Digital BW, The Print

Hi Phil,

> There is no doubt that when you drop from 65,000 levels of gray (16
> bit) to 256 (8 bit), there are pixels that shift in tonality, since
> they are moved to the nearest 256 level gray value.

ALL that happens when you convert from 16 bit to 8 bits is the bottom 8 bits
is lopped off and the top 8 is used...NO "real" "processing" at all is done,
it's simply truncation.  It is shifting tonality, in a sense, but it is
really just truncation.

> But if you convert to 8 bit, either PS
> will assign them to the same gray value OR to adjacent values depending
> on the choices it makes,

See above, that isn't really what happens...

> In the scan, each
> silver grain in the film is made up of numerous pixels

Well, possibly if you have very grainy film, or are scanning at a very high
resolution...typically, with decent exposure, film and processing, you will
have many film grains represented by a single pixel.

> ...But the perception of tone these pixels render
> is effectively an averaging effect, since we are seeing them from very
> "far away" in a sense...

Exactly how halftoning works...

> Posterization will only occur if you have
> a predominance of one color pixel in a region that is visible at the
> viewer's level of resolution.

Correct.  Technically, you ALWAYS have posterization...but whether it is
visible or not what is important.

Regards,

Austin