[filmscanners] Re: 8 bit versus 16

["Robert Logan" <bert_logan@btopenworld.com>]

> of each individual color, true, and it's also 16M
> colors.  Also, you're not likely to get only one
> color out of three.

Yes, but the 16M is just that, a mythical
number that never appears in most images,
the range of colours is typically more
far restricted.

> For most images, there will be
> no visible degradation in the image using only 8
> bits/color.  If you haven't tried an experiment, and
> are only speaking of "theory"

Ive noticed it in practice severally. Notably in
shots with some very variable lighting across
landscapes which contain numerous greens. Playing
with the curves often results in problems when all
256 of the greens in 8 bit are used up. And as
you point out - with grayscale - luminance can
get blown out with too few bits, so why not chrominance.

> you really need to
> try an experiment for your self.  Many people have
> done this experiment, and that's why they say that 8
> bits/color works perfectly for most images.

Yes - 8 bit does work fine for most images, but if
you really want to throw an image into some editing,
then relying on 8 bits is foolhardy if you can get
more to work with.

Remember - filmscanners work with an analogue medium
that contains far more information than 16/8 bits
can capture - now why not only use 4 bits? or 6/7?
8 Bits is no magic number - just as the 16 Million
colours is a myth - in the sense that no digital
image contains all 256*256*256 possibilities.
Heyy - it might contain 3400*120*44 ...

Its well documented in the 3D community that having
24 bit colour internally in 3D processing engines
can result in banding in certain scenes, and thats
why Nvidia and ATI have developed 32 bit engines,
and more.

I think that scanning to capture all the nuances
and working from there is the sensible way.

bert
--
Linux - reaches the parts that other beers fail to reach.

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