bad pixel mask - ascii

Frank Valdes wrote on Nov 15, 2001

Q:  I need to convert a bad pixel mask (.pl format) into an ASCII file.
I only need the coordinates of the flagged pixels but any ASCII output
would help as I could easily format it then. I tried with the 'imtab'
but got a memory error (the chip size is 2kx4k).


A:  Being able to extract only the coordinates of flagged pixels seems like
a useful thing for a general mask manipulation package.  We are investigating
improved support for mask manipulation but currently there is nothing
that does what you ask for in a single command.

It sounds like you are investigating using the TABLES package.  This
certainly has potential but there is another way.

LISTPIXELS is a basic task for converting an image into ascii (and a pl
file can be treated like an image).  So we start with that.  This will
dump coordinates and values for every pixel in the image.  It has a
possibly useful feature for you that the coordinates can be in user
coordinates (wcs=world) as well as pixel coordinates (wcs=logical).  So
the next step is how to get only the non-zero elements.  Because masks
are integer and the way LISTPIX formats the values the zero values will
always be " 0." at the end of each line.  So I suggest using MATCH to
match this pattern and then use the "stop" option to pass only those
lines that don't match.  So the following will do what you want:

cl> listpix mask.pl wcs=logical verbose- | match " 0.$" stop+
1. 2.  1.
3. 2.  1.
5. 2.  1.
 etc
 
Note that if you want just the coordinates the FIELDS task could be
added:


cl> listpix mask.pl wcs=logical verbose- | match " 0.$" stop+ | fields STDIN 1,2
1.   2.   
3.   2.   
5.   2.   
 etc


One thing to realize is that the IRAF command language currently implements
pipes so that each command completes and stores its output before the
next step.  So the listpix command will create a full ascii version of
the mask temporarily.

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Last post on Nov 15, 2001