IRAF Newsletter -- Number 14 -- April 1998

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IMTYPE and the IMRED Spectral Reductions Tasks

As discussed elsewhere in this Newsletter there have been some important changes concerning use of different image disk formats. The goal is to allow you to select the types of image formats and extensions to be used by IRAF image tasks and to allow you to use image names without an explicit extension. These features create additional challenges for the software.

The major spectral reduction tasks in the imred spectroscopy packages-- dofibers , doslit , dohydra , doecslit , doargus , and dofoe --are not fully general in supporting all combinations of image formats and image kernel variable specifications. Further system development is planned to allow scripts to deal with the variety of image types and extensions. If you do nothing at all and continue to use the defaults of ".imh" images then these useful tasks will continue to work as before; this is the most thoroughly tested mode of operation. However if you want to use other image types then this article summarizes what you need to do. Don't panic--you are able to use your favorite image disk format.

The requirement is that you must use the same image type and extension for the input and output, and the extension must be the default for the image type. Start by identifying the image type and extension for your input data; it must all be of the same type. For example, your raw data may be OIF with extension ".imh", STF format with extension ".c0h", or FITS format with extension ".fits". Now look at the imextn variable:

The requirement means that for a particular format the first extension must be that of your input data. From the above example the default is fine for OIF and FITS, but the STF definition would need to be changed to "stf:c0h,??h". If instead of the default ".fits" extension you wanted to use ".fit" you would need to change the FXF part to "fxf:fit,fits".

Now you have to tell the reduction scripts the extension to expect. This is done with the "imtype" variable. Nominally the imtype variable would specify the image type and have some other qualifiers. The reduction scripts require that the first part of the specification be the actual extension followed by the optional qualifiers. So, if you have extension ".c0h" for STF format data you would need to set imtype and imextn as below.

The items in the brackets are optional. To understand what is going on, the reductions scripts use the part before the first comma as the extension for the input data.

To conclude let us consider the three most likely cases. If your input data has the ".imh" extension then you should have the following:

# Acceptable values for .imh input.

These are the defaults provided if you don't change anything in your login files. If your input data has the ".fits" extension then you only need to set imtype to "fits" as shown below.

# Acceptable values for .fits input.

Finally if you want to use ".fit" as the extension then you need to set both "imtype" and "imextn". The following is one way to do it.

# Acceptable values for .fit input.

The imtype variable can include a following ",inherit" or ",noinherit" and you can include fields for other image types or FITS extensions in the imextn variable.

Frank Valdes

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Posted: 07May1998