RE: [APML] What's the Best Way to "Combine" Two Images of Differing Times?

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

John,

That's a lot of gyrations with a lot of programs, but the result sure is
nice!  I'm interested in seeing the individual exposures that went into
the composites.

Dave Kodama




> Wade,
> 	By a staggering coincidence, I just finished a stack of film images!
> My images were stacked to bring out the faintest details, not to preserve
> highlights. Actually, they were more of an experiment with PixInsight DBE
> which I think I finally have the hang of. I aligned the images using
> RegiStar as you did, but my version is old. I don't know if it can produce
> stacks > 16 bit or not, my version can't. For stacking after registration
> I
> use MaxIm DL as I have it for CCD work. I then worked levels and curves as
> much as possible before returning to 16 bit space for my old Photoshop 6.
> I
> would think that this would work with your images as well - adding them
> together but not limiting max pixel values to 16 bit levels. PixInsight
> can
> work with 32+ bit files as well instead of MaxIm. I am still learning this
> software but I think that you can simply add them with pixel math. Season
> to
> taste with curves and levels before reducing the stack to 16 bit. Would
> this
> not help preserve highlights?
>
> 	Here are a couple of stacks from tech pan. In the 32 bit TIFF, stars
> peaked out at a count of 130,000. Way more headroom than the 65,000 limit
> to
> 16 bit files! Other ways of doing this (which I am not familiar with)
> involve layers in Photoshop. I believe that Rob Gendler has an article on
> his web site about this technique. With these large dynamic range file
> formats, applying CCD techniques to old film images is opening up a few
> more
> doors!
>
> http://www.astrofoto.ca/john/ic59.htm
> http://www.astrofoto.ca/john/sh2-216.htm
>
> John Mirtle
> Calgary, Ab. Canada
>
>
> -----Original Message-----
> From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
> On
> Behalf Of Thomas W. Earle
> Sent: Monday, September 19, 2005 10:24 PM
> To: astro-photo@seds.org
> Subject: [APML] What's the Best Way to "Combine" Two Images of Differing
> Times?
>
> For bright objects, such as M42, it is a known fact that combining
> several images at various times helps in getting the full dynamic
> range of this nebula; however, I'm not quite sure what's the best
> way to go about this.  I have Registar, but none of the Functions to
> apply seem like the "perfect" choice.  I feel using them will either
> destroy the shadows or the highlights.  I see that many recommend
> using Ray Gralak's Sigma function; unfortunately, he recommends one
> should have ten or more images to combine for "best" results.
> There's no way I can get 10 shots since each film shot ranges from
> 30 minutes to 3 1/2 hours.  Anybody have a proven technique to get
> the most out two or more images exposed differently?  For example,
> let's say I take three images of M42 at F/5.0: one 30 minute, one 90
> minute, and one 180 minute.  What's the best way to get the full
> dynamic range of these images (i.e. visible structure from the
> center of M42 to its faintest extensions?  Any suggestions or
> comments would be greatly appreciated.
>
> Thanks in advance,
>
> Wade
>
>
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