Does anyone know of the HMI continuum data has its limb darkening subtracted or divided out? The documentation just uses the word ‘removed’, which is not very helpful.
The continuum is 1, so it suggests divided, but it could also have been normalized.
I suspect only the JSOC would know for sure as they wrote the code to do that.
One could go through their code but I think emailing the JSOC (see http://jsoc.stanford.edu/Contacts.html) to ask would be the best option.
To lowest order, limb-darkening correction has to be a scaling factor. Think of it this way: if a point on the Sun gets twice as bright, its limb-darkened value also gets twice as bright. In actuality, limb-darkening correction might be a function of multiple orders depending on what is being corrected for.
The important question is why you are asking this question.