Cmc & cie94

[tcaste]

Hello everyone!
I was wondering if someone could tell me the difference between CMC & CIE94 in layman's terms.
Thanks

 

[gordo]

Hello everyone!
I was wondering if someone could tell me the difference between CMC & CIE94 in layman's terms.
Thanks

They represent different formulas for expressing a color difference. CIE L*a*b* DeltaE values are dependent on the formula used - and there is no universally agreed standard for the formula that should be used.
Some formulas are: DeltaE 76 (sometimes referred simply as DeltaE), DeltaE 94, DeltaE 2000, and DeltaE CMC. In general, DeltaE 76 results in values that are highest, DeltaE CMC values the lowest especially for saturated colors, DeltaE 94 and 2000 are lower than DeltaE 76 but higher than DeltaE CMC.

For example, these two color patches are made up with the indicated CIE L*a*b* values:

The DeltaE between these two colors as reported by the different color difference formulas:
CIE 76: 7.10 (a large difference - unacceptable)
CIE 94: 1.51 (well within typically acceptable variation)
CIE 2000: 1.57 (well within typically acceptable variation)
CMC: 2.26 (within typically acceptable variation)

So, depending on the formula used to calculate the difference in color a measured sample may, or may not, be within acceptable tolerance.

It's therefore important when speaking with someone regarding a color difference that the formula used for calculating DeltaE is known. Otherwise people might choose a formula that suits their own evil purpose. For example, a customer might use CIE 76 to reject a job while a proofing vendor might use CIE 94 to show how good the match is.

best, gordo

 

[tcaste]

Thanks for the info Gordo!

 

[meddington]

I was wondering if someone could tell me the difference between CMC & CIE94 in layman's terms.

They have differing weighting factors for lightness, chroma and hue to more proportionally model human visual perception... whereas the basic delta E 76 formula has no weighting factors and assumes human visual perception is equally sensitive to all colors.

 

[tcaste]

They have differing weighting factors for lightness, chroma and hue to more proportionally model human visual perception... whereas the basic delta E 76 formula has no weighting factors and assumes human visual perception is equally sensitive to all colors.

Could you explain what weighting factors are?
Another question is why isn't their a standard? I would have to assume most people are not using delta E 76.

Thanks

 

[meddington]

Could you explain what weighting factors are?

human visual perception is most sensitive to hue, chroma, then lightness in that order, and sensitivity also depends on the color being viewed. The Delta E 76 formula does not take this into consideration, so weighting factors were developed to put more emphasis on chroma, than lightness, and the result varied based on the color being measured (smaller window of tolerance on oranges, larger on greens, etc).

Here's a good source of info: http://www.xrite.com/documents/literature/en/L10-001_Understand_Color_en.pdf

Another question is why isn't their a standard? I would have to assume most people are not using delta E 76.

I think most people are indeed using delta E 76, though there is a movement within the standards committee to implement delta E 2000.

Hard to discuss delta E formulas in layman's terms as the math and science is extremely complex.

 

[tcaste]

Thanks Gordo & Meddington for help.