# Stochastic Printing DPI?

Does anyone know the DPI for the stochastic screening?

We got a new Heidelberg CTP Suprasetter and we're just testing... and the results are amazing... but the resolution that we're working on are not good enough for that quality. We're using 300 DPI for smaller sizes (40x40cm-20x20cm) and 220 DPI for (60x40cm - 50x70cm).

Testing 300 DPI seems acceptable but we believe that we can use more resolution to get better results.

Does anyone know the correct DPI resolution for it?

• For clarity: you want to know the appropriate dpi for source art? – Yorik Mar 4 '15 at 21:19
• On the one hand, 300dpi is for 2x 150lpi frequency, and 20 microns stochastic is considered to be maybe about 500lpi (derived via dot counting), but I see people saying 600dpi is probably overkill for FM screens. I have had commercial books done by suppliers using stochastic plates (by chance rather than design), and the 300dpi sources worked "just fine." I think FM is "non-uniform sampling" and the 2x sampling requirement is not a perfect fit. I am interested in hearing from someone with a technical perspective. – Yorik Mar 4 '15 at 21:50

I've seen the short answer to this from multiple sources as the following tables (in microns):

Detail rendering equivalency:

• FM 20 = 500 lpi
• FM 25 = 325 lpi
• FM 35 = 325 lpi
• FM 36 = 275 lpi

However the answer to your question is probably much more complex since there's other factors including paper and the consensus that stochastic printing generally has more dot gain, which will increase the size of the dots and has to be compensated for with dot gain compensation curves. There's also different ways of measuring the lpi for FM screens, the table above refers to how many dots are encountered on a 1/16˝ line, whereas there's also a lithographic method where the edges of dots are counted in a given area.

For more details and a general overview, see the Ed article above. For the two methods of measuring the lpi and the source of the tables above see this blog post (by a member of a forum on printing I frequent) and for a discussion of dot gain and other FM production issues see this blog post.

• Thanks for your answers, maybe I'll stay away from stochastic for now, as you say, there's a lot of "other factors" to get it working properly, In the meantime I'll check that blog post. – Ronald Max Davila Mar 5 '15 at 19:36
• I wouldn't necessarily say you should stay away if you're getting better results, but it may be a longer process to calibrate everything right. The truth is it will probably look better even if you aren't using optimal resolutions. Trust your eyes! – yawnercreative Mar 11 '15 at 22:43