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Re: filmscanners: OT: Film grain

On Sun, 1 Jul 2001 11:25:44 +1000  Rob Geraghty (harper@wordweb.com) 

> I was wondering if anyone on the list could explain to me chemically 
> how it
> is that overexposing a colour negative makes the film grain smaller? 

It doesn't:) What happens in that in areas of slight exposure, especially 
where only a single colour-sensitive layer is involved (eg dark blue sky), 
the dye clouds do not overlap and diffuse each other, which is the case in 
more-exposed areas of the image. The few dye-clouds there are thus stick 
out like a sore thumb, and give an appearance of worse grain.

This is rather the opposite to conventional B&W silver halide film 
behaviour, where increasing exposure causes grains to be larger and clump 
together more. In colour neg, the dye clouds are semi-translucent, and 
although larger, greater density means more overlaps and more diffusion.


Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner 
info & comparisons


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