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[filmscanners] RE: Blackpoint & noise, was grain



Mark,

if these are different hardware scans (and not different scans - from disk -
of the same raw file), the fact that the "noise" has exactly the same
pattern in both pictures indicates that it is *not* noise (which is random),
and it is more visible in the picture with bp=1% simply because that picture
is a bit brighter (or, at least, it appears brighter on my monitor).
If they are not, I'd recommend to make two separate scans of the film an
check again...

Alessandro Pardi

> -----Original Message-----
> From: Mark T. [mailto:markthomasz@ozemail.com.au]
> Sent: venerd 15 febbraio 2002 12.22
> To: alessandro.pardi@inferentiadnm.com
> Subject: [filmscanners] Blackpoint & noise, was grain
> 
> 
> 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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