Correct color on inkjet means uniform color; profiles are not enough
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This presentation, made at the recent Fespa 2019 in Munich, shares some of the insights and advances we’ve achieved over the last few years as we’ve worked with many inkjet press vendors to increase their output quality.
Hello, and welcome to a presentation that will share some of the insights and advances we’ve achieved over the last few years as we’ve worked with many inkjet press vendors to increase their output quality.
Today I’m hearing a lot of people telling me that inkjet has equaled offset print quality, which is a hugely broad and ambitious statement. I’d love to be able to just say that it’s true, and that we’ve been an important part of that achievement. But I’m here with my engineering hat on, so like to explore some aspects on inkjet quality and reach a more considered verdict.
What I can say with confidence is that production print inkjet presses can only produce correct color if they are producing uniform color to start with, and that’s what I’m going to be discussing today.
I firmly believe that you cannot fully understand what somebody is saying unless you know who they are, and why they’re saying it.
My name is Martin Bailey, and I’m CTO at Global Graphics Software. We are the company behind
the Mako SDK for creating, editing, transforming and visualizing page description languages;
the Harlequin RIP
The ScreenPro screening engine, which I’ll be covering later in this presentation,
and Fundamentals, a foundation for building DFEs for digital presses.
And we have a couple of sister companies in Global Graphics PLC: URW designs and develops digital fonts for companies like Siemens and Mercedes.
And I’m sure you all know Meteor Inkjet, developers of printhead electronics and associated drivers.
Collectively these technologies represent the broadest technology offering to inkjet OEMs available from a single vendor
I firmly believe that you can only fully understand what somebody is saying if you know who they are, and why they’re saying it.
My name is Martin Bailey, and I’m CTO at Global Graphics Software. We are the company behind key technologies that are used by these OEM partners; I’m sure you’re recognise a few names in this list of some of our OEM customers.
Our best estimate at the moment is that something around the equivalent of 10 billion A4-sized pages are printed per month using Global Graphics software technologies.
Today I want to focus on higher-volume inkjet presses, printing final product.
This is a busy space, with many new vendors developing and selling their first inkjet press … and learning as they do it. Many of those new vendors are not new to print, but they are new to production inkjet.
And we have to remember that the print industry, and the opportunity for inkjet, is much bigger than many people think. It runs the full spectrum from transactional through graphic arts (commercial print, publication, newsprint, books etc), signage, labels and packaging. And increasingly inkjet is expanding into industrial print sectors, where the printing is a part of the product itself.
You’ll probably all know that the ceramic tile industry has flipped from screen printing to inkjet over the last few years. Now we’re all placing bets on who will be next, with wall-coverings, laminate and vinyl tile flooring and textiles for décor all being favourites to expand greatly over the next few years.
But even with all that diversity, almost everyone is claiming to match offset quality. <CLICK>And at every trade show they’re giving away sample prints of jewelry, big cats, portraits, fast cars and Bavarian castles.
Just as a matter of interest, and I probably shouldn’t complain about this while I’m in Munich, but why are all the pictures of castles in Bavaria; I know they’re very photogenic , but a little more variety would be nice!
But what are all these prints really trying to show us?
The message from many of them is at least partly that the inkjet vendors expect offset and flexo press operators and production managers to be examining these prints. Those vendors are therefore giving them something familiar. And that should be taken as an interesting data point, confirming that many printers/converters etc are expanding or switching to inkjet.
So those samples show a lot of detail because that’s what offset and flexo vendors try to show, and therefore what press operators and production managers are expected to look for.
<CLICK>But … does showing a lot of detail really highlight the strengths of a particular inkjet press?
Don’t get me wrong, that’s an important aspect of quality, but it’s not the toughest challenge for inkjet.
<CLICK>What will really impress me will be seeing print samples of very large flat mid-tones and long grads, especially in four-color greys.
So what should you be looking for on those samples?
The answer falls into two groups – small and large scale effects, or micro and macro non-uniformity.
Micro includes effects from single nozzles, or from very small numbers of nozzles interacting; things like mottling, streaking and missing or blocked nozzles. I’ve heard many other names for such effects, including graininess etc.
Macro are the larger effects that are usually described as banding.
Over the last several years we’ve tried to develop a consistent set of terminology within Global Graphics so that we can talk sensibly with our customers and be sure that we all mean the same thing.
In this terminology ‘mottling’ is the orange-peel like effect that you tend to see on less absorbent substrates which arises during drying or curing. It’s perhaps more common with UV inks, but we have seen it with aqueous as well.
<CLICK>Streaking is caused by coalescence of ink drops on the substrate surface, either along or across the print, and usually on more absorbent substrates.
<CLICK>And blocked, clogged or deviated nozzles can occur on any substrate and with pretty much any ink technology.
Macro effects, on the other hand, are features that tend to be in the range of between one and ten or so cm across. They’re often cause by variation of ink pressure or voltage changes within a head, which typically results in a smile or frown shape.
<CLICK>And we also see a certain amount of manufacturing variation between heads, so that one may print lighter or darker than the head next to it in a print bar.
<CLICK>Some types of heads can wear in use, resulting in less regular banding which can change over time.
All of those three causes apply to single-pass inkjet presses, but they also cause issues on multi-pass presses. And in that case the overlapping swathes of the print head add extra potential for problems.
The typical method of correcting these effects is by tweaking head voltages, but that’s a very manual, time-consuming task which can’t always achieve the desired results.
These are some real-world examples. The left-hand two are the best that one of our customers could achieve before they invited us in to help; you can see the banding very clearly.
The one image on the right is from a single-pass press at a much higher magnification; I hope you can see the regular pattern of light and dark; I always hate showing this kind of thing on a projector or in a video because I never know how well it will reproduce fairly subtle detail!
