From: Ben Goren
On Mar 15, 2016, at 1:52 PM, Joe <joemailgroups@gmail.com> wrote:
I must use the eyedropper in ACR and read colors with colorimetric accuracy so that the values for real life targets are the same I measure from the same color patches on screen.
[...]
Is there any solution you can recommend ?
I'm afraid not. The tools designed for colorimetric accuracy aren't very user friendly. The user friendly tools have serious problems with colorimetric accuracy.
Colorimetric accuracy is not the only consideration for a camera profile. The end result for the majority of photographers are visually pleasing images. I've had limited success going the DNG route, and use standard ICC profiles for most work. Camera sensors are imperfect, the range of colors captured in profiling shot(s) limited, light sources neither characterized fully nor matching an assumed model, etc. And those are only first-order effects - further complications include whether the sensor satisfies the Luther condition (aka Maxwell-Ives criterion). My experience has been that camera profiles made where only colorimetric accuracy is the priority suffer when applied to actual captures. Years back we tried characterizing cameras using as wide a range of single-frequency light sources as possible. The resulting profiles were exceptionally accurate. Perfect for product shots of widgets but not much more. Most scenes containing color gradations ended up having visually jarring, ugly transitions. I'm largely I agreement with Ben. The basic premise behind DNG profiles is sound. Characterize a camera using two significantly different but well-behaved light sources interpolate or extrapolate from there based on the lighting in the actual shot. The range of colors and tones on a standard ColorChecker is nowhere sufficient for either building baseline profiles for a specific camera model or fine-tuning for an individual body. Cheers, Ethan