A signal processing apparatus supplied with a signal obtained by performing orthogonal transform on a video signal corresponding to a plurality of pixels includes a correction circuit for correcting the orthogonal-transformed signal, by using correction values obtained by performing orthogonal transform equivalent to the orthogonal transform on measured values obtained by measuring nonuniformity of display characteristics of a display device, which performs display on the basis of a signal processed by the signal processing apparatus. In addition, an inverse orthogonal transform device performs inverse orthogonal transform on a signal corrected by the correction circuit and thereby obtains a corrected video signal.