[filmscanners] Re: 8 bit versus 16

["Preston Earle" <PEarle@triad.rr.com>]

"Brad Davis" <DocBradd@mac.com> wrote: "This is why I think you may be
confusing DPI with bit depth, this comment (above) refers to spatial
resolution, not intensity resolution.  In this issue, (8 bit vs. 16 bit)
the same number of pixels exist in either case, in an 8 bit file, they
may differ by 1/256, no less, in a 16 bit file, they may differ by as
little as 1/65,536.  Thus if one reduces the range of values (say in the
levels setting in PS), there are still levels to provide transitions in
the latter case.  It is unlikely you will reduce the levels to a point
where it is possible to make a discrimination (thus the appearance of
banding)."
-------------------------------

I don't believe I'm confusing bit depth and resolution, I'm probably
just not explaining myself very well. I'm trying to say that if a
scanner can't (or at least "doesn't") scan adjacent pixels of uniform
color as identical values in 8-bit precision, it doesn't matter what the
other eight high-bits are. I don't have a tool to report 16-bit pixel
values, but the 1x1-pixel point-source eyedropper in Photoshop shows
*no* identical 4-pixel squares in a 2820ppi scan from my ScanDual II.
For example, in an area where the pixels should be the same color, four
adjacent pixels have values of 222r201g178b, 220r200g175b, 222r201g176b,
and 200r200g175b. When these "combine" to make a print dot (or some
other visible whatever) the average is 221r200(or201)g176b. If we knew
the decimal values represented by the high bits, it wouldn't change the
average. Thus it is irrelevant what the high-bit values are.

I'm easily confused by anything that smacks of electrical engineering,
so I can be wowed by certain technical explanations. However, *do*
understand "significant digits", and I can't see that values in bits
9-16 have any usefulness if the value of bit 8 is not "significant". (If
two houses are 112 feet apart and two other houses are two miles apart,
the average distance between the houses is not 5,342 feet.)

Maybe at some point in the process the 8th (and 9th, 10th, even 11th or
12th) bit *is* significant, and there is some "noise" added at some
stage of conversion which eliminates the significance of the high bits.
If so, it's valid to use high-bit data before that conversion. After
that conversion, however, high-bit data is irrelevant. It's
less-than-half-cent data in a dollar world.

Preston Earle
PEarle@triad.rr.com


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