Count DPI in printed pic?

[Molly/CA]

We'd like to, or need to, know exactly the dpi a certain press's illustrations in a certain series are being printed at. Is there any easy way to figure this out? We do have a dissecting microscope. Uh, (blush) dumb question, dpi is a linear measurement, isn't it? Dumb question II, are the dots' allotted spaces square?

Thanks again, all you experts and professionals.

Molly

[ktinkel]

We'd like to, or need to, know exactly the dpi a certain press's illustrations in a certain series are being printed at. Is there any easy way to figure this out? We do have a dissecting microscope. Uh, (blush) dumb question, dpi is a linear measurement, isn't it? Dumb question II, are the dots' allotted spaces square?

Thanks again, all you experts and professionals.Printers use something called a screen finder (http://search.store.yahoo.com/cgi-bin/nsearch?follow-pro=1&catalog=pgiinc&vwcatalog=pgiinc&query=screen%20finder) (very inexpensive, in the $10 range). It is transparent plastic with an etched grid; you move it around over a printed image until you find a match and read out the linescreen (LPI) used to print the halftone.

LPI is usually 1.4 to 2 times the dot resolution, so if you see an LPI of 133, the scan could have been about 200 dpi — assuming it was scanned at the final size (which is pretty unusual). Because of the size issue it could be tricky to infer accurately what resolution was used to scan. Photos are often scanned at 300 dpi, however.

Ordinary printing on non-coated paper is usually done with an LPI of 133; printing at newsprint can be as low as 65 but is commonly 85 or 90 LPI. Beautiful art books on coated paper could have an LPI of 175 (or even more).

[Robin Springall]

Expect Peter Arnel to chip in real soon boasting that he does 200 lines as standard! ;)

[Ian Petersen]

Is there any easy way to figure this out?Do you want to count the DPI (resolution of the laser setter) or the LPI (resolution of the raster screen)? The DPI can be anything up to about 4000 which might require your microscope. To find the LPI, find a portion of the image with as few colours as possible - preferably a roughly 50% black - then lay a ruler parallel to the dots and start counting. LPI is simply the number of lines per linear inch. You wont need the microscope. Any household magnifying glass should be good enough.are the dots' allotted spaces square?In theory, a 50% grey should look like a chessboard, i.e. with square dots, but in practice the dots will probably be more or less rounded.

[ktinkel]

Expect Peter Arnel to chip in real soon boasting that he does 200 lines as standard! ;)Oh, well — we should expect no less!

But Molly does not seem to be dealing with a Peter class of printer. I am sure she would prefer to!

[PeterArnel]

hahahaha - of coarse and we are soon going "dotless" great name for Stochastic - printing with 20 micron dots.

[PeterArnel]

Molly
Why do you need to know ??? -
Peter
If its to check the lines per inch - then Kathleen is right. Its years since I have seen one though. In fact I think it was Letterpress years ago

[PeterArnel]

I think printers who print sheet fed these days are normally 175 - 200# Its only old webs that go down to those low screens.
Peter
The fine art printers are running sometimes up to 300#

[PeterArnel]

Kathleen I read this last night - I can never remember seeing one - I have seen one for screen angles . Does it work in a similar way
Peter

[ktinkel]

Kathleen I read this last night - I can never remember seeing one - I have seen one for screen angles . Does it work in a similar wayYes — really low-tech. Lay it on the picture, move it around, line things up, note the reading.

I imagine there must be super-duper high-tech devices for this by now, but these antedeluvian plastic things were very common in my youth. :)

[PeterArnel]

Because we dont plan film any more - its all gone

[ktinkel]

Because we dont plan film any more - its all goneAh, gee. I am so sorry!

Let’s all move to a desert island somewhere!

[Stephen Owades]

A screen finder can be used on printed material as well as on film, although it works much better with black-and-white halftones than on printed color jobs. And of course it won't work with stochastic printing at all.

