G7 GraCol Fan Graph method

[Donateli]

I was wondering if anyone has experience with using the Fan Graph method to calibrate press curves for G7 GraCol. I have stared using he Fan Graph method, and although I am familiar with the method there is something that I must be doing wrong because although my results are reasonably close to our proofs which are calibrated to Gracol standard I still feel they should be closer and I am trying to discover why they are not. I have narrowed it down to a few variables but if any one has already had success with this method I would appreciate any help they can give.
So far the state of the calibration curves is that the yellow is too sharp. I was wondering If it is better to measure the values against a black backing or a white backing? Also is it better to measure the sheet with and AQ coating or without. To measure the gray finder settings I use the D50 illuminant with the 2 degree observer.
Any help that you can give would be greatly appreciated.
Thanks in advance

 

[Bondi_dan]

Re: G7 GraCol Fan Graph method

Hi Donateli,

It is over five years since I used the Graph Paper method so I am a bit rusty in that department.

Things that helped me was to print the Graph Paper(s) on larger A3 paper.

I have seen research on reading on white and black backing and the difference is quite small - I think you are better off reading with white backing.

What is the Lab* of your paper, sometimes optical brighteners can lead you to more yellow than you want. Perfect world is a paper that is a*b* 0.0, -2.0.

I always read sheets with coating applied - it also reduces the opportunity for 'dry back' changing colour of the ink.

Your spectro/densitometer settings are correct for reading the Gray Finder target.

I am traveling for two weeks so may not be able to add to this soon.

Regards,

Dan Wilson

 

[rich apollo]

Sure. I do it all the time.

Coating or not...depends on your final output. If you expect to be coating, then measure coated sheets. If you don't expect to be coating, the measure sheets without aqueous coating.

Have you confirmed your results? You may need to "iterate" to tighten things up. Most of the time I've had to do additional press runs to finish the process. The confirmation run will end up requesting additional curve adjustments. I now handle the NPDC and gray balance adjustments as separate press runs. I've seen evidence that NPDC adjustments have unexpected results on hue.

To quote my friend Trish Wales, "Paper is the fifth color." If your paper differs much from the guidelines then your results will suffer. Make sure you are appropriately defining your gray balance target. The neutrals will be relative to the paper color.

If you don't have anything printed on the backside of your sheets, then go with white backing.

The gray finder method is DIFFICULT. Be patient with yourself. You may also want to enlarge the target. You can also pull gray balance information out of your P2P target. Open your measurement data in Excel and sort the data to find neutral - or the neutral that you want to achieve given your paper color. You might also read the gray finder in as a target and then sort the data to find your neutrals.

What screening are you using? G7 with 175 lpi is pretty easy. G7 with FM screening is much more difficult.

 

[BeauchampT]

I am not very familiar with G7, but in regards to the gray balance versus colour targets, I see that variation all the time. Often the correct colour targets lead to dramatic gray balance hue issues. I have observed that this can indicate some issues with the ink you are using (i.e. trapping issues). Keep track of these issues as they may come in handy in determining changes in the ink you order.