1. A prediction method that predicts, in an illuminating computation of a 3D scene performed by defining a plurality of ray-bundles for a light transport computation for predetermined ray directions, a number of ray-bundle light paths for the light transport computation storable in a predetermined memory region, the prediction method comprising: a first generation step of generating a fragment number map having a predetermined number of pixels, and a mipmap of the fragment number map, for which a pixel value of each pixel is made to be a number of fragments in the 3D scene on a straight line of a ray direction corresponding to a position of the pixel; a derivation step of deriving, in a case where, for a pixel of one layer in the mipmap of the fragment number map generated in the first generation step, ray-bundles for the light transport computation are defined for a corresponding region in the 3D scene corresponding to the pixel, an estimated number of fragments included on average on one light path; and a prediction step of outputting, as a predicted number of light paths of ray-bundles for the light transport computation storable in the predetermined memory region for the pixel of the one layer, a value obtained from a size of the predetermined memory region being divided by the estimated number of fragments derived in the derivation step, wherein, in the derivation step, the estimated number of fragments is derived by a compensation value being added to a number of fragments, which is a pixel value of the pixel of the one layer, the compensation value corresponding to a layer of the pixel.