1. An image processing apparatus comprising: an input unit configured to input image data which includes a plurality of fundamental stimulus values and a spectral auxiliary coefficient and represents an image; and an image processing unit configured to perform image processing on the image data, wherein: wherein the spectral auxiliary coefficient, included in the image data, corresponds to a spectral error between spectral information reconstructed from the plurality of fundamental stimulus values and spectral information of the image, and a second image size corresponding to the spectral auxiliary coefficient representing the image is smaller than a first image size corresponding to the fundamental stimulus values representing the image.