Untitled Document

Dan Margulis Applied Color Theory

Ink Sequencing and Its Effects

Ilya Zhivkov - Question about overprint

Posted by: "Ilya Zhivkov"

Date: Mon Jun 19, 2006 3:14 am (PDT)

in the process of printing is there a difference between printing Cyan over Yellow and Yellow over Cyan ? Same qestion about PANTONE colors ?

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Dan Remaley" n

Date: Mon Jun 19, 2006 5:31 am (PDT)

Some research at PIRA (UK) suggests that the 'correct' sequence is K-C-M-Y.

Black can be first or last but always C-M-Y.

According to their findings, you get "better" 'Reds' with this sequence -

but worse 'Greens'. If you change to M-C-Y the greens are better but the

Reds are horrible - and since humans are real sensitive to Reds, C-M-Y is

the best. Don't know about Pantone.

Questions? Please call . . .

Dan Remaley PIA/GATF

Process Control Manager

412.259.1814

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Re: Ilya Zhivkov - Question about overprint

Posted by: Terry Wyse

Date: Mon Jun 19, 2006 7:09 am (PDT)

Yea, I've got questions.. :-)

That's actually very interesting Dan. It sounds like, in a way, poor ink trap results in "better" colors as long as the sequence is "correct". So, by placing M and Y units next to each and Y over M which, all things being equal, results in less efficient trap of Y over M, you've sort of "improved" the reds. My explanation would be that since 100% M+Y, if trapping perfectly, such as in a laminate proof, results in a kind of "orange" red (too much yellow) due to the fact that magenta is contaminated with yellow thus the overall yellow component in "pure red" is too high. By reducing the wet trap efficiency of Y over M, you're in effect reducing the yellow component and thus should end up with a "redder" red (more magenta) instead of the orange red of perfect Y over M wet ink trap. "Better" colors by taking advantage of the inherent wet ink trap inefficiencies of an offset press. Interesting.

I was at a job a couple of weeks ago and the press (ancient Man-Roland) was the kind with 4 units but units 1-2 shared a common impression cylinder (looked more like a single unit) with a transfer to units 3-4 that also shared a common impression. The sequence was K-C-M-Y which put the M-Y "units" right on top of each other. The result was horrible Y over M ink trap (less than 60% as I recall) but one of the nicest "reds" I've ever seen!

Go figure.

Regards,

Terry Wyse

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Color Management Consulting

G7 Certified Expert

704.843.0858

http://www.wyseconsul.com

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1a. Re: Ilya Zhivkov - Question about overprint

Posted by: "Lee Clawson"

Date: Mon Jun 19, 2006 7:21 pm (PDT)

Ilya,

I'll let others comment on process sequence.

With Pantones you have a range from very opaque to transparent. In addition each is subject to change of color cast as the % tone is reduced. This tends to make any suggested sequence very flexible.

Lee Clawson

2/\V/\7 Studio

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Re: Ilya Zhivkov - Question about overprint

Posted by: Terry Wyse

Date: Mon Jun 19, 2006 7:30 pm (PDT)

Major, major typo in my email. All references to "Y over M" should've read "M over Y".

Must've been a case of inefficient brain trap or something. I'll need to get the tack checked on my th(ink)ing cap before I make any more comments.

:-)

Terry Wyse

On Jun 19, 2006, at 9:36 AM, Terry Wyse wrote:

So, by placing M and Y units next to each and Y over M

which, all things being equal, results in less efficient trap of Y

over M, you've sort of "improved" the reds. My explanation would be

that since 100% M+Y, if trapping perfectly, such as in a laminate

proof, results in a kind of "orange" red (too much yellow) due to the

fact that magenta is contaminated with yellow thus the overall yellow

component in "pure red" is too high. By reducing the wet trap

efficiency of Y over M, you're in effect reducing the yellow

component and thus should end up with a "redder" red (more magenta)

instead of the orange red of perfect Y over M wet ink trap.

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Ron Kelly"

Date: Tue Jun 20, 2006 7:29 am (PDT)

Hah! You sent out a test and we failed, in technicolour.

Nobody jumped on your post. Just proves what a bunch of amateurs and pretenders we are.

All the respect I thought I felt for myself and all "the others" just vanished!

I just want to get one of those th(ink)ing caps; I bet it has all those cool stripes on it that go from violet to scarlet in steps and has a cool little fan thingy like Beaver used to wear on top. Where do I send my money?

