<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Combining Images</TITLE> <META NAME="description" CONTENT="Combining Images"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="next" HREF="node663.html"> <LINK REL="previous" HREF="node661.html"> <LINK REL="up" HREF="node655.html"> <LINK REL="next" HREF="node663.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html9771" HREF="node663.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html9768" HREF="node655.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html9762" HREF="node661.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html9770" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html9772" HREF="node663.html">Mosaicing</A> <B> Up:</B> <A NAME="tex2html9769" HREF="node655.html">Off-line Reduction</A> <B> Previous:</B> <A NAME="tex2html9763" HREF="node661.html">Flat Fielding</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION003435000000000000000"> </A> <A NAME="irac2:combining-images"> </A> <BR> Combining Images </H2> A number of the above steps require the combination of a number of IR images. This can be a sensitive matter because of the continuously varying sky background, and care must be taken to ensure that a suitable multiplicative scaling, or additive shift, is applied to match the sky background in all those frames being combined. Whether shifting or scaling is most appropriate unfortunately depends on the prevailing conditions, and you should experiment to find out which is best. <P> The command <TT>COMBINE/CCD</TT> is used to combine several images. The command itself has a number of options to use DO tables or catalogues, but the simplest version takes the form: <BLOCKQUOTE> <TT>COMBINE/CCD type images output </TT></BLOCKQUOTE> where <TT>type</TT> is one of <TT>BS</TT> (for bias), <TT>FF</TT> (for flat field), <TT>DK</TT> (for dark), <TT>SK</TT> (for sky) and <TT>OT</TT> (for other) and is used to indicate what type of image you are combining; <TT>images</TT> is a comma separated list of images you wish to combine; <TT>output</TT> is the name of the resulting output file. Scaling and/or shifting options can be specified for each of these image types. These parameters can be checked using <TT>SHOW/CCD type</TT>, and be set using <TT>SET/CCD type</TT>, where <TT>type</TT>, using the codes listed above, specifies the type of image whose combination parameters you are interested in. An example is displayed below: <BLOCKQUOTE> <TT>COMBINE/CCD FF kflat1,kflat2,kflat3 kflat </TT></BLOCKQUOTE> will combine the images <TT>kflat1</TT>, <TT>kflat2</TT> and <TT>kflat3</TT> into an output image <TT>kflat</TT> using the combination options specified for the FF image type. <P> <HR> <!--Navigation Panel--> <A NAME="tex2html9771" HREF="node663.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html9768" HREF="node655.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html9762" HREF="node661.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html9770" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html9772" HREF="node663.html">Mosaicing</A> <B> Up:</B> <A NAME="tex2html9769" HREF="node655.html">Off-line Reduction</A> <B> Previous:</B> <A NAME="tex2html9763" HREF="node661.html">Flat Fielding</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
