution analysis.
af{1} = [ 0.0352 0 0 0 -0.0883 -0.1143 0.2339 0 0.7603 0.5875 0.5875 -0.7603 0 0.2339 -0.1143 0.0883 0 0 0 -0.0352]; af{2} = [0 -0.0352 0 0 -0.1143 0.0883 0 0.2339 0.5875 -0.7603 0.7603 0.5875 0.2339 0 -0.0883 -0.1143 0 0 0.0352 0];
To visualize the six directional wavelets, you will modify the wavelet coefficients of a four level real oriented dual-tree wavelet transform of an image of zeros. Create an image of zeros whose size satisfies the following constraints:
The row and column dimensions are divisible by .
The minimum of the row and column size must be greater than or equal to the product of the maximum length of the analysis filters and .
J = 4; L = 3*2^(J+1); N = L/2^J; x = zeros(2*L,3*L); [numrows,numcols] = size(x)
numrows = 192
numcols = 288
Obtain the real oriented dual-tree wavelet transform of the image of zeros down to level 4.
wt = dddtree2('realdt',x,J,Faf,af)
wt = struct with fields:
type: 'realdt'
level: 4
filters: [1x1 struct]
cfs: {[96x144x3x2 double] [48x72x3x2 double] [24x36x3x2 double] [12x18x3x2 double] [12x18x2 double]}
sizes: [14x2 double]
The fourth element in wt.cfs
are the level 4 wavelet coefficients. Insert a 1 in one position of the six wavelet subbands (three orientations two trees) at the coarsest scale, and invert the wavelet transform.
wt.cfs{4}(N/2,N/2+0*N,1,1) = 1; wt.cfs{4}(N/2,N/2+1*N,2,1) = 1; wt.cfs{4}(N/2,N/2+2*N,3,1) = 1; wt.cfs{4}(N/2+N,N/2+0*N,1,2) = 1; wt.cfs{4}(N/2+N,N/2+1*N,2,2) = 1; wt.cfs{4}(N/2+N,N/2+2*N,3,2) = 1; xrec = idddtree2(wt);
Visualize the six directional wavelets.
imagesc(xrec); colormap gray; axis off; title('Real Oriented Dual-Tree Wavelets')
Double-Density Wavelet Transform
Obtain the double-density wavelet transform of an image.
Load the image and obtain the double-density wavelet transform using 6-tap filters (see dtfilters
).
load xbox imagesc(xbox) colormap gray
wt = dddtree2('ddt',xbox,1,'filters1')
wt = struct with fields:
type: 'ddt'
level: 1
filters: [1x1 struct]
cfs: {[64x64x8 double] [64x64 double]}
sizes: [10x2 double]
In the critically sampled 2-D discrete wavelet transform, there is one highpass filter. Filtering the rows and columns of the image with the highpass filter corresponds to extracting details in the diagonal orientation. In the double-density wavelet transform, there are two highpass filters, H1 and H2. Diagonally oriented details are extracted by filtering the image rows and columns with four combinations of the highpass filters. Visualize the diagonal details in the four wavelet highpass-highpass subbands.
H1H1 = wt.cfs{1}(:,:,4); H1H2 = wt.cfs{1}(:,:,5); H2H1 = wt.cfs{1}(:,:,7); H2H2 = wt.cfs{1}(:,:,8); subplot(2,2,1) imagesc(H1H1); title('H1 H1') colormap gray; subplot(2,2,2); imagesc(H1H2); title('H1 H2') subplot(2,2,3) imagesc(H2H1) title('H2 H1') subplot(2,2,4) imagesc(H2H2) title('H2 H2')
Complex Dual-Tree Wavelet Transform
Obtain the complex dual-tree wavelet transform of an image. Show that the complex dual-tree wavelet transform can detect the two different diagonal directions.
Load the image and obtain the complex dual-tree wavelet transform.
load xbox imagesc(xbox) colormap gray
wt = dddtree2('cplxdt',xbox,1,'FSfarras','qshift10')
wt = struct with fields:
type: 'cplxdt'
level: 1
filters: [1x1 struct]
cfs: {[5-D double] [64x64x2x2 double]}
sizes: [5x2 double]
Obtain and display the diagonally oriented details from the two trees.
