Digital BW, The Print

Shaun asked whether others could see dots in the highlights of the MIS VM
inkset when used on an 1160.

I must say that I do not see them at normal viewing distance, but it is
certainly possible that some have eyes good enough to perceive them. (Note
that most commentators, and Kodak in its Print Grain Index Technical
Publication, use 14 inches as the normal viewing distance for prints.)

It is, of course, true that all of the inkjet printing systems have dots,
whether we are talking about the Epson or Piezo driver.  With magnifiers or
high resolution scans, we can clearly see the dot patterns of all of these
systems.  It is also the case that the lightest gray ink in the
variable-tone inkset is somewhat darker than, for example, the Piezo
lightest gray (about 38% v. 27%).  Also, even thought the toner is close to
the same luminance as the gray ink, there might be more color contrast with
it in there.  So, the dots in the variable-tone system are going to be
visible sooner than the dots in the Piezo system as we get closer with
higher power magnifiers.

However, the question I am concerned with is how much this affects the
visual appearance of grain in the print at normal viewing distance.  For
this, I suggest the following method of objectively measuring that relative
"graininess" of the prints using a scanner and Photoshop.

First, I believe most agree that at normal viewing distance the normal
maximum resolution that humans an see is 5 line pairs per millimeter
(lp/mm).  This figure is based on high contrast resolution targets.  As
such, for lower contrast details the resolution would be substantially less.

To "see" 1 lp/mm, it takes two pixels.  So, 5 lp/mm translates into 10
pixels/mm.  This is the same as 250 dpi.

Since this would be for high contrast detail, using the scanner setting of
240 dpi seems like a reasonable resolution to scan at in order for the
scanner to "see" about the same detail as we can see at normal viewing
distance.

So, I scanned 21-step test file images made by my 1160 using the Piezo
driver/ink, and the Epson driver with the MIS variable-tone inkset and the
neutral-cool curve (vmq-nc).

To measure the "graininess" or unevenness, I think the Photoshop Histogram
tool's Standard Deviation calculation gives us a good relative measure.  The
higher the number, the more differences or deviations in values the scanner
saw in the scanned area, as I understand it.

Here are the relative numbers for some representative patches of the 21-step
test prints:

5% patch:  	Piezo 1.08,		vmq-nc 1.96

20% patch:	Piezo 1.32		vmq-nc 1.94

50% patch:	Piezo 2.22		vmq-nc 1.94

75% patch:	Piezo 3.95		vmq-nc 3.03

95% patch:	Piezo 4.16		vmq-nc 3.64

So, on my 1160, the Piezo print does indeed have slightly smoother
highlights.  However, the Epson driver produces slightly smoother mid-tones
and dark-tones.

The reason I originally started to write curves to print Piezo inks through
the Epson driver was to get the smoother tones that the Epson driver could
produce with its Error Diffusion algorithm.

I, personally, cannot see, at normal viewing distances, the differences in
the highlights of prints made with these two systems on my 1160, but I do
not doubt that some have better eyes (even when I'm wearing my reading
glasses).  I can, however, see the differences that often show up in the
very dark, heavily-filtered skies of my prints.  So, I started to print with
the Epson driver even before the advantages of the variable-tone inkset -- I
found that, overall, my prints were smoother.  (I also really liked the
darker blacks that the Epson driver produced.)

Paul
http://www.PaulRoark.com