1. An image processing apparatus comprising: an input unit configured to input image data which includes a fundamental stimulus value and a spectral auxiliary coefficient and represents an image; and an image processing unit configured to perform an image processing for the image data, wherein the spectral auxiliary coefficient corresponds to a spectral error generated when estimating spectral information from the fundamental stimulus value, and an image size corresponding to the spectral auxiliary coefficient representing the image is smaller than an image size corresponding to the fundamental stimulus value representing the image.