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Introduction to Shape Coding
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Outline Introduction Shape Coding Approaches Conclusions
Block-based methods CAE, Modified MMR, ….. Contour-based methods Chain code, BBSC (baseline-based) , ….. Vertex-based binary shape coding Conclusions
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Introduction Why shape coding? Binary Alpha Plane
describes the shape of one VOP Akiyo QCIF format (176 x 144)
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Introduction Shape coding modes Lossy coding
Intra mode ( I VOPs) Inter mode ( P, B VOPs) Lossy coding Progressive (scalable encode)
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CAE method (1) Context-based Arithmetic Encoding Intra mode BAB :
Binary Alpha Block Size : 16 x 16 pixels
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CAE method (2) Binary arithmetic encoding using the context of the neighboring pixels A template of ten pixels is used to predict the current pixel
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CAE method (3) Inter mode MVDs=0 & no inter update 1
Coding mode Coding type MVDs=0 & no inter update 1 MVDs!=0 & no inter update 2 Transparent (all 0) 3 Opaque (all 255) 4 Intra CAE 5 MVDs=0 & inter coded 6 MVDs!=0 & inter coded
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CAE method (4) InterCAE
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CAE method (5) Lossy coding Conversion Ratio (CR) : ¼, ½ or 1
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CAE method (6)
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Contour_based method (1)
Chain code
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Contour_based method (2)
DCC (differential chain code) encode the differential between two consecutive directional links DCC with Huffman Coding Characteristics of one contour
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Contour_based method (3)
EBDCC
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Contour_based method (4)
Starting point Turning points
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Contour_based method (5)
The decoder should know The starting point of tracing Locations of turning points Sequences (one bit per step)
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Contour_based method (6)
Compression results for intra coding MPEG-4 Our method Akiyo 574 542 Bream2 771 606 weather 519 563
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Contour_based method (7)
Lossy coding Reduce the number of TPs ! The slope between two neighboring TPs is compared with Hori_TH : viewed as a horizontal line Vert_TH : viewed as a vertical line
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Contour_based method (8)
563 bits / per VOP 497 bits / per VOP
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Contour_based method (9)
Scalable shape representation TPs are important information! TPs Seq. (1/2) Seq. (additional) Local TPs & seq.
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Contour_based method (10)
H : 9 V : 7 H’ : 5 V’ : 4
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Conclusions Block-based method Contour-based method
High coding efficiency Suitable for hardware implementation Irregular boundary effect & blocking effect Contour-based method Smaller blocking effect on the reconstructed shape Suitable for specific application where semantic shape features are utilized Hardware optimization
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