a) The light from a nonselective diffuse reflector (in the original scene) that is lighted by the normal illumination of the scene.

That white with which the display device stimulates reference white of the original scene.

b) In production context, reference white is defined as the luminance of a white card having 90% reflectance and subjected to scene illumination. It is expected that there will be the capability of some discrimination of surface texture or detail within that portion of the transfer function incorporating reference white.