Digital BW, The Print

Both the Piezo and Epson RGB workflows can produce very good prints.  On the
other hand, I have never seen a perfectly smooth grayscale ramp.  If a
critical tone in a print falls in a spot where the particular workflow and
printer happen to have a flat spot, it can obviously have a detrimental
affect on the final print.

To see the types of defects that affect these workflows, see the comparison
I put in the Files section of this forum.  What I did with these 21-step
test strip prints is run a Photoshop gradient the opposite direction of the
test strip's ramp in order to cancel out the smooth ramp.  Then I increased
contrast to accentuate the defects -- those areas that deviated from a
perfect ramp.

See "Ramp-smoothness.jpg" in the "Image processing" folder of the Files
section of this forum.  The Files section is at
http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/files/

(There are a couple of lines in the 95% and 100% patches that are scanner
defects.)

The Piezo driver does a very good job most of the time, and the Epson driver
with and RGB curve can do a very good job also.

I know from the curves I've seen that the RGB workflows can be affected by
the particular printer characteristics -- that is, some printers work better
with the workflows than others.  I suspect that is also true of the Piezo
driver, but I do not have enough of a sample to know what the range of
performance is.

Of course, not all the RGB curves out there are of equal quality either.

My gut reaction is that the Piezo driver is less affected by
printer-to-printer variation, but then, if your particular printer is one
that doesn't do well with a workflow, the RGB curves approach allows you to
fine-tune your machine.

The RGB curves are also affected by variables such as settings in the Color
Settings of Photoshop and the Epson driver.  It also looks like PS 7 is
different than PS 6, though I still do not have a copy of PS 7 to see what
might be going on.

With the Piezo driver now being separately available, it probably is worth
trying if you're having trouble.

On the other hand, if you like a variable-tone inkset and are having
trouble, learning how to tweak the curves makes a lot of sense.  If you can
identify the area of the problem with the eyedropper in the image file, then
make some blocks that are 1% different in that area and add them to the
21-step test chart, the way the top and bottom 5% have been done with the
posted 21-step test file.  This will allow you to see whether you are
getting a smooth response in the area of concern.  Once you identify the
problem, you can go to the curves and correct it.

The RGB curve is usually mostly free of points.  (The limited number of
points that Photoshop allows per curve is a problem.)  For very small
wiggles at the ends of the curve, I've been using this RGB curve to correct
the situation.  By putting enough points on the 45 degree line (input =
output) you can hold most of the curve as is while adding a bunch of points
in the area where the problem is.  By doing this you can often get enough
points in the critical area of the graph to do the job.

Good luck.

Paul
http://www.PaulRoark.com