API Reference¶
Main interface¶

class
dtcwt.
Transform1d
(biort='near_sym_a', qshift='qshift_a')¶ An implementation of the 1D DTCWT in NumPy.
Parameters:  biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.

forward
(X, nlevels=3, include_scale=False)¶ Perform a nlevel DTCWT decompostion on a 1D column vector X (or on the columns of a matrix X).
Parameters:  X – 1D real array or 2D real array whose columns are to be transformed
 nlevels – Number of levels of wavelet decomposition
Returns: A
dtcwt.Pyramid
like object representing the transform result.If biort or qshift are strings, they are used as an argument to the
biort()
orqshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).

inverse
(pyramid, gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 1D reconstruction.
Parameters:  pyramid – A
dtcwt.Pyramid
like object containing the transformed signal.  gain_mask – Gain to be applied to each subband.
Returns: Reconstructed real array.
The lth element of gain_mask is gain for wavelet subband at level l. If gain_mask[l] == 0, no computation is performed for band l. Default gain_mask is all ones. Note that l is 0indexed.
 pyramid – A
 biort – Level 1 wavelets to use. See

class
dtcwt.
Transform2d
(biort='near_sym_a', qshift='qshift_a')¶ An implementation of the 2D DTCWT via NumPy. biort and qshift are the wavelets which parameterise the transform.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).
forward
(X, nlevels=3, include_scale=False)¶ Perform a nlevel DTCWT2D decompostion on a 2D matrix X.
Parameters:  X – 2D real array
 nlevels – Number of levels of wavelet decomposition
Returns: A
dtcwt.Pyramid
compatible object representing the transformdomain signal

inverse
(pyramid, gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 2D reconstruction.
Parameters:  pyramid – A
dtcwt.Pyramid
like class holding the transform domain representation to invert.  gain_mask – Gain to be applied to each subband.
Returns: A numpyarray compatible instance with the reconstruction.
The (d, l)th element of gain_mask is gain for subband with direction d at level l. If gain_mask[d,l] == 0, no computation is performed for band (d,l). Default gain_mask is all ones. Note that both d and l are zeroindexed.
 pyramid – A


class
dtcwt.
Transform3d
(biort='near_sym_a', qshift='qshift_a', ext_mode=4)¶ An implementation of the 3D DTCWT via NumPy. biort and qshift are the wavelets which parameterise the transform. Valid values are documented in
dtcwt.coeffs.biort()
anddtcwt.coeffs.qshift()
.
forward
(X, nlevels=3, include_scale=False, discard_level_1=False)¶ Perform a nlevel DTCWT3D decompostion on a 3D matrix X.
Parameters:  X – 3D real arraylike object
 nlevels – Number of levels of wavelet decomposition
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  discard_level_1 – True if level 1 highpass bands are to be discarded.
Returns: a
dtcwt.Pyramid
instanceEach element of the Pyramid highpasses tuple is a 4D complex array with the 4th dimension having size 28. The 3D slice
[l][:,:,:,d]
corresponds to the complex higpass coefficients for direction d at level l where d and l are both 0indexed.If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).There are two values for ext_mode, either 4 or 8. If ext_mode = 4, check whether 1st level is divisible by 2 (if not we raise a
ValueError
). Also check whether from 2nd level onwards, the coefs can be divided by 4. If any dimension size is not a multiple of 4, append extra coefs by repeating the edges. If ext_mode = 8, check whether 1st level is divisible by 4 (if not we raise aValueError
). Also check whether from 2nd level onwards, the coeffs can be divided by 8. If any dimension size is not a multiple of 8, append extra coeffs by repeating the edges twice.If discard_level_1 is True the highpass coefficients at level 1 will not be discarded. (And, in fact, will never be calculated.) This turns the transform from being 8:1 redundant to being 1:1 redundant at the cost of nolonger allowing perfect reconstruction. If this option is selected then the first element of the highpasses tuple will be None. Note that
dtcwt.Transform3d.inverse()
will accept the first element being None and will treat it as being zero.

inverse
(pyramid)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 3D reconstruction.
Parameters:  pyramid – The
dtcwt.Pyramid
like instance representing the transformed signal.  biort – Level 1 wavelets to use. See
biort()
.  qshift – Level >= 2 wavelets to use. See
qshift()
.  ext_mode – Extension mode. See below.
Returns: Reconstructed real image matrix.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).There are two values for ext_mode, either 4 or 8. If ext_mode = 4, check whether 1st level is divisible by 2 (if not we raise a
ValueError
). Also check whether from 2nd level onwards, the coefs can be divided by 4. If any dimension size is not a multiple of 4, append extra coefs by repeating the edges. If ext_mode = 8, check whether 1st level is divisible by 4 (if not we raise aValueError
). Also check whether from 2nd level onwards, the coeffs can be divided by 8. If any dimension size is not a multiple of 8, append extra coeffs by repeating the edges twice. pyramid – The


class
dtcwt.
Pyramid
(lowpass, highpasses, scales=None)¶ A representation of a transform domain signal.
Backends are free to implement any class which respects this interface for storing transformdomain signals. The inverse transform may accept a backendspecific version of this class but should always accept any class which corresponds to this interface.

lowpass
¶ A NumPycompatible array containing the coarsest scale lowpass signal.

highpasses
¶ A tuple where each element is the complex subband coefficients for corresponding scales finest to coarsest.

scales
¶ (optional) A tuple where each element is a NumPycompatible array containing the lowpass signal for corresponding scales finest to coarsest. This is not required for the inverse and may be None.


