Wednesday, 18 January 2017

Paper to Pixel to Paper Again: Part 2

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A guide to creating the best looking line art in print in the new digital print world
  
Part 2 
Inking & Screening & Resolution, Oh My!

Greetings!

This is the second installment of Paper to Pixel to Paper Again, a series that explains (in an overly thorough manner) the how-to's of preparing line art (and later in the series, color art!) for print.


***

Last week we started this series by throwing out some caveats, stating some goals, and peeping at my work space and equipment. This week we'll be laying down the basic knowledge you need on order to know the behind some of the things we'll be discussing and doing. f you're impatient to actually, you know, get to it, then sit on your hands for a week and skip this installment!

The past one and a half centuries have seen tremendous changes in the ways images are created, and the ways those same images are reproduced. Since the late 1800s, almost all technical innovation in printing has involved improving the reproduction of what are (misleadingly) called continuous tone images: that is, images that, when viewed in the right circumstances, appear to have smooth gradations of tone and value. If you're viewing a postcard with a reproduced photograph, or looking at a color diagram in a text book, in most viewing distances, these images appear to be smoothly changing values of color. But in reality these images are made up of tiny cells, distributed in an array, that through some miraculous flaw in human vision, work together to create those gradated illusions.





Above: a scanned detail of a Dave Sim commission. Below — an extreme closeup of the resulting print. Notice the array of dots that create the image.

But there are limits to this illusion. Certain people (myself included) have close vision that's significantly sharper than the mean, and are able to see individual printing dots when they're anything other than the finest pitches. More significantly, the sharpness of human vision increases with a corresponding increase in contrast, meaning that extremely high contrast images (say, black on white) represent much sharper visual acuity than a field of color. Additionally, we see another corresponding increase when we're presented with edges. Lastly, fine information that is near or beyond the fine-ness of the screen itself, or oriented in direction in a way that is not perfectly aligned with the screen, can cause all kinds of unintentional visual oddities. 

This is why you will never see a professional publication that has a large chunk of text that is screened and intended to be read. And this is why you should NEVER, NEVER SCREEN LINE ART.

I'm going to belabor this point (who, me?) because it seems to have been forgotten or ignored as screening methods have improved, or as expertise (and money!) have drained from the print fields. Unless you're reproducing in color and intending to show the artist's process as the intent of the print (a la IDW's Artist Series, the Cerebus Archive portfolio series, etc), LINE ART SHOULD NOT BE SCREENED FOR REPRODUCTION.





Above: scans of page 225 of the aborted February 2013 printing of High Society, which, as you can see, was half-toned, as it was supplied to the printer as 8-bit grayscale files. Below is an image from the restored files, produced from the exact same scans as the above images, but treated much differently in the prepress stage. Notice that the dots in the Cerebus image above are strange, gradually changing shapes, moire that is a result of the original halftone screen that makes up his fur passing through a second screening process at the printer.



Imagine, if you will, the simplest of print methods, something along the lines of a stamp. A chunk of potato in which you've carved out an object in relief, maybe your name, carving back the potato from the sections of the images that you wish to remain uninked, and then pressing it against a flat surface slightly moist with ink, and then finally transferring that ink with light pressure onto another surface.

Your resulting print, any unevenness in the ink aside, is a binary. Either a particular area of the paper is inked, or it is not. On, or off, no in-between. And, really, how would you represent in between? You examine your print some more, consider that you really would like to have a “gray” area of, say, 30 percent to augment your totally black and totally white portions of your image. So you cut some parallel hatching lines into a previously fully inked area of your potato, and you print again.

This is line art in microcosm, line art at the beginning, just beyond scraping lines in the sand with a stick, just beyond taking an old torch and dipping it in bison blood and dragging it along the surface of your cave. Primal, black marks on white, any “gray” an illusion created by finer marks of black on white.


Okay, let's skip ahead at least a millennium, where we arrive at the present day.

No longer satisfied with the speed of your potato print, you're now interested in taking your paper line drawings and reproduce them with all the bells of modern technology. A terrifyingly fast, abominably loud web press, running off a thousand copies of your masterpiece in an hour. Between you and that copy are a good dozen technicians and a veritable space-shuttle level of switches and knobs and little blinky lights. How do you ensure your drawing survives the process? How can you signal to these strange, unknowably distant beings what it is you want out of your print?

(And please don't tell me that your desktop laser printer, or the, ahem, helpful staff at your local copy center, are any more knowable or accessible :) )

You need to know how to prepare your files. You need to know what to ask for. And you need to know about resolution.

