Digital BW, The Print

David:

Take any of the 21-step wedge test files available and crop to just 
the steps (eliminate any continious ramp, surrounding background 
space, and seperator lines in the step area) and then use the 
histogram function of your image editing program.  You will see the 
peaks to be equally spaced between 0-255 or 0-100%.  This indicates 
to me that if you print out the step wedge and then scan it and check 
the image as above, you should end up with evenly spaced peaks
(assuming as you said a good scanner).

This is the logic I used when I created the RGB partitioned curves 
for the 1160 (see MIS web site or Files here). During scanning I set 
the blackest black of step wedge test print to 100% (or 0 value) and 
the whitest white (=color of paper) to 0% (255)--that is I expanded 
the maximum range on my paper to the "theoretical" 0-100 range. I 
then tweaked to curves to equally space the other 19 peaks.
 
I have also used this approach to tweak Woolf's lumped (non-
partitioned) single curve work flow.  I haven't tried Jerry Nivin's 
workflow, but I suspect it is the same or similar.  

So my suggestion (don't know if it is technically correct or not, but 
it seems to work for me) is to shoot for equally spaced peaks.

Good Luck.

Jeff Randall


--- In DigitalBlackandWhiteThePrint@y..., David Dyer-Bennet <dd-
b@d...> wrote:
<snip> 
> I noticed recently somebody pointing out that the histogram from a
> step wedge of equal steps should be a nice comb of equally-spaced
> spikes.