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

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Peter Davis writes

>I've been trying to stay out of this, but I had to point out that the
>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.

Related to printing it is of course used to etch a plate which subsequently
is developed then ink is spread over it. A sheet of paper is pressed against
the plate, and picks up the ink in the form of tiny black dots. As Peter
describes this was done orginally with a finely etched grid lines, with the
image projected thru it onto the light sensitive plate. When the film
(plate) is developed, the image you see is made up of tiny dots because
light from the picture passed through the halftone screen on its way to
the film. The brighter spots and darker spots grow in area (on the plate)
related to the gray scale of the image. 

I would like to clarify one point regarding halftones and dithering in my
last post. Of course in both cases the gray scale of the image in both
cases is related to the ratio of black to white. The difference with
halftone is that it is one variable size dot surrounded by white. In
dithering there are more than one dot and the gray scale depth is
determined by the number of uniform dots representing one spot.

Gabriel





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