Why dE cmc with pol filter? And overall why CMC L:C?

[cementary]

I'm kinda-sorta confused to ask, but i don't understand a thing – our ink supplier told us that they measure color difference between sample (digital proof, gmg paper) and mixed ink sample on a circullation paper using dE cmc formula with the following parameters: 2 degree/D50, physical polarization filter, XRite 530 (freshly sertified).

Could you please correct me if i'm wrong: judgin color difference using polarization filter isn't like judgin print result in polarized sunglasses?
I know that polarized filters can be useful for "ink formulation, the correlation between the measured colour co-ordinates and the concentration of the constituent colorants" (ISO 13655)
I read that cmc l:c was designed to use with D65 and for textile industry.

So what's the matter not using ciede2000 formula? And why not wait until ink dryes, rather using polarization filter?

 

[rich apollo]

Delta E calculations are not dependent on any specific illuminant. The illuminant is used for interpreting the spectral measurements, for instance, calculating Lab values.

Polarization may allow the ink vendor to work faster, not having to worry as much about whether a sample is completely dry.

Using deltaE(CMC) versus deltaE(2000) could be a legacy issue. They probably have been using CMC for some time and may not want to create problems for matching earlier ink formulae. Does the 530 support deltaE (2000)? I can't remember. is ther any doctrine that specifies CMC for ink vendors?

 

[cementary]

Supplier referres to BS6923:1988 standard for using this formula.
I've bought that standard and didn't find anything about paper industry practice in it. Standard referres to textile industry (in part where l:c parameters described).

About polarization: tristimulos values will be different with/without filter, won't they?

Don't know about the doctrine, but i'd like to (with argumentarion of course))))

Also i didn't find any tolerances for CMC. Like 2.33 dE for 76.

 

[conger]

IMO using a polarizing filter for color measurement creates as many issues as it tries to solve. Unless you use a polarizing filter at every color measurement step after ink formulating you introduce a change in correlation between samples you are comparing. I'm not saying it won't work but it complicates things unnecessarily.

As mentioned using CMC is more about doing things the way they have always been done. CIE2000 is called out in the latest ISO standards. In our color program we have preferred 2000 and CIE94 before it to CMC. Especially because CMC is typically used with a 2:1 L:C ratio which is more forgiving of lightness differences.

Delta E is dependent on illuminant setting as that is a fundamental component of the L*a*b* values that are used to calculate DE.

 

[cementary]

No Title

The last step for color measurement is actually "watchin' result with human eyes". How one can apply polarization filter to an eye?
Just imagine – a group of color management specialists (from ink formulator to press operator) all of them wearing glassess with specially polarized lenses tryin' to convince customer (without glasses) that expected color and result color are the same ))))) They gonna need also a big polarized piece of glass to put it over the samples (to imitate cross polarized filters in the device)

I mentioned D65 along with textile industry just as part of history of question. In "Color physics for industry" R. McDonald also describes this formula as created for textile industry:

A little note about 2:1 ratio (from 11664-6-2014 CIEISO):
In the textile industry it is common practice to set the lightness parametric factor to 2. However, the experimental conditions leading to this parametric correction to lightness difference sensitivity are not yet well understood.