Digital BW, The Print

Roy,

You wrote:

>I've been working a lot lately transitioning from a 4 ink 1160
>to a 6 ink 7500 as well as using my new QuadTone printing
>software.   To make things easier I ended up using VM-Sepia in
>both printers.

>My first observation is that I agree that the 6 ink system seems
>a fair more difficult to deal with than the 4 ink one.  I'm just
>barely able to get the 7500 to be as dotless as the 1160.

One of the factors is that the 7500 has dots that are more like a 3000 than
an 1160.  But it does have the light inks, so I find it prints smoother than
the 3000.

>A guy trying my system with a 1280 had lots of the same
>problems.

One issue with hextone printers is the built-in midtone cross-overs that
have to be dealt with.

>I did some Q-tip swab tests of the various inks

The only way to be sure about densities is to use the printer.  Loading
black carts and comparing the black-only ("BO") densities may be the best
way for the lighter inks.  I also use "color ink" printing and my "color
test" file (like a quad purge pattern) for comparisons.  However, there is
no way to isolate the light cyan and magenta except by putting it in the
black cart.  (BO printing gives a darker 100% black than "color ink"
printing.)

> I'm
>beginning to think that the light inks are way too dark for
>what the driver software is expecting.  The swab tests give:
>K=161, C=142, c=129, M=59, m=58, Y=63.   These tests
>aren't real accurate but illustrate the issue. Curiously the
>two M's (the sepia toner) have almost the same density

If the light magenta is the same as the full strength magenta, there is a
problem.  The light ink is a 50% greater dilution of the pigments.

>but
>vary in color quite a bit:  M is a reddish orange, m is a much
>browner and less color saturated.

The M should be more saturated.  The density readings are probably the
sampling method problem.

>I then tried printing out 21steps off only C and only M with
>both the Epson driver and with the gimp-print driver.  The
>Epson driver is somewhat tolerant of these densities but
>for cyan steps I get 100%=83 and 50%=59 and for magenta
>I get 100%=59 and 50%=49  so most of the ramp up
>happens in the first 50% and its pretty flat above that.

Do you have Epson OEM ink comparative numbers?

With the measuring method you're using, it's not clear what the density
differences should be.  The 50% reading will be a combination of the light
and dark inks.

The optimum relative densities will, no doubt, vary according to the driver,
but I assume Epson sets a de facto standard.  The best way to find the
relative densities would be to put samples of Epson C & c, M & m, in black
carts and measure the BO densities.

With the VM inkset, it was set up way before the system was that
sophisticated.  With the quads I was working with, I only had one ink per
color.  So, it was not an issue for me.

When the vm system was taken to the hextone system, the inks were based on
an estimate of the 3rd party pigment relationships.  It worked, so mo more
was done.  Once curves are written, backward compatibility rules.

With my 7500, I found the 7000 driver and the vm relationships worked very
well.

>With gimp-print things are quite a lot worse,  its very
>intolerant of wrong densities,

Or "different" densities.  I'm not sure what is "right" or "wrong" with the
various drivers.

>...  But,
>seeing how I have the source code I was able to reset the
>assumed densities in the software.

Can you tell from the software what the assumed densities were?

> After this I was able to
>get great step wedges -- smooth from 0 to 100%.

>So I don't where this should all lead.  Changing ink formulas
>would obviously be a big hassle for all the existing curves.
>I'm thinking of remixing a lighter light cyan for my next load
>of the cartridges but I'm doing my own curves.

For the dual-quad, vm-s system I made for the 7500, I started with a clean
piece of paper.  Unfortunately, the densities I chose appeared to be part of
the problems I ran into with the inkset.  I might start with a clean piece
of paper if I migrate to a different driver (RIP or whatever).

For now, however, I'm going to work around the existing vm de facto
standard.  It works OK for at least most systems.

Paul
http://www.PaulRoark.com