UV brightener & Lab value question

[zcto7]

I have used the eye one pro with measure tool to come up with the lab value's below. I noticed when comparing to the G7 book and bvdm pdf that the different paper grades all have a *a value of 0. While you can see that mine all have something in the *a value. Is this due to optical brighteners in the paper? and will this effect my calibration? We are trying to fingerprint a 4c press and I was going to use Bruce's LabDotGainCalculator2 excel tool to input TVI curves into the harlequin rip.

Measuretool 5.08 Observer angle: 2 deg. - D50 illumination
Lab Color Values:
SM210P proofing paper (raw) = L: 96.3 a: 0.7 b: -3.7
100# Cover Coated = L: 93.9 a: 1.6 b: -3.0
80# Text Coated = L: 93.7 a: 1.4 b: -3.6
Cougar 80# text smooth finish = L:95.6 a:2.4 b:-6.9


Also I don't think the eye-one has a UV filter....it came with an efi bundle for the Kodak DI press.

Thank in advance!
Adam

 

[meddington]

I have used the eye one pro with measure tool to come up with the lab value's below. I noticed when comparing to the G7 book and bvdm pdf that the different paper grades all have a *a value of 0. While you can see that mine all have something in the *a value. Is this due to optical brighteners in the paper?Adam

The b* value would likely be more indicative of the presence of optical brighteners. The lower the b* value, the "more" brighteners are likely to be present, though there is no official means of quantifying the amount, or how it will effect your results by spectral
measurement alone.

and will this effect my calibration?Adam

Really depends on the viewing conditions...the amount of uv in your viewing lights and the amount in the proof/press stock. For a tvi based calibration with the amount of brighteners in your paper (b* of -3) you shouldn't have large visual issues...unless you proof also has brightener issues.

We are trying to fingerprint a 4c press and I was going to use Bruce's LabDotGainCalculator2 excel tool to input TVI curves into the harlequin rip.Adam

Keep in mind that there are sometimes discrepencies between tvi based on density and tvi based on lab values. You be best off using either or, but not mixing...if this is relevent.

Your i1 should have a "uv" indicator on it is it were in fact a uv excluding device.

 

[zcto7]

... Keep in mind that there are sometimes discrepencies between tvi based on density and tvi based on lab values. You be best off using either or, but not mixing...if this is relevent. ...

We also have a really old X-Rite 408 that can do the dot area / Dotgain by using the Yule-Nielson formula. Would this work better? I am kind of skeptical of its accuracy because of its age, but its much faster to measure with.

Would it be ok to only use the lab based tvi values if I stick to only using lab based tvi for everything? or do you mean this will conflict/differ from the iso 12647-2 values I am shooting for since their values where derived from densitometry?

The difference between the two is pretty close in limited testing using test patches from a copier.

Dotgain readings
15- Xrite = 16% Lab= 15.97%
35- Xrite= 28% Lab= 29.8%
50- Xrite = 24% Lab= 25.51%
75- Xrite = 18% Lab= 18.67%

 

[meddington]

We also have a really old X-Rite 408 that can do the dot area / Dotgain by using the Yule-Nielson formula. Would this work better? I am kind of skeptical of its accuracy because of its age, but its much faster to measure with.

Murray-Davies is the preferred formula, but Yule-Nielsen should work so long as the "n" factor is "1". Older densitometers could possibly have issues with the filters, but you could always purchase a T-Ref to verify its performance. Color Reference Cards | PrintTools

Would it be ok to only use the lab based tvi values if I stick to only using lab based tvi for everything? or do you mean this will conflict/differ from the iso 12647-2 values I am shooting for since their values where derived from densitometry?

It may differ from ISO12647-2 TVI values. You could derive target TVI from the Lab/XYZ data from Fogra39 or an associated profile.

The difference between the two is pretty close in limited testing using test patches from a copier.

Dotgain readings
15- Xrite = 16% Lab= 15.97%
35- Xrite= 28% Lab= 29.8%
50- Xrite = 24% Lab= 25.51%
75- Xrite = 18% Lab= 18.67%

Sometimes TVI from LAB/XYZ correlates very well, sometimes a correction factor is needed. I believe it partially depends on the process/inks being used. For offset, I believe a correction factor for cyan is needed for closer correlation to densitometric TVI.

