<!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>Reduction Steps</TITLE> <META NAME="description" CONTENT="Reduction Steps"> <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="node445.html"> <LINK REL="previous" HREF="node443.html"> <LINK REL="up" HREF="node441.html"> <LINK REL="next" HREF="node445.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html6989" HREF="node445.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html6986" HREF="node441.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html6980" HREF="node443.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html6988" 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="tex2html6990" HREF="node445.html">Removing Irrelevant Columns</A> <B> Up:</B> <A NAME="tex2html6987" HREF="node441.html">CCD Detectors</A> <B> Previous:</B> <A NAME="tex2html6981" HREF="node443.html">Discussion</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION002513000000000000000"> </A> <A NAME="reduction-steps"> </A> <BR> Reduction Steps </H2> <P> The software now available is a package for doing relative calibrations of the pixels, for averaging frames, and for cleaning images. Cleaning in this context means removal of instrumental faults and other defects from the images. A list of the relevant commands is provided for reference in the section <A HREF="node453.html#ccd-commands-summary">B.1.10</A> of this appendix. <P> The CCD-reduction involves the steps outlined below. Steps in paranthesis [...] are optional but see the following discussion to determine if they are optional in your particular case. <UL> <LI>[ Remove irrelevant columns of all frames ] <LI>[ Bias correct all frames ] <LI>compute an average DARK <!-- MATH: $\Longrightarrow$ --> <IMG WIDTH="41" HEIGHT="21" ALIGN="BOTTOM" BORDER="0" SRC="img931.gif" ALT="$\Longrightarrow$"> DARK_AVG <LI>[ remove defects from DARK_AVG ] <LI>compute an average FLAT <!-- MATH: $\Longrightarrow$ --> <IMG WIDTH="42" HEIGHT="21" ALIGN="BOTTOM" BORDER="0" SRC="img932.gif" ALT="$\Longrightarrow$"> FLAT_AVG <LI>dark subtraction <!-- MATH: $\Rightarrow$ --> <IMG WIDTH="27" HEIGHT="21" ALIGN="BOTTOM" BORDER="0" SRC="img933.gif" ALT="$\Rightarrow$"> FLAT_AVG = FLAT_AVG - DARK_AVG <LI>[ remove defects from FLAT_AVG ] <LI>[ normalize the FLAT_AVG,( see Eq. (<A HREF="node442.html#ccd-6">B.6</A>)) <!-- MATH: $\Rightarrow$ --> <IMG WIDTH="28" HEIGHT="21" ALIGN="BOTTOM" BORDER="0" SRC="img934.gif" ALT="$\Rightarrow$"> FLAT_NRM ] <LI>dark subtraction <!-- MATH: $\Rightarrow$ --> <IMG WIDTH="27" HEIGHT="21" ALIGN="BOTTOM" BORDER="0" SRC="img935.gif" ALT="$\Rightarrow$"> SCIE_FRM = SCIE_FRM - DARK_AVG <LI>[ remove defects from SCIE_FRM ] <LI>flatfield the scie-frame SCIE_FLAT = SCIE_FRM/FLAT_NRM <LI>compute the average of science frames <!-- MATH: $\Rightarrow$ --> <IMG WIDTH="28" HEIGHT="21" ALIGN="BOTTOM" BORDER="0" SRC="img936.gif" ALT="$\Rightarrow$"> SCIE_AVG </UL>The sections below describe and discuss the various options which are available to perform the needed operations. These sections discuss bias corrections, techniques for computing averages, techniques for cleaning images and removing specific defects, and finally how to use the <TT>COMPUTE</TT> command for dark subtraction and flat fielding. <P> <HR> <!--Navigation Panel--> <A NAME="tex2html6989" HREF="node445.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html6986" HREF="node441.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html6980" HREF="node443.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html6988" 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="tex2html6990" HREF="node445.html">Removing Irrelevant Columns</A> <B> Up:</B> <A NAME="tex2html6987" HREF="node441.html">CCD Detectors</A> <B> Previous:</B> <A NAME="tex2html6981" HREF="node443.html">Discussion</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
