ISO TVI Curve

[Davis.zhou]

Many people discussing the ISO standard now.
There are 6 TVI curves, how does ISO WG to determine the shape of these curves.
For coated paper - type 1, at 150lpi the mid-tone TVI should be 14% +/-4%.
Why the ISO set this TVI - 14%, this definitely relate to the TVI curve shape, but why.
I search on the web, seems there is not much information on this.

 

[fiatlux]

I believe the curves are based on a positive film workflow as ISO 12647-2 states:
"This part of ISO 12647 is
- directly applicable to proofing and printing processes that use colour Separation films as input;
- directly applicable to proofing and printing from printing surfaces produced by filmless methods and to gravure printing as long as direct analogies to film production Systems are maintained

FL

 

[Bob Onn]

The 14% +/- 4% relates to the amount of acceptable dot gain/TVI on a 40% (midtone) patch. The theory is that when printing at ideal weights for cyan, magenta and yellow this would be an acceptable amount of (dot) gain. The black is more often then not printed on curve B which is 3% higher due to black generally being printed at higher density and on unit 1.

The figures are calculated by working through the I.S.O. 12647-2 document from screen frequency, plate output, printing type, paper type, ink type and acceptable figures are arrived at from a 5% patch up to a 95% patch.