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1. (CA2839704) METHOD AND APPARATUS FOR MOTION COMPENSATION PREDICTION
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CLAIMS:
1. A video decoding method for motion compensation performed under an inter-
frame prediction, the method comprising computer executable steps executed by a processor of a video decoder to implement: retrieving samples from a reference picture memory, wherein the samples stored in the reference picture memory are represented with a first bit depth; determining a scaling-up factor for scaling up a sample bit depth from the first bit depth to a second bit depth which is higher than the first bit depth and constant, regardless of the first bit depth of the samples, wherein the second bit depth is set equal to a number of bits available to represent the sample, and the scaling-up factor is set equal to the number of bits available to represent the sample minus the first bit depth of the sample; applying a first fractional sample interpolation subjected to a scaling-up operation with the determined scaling factor on the retrieved samples in a first direction to generate a first set of fractional samples represented with the second bit depth; applying a second fractional sample interpolation on the first set of fractional samples in a second direction to generate a second set of fractional samples represented with the second bit depth; and clipping and scaling down a prediction sample comprising the first and second sets of fractional samples from the second bit depth to the first bit depth.
2. The method according to claim 1, wherein the fractional sample interpolation applies an 8-tap FIR (Finite Impulse Response) filter having one of the following three sets of coefficients to generate a quarter-pel sample: [-1, 4, -10, 58, 17, -5, 1, 0]; [-1, 4, -11, 40, 40, -11, 4, -1]; and [0, 1, -5, 17, 58, -10, 4, -1].
3. The method according to claim 2, wherein the fractional sample interpolation comprises truncating each filtered result so that the fractional samples are represented with the second bit depth.
4. The method according to claim 3, wherein the second bit depth is maintained throughout the first and second fractional interpolation processes.
5. The method according to claim 3, wherein truncating each filtered result
comprises rounding truncated results towards minus infinity.
6. The method according to claim 1, further comprising subtracting an offset from the scaled up samples.
7. A video encoding method for motion compensation performed under an inter-
frame prediction, the method comprising computer executable steps executed by a processor of a video encoder to implement: retrieving samples from a reference picture memory, wherein the samples stored in the reference picture memory are represented with a first bit depth; determining a scaling-up factor for scaling up a sample bit depth from the first bit depth to a second bit depth which is higher than the first bit depth and constant, regardless of the first bit depth of the samples, wherein the second bit depth is set equal to a number of bits available to represent the sample, and the scaling-up factor is set equal to the number of bits available to represent the sample minus the first bit depth of the sample; applying a first fractional sample interpolation subjected to a scaling-up operation with the determined scaling up factor on the scaled-up samples in a first direction to generate a first set of fractional samples represented with the second bit depth; applying a second fractional sample interpolation on the first set of fractional samples in a second direction to generate a second set of fractional samples represented with the second bit depth; and
clipping and scaling down a prediction sample comprising the first and second sets of fractional samples from the second bit depth to the first bit depth.
8. The method according to claim 7, wherein the fractional sample interpolation applies an 8-tap FIR (Finite Impulse Response) filter having one of the following three sets of coefficients to generate a quarter-pel sample: [-1, 4, -10, 58, 17, -5, 1, 0]; [-1, 4, -11, 40, 40, -11, 4, -1]; and [0, 1, -5, 17, 58, -10, 4, -11.
9. The method according to claim 8, wherein the fractional sample interpolation comprises truncating each filtered result so that the fractional samples are represented with the second bit depth.
10. The method according to claim 9, wherein the second bit depth is maintained throughout the first and second interpolation processes.
11. The method according to claim 9, wherein truncating each filtered result comprises rounding truncated results towards minus infinity.
12. The method according to claim 7, further comprising subtracting an offset from the scaled up samples.