1. An imaging apparatus comprising: a plurality of photoelectric conversion units configured to output a plurality of signals by photoelectrically converting light fluxes each having passed through a different pupil region of an imaging optical system; one or more processors; a memory storing instructions which, when the instructions are executed by the one or more processors, cause the imaging apparatus to: generate combined image data corresponding to the light fluxes by combining the plurality of signals corresponding to the light fluxes each having passed through the different pupil regions of the imaging optical system, and generate a single Design rule for Camera File system (DCF) image file including the combined image data and image data of the signal corresponding to a light flux having passed through any one of the different pupil regions of the imaging optical system, and wherein the DCF image file comprises in a data arrangement order: a header section that includes metadata and data of an offset amount to each image area; a thumbnail image section that includes a thumbnail image; an image section, and wherein the combined image data and the image data of the signal corresponding to the light flux having passed through any one of the different pupil regions of the imaging optical system are arranged in the data arrangement order in the image section.