NRAO Home > CASA > CASA Toolkit Reference Manual
image.sepconvolve - Function

1.1.1 Separable convolution


Description

This function does Fourier-based convolution of an image file by a specified separable kernel.

If outfile is given, the image is written to the specified disk file. If outfile is unset, the on-the-fly Image tool returned by this function is associated with a temporary image. This temporary image may be in memory or on disk, depending on its size. When you destroy the Image tool (with the done function) this temporary image is deleted.

You specify which axes of the image you wish to convolve, by what kernel of what width. The kernel types can be shortened to ‘gauss’, ‘hann’ and ‘box’.

You specify the widths of the convolution kernels via the argument widths. The values can be specified as a vector of three different types.

The interpretation of widths depends upon the kernel type.

The scaling of the output image is determined by the argument scale. If you leave it unset, then autoscaling will be invoked which means that the convolution kernels will all be normalized to have unit volume to as to conserve flux.

If you do not leave scale unset, then the convolution kernel will be scaled by this value (it has peak unity before application of this scale factor).

Masked pixels will be assigned the value 0.0 before convolution. The output mask is the combination (logical OR) of the default input pixel mask (if any) and the OTF mask. Any other input pixel masks will not be copied. Use function maskhandler if you need to copy other masks too.

See also the other convolution functions convolve2d, convolve and hanning.

Arguments





Inputs

outfile

Output image file name. Default is unset.

allowed:

string

Default:

axes

Axes to convolve. Default is [0,1,...].

allowed:

intArray

Default:

-1

types

Type of convolution kernel. Vector of strings from ’boxcar’, ’gaussian’, and ’hanning’. Default is appropriately sized vector of ’gaussian’.

allowed:

stringArray

Default:

widths

Convolution kernel widths, Vector of numeric, quantity or string

allowed:

any

Default:

variant

scale

Scale factor. Default is autoscale.

allowed:

double

Default:

-1

region

Region selection. See ”help par.region” for details. Default is to use the full image.

allowed:

any

Default:

region

mask

Mask to use. See help par.mask. Default is none.

allowed:

any

Default:

variant

overwrite

Overwrite (unprompted) pre-existing output file?

allowed:

bool

Default:

false

stretch

Stretch the mask if necessary and possible? See help par.stretch. Default False

allowed:

bool

Default:

false

Returns
image

Example

 
 
"""  
#  
print "\t----\t sepconvolve Ex 1 \t----"  
ia.maketestimage(’xyv’,overwrite=true)  
im2 = ia.sepconvolve(outfile=’xyv.con’, axes=[0,1], types=["gauss","box"], widths=[10,20], overwrite=true)  
im2.done()  
ia.close()  
#  
"""  
 
 

__________________________________________________________________


More information about CASA may be found at the CASA web page

Copyright 2016 Associated Universities Inc., Washington, D.C.

This code is available under the terms of the GNU General Public Lincense


Home | Contact Us | Directories | Site Map | Help | Privacy Policy | Search