Digital BW, The Print

Hi Roy,

> The main point was that the 256 levels i.e. 8-bit
> files are only loosely connected with how many tones you can measure.

Measuring them or not isn't the point.  The point is, how are they derived,
if they are even derived at all.

> In the original Piezo quote there's no mention of
> input or output resolution,

I believe that on the Piezo email list, 100 tones was what the discussion
was.

> 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.

But did the printer intentionally print 148?  I don't believe so.  That's
inconsistency in the systems ability to represent a tone...and is an
important part of my point.

> > > 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?

Everything.  A pixel has a range of values.  A dot does not.  A dot is
simply a dot...and it can only contain one of the colors of available ink.

> The point is
> that there are multiple gray values.

Not for one single dot.

> 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.

You can not dither a dot.

Austin