Patent ID: 7397957

Claim:
A discrete wavelet transform (DWT) unit for encoding and decoding a still image, comprising: an energy calculating section for calculating energy of an input image in a unit of a block having a predetermined number of pixels; an image decomposing section for performing three-level decomposition of the image of the block by decomposing a band, at which a low frequency component is distributed three times, wherein a range of the calculated energy is divided into three partitioned ranges, such that the three partitioned ranges are respectively assigned into a first energy level, a second energy level and a third energy level in an order of a magnitude of the energy; and a coefficient substituting section for substituting 0 (zero) for a coefficient of at least one band in which a high frequency component is distributed among the three-level decomposed bands according to the range to which a value of the energy of the corresponding block belongs.