[Update on 2011-02-15] The 12-tap DCT-based interpolation filter (high efficiency configuration) and 6-tap directional interpolation filter (low complexity configuration) for 1/4 luma sample will be replaced by 8-tap DCT-based interpolation filter for both HE and LC (JCTVC-D344) in the upcoming HM2.0. In addition, the bilinear interpolation filter for 1/8 chroma sample will be replaced by 4-tap DCT-based interpolation filter (JCTVC-D347) in the HM2.0.

Tools adopted in HM0.9 include 12-tap DCT-based interpolation filter (high efficiency configuration) and 6-tap directional interpolation filter (low complexity configuration) for 1/4 luma sample, bilinear interpolation filter for 1/8 chroma sample (both HE and LC), advanced motion vector prediction, bi-direction rounding control, bi-directional prediction for temporal level 0.

12-tap DCT-based Interpolation Filter for luma (HE)

Motion compensation is the key factor for high efficient video compressing, where fractional pel accuracy requir[......]

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Permanent Link: Analysis of Coding Tools in HEVC Test Model (HM 1.0) – Inter Prediction

Why use interpolation in video coding?  

Motion-compensated prediction (MCP) is the key to the success of the modern video coding standards, as it removes the temporal redundancy in video signals and reduces the size of bitstreams significantly. With MCP, the pixels to be coded are predicted from the temporally neighboring ones, and only the prediction errors and the motion vectors (MV) are transmitted. However, due to the finite sampling rate, the actual position of the prediction in the neighboring frames may be out of the sampling grid, where the intensity is unknown, so the intensities of the positions in between the integer pixels, called sub-positions, must be interpolated and the resolution of MV is increased accordingly.  

Interpolation in H.264/AVC  

In H.264/AVC, for the resolution of MV is quarter-pixel, the reference frame is interpolated to be 16 times the size for MCP, 4 times both sides. As shown in Fig. 1(a), the interpolation defined in H.264 includes two stages, inter[......]

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Permanent Link: Adaptive Interpolation Filter for Video Coding

The technique of 1/8-pel interpolation [AD09] was proposed for motion-compensated prediction (MCP) and adopted in KTA software. Three types of interpolation filters are used for 1/2-, 1/4-, and 1/8-pel sub positions, respectively.

• [-3, 12, -39, 158, 158, -39, 12, -3]/256 for 1/2-pel sub positions.
• [-3, 12, -37, 229, 71, -21, 6, -1]/256 and [-1, 6, -21, 71, 229, -37, 12, -3]/256 for 1/4-pel sub positions.
• Bilinear filter for 1/8-pel sub positions.

  The frequency response of the interpolation filter is shown in the following figure. As can be seen, it is almost an ideal low-pass filter with a gain of 8 and a cutoff frequency π/8.

  According to the performance reported in the proposal, the gain on CIF/QCIF sequences is quite significant, i.e., up to 14% bit-rate reduction. I tested this technique based on a set of HD sequences. As shown in Table 1, the R-D performance is measured by BDPSNR [1], i.e., PSNR improvement at the same bit-rate or bit-rate reduction at the same PSNR.

 

 

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Permanent Link: R-D Performance of 1/8-pel MCP on HD Sequences