Disadvantages of non-linear spectral unmixing.

• One needs to know the exact imaging geometry (i.e. incident and viewing angle) under which each image is captured.

• For accurate results one has to have several images of the same scene captured under different imaging geometries.

• For accurate results one has to model the reflectivity function of each material, i.e. how much light is reflected in each direction in each wavelength.

• The equations which relate imaging geometry, reflectance and albedo are non-linear. Any small error in the measured quantities may lead to significant or insignificant error in the result because of the non-linear nature of the equations involved.