At 1:22 PM -0700 6/5/13, Ben Goren wrote:
Cameras are (essentially) linear devices.
Depends on what you mean by essential. For the cameras I've calibrated the raw values for the CC24 gray steps don't track, even after adjusting for flare etc. This hints at the camera not being linear.
Everything else, especially ACR, instead invisibly translates blackbody radiation sliders into those channel multipliers using some secret sauce recipe.
The recipe is plainly readable in the code of the DNG SDK and follows the DNG specification and a well-known matching procedure as documented in the code. Both are public, hardly a secret. As shown in the code ACR doesn't assume black body radiator for D65.
[T]he camera imposes an inherent error. The colorimetric problem starts there, in the camera. I don't know if a sensor or combination of filters can be made that would make a colorimetric match possible.
Agreed. Every camera is a compromise. Lars