EFI Rip + G7 certification

[lchandra]

I just called EFI RIP rep, and they informed me that G7 proofer certification only concern dE and not dH of the primaries.
My question is, the default ISO12647-7 setting on the EFI indicate max dH of 2.5 for all primary. If this is not required, does it mean that my proof will still pass G7 certification, if I change the dH limit?

thank you for your advice

- Levy

[meddington]

Originally Posted by lchandra

I just called EFI RIP rep, and they informed me that G7 proofer certification only concern dE and not dH of the primaries.
My question is, the default ISO12647-7 setting on the EFI indicate max dH of 2.5 for all primary. If this is not required, does it mean that my proof will still pass G7 certification, if I change the dH limit?

thank you for your advice

- Levy

Delta H is notoriously underspecified as a metric for the primaries. The Swop/Gracol Hard copy proofing system certification doesn't speficy dH (or at least it didn't), however, tolerances for ISO 12647-7.2, which would be relevant for the ISO 12647-7 control strip, do specify dH of 2.5 for primaries.

So while dH for primaries isn't required currently for SWOP/Gracol hard copy system certification, it probably should be...and I'd venture to guess that it will be one day. There's a reason for the delta H specification for primaries as a delta E76 of 5 is a barn door without it.


Note that there is currently debate within relevant committees whether delta H is relevant for neutral patches, though this is specified in ISO 12647-7.2.

[lchandra]

Thank you very much for your clarification. I've been using dH until the past month. Then we re-certify all our equipment, upgrade the software, pick better paper, and then....

Everything passes except for the dH.

When requesting assistance from EFI, they told me that dH is not a requirement for G7 proofing system. I was told that if I get the dE as tight as possible, then dH will fall in between. Of course it didn't!

So, yes. I think I'd like to keep the tolerance as tight as possible, and w/out dH requirement, it is a bit of a swing door certification. I might just have to wait until this is an official requirement, so that all the RIP will have this built-in in their system. Sadly.

[meddington]

Originally Posted by lchandra

. I was told that if I get the dE as tight as possible, then dH will fall in between. Of course it didn't!

Yep. A reasonable delta E76 doesn't always mean a dH within tolerance. I think the industry will move toward delta E2000 eventually.

If you have a selective correction feature in the efi rip or profile editor, this might help.

[lchandra]

Meddington,

Thank you for the thorough explanation. Are you familiar with the EFI Rip in general? where would I be able to use the 'selective correction feature'? Is this something that I have to request to them (EFI). How would I be able to use profile editor? will this produce a profile that I can use with EFI Rip as well?

- Levy

[glenncolorguy]

Bear in mind that G7 Certification tolerances apply to G7 certified proofing systems, not necessarily individual proofs.

In other words, in order to become a G7 certified system, the manufacturer must demonstrate that the system is capable of producing proof within strict G7 tolerances, however there is a general agreement that proofs being made in a day-to-day production environment may fall short of this strict requirement and yet still be acceptably accurate.

The G7 committee has been working to craft a separate set of tolerances for production use. A free downloadable verifier is available on the G7 Expert's website. The tolerances specified by the verifier tool not yet finalized and certification of individual G7 proofs is still to some extent a work in progress.

Regards,

Glenn Andrews

[Mike Strickler]

Hi Levy,

Let me try to answer your original question, then move on to this one. First, as Glenn has pointed out, there is currently no specification for individual user proofs in North America as there is in Europe. The default tolerances you see in EFI's Color Verifier come from Fogra. EFI may be an American company, but its proofing products are 100% engineered in Germany, where that division is also administered. Thus those tolerances you see. Here in N.A. IDEAlliance has established specifications for systems, not user proofs. A certified system must be composed of all the same components as present in the system submitted for certification: Same printer, ink, paper, RIP, reference and output profiles. Possession of such a system does not assure that good proofs will result but rather that one may at least assume that good proofs are possible. It is equally true that other systems, for example using other proofing papers and custom profiles, may perform as well as or better than an exact clone of the system described in the official ADS on file with IDEAlliance. Another wrinkle is that the standards (GRACoL, SWOP) may not relate closely to the actual press conditions you are trying to simulate in your proofs. An accurate SWOP proof may not be good enough if, for example, the press substrate is of a different color than specified in SWOP3 or SWOP5.

It is true that dE76 is the metric used throughout GRACoL and SWOP system certification. This should not concern you as a maker of production proofs. I recommend paying close attention to dH on the 3-color gray patches, as this is a good measure of gray balance. I would look for a dH of .5 or better on these patches. I feel the default tolerances in Color Verifier are reasonable, roughly twice as wide as specified for system certification. You can of course change them if you like. Again, bear in mind that there are as yet no official tolerances for individual proofs in North America.

I do not personally feel that dH on primaries is a consistently useful metric for inkjet proofs, as these "solids" are merely simulated and an error there does not tell you, as it does on a laminate proof or press, for example, that there is an ink/colorant problem. I have also occasionally seen a proof with excellent gray balance and contrast that exceeds 2.5 dH on, for example, a yellow solid, an error that is very difficult to see. (In this regard I actually prefer dE, as it also measures the much more visible lightness error.) What's more, pure primary solids are statistically rare in a print job--except in the color bars, of course. This is a problem with standards in general: They tend to test system capability rather than actual individual proof appearance. EFI's new Dynamic Wedge is an interesting development in this regard. It samples the predominant colors in the job and puts them in the color bar, where they can be verified with the same user-adjustable standards as can the standard wedges. It also contains all the spot colors present. This is not part of any official verification regime and likely never will be, but it can be highly relevant to the usefulness of a particular proof.