FYI, there's a nice set of spectral tools within BabelColor CT&A that allow for densitometric TVI and density readings from an i1 without having to use spreadsheets to calculate.

 

[zcto7]

Great, thanks for the help!

I am still stuck on this chart though, this comes from the Media Standard Print 2006 pdf from bvdm. I'm just trying to get the ISO 12647-2 info for free.

This table shows the target dot gain for different grades of paper, but I am confused as why the target TVI is listed in a pair. For example for type 2 paper for CMY it lists a 50% input with a gain of " 14,3 "

Also the dot gains on the table seems a little low to me? (i'm a newbie though!)

Could I just use the GRACcol 2006_Coated1v2 lab values from the icc profile and use those as my target? Or is there a better icc profile to use? (It will be running on a Kodak 5034 DI offset press (Presstek I think)

From what I am told the main press paper is an 80# type 2 sheet but I have to verify with the paper supplier, as I doubt its an expensive sheet.

 

[meddington]

I am still stuck on this chart though, this comes from the Media Standard Print 2006 pdf from bvdm. I'm just trying to get the ISO 12647-2 info for free.

This table shows the target dot gain for different grades of paper, but I am confused as why the target TVI is listed in a pair. For example for type 2 paper for CMY it lists a 50% input with a gain of " 14,3 "

Europe, and other parts of the world use commas to separate whole numbers from tenths. So this is actually 14.3%.

Also the dot gains on the table seems a little low to me? (i'm a newbie though!)

From the film days, Europe used positive film, rather than negative, so dot gain was inherently lower. Legacy curves for US and negative film would be closer to curve C at approx 20%.

Could I just use the GRACcol 2006_Coated1v2 lab values from the icc profile and use those as my target? Or is there a better icc profile to use? (It will be running on a Kodak 5034 DI offset press (Presstek I think)

From what I am told the main press paper is an 80# type 2 sheet but I have to verify with the paper supplier, as I doubt its an expensive sheet.

You could use Gracol, or an "ISO" profile from www.eci.org.

 

[zcto7]

Wow thanks for all of this help, it is much appreciated!

After talking to the pressmen, he want's to use the gracol specs if possible. I checked out the TVI values of both the gracol and eci 09 profile using the spreadsheet and they are both roughly using colums A+B for dotgain.

Should I follow suite and match the press sheets to colums A+B (using a #2 sheet) ? Using the CTP and DI for burning plates, so there is not any film involved. Would using columns C+D be better for my use? I want to try and get as much detail as possible, and am not worried about matching old jobs shot with film. (though I do want to match our proof ! ) I wasn't sure if using the low dot gain would result in an awful looking image or one that wouldn't match the proof.

Again, I greatly appreciate any input you could provide. ( as you might have noticed, our shop won't hire anyone to do this so i'm their last shot )

**Edit**
After more researching, it seems like the 14.3% TVI is normal to shoot for, I also just did a reading on our plates and they have a 12.7% TVI at 50%. They are not being corrected at all, so at the moment i'm linearizing them, that alone should help out with out color troubles.

 

[meddington]

If your interested in hitting gracol specs, have you considered using the G7 methodology? Forgoes tvi as target data for gray balance and print density.

 

[zcto7]

Boy your quick! I just edited my last post before I saw your reply...hopefully linearizing the plates will help out a lot

Yes, we looked into G7, but our (small) shop doesn't have the densitometers with Lab readouts, making gray balance pretty hard (I would imagine). There is definitely a lot of how to about the G7 process.

Another issue would be our 2nd process press, it's an old Heildelburg 5 color that has a lot of wear issues that would make it hard to profile with G7 (so i've been told anyway). Also the learning curve would be a problem for the pressmen as well.

At this point, hitting any standard would be a plus. We have a Xitron Navigator rip with no corrections, and the color right now is horrible. From what i've been told, the press has not been fingerprinted at all.