1. A signal processing device which performs signal processing for converting first image signals into second image signals, said device comprising: class classification means for classifying said second image signals into one of a plurality of classes, according to a level distribution of said first image signals output from imaging means for converting subject light, which is light from a subject, into image signals; control means for controlling said imaging means according to the level distribution of said first image signals; tap coefficient output means for outputting tap coefficients for each of said classes, said tap coefficients gained by a learning process; and computing means for obtaining said second image signals by performing computation using said first image signals output by said imaging means controlled by said control means, and tap coefficients of said class obtained by said class classification means.