Fig 5. Mean reflectance (panel a.) and radiance (panel b.) spectra recovered from 10 pixel samples of an hyperspectral image cube containing each one of the colour targets in Fig 1.

Reflectance spectra in first column of panel a. correspond to the radiance spectra in panel b. after calibrating the radiance responses against a spectrally flat, achromatic surface included in the hyperspectral image cube. Second column in panel a. depicts the result of performing a robust local regression (loess) with a 0.1 span parameter to smooth the peaks observed at about 435 and 545 nm.