Filter description signaling for multi-filter adaptive filtering

Patent metadata

Field	Value
Publication number	US-9819966-B2
Application number	US-201113178415-A
Country	US
Kind code	B2
Filing date	Jul 7, 2011
Priority date	Sep 1, 2010
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

Filtering is applied at an encoder, and filter information describing a set of filters is encoded in the bitstream to enable a decoder to identify the filtering that was applied at the encoder. The decoder receives encoded video data that includes the filter information, decodes the video data, and applies filtering based on the filtering information. The decoder applies the same filtering that was applied at the encoder. To potentially reduce the number of bits needed to reconstruct the set of filters and other filter information as well as to potentially improve decoder performance, filter description syntax describing the set of filters can be included in the bitstream. The filter description syntax may identify a number of filters in a set of filters, a maximum number of filters in a set of filters, and/or identify a shape of filters in a set of filters.

First claim

The invention claimed is:

1. A method of decoding a bitstream of encoded video data, the method comprising:
receiving in the bitstream of encoded video data as part of a higher level coded unit, at a video decoder comprising one or more processors, a first syntax element, wherein a value of the first syntax element identifies a maximum number of filters allowed in a set of filters for a series of video blocks;
receiving, in the bitstream of encoded video data as part of a lower level coded unit, at the video decoder, a second syntax element, wherein a value of the second syntax element identifies a number of filters in the set of filters for the series of video blocks, wherein the number of filters in the set of filters is less than the maximum number of filters, wherein the higher level coded unit is hierarchically higher than the lower level coded unit;
reconstructing the set of filters based on the value of the first syntax element and the value of the second syntax element;
determining a mapping of ranges of an activity metric to filters in the set of filters based on the value of the first syntax element, wherein a number of ranges of the activity metric to be mapped to filters in the set of filters is a function of the maximum number of filters allowed in the set of filters as indicated by the value of the first syntax element;
generating a reconstructed block from a predictive block in a reference frame and a residual block;
determining a value of an activity metric for the reconstructed block;
selecting a filter from the set of filters based on the determined value of the activity metric and the mapping of the ranges of the activity metric to the filters in the set of filters;
applying the filter to samples of the reconstructed block of video as part of a loop filtering operation; and
outputting decoded video data comprising the filtered reconstructed block of video.

2. The method of claim 1 , further comprising:
allocating a portion of memory to storing filters based on the value of the first syntax element.

3. The method of claim 1 , wherein the video decoder implements a Quadtree-based Adaptive Loop Filter (QALF) scheme with multiple filters.

4. The method of claim 1 , wherein the first syntax element is part of a header of a series of video blocks.

5. The method of claim 1 , further comprising:
receiving third syntax element, wherein a value of the third syntax element identifies a shape of filters in the set of filters;
wherein reconstructing the set of filters is further based on the value of the third syntax element.

6. The method of claim 1 , wherein the activity metric comprises a sum-modified Laplacian value.

7. The method of claim 6 , wherein the sum-modified Laplacian value comprises var(i,j) defined approximately according to the following equation:

var
⁡

(

i
,
j

)

=

∑

k
=

-
K

K

⁢

∑

l
=

-
L

L

⁢



2
⁢

R
⁡

(

i
+
k

,

j
+
l

)

-

R
⁡

(

i
+
k
-
1

,

j
+
l

)

-

R
(

i
+
k
+
1

,

j
+
l



+



2
⁢

R
⁡

(

i
+
k

,

j
+
l

)

-

R
⁡

(

i
+
k

,

j
+
l
-
1

)

-

R

Assignees

• Chong In Suk
• Karczewicz Marta
• Chien Wei-Jung
• Qualcomm Inc

Inventors

• Chong In Suk
• Karczewicz Marta
• Chien Wei-Jung

Classifications

• H04N19/182

  the unit being a pixel · CPC title

• H04N19/42

  characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation (H04N19/635 takes precedence) · CPC title

• H04N19/117

  Filters, e.g. for pre-processing or post-processing (sub-band filter banks H04N19/635) · CPC title

• H04N19/14

  Coding unit complexity, e.g. amount of activity or edge presence estimation (H04N19/146 takes precedence) · CPC title

• H04N19/85 Primary

  using pre-processing or post-processing specially adapted for video compression · CPC title