> Some of you might recall the questions I was asking on colour difference
> formulae back in November. Thanks again for the help then. I thought I'd
> point to the discussion I was having in a home theatre display calibration
> forum. It seems the discussion is rather stalemated:
>
> http://www.avsforum.com/avs-vb/showthread.php?t=944837
Tom Huffman wrote:
> It's not surprising that you got different results. Not only is one based on
> CIELUV and the other in CIELAB, but the CIELUV is based on the 1976 standard
> and the CIELAB result is based on the 1994 formulation, where the numbers are
> generally smaller.
This is so wrong it's not funny. Lab and Luv came out together in 1976.
Tom continued:
> EVERY source I've looked at is absolutely clear in asserting the superiority
> of the 1994 calculation over the 1976 calculation.
This statement agrees with the scientific litterature. No doubt.
Tom continued:
> I've not started using the 2000 standard because my understanding is that it
> has not been widely adopted in the way the 94 standard was when it was
> announced and because it is apparently quite complicated to calculate (these
> two factors are probably related).
dE94 and dE2000 are both "CIE color difference metrics". One came out in
1994 and the other in 2000. dE2000 helped resolving lingering differences
between dECMC and dE94.
Tom continued:
> BTW, do you have numbers for the minimal perceptible difference for the 2000
> standard?
It is still 1 dE. Why would that change? dE2000 just offers a better
empirically-rooted metric, just noticeable differences remain the same.
Zoyd wrote:
> The question of perceptional uniformity and the ability of a color model to
> predict color differences are intimately tied together. A perceptually uniform
> model that covers the entire HVS gamut does not exist.
HVS as in Hue, Value, Saturation? HVS is just a linear transformation of
RGB. If these guys are working in a video/REC709 kind of environment, no
doubt good old CIELab has plenty of space to accommodate REC709 kind of HVS.
Zoyd goes on:
> All these models are based on color matching experiments that test different
> portions of the HVS.
Zoyd would definitely benefit from a small trip to MCSL...
He goes on to write:
> The fact that you get better model/data agreement under different conditions
> tells you that the HVS non-linearities are different in different regimes. One
> model will not fit all conditions and it appears that there is enough of a
> difference between reflective and emissive gamuts within present-day print and
> display technology that some dE formulations will better represent errors in
> one regime than they do in the other.
More proprietary views. The CIE is promoting open standards. CIE2000 is
*the* current color difference metric for measuring small color differences
(under 5 dE) across any application. All current scientific litterature
uses dE2000.
I could be wrong.
Roger Breton
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