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

Claim 0:
1. An image decoding apparatus capable of decoding an image 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 apparatus comprising:
a decoding unit configured to decode data corresponding to quantized transform coefficients from the bit stream;
an inverse quantization unit configured to derive transform coefficients from the quantized transform coefficients by using a quantization matrix, the transform coefficients representing frequency components; and
an inverse transform unit configured to derive 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) the inverse quantization unit is configured to derive an N×M array of transform coefficients 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) the inverse transform unit is configured to derive an N×Q array of intermediate values by performing multiplication of the N×M array of transform coefficients and a matrix of a M×Q array, and to derive a P×Q array of prediction residuals for the first block 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) the inverse quantization unit is configured to derive an array of transform coefficients for the second block 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) the inverse transform unit is configured to derive an array of prediction residuals a size of which is the same as the size of the second block 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.