Re: [APML] Benefits of Registar?

["Steve..." <swalters@worldnet.att.net>]

Kevin,

Matt has given you a very good definition of what happens when you stack
images and he is correct that grain is a significant noise component for
most films. There has been a lot of discussion here about what constitutes
"noise". From the perspective of the stacking algorithm, whatever is present
in both is "signal" and anything that is present in one exposure but missing
in another is "noise". This is because the "signal" elements, being present
in both images, will add and therefore increase in magnitude whereas "noise"
components will remain at their original magnitude. For example, a meteor
trail that only appears in one exposure will be half as bright as compared
to elements that are present in both when two exposures are stacked.
Likewise, any other variations due to seeing or tracking will tend to
diminish. For example, if one exposure has stars elongated in one direction
but another exposure has them elongated in a different direction, stacking
will increase the brightness of the central stellar region present in both
images. This does not mean that stacking will compensate for bad seeing or
tracking, you should do the best possible job and toss out those that are
badly exposed. But stacking will help reduce any differences that exist
between exposures. This can also be used to reduce scanner noise by scanning
an image two or more times and then stacking them.

Steve...


----- Original Message -----
From: "Matt BenDaniel" <matt@starmatt.com>
To: <astro-photo@seds.org>
Sent: Wednesday, May 22, 2002 2:22 PM
Subject: Re: [APML] Benefits of Registar?


> Kevin,
>
> RegiStar is one of the best tools to use for stacking. Stacking takes
> multiple shots of the same subjects, registers them, and combines them.
The
> typical combination method is "average". The purpose of this is to
increase
> the signal-to-noise ratio, where the noise is the grain pattern in each
> image. Typically 2 to 10 images are stacked. When the grain is reduced,
> faint detail becomes better defined.
>
> Stacking is not the only way to show more faint detail. Other methods
> include using longer exposure, a darker/clearer/calmer sky, finer grain
> film, filtration (e.g. H-alpha), larger aperture, longer focal length,
> faster focal ratio, recording medium with higher quantum efficiency,
better
> focus, better tracking, etc.
>
> Matt
>
> At 05:18 PM 5/22/2002, Kevin Wigell wrote:
> >Newbie question: Can anyone explain to me what are the benefits of
> >stacking images with Registar (besides grain reduction)?
> >
> >I downloaded the trial version and used it to combine two good film
images
> >of M42. The reduction in grain was obvious, but otherwise I didn't see
any
> >big improvements.
> >
> >Will stacking images with Registar bring out more contrast or fainter
> >details? I have a decent film image of M51 (it's no Tony Hallas or Rob
> >Gendler), but I would like to improve the image contrast (darken the sky
> >background) without losing the fainter details, as well as just bringing
> >out more of the faint stuff. Here it is if anyone wants to look at it:
>
><http://home.twcny.rr.com/kevinwigell/images/M51b.jpg>http://home.twcny.rr.
com/kevinwigell/images/M51b.jpg
> >(I told you it was no Tony or Rob). This is 90 minutes on RG200,
> >unhypered, 10" LX200 f/10. Can I expect to get more of the faint stuff if
> >I stack it with more similar images?
> >
> >Kevin Wigell
>
> --
> Matt BenDaniel
> matt@starmatt.com
> http://starmatt.com
>
>
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