1. A parallax image generating apparatus comprising: a deriving unit configured to derive a parallax vector corresponding to a first pixel of an input image from the input image and depth information associated with the first pixel; a generating unit configured to generate an intermediate image by assigning a pixel value of the first pixel to a pixel of a parallax image designated by the parallax vector; a first calculating unit configured to calculate first weights for respective pixels of the parallax image, such that the deeper a position of a second pixel of the input image indicated by the depth information, the greater a first weight for a pixel of the parallax image corresponding to the second pixel; a setting unit configured to set one or more candidate blocks near a shade-forming-area pixel of the intermediate image, to which pixel the generating unit assigns no pixels, then to calculate sums obtained by multiplying, by respective first weights, pixel values of pixels included in the candidate block, and to set a reference block among one or more candidate blocks in a decreasing order of the sums; a searching unit configured to search a target block similar to the reference block in the input image and/or the intermediate image; and an interpolating unit configured to interpolate a pixel value of the shade-forming-area pixel based on a position of the shade-forming-area pixel relative to the target block.