<!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>How the Data is Processed</TITLE>
<META NAME="description" CONTENT="How the Data is Processed">
<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="node52.html">
<LINK REL="previous" HREF="node50.html">
<LINK REL="up" HREF="node50.html">
<LINK REL="next" HREF="node52.html">
</HEAD>
<BODY >
<!--Navigation Panel-->
<A NAME="tex2html2078"
HREF="node52.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
SRC="icons.gif/next_motif.gif"></A>
<A NAME="tex2html2075"
HREF="node50.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
SRC="icons.gif/up_motif.gif"></A>
<A NAME="tex2html2069"
HREF="node50.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
SRC="icons.gif/previous_motif.gif"></A>
<A NAME="tex2html2077"
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="tex2html2079"
HREF="node52.html">Running REDUCE/CCD</A>
<B> Up:</B> <A NAME="tex2html2076"
HREF="node50.html">Processing the Data</A>
<B> Previous:</B> <A NAME="tex2html2070"
HREF="node50.html">Processing the Data</A>
<BR>
<BR>
<!--End of Navigation Panel-->
<H2><A NAME="SECTION00691000000000000000"> </A>
<A NAME="ccd:how-the-data-is-processed"> </A>
<BR>
How the Data is Processed
</H2>
Before any processing on the input frame is done, the <TT>REDUCE/CCD</TT>
command will first collect all resources needed for the calibration of the
science frame(s). These include the master calibration frames, the overscan
offset, and scaling parameters. So, at this point no operations are
done yet. This is done for efficiency reasons: all standard calibration
arithmetic on the input frame is done in one go. As an example,
suppose the science frame is supposed to be corrected for dark current
and to be flat fielded. From the Association Table the command first
identifies the names of the master dark and flat frames, and checks for
their existence. If they are not present they will be created.
Next, the master dark and flat field will be checked on their
processing status. If they have not been processed yet, that will first be
do by another (recursive) run of the <TT>REDUCE/CCD</TT> command. In this
second run also the scaling factors (<I>i.e.</I> exposure times and
the mean of the flat field frame) will be determined.
<P>
The standard calibration operation is done by a large <TT>COMPUTE/IMAGE</TT>
with the following input:
<BR><P></P>
<DIV ALIGN="CENTER">
<!-- MATH: \begin{equation}
out = (in-scan-biasfrm-darkscale*darkfrm) * flatscale/flatfrm
\end{equation} -->
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP>
<I>out</I> = (<I>in</I>-<I>scan</I>-<I>biasfrm</I>-<I>darkscale</I>*<I>darkfrm</I>) * <I>flatscale</I>/<I>flatfrm</I>
</TD>
<TD WIDTH=10 ALIGN="RIGHT">
(3.11)</TD></TR>
</TABLE>
</DIV>
<BR CLEAR="ALL"><P></P>
Here, <I>out</I> is the output frame, <I>in</I> is the input frame, <I>scan</I> is
the overscan bias value or frame, <I>biasfrm</I> is the master bias,
<I>darkfrm</I> and <I>darkscale</I> are the master dark frame and scaling factor, and
<I>flatfrm</I> and <I>flatscale</I> are the master flat field and the mean value of
the flat field. In the <TT>COMPUTE</TT> <I>biasfrm</I> and <I>darkfrm</I> can also be
constants.
<P>
<HR>
<!--Navigation Panel-->
<A NAME="tex2html2078"
HREF="node52.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
SRC="icons.gif/next_motif.gif"></A>
<A NAME="tex2html2075"
HREF="node50.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
SRC="icons.gif/up_motif.gif"></A>
<A NAME="tex2html2069"
HREF="node50.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
SRC="icons.gif/previous_motif.gif"></A>
<A NAME="tex2html2077"
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="tex2html2079"
HREF="node52.html">Running REDUCE/CCD</A>
<B> Up:</B> <A NAME="tex2html2076"
HREF="node50.html">Processing the Data</A>
<B> Previous:</B> <A NAME="tex2html2070"
HREF="node50.html">Processing the Data</A>
<!--End of Navigation Panel-->
<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
</ADDRESS>
</BODY>
</HTML>