dtcwt.
backend_name
= 'numpy'¶ A string providing a short humanreadable name for the DTCWT backend currently being used. This corresponds to the name parameter passed to
dtcwt.push_backend()
. The default backend isnumpy
but can be overridden by setting the DTCWT_BACKEND environment variable to a valid backend name.

dtcwt.
push_backend
(name)¶ Switch backend implementation to name. Push the previous backend onto the backend stack. The previous backend may be restored via
dtcwt.pop_backend()
.Parameters: name – string identifying which backend to switch to Raises: ValueError – if name does not correspond to a known backend name may take one of the following values:
numpy
: the default NumPy backend. Seedtcwt.numpy
.opencl
: a backend which uses OpenCL where available. Seedtcwt.opencl
.

dtcwt.
pop_backend
()¶ Restore the backend after a call to
push_backend()
. Calls topop_backend()
andpop_backend()
may be nested. This function will undo the most recent call topush_backend()
.Raises: IndexError – if one attempts to pop more backends than one has pushed.

dtcwt.
preserve_backend_stack
()¶ Return a generator object which can be used to preserve the backend stack even when an exception has been raise. For example:
# current backend is NumPy assert dtcwt.backend_name == 'numpy' with dtcwt.preserve_backend_stack(): dtcwt.push_backend('opencl') # ... things which may raise an exception # current backend is NumPy even if an exception was thrown assert dtcwt.backend_name == 'numpy'
Functions to load standard wavelet coefficients.

dtcwt.coeffs.
biort
(name)¶ Load level 1 wavelet by name.
Parameters: name – a string specifying the wavelet family name Returns: a tuple of vectors giving filter coefficients Name Wavelet antonini Antonini 9,7 tap filters. legall LeGall 5,3 tap filters. near_sym_a NearSymmetric 5,7 tap filters. near_sym_b NearSymmetric 13,19 tap filters. near_sym_b_bp NearSymmetric 13,19 tap filters + BP filter Return a tuple whose elements are a vector specifying the h0o, g0o, h1o and g1o coefficients.
See Rotational symmetry modified wavelet transform for an explanation of the
near_sym_b_bp
wavelet filters.Raises:  IOError – if name does not correspond to a set of wavelets known to the library.
 ValueError – if name specifies a
dtcwt.coeffs.qshift()
wavelet.

dtcwt.coeffs.
qshift
(name)¶ Load level >=2 wavelet by name,
Parameters: name – a string specifying the wavelet family name Returns: a tuple of vectors giving filter coefficients Name Wavelet qshift_06 Quarter Sample Shift Orthogonal (QShift) 10,10 tap filters, (only 6,6 nonzero taps). qshift_a Qshift 10,10 tap filters, (with 10,10 nonzero taps, unlike qshift_06). qshift_b QShift 14,14 tap filters. qshift_c QShift 16,16 tap filters. qshift_d QShift 18,18 tap filters. qshift_b_bp QShift 18,18 tap filters + BP Return a tuple whose elements are a vector specifying the h0a, h0b, g0a, g0b, h1a, h1b, g1a and g1b coefficients.
See Rotational symmetry modified wavelet transform for an explanation of the
qshift_b_bp
wavelet filters.Raises:  IOError – if name does not correspond to a set of wavelets known to the library.
 ValueError – if name specifies a
dtcwt.coeffs.biort()
wavelet.
Keypoint analysis¶

dtcwt.keypoint.
find_keypoints
(highpass_highpasses, method=None, alpha=1.0, beta=0.4, kappa=0.16666666666666666, threshold=None, max_points=None, upsample_keypoint_energy=None, upsample_highpasses=None, refine_positions=True, skip_levels=1)¶ Parameters:  highpass_highpasses – (NxMx6) matrix of highpass subband images
 method – (optional) string specifying which keypoint energy method to use
 alpha – (optional) scale parameter for
'fauqueur'
method  beta – (optional) shape parameter for
'fauqueur'
method  kappa – (optiona) suppression parameter for
'kingsbury'
method  threshold – (optional) minimum keypoint energy of returned keypoints
 max_points – (optional) maximum number of keypoints to return
 upsample_keypoint_energy – is nonNone, a string specifying a method used to upscale the keypoint energy map before finding keypoints
 upsample_subands – is nonNone, a string specifying a method used to upscale the subband image before finding keypoints
 refine_positions – (optional) should the keypoint positions be refined to subpixel accuracy
 skip_levels – (optional) number of levels of the transform to ignore before looking for keypoints
Returns: (Px4) array of P keypoints in image coordinates
Warning
The interface and behaviour of this function is the subject of an open research project. It is provided in this release as a preview of forthcoming functionality but it is subject to change between releases.
The rows of the returned keypoint array give the x coordinate, y coordinate, scale and keypoint energy. The rows are sorted in order of decreasing keypoint energy.
If refine_positions is
True
then the positions (and energy) of the keypoints will be refined to subpixel accuracy by fitting a quadratic patch. If refine_positions isFalse
then the keypoint locations will be those corresponding directly to pixelwise maxima of the subband images.The max_points and threshold parameters are cumulative: if both are specified then the max_points greatest energy keypoints with energy greater than threshold will be returned.
Usually the keypoint energies returned from the finest scale level are dominated by noise and so one usually wants to specify skip_levels to be 1 or 2. If skip_levels is 0 then all levels will be used to compute keypoint energy.
The upsample_highpasses and upsample_keypoint_energy parameters are used to control whether the individual subband coefficients and/org the keypoint energy map are upscaled by 2 before finding keypoints. If these parameters are None then no corresponding upscaling is performed. If nonNone they specify the upscale method as outlined in
dtcwt.sampling.upsample()
.If method is
None
, the default'fauqueur'
method is used.Name Description Parameters used fauqueur Geometric mean of absolute values[1] alpha, beta bendale Minimum absolute value[2] none kingsbury Crossproduct of orthogonal highpasses kappa [1] Julien Fauqueur, Nick Kingsbury, and Ryan Anderson. Multiscale Keypoint Detection using the DualTree Complex Wavelet Transform. 2006 International Conference on Image Processing, pages 16251628, October 2006. ISSN 15224880. doi: 10.1109/ICIP.2006.312656. http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=4106857.
[2] Pashmina Bendale, Bill Triggs, and Nick Kingsbury. Multiscale Keypoint Analysis based on Complex Wavelets. In British Machine Vision Conference (BMVC), 2010. http://wwwsigproc.eng.cam.ac.uk/~pb397/publications/BTK_BMVC_2010_abstract.pdf.
Image sampling¶
This module contains function for rescaling and resampling high and lowpass highpasses.
Note
All of these functions take an integer coordinate (x, y) to be the centre of the corresponding pixel. Therefore the upperleft pixel notionally covers the interval (0.5, 0.5) in x and y. An image with N rows and M columns, therefore, has an extent (0.5, M0.5) on the xaxis and an extent of (0.5, N0.5) on the yaxis. The rescale and upsample functions in this module will use this region as the extent of the image.

