Patent ID: 7336811

Claim:
A periodic-pattern suppression method of reducing a spatial frequency component resulting from a stationary grid, contained in an original image signal photographed using said stationary grid, said method comprising the steps of: transforming said original image signal, represented in a real space domain, into a plurality of transformed image signals which can be handled in a frequency domain; and reducing a transformed image signal of said transformed image signals which has a desired frequency range containing a spatial frequency component corresponding to at least a grid array frequency of said stationary grid, which is actually used, in only the vicinity of a grid array direction of said stationary grid, not reducing any of said transformed image signals in a different direction from said vicinity of said array direction of said periodic pattern, and then transforming said transformed image signals into an inverse-transformed signal in said real space domain, wherein said transforming step obtains said plurality of transformed image signals by applying two-dimensional wavelet transformation to said original image signal by the use of a low-pass filter which splits a band so that its response at a frequency greater than the spatial frequency of said stationary grid becomes approximately zero; and said reducing step further applies a process of reducing a component less than a predetermined frequency and then performs inverse wavelet transformation, with respect to a signal of said transformed image signals which contains a spatial frequency component corresponding to said grid array frequency.