CONTEXT ADAPTIVE POSITION AND AMPLITUDE CODING OF COEFFICIENTS FOR VIDEO COMPRESSION

• US 20090086815A1
• Filed: 01/18/2008
• Published: 04/02/2009
• Est. Priority Date: 10/01/2007
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Chen, Wen-hsiung, Chang, Pi Sheng, Tian, Dihong
• Granted Patent: US 8,265,162 B2
• Time in Patent Office: Days
• US Class Current: 375/240.30
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/167 Position within a video image, e.g. region of interest [ROI]
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/60 using transform coding

Abstract

A coding method, apparatus, and medium with software encoded thereon to implement a coding method. The coding method includes encoding the position of non-zero-valued coefficients in an ordered series of quantized transform coefficients of a block of image data, including encoding events using variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context. The coding method further includes encoding amplitudes of the non-zero-valued coefficients using variable dimensional amplitude coding in the reverse order of the original ordering of the series.

Claims

1. A method for operating a coding apparatus, the method comprising:

for an ordered series of quantized transform coefficients of a block of image data, the series having a most likely-to-occur amplitude, and at least one other amplitude including a next-to-most likely-to-occur amplitude, encoding the position of coefficients having other than the most likely-to-occur amplitude, the position encoding including encoding events using variable length coding such that on average, events that are more likely to occur are encoded by respective codewords that are shorter than the respective codewords for events that are less likely to occur, the variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context; and

encoding amplitudes of the coefficients having values other than the most likely-to-occur amplitude using variable dimensional amplitude coding in the reverse order of the original ordering of the series,

such that relatively more likely-to-occur sequences of quantized coefficients are represented by relatively short sets of codewords and relatively less likely-to-occur sequences of quantized coefficients are represented by relatively long sets of codewords,

wherein the context is defined by one or more parameters that when encoding a current event are known or derivable from one or more previously encoded events.

2. A method as recited in claim 1, wherein the position coding method is a one-dimensional position coding method.

3. A method as recited in claim 1, wherein the position coding method is a two-dimensional position coding method.

4. A method as recited in claim 1, wherein 0 is the most-likely-to-occur amplitude and 1 is the next most-likely to occur amplitude.

5. A method as recited in claim 1, wherein one or more parameters of the context include the maximum run-length of the most likely-to-occur amplitude.

6. A method as recited in claim 1, wherein one or more parameters of the context include the most recent run-length of the other than the most likely-to-occur amplitude.

7. A method as recited in claim 1, wherein one or more parameters of the context include an indication of the relative frequency of the coefficients being coded.

8. A method as recited in claim 1, wherein the variable dimensional amplitude coding uses a plurality of variable length code mappings that each maps events to codewords, and includes switching between the code mappings based on the context.

9. A method as recited in claim 8, wherein the one or more parameters of the context on which the switching of code mappings is based include the maximum previously encoded amplitude.

10. A computer-readable medium encoded with computer-executable instructions that when executed by one or more processors of a processing system implement a coding method comprising:

for an ordered series of quantized transform coefficients of a block of image data, the series having a most likely-to-occur amplitude, and at least one other amplitude including a next-to-most likely-to-occur amplitude, encoding the position of coefficients having other than the most likely-to-occur amplitude, the position encoding including encoding events using variable length coding such that on average, events that are more likely to occur are encoded by respective codewords that are shorter than the respective codewords for events that are less likely to occur, the variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context; and

encoding amplitudes of the coefficients having values other than the most likely-to-occur amplitude using variable dimensional amplitude coding in the reverse order of the original ordering of the series,

such that relatively more likely-to-occur sequences of quantized coefficients are represented by relatively short sets of codewords and relatively less likely-to-occur sequences of quantized coefficients are represented by relatively long sets of codewords,

wherein the context is defined by one or more parameters that when encoding a current event are known or derivable from one or more previously encoded events.

11. A computer-readable medium as recited in claim 10, wherein the position coding method is a one-dimensional position coding method.

12. A computer-readable medium as recited in claim 10, wherein the position coding method is a two-dimensional position coding method.

13. A computer-readable medium as recited in claim 10, wherein the variable dimensional amplitude coding uses a plurality of variable length code mappings that each maps events to codewords, and includes switching between the code mappings based on the context.

