Get white balance (K) from white reference?

Question

I am looking for an algorithm which calculates the color temperature (in K) which is the used to set the color temperature in a digital camera. As input the algorithm gets a captured white area of a photo (which is not white if the white balance is wrong). The algorithm should estimate the color temperature until the white area is realy white (I hope it's clear what I mean). One straight forward algorithm would be to linearly probe all temperatures, e.g. set the temperature -> capture a picture -> check color of white area and then select the best match. But how is this correctly done, assuming that I can only capture photos and set the color temperature in the camera (for instance there is no infomation about the color matrices used for white balance calculation, or any other information I could use for the calculation)? Regards,

Answer 1

Good question, but... There is a significant problem between Physics (light wavelength), Physics again (Kelvins) and Electronics (actual color presented on your screen).

Check CIE Diagram, for Kelvins and Nanometers (wavelength)

https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/PlanckianLocus.png/910px-PlanckianLocus.png

Thus that white-ish background can be:

1. some value in nm
2. some value in K (SONY has no clue how to get it right :D)
3. some color that is neither in nm nor in K (again, can be set manually to something pink or neon blue)