Fig. 3

Plots showing calibration and verification data. a shows output from the automated linearisation protocol that uses integration time to calculate the sensor response. Log–log axes highlight the accuracy of the fit at low values and how a linear fit would deviate from this near zero. b shows spectral sensitivity as calculated by the spectral calibration script, comparing HOSI measurements to NIST-traceable calibration data. Plots c and d show the radiance and reflectance data from the HOSI of six pastels illuminated by an Osram XBO lamp, compared to Jeti Specbos calibration data. Quoted error values are in the range 350–750 nm, outside of which error increases in both systems due to low lamp emissions