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Re: filmscanners: Size of scan files

Richard wrote:
> More information in the higher ISO film.

That's an interesting way of looking at it.  I would have said the opposite;
that there is less information lost in *more* noise.

> LZW is a near lossless compression. With the
> lower ISO film, you had less information. And, 
> not necessarily grain information in the 800
> film, you could well have greater gamut/saturation,
> greater light latitude in the 800 film. The Fuji
> 800 films are now pretty darned good on grain size. 
> That's why you used the higher speed film, right?
> To get that information.

No, I used it because it's a fast film and I didn't have a choice when buying
a fuji disposible underwater camera. :)  "Pretty darned good" is a relative
thing.  The grain is OK when printed on photographic paper in a lab, but
it looks pretty darned awful when I scan it.

>This is not a case of "bad" compression. Bad compression is where the 
>algorithm assumes that - say - five pixels are the same, when they 
>really aren't. Then, on expansion, these five pixels show up as the 
>same. That is how you get smaller file sizes. You loose information.

As I mentioned in my original post I know about compression algorithms etc.
 Where I disagree with you is on the definition of "information".  Yes,
the LZW TIFF of a Fuji 800 scan is bigger because there's more variation
between pixels and therefore little compression is possible without loss.
 However I disagree that grain (or grain aliasing) necessarily constitutes
useful "information".

The print film is likely to have more data in terms of latitude, but a lot
less in other respects.  It's kind of like comparing a computer image of
320x200 pixels in 16 bit colour with another of 1024x768 in 8 bit colour.
 The first image can have a lot more tonal information, but the second has
more clarity.


Rob Geraghty harper@wordweb.com


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