To shorten an arithmetic time by effectively intensifying a contour while suppressing the generation of noise and by making computational quantity smaller than that of a DOG (differential of Gaussian) filter.

A deformed contour intensifying filter is used to apply contour intensification to image data. The deformed contour intensifying filter is obtained by folding the four corners of a contour intensifying filter of (5×5) matrix inwards, for example. Therefore, a coefficient in the four corners of the deformed contour intensifying filter is "0". The number of terms in an operation expression for contour intensification is reduced, thereby shortening the arithmetic time.