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<H2><A NAME="SECTION00634000000000000000"> </A><A NAME="1549"> </A><A NAME="1550"> </A>
<BR>
Specifying Pixels in an Image
</H2>
<P>
In some commands it is necessary to specify the columns and rows of
an image to which that command should refer. <BR>
This is done in the following way for e.g. a 2-dim frame:
<TT>frame[x1,y1:x2,y2]</TT>
<BR>
where the column specification, <TT>x</TT> or the row specification,
<TT>y</TT> can be any of
<UL>
<LI>world coordinates, indicated via real or integer numbers: 20.0,300
<LI>pixel numbers, indicated via integers preceded by @: @35,@200
<LI>or a special symbol to indicate
<I>start</I> (<), or <I>end</I> (>) of a row or column;
thus <TT>[@20,</TT><<TT>:@20,</TT>><TT>]</TT> specifies the complete 20th column of
a 2-dimensional image
</UL> <BR>
World coordinates are the physically meaningful coordinates with units such as
wavelengths or arc seconds (which are defined in the descriptor <TT>CUNIT</TT>).
Pixel numbers (starting with 1 for each dimension) are the indices
of an image seen as an array.
<BR>
For example, extracting the complete 12th plane from the 3-dim image stored in
<TT>cube.bdf</TT> is done via
<BR>
<TT>EXTRACT/IMAGE plane12 = cube [</TT><<TT>,</TT><<TT>,@12:</TT>><TT>,</TT>><TT>,@12] </TT>
<BR>
Single pixels can also be written in a more direct way, via
<BR>
<TT>frame[x,y,z] = value</TT>, e.g. to set the pixel in row 27 and column 1023 of
the 2-dim image <TT>lola.bdf</TT> to <TT>1.234</TT>, use
<TT>lola[@1023,@27] = 1.234</TT>
<BR>
The <I>value</I> can also be an <I>expression</I> made up of constants and elements
of any MIDAS data structure, see the subsection <A HREF="node40.html#symbol-substitution">3.6.2</A>.
<BR>
<BR>
Some of the commands dealing with images are:
<BR>
<TT>READ/IMAGE, WRITE/IMAGE, COMPUTE/IMAGE, STATIST/IMAGE,
DELETE/IMAGE, COPY/II</TT>.
<P>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-09</I>
</ADDRESS>
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