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[filmscanners] Re: 8 bit versus 16



I've been thinking more about this 8-bit vs. 16-bit question, and one
thing puzzles me and has generally been ignored in this discussion.
Someone (Arthur, Austin, Laurie, ????) brought up the question of
"noise" in image data, but that issue has been bypassed in these
discussions in favor of other comments. Yet it seems noise is the reason
high-bit data is superfluous. What I'm thinking:

1. High-bit data is very small compared to low bit data. The ninth-bit
is only 0.25% of the value of the full tonal range of 0-100%.

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.

3. When scanners measure and assign digital values to image elements,
adjacent pixels are given discrete values that are generally different
by more than 0.25%, that is, the precision of the measurement is less
than 8-bits for adjacent pixels.

4. Image editing steps which spread existing pixel ranges over larger
ranges do not create more precise intermediate values than the starting
value's precision. If an intermediate pixel value must be created
between two pixels whose values are 128 and 130 (8-bit), the value won't
be more precise if the original values are 127.504 and 129.504 (16-bit).

I don't know how typical CCD scanners scan at lower resolutions than
their maximum. Whether by averaging pixel values along the CCD array and
making larger steps along the film movement, or by some other way, they
still end up with adjacent pixel values that differ by more than 1 unit.
Knowing these values to .5-unit precision doesn't change the average
values reported.

For 16-bit processes to be relevant, wouldn't adjacent pixels have to be
identical to more than 8-bit precision?

Preston Earle
PEarle@triad.rr.com




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