waveletcfs = wt.cfs{1}; subplot(2,2,1) imagesc(waveletcfs(:,:,3,1,1)) title('Diagonal - Tree 1 - Real') colormap gray subplot(2,2,2) imagesc(waveletcfs(:,:,3,1,2)) title('Diagonal - Tree 1 - Imaginary') subplot(2,2,3) imagesc(waveletcfs(:,:,3,2,1)) title('Diagonal - Tree 2 - Real') subplot(2,2,4) imagesc(waveletcfs(:,:,3,2,2)) title('Diagonal - Tree 2 - Imaginary')
Input Arguments
typetree
— Type of wavelet decomposition
'dwt'
| 'ddt'
| 'realdt'
| 'cplxdt'
| 'realdddt'
| 'cplxdddt'
Type of wavelet decomposition, specified as one of 'dwt'
,
'ddt'
, 'realdt'
, 'cplxdt'
,
'realdddt'
, or 'cplxdddt'
. The type,
'dwt'
, produces a critically sampled (nonredundant) discrete
wavelet transform. The other decomposition types produce oversampled wavelet transforms.
'ddt'
produces a double-density wavelet transform with one scaling
and two wavelet filters for both row and column filtering. The double-density wavelet
transform uses the same filters at all stages. 'realdt'
and
'cplxdt'
produce oriented dual-tree wavelet transforms consisting
of two and four separable wavelet transforms. 'realdddt'
and
'cplxdddt'
produce double-density dual-tree wavelet transforms. The
dual-tree wavelet transforms use different filters for the first stage (level).
x
— Input image
matrix
Input image, specified as a matrix with even-length row and column dimensions. Both the row and column dimensions must be divisible by 2L, where L is the level of the wavelet transform. Additionally, the minimum of the row and column dimensions of the image must be greater than or equal to the product of the maximum length of the decomposition (analysis) filters and 2(L-1).
Data Types: double
level
— Level of wavelet decomposition
integer
Level of the wavelet decomposition, specified as a positive
integer. If L is the value of level
,
2L must divide both
the row and column dimensions of x
. Additionally,
the minimum of the row and column dimensions of the image must be
greater than or equal to the product of the maximum length of the
decomposition (analysis) filters and 2(L-1).
fdf
— Level-one analysis filters
matrix | cell array
The level-one analysis filters, specified as a matrix or cell
array of matrices. Specify fdf
as a matrix when typetree
is 'dwt'
or 'ddt'
.
The size and structure of the matrix depend on the typetree
input
as follows:
'dwt'
— This is the critically sampled discrete wavelet transform. In this case,fdf
is a two-column matrix with the lowpass (scaling) filter in the first column and the highpass (wavelet) filter in the second column.'ddt'
— This is the double-density wavelet transform. The double-density DWT is a three-channel perfect reconstruction filter bank.fdf
is a three-column matrix with the lowpass (scaling) filter in the first column and the two highpass (wavelet) filters in the second and third columns. In the double-density wavelet transform, the single lowpass and two highpass filters constitute a three-channel perfect reconstruction filter bank. This is equivalent to the three filters forming a tight frame. You cannot arbitrarily choose the two wavelet filters in the double-density DWT. The three filters together must form a tight frame.
Specify fdf
as a 1-by-2 cell array of matrices
when typetree
is a dual-tree transform, 'realdt'
, 'cplxdt'
, 'realdddt'
,
or 'cplxdddt'
. The size and structure of the matrix
elements in the cell array depend on the typetree
input
as follows:
For the dual-tree complex wavelet transforms,
'realdt'
and'cplxdt'
,fdf{1}
is an N-by-2 matrix containing the lowpass (scaling) and highpass (wavelet) filters for the first tree andfdf{2}
is an N-by-2 matrix containing the lowpass (scaling) and highpass (wavelet) filters for the second tree.For the double-density dual-tree complex wavelet transforms,
'realdddt'
and'cplxdddt'
,fdf{1}
is an N-by-3 matrix containing the lowpass (scaling) and two highpass (wavelet) filters for the first tree andfdf{2}
is an N-by-3 matrix containing the lowpass (scaling) and two highpass (wavelet) filters for the second tree.
df
— Analysis filters for levels > 1
matrix | cell array
Analysis filters for levels > 1, specified as a matrix or
cell array of matrices. Specify df
as a matrix
when typetree
is 'dwt'
or 'ddt'
.
The size and structure of the matrix depend on the typetree
input
as follows:
'dwt'
— This is the critically sampled discrete wavelet transform. In this case,df
is a two-column matrix with the lowpass (scaling) filter in the first column and the highpass (wavelet) filter in the second column. For the critically sampled orthogonal or biorthogonal DWT, the filters indf
andfdf
must be identical.'ddt'
— This is the double-density wavelet transform. The double-density DWT is a three-channel perfect reconstruction filter bank.df
is a three-column matrix with the lowpass (scaling) filter in the first column and the two highpass (wavelet) filters in the second and third columns. In the double-density wavelet transform, the single lowpass and two highpass filters constitute a three-channel perfect reconstruction filter bank. This is equivalent to the three filters forming a tight frame. For the double-density DWT, the filters indf
andfdf
must be identical.
