Digital BW, The Print

Please define exactly what you mean by "separation".  Can you also post the
90% K, 95% K and 100% K L* readings and the blank media white reading.

Again the question is one of gamma.  (I can not speak for the
"posterization" you see.)

An example might help.  I am currently looking at a 101 step wedge in PS (I
can send you the tiff file if you want it).  I assigned the Gray Gamma 2.2
profile (the most broadly used gamma today) to the tiff.  I have set my
Second Color Readout in the Info palette to Lab.  As I run the cursor over
the steps from 100 down, it is not until I get to 94% K that the Lab reading
hits 2.  Would you say that this workspace doesn't have good separation?

If instead I assign Gray Gamma 1.8 to the document I hit Lab 2 at 97% and by
the time I get to 94% K Lab is 5.

I think we can agree that the dynamic range of a printer/ink/paper medium is
defined by the range from ink black to paper white.  Once we have determined
ink loads etc (or Epson has done it for us) that range doesn't change
whether we decide to linearise it (if we can) or whether we change our image
in any way.  So the full scale is still available to us - nothing is lost.
The question at hand is how luminance makes it from black to white - ie
gamma - when we have to map from perfect black in our image file to an
imperfect black on paper at one end and from perfect white to imperfect
white on the other.

In this specific case, we are essentially debating whether the gamma created
by (a) the two limits of our dynamic range, (2) ICC white point scaling at
one end, and (3) Adobe black point compensation is "appropriate".  Or
whether some other shape would form a better basis for work.  (With of
course the assumption that Roy has correctly implemented these.)  It is
worth noting that the colour world faces exactly the same question with no
less importance.  A colour photographer is equally concerned about "shadow
compression".  (Consider a photo with colourful highlights but largely
neutral shadows.)  It is not the absence of hue that makes this issue
important.  Some considerable comfort should be gained from the fact that
Roy has adopted ICC and Adobe practice.

Looking at the movement of Lab in the above two greyscale spaces it is not
unreasonable to see that when we map from a perfect black to imperfect black
on paper, given the eye is good at resetting its perception of black and
white points, that we would want a similar sort of rate of change of
luminance at the black end (and white end) of the scale in the print.













> From: Paul Roark <paul.roark@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Wed, 19 Oct 2005 07:37:34 -0700
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: RE: [Digital BW] ICC v. Transfer Function in Epson driver
> 
> Steve,
> 
> I thought maybe my, in my view too-compressed, low values might just be an
> artifact of a bad un-adjusted distribution and too few points.  So, I tried
> the Create ICC and Print with Preview workflow with a printing setup that
> had a reasonably smooth low end.  I took readings at every 1% point between
> 100% and 95%, then at 5% to 80%, and then at 10% intervals.  I was also
> curious if the program needed even distributions of input data.
> 
> The results were not much different than my previous attempts.  Whereas the
> un-adjusted printing setup separated all the 95% - 100% points reasonably,
> the output adjusted with the Create ICC compressed the dark tones and
> posterized the 95% - 100% range.
> 
> I don't know what caused this, but it's not, in my view, an output that
> efficiently utilizes the grayscale file information.
> 
> Paul
> www.PaulRoark.com
>