D50 vs D65

Patrick_Herold · June 3, 2009, 12:46am

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

Hi Mike,

I think I can speak to some of the differences you are seeing.

When exporting Lab values from MeasureTool you are getting “raw” D50 and D65 flavors of Lab, as expected.

When they are imported into ColorThink (or any other compare tool, probably) they are treated as if they are the same flavor of Lab and delta-E is calculated. As far as I know, this is not correct.

ColorThink calculates D50 and D65 as requested and then the D65 values are adapted back to D50 for the dE differencing calculations. As a result you will also see the “D65” values in ColorThink are different than what you might see in another tool. They are post-adapted values. In this manner the dE calcs reflect the correct comparison (D50 → D50) and the numbers “make sense” on screen.

To be honest, this is off the top of my head. I believe that this is the way it was designed and implemented. I haven’t tested it recently to confirm that it’s working as expected.

I hope this sheds some light on the behaviors

regards,

Steve

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?