Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" <darkroom@i...> wrote:
> Roy,
> 
> > > > 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?
> > > >
> >
> > Hi Austin,
> >
> > Sorry for joining late, but I've been away.
> > Your arguments seem so self-evident that it hard to see what else is
> > going on.  Say you were to create a 8 bit grayscale file with 256
> > separate one inch squares such that each square contained a different
> > gray value -- i.e. 0,1,2,... 255.  Each square has a different
> > gray value and at least theoretically a different gray tone on the
> > print --> thus there are 256 gray tones possible.  This is your
> > argument, right?
> 
> No.  I simply do not believe the Piezo system prints more than 100 tones,
> first off...and if I remember right, that is actually the original claim by
> Jon when Piezo was first introduced...now it's magically jumped to 1000.
> Secondly, I don't believe we can visually distinguish them, and thirdly, I
> simply don't believe that the printers/inks/papers have the ability to print
> 1000 tones...the inks aren't that "pure", the ability to regulate the
> droplets isn't that good...etc. to product 1000 distinguishable tones.

Austin,

I really don't think the Piezo system is any better than you think it is.
I agree that our eyes can only discern on the order of 100 tones so it's
kind of a moot point.  The main point was that the 256 levels i.e. 8-bit
files are only loosely connected with how many tones you can measure.
Since we're talking 1000 tones we certainly can't be talking about human
discernable tones -- we have to be using a high resolution densitometer
or the equivalent.  In the original Piezo quote there's no mention of
input or output resolution, nor detector specs, nor size of samples.
So its at least conceivable that each tone measurement is an average
of multiple input file pixels so the number could easily be greater than
256 tones.   

You wrote the following.  I'm saying the same thing "any number of tones
by dithering".

Austin>> Then you're missing the point of dithering. You can represent ANY number of
Austin>> tones by dithering, it's simply the area that it takes to do so...you simply
Austin>> need to stand further away ;-) 

> 
> I completely understand residual tonality, that isn't the discussion.  There
> simply isn't the tonal resolution (dynamic range if you will ;-) in the
> system to print 1000 tones.  The noise is too high in the hardware alone to
> make that possible.  Print a 100 step wedge, then try printing a 256 step
> wedge...and measure it with the best densitometer you can find.  I guarantee
> you won't get 256 separated tones, much less 1000.  The system works great
> at around 100+, and that fits what we are able to see anyway...

I've got a "good" densitometer not the best.  So I took one of the original
step wedges from using Piezo, put the top gradient under the densitometer.
Paper white is set at 0, the darkest was at 147.  Sliding the paper gradually
thru the meter, the densities just count up, 0,1,2,... easily hitting each
integer value.   So not surprisingly it looks like I have 148 gray tones.
Are there really 148 tones there?  It looks to me like all I've shown is
the resolution of the densitometer.  If I had another decimal digit on would
I get 1480 tones?  I really don't know, probably not.  But I'd bet I could
get a lot higher than 148.

> 
> > The tradeoff of gray levels versus resolution is really the entire
> > basis of what's going on in printing.  Previously in this discussion
> > there was distinction of pixels versus dots, but I think this is
> > an unnecessary and misleading distinction.  Everything we have as
> > far as Epson printers these days are pixels. The very smallest point
> > on a print can contain any of 4 or 6 different gray/black inks drops,
> > plus with variable droplet size and overprint of multiple drops,
> > there are many possible gray values.  So I would call this a
> > pixel not a dot.
> 
> Yeah, but it simply isn't a pixel, unless your "image" contains exactly the
> values that are possible with the inks and droplet size (which is misleading

What difference does it make what values they have?  The point is
that there are multiple gray values.  I just figure if there are 
more than 2 values (black and white) it's better described
as a pixel not a dot.

> by the way), and the fact is, they don't.  The distinction between pixels
> and dots is VERY important, or we would not be dithering, and the printer
> driver does dither.

What's the distinction?  You can and do dither either one.  Dithering just
increases the number of gray tones while sacrificing some resolution.
You can go from 2 to 256, 10 to 256, 256 to 1000.

> 
> Austin

Roy