Supplementary Materials What is the Space of Spectral Sensitivity Functions for Digital Color Cameras?

As shown in Fig. 1, we have measured the spectral sensitivity functions for 28 cameras, including professional DSLRs, point-and-shoot, industrial and mobile cameras (i.e.Nokia N900), using a monochromator and a spectrometer PR655. At each wavelength, the camera spectral sensitivity in RGB channels is calculated by c(λ) = d(λ)/(r(λ) · t(λ)), where d is the raw data recorded by the camera, r is the illuminant radiance measured by the spectrometer, and t is the exposure time of the camera. All other settings (i.e., ISO and aperture) remained the same during the measurement for each camera. The procedure is repeated across the whole visible wavelength from 400 to 720nm with an interval of 10nm.