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I am working on some HST data and am using iraf to reduce the data and I have a couple of questions:1. Is there a task or command that I can use to make a single image consisting of 4 groups from 4 different images? I have 4 seperate images of the 4 chips of the WFPC2 instruments and I would like to have one single image with 4 groups. (I am working with the GEIS format for this)2. What is the syntax to access different groups of a fits image?

[quote:f6bf7fc63c="Guest"]I am working on some HST data and am using iraf to reduce the data and I have a couple of questions:1. Is there a task or command that I can use to make a single image consisting of 4 groups from 4 different images? I have 4 seperate images of the 4 chips of the WFPC2 instruments and I would like to have one single image with 4 groups. (I am working with the GEIS format for this) im> imcopy in.c1h out.fits
imcopy in.c2h out.fits[append]
imcopy in.c3h out.fits [append]
imcopy in.c4h out.fits[append]2. What is the syntax to access different groups of a fits image?[/quote:f6bf7fc63c] im> imheader out.fits[0] # to access the 1st image
imheader out.fits[3] # to access the 3rd extension or 4th image.
Cheers
Nelson Zarate

when I try to use imcopy, i get an empty image. Do you know why it does that?
I know my input image is not blankKushal