Specify df
as a 1-by-2 cell array of matrices
when typetree
is a dual-tree transform, 'realdt'
, 'cplxdt'
, 'realdddt'
,
or 'cplxdddt'
. For dual-tree transforms, the filters
in fdf
and df
must be different.
The size and structure of the matrix elements in the cell array depend
on the typetree
input as follows:
For the dual-tree wavelet transforms,
'realdt'
and'cplxdt'
,df{1}
is an N-by-2 matrix containing the lowpass (scaling) and highpass (wavelet) filters for the first tree anddf{2}
is an N-by-2 matrix containing the lowpass (scaling) and highpass (wavelet) filters for the second tree.For the double-density dual-tree complex wavelet transforms,
'realdddt'
and'cplxdddt'
,df{1}
is an N-by-3 matrix containing the lowpass (scaling) and two highpass (wavelet) filters for the first tree anddf{2}
is an N-by-3 matrix containing the lowpass (scaling) and two highpass (wavelet) filters for the second tree.
fname
— Filter name
character vector | string scalar
fname1
— First-stage filter name
character vector | string scalar
First-stage filter name, specified as a character vector or string scalar. Specifying a
first-level filter that is different from the wavelet and scaling filters in
subsequent levels is valid and necessary only with the dual-tree wavelet
transforms, 'realdt'
, 'cplxdt'
,
'realdddt'
, and 'cplxdddt'
.
fname2
— Filter name for stages > 1
character vector | string scalar
Filter name for stages > 1, specified as a character vector or string scalar. Specifying a
different filter for stages > 1 is valid and necessary only with the
dual-tree wavelet transforms, 'realdt'
,
'cplxdt'
, 'realdddt'
, and
'cplxdddt'
.
Output Arguments
wt
— Wavelet transform
structure
Wavelet transform, returned as a structure with these fields:
type
— Type of wavelet decomposition (filter bank)
'dwt'
| 'ddt'
| 'realdt'
| 'cplxdt'
| 'realdddt'
| 'cplxdddt'
Type of wavelet decomposition used in the analysis returned
as one of 'dwt'
, 'ddt'
, 'realdt'
, 'cplxdt'
, 'realdddt'
,
or 'cplxdddt'
. 'dwt'
is the
critically sampled DWT. 'ddt'
produces a double-density
wavelet transform with one scaling and two wavelet filters for both
row and column filtering. 'realdt'
and 'cplxdt'
produce
oriented dual-tree wavelet transforms consisting of 2 and 4 separable
wavelet transforms. 'realdddt'
and 'cplxdddt'
produce
double-density dual-tree wavelet transforms consisting of two and
four separable wavelet transforms.
level
— Level of wavelet decomposition
positive integer
Level of wavelet decomposition, returned as a positive integer.
filters
— Decomposition (analysis) and reconstruction (synthesis) filters
structure
Decomposition (analysis) and reconstruction (synthesis) filters, returned as a structure with these fields:
FDf
— First-stage analysis filters
matrix | cell array
First-stage analysis filters, returned as an N-by-2 or N-by-3 matrix for single-tree wavelet transforms, or a 1-by-2 cell array of two N-by-2 or N-by-3 matrices for dual-tree wavelet transforms. The matrices are N-by-3 for the double-density wavelet transforms. For an N-by-2 matrix, the first column of the matrix is the scaling (lowpass) filter and the second column is the wavelet (highpass) filter. For an N-by-3 matrix, the first column of the matrix is the scaling (lowpass) filter and the second and third columns are the wavelet (highpass) filters. For the dual-tree transforms, each element of the cell array contains the first-stage analysis filters for the corresponding tree.
Df
— Analysis filters for levels > 1
matrix | cell array
Analysis filters for levels > 1, returned as an N-by-2 or N-by-3 matrix for single-tree wavelet transforms, or a 1-by-2 cell array of two N-by-2 or N-by-3 matrices for dual-tree wavelet transforms. The matrices are N-by-3 for the double-density wavelet transforms. For an N-by-2 matrix, the first column of the matrix is the scaling (lowpass) filter and the second column is the wavelet (highpass) filter. For an N-by-3 matrix, the first column of the matrix is the scaling (lowpass) filter and the second and third columns are the wavelet (highpass) filters. For the dual-tree transforms, each element of the cell array contains the analysis filters for the corresponding tree.
