1. A three-dimensional image processing device for performing image correction processing on a three-dimensionally-viewed image, comprising: a first pixel value being a pixel value of a pixel of interest, the pixel of interest being a processing target; a second pixel value being a pixel value of a peripheral pixel of the pixel of interest; an n-th pixel in a first viewpoint image included in the three-dimensionally-viewed image; a corresponding pixel in a second viewpoint image included in the three-dimensionally-viewed image, the corresponding pixel located in the same spatial location as the n-th pixel; a conversion unit that generates a converted image by performing tone conversion on a third pixel value in an object included in the three-dimensionally-viewed image based on a relationship between the first pixel value and the second pixel value; and a composition unit that synthesizes the n-th pixel and the corresponding pixel using a distribution ratio based on a subject distance of the n-th pixel.