US 10,432,932 B2Granted

Directional deringing filters

AssigneeMozilla Corporation

InventorsJean-Marc Valin, Timothy B. Terriberry

Life of this patent

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Abstract

Systems and methods are described for removing ringing artifacts from a coded image. For each block of coded image data, a direction is identified by selecting a directional block divided into a plurality of pixel lines in one predetermined direction of a set of at least four predetermined directions. The directional block may have a constant value across each pixel line. A parameter related to a sum of a mean-square difference between a pixel value and the pixel average of pixels falling on a pixel line in the directional block that includes the location of the pixel may be calculated for each direction of the set. The direction of the set having a minimum summed mean-square difference is selected as the direction for the block based on the calculated parameter values. A non-linear filter is then applied to each block based on the identified direction for the block.

Claims20

Dependent claims

A method for removing ringing artifacts from a coded image, the method comprising:

receiving, by a processor, coded image data for an image that has undergone quantization;
dividing, by a processor, the received coded image data into a plurality of blocks;
identifying, by the processor, a direction for each block of the coded image data, the identifying comprising:
selecting a directional block, the directional block having the same number of pixels as the block and being divided into a plurality of pixel lines, the pixel lines having one of a set of at least four predetermined directions, the directional block having a constant value across each pixel line;
calculating a parameter related to a sum of a mean-square difference between a pixel value of each pixel of the block, each pixel having a location in the block, and the pixel average of pixels falling on a pixel line of the directional block that includes the location in the block of the corresponding pixel;
repeating the calculating the parameter for each of the set of at least four predetermined directions;
and
selecting the direction of the set of at least four predetermined directions having a parameter value related to a minimum summed mean-square difference as the direction for the block;
applying a non-linear filter, by the processor, to each block of the coded image data, the non-linear filter for each block being based on the identified direction for the block, thereby transforming the blocks of the image into filtered blocks of the image, the nonlinear filter having a definition of:
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storing, by the processor, the filtered blocks of the image in a data store.

80 more elements

A decoder that utilizes a directional deringing filter to remove artifacts from a coded image, the decoder comprising:

a memory that stores coded image data for the coded image, the coded image having been quantized;
and
a processor, the processor executing instructions to:
receive the coded image data;
divide the received coded image data into a plurality of blocks;
identify a direction for each block of the coded image data, the identifying comprising:
selecting a directional block, the directional block having the same number of pixels as the block and being divided into a plurality of pixel lines, the pixel lines having one of a set of at least four predetermined directions, the directional block having a constant value across each pixel line;
calculating a parameter related to a sum of a mean-square difference between a pixel value of each pixel of the block, each pixel having a corresponding location in the block, and the pixel average of pixels falling on a pixel line of the directional block that includes the location in the block of the corresponding pixel;
repeating the calculating the parameter for each of the set of at least four predetermined directions;
and
selecting the direction of the set of at least four predetermined directions having a parameter value related to a minimum summed mean-square difference as the direction for the block;
apply a non-linear filter to each block of the coded image data, the non-linear filter for each block being based on the identified direction for the block, thereby transforming the blocks of the image into filtered blocks of the image, the nonlinear filter having a definition of:
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with a threshold function defined as
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=
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otherwise
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and
store the filtered blocks of the image in a data store.

83 more elements

A computer program product comprising computer-readable program code to be executed by one or more processors when retrieved from a non-transitory computer-readable medium, the program code including instructions to:

receive coded image data for an image that has undergone quantization;
divide the received coded image data into a plurality of blocks;
identify a direction for each block of the coded image data, the identifying comprising:
selecting a directional block to compare with a block of the plurality of blocks, the directional block having the same number of pixels as the block and being divided into a plurality of pixel lines, the pixel lines having one of a set of at least four predetermined directions, the directional block having a constant value across each pixel line;
calculating parameter related to a sum of a mean-square difference between a pixel value of each pixel of the block, each pixel having a location in the block, and the pixel average of pixels falling on a pixel line of the directional block that includes the location in the block of the corresponding pixel;
repeating the calculating the parameter for each of the set of at least four predetermined directions;
and
selecting the direction of the set of at least four predetermined directions having parameter value related to a minimum summed mean-square difference as the direction for the block;
apply a non-linear filter to each block of the coded image data, the non-linear filter for each block being based on the identified direction for the block, thereby transforming the blocks of the image into filtered blocks of the image, the nonlinear filter having a definition of:
y
⁡
(
n
)
=
x
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(
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)
+
1
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∑
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=
-
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≠
0
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=
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+
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-
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(
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,
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with a threshold function defined as
f
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(
d
,
T
)
=
{
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,

d

<
T
0
,
otherwise
;
and
store the filtered blocks of the image in a data store.

80 more elements

A method for removing ringing artifacts from a coded image, the method comprising:

receiving, by a processor, coded image data for an image that has undergone quantization;
dividing, by a processor, the received coded image data into a plurality of blocks;
identifying, by the processor, a direction for each block of the coded image data;
applying a conditional replacement filter, by the processor, to each block of the coded image data, the conditional replacement filter having a definition of:
y
⁡
(
n
)
=
x
⁡
(
n
)
+
1
W
⁢
∑
k
=
-
M
,
k
≠
0
k
=
M
⁢
w
k
⁢
f
⁡
(
x
⁡
(
n
+
k
)
-
x
⁡
(
n
)
,
T
)
with a threshold function defined as
f
⁡
(
d
,
T
)
=
{
d
,

d

<
T
0
,
otherwise
,
the conditional replacement filter being applied using a predetermined number of taps, where each tap corresponds to a pixel on a line of pixels, within a block, having the identified direction for the block, the line of pixels having a center pixel, the applying the conditional replacement filter comprising:
for each pixel of the block, calculating a difference between an input value for each tap of the predetermined number of taps and a center pixel value;
and
comparing, for each tap, the difference to a threshold, wherein the input value for each tap is replaced by the center pixel value when the difference is greater than or equal to the threshold;
and
storing, by the processor, the filtered blocks of the image in a data store.

78 more elements

Dependencies are inferred from the claim text.

Facts

Application: 15/200,549Filed 1 Jul 2016 · us provisional application
Priority: 10 Jul 2015
Published: US 2017/0013260 A112 Jan 2017
Granted: 1 Oct 2019
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

H04N 19/117
Characterised by the element, parameter or selection affected or controlled by the adaptive coding: filters, e.g. for pre-processing or…
H04N 19/124
Characterised by the element, parameter or selection affected or controlled by the adaptive coding: quantisation
H04N 19/136
Characterised by the element, parameter or criterion affecting or controlling the adaptive coding: incoming video signal characteristics or properties
H04N 19/176
The unit being an image region, e.g. an object: the region being a block, e.g. a macroblock