I am trying to derive the material reflectance values from a color picker tool(say MS Paint). My understanding is to first gamma decode(raise to the power of 2.2) the RGB values from the color picker, so to bring it back to linear space, and then use it in Radiance mat definition.
However in the “Rendering with Radiance” book by Greg Ward section 5.1.4 "Estimating Surface Color"
Here is a cropped snapshot of the formula from the above links to the scan copied of the two pages.
My question is, should the sRGB values from the color picker not be raised to the power of 2.2(decoding) rather than 1/2.2(encoding)?
For example for BS4800 “18-B-25 Dark admiralty grey / Merlin” colour sample, this webpage shows sRGB=104,112,116 and LRV value as approx. 16%. This matches closely to my understanding of (112/256) ^ 2.2 = 0.16 (just for the green component).