DPI vs LPI

J
Posted By
JasonSmith
Apr 9, 2004
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276
Replies
3
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Closed
No, I’m not talking about file resolution, I’m talking about image setters.

Basically we have some wide format Roland HiFi’s that have a max resolution of 1440x1440dpi.

Feasibly what’s the highest LPI AM screening that I could expect with this resolution? What’s the typical DPI/LPI relationship?

While we have some fantastic FM screening, I’m in experimental mode right now and am playing around with AM screening.
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RW
Rene_Walling
Apr 9, 2004
printer dpi and lpi relationship can be calculated as follows:

No. of shades of grey = (printer resolution in dpi / line screen in lpi) squared + 1

So a 600 dpi printer outputing a 60 lpi screen will allow you 101 shades of grey

Your Roland outputing the same would give you 577 shades of gray

Now the optimum lpi/dpi relationship is one where you have the finest linescreen while not loosing any of the 256 shades of grey in a PS document.

Thus we have

linescreen = printer resolution / sq.root of (256-1)

in the Roland’s case we have: 1440/16 = 90 lpi (rounding off the square root of 255 to 16)
J
JasonSmith
Apr 9, 2004
Wow. Thanks, very interesting.

Ironically I just tried a 95LPI setting and looks pretty darn good (for 95lpi).

The rosettes seem to get lost around 135LPI. I realize this isnt the type of machine needed for that type of output.

I just remembered – the Rolands use variable dot technology, so the ‘inferred’ output of the device may be higher.
RW
Rene_Walling
Apr 9, 2004
I forgot to mention that the above formula is for "traditional" screened outputs, stochastic screens, variable dot technology, and other such niceties surely change it, but I don’t know how.

Guess I could try to figure it out, but it would take way too much time and energy.

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