[Alt-photo] Re: Stochastic screening in Gum

[Ian Hooper]

I've tried stochastic screened negs output on an imagesetter with varied 
results.

Things to consider:  too small of a dot will not 'hold' in the 
highlights;  negative and paper have to be very tightly sandwiched; the 
more 'point source' the light, the better; the more dense the ink (in 
terms of uv blocking) the better.   Also, bear in mind that most FM 
screens are geared towards offset printing, which is a very different 
animal than gum. There is a lot more to high-end FM screening than a 
simple dither algorithm; hybrid AM/FM screens with complex error 
diffusion are required to hold the highlights and avoid ugly "wormies" 
(a mottled/stippled artifact).

The JPD (just-printable dot) has to be determined by trial and error; 
the paper surface, sizing, and gum qualities all be significant variables.

That all being said, it can work very well, but is definitely a quite a 
few steps away from "analog gum".  YMMV :)

-Ian

On 06/12/2013 6:21 PM, Peter Friedrichsen wrote:
> Has anyone applied a stochastic screen to gum printing? This is a half 
> tone technique that uses dot frequency to emulate color/greyscale. The 
> smaller the dot size, the more photographic the rendition. My UV box 
> generates diffuse UV light so I think that may not be as effective as 
> a more point sourced arc type UV lamp.
>
> Has anyone done anything like this before? I was wondering what the 
> minimum dot size that could be realized from a contact negative?
>
> Peter Friedrichsen
>
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