No, seriously, I don't know what the heck a wet trap is except when I'm jogging and it's been raining a bit. What does that term mean?

Ron Kelly

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Henry"

Date: Tue Jun 20, 2006 10:12 am (PDT)

Inks that print wet-on-wet tend to mix with each other. Sequence can be a factor. For instance, if M prints before Y the "contamination"(not really a good word for this) is different than if Y prints before M. A measurement comparing the solids to the overprints offers a numeric figure for trapping. It is more complex than this, but this is the gist.

Digital "presses" such as the Indigo, are not wet-on-wet, and have near perfect trapping compared to traditional presses.

A great deal of color variability can be found in the combination of different ink sets, ink sequences, and substrates. The Pantone guides are very specific with regard to the printing method they are produced. The inkset they use may conform to a certain ISO, but that doesn't mean that the results of their process builds will match their guides. It is only a guide. All too often, they are considered as some sort of law, rather than a guide.

A design may contain a color for which a certain ink sequence will give a better match, but that same sequence may ruin the other elements on the page. Funny how anything ever gets printed.

Henry Davis

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Ron Kelly"

Date: Tue Jun 20, 2006 11:10 am (PDT)

Henry:

Thanks for the introduction.

It makes sense that this type of thing (interaction bewteen inks varying depending on print order) should occur.

It's the terms of reference that make it confusing. I'm used to thinking about "trapping" as being a thin line of overprint between plates.

As in, I must allow for trap when placing type of a different colour on a sky, lest I get the dreaded white hairline effect. So I am used to thinking that trapping is a sort of size adjustment, and you're telling me that it has more to do with the interaction of the various inks.

It looks as though "trapping" and "mixing" are interchangeable in this instance?

I still can't quite figure out where "trap" came from; that has more of a "capture" connotation than a "mixing" connotation.

At least we can all feel secure in that presses and the English language are both very consistent, with little room for ambiguities.

Ron Kelly

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Re: Ilya Zhivkov - Question about overprint

Posted by: Terry Wyse

Date: Tue Jun 20, 2006 12:52 pm (PDT)

On Jun 19, 2006, at 11:32 PM, Ron Kelly wrote:

Terry:

Hah! You sent out a test and we failed, in technicolour.

Yea, that's it, I was just TESTING all of you! It wasn't my fault after all!

No, seriously, I don't know what the heck a wet trap is except when

I'm jogging and it's been raining a bit.

What does that term mean?

Well, after my typo I'm not sure I'm qualified to answer but I'll give it a go.....

MOST folks think of trap or "trapping" only in terms of registration. You know, chokes/spreads, skinnies/fatties, whatever term floats your boat.

"Trap" or wet ink trap on a press refers to how efficiently one ink, usually a solid, prints on top of another ink. The way it's measured, using a densitometer, is first the solid primary inks are measured as they print on paper only and then a measurement is taken of the solid overprint of both inks. The value is expressed as a percentage of how well the overprinting ink printed on top of the other ink compared to this same overprinting ink as it printed directly on the paper. So it's a measure of the "efficiency" of one primary ink overprinting another as compared to printing on pure paper.

The repercussions of poor ink trap would be serious hue shifts with overprints. IOW, if you had poor trap of magenta over cyan ink, there would a hue shift from a proper purple/blue hue to a more cyan-ish blue. The opposite would be true if the ink sequence resulted in cyan over magenta, the result being a too purple/magenta-ish blue. Besides ink sequence, good or bad ink trap is generally a function of ink tack and/or water balance. By the way, UV-cured inks, at least ones using inter-deck (between unit) drying, produce near perfect ink trap because the ink is dried/cured before the next ink is laid down. While this SOUNDS like good thing, the danger is in using a separation profile in Photoshop that assumes and corrects for the expected ink trapping inefficiency of a typical wet ink. If you were preparing a job that was going to print using UV-cured inks, you'd either want a profile from that actual press/ink combo or perhaps have a profile created from a laminate proof where the "ink" trap is perfect.

Shameless Color Management Plug:

Even though film laminate proofs were used for years in prepress and still live on in digital dot-proofers like Fuji FinalProofs and Kodak Approvals, this is one primary area where these types of proofing systems fail in my opinion. Since they are created using a photographic process using, typically, dyes, they generally have 100% or perfect "ink" trap. A typical press on the other hand can have anywhere from about 60-90% ink trap values depending on the overprint combination.

