CHROMiX

D50 vs D65

I was comparing Lab measurements exported out of Profilemaker MeasureTool ast both D50 and D65, then attempted to do the same within a ColorThink worksheet from a single spectral data set, but got vastly different results. I would expect to get the same results.

In the first instance I open a spectral measurement file in MeasureTool and exported both D50 and D65 Lab values, then dropped in a Colorthink worksheet and compared them

Next, I dropped the spectral file in a worksheet, then dropped the same measurement file again, and changed the Color setup to CIEstdD65 (6430K) and compared. I was expecting near the same delta values as in the first method.

There appears to be a major difference between D65 out of MeasureTool and CIED65 (6430) in Colorthink…anyone care to comment?

Results below:

Exported from MeasureTool and compared in ColorThink:

dE Report

Number of Samples: 1617

Delta-E Formula dE76

Overall - (1617 colors)

Average dE: 1.49
Max dE: 3.70
Min dE: 0.00
StdDev dE: 0.82

Best 90% - (1454 colors)

Average dE: 1.32
Max dE: 2.61
Min dE: 0.00
StdDev dE: 0.69

Worst 10% - (163 colors)

Average dE: 2.95
Max dE: 3.70
Min dE: 2.61
StdDev dE: 0.27


Calculated D50 and CIEstdD65 within Colorthink and compared


dE Report

Number of Samples: 1617

Delta-E Formula dE76

Overall - (1617 colors)

Average dE: 10.07
Max dE: 16.69
Min dE: 4.20
StdDev dE: 2.84

Best 90% - (1454 colors)

Average dE: 9.50
Max dE: 13.92
Min dE: 4.20
StdDev dE: 2.39

Worst 10% - (163 colors)

Average dE: 15.10
Max dE: 16.69
Min dE: 13.96
StdDev dE: 0.81



Steve responded to this question in the ColorSync mailing list. I will post his response here:

At 11:33 AM -0400 6/2/09, Michael Eddington wrote:
Thanks for all the information.

Let me ask this question, what differences would one expect between D65 lab values derived from spectral data versus D65 values chromatically adapted from XYZ?

For example, say someone is measuring sample with a handheld with D65 as the user defined illuminant, versus, spectral data exported out of MeasureTool , PatchTool or ColorThink. If someone were to set up a workflow for proofing and process control utilizing D65, what kind of issues could they potentially run into?

So MeasureTool is deriving D65 from XYZ data rather than from spectral? Why then is this only an option when spectral data is present?