Re: xyZ to LAB and dE (2000)
Re: xyZ to LAB and dE (2000)
- Subject: Re: xyZ to LAB and dE (2000)
- From: Graeme Gill <email@hidden>
- Date: Sun, 25 Nov 2007 13:29:54 +1100
Steve Kale wrote:
I¹m also getting errors in my dE calculations albeit I can¹t for the life of
me find the error. I¹m comparing target SMPTE-C Rec601 R, G, B, C, M, Y and
white values with measures from a calibrated display. My dE for R, G, M, Y
and White are very, very close but not exactly those generated by Bruce¹s
colour difference calculator but Blue and Cyan are way off. It¹s
frustrating because I¹ve been over the formulae a dozen times. Any ideas?
What I've found is that the example spreadsheets created by the
originators of such standards, are sometimes a bit loose on their
accuracy compared with (say) implementing the same calculations with
doubles in C. de2000 has some extra issues as well. These
are mentioned in the following paper:
"The CIEDE2000 Color-Difference Formula: Implementation Notes,
Supplementary Test Data, and Mathematical Observations", by
Gaurav Sharma, Wencheng Wu and Edul N. Dalal,
Color Res. Appl., vol. 30, no. 1, pp. 21-30, Feb. 2005.
If you google the title, it's downloadable from Gaurav Sharma's website.
I did an implementation in icclib in the Argyll source code.
It's in argyll/icc/icclib.c and the function is called "icmCIE2Ksq",
and the test harness testDE2K.c is also included in the source.
Graeme Gill.
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