Avoiding the Dreaded Moire-- Press Tests and Adventures in Modern Printing

Sean Michael Robinson:

Greetings all!

Last week our new printer Marquis put a test form of Going Home pages on the press in preparation for the new fully-restored edition that will be going to press as soon as they can schedule us.

As I've mentioned a few times before, wet proofs (in the previous era of printing, otherwise known as "proofs") are the only real way to know, with any amount of reliability, what your print product will actually look like on press. So-called "proofs" these days are actually output on a laser printer or plotter, and don't reflect the resolution or the gain you'll experience actually on-press. So getting a wet proof is the only real way to get an idea of what your book will actually look like.

In this case, my mission was two-fold. One — get an idea of how much gain we could expect on-press, as a trade-off with the blacks density. This was a pretty minor consideration this time, as I now have a pretty good idea of the type of results they're capable of on their web presses with our selected paper (Rolland Enviro Satin). 

Which leaves us with the main goal — to ensure there's no moire.

I've written about moire here before. In a basic way, moire is the third unintended visual pattern that appears when you sample one repeating pattern with another. Take a look out your screen door. Everything you see through the screen is filtered through those perfectly repeating boxes. Because the boxes are mechanically predictable, you most likely don't notice you're looking through a screen at all. But now imagine that, instead of gazing out at your backyard through the screen door, you were looking at another piece of screen, pressed up against the first one. Unless that second piece of screen were to be perfectly aligned with the first, what you would see would be a third pattern, unrelated except through math, that would change with every movement of the second piece of screen.

Make that second piece of screen a different pitch (smaller or larger apetures) or a different shape, and the resulting pattern would be even more wildly different.

This is in essence what moire is. And this is the struggle that has kept many classic comics techniques from cleanly making the leap to digital printing. 

Pixels are the unit of sampling for all visual digital data. A square unit. Mechanical tone (zip-a-tone, Letratone, whatever you'd like to call it), staple of 20th Century cartooning, is composed completely of mechanically-produced perfectly-distributed circles. Sampling circles with squares leaves you a lot of room for error. 

A by no means comprehensive list of Things That Can Cause Moire —

1. Scanning at a resolution that doesn't adequately capture the dot tone (even worse- having your inadequate-resolution scan sharpened automatically by your scan software before you upscale or do anything else to the file!)
2. Working in a resolution space too small to accommodate the pitch of the dot tone
3. Half-toning line art with dots (which is why line art should always be submitted to a printer as a 1-bit TIFF file, along with instructions not to half-tone the images)
4. Resizing or rotating 1-bit TIFF files
5. Resizing or rotating at-size files that are already really sharpened or have little to no ambiguous edges left
6. Resizing or rotating tone many times, especially in small increments

You'll notice the lack of precision in this. This MIGHT. That MAY. You really don't know until your book is on press. You just have to do your best to avoid the things that increase the likelihood of moire, and then cross those proverbial fingers.

All of the above made it easy to pick the pages for the test signature.  Each had to meet some of the following criteria —

a) tone with a high lpi rating (lines per inch, i.e. tiny-dotted tone)

The greater the dot pitch (i.e. the smaller the tone), the greater the risk of moire, as the circles (dots in the dot tone) are being sampled by a smaller number of squares (pixels). (This fact is the rationale behind my decision to work in the resolution space (2400 ppi) that we're using for this entire project, despite that resolution being double the res used by most professional line art print projects. Conveniently, it also enables me to be a lot more flexible with the files — including shrink them uniformly, and resize them to a much greater degree than would otherwise be possible)

b) tone that was exposed, meaning, large areas of it across the page, unbroken by other visual elements

The eye is more forgiving of any visual anomalies that are broken up with other visual elements. Thus, moire, or dirtiness of tone caused by slur in the print stage or overly-fibrous paper, are much more visible when it's a big old hunk of tone uninterrupted by other drawing elements. Additionally, picking tone that had the same density across the page enabled me to better parse how much dot gain was happening across the page.

c) pages with similar or identical tone that were digitally processed differently, or from different sources

Since there are so many ways to screw up (see the above!), it was important to me to make sure that I selected pages from each different source of page (original artwork vs. photo negative made during the monthly production of the book), as well as from each scanner (original artwork having been scanned by both Sandeep and Gerhard, with the same type of scanner, but with slightly different settings and treated slightly differently on my end). The pages that have been problems in the past have been flukes of the media or the scan — some difference in the scanner or scanning procedure that, when treated similarly to other pages of the same type, ended up in moire-ville. (Not a pleasant place to live — everything is plaid.) So covering my bases this time meant each type of scan being represented, a much easier task now that almost all of the book is original art scanned by only two people on almost identical scanners!

d) pages with any other unusual considerations

There are a few pages that had the unfortunate combination of fine-pitched dot tone and the photocopier, i.e. had tone elements photocopied to produce the finished artwork. I wanted to make sure that these elements wouldn't be too dirty-looking on press. I also added a few pages with very dark (40 percent or greater) tone, to better judge dot gain and slur (fine dark tone more easily reveals limitations of press and paper, as the dots of the tone are oriented so tightly together that they easily run into each other, causing visible noise in the tone. Check out pages 352-355 in the previous editions of Going Home to see a good example.)

Lucky for me, Marquis currently only has Rolland Enviro Satin in larger rolls, which means that the test form would be 32 pages long. I sent the following pages —

107, 121, 135, 172, 173, 182-185, 196-197, 202, 256, 285-286, 291-292, 325, 336-339, 351, 353, 355-356, 360, 363-367

The results? Damn good! And thanks to my paranoid working methods, not a lick of moire this time.

The (minor) downside first — no matter how good the printing is, there are limitations to web offset printing, specifically, variation in the impression across a given form. I.e. each page has a different amount of gain and blacks density depending on where it was located on the form. This is unavoidable when printing on a web press, and although it can be minimized by maintenance and condition of the press, there will always be some amount of variation. (If you've ever seen a press in action, you'll know what a marvel it is it works at all! All that paper, moving at that speed... sheesh.)

That being said, there is a minimal amount of dot gain present, and the impression is very clean, even on the areas with dense and dark tone. Compared to the original printings, we are worlds away. Here are some side by side comparisons.

In the multi-page pan shot towards the end of the book there's a tight dot tone that grades from a dark 40 percent to a lighter 20 percent over the course of the seven page sequence. Here's the top panel of page 356, from the middle of that sequence. These are raw scans from my second-printing trade (above) and the press test (below).

And here's a one-to-one comparison. At top, the file that was sent to Marquis, at size (1 to 1 pixels). The tone reads 37 percent at this particular portion of the image. (Was it a graded tone?)

Below is a closeup of the exact same area of the actual press test. The tone has expanded only fractionally, to 39 percent. You can see the bit of slur present in the way the dots are slightly deformed.

And below that is the same area from my second edition printing. The tone clocks in here at 60 percent, and as you can see, there's a ton of dirtiness in the impression.

As I said, this is the extreme — what just happens to be the worst-printed page of the sequence in both the original printing and the press test. But I think it's a fair representation overall of how different this book will look from previous printings.

Which is to say, the march forward continues. This'll be the slickest volume yet.

....and meanwhile, I've managed to go way over on time here, lost in the weeds. Be sure to check this space over the next few weeks for more Going Home before and after comparisons, and if you have any questions for me, I'll see you in the comments!

(Special parenthetical-- also taking suggestions for the image/enlargement for the last page of the book, i.e. the Aardvark-Vanaheim address page. Have a favorite image from Going Home that has thematic resonance for the volume, and would look good large? Let me know in the comments!)