It has now been 20 years since the seminal work by Finlayson et al. on the use/nof spectral sharpening of sensors to achieve diagonal color constancy. Spectral sharpening is/nstill used today by numerous researchers for different goals unrelated to the original goal/nof diagonal color constancy e.g., multispectral processing, shadow removal, location of/nunique hues. This paper reviews the idea of spectral sharpening through the lens of what/nis known today in color constancy, describes the different methods used for obtaining a set/nof sharpening sensors and presents an overview of the many different uses that have been/nfound for spectral sharpening over the years.

This work was supported by European Research Council, Starting Grant ref. 306337, and by Spanish/ngrants ref. TIN2011-15954-E, and ref. TIN2012-38112