[filmscanners] Blackpoint & noise, was grain

["Mark T." <markthomasz@ozemail.com.au>]

Now I'm confused (so what's new)..

Why would adjusting the black point *up* cause noise to appear, given that the 
adjustment I'm making isn't sufficient to affect the deep shadow detail?  This 
seems backward to me - if I increase the black point, am I not telling the 
scanner to throw away some of my deepest blacks (ie shadow detail), and 
therefore some of the noise (if there was any) should go with it..?

I'm seeing the reverse.  Well, it's Friday, late, and maybe my mind is going..

Anyway, if anyone wants to see what I mean, and can then humour me and explain 
in words of few syllables :-), the samples and more info are here:

http://members.ozemail.com.au/~markthomasz/problems/blackpt.htm

(As it may affect your decision to visit, it's about a 270K download 
altogether.)

Thanks for any enlightenment..

mark t

Tony wrote:
>> (markthomasz..) wrote:
>
>> I've noticed that on some transparency films, I get a grain-like effect
>> in shadows when I use a black point other than zero (in Vuescan).  I
>> haven't yet looked into exactly what is happening, but the 'noise'
>> vanishes as soon as I set bp to 0.
>>
>> So it is obviously not CCD noise
>
>What you describe is very likely CCD noise. On well behaved scanners most
>of it is below the black point on any film you want to scan, on less
>fortunate models it climbs up toward the midtones and you can't just chop
>it off without sacrificing shadow detail.
>
>Regards
>
>Tony


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