Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Pieris Berreitter" 
<pieris@y...> wrote:
> 
> A skeptic recently said to me, "Ansel Adams cannot be compressed into
> 256 shades of gray." I have seen plenty of literature that says we
> cannot distinguish anything close to 256 different shades of gray
> (I've seen the number 64 mentioned a couple times), making this
> statement look a bit uninformed. But it nevertheless got me thinking:
> 
> How many discrete levels of gray (measured with a 12-bit scanner or
> densitometer) do we get out of a quadtone inkjet? Can careful curve
> mapping actually pull out a distinct 256 values? The answer "enough"
> is good enough for the subjective viewer, but being curious...
> 
> Just wondering if anyone has done this, or if it should be my exercise
> for this weekend. 
> 
> -Pieris

I think studies have been done that put the number of distinguishable
grays on paper by the human eye somewhere near 100.   But you need
more than that because in a smooth gradation you don't want two
distinguishable grays right next to each other.  That would show a
transition.  To get a smooth transition you need at least a gray in between 
that doesn't appear distinguishable from either of the other two.
This probably puts you in the ballpark of 256 grays.

I think this is the main fuel for the ongoing debate of 8 bit vs 16 bit
workflow and image files.  This argument misses an important issue
I believe.   Sure 8 bits = 256 values, but any measurement of gray 
value contains many pixels or many ink dots on paper.  On an Epson
printer printing at 1440x720 a small 1/16 inch square is made up of
over 4000 potential dots of several inks.  How many different grays
you can measure has a lot more to do with the specs of the densitometer
rather than the 8 bit pixel data.  It may seem counter-intuitive but 
you can easily measure more that 256 grays with just an 8 bit file.

What is important if you do get to measuring grays is that they are 
reasonably even-spaced over the whole range.

Roy