dtcwt.sampling.
sample
(im, xs, ys, method=None)¶ Sample image at (x,y) given by elements of xs and ys. Both xs and ys must have identical shape and output will have this same shape. The location (x,y) refers to the centre of
im[y,x]
. Samples at fractional locations are calculated using the method specified by method (or'lanczos'
if method isNone
.)Parameters:  im – array to sample from
 xs – x coordinates to sample
 ys – y coordinates to sample
 method – one of ‘bilinear’, ‘lanczos’ or ‘nearest’
Raises: ValueError – if
xs
andys
have differing shapes

dtcwt.sampling.
sample_highpass
(im, xs, ys, method=None, sbs=None)¶ As
sample()
except that the highpass image is first phase shifted to be centred on approximately DC, and has additional ‘sbs’ input allowing selection and reordering of subbands. This is useful mainly when the exact locations one wishes to sample from vary by subband.‘sbs’ should ordinarily be a numpy array of subband indices, in ascending order, e.g., np.array([0,2,3,5]) for just subbands 0, 2, 3 and 5; The returned array will be flattened to just 4 subbands. Pass [0,1,2,3,4,5] for all subbands.
Take care when reordering, preferably keeping the ‘sbs’ array outside the scope of this function to keep track of the new indices.
 Forshaw, Feb 2014.

dtcwt.sampling.
rescale
(im, shape, method=None)¶ Return a resampled version of im scaled to shape.
Since the centre of pixel (x,y) has coordinate (x,y) the extent of im is actually \(x \in (0.5, w0.5]\) and \(y \in (0.5, h0.5]\) where (y,x) is
im.shape
. This returns a sampled version of im that has the same extent as a shapesized array.

dtcwt.sampling.
rescale_highpass
(im, shape, method=None, sbs=None)¶ As
rescale()
except that the highpass image is first phase shifted to be centred on approximately DC, and has additional ‘sbs’ input allowing selection and reordering of subbands. This is useful mainly when the exact locations one wishes to sample from vary by subband.‘sbs’ should ordinarily be a list of subband indices, in ascending order, e.g., np.array([0,2,3,5]) for just subbands 0, 2, 3 and 5; The returned array will be flattened to just 4 subbands. Pass [0,1,2,3,4,5] for all subbands.
Take care when reordering, preferably keeping the ‘sbs’ array outside the scope of this function to keep track of the new indices.
 Forshaw, Feb 2014.

dtcwt.sampling.
upsample
(image, method=None)¶ Specialised function to upsample an image by a factor of two using a specified sampling method. If image is an array of shape (NxMx...) then the output will have shape (2Nx2Mx...). Only rows and columns are upsampled, depth axes and greater are interpolated but are not upsampled.
Parameters:  image – an array containing the image to upsample
 method – if nonNone, a string specifying the sampling method to use.
If method is
None
, the default sampling method'lanczos'
is used. The following sampling methods are supported:Name Description nearest Nearestneighbour sampling bilinear Bilinear sampling lanczos Lanczos sampling with window radius of 3

dtcwt.sampling.
upsample_highpass
(im, method=None)¶ As
upsample()
except that the highpass image is first phase rolled so that the filter has approximate DC centre frequency. The upshot is that this is the function to use when resampling complex subband images.
Image registration¶
Note
This module is experimental. It’s API may change between versions.
This module implements function for DTCWTbased image registration as outlined in [1]. These functions are 2Donly for the moment.

dtcwt.registration.
estimatereg
(source, reference, regshape=None, levels=None)¶ Estimate registration from which will map source to reference.
Parameters:  source – transformed source image
 reference – transformed reference image
The reference and source parameters should support the same API as
dtcwt.Pyramid
.The local affine distortion is estimated at at 8x8 pixel scales. Return a NxMx6 array where the 6element vector at (N,M) corresponds to the affine distortion parameters for the 8x8 block with index (N,M).
Use the
velocityfield()
function to convert the return value from this function into a velocity field.If notNone, levels is a sequence of sequences of 0based level indices to use when calculating the registration. If None then a default set of levels are used.

