casacore::Convolver< FType > Class Template Reference

Forward Declarations. More...

#include <Convolver.h>

Public Member Functions
	Convolver ()
	When using the default constructor the psf MUST be specified using the setPsf function prior to doing any convolution. More...
	Convolver (const Array< FType > &psf, Bool cachePsf=False)
	Create the cached Transfer function assuming that circular convolution will be done. More...
	Convolver (const Array< FType > &psf, const IPosition &imageSize, Bool fullSize=False, Bool cachePsf=False)
	Create the cached Transfer function assuming that linear convolution with an array of size imageSize will be done. More...
	Convolver (const Convolver< FType > &other)
	The copy constructor and the assignment operator make copies (and not references) of all the internal data arrays, as this object could get really screwed up if the private data was silently messed with. More...
Convolver< FType > &	operator= (const Convolver< FType > &other)
	~Convolver ()
	The destructor does nothing! More...
void	linearConv (Array< FType > &result, const Array< FType > &model, Bool fullSize=False)
	Perform linear convolution of the model with the previously specified psf. More...
void	circularConv (Array< FType > &result, const Array< FType > &model)
	Perform circular convolution of the model with the previously specified psf. More...
void	setPsf (const Array< FType > &psf, Bool cachePsf=False)
	Set the transfer function for future convolutions to psf. More...
void	setPsf (const Array< FType > &psf, IPosition imageShape, Bool fullSize=False, Bool cachePsf=False)
	Set the transfer function for future convolutions to psf. More...
const Array< FType >	getPsf (Bool cachePsf=True)
	Get the psf currently used by this convolver. More...
void	setFastConvolve ()
	Set to use convolution with lesser flips. More...

Private Member Functions
void	makeXfr (const Array< FType > &psf, const IPosition &imageSize, Bool linear, Bool fullSize)
void	makePsf (Array< FType > &psf)
IPosition	defaultShape (const Array< FType > &psf)
IPosition	extractShape (IPosition &psfSize, const IPosition &imageSize)
void	doConvolution (Array< FType > &result, const Array< FType > &model, Bool fullSize)
void	resizeXfr (const IPosition &imageShape, Bool linear, Bool fullSize)
void	validate ()

Private Attributes
IPosition	thePsfSize
IPosition	theFFTSize
Array< typename NumericTraits< FType >::ConjugateType >	theXfr
Array< FType >	thePsf
FFTServer< FType, typename NumericTraits< FType >::ConjugateType >	theFFT
FFTServer< FType, typename NumericTraits< FType >::ConjugateType >	theIFFT
Bool	valid
Bool	doFast_p

Detailed Description

template<class FType>
class casacore::Convolver< FType >

Forward Declarations.

A class for doing multi-dimensional convolution

Intended use:

Public interface

Review Status

Reviewed By:

Brian Glendenning

Date Reviewed:

1996/05/27

Test programs:

tConvolution

Prerequisite

• The mathematical concept of convolution

Etymology

The convolver class performs convolution!

Synopsis

This class will perform linear or circular convolution on arrays.

The dimension of the convolution done is determined by the dimension of the point spread function (psf), so for example, if the psf is a Vector, one dimensional convolution will be done. The dimension of the model that is to be convolved must be at least the same as the point spread function, but it can be larger. If it is then the convolution will be repeated for each row or plane of the model.
Tip:
This class strips all degenerate axes when determining the dimensionality of the psf or model; So a psf with shapes of [1,1,16] or [16,1,1] is treated the same as a Vector of length 16, and will result in one dimensional convolutions along the first non-degenerate axis of the supplied model;

Repeated convolution can only be done along the fastest moving axes of the supplied image. For example, if a one dimensional psf is used (so that one dimensional convolution is being done), and a cube of data is supplied then the convolution will be repeated for each row in the cube. It is not currently possible to have this class do repeated one dimensional convolution along all the columns or along the z axis. To do this you need to use an iterator external to the class to successively feed in the appropriate slices of your Array.

The difference between linear and circular convolution can best be explained with a one dimensional example. Suppose the psf and data to be convolved are:

psf = [0.5 1.1];  data = [1  0  0  0  0  0]

then their linear and circular convolutions are:

circular convolution =         [1.1  0  0  0.5]
linear convolution =         [1.1  0  0  0  0]    (fullSize == False)
linear convolution =   [0.5  1.1  0  0  0  0  0] (fullSize == True)

The circular convolution "wraps around" whereas the linear one does not. Usage of the fullSize option is explained below. As can be seen from the above example this class does not normalise the convolved result by any factor that depends on the psf, so if the "beam area" is not unity the flux scales will vary.

