Gracol 7

General Color & Graphics Press Calibration & Profiling
1

Guidelines for calibrating and printing to Gracol 7 www.gracol.com

We are going to have some press time to look at Gracol 7. Read through the how to last night and had some questions.

So will read through again and throw out the questions as I see them.

Calibrating a proofing system. The big difference in a proofing system is fixed SIDs, grey balance is achieved by separate rip curves.

So you would adjust the desired curves to get the a* 0.0 b* -2.0 values on a proofer??? Would you then profile the proofer, would this not affect the neutral grey when you reapply the profile. Or are they talking about not using profiles and just running to grey balance without the profiles???

Press Calibration Run

Print to nominal densities. I already know our Bengal Inks at the proper SID will not have the L.A.B. values needed. I am not sure what to do here. We are running the same inks the Gracol Press runs did??? I believe we should ignore the SID values and run to the LAB values???

They say use a non-polarized density. With Gracol 6 we used a XRite 500 series with a the polarizing filter. We find that with the filter measuring wet densities we produce a good image. If we tried to run to Gracol 6 wet densities on our XRite ATD with out a polarizing filter our dried back press sheets lack contrast. So I question these values. Unless they are giving some dry back time. Wet Black density will measure 1.70 through polarizing filter but measure 2.20 with out the filter. Gracol 6 S.I.D. values only worked for us with wet densities on press with the polarizing filter without only the dry values worked.

Forcing the device to Gracol 7 curves

Plot the curves Redraw the target above 50%, so do you just swing it down preserving the shape. Or why would you do this. Why not just build the curves to do this??? Why doesn’t this disqualify the whole test???

Step 5 0r step 8, This is just two ways to achieve the same thing

Second Press run should work to density - fine tuned to 50% cmy patch lab values

2

Not all proofing systems are Fixed SID…A Kodak Approval for example. In this case you could approach the proofer very similar to the press. Adjusting densities until neutrality is achieved, then adjust TVI until the NPD is within tolerance.

For a fixed SID proofer, I suppose you would adjust the curves seapratelyas described in section 8 (section 8…Klinger?) Of course if your talking an inkjet device, this would all be done with ICC (or proprietary) profiling.

A graph redraw might be needed if the SIDs during the press run were adjusted to meet the NPD at 50%, but the SIDS don’t match that of the Gracol 7 curve. I suppose they’re placing the emphasis on the midtone NPD rather than SIDS, which makes sense. The redraw would be necessary to prevent banding or other anomolies that might occur if you attempted to force say the 90% to meet Gracol, but not the SIDS. After all, if you could have hit the SIDS while maintaining NPD, you would have right?

3

On 1/8/06 5:02 PM, “mikec” mikec@lawtonprinting.com wrote:

Calibrating a proofing system. The big difference in a proofing system is
fixed SIDs, grey balance is achieved by separate rip curves.

So you would adjust the desired curves to get the a* 0.0 b* -2.0 values on a
proofer??? Would you then profile the proofer, would this not affect the
neutral grey when you reapply the profile. Or are they talking about not using
profiles and just running to grey balance without the profiles???

It is your choice to use profiles or not in a “dot proofer.” I would guess
that most halftone laminate proofers are run without profiles, and just
curved to match the press sheet.

Press Calibration Run

Print to nominal densities. I already know our Bengal Inks at the proper SID
will not have the L.A.B. values needed. I am not sure what to do here. We are
running the same inks the Gracol Press runs did??? I believe we should ignore
the SID values and run to the LAB values???

In one of the GRACoL calibration runs, they discovered that one of the inks
was off target. They ran anyway, and the results were acceptable. If your
inks are too far from the 12674-2 targets in Lab, it might not match the
GRACoL runs in more saturated areas, which is less important, but in the
highlight to midtone range it should be close.

