Surface-illuminant ambiguity
= Surface-illuminant ambiguity
In a diffuse spectral model $N(\lambda)=E(\lambda)R(\lambda)$, choose any positive $g$ for which $R/g$ remains an admissible <reflectance>. Then $E'=Eg$ and $R'=R/g$ preserve $N$ exactly. Thus outgoing spectral information alone does not uniquely identify <reflectance> and illumination; three-channel receptor sampling introduces further ambiguity.