re:Digital vs Analog (and where to get a cheap scanner)

[P3D Peter Davis <pfd@xxxxxxxxxxxxxxxx>]

At 08:59 PM 12/12/96 -0600, you wrote:
>Peter Davis comments:
>
>>practice of halftoning was originally done by projecting a photograph
>>through a piece of glass with a finely etched grid of lines.  The
>>transmission properties of that grid resulted in the halftoning effect.  The
>>piece of glass had no intelligence or algorithm to accomplish it.
>
>That's not halftoning.  I'm not sure what it is (besides possibly
>just an 'effect') but it isn't halftoning.

Guess again.  It's halftoning.  That is the early technology for getting dot
patterns from continuous tone images.

>>In signal processing terms, halftoning is really a form of "error
>>dispersion."
>
>No, it's dithering that's error dispersion.

Actually, they both are forms of error diffusion, which is the term I should
have used.  In the digital world, halftoning and dithering are harder to
distinguish, because the size of halftone dots is really determined by the
number of pixels used to form those dots.  However, in general, halftoning
uses regular arrangements of dots of variable size (and shape) in a pattern
of some given density.

In addition to Foley and Van Dam (not to mention Feiner and Hughes), you
should also look at Ulichney's _Digital Halftoning_ for a good detailed
overview of the subject.  Both techniques essentially trade off spatial
resolution for tonal.

>>So, quantization alone does not make something analog or digital.
>
>I would disagree; the characteristic of a quantity changing or being
>stored in discrete steps is the fundamental property of being 'digital'.

So you would argue that all halftoned images, including ones produced
optically, are "digital?"

-pd
--------
                                Peter Davis
                   URL:  http://www.ziplink.net/~pfd/

                 "Nondescript -- the one word oxymoron."


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