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.

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.

> Assume you didn't partition the inks at all. Then each channel
> would try to
> print the entire range of 256 levels. One would have a Dmax of
> 100% and the
> others say 75%, 50% and 25%. As these four channels are printed together
> wouldn't this produce intermediate levels between the 256 input levels?

You're missing my point.  I am not saying that it isn't physically
impossible to print more than 256 tones, in fact, you don't need four inks
for it...just a large enough space to allow for the number of tones, using a
dither pattern.  The point is, with a given number of input tones, how does
it derive these other tones?  There MAY be other "perceivable" (which I
doubt anyway, since I still contend that it doesn't print more than 100
anyway, nor can we distinguish much more than 100 our selves) tones...but
they weren't part of the original image.

> 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.

> 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...

Austin