Switch-select single frame reference
Coding techniques for a video image compression system involve improving an image quality of a sequence of two or more bi-directionally predicted intermediate frames, where each of the frames includes multiple pixels. One method involves determining a brightness value of at least one pixel of each bi-directionally predicted intermediate frame in the sequence as an equal average of brightness values of pixels in non-bidirectionally predicted frames bracketing the sequence of bi-directionally predicted intermediate frames. The brightness values of the pixels in at least one of the non-bidirectionally predicted frames is converted from a non-linear representation.
1. A method for inter-frame prediction decoding of a bitstream, the method comprising:
receiving a bitstream at a decoder, the bitstream including a plurality of inter-frame predicted frames, a plurality of intra-frame predicted frames, and a 2-bit code, wherein the 2-bit code designates a previous frame as a reference frame of choice;
selecting, at the decoder, a reference frame from a set of candidate reference frames for forward inter-frame prediction based on the 2-bit code, the set of candidate reference frames comprising at least three referenceable frames;
decoding, by the decoder, a macroblock of a first inter-frame predicted frame by frame reference to the selected reference frame; and
applying a displacement filter to pixel values of the selected reference frame for sub-pixel interpolation, the displacement filter having negative lobes,
wherein the set of candidate reference frames for forward inter-frame prediction includes:
(i) a most recent previous frame in display order from the first inter-frame predicted frame, and
(ii) an intra-frame predicted frame more distant in previous display order than the most recent previous frame from the first inter-frame predicted frame.
2. The method of claim 1 wherein the bitstream includes a 2-bit code for changing the reference frame of choice for each of a plurality of macroblocks of the first inter-frame predicted frame.
3. The method of claim 1 wherein the most recent previous frame is an inter-frame predicted frame.
4. The method of claim 1 wherein the most recent previous frame is an intra-frame predicted frame.
5. A method for inter-frame prediction decoding of a bitstream, the method comprising:
receiving a bitstream at a decoder, the bitstream including inter-frame predicted frames, intra-frame predicted frames, and a code for reference frame selection;
selecting, at the decoder, a reference frame from a set of candidate reference frames for forward inter-frame prediction based on the code, the set of candidate reference frames comprising at least three referenceable frames; and
decoding, by the decoder, a macroblock of a first inter-frame predicted frame by frame reference to the selected reference frame,
applying a displacement filter to pixel values of the selected reference frame for sub-pixel interpolation, the filter having negative lobes,
wherein the set of candidate reference frames for forward inter-frame prediction includes:
(i) a most recent previous frame in display order from the first inter-frame predicted frame, and
(ii) two frames more distant in previous display order than the most recent previous frame from the first inter-frame predicted frame.
6. The method of claim 5 wherein the bitstream includes a 2-bit code for changing the reference frame of choice for each of a plurality of macroblocks of the first inter-frame predicted frame.
7. The method of claim 5 wherein the most recent previous frame is an inter-frame predicted frame.
8. The method of claim 5 wherein the most recent previous frame is an intra-frame predicted frame.
9. A method for inter-frame prediction decoding of a bitstream, the method comprising:
receiving a bitstream at a decoder, the bitstream including a plurality of inter-frame predicted frames, a plurality of intra-frame predicted frames, and a 2-bit switch-select code, wherein the 2-bit switch-select code designates a single previous frame as a reference frame of choice;
selecting, at the decoder, a single reference frame from a set of candidate reference frames for forward inter-frame prediction based on the 2-bit switch-select code, the set of candidate reference frames comprising at least three referenceable frames;
decoding, by the decoder, a macroblock of a first inter-frame predicted frame by frame reference to the selected reference frame; and
applying a displacement filter to pixel values of the selected reference frame for sub-pixel interpolation, the displacement filter having negative lobes,
wherein the set of candidate reference frames for forward inter-frame prediction includes:
(i) a most recent previous frame in display order from the first inter-frame predicted frame, and
(ii) an intra-frame predicted frame more distant in previous display order than the most recent previous frame from the first inter-frame predicted frame.
10. The method of claim 9 wherein the bitstream includes a 2-bit code for changing the reference frame of choice for each of a plurality of macroblocks of the first inter-frame predicted frame.
11. The method of claim 9 wherein the most recent previous frame is an inter-frame predicted frame.
12. The method of claim 9 wherein the most recent previous frame is an intra-frame predicted frame.
13. A method for inter-frame prediction decoding of a bitstream, the method comprising:
receiving a bitstream at a decoder, the bitstream including inter-frame predicted frames, intra-frame predicted frames, and a switch-select code for reference frame selection of a single reference frame;
selecting, at the decoder, a single reference frame from a set of candidate reference frames for forward inter-frame prediction based on the switch-select code, the set of candidate reference frames comprising at least three referenceable frames;
decoding, by the decoder, a macroblock of a first inter-frame predicted frame by frame reference to the selected reference frame; and
applying a displacement filter to pixel values of the selected reference frame for sub-pixel interpolation, the filter having negative lobes,
wherein the set of candidate reference frames for forward inter-frame prediction includes:
(i) a most recent previous frame in display order from the first inter-frame predicted frame, and
(ii) two frames more distant in previous display order than the most recent previous frame from the first inter-frame predicted frame.
14. The method of claim 13 wherein the bitstream includes a 2-bit code for changing the reference frame of choice for each of a plurality of macroblocks of the first inter-frame predicted frame.
15. The method of claim 13 wherein the most recent previous frame is an inter-frame predicted frame.
16. The method of claim 13 wherein the most recent previous frame is an intra-frame predicted frame.