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RESEARCH PRODUCT

Hyperspectral imager calibration using ceramic color tiles (Conference Presentation)

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Sets of chromatic and neutral ceramic tiles are widely used as measurement standards for reflectance factors in color applications. The usual instrument for color measurements is a spectrophotometer that measures the tiles using either a 0:45 or 45:0 illumination and viewing geometry, or with an integrating sphere in order to measure the reflectance factor in either specular excluded or specular included conditions. Having the corresponding measurements of the tile set from a calibrated instrument, systematic errors in the instrument under study can be diagnosed and corrected using a model of the errors and fitting it to the difference in measurements. One such is the Berns-Petersen model, which models photometric scale errors as well as wavelength registration and bandwidth errors using the spectra and its derivatives from the studied instrument. This allows for a simple multilinear regression to be used for recovering the model coefficients either collectively or separately for each wavelength band. In this study we examine the potential of a ceramic tile set for transferring the calibration from a calibrated spectrophotometer to a hyperspectral imager using the Berns-Petersen model. In particular we compare different approaches that are needed for matching the measurements from the two instruments with respect to the differences in the spectral and spatial resolution that need to be considered for the application of the regression procedure to be possible. We also compare the effectiveness of the procedure when using single model parameters for the whole imaging sensor to that obtained by doing the procedure separately for different spatial regions of the imager. The accuracy of the imager before and after the procedure is evaluated both in absolute radiometric terms as well as colorimetric quantities. We also examine the effect of using different subsets of the available full set of ceramic tiles for the resulting model fit.