Jeff, I've been using your curves on an 1160 with MIS FS and I have to say i
think they are spot on. Shadow speration is better than with the piezo
driver. The only criticism I would have is that the 'scalloped' edges of the
wedge are more 3d in piezo. But anyone thinking of trying inkjet printing
could go a long way with FS and your curves.
Julian
----- Original Message -----
From: "Jeff Randall" <jrandall@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Monday, September 16, 2002 2:59 AM
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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