Yes Sir, you are absolutely right!
The reason I did this evaluation was to find out about the accuracy of the profiles. The ColorChecker target has just 24 fields and the profiles generated by Color Checker Passport or Adobe DNG Profile Editor are automatically adjusted to reproduce these 24 fields optimally. It is quite possible that other colours would be reproduced diffeently.
Now, the color checker colours are chosen very carefully, the skin tone fields for instance have spectral reflectance very similar to human skin. So the ColorChecker is a good target.
The test I was to use a well known reference target with far more colours. The chart I used was one from Wolfgang Faust and it included Lab values for each field.
So I made a carefully exposed shot of the IT8 target and a ColorChecker. Exposure was adjusted so the ColourChecker's light grey and black fields were rendered properly and the files were exported as 16 bit tiffs in Profoto RGB. These TIFFs were than read using Argyll CMS and the lab values were saved as a text files (CGATS? I don't recall). The LAB values were than compared with the reference values coming with the IT8 target.
What I have found?
The Adobe Standard Profile was pretty exact on my Sony Alpha 99, but using the Adobe DNG Profile improved it very slightly. The difference was so small that I stayed with the Adobe Standard Profile.
With my P45+ I also compared with Capture One. On the P45+ the Adobe DNG Editor generated profile was slightly more accurate than the Adobe Standard profile. Capture One, using linear curve, gave more accurate colour than Lighroom with either profile. The default "film curve" gave worse results than Lightroom. These data were evaluated using CIEDE 2000 DeltaE* values. These data include luminance and luminance is certainly affected by choice of gradation curve.
The Sony Alpha in LR was more accurate than the P45+ in either C1 or LR. C1 was less accurate than LR on the Sony Alpha SLT.
The result? I use Adobe Standard profile on the Sony. With the P45+ I use a DNG profile tuned automatically with the DNG Profile Editor.
Best regards
Erik
Erik, to clarify, you used the 24-patch target to make the profile and then used the IT8 target as a reference to check the resulting profile, right? I don't see a way in the editor to use the IT8 target in the editor itself. Thx.