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Outline
 Introduction
 Macroblock partition analysis
 Partition type decision
 Partition type distribution
 Experimental result
 Conclusion
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Introduction
 Goal:
 To retain high visual quality of foreground (FG) region.
 To achieve low bit-rate background (BG) coding.
 Proposed method:
 Using different RD λ value for FG/BG region.
 Heuristically assign macroblock partition types for video
foreground and background coding.
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introduction
 For the efficiency of encoding pictures in H.264, 16 × 16
skip type MB for P-frame and 16 × 16 direct type MB for
B-frame are introduced.
 For selecting a suitable partition, an RD optimization
criterion defined by :
where B: macroblock, : the reconstruction MB after
decoding, Q: quantization parameter.
 resulting in costly search in deciding a MB partition.
 λ is set to balance distortions and rates.
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Partition Type Decision
 The decision process of MB partitions can be significantly
simplified if the FG/BG segmentations of a video sequence
are obtained.
 To heuristically assign appropriate MB partitions to
encode the FG/BG MBs in the inter-prediction process.
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Partition Type Distribution (1/4)
 To achieve a quality-oriented coding process optimal-λ RD
optimization
 A small λ is set for foreground MBs.
 A large λ value is used for background blocks.
 The FG and BG masks for image frames are manually
marked.
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Partition Type Distribution (2/4)
 Experimental settings:
 Each MB having at least a foreground pixel is marked as
foreground.
 59 image frames of each video sequence are encoded in the
order of IBPBPBI…..
 The default QP value is set to 28.
 The default λ parameter are = 27.41 for I- and P- frames
and = 73.11 for B-frames.

is set for foreground, and
is for the
background.
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Partition Type Distribution (3/4)
 The block size of I4x4 are used most to generate high
quality intra-coded MBs for I-frames.
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Partition Type Distribution (4/4)
 The P-frame and B-frame block partition type distribution:
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proposed scheme
 For I-frame
 Choose I4×4 for foreground and I16×16 for background.
 For P-frame and B-frame
 Choose 16×16 MB size, skip for P-frame, direct 16×16 for Bframe to yield low bit-rate background compressions.
 Using different λF and λB.
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Experimental result (1/4)
 Three methods are compared:
 the standard RD optimization
 the optimal-λ RD optimization
 the proposed scheme
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Experimental result (2/4)
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Experimental result (3/4)
 For I-frames, though the size of I4×4 gives better coding
quality for the foreground, the adoption of partition size
I16×16 is somehow not decisive for background coding
size reduction.
 Even the optimal-λ method can only lower the coding
sizes by a very small amount.
 For intra predictions, block size settings are not a major
factor to compression sizes.
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Experimental result (4/4)
 The comparisons of :
 the entire encoding time
 the average PSNR for FG
 the total BG bit size
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Contribution and conclusion
 Coding FG, BG with different λ parameters.
 optimal-λ method
 Heuristic assignment of macroblock partition types.
 Once a more specific compression objective is given,
exhausted searches for best macroblock partitions may
not be required.
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