dtcwt.registration.
velocityfield
(avecs, shape, method=None)¶ Given the affine distortion parameters returned from
estimatereg()
, return a tuple of 2D arrays giving the x and y components of the velocity field. The shape of the velocity component field is shape. The velocities are measured in terms of normalised units where the image has width and height of unity.The method parameter is interpreted as in
dtcwt.sampling.rescale()
and is the sampling method used to resize avecs to shape.

dtcwt.registration.
warp
(I, avecs, method=None)¶ A convenience function to warp an image according to the velocity field implied by avecs.

dtcwt.registration.
warptransform
(t, avecs, levels, method=None)¶ Return a warped version of a transformed image acting only on specified levels.
Parameters:  t – a transformed image
 avecs – an array of affine distortion parameters
 levels – a sequence of 0based indices specifying which levels to act on
t should be a
dtcwt.Pyramid
compatible instance.The method parameter is interpreted as in
dtcwt.sampling.rescale()
and is the sampling method used to resize avecs to shape.Note
This function will clone the transform t but it is a shallow clone where possible. Only the levels specified in levels will be deepcopied and warped.
Plotting functions¶
Convenience functions for plotting DTCWTrelated objects.

dtcwt.plotting.
overlay_quiver
(image, vectorField, level, offset)¶ Overlays nicely coloured quiver plot of complex coefficients over original fullsize image, providing a useful phase visualisation.
Parameters:  image – array holding grayscale values on the interval [0, 255] to display
 vectorField – a single [MxNx6] numpy array of DTCWT coefficients
 level – the transform level (1indexed) of vectorField.
 offset – Offset for DTCWT coefficients (typically 0.5)
Note
The level parameter is 1indexed meaning that the third level has index “3”. This is unusual in Python but is kept for compatibility with similar MATLAB routines.
Should also work with other types of complex arrays (e.g., SLP coefficients), as long as the format is the same.
Usage example:
import dtcwt import dtcwt.plotting as plotting
mandrill = datasets.mandrill()
transform2d = dtcwt.Transform2d() mandrill_t = transform2d.forward(mandrill, nlevels=5)
plotting.overlay_quiver(mandrill*255, mandrill_t.highpasses[1], 5, 0.5)
Miscellaneous and lowlevel support functions¶
Useful utilities for testing the 2D DTCWT with synthetic images

dtcwt.utils.
appropriate_complex_type_for
(X)¶ Return an appropriate complex data type depending on the type of X. If X is already complex, return that, if it is floating point return a complex type of the appropriate size and if it is integer, choose an complex floating point type depending on the result of
numpy.asfarray()
.

dtcwt.utils.
as_column_vector
(v)¶ Return v as a column vector with shape (N,1).

dtcwt.utils.
asfarray
(X)¶ Similar to
numpy.asfarray()
except that this function tries to preserve the original datatype of X if it is already a floating point type and will pass floating point arrays through directly without copying.

dtcwt.utils.
drawcirc
(r, w, du, dv, N)¶ Generate an image of size N*N pels, containing a circle radius r pels and centred at du,dv relative to the centre of the image. The edge of the circle is a cosine shaped edge of width w (from 10 to 90% points).
Python implementation by S. C. Forshaw, November 2013.

dtcwt.utils.
drawedge
(theta, r, w, N)¶ Generate an image of size N * N pels, of an edge going from 0 to 1 in height at theta degrees to the horizontal (top of image = 1 if angle = 0). r is a twoelement vector, it is a coordinate in ij coords through which the step should pass. The shape of the intensity step is half a raised cosine w pels wide (w>=1).
T. E . Gale’s enhancement to drawedge() for MATLAB, transliterated to Python by S. C. Forshaw, Nov. 2013.

dtcwt.utils.
reflect
(x, minx, maxx)¶ Reflect the values in matrix x about the scalar values minx and maxx. Hence a vector x containing a long linearly increasing series is converted into a waveform which ramps linearly up and down between minx and maxx. If x contains integers and minx and maxx are (integers + 0.5), the ramps will have repeated max and min samples.

dtcwt.utils.
stacked_2d_matrix_matrix_prod
(mats1, mats2)¶ Interpret mats1 and mats2 as arrays of 2D matrices. I.e. mats1 has shape PxQxNxM and mats2 has shape PxQxMxR. The result is a PxQxNxR array equivalent to:
result[i,j,:,:] = mats1[i,j,:,:].dot(mats2[i,j,:,:])
for all valid row and column indices i and j.

dtcwt.utils.
stacked_2d_matrix_vector_prod
(mats, vecs)¶ Interpret mats and vecs as arrays of 2D matrices and vectors. I.e. mats has shape PxQxNxM and vecs has shape PxQxM. The result is a PxQxN array equivalent to:
result[i,j,:] = mats[i,j,:,:].dot(vecs[i,j,:])
for all valid row and column indices i and j.

dtcwt.utils.
stacked_2d_vector_matrix_prod
(vecs, mats)¶ Interpret mats and vecs as arrays of 2D matrices and vectors. I.e. mats has shape PxQxNxM and vecs has shape PxQxN. The result is a PxQxM array equivalent to:
result[i,j,:] = mats[i,j,:,:].T.dot(vecs[i,j,:])
for all valid row and column indices i and j.
Compatibility with MATLAB¶
Functions for compatibility with MATLAB scripts. These functions are intentionally similar in name and behaviour to the original functions from the DTCWT MATLAB toolbox. They are included in the library to ease the porting of MATLAB scripts but shouldn’t be used in new projects.
Note
The functionality of dtwavexfm2b
and dtwaveifm2b
has been folded
into dtwavexfm2
and dtwaveifm2
. For convenience of porting MATLAB
scripts, the original function names are available in the dtcwt
module as aliases but they should not be used in new code.

