Andrea,
the atan2deg looks ok to me. The result is here the same with ICC Examin.
Lcms has a similiar function integrated (cmsCIE2000DeltaE). So you can
look at various implementations sources.
regards
Kai-Uwe Behrmann
+ development for color management
+ imaging / panoramas
+ email: [EMAIL PROTECTED]
+ http://www.behrmann.name
Am 22.02.06, 10:20 +0100 schrieb Andrea Galligani:
> Hi,
>
> I have some questions about delta E calculation.
>
> I calculated the delta E between this lab points:
> L = 54.44073903
> a = -34.82222743
> b = 0.18986800
>
> L = 54.92340686
> a = -33.45703125
> b = 0.00000000
>
> using several formulas obtaing this values:
>
> cmsDeltaE = 1.460
> cmsCIE94DeltaE = 0.719
> cmsCMCdeltaE = 0.769
> deltaCIE00( 1.0, 1.0, 1.0 ) = 52.908
>
> Is it right deltaCIE00 produces a so big value?
>
> I tried a debug using the following spreadsheet and related article
> http: //www.ece.rochester.edu/~gsharma/ciede2000/dataNprograms/CIEDE2000.xls
> http: //www.ece.rochester.edu/~gsharma/ciede2000/ciede2000noteCRNA.pdf
>
> and I found a possible cause in the line
> double h_ps = atan2deg(a_ps, b_ps);
>
> This function should return 180 and return 0 instead.
>
> If I modify the function in this way
>
> static
> double atan2deg(double b, double a)
> {
> double h;
>
> /*if (a == 0)
> h = 0;
> else*/
> h = atan2(a, b);
>
> h *= (180. / M_PI);
>
> while (h > 360.)
> h -= 360.;
>
> while ( h < 0)
> h += 360.;
>
> return h;
>
> }
>
> I obtain a value 0.72243850693447653.
>
> Is it correct?
>
> Can I have your opinion about this modification?
>
> Is there a way to speficy parameters in cmsCIE94DeltaE and
> cmsCMCdeltaE similarly to deltaCIE00?
>
> Regards,
> Andrea
>
> --
> Andrea Galligani __\/__
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