Digital BW, The Print

----- Original Message -----
From: "Austin Franklin" <darkroom@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Saturday, August 03, 2002 8:15 PM
Subject: RE: [Digital BW] Number of tones was Re: Do inkjets dither or not?


> 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.

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? 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.

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.

Martin