1. An image processing apparatus, comprising: a storage unit that stores a look-up table having one or more pieces of association information for associating a whole or part of one or more first images with a whole or part of at least one second image, which is an image whose load on a brain has been adjusted compared with that of the first image and which is an image of a same object as the first image; an image accepting unit that accepts one or more images; a mapping unit that acquires a whole or part of one or more second images associated with a whole or part of the one or more images accepted by the image accepting unit, using association information from among the one or more pieces of association information; and an image output unit that outputs at least one output image, which is the whole of the at least one second image acquired by the mapping unit or a group of part of the at least one second image acquired by the mapping unit, wherein at least two pairs of a type identifier for identifying a type of look-up table and the look-up table associated with the type identifier are stored in the storage unit, and the mapping unit comprises: a type identifier acquiring part that acquires the type identifier for identifying the type of look-up table that is to be used; and an output image acquiring part that acquires, as the whole or part of an output image, the whole or part of a second image associated with the whole or part of an image accepted by the image accepting unit, using association information from among the association information contained in the look-up table associated with the type identifier.