image.continuumsub

Image plane continuum subtraction

Synopsis
continuumsub(outline, outcont, region, channels, pol, fitorder, overwrite)

Arguments

outline	in	Output line image filename
		Allowed:	String
		Default:	unset
outcont	in	Output continuum image filename
		Allowed:	String
		Default:	'continuumsub.im'
region	in	Region over which continuum subtraction is desired
		Allowed:	Region
		Default:	whole image
channels	in	Channels to use for continuum estimation
		Allowed:	Vector<Int>
		Default:	All
pol	in	Polarization to process
		Allowed:	String from "I Q U V XX RR" etc.
		Default:	unset
fitorder	in	Polynomial order for continuum estimation
		Allowed:	Int
		Default:	0
overwrite	in	Auto-overwrite output files if they exist?
		Allowed:	Boolean
		Default:	F

Returns
Image tool containing the continuum-subtracted result.

Description

This function packages the relevant image tool functionality for simple specification and application of image plane continuum subtraction. All that is required of the input image is that it have a non-degenerate Spectral axis.

The user specifies region, the region of the input image over which continuum subtraction is desired (otherwise the whole image will be treated); channels, the subset of channels on the spectral axis to use in the continuum estimation, specified as a vector; pol, the desired single polarization to treat (otherwise all pols, if a polarization axis exists, will be treated); fitorder, the polynomial order to use in the estimation. Optionally, output line and continuum images may be written by specifying outline and outcont, respectively. If outline is not specified, a virtual image tool is all that is produced. If outcont is not specified, the output continuum image will be written in 'continuumsub.im'.

In principle, the region may be specified interactively, e.g., using the viewer. At the moment, such regions are typically degenerate on the spectral axis, and so must be manually extended along the this axis, or continuumsub will complain about insufficient spectral channels in the region of interest. Interface improvements in the management of regions currently under consideration will improve the mechanism for doing this.

Example

 
- im1 := image('test1.im');
- im1csub:=im.continuumsub(region=drm.quarter(),channels=[3:8,54:60],fitorder=0);

In this first example, the continuum emission in each pixel of the inner quarter of the input image is estimated by averaging (fitorder=0) channels 3-8 and 54-60. im1csub is an image tool containing the result (only the inner quarter of the original image).

 
- im2 := image('test2.im');
- im2csub:=im.continuumsub(channels=[3:8,54:60],pol='I',fitorder=2);

In this second example, the Stokes I continuum emission in each pixel of the whole input image is estimated with a 2nd-order polynomial fit to channels 3-8 and 54-60. The output image tool (im2csub) contains only Stokes I, even if the original image had other stokes planes.

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	Package	general
	Module	images
	Tool	image

image.continuumsub - Function