Patent ID: 8611680

Claim:
A method for removing image noise, which is generated when image data compression-encoded in a given format is decoded to reproduce an image, comprising: a) a deduction step for examining a digital frequency response of image data composing an image of a complete image or a frame of an image, and which have been compression-encoded and decoded, to deduce analog frequency characteristics of the image before compression encoding, wherein in the deduction step, a cutoff frequency is calculated from FFT data obtained by performing an FFT on an image for one frame of a moving image, based on an assumption that the analog frequency characteristics of the image before compression encoding are the analog frequency characteristics of a lowpass filter having attenuation characteristics of a given order; b) a parameter setting step for changing a parameter of a sampled-data H ∞ filter in accordance with a deduction result by the deduction step, the parameter being a filter coefficient; and c) a processing step for performing a filtering process on the image data after the image data is decoded and before the image data is converted by using the sampled-data H ∞ filter having a parameter calculated by solving a computational equation with H ∞ control under a predetermined condition or with a rigorous calculation which corresponds to the H ∞ control, the computational equation being obtained by approximately converting a conditional equation to a finite-dimensional discrete-time system, and the conditional equation being set to design the sampled-data H ∞ filter so as to reduce an error between an original analog image signal and an analog image signal obtained through an analog to digital conversion, a coding and decoding process, and a digital to analog conversion.