1. Adaptive Context-Based Arithmetic Coding of Arbitrary Contour Maps Armando J. Pinho IEEE SIGNAL PROCESSING LETTERS, VOL. 8, NO. 1,JANUARY 2001

2. Outline Contour Map Differential Chain-Coding Transition Point Experimental Results Conclusion

3. Contour Map

4. DIFFERENTIAL CHAIN- CODING r 1, c 1, s 1 1, s 1 2,…, s 1 n1, …, r k, c k, s k 1, s k 2,…, s k nk (r i, c i ) denotes a pair of image coordinates marking the start of a chain s i j represent the construction of the chains

5. DIFFERENTIAL CHAIN- CODING (con’t) Two type of Contour map : Closed and Open Closed Contours –There are four instructions of s i j : A (go-Ahead) L (turn-left) R (trun-right) + (ramification)

6. DIFFERENTIAL CHAIN- CODING (con’t) Example ： –0,1,L,R,+,A,A,R,+,A,L,L,+,L,A,A,L,R, 3,3,+,A,A,L,R,A

7. DIFFERENTIAL CHAIN- CODING (con’t) Open Contours –An additional instruction is required indicating end-of-chain A (go-Ahead) L (turn-left) R (trun-right) + (ramification) - (end of chain)

8. DIFFERENTIAL CHAIN- CODING (con’t) Example ： –0,2,A,+,A,+,R,-,+,A,A,L,R,L,+,R,A,L,A,A,2,0,-

9. TRANSITION POINT Four symbols {V,H,C,  } =>

10. TRANSITION POINT(con’t) At beginning of each row or column ， the pen is up While moving across a row ， the pen changes state (up to down or down to up) if it encounters a corner or a horizontal transaction point (C or H) While moving across a column ， the pen changes state (up to down or down to up) if it encounters a corner or a horizontal vertical point (C or V)

11. TRANSITION POINT(con’t) Adaptive CAE(context-based arithmetic encoder) compression methods : (a) Context are calculated in the domain of transition point (Ar-Tr) ， there are 4 6 possible contexts (b) Context are calculated in the domain of contour map (Ar-Ct) ， there are 2 8 possible contexts

12. EXPERIMENTAL RESULTS “couple “ image into 9327 regions(55519 active contour elements)

13. EXPERIMENTAL RESULTS(con’t) Number of active contour elements(x1000) 20 40 60

14. EXPERIMENTAL RESULTS(con’t) Number of active contour elements(x1000)

15. Conclusion The proposed method behaves better than differential chain code or on the MPEG-4 shape coder. Compression efficiency increases when the contour complexity increases.