An image-processing method determines the interpolation reliability for interpolated pixels in a progressive image, generated by interpolation of an interlaced image, by combining at least any of a first interpolation reliability determined based on the absolute value of the difference between pixels in an upper line and pixels in a lower line used to calculate the value of the interpolated pixels, a second interpolation reliability determined based on the width of the region used to determine the pixels in the upper line and the pixels in the lower line used to calculate the value of the interpolated pixels, and a third interpolation reliability determined by combining the change in luminance for the upper line and the change in luminance for the lower line within the region.