Stochastic dot printing

[loco]

I'm looking into screen printing or at least doing some homeworker on this process for art prints. Is there a filter you can buy or is it already and option when you convert to a bitmap in photoshop. I'm also no sure if the radom dot pattern comes in different sizes. I just want to try this on some of my own art stuff just to see the difference


-loxo

[loco]

I just learned something

You can change the dot size (stochastic) just like you do a halftone dot when you convert it over to a bitmap in photoshop

-loco

[fantasygoat]

Perhaps do a process thread?

[loco]

I'm going to do some tests and see how it comes out

I have to work with the stochastic dot size and the right mesh count. Along with ink drying in the screen

I have to make some more calls and try and figure this out

-loco

[Andymac]

40 micron dot

187 ppi

305 mesh

thin your ink more than normal, or use process inks or process base

(this all for paper)

you have to get good film output to get good dots.

you can get interference lines (like moire) if your ppi divides too evenly into your mesh count (like 150ppi on 300-305 mesh)

one thing you don't seem to get is interference between colours.

go for it Henry - It's not THE answer, but it is one of them.

[loco]

I'll use this as a starting point.

Would you suggest imagesetter film?

-loco

[Andymac]

yes to start. the problem you will find is many people who operate imagesetters won't be able to figure out how to change their dot size. Or at least we had a problem. finally found an offset printer who did them fine - we got him to output the same image with about 4 different dot sizes/ppi then test printed.

this is probably more of a problem for me because i was always dealing through designers and 3rd parties trying to get the films I needed - I think you have a better idea of the mechanics/software involved. Plus it was a few years ago I was doing the stuff. things might be easier done now.

[loco]

I'll do the files myself and just have them output

If I ask to many question they get lost. I know what I need and most people that output film have no clue what I'm talking about.

-loco

[fantasygoat]

In the experiments I've done, I've been using Photoshop to generate the images by setting the DPI to the number (ie. 187) and then scaling the image up to the actual DPI (ie. 300).

Unfortunately this tends to produce square dots.

Is there some way to produce round dots that are of the correct width?

[Andymac]

wouldn't have a clue.

the idea is the dots are so small to the nakkid eye you can't tell - they are granular, random. much like inkjet prints (this is where this FM stochastic dot idea comes from)

The basic theory here that makes this superior to halftones for screenprinters is the dots remain the same size - and so you as a printer want to find the smallest dot you can print on your film, expose on your screen, and hold during your run.
Contrast this with halftones, where highlight dots get smaller and smaller, giving you drop out in the lightest tones and a more compressed tonal range. If this dropout is random and used in process colour work, you can get some blotchy off colour results. IN the dark areas, there is more tendency to blurr together, and in the midtones you get banding when the dot turns into a hole.

there would be more stochastic printing and output available if the concept had caught on with offset printers, and the print industry got into it. Unfortunately, offset like their halftones - they have a comfort level, and most output/testing/proofing equipment is calibrated for halftones. Offset dictates prepress in the graphics trades. Screenprinting for the most part follows.

National Geographic magazine, which has a rep for the best colour printing around, switched to stochastic in the 1990s when they saw the difference. Most others didn't. So here we are.

Like I said before, it is not the end-all be-all. Just another technique.