FOGRA39 compliance on press and or proofing papers darker than expected white point

[Frank Nunez]

Hey all, I'm doing proofs for a book and am in a situation where I'd love some of your thoughts? I think it might be useful in general to get a discussion going on this because while I see a lot of posts here and there on whitepoint, I feel like the everyday problem of press stocks being darker or yellower than inkjet proofing stocks has not really been well addressed by the RIP manufacturers (at least not that I can find). Maybe we can change that here.

My situation is the following :

The press claims to be FOGRA39 compliant (a SPEC of a paper white L95, A0, B-2 from color.org data set for FOGRA39)

The press paper for job is Gardamatte Ultra (I'm guessing without a sample it's well below L95)

So I'm using a darker, neutral proofing paper from Pantone calleld S3 (L92, A0, B0) for an anticipated closer visual match for now in inkjet proofing while we wait for a press proof to give us more details but I can't get it to pass verification in the RIP I think due to the darker white point.

I'm assuming then that the press paper itself wouldn't pass verification in my inkjet proofing system (say if theoretically even coated with inkjet receiver) due to darker paper white.

1) How can a press be FOGRA39 compliant if they are using a paper which is darker than the tolerances allowed for FOGRA39 compliance?

2) If someone in prepress like myself wants to work with a press claiming FOGRA39 compliance on stocks whose whitepoint falls below the delta E tolerances for FOGRA, what can be done? Is FOGRA39 somehow "scaleable" to darker whitepoints (ie is this maybe what the press is doing, and can I do that and pass verification)?

I understand I could use brighter proofing stock than the Pantone S3, and print scum dots to simulate paper white, but then are all of the other values and colors scaled proportionally somehow in the verification process? What if I got the press stock coated by that company that coats press paper with inkjet receiver (I'm not being serious but asking theoretically...) how would I get that to pass FOGRA39 verification in my RIP? If a bright paper which subsequently has a scum dot or "painted" paper white simulation in proofing can pass, why not a solution for a paper stock of lesser than FOGRA39 paper white (or is there a solution?). Also, how can values be scaled proportionally across the gamut in a scum dot solution where already to go from L95 FOGRA39 expected white to L92, we would need to sacrafice 3% of the color control values (in FOGRA39 dataset, C3, M3, Y3 would get us to roughly L92).

I'm excited to hear everyone's different methods and thoughts on this, thanks in advance all ! Frank

 

[cementary]

Substrate corrected printing is your answer.
You should take fogra39 charset, recalculate it to new white point, create ICC profile from that new set, put this profile in your proofing software and print your proof. You will need real paper white lab value for that.
if the press you're talking 'bout is really fogra39 compliant then you would probably see close match of print and proof in p1 viewing conditions.
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[Frank Nunez]

Hi Cementary, thanks for the fast response. I found a paper from 2011 called "Substrate Correction in ISO 12647-2" (http://rycppr.cias.rit.edu/pdf/2011_...ate%20Corr.pdf) and am looking at it now, but for your recommendation around this, do you suggest a simple linear transform across all values,

For example:

Actual Paper White L value for press stock = 92
FOGRA39 Spec Paper White L value = 95

Whereas, 92/95 = 96.8%...
...I would then multiply all LAB values in the fogra39 charset by 96.8%, then use this new charset as a reference file while making a new ICC, and set this reference char set as the transform ICC in my proofing workflow in place of the old FOGRA39?

I think I might be missing a step in getting from Reference file into ICC, would love clarification if you have a minute?
Also wondering about how paper color from the a* and b* values on say a yellowish press stock might need to be factored during the transform into the off white paper white's influence on all of the colors, or is this done automatically by the RIP during ICC creation from the reference profile, or maybe by the color mgt engine during softproofing and conversions pre-printing?

Thanks so much! Frank

 

[cementary]

...I would then multiply all LAB values in the fogra39 charset by 96.8%

definitely no

I think I might be missing a step

You should try this link to learn all the info you might be need of. On the right you'll see lots of useful links along with attached to this post substrate correction calculator.
Also you may be interested in some standards, 15339 series for sure

 

[Frank Nunez]

Awesome, precise and rich information in your answer/links, thanks so much Cementary!! Frank