Image decoding apparatus and image coding apparatus
An image decoding apparatus including a header decoder configured to decode, from coded data, a flag indicating whether dependent quantization is enabled and a flag prohibiting transform skip residual quantization, and a TU decoder configured to decode a transform coefficient in a TU block in an RRC mode in which a LAST position is coded, the LAST position corresponding to a decoding start position for the transform coefficient, or a TSRC mode in which the LAST position is not coded. The TU decoder performs dependent quantization in the RRC mode in a case that the transform coefficient for transform skip is decoded in the TSRC mode, and does not perform dependent quantization in the RRC mode in a case that the transform coefficient for transform skip is decoded in the RRC mode.
1. A decoder for decoding residual coding information, the decoder comprising:
a header decoder that decodes
(i) a transform skip enabled flag in a sequence parameter set,
(ii) a residual coding disabled flag specifying whether a transform skip residual coding is used, based on a value of the transform skip enabled flag being equal to one and
(iii) the transform skip flag specifying whether a transform is applied to an associated block or not, based on a value of the transform skip enabled flag being equal to one; and
a TU decoder that decodes a transform coefficient data by using a regular residual coding which is used for decoding a syntax element specifying a position of a last significant coefficient in a scanning order within a transform block or the transform skip residual coding which is a decoding without a transform,
wherein:
if a value of the transform skip flag is equal to zero or a value of the residual coding disabled flag equal to one, the TU decoder uses the regular residual coding,
otherwise, the TU decoder uses the transform skip residual coding, and
a value of the residual coding disabled flag is inferred to be equal to zero, when the residual coding disabled flag is not present.
2. An encoder for encoding residual coding information, the encoder comprising:
a header encoder that encodes
(i) a transform skip enabled flag in a sequence parameter set,
(ii) a residual coding disabled flag specifying whether a transform skip residual coding is used, based on a value of the transform skip enabled flag being equal to one and
(iii) the transform skip flag specifying whether a transform is applied to an associated block or not, based on a value of the transform skip enabled flag being equal to one; and
a TU encoder that encodes a transform coefficient by a regular residual coding which is used for generating a syntax element specifying a position of a last significant coefficient in a scanning order within a transform block or the transform skip residual coding which is a coding without a transform,
wherein:
if a value of the transform skip flag is equal to zero or a value of the residual coding disabled flag equal to one, the TU decoder uses the regular residual coding,
otherwise, the TU decoder uses the transform skip residual coding, and
a value of the residual coding disabled flag is inferred to be equal to zero, when the residual coding disabled flag is not present.
3. A method for decoding residual coding information, the method including:
decoding a transform skip enabled flag in a sequence parameter set,
decoding a residual coding disabled flag specifying whether a transform skip residual coding is used, based on a value of the transform skip enabled flag being equal to one, and
decoding the transform skip flag specifying whether a transform is applied to an associated block or not, based on a value of the transform skip enabled flag being equal to one; and
decoding a transform coefficient data by using a regular residual coding which is used for decoding a syntax element specifying a position of a last significant coefficient in a scanning order within a transform block or the transform skip residual coding which is a decoding without a transform,
wherein:
if a value of the transform skip flag is equal to zero or a value of the residual coding disabled flag equal to one, the regular residual coding is used,
otherwise, the transform skip residual coding is used, and
a value of the residual coding disabled flag is inferred to be equal to zero, when the residual coding disabled flag is not present.