Method of decoding data and apparatus therefor

• US 7,796,065 B2
• Filed: 12/07/2006
• Issued: 09/14/2010
• Est. Priority Date: 12/07/2005
• Status: Active Grant

• Current Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Original Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Inventors: Fenney, Simon
• Primary Examiner(s): Nguyen; Khai M
• Application Number:
  US12/086,217
• Publication Number:
  US 20090278715A1
• Time in Patent Office: 1,377 Days
• Field of Search: 341/107, 382/247
• US Class Current: 341/107
• CPC Class Codes: H03M 7/4006 Conversion to or from arithmetic code
• CPC Class Codes: H04N 19/436 using parallelised computational arrangements
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

Incoming decoded data (1), for example from an H264 decoder, is fed to an encoder unit (2) that entropy encodes the decoded data using a parallel encoding scheme that includes context-based arithmetic encoding. The syntax is chosen so that the context does not depend on the immediately previously encoded symbol. The output of the encoder (2) is fed to a FIFO memory whose output is fed to a complimentary decoder (4) whose output produces a delayed copy of the incoming decoded data (1).

Claims

1. A method of decoding context based adaptive arithmetic entropy coded data comprising the steps of;

a) decoding first encoded data to produce first decoded data,

b) entropy encoding the first decoded data using a parallel encoding scheme that includes context-based adaptive arithmetic encoding for at least portions of symbols contained in the first decoded data to produce second encoded data, an N-bit symbol being encoded and divided into multiple streams, at least two of the streams being encoded in parallel using a corresponding number of arithmetic encoding units,

c) storing the second encoded data in a first in first out, FIFO, memory,

d) reading the second encoded data from the FIFO memory, and

e) decoding the second encoded data read from the FIFO memory to produce second decoded data, the second decoded data being the decoded entropy coded data.

2. A method as claimed in claim 1 in which in step b) the number of contexts is smaller than those used for originally encoding the data.

3. A method as claimed in claim 1 in which in step b) a specific syntax is interpreted and the context for the arithmetic encoding is selected based on the syntax element being encoded, the syntax being arranged to ensure that the context does not depend on the immediately previously encoded symbol.

4. A method as claimed in claim 1 in which in step b) arithmetic coding is not used for encoding data that are approximately equiprobable.

5. A method as claimed in claim 4 in which data that are approximately equiprobable are encoded using a variable length coding scheme.

6. A method as claimed in claim 1 in which in step b) arithmetic coding is not used for encoding data that have a low probability of occurrence.

7. A method as claimed in claim 6 in which data that have a low probability of occurrence are encoded using a variable length coding scheme.

8. Apparatus for decoding context-based adaptive arithmetic entropy encoded data comprising a first decoder for decoding first encoded data to form first decoded data, an encoder for encoding the first decoded data, the encoder being configured to use a parallel encoding scheme that includes context-based adaptive arithmetic encoding for at least portions of the first decoded data to produce second encoded data, a first in first out, FIFO, memory for storing the second encoded data, and a second decoder for reading the second encoded data from the output of the FIFO memory and decoding the second encoded data to produce the decoded context-based adaptive arithmetic entropy encoded data, wherein the encoder is also configured to encode an N-bit symbol, divide the N-bit symbol into multiple streams and encode at least two of the streams in parallel using a corresponding number of arithmetic encoding units.

9. Apparatus as claimed in claim 8 in which the encoder includes a state machine arranged to interpret a specific syntax to select the context for the arithmetic encoder based on the syntax element being processed, the syntax being chosen to ensure that the context is not dependent on an immediately previous symbol.

10. Apparatus as claimed in claim 9 in which the decoder includes a state machine arranged to interpret a specific syntax to select the context for the arithmetic decoder based on the syntax element being processed, the syntax being chosen to ensure that the context is not dependent on an immediately previously decoded symbol.

11. Apparatus as claimed in claim 8 in which the number of contexts is smaller than the number of contexts used to encode the originally encoded data.

12. Apparatus as claimed in claim 8 comprising a single FIFO memory in which the encoder comprises means for interleaving the encoded data streams before writing it to the FIFO memory and the second decoder comprises means for de-interleaving the data streams read from the FIFO memory.

13. Apparatus as claimed in claim 8 in which the encoder comprises means for encoding portions of the data bits representative of each symbol that are likely to be equiprobable or unlikely to be present using a variable length coding scheme.

14. Apparatus as claimed in claim 8 comprising a plurality of encoders for encoding the first decoded data, means for applying symbols to the encoders in a round robin fashion, and a corresponding plurality of decoders for decoding the second encoded data, each decoder being arranged to produce a decoded symbol in turn.