Patent ID: 7142720

Claim:
An inverse orthogonal transform method for reconstructing an original image by quantizing the result of two-dimensional orthogonal transform on each block of image data comprising NXN picture elements, decoding input codes which are obtained by encoding, dequantizing the result, and finally performing two-dimensional inverse orthogonal transform; said inverse orthogonal transform method comprising: dividing each column of a coefficient matrix comprising N rows and N columns, a result of two-dimensional orthogonal transform on said image data block, into one-dimensional partial sequences each comprising a predetermined number of components, extracting from the one-dimensional partial sequences a one-dimensional partial sequence comprising significant coefficients, which are positioned in any position of the one-dimensional partial sequence, containing a value other than zero, performing an operation equivalent to one-dimensional orthogonal transform on each component of said extracted one-dimensional partial sequence, outputting the operation result corresponding to said extracted partial sequence as the component of a column corresponding to the result of one-dimensional inverse transform, and performing the second-dimensional orthogonal transform on the result of said one-dimensional inverse transform.