dtcwt.compat.
dtwavexfm
(X, nlevels=3, biort='near_sym_a', qshift='qshift_a', include_scale=False)¶ Perform a nlevel DTCWT decompostion on a 1D column vector X (or on the columns of a matrix X).
Parameters:  X – 1D real array or 2D real array whose columns are to be transformed
 nlevels – Number of levels of wavelet decomposition
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.
Returns Yl: The real lowpass image from the final level
Returns Yh: A tuple containing the (N, M, 6) shape complex highpass subimages for each level.
Returns Yscale: If include_scale is True, a tuple containing real lowpass coefficients for every scale.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Example:
# Performs a 5level transform on the real image X using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Yl, Yh = dtwavexfm(X,5,'near_sym_b','qshift_b')

dtcwt.compat.
dtwaveifm
(Yl, Yh, biort='near_sym_a', qshift='qshift_a', gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 1D reconstruction.
Parameters:  Yl – The real lowpass subband from the final level
 Yh – A sequence containing the complex highpass subband for each level.
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  gain_mask – Gain to be applied to each subband.
Returns Z: Reconstructed real array.
The lth element of gain_mask is gain for wavelet subband at level l. If gain_mask[l] == 0, no computation is performed for band l. Default gain_mask is all ones. Note that l is 0indexed.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Example:
# Performs a reconstruction from Yl,Yh using the 13,19tap filters # for level 1 and the Qshift 14tap filters for levels >= 2. Z = dtwaveifm(Yl, Yh, 'near_sym_b', 'qshift_b')

dtcwt.compat.
dtwavexfm2
(X, nlevels=3, biort='near_sym_a', qshift='qshift_a', include_scale=False)¶ Perform a nlevel DTCWT2D decompostion on a 2D matrix X.
Parameters:  X – 2D real array
 nlevels – Number of levels of wavelet decomposition
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.
Returns Yl: The real lowpass image from the final level
Returns Yh: A tuple containing the complex highpass subimages for each level.
Returns Yscale: If include_scale is True, a tuple containing real lowpass coefficients for every scale.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Example:
# Performs a 3level transform on the real image X using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Yl, Yh = dtwavexfm2(X, 3, 'near_sym_b', 'qshift_b')

dtcwt.compat.
dtwaveifm2
(Yl, Yh, biort='near_sym_a', qshift='qshift_a', gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 2D reconstruction.
Parameters:  Yl – The real lowpass subband from the final level
 Yh – A sequence containing the complex highpass subband for each level.
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  gain_mask – Gain to be applied to each subband.
Returns Z: Reconstructed real array
The (d, l)th element of gain_mask is gain for subband with direction d at level l. If gain_mask[d,l] == 0, no computation is performed for band (d,l). Default gain_mask is all ones. Note that both d and l are zeroindexed.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Example:
# Performs a 3level reconstruction from Yl,Yh using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Z = dtwaveifm2(Yl, Yh, 'near_sym_b', 'qshift_b')

dtcwt.compat.
dtwavexfm2b
(X, nlevels=3, biort='near_sym_a', qshift='qshift_a', include_scale=False)¶ Perform a nlevel DTCWT2D decompostion on a 2D matrix X.
Parameters:  X – 2D real array
 nlevels – Number of levels of wavelet decomposition
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.
Returns Yl: The real lowpass image from the final level
Returns Yh: A tuple containing the complex highpass subimages for each level.
Returns Yscale: If include_scale is True, a tuple containing real lowpass coefficients for every scale.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Example:
# Performs a 3level transform on the real image X using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Yl, Yh = dtwavexfm2(X, 3, 'near_sym_b', 'qshift_b')

dtcwt.compat.
dtwaveifm2b
(Yl, Yh, biort='near_sym_a', qshift='qshift_a', gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 2D reconstruction.
Parameters:  Yl – The real lowpass subband from the final level
 Yh – A sequence containing the complex highpass subband for each level.
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  gain_mask – Gain to be applied to each subband.
Returns Z: Reconstructed real array
The (d, l)th element of gain_mask is gain for subband with direction d at level l. If gain_mask[d,l] == 0, no computation is performed for band (d,l). Default gain_mask is all ones. Note that both d and l are zeroindexed.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Example:
# Performs a 3level reconstruction from Yl,Yh using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Z = dtwaveifm2(Yl, Yh, 'near_sym_b', 'qshift_b')

