Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Paul D. DeRocco" 
<pderocco@i...> wrote:
> > From: Roy Harrington [mailto:roy@h...]
> >
> > The data files from MeasureTool have all the Lab data and some other info.
> > I wrote Calc-Density mainly to get the linearize data, but it is
> > very helpf= ul
> > to look at the full Lab info.   I just about always read the MT
> > file into a=
> > AppleWorks spreadsheet and graph the L, a, and b data -- takes about 30
> > seconds or less.   Lab is actually very convenient, L should be a straight
> > line, a and b should smoothly go from paper white to ink black.
> 
> Do you have some sense about how much wiggle you can tolerate in the
> grayscale (in terms of ab value variation) before it's visible?
> 
> --
> 
> Ciao,               Paul D. DeRocco
> Paul                mailto:pderocco@i...

That's a good question and I'd like to know what people can see as well.
Here's a few a,b value reference points:

EEM paper  is  (1,-5)        -- quite blue
PhotoRag   is  (.8, -1.2)   -- almost neutral
it;s pretty easy to see this, so 4 units is significant

50% of carbon ink is about (3,6)  -- definitely warm
50% of sepia curve is about (6,12) -- very warm 

Eboni black is about (.5,.75)  -- slightly warmish neutral

I'd be inclined to say wiggles less than +/- 1 are not noticeable and maybe
a fair amount more.   I also think it's mainly the midtones that show the
color.  No matter what, you have to go from paper white to dMax black.
So on EEM b has to change about 6 units.  With carbon only, you don't
get any choice and you pass neutral very quickly.  By about 13% b is positive,
and most people seem to accept that visually.   With a neutral curve there's
a lot more choices -- should it gradually climb the whole way meaning
negative b most of the way or should is climb quickly to zero and then level out.

Roy