profitConvolvePSF: High level image convolution

Description Usage Arguments Details Value Author(s) See Also Examples

View source: R/profitConvolvePSF.R

Description

A high level interface to fast convolution that takes a user supplied image and point spread function (PSF) as inputs. This routine calls lower level functions like profitBruteConv and also implements FFT-based convolution using either R's built-in FFT or the 'fftw' interface to the FFTW library (the latter is usually significantly faster).

Usage

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profitConvolvePSF(image, psf, calcregion, docalcregion=FALSE, 
  options=list(method="Bruteconv"), sky = 0, plot = FALSE, ...)

Arguments

image

The image matrix to be convolved by the point spread function (PSF).

psf

The point spread function (PSF) image matrix that ProFit will use to convolve the image. This can have odd sizes in each dimension. If the dimension has an even size then the function will internally interpolate it onto an odd sized grid 1 element larger. The PSF will be automatically rescaled so it sums to 1 before convolution to ensure flux conservation in the model.

options

Additional options for model convolution parsed as a list. option$method inputs allowed are Bruteconv (brute force convolution), FFTconv (FFT convolution using the R fft function) and FFTWconv (FFT using the FFTW library). If using FFTconv or FFTWconv you will also need to supply a fft list. In practice this is one of the list outputs of profitBenchmarkConv (see Examples).

calcregion

Logical matrix; logical image matrix the same size as the input image matrix. If docalcregion=TRUE, then pixels in calcregion that are TRUE (or 1) will have the convolution calculated, pixels with FALSE (or 0) values will be set to 0. This is included to increase computation speed in situations where only a small region of the full image contains the galaxy of interest for fitting. In this case pixels a long way from the segmentation region for the galaxy will not need to be convolved in order to calculate the correct likelihood within the segmentation.

docalcregion

Logical; should the calcregion logical matrix be used to define a subset of pixels to be convolved.

sky

Numeric scalar; the sky level of the image. This is important to ensure the convolution works well at the edges, since the padded regions outside the image bounds will be effectively set to the sky value. If this is much higher of lower than the true sky then you may see artefacts.

plot

Logical; should a magimage plot of the output be generated?

...

Further arguments to be passed to magimage. Only relevant is plot=TRUE.

Details

In the regime where one image is significantly (a factor of a few) smaller than the other image, this tends to be faster than FFT based convolution due to the lack of image padding and other overheads. PSF images tend to be only dozens of pixels and images 100s, so brute force convolution is the standard approach used in ProFit. This function offers a convenient high level interface to link{profitBruteConv}, which can only accept odd size dimensions for the PSF.

Value

Matrix; convolved image matrix the same size as the input image matrix.

Author(s)

Aaron Robotham & Dan Taranu

See Also

profitBruteConv, profitMakePointSource, profitBenchmarkConv

Examples

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model = list(
	sersic = list(
		xcen   = c(180, 60),
		ycen   = c(90, 10),
		mag = c(15, 13),
		re  = c(14, 5),
		nser  = c(3, 10),
		ang  = c(46, 80),
		axrat  = c(0.4, 0.6),
		box = c(0.5,-0.5)
	)
)

model.image=profitMakeModel(model=model, dim=c(200,200))$z

psf=profitMakeGaussianPSF()

#Do some benchmarking:

temp=profitBenchmarkConv(model.image, psf=psf)

#Check the best:

temp$best

#And we can use all three:

magimage(profitConvolvePSF(model.image, psf, options=list(method='Bruteconv')))
magimage(profitConvolvePSF(model.image, psf, options=list(method='FFTconv', fft=temp$fft)))
magimage(profitConvolvePSF(model.image, psf, options=list(method='FFTWconv', fft=temp$fft)))

Example output

Loading required package: FITSio
Loading required package: LaplacesDemon
Loading required package: magicaxis
Loading required package: MASS
Loading required package: plotrix
Loading required package: sm
Package 'sm', version 2.2-5.6: type help(sm) for summary information

Attaching package: 'sm'

The following object is masked from 'package:MASS':

    muscle

Loading required package: mapproj
Loading required package: maps
Loading required package: R2Cuba
Loading required package: RColorBrewer
Warning message:
no DISPLAY variable so Tk is not available 
[1] "Bruteconv 5.310e+01 ms, FFTconv 2.530e+01 ms, FFTWconv 2.010e+01 ms"
$name
[1] "FFTWconv"

$time
[1] 1.632

ProFit documentation built on July 23, 2019, 9:04 a.m.