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[filmscanners] Re: 8 bit versus 16




On Monday, September 22, 2003, at 02:04  PM, Brad Davis wrote:

> On 22/9/03 12:09, "Preston Earle" <PEarle@triad.rr.com> wrote:
> ...
>>
>> 2. All visible files are the product of a final
>> resize/pixel-combination
>> of some sort, at least until we get 2800x4200 or larger video screens.
>
> I don't think this is relevant, there are places in this note where I
> suspect that you may be confusing DPI and bit depth at a pixel.  This
> conversation is only about bit depth.
>
>> ...
>> For 16-bit processes to be relevant, wouldn't adjacent pixels have to
>> be
>> identical to more than 8-bit precision?
>
> Yes, exactly, a 16 bit representation is more nearly continuous than 8
> bit.
> The fact that 8 bits look continuous is an artifact of our perceptual
> system
> which can't discriminate that many levels ( and some of the work of
> printer
> drivers to smooth things out for the resolution of the printer).  Most
> people can't resolve much more than 2^5th (32) levels, some 2^6th
> (64), very
> few much more than that.  ( Of course I presume everyone here can
> resolve
> 2^7th or 128 levels.)  Much of the variability in this measure is a
> function
> of differing assumptions and different methodology in measuring it, the
> generally accepted number is 6 +/-1 bits with few people getting much
> over 6
> bits.
>>
>> Preston Earle
>> PEarle@triad.rr.com
>

Brad,

You are probably right that  --   "This conversation is only about bit
depth."

But I think that is one of the main shortcomings of the discussion.
Resolution
(DPI or more accurately PPI) and bit depth are certainly very different
and
clear properties of an image file.  However the criteria for comparison
is always
a print that the human eye looks at to evaluate.  At this level PPI and
bit depth
are no longer independent and well defined properties of the image.

Fewer levels of gray (i.e. less bit depth) is easily compensated for by
a higher
resolution --- that's the basic principle of halftoning or of
stochastic dithering in
printing.

Roy

-
Roy Harrington
roy@harrington.com
Black & White Photo Gallery
http://www.harrington.com

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