1. An image pickup system comprising: a verification unit for verifying reliability of a plurality of image signals obtained by at least one color image sensor system with different spectral characteristics of the at least one color image sensor system; a correction unit for performing a correction processing on the plurality of image signals on the basis of the reliability; and an estimation unit for performing an estimation for an unknown spectral characteristic related to a subject or an illumination light on the basis of the plurality of image signals on which the correction processing is performed.