Digital BW, The Print

----- Original Message -----
From: "Austin Franklin" <darkroom@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Sunday, August 04, 2002 7:05 AM
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.
>
> 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? You know more about printer drivers than I do but this seems
unlikely. If I send 256 levels to an ink with a Dmax of 1.7 can I get 256
levels of gray, right? What if the Dmax is 1.3? 1.0? 0.5? You still have 256
levels but since the range is smaller the difference between the levels gets
smaller.
>
> 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.
>
> > 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.

The other tones are simply interpolations between any 2 of the 256 levels. I
do agree with you on the figure of 100 being a reasonable limit to what we
can readily distinguish differences in tone. Just print out a copy of
Tyler's "Z" which consists of 10 squares each containing a gradient so the
squares cover 1 to 10%, 11 to 20%, etc. There is a large "Z" in each box
that is at the mid point in the gradient. (The file is in the Files section)
It is pretty tough to distinguish between a 1% change in tone.

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.

>
> > 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?

>
> > 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.

2) Yes and no. If there were 1000 levels and we can only distinguish a 1%
differences in levels then in the 1000 level print we could not distinguish
between 10 and 11 or 10 and 15 but we could distinguish between 10 and 20.
We could also distinguish between 11 and 21, 12 and 22, 703 and 713 etc. So
within the 1000 levels you would have what, 990 distinguishable tonal pairs?
I think this is the value of having more than just 100 levels in a print. 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.

Martin