Intra block copy mode for screen content coding
A video block of a current picture may be coded in an intra block copy (IBC) mode. Weighted prediction may be disabled for the IBC-coded screen content video block. Fractional block vectors may be used for the chroma components of the IBC-coded video block. An interpolation filter may be utilized to generate chroma prediction samples for the video block. A decoded version of the current reference picture may be added to both reference picture list LO and reference picture list L 1 that are associated with the IBC-coded video block. When constrained intra prediction is applied, reference samples that may be used to predict an intra-coded video block may be limited to those in intra-coded neighboring blocks. The range of IBC searches may be restricted by imposing a maximum absolute value for block vectors.
1. A method for video decoding, the method comprising:
obtaining a chroma block vector associated with a current coding unit (CU) of a current picture,
wherein the chroma block vector has a fractional pixel resolution;
determining whether reference samples are available for deriving a chroma reference sample based on the chroma block vector, wherein the reference samples are determined to be available if the reference samples are located in a decoded area of the current picture and in a same slice or tile as the current CU; and
based on a determination that the reference samples are available for deriving the chroma reference sample:
deriving the chroma reference sample for the current CU by at least applying an interpolation filter to the reference samples such that the derived chroma reference sample corresponds to a fractional sample position; and
decoding the current CU based on the derived chroma reference sample, wherein the decoding is performed with temporal motion vector prediction (TMVP) enabled when intra block copy (IBC) and constrained intra prediction (CIP) are enabled for the current CU.
2. The method of claim 1 , wherein the reference samples are located at respective integer sample positions determined based on at least the chroma block vector.
3. The method of claim 1 , wherein the chroma block vector is determined to have the fractional pixel resolution in response to determining that the chroma block vector points to one or more fractional chroma sample positions.
4. The method of claim 1 , wherein the interpolation filter comprises a 4-tap interpolation filter.
5. The method of claim 1 , further comprising:
determining that the current picture is associated with a pseudo reference picture that corresponds to a decoded version of the current picture; and
adding the pseudo reference picture to a first reference picture list associated with the current picture and to a second reference picture list associated with the current picture.
6. A video decoding device, comprising:
a processor configured to:
obtain a chroma block vector associated with a current coding unit (CU) of a current picture, wherein
the chroma block vector has a fractional pixel resolution;
determine whether reference samples are available for deriving a chroma reference sample based on the chroma block vector, wherein the reference samples are determined to be available if the reference samples are located in a decoded area of the current picture and in a same slice or tile as the current CU; and
based on a determination that the reference samples are available for deriving the chroma reference sample based on the chroma block vector:
derive the chroma reference sample for the current CU by at least applying an interpolation filter to the reference samples associated with the current CU such that the derived chroma reference sample corresponds to a fractional sample position; and
decode the current CU based on the derived chroma reference sample, wherein the decoding is performed with temporal motion vector prediction (TMVP) enabled when intra block copy (IBC) and constrained intra prediction (CIP) are enabled for the current CU.
7. The video decoding device of claim 6 , wherein the reference samples are located at respective integer sample positions determined based on at least the chroma block vector.
8. The video decoding device of claim 6 , wherein the processor is configured to determine that the chroma block vector has the fractional pixel resolution based on a determination that the chroma block vector points to one or more fractional chroma sample positions.
9. The video decoding device of claim 6 , further comprising a memory operatively connected to the processor.
10. The video decoding device of claim 6 , wherein the processor is further configured to:
determine that the current picture is associated with a pseudo reference picture that corresponds to a decoded version of the current picture; and
add the pseudo reference picture to a first reference picture list associated with the current picture and to a second reference picture list associated with the current picture.
11. A method for video encoding, the method comprising:
determining a chroma block vector associated with a current coding unit (CU) of a current picture, wherein the chroma block vector points to a fractional sample location;
determining whether reference samples are available for deriving a chroma reference sample based on the chroma block vector, wherein the reference samples are determined to be available if the reference samples are located in a decoded area of the current picture and in a same slice or tile as the current CU; and
responsive to determining that the reference samples are available for deriving the chroma reference sample:
deriving the chroma reference sample for the current CU, wherein the chroma reference sample is associated with the fractional sample location and is derived by applying an interpolation filter to the reference samples;
determining one or more prediction residuals for the current CU based at least on the derived chroma reference sample; and
encoding the one or more prediction residuals and the chroma block vector, wherein the encoding is performed with temporal motion vector prediction (TMVP) enabled when intra block copy (IBC) and constrained intra prediction (CIP) are enabled for the current CU.
12. A video encoding device, comprising:
a processor configured to:
determine a chroma block vector associated with a current coding unit (CU) of a current picture, wherein the chroma block vector points to a fractional sample location;
determine whether reference samples are available for deriving a chroma reference sample based on the chroma block vector, wherein the reference samples are determined to be available if the reference samples are located in a decoded area of the current picture and in a same slice or tile as the current CU; and
responsive to determining that the reference samples are available for deriving the chroma reference sample:
derive the chroma reference sample for the current CU, wherein the chroma reference sample is associated with the fractional sample location and is derived by applying an interpolation filter to the reference samples;
determine one or more prediction residuals for the current CU based at least on the derived chroma reference sample; and
encode the one or more prediction residuals and the chroma block vector, wherein the encoding is performed with temporal motion vector prediction (TMVP) enabled when intra block copy (IBC) and constrained intra prediction (CIP) are enabled for the current CU.