ISO 12647-2:2009 - TVI compensation curves

[AlexCur]

Hi guys,


Please, could you clarify some points about ISO 12647-2, TVI compensation curve?

I don´t have much practical experience and I am trying to understanding which reference should be used for 70 l/cm or 80 l/cm, considering that FOGRA39 was created using 60 l/cm, curves A and B.

I got confused based on this part of norm (picture: 60_70cm), 60 l/cm with 14% and 70 l/cm with 16%. It means to me (and don´t make sense) that once you increase your screen ruling you shouldn´t use curve A and B, but B and C respectively, allowing more dot gain for something supposed to have same appearance independent of screen ruling.

At same time 12647-2:2013 says to use the same curve A (picture: 60to80cm_A) for a range of screen ruling. I also took as reference “bvdm_MediaStandard_Print_2018” document, pages 34 and 37 to conclude that you can use same curve for a range of screen rulings for FOGRA 39 and FOGRA 51.


How are you actually proceeding?


Thank you.

 

[SteveSuffRIT]

Hi AlexCur,

I read your post a few times and still not sure of what you are asking?
Can you rephrase it again so I can better understand it?
Per 2013, if printing on coated paper (PS1), you should use curve A which has 16% TVI at 60-80 lcm.
For AM screens, as you increase lpi, you get more TVI.
Steve Suffoletto

 

[AlexCur]

Steve Suffoletto, thank you for your time.

Rephrasing, should I use the same procedure for 12647-2:2009, same curve for a range of screen ruling (60-80 lcm)?

You think, why 12647-2:2009? Because we are in a slow pace moving to 2013 version.

Even though, Idealliance is working hard to spread the G7 methodoly, then TVI will not be a great concern.

 

[gordo]

Steve Suffoletto, thank you for your time.

Rephrasing, should I use the same procedure for 12647-2:2009, same curve for a range of screen ruling (60-80 lcm)?

You think, why 12647-2:2009? Because we are in a slow pace moving to 2013 version.

Even though, Idealliance is working hard to spread the G7 methodoly, then TVI will not be a great concern.

Interesting to see that the ISO curves remain obtuse and still reference the wrong target.

 

[SteveSuffRIT]

We know as the screen ruling frequency increases, so does the tone value, mostly due to optical light absorption making the dots look darker, therefore larger. For example, (not real data), 133 lpi = 13%, 150 lpi = 15%, 175 lpi = 17%. The range difference in tone value is 4% (17-13), the same as the tolerance limit in ISO. So you could use a single curve for lpi between 133-175 but they will probably look slightly different, 133 being lighter, 175 being darker.
Steve Suffoletto

 

[gordo]

We know as the screen ruling frequency increases, so does the tone value, mostly due to optical light absorption making the dots look darker, therefore larger. For example, (not real data), 133 lpi = 13%, 150 lpi = 15%, 175 lpi = 17%. The range difference in tone value is 4% (17-13), the same as the tolerance limit in ISO. So you could use a single curve for lpi between 133-175 but they will probably look slightly different, 133 being lighter, 175 being darker.
Steve Suffoletto

Which is idiotic. Dot gain is a process control metric - not a target. ISO should have defined a tone reproduction curve and whatever dot gain curve is required to achieve it is the curve that should be used. Rant over.

 

[AlexCur]

We know as the screen ruling frequency increases, so does the tone value, mostly due to optical light absorption making the dots look darker, therefore larger. For example, (not real data), 133 lpi = 13%, 150 lpi = 15%, 175 lpi = 17%. The range difference in tone value is 4% (17-13), the same as the tolerance limit in ISO. So you could use a single curve for lpi between 133-175 but they will probably look slightly different, 133 being lighter, 175 being darker.
Steve Suffoletto

Steve, thank you for the explanations.