1. An image processing apparatus that, for a stereoscopic video image formed of a set of an image for left eye and an image for right eye, corrects gradation of a first image, which is one image from among the image for left eye and the image for right eye, and gradation of a second image, which is the other image from, among the image for left eye and the image for right eye, the image processing apparatus comprising: a detection unit that detects parallax between the first image and second image; and a correction unit that decides on a corresponding gradation conversion curve, for each pixel in the first image and the second image, in order to correct a gradation value of the pixel, and corrects the gradation value, wherein the correction unit detects a pixel in the second image corresponding to a pixel in the first image on the basis of the parallax, and corrects a gradation value of the pixel in the first image and a gradation value of the pixel in the second image corresponding to the pixel in the first image by using a single gradation conversion curve.