Apparatus and method for lossless coding and decoding

1. A lossless coding apparatus, the apparatus comprising:

an extraction unit to extract a context of a first symbol among sequential symbols based on a value of a preceding symbol among the sequential symbols;

a determination unit to determine a group including the extracted context among a plurality of context groups, wherein at least one of the plurality of context groups is generated by grouping a plurality of different contexts based on a probability of each of the plurality of contexts such that when a probability difference between a first context and a second context is smaller than a predetermined threshold value, the determination unit includes the first context and the second context in an identical context group;

a memory to store a probability model corresponding to each of the plurality of context groups; and

an encoder to encode the first symbol and generate a bitstream, based on the probability model and the determined group.

2. The apparatus of claim 1 , wherein a number of the plurality of context groups is generated to be smaller than a number of different contexts to reduce an amount of memory space needed to store the plurality of context groups.

3. The apparatus of claim 1 , further comprising:

a re-indexing table to store re-indexing information about the sequential symbols; and

a re-indexing unit to re-index the first symbol and to generate a second symbol, based on the stored re-indexing information and the extracted context, wherein the encoder encodes the second symbol and generates the bitstream.

4. The apparatus of claim 1 , wherein the extraction unit extracts the context of the first symbol based on a second symbol existing in an identical location to the first symbol among previous frames of the first symbol and a third symbol, which is a previous symbol of the first symbol.

5. The apparatus of claim 1 , wherein the probability model is determined based on a frequency of occurrence of each symbol during training of the sequential symbols.

6. A lossless decoding apparatus, the apparatus comprising:

an extraction unit to extract a context of a first bitstream among serial bitstreams from a previously decoded symbol, wherein the extraction unit extracts the context of the first bitstream based on a preceding bitstream among the serial bitstreams;

a determination unit to determine a group including the extracted context from among a plurality of context groups, wherein at least one of the plurality of context groups is generated by grouping a plurality of different contexts based on a probability of each of the plurality of contexts such that when a probability difference between a first context and a second context is smaller than a predetermined threshold value, the determination unit includes the first context and the second context in an identical context group;

a memory to store a probability model corresponding to each of the plurality of context groups; and

a decoder to decode the first bitstream and to generate a first symbol, based on the probability model and the determined group.

7. The apparatus of claim 6 , wherein a number of the plurality of context groups is generated to be smaller than a number of different contexts to reduce an amount of memory space needed to store the plurality of context groups.

8. The apparatus of claim 6 , further comprising:

a re-indexing table to store re-indexing information about the first symbol; and

a re-indexing unit to re-index the first symbol, and to generate and output a second symbol based on the stored re-indexing information and the extracted context.

9. The apparatus of claim 6 , wherein the extraction unit extracts the context of the first bitstream based on a second bitstream existing in an identical location to the first bitstream among previous frames of the first bitstream and a third bitstream, which is a previous bitstream of the first bitstream.

10. A lossless coding method, the method comprising:

extracting a context of a first symbol among sequential symbols based on a value of a preceding symbol among the sequential symbols;

determining a group including the extracted context from among a plurality of context groups, wherein at least one of the plurality of context groups is generated by grouping a plurality of different contexts based on a probability of each of the plurality of contexts such that when a probability difference between a first context and a second context is smaller than a predetermined threshold value, the first context and the second context are included in an identical context group;

reading a probability model corresponding to each of the plurality of context groups in a memory; and

encoding the first symbol and generating a bitstream, based on the probability model and the determined group.

11. The method of claim 10 , further comprising:

estimating a probability corresponding to each of a plurality of contexts;

grouping each of the plurality of contexts based on the estimated probability and generating the plurality of context groups.

12. The method of claim 10 , further comprising:

reading re-indexing information in a re-indexing table, which stores re-indexing information about the sequential symbols; and

re-indexing the first symbol and generating a second symbol, based on the extracted context and the read re-indexing information,

wherein the coding of the first symbol and generating of the bitstream encodes the second symbol instead of the first symbol and generates the bitstream.

13. The method of claim 10 , wherein the extracting of the context of the first symbol extracts based on a second symbol existing in an identical location to the first symbol among previous frames of the first symbol and a third symbol, which is a previous symbol of the first symbol.

14. At least one non-transitory medium comprising computer readable code to control at least one processing element in a computer to implement the method of claim 10 .

15. A lossless decoding method, the method comprising:

extracting a context of a first bitstream among serial bitstreams from a previously decoded symbol, wherein the context of the first bitstream is extracted based on a preceding bitstream among the serial bitstreams;

determining a group including the extracted context among a plurality of context groups, wherein at least one of the plurality of context groups is generated by grouping a plurality of different contexts based on a probability of each of the plurality of contexts such that when a probability difference between a first context and a second context is smaller than a predetermined threshold value, the first context and the second context are included in an identical context group;

reading a probability model corresponding to each of the plurality of context groups in a memory; and

decoding the first bitstream and generating the first symbol, based on the probability model and the determined group.

16. The method of claim 15 , further comprising:

estimating a probability corresponding to each of a plurality of contexts; and

grouping each of the plurality of contexts and generating the plurality of context groups based on the estimated probability.

17. The method of claim 15 , further comprising:

reading re-indexing information in a re-indexing table, which stores re-indexing information about the first symbol;

re-indexing the first symbol and generating a second symbol, based on the extracted context and the read re-indexing information; and

outputting the second symbol.