Video coder providing implicit coefficient prediction and scan adaptation for image coding and intra coding of video
A predictive video coder performs gradient prediction based on previous blocks of image data. For a new block of image data, the prediction determines a horizontal gradient and a vertical gradient from a block diagonally above the new block (vertically above a previous horizontally adjacent block). Based on these gradients, the encoder predicts image information based on image information of either the horizontally adjacent block or a block vertically adjacent to the new block. The encoder determines a residual that is transmitted in an output bitstream. The decoder performs the identical gradient prediction and predicts image information without need for overhead information. The decoder computes the actual information based on the predicted information and the residual from the bitstream.
1. A method of decoding MPEG-4 video signals, the method comprising:
determining a first gradient between a DC coefficient DC A of a block A, horizontally adjacent to and left of a block X, and a DC coefficient DC B of a block B, vertically adjacent to and above the block A;
determining a second gradient between DC B and a DC coefficient DC C of a block C vertically adjacent to and above the block X;
when the first gradient is less than the second gradient, generating a quantized DC coefficient DC X for the block X by adding a quantized differential DC coefficient for the block X to a quantized DC coefficient of block C; and
otherwise, generating the quantized DC coefficient DC X for the block X by adding the quantized differential DC coefficient for the block X to a quantized DC coefficient of block A.
2. The method of claim 1 , wherein the quantized differential DC coefficient is received from an MPEG-4 video bitstream.
3. The method of claim 1 , further comprising:
when an AC prediction is used as indicated by a received AC prediction flag:
if the first gradient is less than the second gradient, predicting a first row of AC coefficients in the block X from a co-located first row of AC coefficients in the block C to yield a predicted first row of AC coefficients;
otherwise, predicting a first column of AC coefficients in the block X from a co-located first column of AC coefficients in the block A to yield a predicted first column of AC coefficients; and
generating quantized AC coefficients by adding a received first row of quantized differential AC coefficients in the block X to a quantized set of the predicted first row of AC coefficients or adding a received first column of quantized differential AC coefficients in the block X to a quantized set of the predicted first column of AC coefficients.
4. The method of claim 1 , wherein the blocks A, B, and C are inside a boundary of a video object plane containing the block X.
5. The method of claim 1 , wherein the generating the quantized DC coefficient DC X is performed independently for blocks of luminance data and for blocks of chrominance data.
6. The method of claim 1 , further comprising selecting a scan order for the block X based on whether the quantized DC coefficient DC X is generated using the quantized DC coefficient DC A from the block A or the quantized DC coefficient DC C from the block C.
7. A non-transitory computer-readable storage medium storing instructions which, when executed by a decoder, cause the decoder to perform operations of decoding MPEG-4 video signals, the operations comprising:
determining a first gradient between a DC coefficient DC A of a block A, horizontally adjacent to and left of a block X, and a DC coefficient DC B of a block B, vertically adjacent to and above the block A;
determining a second gradient between DC B and a DC coefficient DC C of a block C vertically adjacent to and above the block X;
when the first gradient is less than the second gradient, generating a quantized DC coefficient DC X for the block X by adding a quantized differential DC coefficient for the block X to a quantized DC coefficient of block C; and
otherwise, generating the quantized DC coefficient DC X for the block X by adding the quantized differential DC coefficient for the block X to a quantized DC coefficient of block A.
8. The non-transitory computer readable storage medium of claim 7 , wherein the quantized differential DC coefficient is received from an MPEG-4 video bitstream.
9. The non-transitory computer readable storage medium of claim 7 , the operations further comprising:
when an AC prediction is used as indicated by a received AC prediction flag:
if the first gradient is less than the second gradient, predicting a first row of AC coefficients in the block X from a co-located first row of AC coefficients in the block C to yield a predicted first row of AC coefficients;
otherwise, predicting a first column of AC coefficients in the block X from a co-located first column of AC coefficients in the block A to yield a predicted first column of AC coefficients; and
generating quantized AC coefficients by adding a received first row of quantized differential AC coefficients in the block X to a quantized set of the predicted first row of AC coefficients or adding a received first column of quantized differential AC coefficients in the block X to a quantized set of the predicted first column of AC coefficients.
10. The non-transitory computer readable storage medium of claim 7 , wherein the blocks A, B, and C are inside a boundary of a video object plane containing the block X.
11. The non-transitory computer readable storage medium of claim 7 , wherein the generating the quantized DC coefficient DC X is performed independently for blocks of luminance data and for blocks of chrominance data.
12. The non-transitory computer readable storage medium of claim 7 , the operations further comprising selecting a scan order for the block X based on whether the quantized DC coefficient DC X is generated using the quantized DC coefficient DC A from the block A or the quantized DC coefficient DC C from the block C.
13. A decoder for decoding MPEG-4 video signals, the decoder comprising:
a processor;
a first module configured to control the processor to determine a first gradient between a DC coefficient DC A of a block A, horizontally adjacent to and left of a block X, and a DC coefficient DC B of a block B, vertically adjacent to and above the block A;
a second module configured to control the processor to determine a second gradient between DC B and a DC coefficient DC C of a block C vertically adjacent to and above the block X;
a third module configured, when the first gradient is less than the second gradient: to generate a quantized DC coefficient DC X for the block X by adding a quantized differential DC coefficient for the block X to a quantized DC coefficient of block C; and
otherwise, to generate the quantized DC coefficient DC X for the block X by adding the quantized differential DC coefficient for the block X to a quantized DC coefficient of block A.
14. The decoder of claim 13 , wherein the quantized differential DC coefficient is received from an MPEG-4 video bitstream.
15. The decoder of claim 13 , further comprising:
a further module, when an AC prediction is used as indicated by a received AC prediction flag, configured to control the processor:
if the first gradient is less than the second gradient, to predict a first row of AC coefficients in the block X from a co-located first row of AC coefficients in the block C to yield a predicted first row of AC coefficients;
otherwise, to predict a first column of AC coefficients in the block X from a co-located first column of AC coefficients in the block A to yield a predicted first column of AC coefficients; and
to generate quantized AC coefficients by adding a received first row of quantized differential AC coefficients in the block X to a quantized set of the predicted first row of AC coefficients or adding a received first column of quantized differential AC coefficients in the block X to a quantized set of the predicted first column of AC coefficients.
16. The decoder of claim 13 , wherein the blocks A, B, and C are inside a boundary of a video object plane containing the block X.
17. The decoder of claim 13 , wherein the third module configured to generate the quantized DC coefficient DC X further generates the quantized DC coefficient DC X independently for blocks of luminance data and for blocks of chrominance data.
18. The decoder of claim 13 , further comprising a fourth module configured to control the processor to select a scan order for the block X based on whether the quantized DC coefficient DC X is generated using the quantized DC coefficient DC A from the block A or the quantized DC coefficient DC C from the block C.