[APML] Photoshop tip for healing star elongation- is this useful?

[Alan Voetsch <critter12952@yahoo.com>]

Hi all,

The following is an attached reply that Ron Wodaski made to a question on
the SBIG users group. I'd like to know if this is a valid technique for
film users. I don't see a problem with it, but I'm going to leave it up to
more knowledgeable PS masters. I'm cleaning out my folders and would like
to know if this is worth saving, or if there is a better method available.

Thanks,
Alan

P.S. His post also brings up the fact that I have no idea what 'Layers'
are. I'll need to find out more about how and when to use them. Be afraid,
very afraid. :-) 

--- Ron Wodaski <ronw@nwlink.com> wrote:
> To: <SBIG@yahoogroups.com>
> From: "Ron Wodaski" <ronw@nwlink.com>
> Date: Tue, 27 Aug 2002 12:51:43 -0700
> Subject: [SBIG] Photoshop tip for healing star elongation (was:
> MaxIM/CCD)
> 
> Here's a Photoshop tip for dealing with elongated stars. I don't recall
> where I picked it up (probably in one of the Yahoo groups, maybe even
> right
> here).
> 
> Photoshop doesn't allow sub-pixel movements of a layer. Enlarge the
> image
> 400 or 800%, make the moves suggested below, and then shrink the image
> back
> to 100% when done.
> 
> * If the stars are elongated in a single direction (linear elongation),
> make
> one copy of the layer after enlargement. Make sure this layer is ABOVE
> the
> original in the Layers palette.
> 
> * Change the blend mode of the new layer to "Darken."
> 
> * Hold down the Control key and use the arrow keys to shift the new
> layer
> one pixel at a time. (Keep in mind that these pixels are 1/4th or 1/8th
> pixels in the final image when you go back to 100%.) Note how moving the
> layer will darken the stars from one side, enabling you to make the
> stars
> more circular. Find the best shift that circularizes the stars without
> obliterating the smallest stars. Usually, a shift of 1-2 pixels is all
> that
> you can do without having a negative impact on  the overall image.
> Larger
> shifts will create artifacts in nebulae and galaxies.
> 
> Once you find the best shift, convert back to 100%. For example, if you
> increased the image size to 400%, to get back to the original size,
> resize
> to 25%. (You can use other enlargements besides 400% and 800%, by the
> way.
> But those two enlargement factors are less likely to cause artifacts
> related
> to interpolation.)
> 
> This won't cure really bad elongation, but it is surprisingly effective
> on
> small to moderate elongations.



__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com

--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>