Methods and devices for coding and decoding the position of the last significant coefficient
Methods and devices are described for entropy coding data using an entropy coder to encode quantized transform domain coefficient data. Last significant coefficient information is signaled in the bitstream using two-dimensional coordinates for the last significant coefficient. The context for bins of one of the coordinates is based, in part, upon the value of the other of the coordinates. In one case, instead of signaling last significant coefficient information, the number of non-zero coefficients is binarized and entropy encoded.
1. A method for encoding quantized transform domain coefficient data in an encoder having a processor, the method comprising:
determining, with the processor, a first coordinate in a two-dimensional coordinate system and a second coordinate in a two-dimensional coordinate system that together specify a last-significant-coefficient position within a block of the quantized transform domain coefficient data; and
entropy encoding, with the processor, the first coordinate and the second coordinate by determining a context for encoding of one of the coordinates based upon the value of the other of the coordinates.
2. The method claimed in claim 1 , wherein entropy encoding includes binarizing the first coordinate and the second coordinate and entropy encoding each bin of the binarized first coordinate and each bin of the binarized second coordinate.
3. The method claimed in claim 1 , wherein the first coordinate comprises an index to an anti-diagonal line in the block passing through the last-significant-coefficient position, and the second coordinate comprises a position of the last-significant-coefficient on the anti-diagonal line.
4. The method claimed in claim 1 , wherein entropy encoding includes encoding using Huffman codes.
5. The method claimed in claim 4 , wherein encoding includes selecting a Huffman tree containing the Huffman codes, and wherein the selection of the Huffman tree is based at least in part upon a quantization parameter value.
6. The method claimed in claim 1 , further comprising first determining that the first coordinate is zero and second coordinate is non-zero and, as a result, decrementing the value of the second coordinate by one before encoding the second coordinate.
7. An encoder for encoding quantized transform domain coefficient data, the encoder comprising:
a processor;
a memory; and
an encoding application stored in memory and containing instructions that, when executed, cause the processor to
determine a first coordinate in a two-dimensional coordinate system and a second coordinate in a two-dimensional coordinate system that together specify a last-significant-coefficient position within a block of the quantized transform domain coefficient data, and
entropy encode the first coordinate and the second coordinate by determining a context for encoding of one of the coordinates based upon the value of the other of the coordinates.
8. The encoder claimed in claim 7 , wherein the instructions, when executed, cause the processor to entropy encode by binarizing the first coordinate and the second coordinate and entropy encoding each bin of the binarized first coordinate and each bin of the binarized second coordinate.
9. The encoder claimed in claim 7 , wherein the first coordinate comprises an index to an anti-diagonal line in the block passing through the last-significant-coefficient position, and the second coordinate comprises a position of the last-significant-coefficient on the anti-diagonal line.
10. The encoder claimed in claim 7 , wherein the instructions, when executed, cause the processor to entropy encode using Huffman codes.
11. The encoder claimed in claim 10 , wherein the instructions, when executed, cause the processor to select a Huffman tree containing the Huffman codes, and wherein the selection of the Huffman tree is based at least in part upon a quantization parameter value.
12. The encoder claimed in claim 7 , wherein the instructions, when executed, cause the processor to first determine that the first coordinate is zero and second coordinate is non-zero and, as a result, decrement the value of the second coordinate by one before encoding the second coordinate.
13. A method for decoding a bitstream of encoded data to reconstruct quantized transform domain coefficient data in a decoder having a processor, the method comprising:
entropy decoding, with a processor, a portion of the encoded data to reconstruct a first coordinate and a second coordinate that together specify a last-significant-coefficient position within a block of the quantized transform domain coefficient data, including
determining a context for entropy decoding the first coordinate, and
determining a context for entropy decoding the second coordinate based upon the reconstructed value of the first coordinate.
14. The method claimed in claim 13 , wherein entropy decoding includes entropy decoding the bins of a binarized first coordinate and the bins of a binarized second coordinate and reconstructing the first coordinate and the second coordinate from their respective decoded bins.
15. The method claimed in claim 13 , wherein the first coordinate comprises an index to an anti-diagonal line in the block passing through the last-significant-coefficient position, and the second coordinate comprises a position of the last-significant-coefficient on the anti-diagonal line.
16. The method claimed in claim 13 , wherein entropy decoding includes decoding using Huffman codes.
17. The method claimed in claim 16 , wherein decoding includes selecting a Huffman tree containing the Huffman codes, and wherein the selection of the Huffman tree is based at least in part upon a quantization parameter value.
18. The method claimed in claim 13 , further comprising determining that the first coordinate is zero and, as a result, incrementing the value of the reconstructed second coordinate by one after decoding the second coordinate.
19. A decoder for decoding a bitstream of encoded data to reconstruct quantized transform domain coefficient data, the decoder comprising:
a processor;
a memory; and
a decoding application stored in memory and containing instructions that, when executed, cause the processor to
entropy decode a portion of the encoded data to reconstruct a first coordinate and a second coordinate that together specify a last-significant-coefficient position within a block of the quantized transform domain coefficient data, including
determining a context for entropy decoding the first coordinate, and
determining a context for entropy decoding the second coordinate based upon the reconstructed value of the first coordinate.
20. The decoder claimed in claim 19 , wherein the instructions, when executed, cause the processor to entropy decode by entropy decoding the bins of a binarized first coordinate and the bins of a binarized second coordinate and reconstructing the first coordinate and the second coordinate from their respective decoded bins.
21. The decoder claimed in claim 19 , wherein the first coordinate comprises an index to an anti-diagonal line in the block passing through the last-significant-coefficient position, and the second coordinate comprises a position of the last-significant-coefficient on the anti-diagonal line.
22. The decoder claimed in claim 19 , wherein entropy decoding includes decoding using Huffman codes.
23. The decoder claimed in claim 22 , wherein the instructions, when executed, cause the processor to entropy decode by selecting a Huffman tree containing the Huffman codes, and wherein the selection of the Huffman tree is based at least in part upon a quantization parameter value.
24. The decoder claimed in claim 18 , wherein the instructions, when executed, cause the processor to determine that the first coordinate is zero and, as a result, increment the value of the reconstructed second coordinate by one after decoding the second coordinate.