Patent ID: 11962806
Assignee: CANON KABUSHIKI KAISHA
Field: Audio-visual technology (Electrical engineering)
Classification: CPC H | IPC H

Claim 7:
8. An image decoding method in which an image is decodable from a bit stream by using a plurality of blocks including a first block of a P×Q array of pixels, where P and Q are integers, the image decoding method comprising:
decoding data corresponding to quantized transform coefficients from the bit stream;
deriving transform coefficients from the quantized transform coefficients by using a quantization matrix, the transform coefficients representing frequency components; and
deriving prediction residuals from the transform coefficients by performing inverse transform processing on the transform coefficients,
wherein, in a case where a target block is the first block,
(i) an N×M array of transform coefficients is derived from an N×M array of quantized transform coefficients by using a quantization matrix of an N×M array of elements, wherein N is an integer satisfying N<P, and M is an integer satisfying M<Q, and
(ii) an N×Q array of intermediate values is derived by performing multiplication of the N×M array of transform coefficients and a matrix of a M×Q array, and a P×Q array of prediction residuals for the first block is derived by performing multiplication of a matrix of a P×N array and the N×Q array of intermediate values, and

wherein, in a case where a target block is a second block smaller than the first block,
(i) an array of transform coefficients for the second block is derived from an array of quantized transform coefficients for the second block by using a quantization matrix for the second block, wherein a size of the array of transform coefficients for the second block, a size of the array of quantized transform coefficients for the second block, and a size of the quantization matrix for the second block are the same as a size of the second block, and
(ii) an array of prediction residuals a size of which is the same as the size of the second block is derived by performing multiplication using at least the array of transform coefficients for the second block and a matrix a size of which is the same as the size of the second block.