An inkjet system however, using a properly color-managed front-end, has the potential for more accurate press proofing since it can accurately simulate the real ink trap of a press, as long as the ICC profile or device link profile being used accurately reflects the actual ink trap characteristics of the press in question.And even dot proofers (FinalProofs, Approvals) can show proper ink trap when driven by a color-managed front-end which they cannot do with simple calibration curves alone.

:-)

Regards,

Terry Wyse

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Henry"

Date: Tue Jun 20, 2006 2:35 pm (PDT)

Ink Trapping is the term that describes this, whereas Trapping or Trap generally refers to what you have described. The terms are often confused. Printers use both terms, but designers seldom have a need to consider Ink Trapping.

The ink trap itself is a similar concept, in a way. Imagine a large dot of Magenta that is partially overprinted by a large Yellow dot. If you magnify this, you would see two circles of color that partially overlap. In this way, ink trapping is similar to trapping, only on a smaller scale. With wet ink trapping, the resulting color would consist of "pure" Magenta, a mix of Magenta and Yellow, and "pure" Yellow. This is where the "mixing" occurs. Different inksets will have different measured "efficiency" of the ink trapping, which will cause a variation in the resulting color. Ink tack, target densities, humidity and stock can all figure into ink trapping.

It's just jargon, and it gets confusing between disciplines, such as when a printer tells a designer that a certain color is difficult to match due to trapping. they will probably be thinking about two different things.

Henry Davis

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Henry"

Date: Tue Jun 20, 2006 4:03 pm (PDT)

On Jun 20, 2006, at 2:10 PM, Terry Wyse wrote:

Shameless Color Management Plug:

Even though film laminate proofs were used for years in prepress and

still live on in digital dot-proofers like Fuji FinalProofs and Kodak

Approvals, this is one primary area where these types of proofing

systems fail in my opinion. Since they are created using a

photographic process using, typically, dyes, they generally have 100%

or perfect "ink" trap. A typical press on the other hand can have

anywhere from about 60-90% ink trap values depending on the overprint

combination. An inkjet system however, using a properly color-managed front-end,

has the potential for more accurate press proofing since it can

accurately simulate the real ink trap of a press, as long as the ICC

profile or device link profile being used accurately reflects the

actual ink trap characteristics of the press in question.

And even dot proofers (FinalProofs, Approvals) can show proper ink

trap when driven by a color-managed front-end which they cannot do

with simple calibration curves alone.

Wouldn't the lower opacity of the laminate proof dots help simulate trapping?

Henry Davis

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Re: Ilya Zhivkov - Question about overprint

Posted by: "J Walton"

Date: Wed Jun 21, 2006 1:24 am (PDT)

What makes you think laminate proofs have lower opacity? From what I can

recall the densities are reasonably close to SWOP on Kodak and Fuji systems.

I'm sure someone on the list would know better than me on that point,

though.

To answer your question: With wet trapping, as the ink piles on top of other

colors it becomes less dense than when it's by itself. So 100M or 100C by

itself looks pretty good, but a 100M100C purple looks weak.

It's not that the laminate proof is necessarily bad, but rather that the

press is unable to keep up without running one color at a time. In my

experience this isn't a big issue when matching press proofs to contract

proofs. Technically, though, the previous post is correct in that using an

ICC profile with either an inkjet or laminate proof would help to predict

wet trap *assuming the conditions are the same when the job is run.*

Of course, that would require profiling the press. Some people don't like

that. ;-)

-----

J Walton

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Laurentiu Todie"

Date: Wed Jun 21, 2006 5:21 am (PDT)

It looks like "the amateurs" did pretty well in the end, on the topics of: Wet on Wet Ink Trapping and Monitors (but not so good on HiFi :(

Profiling the press makes a lot of sense since the inks offset from plate to paper to blanket also, not just the other way around (meknows, though me ain't an expert)

This last few days were interesting in a new way,

Laurentiu Todie

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Re: Ilya Zhivkov - Question about overprint

Posted by: "Pylant, Brian"\3

Date: Wed Jun 21, 2006 2:15 pm (PDT)

Some research at PIRA (UK) suggests that the 'correct'

sequence is K-C-M-Y.

Black can be first or last but always C-M-Y.

This answer is completely dependent on the printing method, though, and the above is not always true. After speaking to our ink supplier, and a ton of real-world testing, we use Y-M-C-K as the default order for our full-color on-disc printing (which is silkscreen). But even then we'll switch the order depending on the specific artwork on press at the time.

BRIAN PYLANT

Manager, Electronic Prepress

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