Question regarding G7 calibration / UV filters / optical brighteners

[cjs]

We have been using an i1 pro with a UV filter with ProfileMaker to build profiles and calibrate our Epson proofers on various media (proofing paper, canvas, photo paper).

We also have an older i1 pro that does not have a UV filter, that we rarely use.

We are currently using the one with the UV filter to read in P2P targets for G7 calibration of our offset presses. We use the IDEAlink curve software to generate the gray balanced curve and manually enter the curve data into our Heidelberg Meta RIP.

In the pressroom we do not have UV filters on our handheld densitometers, nor our Intellitrax scanners. These devices have been calibrated by Xrite recently and are reading about the same as each other, but drastically different than our i1.

When reading with the handheld densitometer, I have noticed that our current press stocks are very negative in the B value (-4 to -5) --- a clear sign of optical brighteners. The i1 with the UV filter reads the paper color as closer to white (a=-0.17, b=-0.15).

My question is: which i1 reader would you use to do G7 press/plate calibration? The pressroom manager thinks we should use the old one without the filter instead so that all our numbers are the same. I think we should instead put UV filters on the devices in the pressroom (likely to be too expensive).

Thanks in advance for any input on this topic.

-CJS

 

[Bret Hesler]

Use the old, non-uv filtered i1. Send it back to x-rite for re-certification to be sure it is functioning properly. Almost all #1 and #2 coated sheets are brightened, and fall right in line with the non-uv readings you stated, and just out of spec for ISO/Gracol.

In my opinion, UV filtration is effectively ignoring optical brighteners rather than compensating for them. When you view the press sheets in a light booth with UV coming from the bulbs, you see the effect of the optical brighteners. You can't take measurements with with that effect turned off, and expect to get a good visual match.

Bret

 

[meddington]

My question is: which i1 reader would you use to do G7 press/plate calibration? The pressroom manager thinks we should use the old one without the filter instead so that all our numbers are the same. I think we should instead put UV filters on the devices in the pressroom (likely to be too expensive).

I would agree with your pressroom manager and have all devices measuring as close to each other as possible. I'm not really a big proponent of uv filteration and feel they are not the optimal solution to the issue of optical brighteners as they do not take into consideration the viewing conditions (amount of uv in your lighting and how it excites the substrate), and what the eye perceives.

 

[Colorblind]

This is from "Real World Color Management" second edition, page 167, about the use of UV filter:

"Bruce (Bruce Fraser is one of the authors) sees this as the colorimetric equivalent of sticking your fingers in your ears and yelling lalalalala - it deals with the problem by pretending that it isn't there..."

I totally agree with that.

 

[cjs]

Thanks guys for the feedback. Sounds pretty unanimous that UV filtering is not preferred in G7 plate calibration. Would that also go for proof calibration / profile making?

Thanks,

-CJS

 

[Bret Hesler]

Same for profiling, no filtration.

And by the way, I am against OB free proofing papers. Press stock has them, if the proofing paper doesn't, you have increased chances of metamerism failure.

Bret

 

[edwinb]

its just as important to ensure standard viewing conditions otherwise it will still look wrong.
edwin