[PeterArnel]

I thought that was the aim - it will all be virtual soon

[Molly/CA]

Gee, I didn't know picture printing was so interesting and so fast-developing.

Why we need/want to know: this division of this press insists that it can't possibly use anything but slides for any photos that will appear in its series. Digital photos? Oh no no no. We couldn't possibly use anything that low-quality.

The in-text photos can be no wider than 3.5" (margin to margin width) and are generally 2+" vertically --standard 8 to 6 photo proportion for most. We're not impressed with the quality of the photos in the series books they gave us and we think there's something fishy, probably to do with the competence or lack thereof of their graphics staff, which seems to consist of one person whose main contribution has been to complain that the seiners in one picture seem to be wearing '80's clothes' (we think she thinks the chest-high waders some are wearing are bib overalls but we're not sure) and to try to send us a JPEG of a photo of a non-native fish taken by some friend of hers, to use instead of the one of a CA species we'd supplied. We never did see this picture as she couldn't figure out how to attach it to her e-mails. We know that it was about a 400kb file but we don't know if that was a reduction of the original. Our EOS CRW (Canon Raw Format) files expand out to about 35mb as TIFFs and the Nikon 8000 slide scanner files run about 68mb, and we never did get an answer when we said that would be what we'd be providing as digital photos and could they handle that file size.

This book's done but there are two more coming up.

The editor that's now working with us is new.

We need some ammunition so we can try to shoot down the demand for slides. So many of my husband's were irreplaceable and even more of his co-author's for the next two books are irreplaceable. We think they go to Hong Kong but they won't tell us.

Does that help?

[Molly/CA]

Answer # 2 to 'why do we need to know' --maybe what we need is an impressive vocabulary so we can throw in a lot of jargon/ shop talk words, more than actual knowledge! That's worked before.

[Molly/CA]

Thanks for the link. You sure know how to push my shoppers' button. Moleskines, typography books (I think I found Bringhurst's Typography by myself --well, Amazon & I-- and it is really fun, I love it) and now magnifiers.

m

[ktinkel]

I thought that was the aim - it will all be virtual soonThen what will future archaeologists have to study?

[ktinkel]

Answer # 2 to 'why do we need to know' --maybe what we need is an impressive vocabulary so we can throw in a lot of jargon/ shop talk words, more than actual knowledge! That's worked before.Ah. For that I have a recommendation: the 1992 edition (none of the earlier editions) of the Graphic Arts Encyclopedia (http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=599717529&searchurl=an%3DStevenson%26y%3D10%26tn%3DGraphic%2 BArts%2BEncyclopedia%26isbn%3D007048113X%26x%3D41) by George A. Stevenson. It is not cheap, but it should give you access to all the jargon (and useful information) about printing processes in use up to the 1990s, anyway. (We have Peter, Robin, and others here for changes since then!)

Although printing is changing rapidly, this book has answered a lot of questions for me even recently. And you cannot beat it for getting up on the nomenclature.

[PeterArnel]

I think now that people know what you are doing - every one will put their two pennyworth in. The old addage is the dpi should be twice the screen ruling
but normally 300 dpi is fine
Peter

[Steve Rindsberg]

Then what will future archaeologists have to study?
Virtually nothing.

[PeterArnel]

Can you image that in a 1000 years - if all that was left - is what has been written on this site in the last year- They would have a field day (well years) analysing it

Peter

[ktinkel]

Can you image that in a 1000 years - if all that was left - is what has been written on this site in the last year- They would have a field day (well years) analysing it Most of it would seem like gibberish, I bet — since most of what we discuss would have gone poof.

But I bet there will still be lots of real books that survive.

[terrie]

molly: this division of this press insists that it can't possibly use anything but slides for any photos that will appear in its series. Digital photos? Oh no no no. We couldn't possibly use anything that low-quality.
These people are just too totally clueless and stupid!!! Is there any possibility of using a different publisher for your next book?

Terrie