RESOLUTION

In order to actually, you know, get to the part of this series where we actually DO something, I'm going to need you to take for granted a few facts. Rest assured I'll come back to them in future installments, and rest assured, I'll be happy to argue with you about them in the comments.

When you're preparing color or grayscale images for print, that is, images intended to be reproduced as (not actually) continuous-tone images, the limit of your effective resolution is the screen that these images will pass through. The fineness of a screen is measured in LPI — lines per inch. A printer printing on an extremely coarse surface — a cardboard box, newsprint, some kind of screenprinting application etc — will use a really coarse screen, sometimes as coarse as 40 LPI. Printing on a sheetfed offset press on coated paper, or on a very good one-off digital press on coated paper, the LPI might be as high as 300 LPI.

A good rule of thumb for supplying files that WILL be half-toned is, the maximum effective resolution is twice the line screen resolution. So, if your printer will be screening your final image at 200 LPI, 400 pixels per inch is the highest effective resolution you can supply. Anything above that is pointless, as it's lost in the screen. (This is not the case if you're suppling some elements separately, a in a PDF, where you can have images with different resolutions and color spaces coexisting in the same document. More on this later!)

Conversely, when you're printing WITHOUT a screen — whether that's in black, or using a spot color — your only resolution limit is your vision, and the resolution of the output device, whether that's a laser printer or a plate setter at the printer.

Without further ado, here are the resolutions you should be aiming for for suppling files to your printer —

Color or Grayscale--

as low as 100 PPI in some extreme circumstances, as high as 600 PPI on coated stock with good printing should be dependent on the destination LPI. Remember, it's easier to downscale than upscale! I always scan any color art that's going to leave me permanently (go to a client, etc) at-size at 600 ppi, as a safety.

Line art/bitmap--
1200 ppi for laser printers and other digital printers (600 PPI might be acceptable on rough paper if there are no very fine lines or repeating tones present)
1200 or 2400 for web or sheetfed offset with fine lines and tones.

But, fortunately, since we're dealing with line art, just because you're SUPPLYING line art files at that resolution, doesn't mean you need to scan at that resolution!

… and that's all we have time for next week. Next week — we finally (for real!) get to it!Thoughts? Questions? Quibbles? Hit me up in the comments!

Sean Michael Robinson is a writer, artist, and musician. See more at LivingtheLine.com.

21 comments:

Travis Pelkie said...

I've seen stuff like those fuzzy images in the middle of this post in a printed comic. Horrid! Thank goodness you saved us from that, Sean!

A wooden potato?

Jeff Seiler said...

Sorry to interrupt the discussion, but I just learned that the winning bid for the 1-of-1 Black Angel CIH?s was $103.50.

I was told that my bid of $200 was accepted. And, entered.

Can someone clear this up for me?

SamC said...

Jeff, assuming the bid on your behalf was the Jan 15 one, that's how eBay works. The winning bidder is whoever bid the most, but the winning bid is the next bid increment higher than the second highest bid (it's a bit more complicated than that, but that's the basic idea). Whether your high bid (the most you're willing to pay) was $105, $200 or $10,000, you'd win it at $102.50 if the highest anyone else would go is $101.

Jeff Seiler said...

Sean, even with all the supposed lines looking like rows of dots, she still looks beautiful, right?

I mean, that was kind of the overriding idea, right?

But, you are doing a fantastic (and I mean that in the literal sense) of cleaning up the pages. I don't get how you do it.

But, I think that you must pay as much attention to every page, looking for the odd line reprinting error as I do, looking for the occasional typo.

Together, we make a good, if unheralded, team.

Altso, please check out my entry, ahem, whenever Tim gets around to it, about *my* process in proofreading Church & State, vol. II.

There's a couple of what I think are interesting entries.

Carson Grubaugh said...

I may have to make some of my students read these. Such an invaluable resource!

Sean R said...

Hey Jeff,

"But, I think that you must pay as much attention to every page, looking for the odd line reprinting error as I do, looking for the occasional typo."

Unless you spent, say, over 250 hours proofreading Cerebus Volume One, or over 350 or so hours on Church and State II, then I'd say this is a safe bet. :)

Jeff Seiler said...

Okay, Sean, (and, not knowing you personally), I TOTALLY give it up to you. You do a yeoman's work.

But, please, somebody, throw a bone to the isolated homebody who pores over every SINGLE word (AND punctuation mark), just so he can be a part of the the project.

Well...

It's not *that* bad. I do get the occasional "we're not friends" comment from Dave, and I think A-V, Inc., appreciates the proofreading, and I certainly appreciate the income.

