1. An imaging device comprising: an image acquisition unit comprising a lens which collects light from an object to form an image of the object, and an imaging element which captures the image, the imaging element comprising a plurality of pixel groups controlled to have different exposure periods, such that the image acquisition unit acquires the image as an original image in which pixels with different exposure periods coexist; and a processor configured to perform processes comprising: a corrected-image generating process which generates corrected images individually for the plurality of pixel groups, the corrected images being generated by interpolating pixel values and executing exposure correction; and an HDR combining process which combines the corrected images respectively generated for the plurality of pixel groups by the corrected-image generating process, wherein, in a case in which a difference between (i) a first pixel value of a first pixel in the corrected image corresponding to a first one of the pixel groups, in the first pixel value being acquired by exposure, and (ii) a second pixel value of a second pixel in the corrected image corresponding to a second one of the pixel groups, the second pixel value being generated by interpolation, and the first and second pixels being at the same position, is greater than or equal to a predetermined threshold, the processor, in the HDR combining process, increases a combining ratio by which the first pixel in the corrected image corresponding to the first one of the pixel groups is combined.