<!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>Using the COMPUTE Command</TITLE> <META NAME="description" CONTENT="Using the COMPUTE Command"> <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="node450.html"> <LINK REL="previous" HREF="node448.html"> <LINK REL="up" HREF="node441.html"> <LINK REL="next" HREF="node450.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html7044" HREF="node450.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html7041" HREF="node441.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html7035" HREF="node448.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html7043" 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="tex2html7045" HREF="node450.html">Examples and Hints</A> <B> Up:</B> <A NAME="tex2html7042" HREF="node441.html">CCD Detectors</A> <B> Previous:</B> <A NAME="tex2html7036" HREF="node448.html">Cleaning Images</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION002518000000000000000"> Using the COMPUTE Command</A> </H2> <P> The <TT>COMPUTE/IMAGE</TT> command can be used to perform the operation of dark subtraction and flat fielding. The <TT>COMPUTE/IMAGE</TT> command is a very general purpose command and is described in great detail in Vol. A, Appendix A. The functionality of <TT>COMPUTE/IMAGE</TT> for the current purpose is explained below. <P> To do a dark subtraction enter the following:<BLOCKQUOTE> <TT>COMPUTE/IMAGE DENOM = FLAT_AVG-DARK_AVG</TT></BLOCKQUOTE>where <TT>DENOM</TT> is the result frame, <TT>FLAT_AVG</TT> is the average of flat fields, and <TT>DARK_AVG</TT> is the average of dark frames. <P> To flat-field a data frame, enter the following:<BLOCKQUOTE> <TT>COMPUTE/IMAGE SCIE_FLAT = (SCIE_IN-DARK_AVG)/DENOM</TT></BLOCKQUOTE>where <TT>SCIE_FLAT</TT> is the flat fielded science frame, <TT>SCIE_IN</TT> is the input data frame, <TT>DARK_AVG</TT> is the average of dark frames, and <TT>DENOM</TT> is the dark subtracted flat field from above. <P> <BR><HR> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
