<!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>Noise</TITLE> <META NAME="description" CONTENT="Noise"> <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="node208.html"> <LINK REL="previous" HREF="node206.html"> <LINK REL="up" HREF="node201.html"> <LINK REL="next" HREF="node208.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html3989" HREF="node208.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html3986" HREF="node201.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html3980" HREF="node206.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html3988" 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="tex2html3990" HREF="node208.html">Other Images</A> <B> Up:</B> <A NAME="tex2html3987" HREF="node201.html">Test Data</A> <B> Previous:</B> <A NAME="tex2html3981" HREF="node206.html">1-Dimensional Images (``Spectra'')</A> <BR> <BR> <!--End of Navigation Panel--> <H1><A NAME="SECTION001440000000000000000"> Noise</A> </H1> Real data always comes with some noise, and it is important that the software does not worsen the noise spectrum (in pixel as well as in data space) more than necessarily. With the command CREATE/RANDOM_IMAGE, images with various random-number distributions can be generated. For most purposes it will be sufficient to just add such an image (using COMPUTE/IMAGE) to the frame with the test pattern. This would simulate the case where there is only detector read-out noise. If for some reason the simulation of photon noise is more desirable, this case can be approximated by scaling (again using COMPUTE/IMAGE) the amplitude of a suitable noise distribution (output of CREATE/RANDOM_IMAGE) with the square root of the pattern before it is added to the pattern frame. Evidently, all kinds of combinations of these two cases can be used. <P> If the STMODEL context is available (activated by <TT>SET/CONTEXT MODEL</TT> in a MIDAS session), then the command <TT>HPOIS</TT> may also be used for the simulation of noise. <P> <BR><HR> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
