Halftone dot screens

To whom it may concernbr>
I used to be in that business. The half tone screen was to be exposed so
that any and all white space was to have 5 to 10 percent black dots. Faces were
to be 50 percent (thus the name "half-tone"). and all solid black areas were
so posed to have about 10 percent white dots.

Under a magnifying glass the faces were supposed to look like a checkerboard.

When you got it that way, everything else took care of itself.

Len

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On 26-Aug-07, AmerPilots%40aol.com">AmerPilotsaol.com wrote:

> I used to be in that business.

Me, too. I worked in pre-press for many years.

> The half tone screen was to be exposed so that any and all
> white space was to have 5 to 10 percent black dots.

Yep. If you let highlights go solid (on the neg) it looks slightly
posterized at the point where it finally loses its dot. Also, the press
could never hold a dot smaller than 5%.

I remember using a rule-of-thumb in DTP classes I took, related to press
requirements. Take the required lines-per-inch (specified by the press
house) and double it for the required pixels-per-inch of your digital
image. This is because LPI measures just the 'dots' of the halftone
screen. PPI needs to measure the 'dots' *and* the spaces between them.

I think the conversion of digital images to true half-tone screen is
more complicated, and I remeber the true ratio isn't really 1:2, but
it's close enough.

Another point regarding commercial half-tone printing - higher LPI
doesn't always look better. If the press you're running on (or the
paper) doesn't support it, higher LPI will just plug up and your shadow
areas will look muddy.

Twenty years ago, we prepared most typical commercial jobs at 133 LPI,
and higher-quality brochures and media work at 150 LPI. 85 LPI was
typical for newspaper work.

After the years I spent 'spotting' negatives for shipping (cleaning up
the dots with a needle and magnifier), I got a real kick out of seeing a
billboard one day near ground level. I probably exaggerate, but the dots
seemed almost as big as my head!

--
Richard Mattsson - http://www.kiva.net/~mattsson/
Audio Video Art -- http://www.audiovideoart.com

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