RE: [APML] Wondering about histograms

[Alan Voetsch <alanv12952@yahoo.com>]

Het Carlos,

Many thanks for the lessons, this has been very helpful. I'll give
multiple scanning a try and see if there's improvement.

Alan

--- "Carlos Milovic F." <cmilovic@yahoo.es> wrote:
> There are "two types" of multiple scans. There are some softwares
> that makes that automatically, I think that it was for some Nikon or
> Minolta scanners. Basically, it scans each frame several times and
> combines the shots in any way.
>  
> With your SS400 what you have to do is just scan your images a lot of
> times... say 4 or 8 times. Becouse the film holder isn't always
> located at the same position, and the result will not be the same,
> you'll have to register (align) each frame to a reference one (for
> example your first scan). You may use RegiStar or other software for
> that, but I think that it would be quite good to try just
> translations (x,y shifts).
> Multiple scans will reduce the noise introduced by the scanner and
> you'll end with a smoother histogram.
>  
> Oh, by the way... noise introduces an effect of widening the gaussian
> like zone of the histograms. So, if you have two images, that just
> have different amounts of noise, you'll see a narrower one with the
> less noisy. Try this with the histogram of a image after and before
> noise reduction techniques.
> And another btw: vignetting/uneven field illumination also
> contributes to this effect!



SCT Astrophotography: http://www.pbase.com/avoetsch/astrophotography
FS-102 G-11/Gemini: http://www.pbase.com/avoetsch12952/tak_fs102
& http://www.pbase.com/avoetsch12952/fs102
& http://www.pbase.com/avoetsch12952/takpf

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com 
_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo