Reflectance meausrement using macbethcal utility


I am using Radiance macbethcal to estimate the material reflectance. If I
get the calibrated HDR image, how could I determine the RGB/reflectance?
Should I pick a point in the generated HDR image to retrieve the RGB
values, and then directly set the RGB to material RGB in Radiance?
Is there any Radiance tool to directly obtain RGB value of a given pixel?