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
Rob Geraghty harper@wordweb.com
