1. Adapting Wavelet Compression to Human Motion Capture Clips Philippe Beaudoin 1 Pierre Poulin 1 Michiel van de Panne 2 1 Université de Montréal, LIGUM 2 University of British Columbia, Imager

2. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 2 A need for compression? Motion capture is very popular Motion capture rapidly produces huge collections of data Escalating cost of the memory hierarchy (ie. Martin Walker talk)  Lossy compression

3. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 3 What is a good compression? Depends on the application We aim for: –Small cache footprint –Access to subset of joint data –Accurate foot placement –Independent motion clips Best ratio may not be the target

4. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 4 Which kind of compression? Joint correlation –2:1 up to 4:1 (PCA) Joint + temporal coherence –Cannot access individual signals –30:1 up to 35:1 [Arikan 06] Temporal coherence alone –35:1 (this work) –Access to subset of joint data –Low computational requirements

5. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 5 Preliminary details… A pose is… –Root position (3 signals) –Euler angles of joints (59 signals) Motion is sampled at 120 hz No preprocessing or format conversion before compression

6. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 6 Standard wavelet compression Cubic interpolating bi-orthogonal wavelet basis [Sweldens 98] Not specially targeted to motion capture

7. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 7 Standard wavelet compression Wavelet transform 62 signals Keep the largest coefficients from all the transformed signals Yield vector w i (1 ≤ i ≤ 62) counting how many coefficients are kept for each signal

8. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 8 Vector w i

9. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 9 Optimized coefficient selection w i minimizes RMS error in the DOF Quality depends much more on positional distortion Optimally redistribute coefficients? –Too costly!

10. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 10 Optimized coefficient selection Motion capture data is hierarchical Build vector m i that favors some signals more than others Fixed choice for m i ? Bad! –Depends on complexity of signals –Depends on the poses

11. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 11 Start with m i = w i

12. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 12 Randomly select i reduce m i

13. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 13 Find optimal j increase m j Repeat…

14. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 14 Inverse kinematics correction Problem: Noticeable sliding feet Change distortion metric? –Assumption breaks down, difficult to find a good m i Instead, add positional channels for the feet, use IK

15. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 15 Inverse kinematics correction Signals encode difference between compressed position and true feet position Wavelet compress these signals independently

16. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 16 Final details… Quantize to 16 bits Run-length encode 0s Optionally use lempel-ziv independently on each clip

17. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 17 Results Tested on 1 sec. to 45 sec. clips Compression ≈ 300 ms/frame Decompression ≈ 30 μs/frame(no IK) ≈ 300 μs/frame(with IK)

18. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 18 Video

19. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 19 Conclusion Tractable coefficient search space adapted to motion capture data Fast decompression Access to subset of joints Independent clips 35:1 compression ratio

20. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 20 Future Work Metric for perceived quality in a motion capture animation Explore large-scale redundancies (see our technical report) Level-of-detail streaming

21. Adapting Wavelet Compression to Human Motion Capture Clips Beaudoin, Poulin, van de Panne – Graphics Interface 2007 21 Questions?