Grey balance question

[gordo]

Is there a specifified tolerance for grey balance in GRACoL/ISO 12647 production printing? There seems to be a tolerance for calibrating/setting up the press but not for actual production work (at least I can't find it). Also, the G7 guide for press operators says that the press setup/calibration tolerance is 1.5 C* but doesn't say what C* is or how measured. Can anyone shed some light?

 

[D Ink Man]

I'd answer, but I think it's a trick box.

 

[gordo]

I'd answer, but I think it's a trick box.

No trick. Honest question.

I'm assuming C* is the c* in L*c*h*.

 

[Stephen Marsh]

No trick. Honest question.

I'm assuming C* is the c* in L*c*h*.

Gordo, for proofing ISO 12647 conditions such as Fogra 39:

< 1.5 ΔH (dE76/dEab)


Stephen Marsh

 

[gordo]

Gordo, for proofing ISO 12647 conditions such as Fogra 39:

< 1.5 ΔH (dE76/dEab)


Stephen Marsh

Thanks, but is there a tolerance for production press sheets?

 

[Stephen Marsh]

Gordo, I believe that they are the same, however I don't have any reference at hand.

Stephen Marsh

 

[gordo]

Gordo, I believe that they are the same, however I don't have any reference at hand.

Stephen Marsh

Thanks Stephen. I doubt that an offset press could stay within a < 1.5 ΔH as measured onthe grey balance patch in the color bar during a production run. If you find the tolerance published somewhere I'd love to see it. I would have thought this would be a well documented easy to find spec (with all the emphasis on grey balance) - but apparently not.

 

[kansasquaker]

Gordo, I'm pretty sure there isn't a specific tolerance for production work. I don't know if this is true, but it was explained to me that given the nature and variety of presses and press work, they didn't want to define a specific quality standard. The printer and the customer are to establish an acceptable tolerance. However, in my experience, this is usually the customer's defacto tolerance, not an explicit measurable standard.

 

[cementary]

Is there a specifified tolerance for grey balance in GRACoL/ISO 12647 production printing? There seems to be a tolerance for calibrating/setting up the press but not for actual production work (at least I can't find it). Also, the G7 guide for press operators says that the press setup/calibration tolerance is 1.5 C* but doesn't say what C* is or how measured. Can anyone shed some light?

Gordo, there are some tolerances one can fint in ISO/PAS 15339-1:2015. Quite reasonable from my point. However they are suggested only.

 

[gordo]

Gordo, there are some tolerances one can fint in ISO/PAS 15339-1:2015. Quite reasonable from my point. However they are suggested only.

Thanks, but I can't rationalize $130 Cdn to (maybe) find out what the tolerance is for grey balance in production printing. If there is such a tolerance shouldn't it be widely published wherever general print specifications are referenced?

 

[cementary]

Thanks, but I can't rationalize $130 Cdn to (maybe) find out what the tolerance is for grey balance in production printing. If there is such a tolerance shouldn't it be widely published wherever general print specifications are referenced?

For a person who looking for answers no doubt that's not a rational price. But for commercial organization that's not so big price I think

 

[Morgan Manning]

Could it be you're talking dE Ch (Chroma)? Back at Heidelberg, we did a lot with mini-spots and tracking and adaptation of changes on the press.
I can share a couple of ideas, hope they help a little. Information courtesy of Color Toolbox 2015 (nothing but good things to say about CTB):

Chroma difference dECh describes color casts that are percieved much more in the neutral gray areas of an image than in chromatic areas.
dECh is the geometric distance between reference and target on the ab plane.

3.0 was the tolerance, but we always aimed for 1.5 or less. It was keyed off the 25/19/19, 50/40/40 and 75/66/66

How much GCR you're adding to the process could bring that number down...