The "centre" of the convolution is at the point (NX/2, NY/2) (assuming a 2 dimensional psf) where the first point in the psf is at (0,0) and the last is at (NX-1, NY-1). This means that a psf that is all zero except for 1 at the "centre" pixel will when convolved with any model leave the model unchanged.

The convolution is done in the Fourier domain and the transform of the psf (the transfer function) is cached by this class. If the cached transfer function is the wrong size for a given model it will be automatically be recomputed to the right size (this will involve two FFT's)

Each convolution requires two Fourier transforms which dominate the computational load. Hence the computational expense is n Log(n) for 1 dimensional and n^2 Log(n) for 2 dimensional convolutions.

The size of the convolved result is always the same as the input model unless linear convolution is done with the fullSize option set to True. In this case the result will be larger than the model and include the full linear convolution (resultSize = psfSize+modelSize-1), rather than the central portion.

If the convolver is constructed with an expected model size (as in the example below) then the cached transfer function will be computed to a size appropriate for linear convolution of models of that size. If no model size is given then the cached transfer function will be computed with a size appropriate for circular convolution. These guidelines also apply when using the setPsf functions.

Tip:
If you are intending to do 'fullsize' linear convolutions you should also set the fullsize option to True as the cached transfer function is a different size for fullsize linear convolutions;

For linear convolution the psf can be larger, the same size or smaller than the model but for circular convolution the psf must be smaller or the same size.

The size of the cached transfer function (and also the length of the FFT's calculated) depends on the sizes of the psf and the model, as well as whether you are doing linear or circular convolution and the fullSize option. It is always advantageous to use the smallest possible psf (ie. do not pad the psf prior to supplying it to this class). Be aware that using odd length images will lead to this class doing odd length FFT's, which are less computationally effecient (particularly is the length of the transform is a prime number) in general than even length transforms.

There are only two valid template types namely,

1. FType=Float or
2. FType=Double

and the user may prefer to use the following typedef's:

FloatConvolver (= Convolver<Float>) or
DoubleConvolver (= Convolver<Double>)  

rather than explicitly specifying the template arguements.
Tip:
The typedefs need to be redeclared when using the gnu compiler making them essentially useless;

When this class is constructed you may choose to have the psf explicitly stored by the class (by setting cachePsf=True). This will allow speedy access to the psf when using the getPsf function. However the getPsf function can still be called even if the psf has not been cached. Then the psf will be computed by FFT'ing the transfer function, and the psf will also then be cached (unless cachePsf=Flase). Cacheing the psf is also a good idea if you will be switching between different sized transfer functions (eg. mixing linear and circular convolution) as it will save one of the two FFT's. Note that even though the psf is returned as a const Array, it is possible to inadvertently modify it using the array copy constructor as this uses reference symantics. Modifying the psf is NOT recommended. eg.

DoubleConvolver conv();
{
Matrix<Double> psf(20,20); 
conv.setPsf(psf);
}
Matrix<Double> convPsf = conv.getPsf(); // Get the psf used by the convolver
convPsf(0,0) = -100;                    // And modify it. This modifies
// This internal psf used by the 
// convolver also! (unless it is
// not caching the psf)

Example

Calculate the convolution of two Matrices (psf and model);

 Matrix<Float> psf(4,4), model(12,12);
...put meaningful values into the above two matrices..\.
 FloatConvolver conv(psf, model.shape());
 conv.linearConv(result, model); // result = Convolution(psf, model)

Motivation

I needed to do linear convolution to write a clean algorithm. It blossomed into this class.

Thrown Exceptions

• AipsError: if psf has more dimensions than the model.

To Do

• the class should detect if the psf or image is small and do the convolution directly rather than use the Fourier domain
• Add a lattice interface, and more flexible iteration scheme
• Allow the psf to be specified with a Function.

Definition at line 231 of file Convolver.h.

Constructor & Destructor Documentation

Convolver() [1/4]

template<class FType >

casacore::Convolver< FType >::Convolver ( )

inline

When using the default constructor the psf MUST be specified using the setPsf function prior to doing any convolution.

Definition at line 237 of file Convolver.h.

Convolver() [2/4]

template<class FType >

casacore::Convolver< FType >::Convolver	(	const Array< FType > &	psf,
		Bool	cachePsf = False
	)

Create the cached Transfer function assuming that circular convolution will be done.

Convolver() [3/4]

template<class FType >

casacore::Convolver< FType >::Convolver	(	const Array< FType > &	psf,
		const IPosition &	imageSize,
		Bool	fullSize = False,
		Bool	cachePsf = False
	)

Create the cached Transfer function assuming that linear convolution with an array of size imageSize will be done.

