Re: halftones

[P3D Gary Nored <gnored@xxxxxxx>]

P3D RJ Thorpe wrote:
> 
> Marvin Jones writes
> > > Peter Davis writes
> > > >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.
> > >
> > > Gregory J. Wageman writes
> > > >That's not halftoning.  I'm not sure what it is (besides possibly
> > > >just an 'effect') but it isn't halftoning.
> > >
> > When I worked for a time in a print shop many years ago, that's exactly how
> > we created halftones, except we used a sheet of plastic gel with a fine dot
> > pattern of a certain density, depending on the dpi we wished to achieve in
> > the final product. My boss at the time had been producing them that way
> > since the '20s, and I know they are still produced that way now. In fact,
> > I've never heard of any other method of producing them!
> 
> I missed the origianal thread so I don't know exactly what Mr Davis was
> refering
> to. Perhaps this was one of the original methods of halftoning that has
> since
> evolved.
> 
> Mr Jones's explanation is pretty good in its general thrust but it is
> wrong in
> just about every detail. His explanation is a mixture of printing tints
> and
> halftones. Tints have a "certain density", black. The size of the dot
> yields a
> certain percentage tint for any particular number of "lines (or dots)
> per inch".
> Halftones screens, on the other hand, have a similar "dot size" and
> "lines
> per inch" structure, but they fade in and out across the gray scale. The
> centers of the dots are black (dense) and the centers of the space
> between the dots is clear (not dense). The transition is gradual. The
> brighter the light,
> the more it "burns" through the screen. Ortho film can only produce
> black and
> white, no grays. So the brighter an area is in the original photo, the
> greater
> effect it will have on the dots in the halftone neg.
> 
> Many prints shops still use this method when shooting through a copy
> camera.
> But I haven't specified this process for years. Nowadays, Just about all
> prints
> are scanned and inserted electronically into page makeup programs like
> PageMaker
> or Quark. The service bureau produces the halftones or color separations
> simply
> by running the film out the same way as if there were no pictures in it
> at all.
> The computer program takes care of it all.
> 
> --
> RJ Thorpe
> Cedar Rapids, IA
> mailto:thorpe@xxxxxxxx
> http://www.skep.com================= 
Everyone's aware, aren't they, that some folks on this endless thread
are talking digital. Some are talking offset printing. 

Old fashioned halftone printing is still alive and well, though 
hopefully not for long. But to get closer to the subject of 3D,
I have a couple of books from Cignus Graphics. One is 3D Insects,
the other 3D Flowers (my crude translation). All these color images
are printed using "random stochastic screens." The term is self-
explanatory, I suppose, but it's implementation is a puzzle to me.
However it's done, these small images are really beautiful, 
particularly when freeviewed (to bypass the little plastic lens-
like inserts). The thing about the random stochastic printing is that
the image quality appears much better than prints I've seen that 
were made with traditional screening techniques. The tradeoff, is
there is some slight retinal rivalry evenly distributed across the
photograph. It's very slight, but it gives the images a sort of
peculiarly "vibrant" an appearance. I've gotten used to it, and
look forward to owning more of these little books. They are really
very nice little books -- good photography, well printed on a fine
white glossy paper.

Now that I've managed to get the discussion redirected to 3D ;-)


Gary


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