Re: brief note on astrometry of Mark IV comatic images

[hjohnson@pluto.njcc.com (Herbert R Johnson)]

On Wed, 31 May 2000 23:20:30 -0500, Tom Droege <droege@wwa.com> wrote:
*>I think the real problem comes when two faint stars are close.  It is then 
*>hard to tell if there are two stars.  The star is just smeared out.   This 
*>is OK, except sometimes due to the position on an image it might appear as 
*>two stars and sometimes as one.

The issue of appearance kinda begs the question. What you see on the screen
may not be what you get via your software, to stretch an aphorism. The
visual appearance of a star image depends on the black threshold, the
white threshold, and the pixel map or pallette (from pixel value to
displayed value). I would guess, thinking as I type, that you'd want
to use the same criteria as your star-finding program for the thresholds.
As for the palette, for this purpose I'd suggest mapping ALL the pixels
between the thresholds as "white": then any overlap would be pretty clear
to a visual observer. That is, to the extent you look at every part of
the image with a coarse pixel resolution so you can resolve individual stars.

I like my other suggestion better, check the star lists for adjacency, that
you can automate.

Herb Johnson

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