An image data processing apparatus includes: an image data acquisition unit for acquiring low resolution image data and high resolution image data; and a confidence data determination unit for determining confidence data which indicates a level of confidence in a pixel value in the high resolution image data. The determination unit determines the level of confidence of a target pixel in the high resolution image data based on a comparison between a first and a second evaluation value. The first evaluation value is determined based on pixel values of neighboring pixels in a pixel position in the low resolution image data corresponding to a pixel position of the target pixel in the high resolution image data. The second evaluation value is determined based on the pixel values of the neighboring pixels, using a method that is different from the first evaluation value.