Digital BW, The Print

Oh Anthony,

> Inkjet printers, like offset presses, use essentially opaque inks
> in four or
> more colors, usually cyan, yellow, magenta, and black.  Since
> these inks are
> opaque, their darknesss on paper cannot be varied, nor can one color be
> printed on top of another to blend the two.

That is true...but...

> So, in order to create
> variations in the darkness of the printing, the inks must be divided into
> dots of variable size.

That is simply not true.  SOME printers do have variable sized dots...but
not all do.

> When the dots are large and closely spaced, the
> printing appears dark (from a suitable distance).  When the dots are small
> and widely spaced, the printing appears light.

Spacing is typically not variable, it is fixed at 1440 (720, 2880...etc.) or
what ever it is...and doesn't vary for an individual image.  In other words,
the spacing is the same, no matter what the dot size is, and it is the dot
size (if it's a variable dot sized printer) and/or how many dots there are
over an area that determines light/dark.

Also, some printers that DO have a variable dot size, only allow ONE dot
size for an entire image, it is not variable across that image.

> Printing a single pixel on paper requires a halftone dot of each color.

No, it requires printing a lot more than "a" dot of each color...

> As a result of all this, a 2880-dpi inkjet printer cannot print anywhere
> near 2880 pixels per inch.  It prints far less, and there is an inverse
> relationship between the number of intermediate tones it can print and the
> resolution (because more tones requires more variability in dot size, but
> that means that individual halftone dots must be made up of more machine
> dots, which further reduces resolution).

It is not the only the variability in dot size, but the dither/halftone
method far more so than the variability in dot size...and as I've said, a
lot of printers don't vary the dot size.  I think you aren't quite up on how
halftoning/dithering works.

> So ... if the inkjet printer manages 2880 dpi, and you want 256 levels of
> black or green or whatever, you'll need 256 machine dots per halftone dot.

That's not true with stochastic screening techniques, and if variable dot
sizes are used...as well as multiple ink colors, like the graytone inks we
use.  It's simply not as empirical as you make it out to be.

Sigh.

Austin