Digital BW, The Print

Jeff,

I agree with your conclusion:  "I am now convinced that there is no single
*correct* answer to what density should the 50% grayscale patch be."

For me, the practical answer was actually very simple.  I was printing
Piezo -- and still want to be able to -- with the same files that I was
using the Epson driver to print.  So, consistency with the Piezo driver was
controlling as to where I put the 50% point for the curves I wrote -- or
will write in the future.

Paul
____________________________
  -----Original Message-----
  From: Jeff Randall [mailto:jrandall@...]
  Sent: Sunday, September 15, 2002 4:59 PM
  To: DigitalBlackandWhiteThePrint@yahoogroups.com
  Subject: [Digital BW] GS Midpoint Density/Brightness was Info Box as it
relates to Roark Curves


  Paul:

  I wouldn't expect the density (= log(1/reflectance) to be linear or
  that the 50% grayscale patch to have a density midway between approx.
  0 and 1.6 using the MIS inksets -- it should perceptually be midway
  between the two extreams.   The often used 18% gray card has a
  reflected density of about 0.74 (log(1/0.18)).  However the two
  questions I haven't found real answers to are: 18% is the middle of
  what range and is perceived under what conditions?  If 18%
  reflectance is the perceptual middle of the 0 to approx. 2.0 range
  shown in the Kodak Q-13 card, then the middle of the range for
  quad/hex inkjet prints with a range of 0 to approx. 1.6 range should
  be a little lighter (nearer to your approx. 0.6). Or is 18% the
  middle of a broader range like 0 to 2.5 or......

  Other than the middle of what range, the other variable, is the
  viewing conditions, at least the intensity of the viewing lightsource
  and maybe even the spectral composition.  The *uncontrolled*
  experiments that I have conducted of viewing the Q-13 wedge (and
  wedges I've printed using the MIS FS and FSE inksets) under indirect
  sunlight, full sun light, Ott-light, and incandesant light all
  perceptually give me slighly different mid points.  Also varying the
  background (light or dark) also changes my perception.

  The short of it is that I am now convinced that there is no single
  *correct* answer to what density should the 50% grayscale patch be.
  The eye is just too adaptive.  There is some discussion of the 18%
  gray card in the Accurate Image Manipulation website, www.aim-dtp.net.

  BTW, now that I have a Swatchbook (thanks for convincing me) and can
  accurately measure densities, I find that the 1160 curves I developed
  yield a 50% grayscale = approx. 0.6.

  Jeff Randall

  --- In DigitalBlackandWhiteThePrint@y..., "Paul Roark"
  <paul.roark@v...> wrote:
  > Cleavis,
  >
  > >[Is] there a reliable relationship between the
  > >info box (Photoshop) and the output tone once the curve is applied?
  >
  > >If you have a K only sampler, will that indicate a percentage tone
  > >laid down by the ink?
  >
  > I hope so.
  >
  > The simple answer is that when the eyedropper in Photoshop reads a
  patch as
  > 0% -- pure white -- the printer is supposed to put zero ink there,
  and if
  > the eyedropper reads a patch as "100%" -- "pure black" -- the
  printer should
  > be laying down as much black ink as possible.
  >
  > However, there is a question as to how one measures the print
  densities and
  > what a "linear" output should be.  That is, between those obvious
  end
  > points, what should the "gamma" or slope of the curve be?  How
  dense should
  > the 50% patch should be?
  >
  > If you print the grayscale ramp with many printers, the 50% patch
  might be
  > lighter or darker than the 50% patch that results from one of the
  vm curves
  > or from the Piezo driver.  And, what the "50%" patch on a test
  strip will
  > read on a desktop scanner is a function of how the scanner gamma is
  set.
  >
  > I called Epson to see if there was any way to get my scanner to
  be "linear."
  > There isn't.  They don't claim that any particular setting will
  give any
  > particular slope to the curve.  It's all just relative.
  >
  > The densitometers are a more reliable way to see what the densities
  are.
  > The average 50% patch on the old PiezoBW test strips I've made and
  seen is
  > about 0.61 - 0.62, and 0.61 is what I use for the vm curves.  This
  is
  > clearly not half way between the paper white -- about 0.04 -- and
  the VM-K
  > 100% patch density of about 1.65 (depending on printer and paper
  type
  > setting).
  >
  > So, the only simple answer relates to the end points.  After that,
  one has
  > an open question as to what the "50%" patch should read.  The three
  test
  > strips that are in my fader had 50% patch readings as follows:
  2200 - 0.57,
  > MIS Archival color - 0.60, and PiezoTone-S - 0.69.
  >
  > Paul
  > http://www.PaulRoark.com


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