1. A signal processing system comprising: a base vector acquisition unit configured to acquire (i) a dedicated base vector based on a known spectral characteristic of a subject as an identification target having the known spectral characteristic, the known spectral characteristic being a spectral reflectance characteristic for wavelengths including wavelengths of a visible range, and (ii) a general-purpose base vector together with the dedicated base vector, the general-purpose base vector being used in estimation of a spectral characteristic of an arbitrary subject; a system spectral characteristic acquisition unit configured to acquire a spectral characteristic of an imaging system including a spectral characteristic concerning a color imaging system used for image acquisition of subjects including the subject as the identification target and a spectral characteristic concerning illumination light used for image acquisition of the subjects by the color imaging system; a calculation unit configured to calculate (i) a weighting factor concerning the dedicated base vector using an image signal, the dedicated base vector, and the spectral characteristic of the imaging system, and (ii) a weighting factor concerning the general-purpose base vector using the image signal, the general-purpose base vector, the dedicated base vector, and the spectral characteristic of the imaging system; and an output signal calculation unit configured to calculate an output signal as an identification result of the subject which is the identification target based on the weighting factor concerning the dedicated base vector and the weighting factor concerning the general-purpose base vector calculated by the calculation unit.