Re: [APML] First images posted: vignetting correction,circular cropping

["D. Kodama" <kodama@alumni.caltech.edu>]

Ray,

If you've achieved fully automatic processing of your images, that's
pretty impressive.  Isn't that the holy grail for image processing?  I'm
curious to know some details of how this is achieved.  A step-by-step
description showing the result of the processing step would be very
interesting.  One of the things I had hoped for when I first started
shooting astrophotos was to develop a standardized set of processing
procedures so as to be able to compare images easily as well as to remove
variations caused by how I was looking at things at the time I processed a
shot.  But it seemed impossible to get even close to doing that,
especially with point-and-click oriented tools like photoshop which lack
scripting capability.  Tell me more!

Dave

PS: "you never publish your results until you are entirely happy
 with them" -- Uh oh, with that as a guideline, I shouldn't be putting
anything online...



>
> Hi folks.
>
> Since I joined the list about a year ago, some of you may have noticed
> that I talk the talk, but wondered if I walk the walk? (;-))
>
> I guess that being a research astronomer has instilled a very cautious
> attitude: you never publish your results until you are entirely happy
> with them, and are confident that you've covered all the angles and
> gotchas. Since my hobby astrophoto "data" is of limited quantity and
> imperfect quality, I have concentrated on squeezing the most out of them
> by developing my own digital processing methods. The problem with this
> is that it can go on forever - one is never entirely satisfied with the
> result. Little gotchas always remain, especially the higher order
> residuals when one tries to do photographic vignetting correction..
>
> But now I've decided to just say "that'll do, pig" to myself, and start
> publishing some of my images online. I'd like to thank Dave Kodama for
> prompting me to do this - if he hadn't asked me recently to show an
> example of my circular cropping technique, I might not have taken that
> step yet!
>
> The first example is here:
> http://tinyurl.com/9re5f
>
> It is a nice illustration of a few things you don't often see:
> - Medium format (6x4.5cm) through a bog-standard 2" focuser
> - Use of a fast achromat (what, no APO?!) with medium format
> - Use of a fast refractor out to a wide field (wider than on 35mm)
> without a field flattener/reducer
> - Manual guiding (in this day and age!)
> - Use of a heavy-duty mount which is actually very affordable (EQ6)
> - Automated multi-scan scaling & coaddition with scanner saturation
> removed by masking
> - Automated rebate intensity subtraction and rebate cropping
> - Automated channel registration (lateral colour correction)
> - Automated vignetting/gradient correction (could be a bit better)
> - Automated circular cropping (- Dave, this is what you wanted to see)
> - Automated levels set by image's own statistics, for final RGB
> recombination
>
> I guess this is the point where I am supposed to say: "Comments &
> criticisms welcome" !
>
> Ray "who is still a bit apprehensive about releasing flawed results"
> Butler
>
> --
> Dr. Ray Butler
> Lecturer, Physics Department & Computational Astrophysics Laboratory,
> National University of Ireland - Galway,
> University Road, Galway, Ireland.
> Web: www.nuigalway.ie/physics/ 	Email: ray.butler-AT-nuigalway.ie
> Tel: +353-91-493788 		FAX: +353-91-494584
>
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