Digital BW, The Print

I simply want a RIP that is calibrated to print what I ask.  One that
doesn't change my image if it is all in-gamut and no tonal compression is
necessary. I, like Ansel did, want to know that if I expose a part of the
scene to a particular density that it will end up there in the print - the
rest of the parts of the print will fall as they are exposed...unless I
choose to modify their exposure with a PS curve (he clipped - or dodged and
burned). When I do this curve I want to know that it is this curve which
alters the image and nothing else.  Nice and simple.  One can debate to what
benchmark (gamma 1.8, 2.2, LAB or whatever) the system should be calibrated
but let it at least be calibrated to what we decide and have that
calibration be consistent in its application.

I started where you are now.  Targeting middle grey is what Paul does
manually (he just chose a different grey from the one you are about to try).
You will find that for each ink .txt file you will need a different curve to
reset your mid grey to whatever density you choose as your reference.  (This
is because QTR is not calibrated to a defined space.)  And your curve will
affect the results of the other parts of the image in different ways.  You
will need a curve just to get a QTR ink curve to print your selected Kodak
grey at 50% - just to get a known value for 1 step.  The curve to achieve
this for EEM is different for EPSG - in fact for any ink/paper combination.
The tonal compression that occurs is then a result of two curves - the one
you did and the one implicit in the RIP calibration (the latter not
visible).  

If the system were calibrated as I am proposing you will find that ANY PS
curve you use to manage the necessary image file compression to the printer
space will not affect your mid grey as long as your curve passes through
128/128 - ie unless you change it on purpose - nice and visual.  If all
image values are in gamut it prints perfectly.  If I know my paper's dynamic
range (dMin and dMax) I can look at the histogram and see straight away what
is in gamut and what is not.  I can then do whatever curve I want to
directly manage out-of-gamut tones (remember we have to manually manage
these because we don't have colorsync and one of its 4 options doing it for
us) and then, with an in-gamut image on screen where I can see it, get it to
print perfectly - no guessing.  This curve - up in front of me in PS...I can
see by its shape the exact nature by which inputs are mapped to printed
outputs - defines the image's complete change from file (exposure) to print
(rendition).

You are right that it is how you choose to work but why make yourself have
to guess the system?  The whole point of calibration is to know in advance
the result you will get.

A word on soft proofing.  When you do a soft proof in a color managed world
you are looking at the combined effect of two things: (a) a determination of
what is out of gamut, (b) the effect of the method selected for dealing with
out of gamut colour (absolute, relative, perceptual etc) and (c) a complete
management of the different shape (gamma etc) of the two spaces.  (a) is
determined when the printer profile is compared with the image file.  In B&W
this is easy - it is just the pixels with values outside dMin to dMax and
these two points are calculated very easily.  As I said before you can see
these just by looking at the histogram.  Because (b) is such a complicated
exercise in the colour world those ingenious folks who developed colorsync
gave us four methods to choose from and then once selected the remapping is
done automatically.  Again, in a B&W world dealing with out-of-gamut values
is infinitely easier.  We know where they are as I said. And they can be
dealt with with a simple curve. With regard to (c), if we are not concerned
with hue, it is very easy to calibrate the printer to match the workspace
(whatever that may be!) and so (c) is very unnecessary in a B&W hueless
world. I would liken our current situation to making things way more
difficult than they need to be and then finding soft proofing to pull us out
of a situation that we needn't have been in in the first place!

Well even if I am not winning at least I have got you thinking.  Come back
when you have had some fun with those curves  ;-)


Steve


> From: Keith Douglas <kdouglas@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Tue, 07 Dec 2004 09:19:41 -0800
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: Re: [Digital BW] Tonal range and linearization
> 
> 
> Steve,
> 
> I think you and Tyler are at an impass.  You believe that the absolute
> value (of brightness) matters.  Tyler believes that everything is relative.
> 
> In terms of "the literature", Tyler is right.  The commonly held belief is
> that the absolute value of brightness doesn't matter.  That the human
> vision system will adapt to the scenes or images dynamic range.  See
> "Digital Image Processing", by William K. Pratt or similar works for a
> complete discussion of why this is.
> 
> I'm more of a relativist, too.  The curves I create are visually linear
> from paper-white to ink-black with middle grey falling where it may.  But
> this discussion has made me reconsider this approach and question my
> assumptions.  Or, at least made me consider an alternative: I'm going to
> create some curves that put printed middle-grey at Kodak middle grey, but
> that also make my displayed contrast equal my printed contrast.  Let the
> S-curve fall where it may!
> 
> Really, there is no right or wrong here.  It's just how you choose to work.
> 
> -Keith
> 
>