An image processing apparatus configured to process an enlarged image obtained by enlarging an input image (DORG), the enlarged image having a fold-over component in a frequency spectrum thereof, the image processing apparatus comprising: a first intermediate image generating means comprising a band-pass filter (1A, 1B) for generating a first intermediate image by extracting a component in a frequency band in the enlarged image, so as to remove the fold-over component, wherein said frequency band is between a first frequency (Fd) lower than Fn/2 and a second frequency (Fe) higher than Fn/2, where Fn is the Nyquist frequency of the input image (DORG); a second intermediate image generating means for generating a second intermediate image from the first intermediate image, the second intermediate image generating means comprising a non-linear processing means for generating a high-frequency component (D2A) corresponding to a high-frequency region above said frequency band, and a high-frequency component image generating means for extracting the high-frequency component (D2B) as the second intermediate image generated by the non-linear processing means; and an adding means for adding the enlarged image and the second intermediate image, wherein the non-linear processing means comprises: a zero-crossing point decision means (311h; 311v) configured to identify, as a zero-crossing point, a point in the first intermediate image where pixel values change from positive to negative or from negative to positive; and a signal amplifying means (312h; 312v) configured to generate the high-frequency component (D2A) by amplifying the pixel values of the pixels preceding and following the zero-crossing point with an amplification factor greater than 1, the amplification factor for the pixel values of other pixels being 1. a first intermediate image generating means comprising a band-pass filter (1A, 1B) for generating a first intermediate image by extracting a component in a frequency band in the enlarged image, so as to remove the fold-over component, wherein said frequency band is between a first frequency (Fd) lower than Fn/2 and a second frequency (Fe) higher than Fn/2, where Fn is the Nyquist frequency of the input image (DORG); a second intermediate image generating means for generating a second intermediate image from the first intermediate image, the second intermediate image generating means comprising a non-linear processing means for generating a high-frequency component (D2A) corresponding to a high-frequency region above said frequency band, and a high-frequency component image generating means for extracting the high-frequency component (D2B) as the second intermediate image generated by the non-linear processing means; and an adding means for adding the enlarged image and the second intermediate image, wherein the non-linear processing means comprises: a zero-crossing point decision means (311h; 311v) configured to identify, as a zero-crossing point, a point in the first intermediate image where pixel values change from positive to negative or from negative to positive; and a signal amplifying means (312h; 312v) configured to generate the high-frequency component (D2A) by amplifying the pixel values of the pixels preceding and following the zero-crossing point with an amplification factor greater than 1, the amplification factor for the pixel values of other pixels being 1. a zero-crossing point decision means (311h; 311v) configured to identify, as a zero-crossing point, a point in the first intermediate image where pixel values change from positive to negative or from negative to positive; and a signal amplifying means (312h; 312v) configured to generate the high-frequency component (D2A) by amplifying the pixel values of the pixels preceding and following the zero-crossing point with an amplification factor greater than 1, the amplification factor for the pixel values of other pixels being 1.