filmscanners: creating correction curves from scanned calibration chart?

["michael shaffer" <rarewolf@roadrunner.nf.net>]

I have a scan of a photographed color chart, and I also have the logD
reflectance values for the patchs.  I want to create Photoshop curves for
correcting the scan ... for example, assuming gamma=2.2 working space, I
calculate a value of 117 for 18% reflectance:

gray_value == (0.18^(1/2.2))*255 = 117 .  Similarly,

logD (18%) = .745 implies (1/(10^logD))^(1/2.2)*255 = 117

(sorry ... it looks much better in a spreadsheet)

so ... if my scanned RGB values for 18% gray are 115/118/116, I should
create a curve for transforming these to 117/117/117.  If correct, I have 2
questions:

(1)  Although I may be satisfied with neutralizing gray patchs, if I have
similar logD numbers for the colored patchs, can I apply the same formula to
each of the RGB channels?

(2)  What is the best way to create the curves?  For example, I would like
to use the target for the "curve's" gray eyedropper to change the curve such
that 115/118/116 becomes 117/117/117, ... and for a different gray,
155/159/154 becomes 157/157/157 ... but the gray eyedropper doesn't seem to
work this way(?)

tia ... shAf  :o)