A spectrum extrapolation method for image magnification
Hitoshi Takami, S. Nakano, Koichi Ichige, R. Ishii · 2005
There are many kinds of interpolation methods to magnify an image. These methods proposed how to insert values between two neighbor values in an image. In general, a high-frequency band outside of a band-limitation cannot be obtained by using interpolation methods. Therefore a magnified image by an interpolation method blurs. This paper presents an extrapolation method to estimate high-frequency band theoretically. In the proposal method, we exploit the discrete Fourier transform (DFT) and the discrete Hilbert transform (DHT) in order to divide a frequency response into three components, a magnitude response, a minimum phase response and an all-pass phase response. These three responses are extrapolated respectively. Applying this method to an image, we can obtain a better image than that by using interpolation methods. By using a high pass filter, we verified that the obtained magnified image shaped the silhouette and had a spectrum in a high frequency band.