[topherclay]

Do you mean converting the RGB value to LAB values in the CIELAB color space and doing the interpellation there?

Is there a better way to do it?

[CarVac]

No, you just need to linearize the brightness.

[drjasonharrison]

Typically this is done by using a look-up table to convert the 8-bit gamma encoded intensities to 10-bit (or more) linear intensities. You can use the same look-up table for R, G, and B. Alpha should be linear.