They say use a non-polarized density. With Gracol 6 we used a XRite 500 series
with a the polarizing filter. We find that with the filter measuring wet
densities we produce a good image. If we tried to run to Gracol 6 wet
densities on our XRite ATD with out a polarizing filter our dried back press
sheets lack contrast. So I question these values. Unless they are giving some
dry back time. Wet Black density will measure 1.70 through polarizing filter
but measure 2.20 with out the filter. Gracol 6 S.I.D. values only worked for
us with wet densities on press with the polarizing filter without only the dry
values worked.

I believe Gracol 6 densities were non polarized, dry ink values. It sounds
like the inks you use are capable of producing a gamut larger than the
Gracol gamut. Using your setup, the images may look better than with the
GRACoL method, but the idea is to match a specified condition (calibrated
proofer, another company’s printing press, …) If both presses/proofers are
calibrated using the GRACoL method, the printed results will be close.

After the Gracol run we did, we spread out the sheets from the previous
gracol runs, and they were pretty close. Different ink companies, different
papers, presses, and all the other variables, and we ran only to the
numbers, not to a proof or the other sheets.

Forcing the device to Gracol 7 curves

Plot the curves Redraw the target above 50%, so do you just swing it down
preserving the shape. Or why would you do this. Why not just build the curves
to do this??? Why doesn’t this disqualify the whole test???

If you run a 2.20 black, and the gracol Black is at 1.8, the curves would
tell you to make your 100 a 90 or something like that. Same holds with the
3/c overprint. Depending on your ink trapping, your 3/c overprint may be
higher or lower density then the GRACoL target.

Step 5 0r step 8, This is just two ways to achieve the same thing

Second Press run should work to density - fine tuned to 50% cmy patch lab
values

That is how it is supposed to work. Good Luck.

Bret Hesler
L.P. Thebault Company

Post generated from email list

4

Bret

Did you then adopt the Gracol 7 full time or just for the press run???

If so how has it been. Which inks did you use the Gans Bengal process??

When you came back for the press run after the calibration run was there much of a press curve that needed built and did you send your plates with no linear process.

Mike

5

We are running the gracol curves full time.

We use Superior inks.

The curve was small, but we use it, not linear plates.

Bret

On 1/9/06 1:11 PM, “mikec” mikec@lawtonprinting.com wrote:

Bret

Did you then adopt the Gracol 7 full time or just for the press run???

If so how has it been. Which inks did you use the Gans Bengal process??

When you came back for the press run after the calibration run was there much
of a press curve that needed built and did you send your plates with no linear
process.

Mike

Sent from colorforums.com
To start new topics, do not reply to this message. Cut and paste the forum
address into a new email.
Return to www.colorforums.com for subscription administration
(c)2004-5 CHROMiX, Inc.

Post generated from email list

6

I am in the process now of doing the gracol7. My proofer is an hp5000 using Bestcolor for color managing the proofer. We calibrate the proofer to each paper for proofing. The proofer is calibrated and probably the most consistent part of our proofing process.

just a side note… in the days of film we used the matchprint system and we heard more people complaining about color than we do today from the proofer…

So I am happy with the proofer and customers are happy with proof so as backwards as this is my goal is to make press match proof. The gracol number I took and the way I read it is to do the following.

  1. Calibrate my Delta to out put lineriar plates
  2. Entered a process curve to meet my goal dot gain
    a. Black 18%
    b. Magenta 14%
    c. Yellow 14%
    d. Cyan 16%
  3. Output test plates using this process
  4. Pressman ran press up to consistant densities that work best on her press.
    a. Black 1.70
    b. Magenta 1.35
    c. Yellow 1.25
    d. Cyan 1.35
  5. From this run I take dot gain reading from stock.
  6. I take these numbers back to my Delta in enter them in to a measured curve that will bring my gain down to my goal gains listed in # 2.
  7. My initial testing matched the proof well.

My neutral gray way a little warm so I now I need to make a few adjust ments but My goal from this process is to have my 4c GTO running the same dot gain on both coated and uncoated sheet. I hope this wil give me the same feel and weigt of color on each sheet.

My question now is is this how other are doing this because I am still in the testing any input will be awsome

thanks