FRf
— First-level reconstruction filters
matrix | cell array
First-level reconstruction filters, returned as an N-by-2 or N-by-3 matrix for single-tree wavelet transforms, or a 1-by-2 cell array of two N-by-2 or N-by-3 matrices for dual-tree wavelet transforms. The matrices are N-by-3 for the double-density wavelet transforms. For an N-by-2 matrix, the first column of the matrix is the scaling (lowpass) filter and the second column is the wavelet (highpass) filter. For an N-by-3 matrix, the first column of the matrix is the scaling (lowpass) filter and the second and third columns are the wavelet (highpass) filters. For the dual-tree transforms, each element of the cell array contains the first-stage synthesis filters for the corresponding tree.
Rf
— Reconstruction filters for levels > 1
matrix | cell array
Reconstruction filters for levels > 1, returned as an N-by-2 or N-by-3 matrix for single-tree wavelet transforms, or a 1-by-2 cell array of two N-by-2 or N-by-3 matrices for dual-tree wavelet transforms. The matrices are N-by-3 for the double-density wavelet transforms. For an N-by-2 matrix, the first column of the matrix is the scaling (lowpass) filter and the second column is the wavelet (highpass) filter. For an N-by-3 matrix, the first column of the matrix is the scaling (lowpass) filter and the second and third columns are the wavelet (highpass) filters. For the dual-tree transforms, each element of the cell array contains the first-stage analysis filters for the corresponding tree.
cfs
— Wavelet transform coefficients
cell array of matrices
Wavelet transform coefficients, specified as a
1-by-(level
+1) cell array of matrices. The size and
structure of the matrix elements of the cell array depend on the type of wavelet
transform, typetree
as follows:
'dwt'
—cfs{j}(:,:,d)
j = 1,2,...
level
is the level.d = 1,2,3 is the orientation.
cfs{level+1}(:,:)
are the lowpass, or scaling, coefficients.
'ddt'
—cfs{j}(:,:,d)
j = 1,2,...
level
is the level.d = 1,2,3,4,5,6,7,8 is the orientation.
cfs{level+1}(:,:)
are the lowpass, or scaling, coefficients.
'realdt'
—cfs{j}(:,:,d,k)
j = 1,2,...
level
is the level.d = 1,2,3 is the orientation.
k = 1,2 is the wavelet transform tree.
cfs{level+1}(:,:,k)
are the lowpass, or scaling, coefficients.
'cplxdt'
—cfs{j}(:,:,d,k,m)
j = 1,2,...
level
is the level.d = 1,2,3 is the orientation.
k = 1,2 is the wavelet transform tree.
m = 1,2 are the real and imaginary parts.
cfs{level+1}(:,:,k,m)
are the lowpass, or scaling, coefficients.
'realdddt'
—cfs{j}(:,:,d,k)
j = 1,2,...
level
is the level.d = 1,2,3,4,5,6,7,8 is the orientation.
k = 1,2 is the wavelet transform tree.
cfs{level+1}(:,:,k)
are the lowpass, or scaling, coefficients.
'cplxdddt'
—cfs{j}(:,:,d,k,m)
j = 1,2,...
level
is the level.d = 1,2,3,4,5,6,7,8 is the orientation.
k = 1,2 is the wavelet transform tree.
m = 1,2 are the real and imaginary parts.
cfs{level+1}(:,:,k,m)
are the lowpass, or scaling, coefficients.
Each orientation corresponds to a particular subband. The double-density
transforms 'ddt'
, 'realdddt'
, and
'cplxdddt'
generate wavelet coefficients of eight
orientations. The other transforms, 'dwt'
,
'realdt'
, and 'cplxdt'
generate wavelet
coefficients of three orientations. The correspondence to subbands is as
follows.
typetree | Orientations |
---|---|
'dwt' , 'realdt' ,
'cplxdt' |
|
'ddt' , 'realdddt' ,
'cplxdddt' |
|
sizes
— Sizes of components
integer-valued matrix
Sizes of components in cfs
, returned as an N-by-2
integer-valued matrix. The value of N depends on the level of wavelet
decomposition and the type of wavelet decomposition: N = 2 +
level
× (number of orientations).
cfs(1,:)
= dimensions of input image.cfs(2+level,:)
= dimensions of scaling coefficients.cfs(1+no×(i–1)+(1:no),:)
= dimensions of leveli
detail coefficients, whereno
is the number of orientations.
Version History
Introduced in R2013b
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