1. An image processing device comprising an image signal correction unit that executes correction processing for a pixel signal of an input image, wherein the image signal correction unit inputs, as the input image, a mosaic image in which pixel blocks configured of a plurality of same-color pixels are arrayed, from among constituent pixels of the input image, detects pixel value gradients in eight directions in a conversion-target pixel location that is targeted for color conversion processing, decides an interpolated pixel value calculation mode for the conversion-target pixel on the basis of the pixel value gradients in the eight directions, and calculates an interpolated pixel value for the conversion-target pixel location in accordance with the decided processing mode.