Digital BW, The Print

----- Original Message -----
From: "John Brownlow" <lists@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, March 27, 2002 5:51 PM
Subject: Re: [Digital BW] Dynamic Range Definitions and Print Tones


> On 3/27/02 mwesley250@... wrote:
>
> >Finally the "number of tones" present in a print does not depend upon the
> >dynamic range or the range or the min and max. A print is an analog image
> >and by definition has continuous tones that flow from one to another
> >without any step change or gaps. Just as the sun sets in a smooth motion
> >and not in increments, so the shades of gray flow in a continuous tone
print.
> >
> >A silver print or negative is continuous tone by the nature of the
> >chemical processes that produced it and an inkjet print is continuous
> >tone by virtue of the dither pattern, variable droplet size, etc. that
> >are used to produce it from a stepped digital file. By the definition of
> >continuous tone there are no steps and any tone value between the limits
> >of min and max can be created. Even though our eyes and instruments
> >cannot distinguish between two tones, if they are too close together in
> >value, does not change the fact that an infinite number of tones are
> >available to the print maker in either silver or ink to create their
image.
>
> Both of these statements are true and not true. In a sort of general
> hand-wavy practical way they are true, but they are inaccurate when you
> get close to them.
>
> 1. No analog systems are continuous at the quantum level.

Hmmm. That is the same as saying there are no analog systems since the very
concept of analog means continuous.

> Not even the
> sun crossing the sky.

The rotation of the earth occurs in small steps and not in a continuous
motion? An apple falls to the ground in distinct intervals? I know back to
my rubber example but reality moves form state to state hitting all the
positions in between without breaks or step changes.

> Quantum noise is a limiting factor in many micro-
> electronic systems.

This is true. Noise is always an issue in electronic systems.
>
> 2. A silver print or negative is not continuous at the granular level in
> terms of its representation of the scene.

Only with 400 ASA film in Xtol. (Just kidding your methods match you style
perfectly.)

Not as a representation of the scene perhaps but it is still a continuous
tone that imperfectly recorded the tones of the scene. Getting down to a
microscopic level and examining the crystal growth, bloom and infectious
development things look uneven but they vary continuously and somewhat
unpredictably. The important thing is that you can control the system to hit
any density not a finite number of densities. (Besides if you developed your
negs in Pyro this would not be an issue.<G> )
>
> 3. An inkjet print is certainly not continuous since each channel is
> (currently) only capable of representing 256 shades of gray.

Strictly speaking you have 6 channels so you should have 1536 combinations.
This is increased by the blending provided by dither patterns and bleeding.
>
> All of these things appear continuous if you squint hard enough but we
> are not squinting in this discussion.

I don't have to squint at all to look at the real world and see that is full
of continuous tones and motions. Remember the idea of usable or meaningful
values. Taking things down to the level of quantum mechanics may not be
helpful in establishing values to assess the relative merits of one printing
medium over another.
>
> It is *absolutely not true* that an inky printmaker has an infinite
> number of tones available. All bw output processes currently only output
> 8 bits or 256 tones. A quadtone system is *theoretically* capable of
> representing many more tones... 256 to the power 4 in fact, which is a
> hell of a lot, but no drivers that I am aware of address this ability.

Well you can control where those 256 bits fall within a tonal range and if
you can do that, any tone is available to you even if you can only get a
finite number of them into a particular print. Think of it this way. Within
the range, what density can't I reproduce in an inkjet print?

Actually I think the Epson or Piezo drivers are getting you more than 256
tones out of an ink set. Check it out by doing a black ink only print and a
full quad print. It is interesting that the single ink gets you about 90%
there (100% in some cases if the grain size is a good match to the dither
pattern) and the rest of the quad/hex inks fill in the remaining. For my
work I couldn't live with just 256 shades of gray and would still be
sloshing around in the dark.

Martin Wesley