Legalities of color-and why are my RGB values inconsistent?

Question

Hi there,
I have a client who is trying to trademark their logo and the RGB values. I have sent them the files and corresponding RGB values, but when they check the files in their mac Digital Color Meter they come up with different values. On my own computer, the values are consistent in the DCM and Photoshop, although I opened it on another computer and found that while the values were still correct when I open the files in Photoshop, the DCM values were incorrect there too.
Does anybody have any history with this? Should I just tell them to ignore their DCM and that Photoshop is correct, or am I doing something wrong with profiles or something? It wouldn't be such a big deal but for the legal implications behind it...
Thanks for any help!!
Eli

Answer 1

I was referring to "Scene Referred" CCchart Lab reference numbers derived from measurements taken of this chart from a spectrophotometer. You'll note the black patch is at L20 according to X-rite. The white patch is quite easy to attain L96 without clipping during exposure of the CCchart to build the profile from using DNG Profile Editor.
What's not easy to control during exposure is the contrast ratio recorded by the camera. Adjusting the middle slider in Levels or the Contrast slider in ACR will show just how much contrast affects hue and saturation viewed on a display. Reality doesn't behave this way.
Contrast/Luminance ratio's are disregarded or barely adjusted for in the DNG CCchart Wizard to come up with proper hue/saturation levels for each of the 18 color patches. The contrast adjusts required to get all 24 patches to match exactly (especially black at L20) makes the image not look right or follow a normal human visual response or perception.
You can adjust contrast in the image after applying the new profile to get a reasonably correct look but quite a few of the 24 patches go off the charts according to the X-rite reference Lab numbers. The whole reason for going by the Lab numbers in profiling a device like a DSLR in the first place is to maintain consistency image to image by using measured results. As you can see this is not possible to achieve in a photograph except maybe in a controlled studio environment, but it does work when trying to match single spot colors that aren't influenced by the surround effect that affects human perception inherent in a photographed scene. A pleasing photograph is not about accurate numbers.
A spectrophotometer is a static device that only reads and measures color wave lengths from color patches and converts them to Lab numbers. It's not a constantly adjusting device like our eyes which adapts to hue, saturation, color temp and contrast levels in any given scene.
I'm going to post three images of a CCchart exposed under a high noon sun that I used to build two different DNG profiles. The first is using ACR default DNG converted source image and doing a straight dual illuminant table profile according to instructions. They're screenshots that include Apple's DCM to show how the black patch changes to accommodate exact Lab numbers as opposed to achieving a pleasing look. You'll note the more the image is made to "pop" the less accurate the Lab readouts and appearance.