The entire matter of establishing meaningful proof standards is very much under discussion at IDEAlliance at the moment, and some if its participants are your correspondents in this very thread. Stay tuned.

As for "Selective Correction" in the RIP, I'm unsure what feature you're referring to. Colorproof XF has a relinearization tool, an L*a*b* optimization for tightening the proof-reference match, and a profile white point editor, which can help you match your proof to a "nonstandard" proof substrate color, which in reality is pretty much all press substrates.

Please feel free to contact me for further information on proofing in general and EFI Colorproof in particular.

Best regards,

Mike Strickler
Certified Implementer, EFI Proofing Products
IDEAlliance G7 Expert

MSP Graphic Services
MSP Graphic Services: Prepress and Color Management
707.664.1628

Originally Posted by lchandra

Meddington,

Thank you for the thorough explanation. Are you familiar with the EFI Rip in general? where would I be able to use the 'selective correction feature'? Is this something that I have to request to them (EFI). How would I be able to use profile editor? will this produce a profile that I can use with EFI Rip as well?

- Levy

[meddington]

Hi Mike,

Originally Posted by Mike Strickler

I recommend paying close attention to dH on the 3-color gray patches, as this is a good measure of gray balance. I would look for a dH of .5 or better on these patches.

One of the problems with dH by itself as a metric for neutrals as it doesn't take chroma into account. This can be a problem as a slight cast in the reference neutral could mean that a significant and largely visible difference in chroma in the sample can report a dH or zero (slightly green reference, gleaming green sample along the same hue angle, zero dH). Or, here's an example (from Mike Rodriguez) that compares dH to a proposed metric dF (which is essentially deltaE minus the lightness component).

Reference Neutral: Lab = 50 0 0
Sample Neutral: Lab = 53 4 0

Delta-E = sqrt( 9 + 16 + 0) = 5
Delta-H = sqrt( 25 - 9 - 16) = 0
Delta-F = sqrt( 16 + 0 ) = 4

These are extreme examples, but I'm of the opinion that dH in and of itself can be misleading for neutrals in some cases and you'd want to couple it with another metric (dE76, or replace it with dF or dE2000).

Originally Posted by Mike Strickler

I do not personally feel that dH on primaries is a consistently useful metric for inkjet proofs, as these "solids" are merely simulated and an error there does not tell you, as it does on a laminate proof or press, for example, that there is an ink/colorant problem...... pure primary solids are statistically rare in a print job--except in the color bars, of course.

Great point. The solids are probably the least likely color patches to occur in live imagery, yet often the most heavily weighted.

Originally Posted by Mike Strickler

EFI's new Dynamic Wedge is an interesting development in this regard. It samples the predominant colors in the job and puts them in the color bar, where they can be verified with the same user-adjustable standards as can the standard wedges. It also contains all the spot colors present. This is not part of any official verification regime and likely never will be, but it can be highly relevant to the usefulness of a particular proof.

This is indeed a useful feature...downright nifty even. Unfortunately it really can't maintain verfiable relevance outside of an in-house check for accuracy as those who receive the proofs would have no practical means of evaluating the strip themselves. So you'd want to include a more standard colorbar as well. Another really cool feature is the ability to optimize the Lab values for the particular image based on the dynamic wedge measured results. This is the quickest correction toward a passable verification I've seen. Unfortunately, the correction appears to be only applied to the dynamic wedge patches and associated imagery, so it won't "optimize" for example, color representing patches of an ISO 12647-7 control strip..again, making exchanging proofs with verifiable proof of conformance to a reference a little tricky.

Originally Posted by Mike Strickler

As for "Selective Correction" in the RIP, I'm unsure what feature you're referring to. Colorproof XF has a relinearization tool, an L*a*b* optimization for tightening the proof-reference match, and a profile white point editor, which can help you match your proof to a "nonstandard" proof substrate color, which in reality is pretty much all press substrates.

I originally suggested the selective correction, but I'm not intimately familiar with EFI's features. GMG for instance has a feature that lets you select particular patches and "edit" them while selecting the "range" of adjacent patches that will be affected. This could be useful in correcting minor issues in solids for example while still maintaining the integrity of the original profile. This is often unecessary, and usually only relevant when trying to get particular patches to pass a particular tolerance that is being required of the proof supplier...allude back up to your point on solid patch relevance.


best,

mike

[lchandra]

Hi Mike Strickler,

This brings up another question, although separate from the G7 certification issue. As a proofing house, we're also requested to proof ISOcoatedv2_eci proofs or FOGRA etc. How does this fall within EFI's drive?
When doing the same setting as GRACoL or SWOP 3, my ISO1267-7 color bar measurement doesn't pass in the dH <2.5 requirement, which you mentioned as a requirement in europe.
Should I approach this differently?

Thanks again

- Levy