I'm just saying, we all do our part, in this great project.

Dave?

Since this is how we're communicating these days (not being friends and all)...

Thank you for all of the previous things you've written about my proofreading. I know we don't always agree, and I can be a bit punctilious, but I think we see eye to eye on most things that are on the printed page.

Well, except for the OED stuff, but I'm working on it.

Jeff Seiler said...

So, SamC, does that mean I won? At $200, or $103? Enquiring minds want to know.

Plus, I may have to dig out my wallet.

Steve said...

CIH? hijacking continues...

There were 6 bidders in the auction, several putting in multiple bids - which shows some level of interest since they increased their bids rather than eBay's automatic increments (I believe).

Sandeep could tell us how many 'watchers' and how many 'page views' there were as well.

Just to be mean I'd planned on putting in a $190 bid, knowing Jeff had one in at $200.

But I didn't get home from work early enough...

Steve

Dave Sim said...

Jeff - I told Fisher that you were "in" up to and including $200 US. I assumed that that meant you wanted him to bid UP TO that price -- not just bid $200. I hope the winning bid is yours/Fisher's. Sandeep and I had a bunch of other things to talk over today so the auction never came up and I have no idea what Dave Fisher looks like on eBay.

Jeff - This is how I communicate with everyone these days with the exception of Sean, Eddie and Sandeep (the former two by fax and Sandeep in person). To be honest, an hour of socializing online a day puts me well past my social threshold. WELL past.

Dave Sim said...

Sean - I appreciate your diplomacy in these posts. Half-tone screening of line art really has become the default position of many publishers. The idea being that...what?...you're getting ALL of the art because that which isn't sufficiently clear is still there as a series of dots? It's a strange way to look at it.

Maybe you could cite publishers and books that impress you with their fidelity to the work. For one thing, it's a much shorter list!

Jeff Seiler said...

Well, Dave, just let me know how much to send and when. It'll be there.

Going out tonight to our monthly Parrothead club meeting to find out whether or not I've been elected Vice-President. I don't expect great returns. But, I will stay the course of being involved and speaking truth to power.

They hate that.

Tony Dunlop said...

Huh, Jeff - kind of reminds me of that old cliche' about why college faculty meetings tend to be so nasty - "because there's so little at stake."

Dave Sim said...

"Some Parrotheads see things as they are and ask, 'Why?' Jeff Seiler sees things as they never were and asks, 'Why not?'" paid for by the JEFF SEILER FOR PARROTHEAD PRESIDENT 2020 Committee.

Your comic books are on the way in the mail. Just send a cheque for half the amount made out to Sandeep and half made out to me. OUR comic books. Not Aardvark-Vanaheim's. OUR comic books.

Jeff Seiler said...

Aw, you made me blush. I lost. By a vote of 43 to 4. One of the four was me. I'm pretty sure I know who two of the other three are, but I sure would like to know who that fourth one was.

The other 43 can go...

Ahem. I'm not bitter. I'm not. No, really.

Dave Sim said...

You can console yourself that you won in the Parrothead Electoral College.

Travis Pelkie said...

There are 47 people who like Jimmy Buffett? Not just in Jeff's neck of the woods, but anywhere?

Jeff Seiler said...

Dave? Thank you.

Tra-viiis?

Jimmy has sold out every venue he's been to, in ten minutes, for the past...um, I don't know...30?...years.

He has recorded nearly 50 albums/cd's. Some really bad stuff and some trascendental stuff. There are songs that he sings that will make you lol, songs that will make you cry, and songs that just make you feel good.

And, yes, Dave, he's a feminist, but there's always trade-offs in life.

I can live with myself on that one.

'Cause there are songs like A Pirate Looks at Forty, and Blue Guitar, and Volcano, and Chanson Pour Les Enfants.

But, Trav, I also really like me some Garth, some Johann Sebastian, some opera (well, not much), some Sondheim, etc.

To each his own.

Travis Pelkie said...

Ah, I knew I was poking a bear there, Jeff! I was just funnin' ya.

However, what "truth to power" do you have to tell to a Jimmy Buffett fan club?

"Perhaps we are ALL lost shakers of salt?"?

j/k!

Jeff Seiler said...

You would not believe how political most Parrothead clubs are and how much crap they try to pull. All with a big ol' smile on their faces. Very, very cliquish. I just try to get them to follow the rules.

They hate that.

Travis Pelkie said...

"Point of order: we can't ALL wear the Carmen Miranda outfit! It's my turn this meeting! Get your own fruit headdress and wear it NEXT time!"