Method and apparatus for encoding or decoding blocks of pixel

Patent metadata

Field	Value
Publication number	US-2016309172-A1
Application number	US-201415102508-A
Country	US
Kind code	A1
Filing date	Dec 10, 2014
Priority date	Dec 10, 2013
Publication date	Oct 20, 2016
Grant date	—

Abstract

The invention concerns a method and a device for processing a current pixel block of an image using a palette prediction mode according to HEVC RExt. The mode uses a current palette to build a predictor block of indexes to predict the current pixel block. The current palette comprises entries associating entry indexes with pixel values. The method comprises predicting the current palette from entries of two or more palettes that are palettes previously used to process blocks of pixels. A palette predictor may be used that is built from the two or more palettes, preferably from the last used palette for a coding unit in the current coding entity and from the previously used palette for which a flag bitmap indicates whether or not its elements have been copied into the last used palette. Accordingly, the coding of the palette mode is improved.

First claim

1 . A method for processing a current block of pixels of an image using a palette coding mode, the palette coding mode using a current palette that comprises a set of entries associating respective entry indexes with corresponding pixel values, the method comprising:
a step of predicting the current palette using a palette predictor built from entries of two or more palettes, the two or more palettes being palettes previously used to process blocks of pixels, wherein the prediction of the current palette comprises selecting an entry from a given palette of the two or more palettes as an entry of the palette predictor and selecting all the entries from another of the two or more palettes as entries of the palette predictor, said another palette being used to process the block of pixels immediately preceding the current block, wherein said selection of an entry from the given palette being is based on a 10 bitmap of flags, each flag defining whether or not a corresponding entry in the given palette is selected as an entry in the another palette, and includes selecting an entry of the given palette corresponding to a flag of the bitmap that defines no selection of the entry as the entry of the given palette to be included in the palette predictor for predicting the current palette.

2 . (canceled)

3 . The method of claim 1 , wherein said another palette is the palette used to process a block of pixels immediately preceding the current block of pixels in the image.

4 . The method of claim 3 , wherein the given palette is the palette used to process a block of pixels in the image immediately preceding the block of pixels immediately preceding the current block of pixels in the image.

5 . The method of claim 1 , wherein the bitmap of flags includes at least one element at a predefined position in the bitmap for signalling whether or not the bitmap includes, after the predefined position, at least one additional flag that defines selection of an entry of the given palette to generate the another palette.

6 - 7 . (canceled)

8 . The method of claim 1 , wherein the current palette is predicted from the palette predictor using a bitmap of flags, each flag of which defining whether or not a corresponding entry in the palette predictor is selected as an entry to generate an entry in the current palette.

9 . The method of claim 1 , wherein an entry of the two or more palettes is added to the palette predictor being built if there is no similar entry already in the palette predictor being built.

10 . A method of encoding a sequence of digital images into a bitstream, at least one block of an image being encoded using a palette coding mode comprising the method of processing a current block of pixels according to claim 1 .

11 . A method of decoding a bitstream comprising an encoded sequence of digital images, at least one block of an image having been encoded using a palette coding mode, comprising the method of processing a current block of pixels according to claim 1 .

12 . A device for processing a current block of pixels of an image using a palette coding mode, the palette coding mode using a current palette that comprises a set of entries associating respective entry indexes with corresponding pixel values, the device comprising:
a prediction unit configured to predict the current palette using a palette predictor built from entries of two or more palettes, the two or more palettes being palettes previously used to process blocks of pixels, wherein the prediction of the current palette comprises selecting an entry from a given palette of the two or more palettes and selecting all the entries from another of the two or more palettes as entries of the palette predictor, said another palette being used to process the block of pixels immediately preceding the current block, wherein said selection of an entry from the given palette is based on a bitmap of flags, each flag defining whether or not a corresponding entry in the given palette is selected as an entry in the another palette, wherein the prediction unit is configured to select an entry of the given palette, corresponding to a flag of the bitmap that defines no selection of the entry, as the entry of the given palette to be included in the palette predictor for predicting the current palette.

13 . A device for processing a current block of pixels of an image using a palette coding mode, the palette coding mode using a current palette that comprises a set of entries associating respective entry indexes with corresponding pixel values, the device having a processor and memory configured to implement a method comprising:
a step of predicting the current palette using a palette predictor built from entries of two or more palettes, the two or more palettes being palettes previously used to process blocks of pixels, wherein the prediction of the current palette comprises selecting an entry from a given palette of the two or more palettes as an entry of the palette predictor and selecting all the entries from another of the two or more palettes as entries of the palette predictor, said another palette being used to process the block of pixels immediately preceding the current block, wherein said selection of an entry from the given palette is based on a bitmap of flags, each flag defining whether or not a corresponding entry in the given palette is selected as an entry in the another palette, and includes selecting an entry of the given palette corresponding to a flag of the bitmap that defines no selection of the entry as the entry of the given palette to be included in the palette predictor for predicting the current palette.

14 . A device for encoding a sequence of digital images into a bitstream comprising a processor and memory configured to perform a method comprising:
a step of predicting the current palette using a palette predictor built from entries of two or more palettes, the two or more palettes being palettes previously used to process blocks of pixels, wherein the prediction of the current palette comprises selecting an entry from a given palette of the two or more palettes as an entry of the palette predictor and selecting all the entries from another of the two or more palettes as entries of the palette predictor, said another palette being used to process the block of pixels immediately preceding the current block, wherein said selection of an entry from the given palette is based on a bitmap of flags, each flag defining whether or not a corresponding entry in the given palette is selected as an entry in the another palette, and includes selecting an entry of the given palette corresponding to a flag of the bitmap that defines no selection of the entry as the entry of the given palette to be included in the palette predictor for predicting the current palette.

15 . A device for decoding a bitstream comprising a sequence of digital images comprising a processor and memory configured to perform a method comprising:
a step of predicting the current palette using a palette predictor built from entries of two or more palettes, the two or more palettes being palettes previously used to process blocks of pixels, wherein the prediction of the current palette comprises selecting an entry from a given palette of the two or more palettes as an entry of the palette predictor and selecting all the entries from another of the two or more palettes as entries of the palette predictor, said another palette being used to process the block of pixels immediately preceding the current block, wherein said selection of an entry from the given palette is based on a bitmap of flags, each flag defining

Assignees

• Canon Kk

Inventors

• Laroche Guillaume
• Gisquet Christophe
• Onno Patrice

Classifications

• H04N19/593

  involving spatial prediction techniques · CPC title

• H04N19/176 Primary

  the region being a block, e.g. a macroblock · CPC title

• H04N19/186 Primary

  the unit being a colour or a chrominance component · CPC title

• H04N19/94

  Vector quantisation · CPC title

• H04N19/463 Primary

  by compressing encoding parameters before transmission · CPC title