Unified transform type signaling and transform type dependent transform coefficient level coding

An apparatus for encoding a picture using predictive coding and block-based transform residual coding, comprising:

• a processor;
• and
• a memory having instructions which, when executed by the processor, cause the apparatus to:
• select, for a predetermined transform block, a transformation out of a predetermined list of transformations, the selected transformation comprising an identity transformation and at least one non-identity transformation,
• derive a prediction for the predetermined transform block,
• encode, for the predetermined transform block, a block of coefficients into a data stream by encoding for a current coefficient a significance flag indicative of whether the current coefficient is zero or not using a context, wherein:
• when the selected transformation is the identity transformation, the context depends on a number of coefficients being non-zero among a first set of coefficients immediately neighboring the current coefficient, and
• when the selected transformation is one of the at least one non-identity transformation, the context depends on values of a second set of coefficients and a position of the current coefficient, the second set of coefficients including at least one coefficient immediately neighboring the current coefficient and at least one coefficient positioned further away from the current coefficient than any of the coefficients immediately neighboring the current coefficient,
• the block of coefficients is related to a residual sample array according to the selected transformation, and the predetermined transform block is reconstructible by correcting the prediction for the predetermined transform block using the residual sample array.

A method for decoding a picture using predictive coding and block-based transform residual coding, comprising

• selecting, for a predetermined transform block, a transformation out of a predetermined list of transformations, the selected transformation comprising an identity transformation and at least one non-identity transformation,
• decoding, for the predetermined transform block, a block of coefficients from a data stream by decoding for a current coefficient a significance flag indicative of whether the current coefficient is zero or not using a context, wherein:
• when the selected transformation is the identity transformation, the context depends on a number of coefficients being non-zero among a first set of coefficients immediately neighboring the current coefficient, and
• when the selected transformation is one of the at least one non-identity transformation, the context depends on values of a second set of coefficients and a position of the current coefficient, the second set of coefficients including at least one coefficient immediately neighboring the current coefficient and at least one coefficient positioned further away from the current coefficient than any of the coefficients immediately neighboring the current coefficient
• deriving from the block of coefficients a residual sample array for the predetermined transform block so that the block of coefficients is related to the residual sample array according to the selected transformation, and
• correcting a prediction for the predetermined transform block using the residual sample array to reconstruct the predetermined transform block.

A method for encoding a picture using predictive coding and block-based transform residual coding, comprising

• selecting, for a predetermined transform block, a transformation out of a predetermined list of transformations, the selected transformation comprising an identity transformation and at least one non-identity transformation,
• deriving a prediction for the predetermined transform block,
• encoding, for the predetermined transform block, a block of coefficients into a data stream by encoding for a current coefficient a significance flag indicative of whether the current coefficient is zero or not using a context, wherein:
• when the selected transformation is the identity transformation, the context depends on a number of coefficients being non-zero among a first set of coefficients immediately neighboring the current coefficient, and
• when the selected transformation is one of the at least one non-identity transformation, the context depends on values of a second set of coefficients and a position of the current coefficient, wherein the second set of coefficients include at least one coefficient immediately neighboring the current coefficient and at least one coefficient positioned further away from the current coefficient than any of the coefficients immediately neighboring the current coefficient,
• wherein the block of coefficients is related to a residual sample array according to the selected transformation, and the predetermined transform block is reconstructible by correcting the prediction for the predetermined transform block using the residual sample array.

A data stream encoded by a method for encoding a picture using predictive coding and block-based transform residual coding, comprising

• selecting, for a predetermined transform block, a transformation out of a predetermined list of transformations, the selected transformation comprising an identity transformation and at least one non-identity transformation,
• deriving a prediction for the predetermined transform block,
• encoding, for the predetermined transform block, a block of coefficients into the data stream by encoding for a current coefficient a significance flag indicative of whether the current coefficient is zero or not using a context, wherein:
• when the selected transformation is the identity transformation, the context depends on a number of coefficients being non-zero among a first set of coefficients immediately neighboring the current coefficient, and
• when the selected transformation is one of the at least one non-identity transformation, the context depends on values of a second set of coefficients and a position of the current coefficient, wherein the second set of coefficients include at least one coefficient immediately neighboring the current coefficient and at least one coefficient positioned further away from the current coefficient than any of the coefficients immediately neighboring the current coefficient,
• wherein the block of coefficients is related to a residual sample array according to the selected transformation, and the predetermined transform block is reconstructible by correcting the prediction for the predetermined transform block using the residual sample array.