dtcwt.compat.
dtwavexfm3
(X, nlevels=3, biort='near_sym_a', qshift='qshift_a', include_scale=False, ext_mode=4, discard_level_1=False)¶ Perform a nlevel DTCWT3D decompostion on a 3D matrix X.
Parameters:  X – 3D real arraylike object
 nlevels – Number of levels of wavelet decomposition
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  ext_mode – Extension mode. See below.
 discard_level_1 – True if level 1 highpass bands are to be discarded.
Returns Yl: The real lowpass image from the final level
Returns Yh: A tuple containing the complex highpass subimages for each level.
Each element of Yh is a 4D complex array with the 4th dimension having size 28. The 3D slice
Yh[l][:,:,:,d]
corresponds to the complex higpass coefficients for direction d at level l where d and l are both 0indexed.If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).There are two values for ext_mode, either 4 or 8. If ext_mode = 4, check whether 1st level is divisible by 2 (if not we raise a
ValueError
). Also check whether from 2nd level onwards, the coefs can be divided by 4. If any dimension size is not a multiple of 4, append extra coefs by repeating the edges. If ext_mode = 8, check whether 1st level is divisible by 4 (if not we raise aValueError
). Also check whether from 2nd level onwards, the coeffs can be divided by 8. If any dimension size is not a multiple of 8, append extra coeffs by repeating the edges twice.If discard_level_1 is True the highpass coefficients at level 1 will be discarded. (And, in fact, will never be calculated.) This turns the transform from being 8:1 redundant to being 1:1 redundant at the cost of nolonger allowing perfect reconstruction. If this option is selected then Yh[0] will be None. Note that
dtwaveifm3()
will accepts Yh[0] being None and will treat it as being zero.Example:
# Performs a 3level transform on the real 3D array X using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Yl, Yh = dtwavexfm3(X, 3, 'near_sym_b', 'qshift_b')

dtcwt.compat.
dtwaveifm3
(Yl, Yh, biort='near_sym_a', qshift='qshift_a', ext_mode=4)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 3D reconstruction.
Parameters:  Yl – The real lowpass subband from the final level
 Yh – A sequence containing the complex highpass subband for each level.
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  ext_mode – Extension mode. See below.
Returns Z: Reconstructed real image matrix.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).There are two values for ext_mode, either 4 or 8. If ext_mode = 4, check whether 1st level is divisible by 2 (if not we raise a
ValueError
). Also check whether from 2nd level onwards, the coefs can be divided by 4. If any dimension size is not a multiple of 4, append extra coefs by repeating the edges. If ext_mode = 8, check whether 1st level is divisible by 4 (if not we raise aValueError
). Also check whether from 2nd level onwards, the coeffs can be divided by 8. If any dimension size is not a multiple of 8, append extra coeffs by repeating the edges twice.Example:
# Performs a 3level reconstruction from Yl,Yh using the 13,19tap # filters for level 1 and the Qshift 14tap filters for levels >= 2. Z = dtwaveifm3(Yl, Yh, 'near_sym_b', 'qshift_b')
Backends¶
The following modules provide backendspecific implementations. Usually you won’t need to import these modules directly; the main API will use an appropriate implementation. Occasionally, however, you may want to benchmark one implementation against the other.
NumPy¶
A backend which uses NumPy to perform the filtering. This backend should always be available.

class
dtcwt.numpy.
Pyramid
(lowpass, highpasses, scales=None)¶ A representation of a transform domain signal.
Backends are free to implement any class which respects this interface for storing transformdomain signals. The inverse transform may accept a backendspecific version of this class but should always accept any class which corresponds to this interface.

lowpass
¶ A NumPycompatible array containing the coarsest scale lowpass signal.

highpasses
¶ A tuple where each element is the complex subband coefficients for corresponding scales finest to coarsest.

scales
¶ (optional) A tuple where each element is a NumPycompatible array containing the lowpass signal for corresponding scales finest to coarsest. This is not required for the inverse and may be None.


class
dtcwt.numpy.
Transform1d
(biort='near_sym_a', qshift='qshift_a')¶ An implementation of the 1D DTCWT in NumPy.
Parameters:  biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.

forward
(X, nlevels=3, include_scale=False)¶ Perform a nlevel DTCWT decompostion on a 1D column vector X (or on the columns of a matrix X).
Parameters:  X – 1D real array or 2D real array whose columns are to be transformed
 nlevels – Number of levels of wavelet decomposition
Returns: A
dtcwt.Pyramid
like object representing the transform result.If biort or qshift are strings, they are used as an argument to the
biort()
orqshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).

inverse
(pyramid, gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 1D reconstruction.
Parameters:  pyramid – A
dtcwt.Pyramid
like object containing the transformed signal.  gain_mask – Gain to be applied to each subband.
Returns: Reconstructed real array.
The lth element of gain_mask is gain for wavelet subband at level l. If gain_mask[l] == 0, no computation is performed for band l. Default gain_mask is all ones. Note that l is 0indexed.
 pyramid – A
 biort – Level 1 wavelets to use. See

class
dtcwt.numpy.
Transform2d
(biort='near_sym_a', qshift='qshift_a')¶ An implementation of the 2D DTCWT via NumPy. biort and qshift are the wavelets which parameterise the transform.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).
forward
(X, nlevels=3, include_scale=False)¶ Perform a nlevel DTCWT2D decompostion on a 2D matrix X.
Parameters:  X – 2D real array
 nlevels – Number of levels of wavelet decomposition
Returns: A
dtcwt.Pyramid
compatible object representing the transformdomain signal

inverse
(pyramid, gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 2D reconstruction.
Parameters:  pyramid – A
dtcwt.Pyramid
like class holding the transform domain representation to invert.  gain_mask – Gain to be applied to each subband.
Returns: A numpyarray compatible instance with the reconstruction.
The (d, l)th element of gain_mask is gain for subband with direction d at level l. If gain_mask[d,l] == 0, no computation is performed for band (d,l). Default gain_mask is all ones. Note that both d and l are zeroindexed.
 pyramid – A


