Patent ID: 8559500

Claim:
A method of inverse transform and sub-sampling having low computational complexity, comprising: separating input signals into high-frequency signals and low-frequency signals; expressing said high-frequency signals as a high frequency matrix in spatial domain, and expressing said low-frequency signals as a low frequency matrix in spatial domain; performing compensation computations according to H 1 −1 ×H 2 ×Y 3 +Y 2 ×K 2 ×K 1 −1 ×H 1 −1 ×H 2 ×Y 4 ×K 2 ×K 1 −1 , wherein H 1 −1 is the inversed first portion of the combined matrix from the down-scale matrix and the transposed inverse transform matrix, H 2 is the second portion of the combined matrix from the down-scale matrix and the transposed inverse transform matrix, Y 3 is the left-bottom portion of the frequency-domain coefficient matrix, Y 2 is the right-top portion of the frequency-domain coefficient matrix, Y 4 is the right-bottom portion of the frequency-domain coefficient matrix, K 2 is the second portion of the combined matrix from the inverse transform matrix and the transposed down-scale matrix, K 1 −1 is the inversed first portion of the combined matrix from the inverse transform matrix and the transposed down-scale matrix; obtaining compensation values for non-zero high-frequency signals; adding separated low-frequency signals with said compensation values; selecting a dimension of an inverse transform matrix depending on actual sub-sampling requirements for said inverse transform and said sub-sampling; said dimension of said inverse transform matrix being less than that of an original inverse transform matrix; integrating a matrix of said inverse transform with said matrix of said sub-sampling in cooperation with compensated frequency-domain coefficients, in proceeding with said inverse transform and said sub-sampling of said matrix; separating said input signals into said high-frequency signals and said low-frequency signals being based on ways of sub-sampling; determining the dimension of the inverse transform matrix according to reduction ratios of a frame length and width; utilizing an original frame size L 1 ×W 1 in reducing a frame size into L 2 ×W 2 ; reducing said dimension of said inverse transform matrix through reduction ratios of L 2 /L 1 and W 2 /W 1 ; realizing a frame-size reduction transform, and determining a plurality of said low-frequency signals; and performing an inverse transform and a sub-sampling for a result of additions.