<!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>Bad Pixel Detection and Removal</TITLE> <META NAME="description" CONTENT="Bad Pixel Detection and Removal"> <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="node657.html"> <LINK REL="previous" HREF="node655.html"> <LINK REL="up" HREF="node655.html"> <LINK REL="next" HREF="node657.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html9705" HREF="node657.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html9702" HREF="node655.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html9696" HREF="node655.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html9704" 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="tex2html9706" HREF="node657.html">Construction of Flat Fields</A> <B> Up:</B> <A NAME="tex2html9703" HREF="node655.html">Off-line Reduction</A> <B> Previous:</B> <A NAME="tex2html9697" HREF="node655.html">Off-line Reduction</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION003431000000000000000"> </A> <A NAME="irac2:bad-pixel-detection-and-removal"> </A> <BR> Bad Pixel Detection and Removal </H2> Before most of the reduction process can be conducted, bad pixel values must be removed. This is usually achieved by flagging pixels above or below some threshold value as bad, and replacing their values by those of nearby, non-bad pixels. The LAMP ON or LAMP OFF flat field images are a good place to start to define your bad-pixel map. To determine the threshold values to use, you should examine the statistics of the image and set thresholds 5 to 10 standard deviations away from the mean in both positive and negative directions. The exact thresholds for determination of bad pixels will depend on the details of your flat field observations - filter, objective lens, integration time and lamp voltage - so you should experiment with different values until you obtain a satisfactory result. <P> Because IR arrays are sensitive to thermal cycling and to atmospheric contamination, the bad pixel lists change over time. Recent lists are available via the ESO WWW pages for comparison to bad pixel maps you generate yourself, but are unlikely to perfectly match the list derived from your own data. <P> In MIDAS, bad pixel detection is possible with the command <TT> MASK/IRAC2</TT>; the command <TT>CMASK/IRAC2</TT> can be used for bad pixel removal. Refer to the MIDAS manual for further documentation of these commands. <P> <HR> <!--Navigation Panel--> <A NAME="tex2html9705" HREF="node657.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html9702" HREF="node655.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html9696" HREF="node655.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html9704" 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="tex2html9706" HREF="node657.html">Construction of Flat Fields</A> <B> Up:</B> <A NAME="tex2html9703" HREF="node655.html">Off-line Reduction</A> <B> Previous:</B> <A NAME="tex2html9697" HREF="node655.html">Off-line Reduction</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
