1. Image Repairing: Robust Image Synthesis by Adaptive ND Tensor Voting IEEE Computer Society Conference on Computer Vision and Pattern Recognition Jiaya Jia, Chi-Keung Tang Computer Science Department The Hong Kong University of Science and Technology

2. Motivation Main difficulties to repair a severely damaged image of natural scene –Mixture of texture and colors –Inhomogeneity of patterns –Regular object shapes

3. Motivation Given as few as one image without additional knowledge, we address: –How much color and shape information in the existing part is needed to seamlessly fill the hole? –How good can we achieve in order to reduce possible visual artifact when the information available is not sufficient. Robust Tensor Voting method is adopted

4. Tensor Voting Review Tensors: compact representation of information Tensor encoding: 3D tensor Ball tensor: uncertainty in all directions Plate tensor: certainty of directions in a plate Stick tensor: certainty along two opposite directions

5. Tensor Voting Review Voting process is to propagate local information P Osculating circle

6. Image repairing system Input Damaged Image Texture-based Segmentation Statistical Region Merging Curve Connection Adaptive Scale Selection N ND Tensor Voting Output Repaired Image Complete Segmentation Image synthesis

7. Segmentation JSEG [Deng and Manjunath 2001] –color quantization –spatial segmentation Mean shift [Comanicu and Meer 2002] Deterministic Annealing Framework [Hofmann et al 1998]

8. Texture-based Segmentation

9. Statistical Region Merge (M + 1)D intensity vector for each region P i, where M is the maximum color depth in the whole image. histogramgradient if

10. Why Region Merge? Decrease the complexity of region topology Relate separate regions P1P1 P5P5 P3P3 P4P4 Damaged area P2P2

11. Curve Connection 2D tensor voting method P1P1 P5P5 P3P3 P4P4 P2P2 Z X P2P2 P4P4

12. Why Tensor Voting? The parameter of the voting field can be used to control the smoothness of the resulting curve. Adaptive to various hole shapes Small Scale Large Scale Without hole constraint With hole constraint

13. P4P4 Connection Sequence Topology of surrounding area of the hole can be very complex Greedy algorithm –Always connect the most similar regions P1P1 P5P5 P3P3 Damaged area P2P2 P 2 and P 4 P 3 and P 5 P1P1

14. Complete Segmentation

15. Image repairing system Input Damaged Image Texture-based Segmentation Statistical Region Merging Curve Connection Adaptive Scale Selection N ND Tensor Voting Output Repaired Image Complete Segmentation Image synthesis

16. ND Tensor Voting Tensor encoding –Each pixel is encoded as a ND stick tensor 5 5 Stick tensor Scale N=26

17. ND Tensor Voting Voting process in ND space –An osculating circle becomes an osculating hypersphere. –ND stick voting field is uniform sampling of normal directions in the ND space. sample

18. Adaptive Scaling texture inhomogeneity in images gives difficulty to assign only one global scale N [Lindeberg et al 1996]. For each pixel i in images, we calculate: trace(M) measures the average strength of the square of the gradient magnitude in the window of size N i

19. Adaptive Scaling For each sample seed: –Increase its scale Ni from the lower bound to the upper bound –If trace( ) < trace( ) - α where α is a threshold to avoid small perturbation or noise interference, set Ni - 1 → Ni and return –Otherwise, continue the loop until maxima or upper bound is reached

20. Results

25. Limitations Lack of samples. Meaningful and semi- regular objects.

26. Conclusion An automatic image repairing system. Region partition and merging. Curve connection by 2D tensor voting. ND tensor voting based image synthesis. Adaptive scale.