class
dtcwt.numpy.
Transform3d
(biort='near_sym_a', qshift='qshift_a', ext_mode=4)¶ An implementation of the 3D DTCWT via NumPy. biort and qshift are the wavelets which parameterise the transform. Valid values are documented in
dtcwt.coeffs.biort()
anddtcwt.coeffs.qshift()
.
forward
(X, nlevels=3, include_scale=False, discard_level_1=False)¶ Perform a nlevel DTCWT3D decompostion on a 3D matrix X.
Parameters:  X – 3D real arraylike object
 nlevels – Number of levels of wavelet decomposition
 biort – Level 1 wavelets to use. See
dtcwt.coeffs.biort()
.  qshift – Level >= 2 wavelets to use. See
dtcwt.coeffs.qshift()
.  discard_level_1 – True if level 1 highpass bands are to be discarded.
Returns: a
dtcwt.Pyramid
instanceEach element of the Pyramid highpasses tuple is a 4D complex array with the 4th dimension having size 28. The 3D slice
[l][:,:,:,d]
corresponds to the complex higpass coefficients for direction d at level l where d and l are both 0indexed.If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).There are two values for ext_mode, either 4 or 8. If ext_mode = 4, check whether 1st level is divisible by 2 (if not we raise a
ValueError
). Also check whether from 2nd level onwards, the coefs can be divided by 4. If any dimension size is not a multiple of 4, append extra coefs by repeating the edges. If ext_mode = 8, check whether 1st level is divisible by 4 (if not we raise aValueError
). Also check whether from 2nd level onwards, the coeffs can be divided by 8. If any dimension size is not a multiple of 8, append extra coeffs by repeating the edges twice.If discard_level_1 is True the highpass coefficients at level 1 will not be discarded. (And, in fact, will never be calculated.) This turns the transform from being 8:1 redundant to being 1:1 redundant at the cost of nolonger allowing perfect reconstruction. If this option is selected then the first element of the highpasses tuple will be None. Note that
dtcwt.Transform3d.inverse()
will accept the first element being None and will treat it as being zero.

inverse
(pyramid)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 3D reconstruction.
Parameters:  pyramid – The
dtcwt.Pyramid
like instance representing the transformed signal.  biort – Level 1 wavelets to use. See
biort()
.  qshift – Level >= 2 wavelets to use. See
qshift()
.  ext_mode – Extension mode. See below.
Returns: Reconstructed real image matrix.
If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).There are two values for ext_mode, either 4 or 8. If ext_mode = 4, check whether 1st level is divisible by 2 (if not we raise a
ValueError
). Also check whether from 2nd level onwards, the coefs can be divided by 4. If any dimension size is not a multiple of 4, append extra coefs by repeating the edges. If ext_mode = 8, check whether 1st level is divisible by 4 (if not we raise aValueError
). Also check whether from 2nd level onwards, the coeffs can be divided by 8. If any dimension size is not a multiple of 8, append extra coeffs by repeating the edges twice. pyramid – The


dtcwt.numpy.lowlevel.
colfilter
(X, h)¶ Filter the columns of image X using filter vector h, without decimation. If len(h) is odd, each output sample is aligned with each input sample and Y is the same size as X. If len(h) is even, each output sample is aligned with the mid point of each pair of input samples, and Y.shape = X.shape + [1 0].
Parameters:  X – an image whose columns are to be filtered
 h – the filter coefficients.
Returns Y: the filtered image.

dtcwt.numpy.lowlevel.
colifilt
(X, ha, hb)¶ Filter the columns of image X using the two filters ha and hb = reverse(ha). ha operates on the odd samples of X and hb on the even samples. Both filters should be even length, and h should be approx linear phase with a quarter sample advance from its mid pt (i.e :math:`h(m/2) > h(m/2 + 1)).
ext left edge right edge ext Level 2: !  !  ! +q filt on x b b a a a a b b q filt on o a a b b b b a a Level 1: !  !  ! odd filt on . b b b b a a a a a a a a b b b b odd filt on . a a a a b b b b b b b b a a a a
The output is interpolated by two from the input sample rate and the results from the two filters, Ya and Yb, are interleaved to give Y. Symmetric extension with repeated end samples is used on the composite X columns before each filter is applied.

dtcwt.numpy.lowlevel.
coldfilt
(X, ha, hb)¶ Filter the columns of image X using the two filters ha and hb = reverse(ha). ha operates on the odd samples of X and hb on the even samples. Both filters should be even length, and h should be approx linear phase with a quarter sample advance from its mid pt (i.e. \(h(m/2) > h(m/2 + 1)\)).
ext top edge bottom edge ext Level 1: !  !  ! odd filt on . b b b b a a a a a a a a b b b b odd filt on . a a a a b b b b b b b b a a a a Level 2: !  !  ! +q filt on x b b a a a a b b q filt on o a a b b b b a a
The output is decimated by two from the input sample rate and the results from the two filters, Ya and Yb, are interleaved to give Y. Symmetric extension with repeated end samples is used on the composite X columns before each filter is applied.
Raises ValueError if the number of rows in X is not a multiple of 4, the length of ha does not match hb or the lengths of ha or hb are noneven.
OpenCL¶
Provide lowlevel OpenCL accelerated operations. This backend requires that PyOpenCL be installed.

class
dtcwt.opencl.
Pyramid
(lowpass, highpasses, scales=None)¶ An interfacecompatible version of
dtcwt.Pyramid
where the initialiser arguments are assumed to bypyopencl.array.Array
instances.The attributes defined in
dtcwt.Pyramid
are implemented via properties. The original OpenCL arrays may be accessed via thecl_...
attributes.Note
The copy from device to host is performed once and then memoized. This makes repeated access to the hostside attributes efficient but will mean that any changes to the deviceside arrays will not be reflected in the hostside attributes after their first access. You should not be modifying the arrays once you return an instance of this class anyway but if you do, beware!