14. An apparatus comprising:

a Context Adaptive Position and Amplitude Coding (CAPAC) encoder operative to encode an ordered sequence of quantized transform coefficients of a block of image data, the sequence having a most likely-to-occur amplitude, and at least one other amplitude including a next-to-most likely-to-occur amplitude, the CAPAC encoder including a position encoder operative to encode the position of coefficients having other than the most likely-to-occur amplitude, the position encoder operative to encode events using variable length coding such that on average, events that are more likely to occur are encoded by respective codewords that are shorter than the respective codewords for events that are less likely to occur, the variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context; and

an amplitude encoder operative to encode amplitudes of the coefficients having values other than the most likely-to-occur amplitude using variable dimensional amplitude coding in the reverse order of the original ordering of the series,

such that relatively more likely-to-occur sequences of quantized coefficients are represented by relatively short sets of codewords and relatively less likely-to-occur sequences of quantized coefficients are represented by relatively long sets of codewords,

wherein the context is defined by one or more parameters that when encoding a current event are known or derivable from one or more previously encoded events.

15. An apparatus as recited in claim 14, wherein the variable dimensional amplitude coding uses a plurality of variable length code mappings that each maps events to codewords, and includes switching between the code mappings based on the context.

16. A method of operating a decoding apparatus, the method comprising:

recognizing codewords in a set of concatenated codewords, the codewords formed by a coding method comprising;

for an ordered series of quantized transform coefficients of a block of image data, the series having a most likely-to-occur amplitude, and at least one other amplitude including a next-to-most likely-to-occur amplitude, encoding the position of coefficients having other than the most likely-to-occur amplitude, the position encoding including encoding events using variable length coding such that on average, events that are more likely to occur are encoded by respective codewords that are shorter than the respective codewords for events that are less likely to occur, the variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context; and

encoding amplitudes of the coefficients having values other than the most likely-to-occur amplitude using variable dimensional amplitude coding in the reverse order of the original ordering of the series,

such that relatively more likely-to-occur sequences of quantized coefficients are represented by relatively short sets of codewords and relatively less likely-to-occur sequences of quantized coefficients are represented by relatively long sets of codewords; and

decoding the recognized codewords using a plurality of code mappings,

wherein the context is defined by one or more parameters that when encoding a current event are known or derivable from one or more previously encoded events.

17. A decoding method as recited in claim 16, wherein the position coding method is a one-dimensional position coding method.

18. A decoding method as recited in claim 16, wherein the position coding method is a two-dimensional position coding method.

19. A decoding method as recited in claim 16, wherein the variable dimensional amplitude coding uses a plurality of variable length code mappings that each maps events to codewords, and includes switching between the code mappings based on the context.

20. A computer-readable medium encoded with computer-executable instructions that when executed by one or more processors of a processing system implement a decoding method comprising:

recognizing codewords in a set of concatenated codewords, the codewords formed by a coding method comprising;

for an ordered series of quantized transform coefficients of a block of image data, the series having a most likely-to-occur amplitude, and at least one other amplitude including a next-to-most likely-to-occur amplitude, encoding the position of coefficients having other than the most likely-to-occur amplitude, the position encoding including encoding events using variable length coding such that on average, events that are more likely to occur are encoded by respective codewords that are shorter than the respective codewords for events that are less likely to occur, the variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context; and

encoding amplitudes of the coefficients having values other than the most likely-to-occur amplitude using variable dimensional amplitude coding in the reverse order of the original ordering of the series,

such that relatively more likely-to-occur sequences of quantized coefficients are represented by relatively short sets of codewords and relatively less likely-to-occur sequences of quantized coefficients are represented by relatively long sets of codewords; and

decoding the recognized codewords using a plurality of code mappings,

wherein the context is defined by one or more parameters that when encoding a current event are known or derivable from one or more previously encoded events.

21. An apparatus for decoding comprising:

a codeword recognizer operative to recognize codewords in a set of concatenated codewords, the codewords formed by a coding method comprising;

for an ordered series of quantized transform coefficients of a block of image data, the series having a most likely-to-occur amplitude, and at least one other amplitude including a next-to-most likely-to-occur amplitude, encoding the position of coefficients having other than the most likely-to-occur amplitude, the position encoding including encoding events using variable length coding such that on average, events that are more likely to occur are encoded by respective codewords that are shorter than the respective codewords for events that are less likely to occur, the variable length coding using a plurality of variable length code mappings that each maps events to codewords, the position encoding including switching between the code mappings based on the context; and

encoding amplitudes of the coefficients having values other than the most likely-to-occur amplitude using variable dimensional amplitude coding in the reverse order of the original ordering of the series,

such that relatively more likely-to-occur sequences of quantized coefficients are represented by relatively short sets of codewords and relatively less likely-to-occur sequences of quantized coefficients are represented by relatively long sets of codewords; and

a codeword decoder operative to decode the recognized codewords, the codeword decoder using a set of code mappings,

wherein the context is defined by one or more parameters that when encoding a current event are known or derivable from one or more previously encoded events.