1. A method for interpolating captured color image data by interpolating, based on captured color image data having single-color image data for each pixel, pixel data on other colors of each pixel, the method comprising: a correlation detecting step of detecting correlation between image data of an object pixel and image data of peripheral pixels located in at least two directions selected from among horizontal, vertical, and diagonal directions relative to the object pixel; a first correlation determining step of determining a direction having strong correlation, based on the correlation detected; a second correlation determining step of determining, for the direction determined as having a strong correlation, correlation between the image data of the object pixel and image data of a pixel located in which direction relative to a location of the object pixel is strong; an interpolation step of calculating image data on a color for interpolation of the object pixel, in which a weight to be applied to image data of the pixel located in the direction determined at the second correlation determining step as having stronger correlation is increased based on image data of a peripheral pixel for a color same as the color for interpolation, located in the direction determined at the first correlation determining step as having stronger correlation, based on results of the determinations made at the first and second correlation determining steps.