cl_lowpass
¶ The CL array containing the lowpass image.

cl_highpasses
¶ A tuple of CL arrays containing the subband images.

cl_scales
¶ (optional) Either
None
or a tuple of lowpass images for each scale.


class
dtcwt.opencl.
Transform2d
(biort='near_sym_a', qshift='qshift_a', queue=None)¶ An implementation of the 2D DTCWT via OpenCL. biort and qshift are the wavelets which parameterise the transform.
If queue is nonNone it is an instance of
pyopencl.CommandQueue
which is used to compile and execute the OpenCL kernels which implement the transform. If it is None, the first available compute device is used.If biort or qshift are strings, they are used as an argument to the
dtcwt.coeffs.biort()
ordtcwt.coeffs.qshift()
functions. Otherwise, they are interpreted as tuples of vectors giving filter coefficients. In the biort case, this should be (h0o, g0o, h1o, g1o). In the qshift case, this should be (h0a, h0b, g0a, g0b, h1a, h1b, g1a, g1b).Note
At the moment only the forward transform is accelerated. The inverse transform uses the NumPy backend.

forward
(X, nlevels=3, include_scale=False)¶ Perform a nlevel DTCWT2D decompostion on a 2D matrix X.
Parameters:  X – 2D real array
 nlevels – Number of levels of wavelet decomposition
Returns: A
dtcwt.Pyramid
compatible object representing the transformdomain signalNote
X may be a
pyopencl.array.Array
instance which has already been copied to the device. In which case, it must be 2D. (I.e. a vector will not be autopromoted.)

inverse
(pyramid, gain_mask=None)¶ Perform an nlevel dualtree complex wavelet (DTCWT) 2D reconstruction.
Parameters:  pyramid – A
dtcwt.Pyramid
like class holding the transform domain representation to invert.  gain_mask – Gain to be applied to each subband.
Returns: A numpyarray compatible instance with the reconstruction.
The (d, l)th element of gain_mask is gain for subband with direction d at level l. If gain_mask[d,l] == 0, no computation is performed for band (d,l). Default gain_mask is all ones. Note that both d and l are zeroindexed.
 pyramid – A


dtcwt.opencl.lowlevel.
axis_convolve
(X, h, axis=0, queue=None, output=None)¶ Filter along an of X using filter vector h. If h has odd length, each output sample is aligned with each input sample and Y is the same size as X. If h has even length, each output sample is aligned with the mid point of each pair of input samples, and the output matrix’s shape is increased by one along the convolution axis.
After convolution, the
pyopencl.array.Array
instance holding the deviceside output is returned. This may be accessed on the host viato_array()
.The axis of convolution is specified by axis. The default direction of convolution is columnwise.
If queue is non
None
, it should be apyopencl.CommandQueue
instance which is used to perform the computation. IfNone
, a default global queue is used.If output is non
None
, it should be apyopencl.array.Array
instance which the result is written into. IfNone
, an output array is created.

dtcwt.opencl.lowlevel.
coldfilt
(X, ha, hb, queue=None)¶ Filter the columns of image X using the two filters ha and hb = reverse(ha). ha operates on the odd samples of X and hb on the even samples. Both filters should be even length, and h should be approx linear phase with a quarter sample advance from its mid pt (i.e. \(h(m/2) > h(m/2 + 1)\)).
ext top edge bottom edge ext Level 1: !  !  ! odd filt on . b b b b a a a a a a a a b b b b odd filt on . a a a a b b b b b b b b a a a a Level 2: !  !  ! +q filt on x b b a a a a b b q filt on o a a b b b b a a
The output is decimated by two from the input sample rate and the results from the two filters, Ya and Yb, are interleaved to give Y. Symmetric extension with repeated end samples is used on the composite X columns before each filter is applied.
Raises ValueError if the number of rows in X is not a multiple of 4, the length of ha does not match hb or the lengths of ha or hb are noneven.

dtcwt.opencl.lowlevel.
colfilter
(X, h)¶ Filter the columns of image X using filter vector h, without decimation. If len(h) is odd, each output sample is aligned with each input sample and Y is the same size as X. If len(h) is even, each output sample is aligned with the mid point of each pair of input samples, and Y.shape = X.shape + [1 0].
The filtering will be accelerated via OpenCL.
Parameters:  X – an image whose columns are to be filtered
 h – the filter coefficients.
Returns Y: the filtered image.

dtcwt.opencl.lowlevel.
colifilt
(X, ha, hb, queue=None)¶ Filter the columns of image X using the two filters ha and hb = reverse(ha). ha operates on the odd samples of X and hb on the even samples. Both filters should be even length, and h should be approx linear phase with a quarter sample advance from its mid pt (i.e :math:`h(m/2) > h(m/2 + 1)).
ext left edge right edge ext Level 2: !  !  ! +q filt on x b b a a a a b b q filt on o a a b b b b a a Level 1: !  !  ! odd filt on . b b b b a a a a a a a a b b b b odd filt on . a a a a b b b b b b b b a a a a
The output is interpolated by two from the input sample rate and the results from the two filters, Ya and Yb, are interleaved to give Y. Symmetric extension with repeated end samples is used on the composite X columns before each filter is applied.

dtcwt.opencl.lowlevel.
get_default_queue
(*args, **kwargs)¶ Return the default queue used for computation if one is not specified.
This function is memoized and so only one queue is created after multiple invocations.