METHODS AND SYSTEMS FOR POST-RECONSTRUCTION FILTERING
Systems and methods are described for video coding using adaptive Hadamard filtering of reconstructed blocks, such as coding units. In some embodiments, where Hadamard filtering might otherwise encompass samples outside the current coding unit, extrapolated samples are generated for use in the filtering. Reconstructed samples from neighboring blocks may be used in the filtering where available (e.g. in a line buffer). In some embodiments, different filter strengths are applied to different spectrum components in the transform domain. In some embodiments, filter strength is based on position of filtered samples within the block. In some embodiments, filter strength is based on the prediction mode used to code the current block.
1 . A method comprising:
reconstructing a plurality of samples in a current block of samples;
applying a transform to a first set of samples, including at least a subset of the reconstructed samples in the current block and at least one reconstructed sample outside the current block, to generate a set of spectrum components;
applying a filter to at least one of the spectrum components to generate a set of filtered spectrum components; and
applying an inverse of the transform to the filtered spectrum components to generate a plurality of filtered samples corresponding to the first set of samples.
2 . An apparatus comprising one or more processors configured to perform:
reconstructing a plurality of samples in a current block of samples;
applying a transform to a first set of samples, including at least a subset of the reconstructed samples in the current block and at least one reconstructed sample outside the current block, to generate a set of spectrum components;
applying a filter to at least one of the spectrum components to generate a set of filtered spectrum components; and
applying an inverse of the transform to the filtered spectrum components to generate a plurality of filtered samples corresponding to the first set of samples.
3 . The method of claim 1 , wherein the transform is a Hadamard transform and the spectrum components are Hadamard spectrum components.
4 . The method of claim 1 , wherein the first set of samples further comprises at least one extrapolated sample outside the current coding unit, further comprising generating an extrapolated sample value for the extrapolated sample based on the reconstructed samples in the current coding unit.
5 . The method of claim 1 , wherein the first set of samples further comprises at least one extrapolated sample outside the current coding unit, further comprising generating an extrapolated sample value for the extrapolated sample based on the reconstructed samples in the current coding unit, wherein generating the extrapolated sample value is performed using at least one extrapolation method selected from the group consisting of linear extrapolation, cubic extrapolation, bilinear extrapolation, and bi-cubic extrapolation.
6 . The method of claim 1 , wherein the current coding unit is intra coded, and wherein the first set of samples further comprises at least one predicted sample outside the current coding unit, further comprising generating a predicted sample value for the predicted sample using an intra coding mode of the current coding unit.
7 . The method of claim 1 , wherein the current coding unit is inter coded, wherein the first set of samples further comprises at least one predicted sample outside the current coding unit, further comprising generating a predicted sample value for the predicted sample using a motion vector of the current coding unit.
8 . The method of claim 1 , wherein the current coding unit is inter coded, wherein the first set of samples further comprises at least one predicted sample outside the current coding unit, further comprising generating a predicted sample value for the predicted sample using a rounded version of the motion vector of the current coding unit.
9 . The method of claim 1 , wherein the first set of samples further comprises at least one padded sample outside the current coding unit, further comprising using, as a padded sample value for the padded sample, the value of a reconstructed sample adjacent to the padded sample.
10 . The method of claim 1 , wherein the first set of samples comprises at least sixteen samples.
11 . The method of claim 1 , wherein applying a filter to at least one of the Hadamard spectrum components comprises determining
F
(
i
,
σ
)
=
R
(
i
)
2
R
(
i
)
2
+
m
*
σ
2
*
R
(
i
)
where R(i) is a Hadamard spectrum component and F(i, σ) is the corresponding filtered Hadamard spectrum component.
12 . The method of claim 1 , further comprising storing the filtered samples in a decoded picture buffer.
13 . The method of claim 1 , performed by a video encoder.
14 . The method of claim 1 , performed by a video decoder.
15 . The apparatus of claim 2 , wherein the apparatus is a decoder.
16 . The apparatus of claim 2 , wherein the transform is a Hadamard transform and the spectrum components are Hadamard spectrum components.
17 . The apparatus of claim 2 , wherein the first set of samples further comprises at least one extrapolated sample outside the current coding unit, further comprising generating an extrapolated sample value for the extrapolated sample based on the reconstructed samples in the current coding unit.
18 . The apparatus of claim 2 , wherein the first set of samples comprises at least sixteen samples.
19 . The apparatus of claim 2 , wherein applying a filter to at least one of the Hadamard spectrum components comprises determining
F
(
i
,
σ
)
=
R
(
i
)
2
R
(
i
)
2
+
m
*
σ
2
*
R
(
i
)
where R(i) is a Hadamard spectrum component and F(i, σ) is the corresponding filtered Hadamard spectrum component.
20 . The apparatus of claim 2 , further configured to store the filtered samples in a decoded picture buffer.