Convolver() [4/4]

template<class FType >

casacore::Convolver< FType >::Convolver

(

const Convolver< FType > &

other

)

The copy constructor and the assignment operator make copies (and not references) of all the internal data arrays, as this object could get really screwed up if the private data was silently messed with.

~Convolver()

template<class FType >

casacore::Convolver< FType >::~Convolver

(

)

The destructor does nothing!

Member Function Documentation

circularConv()

template<class FType >

void casacore::Convolver< FType >::circularConv	(	Array< FType > &	result,
		const Array< FType > &	model
	)

Perform circular convolution of the model with the previously specified psf.

Return the answer in result.

defaultShape()

template<class FType >

IPosition casacore::Convolver< FType >::defaultShape ( const Array< FType > &  psf )

private

doConvolution()

template<class FType >

void casacore::Convolver< FType >::doConvolution ( Array< FType > &  result, const Array< FType > &  model, Bool  fullSize  )

private

extractShape()

template<class FType >

IPosition casacore::Convolver< FType >::extractShape ( IPosition &  psfSize, const IPosition &  imageSize  )

private

getPsf()

template<class FType >

const Array<FType> casacore::Convolver< FType >::getPsf

(

Bool

cachePsf = True

)

Get the psf currently used by this convolver.

linearConv()

template<class FType >

void casacore::Convolver< FType >::linearConv	(	Array< FType > &	result,
		const Array< FType > &	model,
		Bool	fullSize = False
	)

Perform linear convolution of the model with the previously specified psf.

Return the answer in result. Set fullSize to True if you want the full convolution, rather than the central portion (the same size as the model) returned.

makePsf()

template<class FType >

void casacore::Convolver< FType >::makePsf ( Array< FType > &  psf )

private

makeXfr()

template<class FType >

void casacore::Convolver< FType >::makeXfr ( const Array< FType > &  psf, const IPosition &  imageSize, Bool  linear, Bool  fullSize  )

private

operator=()

template<class FType >

Convolver<FType>& casacore::Convolver< FType >::operator=

(

const Convolver< FType > &

other

)

resizeXfr()

template<class FType >

void casacore::Convolver< FType >::resizeXfr ( const IPosition &  imageShape, Bool  linear, Bool  fullSize  )

private

setFastConvolve()

template<class FType >

void casacore::Convolver< FType >::setFastConvolve

(

)

Set to use convolution with lesser flips.

setPsf() [1/2]

template<class FType >

void casacore::Convolver< FType >::setPsf	(	const Array< FType > &	psf,
		Bool	cachePsf = False
	)

Set the transfer function for future convolutions to psf.

Assume circular convolution will be done

setPsf() [2/2]

template<class FType >

void casacore::Convolver< FType >::setPsf	(	const Array< FType > &	psf,
		IPosition	imageShape,
		Bool	fullSize = False,
		Bool	cachePsf = False
	)

Set the transfer function for future convolutions to psf.

Assume linear convolution with a model of size imageSize

validate()

template<class FType >

void casacore::Convolver< FType >::validate ( )

private

Member Data Documentation

doFast_p

template<class FType >

Bool casacore::Convolver< FType >::doFast_p

private

Definition at line 323 of file Convolver.h.

theFFT

template<class FType >

FFTServer<FType, typename NumericTraits<FType>::ConjugateType> casacore::Convolver< FType >::theFFT

private

Definition at line 308 of file Convolver.h.

theFFTSize

template<class FType >

IPosition casacore::Convolver< FType >::theFFTSize

private

Definition at line 305 of file Convolver.h.

theIFFT

template<class FType >

FFTServer<FType, typename NumericTraits<FType>::ConjugateType> casacore::Convolver< FType >::theIFFT

private

Definition at line 309 of file Convolver.h.

thePsf

template<class FType >

Array<FType> casacore::Convolver< FType >::thePsf

private

Definition at line 307 of file Convolver.h.

thePsfSize

template<class FType >

IPosition casacore::Convolver< FType >::thePsfSize

private

Definition at line 304 of file Convolver.h.

theXfr

template<class FType >

Array<typename NumericTraits<FType>::ConjugateType> casacore::Convolver< FType >::theXfr

private

Definition at line 306 of file Convolver.h.

valid

template<class FType >

Bool casacore::Convolver< FType >::valid

private

Definition at line 322 of file Convolver.h.

---

The documentation for this class was generated from the following file:

• scimath/Mathematics/Convolver.h