Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Peter 
Nelson" <peter@s...> wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy 
Harrington" 
> 
> 
> > Very nice write up about inks and dithering an all.  A minor
> > nitpick is that you show how 2 inks give more gray values.
> > Quite true, but its even more dramatic than that -- the 2x2
> > pattern can give 15 possible grays without overprint .
>  
> How do you figure?  I think you counted duplicates.  Say we call 
> black "1" and gray "0.5".    I say the possible values are 0, 0.5,
> 1, 1.5, 2, 2.5, 3, 3.5, and 4.     Don't forget there are several 
> different patterns that add up to 1.5 or 2.5. 
> 
> >                  One of the crucial issues if how much
> > lighter the light ink is.  I think most light inks are quite a
> > bit lighter than 50%.
> 
> That only helps a little - it eliminates the duplicates 
> resulting from two 0.5's adding up to a 1, i.e., 1.5,  
> 2.5 and 3 in the prior example.   Say we called gray 0.3.
> Then you get 0, 0.3, 1, 1.3, 1.6, 1.9, 2, 2.3, 2.6, 3, 3.3,
> and 4.  The downside is that the new values are nonlinear.

.25 works pretty well 0, .25, .5 , .75, 1, 1.25, 1.50, 1.75, 2.0,
2.25, 2.5, 3.0, 3.25, 4.0.

But the 2x2 example is simplified anyway - with a real dithering
system the number of combinations for 2 inks is many more
that for 1 ink.  The results are much better than twice as
good.  The difference between a black-only print and a
black/light black print is very dramatic.

Roy