Both micro and macro non-uniformity are usually highly directional on the output, so we’re finding a test that’s been used in the décor space for a very long time quite useful in assessing quality. That’s the porthole test.
Viewers look at a piece of print through some form of window; the porthole. If they can tell in which direction the substrate or print heads moved when printing it, then it’s a fail.
So, there are things that are hard to get right on inkjet, and you can see the problems at normal viewing distances. What does that mean in practice?
For signage, graphic arts, labels and packaging the bottom line is that a buyer is more likely to reject a print, to demand some form of compensation, or simply to take their next job to a different supplier. All of those really mess up your bottom line.
In practice we’ve found that pretty much every company printing with high-volume inkjet has developed a simple metric<CLICK>: “what proportion of jobs submitted by my buyers can I print on this press and be confident that I will get paid?”
And there are a lot of companies struggling along with a value in the range between 40% and 80%, even as low as 30% in some more specialized markets. We’ve also talked with companies who have unused presses gathering dust in the corner, because they concluded that they could not make a profit running them, often because their payment confidence level was too low, or the maintenance load was too high.
I’m sure none of the vendors at FESPA want their equipment to be in that state; I certainly know we don’t!
And then if you look at some of the print sectors touted as “the next big thing”, in décor, textiles, and some parts of labels and cartons … there’s an added complication.
This drop of wall-covering will be hung right next to that one; the color and tone had better match.
This tile will be laid next to that one.
This curtain will hang next to that one.
This piece of fabric will be sewn onto that one for fashion or furnishing.
This boxed product will be next to that one on the shelf.
<CLICK>Sometimes the printed design is such that variation is acceptable, such as when emulating natural wood with significant variation within the design on laminate flooring. But much of the time it’s not. So these opportunity markets just raise the challenge a bit further.
And for all inkjet markets, building and maintaining a press without issues takes more time and money than most of us would like.
In extreme cases it’s difficult even to make a color profile because color varies so much across the test patches.
<CLICK>In other words, you can end up with a real lemon. <CLICK>Except that it’s not even a good lemon!
OK, enough of my belly-aching. If inkjet was easy then everyone would be doing it!
Well, OK, there are a lot of people building presses, and that’s where Global Graphics comes in, to help make them print well.
So let me share some details of the technologies that we’re using for that.
How does an OEM solve a problem like inkjet?
First: do what you can in a reasonable time and at a reasonable cost to fix stuff mechanically, in the electronics, in the ink, etc. At the very least, achieve stability. I’m sure we all know that systematically correcting an unstable system is much, much harder than a stable one, if it can be corrected at all.
Once you’re at that point, we’re finding that software is a much faster and more cost-effective way to address the remaining non-uniformities than doing more in hardware.
From the Global Graphics stable we have Advanced Inkjet Screens for mottling and streaking, and PrintFlat for banding.
If you’re struggling with blocked or deviated nozzles our sister company, Meteor Inkjet, has a solution in their technology.
And we have customers using our technologies for both single-pass and multi-pass printing.
Let’s look at each of those in a bit more detail.
Advanced Inkjet Screens comprises two base screen designs. The Mirror screens are designed to mitigate mottling effects on poorly wetting substrates, while the Pearl screens are designed to mitigate streaking on absorbent media.
Both of these are already being used in production.
And the primary mechanism to apply Advanced Inkjet Screens is using our stand-alone screening engine, ScreenPro.
It’s highly versatile because it just needs un-screened raster as an input, and it will deliver screened raster on the output, configurable to apply any number of drop sizes from 1 up to 15 (although I’m not sure we’ve worked with anyone using more than 5 drop sizes in real production yet).
Because of that versatility it can be used with virtually any RIP. It’s currently in use taking rasters from Harlequin, Esko, ColorGate and Caldera RIPs. And, or course, in sectors where the job is originated in a raster format in device colors you don’t need a RIP at all.
It’s also very scalable, and we can work with our OEM partners to integrate full shared-memory pipelines direct to electronics for very high-speed presses.
As you can see, ScreenPro won a Printing Industry of America Intertech award last year.
And finally, the most recent addition to our inkjet quality technology is PrintFlat. This is a feature within ScreenPro that corrects tonality to hide banding, based on measurements from the press.
Because it’s done in software it can adjust every nozzle separately, and doesn’t need a specialist engineer to make press adjustments. In other words, it greatly reduces the time and cost both of building a press and of maintaining it.
Let’s take a look at what PrintFlat can do in real-world situations
Firstly: the top one of these images is a photograph of a large-format outdoor signage from the same customer who produced the prints with the bands that I showed earlier. This time with PrintFlat.
Blue skies are amazingly hard to print well, almost as difficult as flesh tones.
We have another PrintFlat engagement where our customer simply could not make color profiles because the output was too inconsistent. Now they can, and they’re generating very nice color.
But don’t just take our word for it. <CLICK>This video was made with one of our OEM partners.
If you’ve found today’s presentation interesting or useful, there’s a lot more information available on our web site, including white papers and PDF and video case studies showing the benefits that a couple of our OEM partners have achieved from using our technologies.
I also have some copies of our case studies with me here, and some real print samples showing the impact of PrintFlat; please come up after the presentation to get a copy of a case study or to look at the samples.
This is probably a good time to repeat that our model is to supply technology to inkjet vendors, to people building inkjet presses. If you’re using inkjet presses to print, and you’re struggling with any of the problems that I’ve been describing today please either come and talk to us after this presentation, or pass on our information to your vendors.
Our focus is on solving problems in this industry, and sometimes an inkjet press vendor takes a while to realize not only that they have a problem, but that there is a solution available for it. You can help with that education!
And with that, does anyone have any questions?