introduction to shape coding. outline introduction shape coding approaches –block-based methods...
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Introduction to
Shape Coding
Outline
Introduction Shape Coding Approaches
– Block-based methods• CAE, Modified MMR, …..
– Contour-based methods• Chain code, BBSC (baseline-based) , …..• Vertex-based binary shape coding
Conclusions
Introduction
Why shape coding? Binary Alpha Plane
– describes the shape of one VOP
Akiyo
QCIF format (176 x 144)
Introduction
Shape coding modes– Intra mode ( I VOPs)– Inter mode ( P, B VOPs)
Lossy coding Progressive (scalable encode)
CAE method (1)
Context-based Arithmetic Encoding Intra mode
BAB :Binary Alpha BlockSize : 16 x 16 pixels
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
CAE method (3)
Inter modeCoding mode Coding type
0 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
CAE method (4)
InterCAE
CAE method (5)
Lossy coding
Conversion Ratio (CR) : ¼, ½ or 1
downsampling
upsampling
MxCR
MxCR
M
M
conversion error
M
M
CAE method (6)START
N
SET CR=1/4
END
Y
N
Y
SET CR=1
SET CR=1/2
There is at least one Error-PB in MB
There is at least one Error-PB in MB
Contour_based method (1)
Chain code
Contour_based method (2)
DCC (differential chain code)– encode the differential between two
consecutive directional links DCC with Huffman Coding Characteristics of one contour
Contour_based method (3)
EBDCC
Contour_based method (4)Starting point
Turning points
Contour_based method (5)
The decoder should know– The starting point of tracing– Locations of turning points– Sequences (one bit per step)
Contour_based method (6)
Compression results for intra coding
MPEG-4 Our method
Akiyo 574 542
Bream2 771 606
weather 519 563
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
Contour_based method (8)
563 bits / per VOP 497 bits / per VOP
Contour_based method (9)
Scalable shape representation– TPs are important information!
TPs Seq. (1/2)
Seq. (additional)
Local TPs & seq.
Contour_based method (10)
H : 9 V : 7
H’ : 5 V’ : 4
Conclusions
Block-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