METHOD FOR TRANSFORMING AND INVERSE-TRANSFORMING IMAGE, AND APPARATUS USING THE SAME

摘要

PURPOSE: A method for transforming or reversely transforming an image and a device for encoding or decoding an image using the method are provided to increase operation speed. CONSTITUTION: A substituted discrete cosine transform matrix is obtained by substituting values based on a trigonometric function with predetermined rational values(1510). The values based on the trigonometric function are obtained from elements of an NxN transformation matrix. A scaling matrix compensates for a difference between the result value of the substituted discrete cosine transform matrix and the result value of an original discrete cosine transform matrix(1520). The NxN blocks is transformed by using the substituted discrete cosine transform matrix(1530). The transformed NxN block is quantized using the scaling matrix and a quantization step(1540). [Reference numerals] (1510) Obtaining a substituted discrete cosine transform matrix(A) by substituting values based on a trigonometric function with predetermined rational values in elements of an NxN transform matrix used for one-dimensional discrete cosine transform of an NxN(N is an integer) block; (1520) Obtaining a scaling matrix(S) for compensating the difference between the result value of the substituted discrete cosine transform matrix(A) and the result value of an original discrete cosine transform matrix(Original_A) using the substituted discrete cosine transform matrix(A) and the transposed matrix(A^T) of the substituted discrete cosine transform matrix(A); (1530) Transforming the NxN block using the substituted discrete cosine transform matrix(A); (1540) Quantizing the transformed NxN block using the scaling matrix(S) and a quantization step; (AA) Start; (BB) End