Digital BW, The Print

> >
> > > > Tyler,
> > > >
> > > > Before responding to your post, I have one simple question for you.
> > > >
> > > > If the file only contains 256 levels of gray, and IF (BIG
> IF) what you
> > > claim
> > > > is true, that standard Piezo is capable of 1000 tones, where do
> > > the extra
> > > > 744 levels of gray come from?  How, exactly, are they derived?
> > > >
> > >
> > > Austin,
> > >
> > > If the same 256 levels of gray pixels are fed to the printer and
> > > it has four
> > > channels each with a different shade of gray ink, it would seem to
> follow
> > > that each channel will print those 256 levels differently resulting in
> > > overall tonal interpolation. Lower than 1024 but greater than 256.
> >
> > How do you feed in 256 graytones, and now claim that each ink
> now has 256
> > graytones...that's a huge leap of something, and, at least to
> me, makes no
> > sense.
>
> Austin,
>
> Do you believe that the driver of a CMYK printer sends precisely 64 levels
> of gray to each channel or that a CcMmYK printer sends 42.7 levels to each
> channel?

Martin,

No, that's not how dithering works.  It derives a dither pattern that
consists of dot placement, and color...there is no separation into four
channels as you say.  Each ink is either a dot or not, 256 levels aren't
sent to each color ink.

> > It's the combination of dithering AND the four inks that allows
> the number
> > of tones.  The four inks mean that a smaller area is needed to dither a
> > particular tone.
>
> True but I still doubt that you are getting an exact input/output match.

Oh I agree...but I'm only questioning 1000 tones, not that you get a precise
input/output match...as I know you don't.  I only expect Piezo to give me
100 tones in fact...

> The other tones are simply interpolations between any 2 of the
> 256 levels.

That's one of my points...I simply don't believe it works that way.  I've
designed halftone/dither algorithms, and typically, the number of tones is
REDUCED from what is in the file...there isn't a tonal expansion.  This is
typically for practical reasons, as more tones takes more area, and reduces
resolution...and as I've said, more than 100 tones aren't necessarily usable
anyway.  Again, it's the 1000 number I'm questioning.  If it did 256, I'd be
happy with that...

> Prudence would make want to output something considerably higher than the
> minimum though. So if 100 is close to the minimum you need to simulate
> continuous tone I would be inclined to use double that but in any case 256
> tones would seem to fill the bill just fine.

Agreed.

> >
> > > In
> > > practice the inks are partitioned so that each covers a specified
> > > segment of
> > > the 256 levels input to the driver but the crossover points
> > > overlap a great
> > > deal with multiple inks being applied in the same tonal range.
> >
> > > The only way
> > > to I can see to get a precise 256 levels would perhaps be to use a
> single
> > > ink.
> >
> > Absolutely not.  You can get any number of tones OUTPUT from
> any number of
> > inks.  It's a matter of what the driver does.  If the driver
> simply output
> > 256 tones, then it outputs 256 tones, and that is not number of ink
> > dependant.
>
> So theoretically you could get 1000 tones form 4 inks as ConeTech claims?

We are talking about two different things.  The INPUT file is 8 bits, which
is 256 tones, period.  The fact that you can make as many tones as you want
with a dither pattern and one or multiple inks isn't in question.  Whether
Piezo DOES it or not is what's in question.  It simply isn't practical as
far as I can tell.

> >
> > > I think the analogy to the pixel discussion is very apt.
> While we input
> > > pixel information to the printer is does not print pixels.
> The same with
> > > levels of gray. We may input levels but the driver and the
> nature of the
> > > inks produces an interpretation of those levels in a manner
> designed to
> > > convince our eyes that they are observing a continuous tone image.
> >
> > Well, I'll go back to my claim that 1) it doesn't produce 1000
> tones, that
> > is physically impossible, and 2) that we can't distinguish them
> anyway...
>
> 1) Wait a minute you just said it was possible <G>, but I agree that it
> probably doesn't.

It is THEORETICALLY possible, but not with this particular system.  There is
probably too much variance in the ink tonality, as well as the ability to
control drop size that would limit it.

> I
> suspect that the effect of additional levels beyond 100 improves the
> appearance of the print but like resolution at a certain point additional
> levels do not offer improvement.

I agree with that, but not 1000.

Austin