RE: [APML] Star Shaping

[Jon Kolb <jkolb@mindport.com>]

Matt,

Good article.  In PW, I believe (haven't tried it yet) the analog recipe
would be thus:

1) Create a brightness curve mask to select the stars by using Mask/New.
Click on the brightness curve icon, adjust the curve to select only the
brightest pixels, check what gets selected and refine if needed, then click
OK.

2) Using Transformation/Gray/Brightness Curve, shape the curve as in the
article, but first be sure to select the mask you created above, and leave
the mask amount sliders where they are so that you only affect the stars.
Use Preview or Apply to check and refine your work, then click OK when
you're done.

The brightness curve mask can be useful for other things as well.  It can be
used to exclude the stars when adjusting the Brightness Curve or Color
Curves so that only a nebula or something gets affected.  It can also be
used to exclude the stars when doing a Gaussian blur to keep the stars sharp
(sort of the opposite of "star shaping").

One concern I would have is using the star shaping technique with images
taken on Newtonian or Cassegrain scopes.  It seems that the distinctive
diffraction spikes, something I really like, would get softened, too.  Sharp
spikes are a sign of good focus and I think add to the beauty of the image -
something I wouldn't want to lose.  Of course, only trying out the procedure
will determine if this is an issue.

Sincerely,
Jon Kolb
Adventures in Astrophotography
http://home.datawest.net/jkolb/
jkolb@mindport.com
  

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