image.tofits - Function

Convert the image to a FITS file

Synopsis
tofits(outfile, velocity, optical, bitpix, minpix, maxpix, region, mask, overwrite, dropdeg, deglast, async)

Arguments

outfile	in	FITS file name
		Allowed:	String
		Default:	Input name + `.fits'
velocity	in	prefer velocity (rather than frequency) as primary spectral axis?
		Allowed:	Bool
		Default:	F
optical	in	use the optical (rather than radio) velocity convention?
		Allowed:	Bool
		Default:	T
bitpix	in	Bits per pixel
		Allowed:	-32 (floating point) or 16 (integer)
		Default:	-32
minpix	in	Minimum pixel value for BITPIX=16
		Allowed:	Float
		Default:	Autoscale
maxpix	in	Maximum pixel value for BITPIX=16
		Allowed:	Float
		Default:	Autoscale
region	in	The region of interest
		Allowed:	Region tool
		Default:	Whole image
mask	in	OTF mask
		Allowed:	Boolean LEL expression or mask region
		Default:	None
overwrite	in	Overwrite (unprompted) pre-existing output file ?
		Allowed:	T or F
		Default:	F
dropdeg	in	Drop degenerate axes ?
		Allowed:	T or F
		Default:	F
deglast	in	Put degenerate axes last in header ?
		Allowed:	T or F
		Default:	F
async	in	Run asynchronously?
		Allowed:	Bool
		Default:	!dowait

Returns
T or fail

Description

This function converts the image into a FITS file.

If the image has a rest frequency associated with it, it will always write velocity information into the FITS file. By default the frequency information will be primary as it is better defined than velocity information. If you select velocity=T then by default the velocity is written in the optical convention, but if optical=F it will use the radio convention instead.

The FITS definition demands equal increment pixels. Therefore, if you write velocity information as primary and use the optical velocity definition, the increment is computed at the spectral reference pixel. If the bandwidth is large, this may incur non-negligible coordinate calculation errors far from the reference pixel.

By default the image is written as a floating point FITS file (bitpix= -32). Under rare circumstances you might want to save space and write it as scaled 16 bit integers (bitpix = 16). You can have tofits calculate the scaling factors by unsetting minpix and maxpix (the default). If you set minpix and maxpix, values outside of that range will be truncated. This can be useful if all of the FITS images dynamic range is being used by a few high or low values and you are not interested in preserving those values exactly. Besides the factor of two space savings you get by using 16 instead of 32 bits, integer images usually also compress well (for example, with the standard GNU software facility gzip).

If the specified region-of-interest extends beyond the image, it is truncated.

The output mask is the combination (logical OR) of the default input pixel mask (if any) and the OTF mask.

Sometimes it is useful to drop axes of length one (degenerate axes) because not all FITS readers can handle them. Use the dropdeg argument if you want to do this.

Example

- ok := im.tofits('MYFILE.FITS')             # write FITS image file
- ok := im.tofits('MYFILE2.FITS', bitpix=16) # Write as scaled 16 bit integers

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	Package	general
	Module	images
	Tool	image