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<H2><A NAME="SECTION0011102000000000000000">
Image Formats</A>
</H2>
One and two dimensional images are produced by echelle commands.
These images are standard MIDAS frames, sampled in the following spaces:
<UL>
<LI>pixel-pixel space: corresponds to 2D raw images, with the sampling
units <TT>PIXEL</TT> in both dimensions.
<LI>pixel-order space: corresponds to 2D extracted images,
produced by the command <TT>EXTRACT/ECHELLE</TT>.
Unit in the <I>x</I>-axis is <TT>PIXEL</TT>,
unit in the <I>y</I>-axis is <TT>ORDER</TT>, sequential echelle order number.
<LI>wavelength-order space: corresponds to 2D extracted images, with
uniform sampling steps in wavelength, produced by the command <TT> REBIN/ECHELLE</TT>. Unit in the <I>x</I>-axis is Ångstrøm , unit in the <I>y</I>-axis
is <TT>ORDER</TT>, sequential echelle order number. These images <I>are not
standard</I>, in the sense that the descriptors <TT>START(1)</TT> and <TT> NPIX(1)</TT> are meaningless. The starting position for each order is defined
in the descriptor <TT>WSTART</TT>, and the number of pixels per order is
given by <TT>NPTOT</TT>, both descriptors are arrays of <TT>NPIX(2)</TT>
elements. This deviation from the standard is due, obviously, to the
different spectral range of each
echelle order.
<LI>wavelength space: corresponds to 1D images, sampled at constant
wavelength steps. These images are produced by the command
<TT>MERGE/ECHELLE</TT>. Unit in the <I>x</I>-axis is Ångstrøm .
</UL>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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