1. VIZARD II: A Reconfigurable Interactive Volume Rendering System WSI / GRIS, Universität Tübingen ‡ Philips Research, Hamburg † Viatronix *ATI M. Meißner †, U. Kanus, G. Wetekam, J. Hirche, A. Ehlert, W. Straßer, M. Doggett*, P. Forthmann ‡, and R. Proksa ‡

2. WSI/GRIS, University of Tübingen 09/02/2002 Overview Motivation Features System RPU Results & Future Work Acknowledgments

3. WSI/GRIS, University of Tübingen 09/02/2002 Motivation Need for interactive frame rates, the highest possible image quality, interactive change of parameters, and different rendering modes. Learn from PC graphics (& from keynote): Software (CPU) scales only with Moore’s Law but hardware can additionally scale by implementing the full algorithm (pipeline) in hardware and possibly parallel pipelines (SIMD)

4. WSI/GRIS, University of Tübingen 09/02/2002 Motivation However, hardware (ASIC) is expensive, pays out only for large quantities, and change/ adaption in design requires new fabrication. Thus, combine the performance of special purpose hardware with (almost) the flexibility of a software solution using reconfigurable logic (FPGA). Board can be re-used for other applications, e.g. volume reconstruction (Philips)

5. WSI/GRIS, University of Tübingen 09/02/2002 Overview Motivation Features System RPU Results & Future Work Acknowledgments

6. WSI/GRIS, University of Tübingen 09/02/2002 Features Rays are cast from viewplane: Flexible sampling rate Trilinear interpolation Post-classification Per sample Phong shading High precision compositing Acceleration Techniques: Geometry based space leaping Early ray termination

7. WSI/GRIS, University of Tübingen 09/02/2002 Features Ensure high(est) image quality by: unlimited ray-casting including parallel and perspective projections complex gradient filters mandatory for correct GM (  gradient as per voxel property) Left: Original volume rendering Right: Central difference, GM (>1), result depends on object orientation due to non symmetric gradient filter

8. WSI/GRIS, University of Tübingen 09/02/2002 Features Ensure high(est) image quality by: full classification with material properties on a per sample base additional interval based classification mode (pre-integration) and accurate combination with Phong shading [Meissner et al. GI2002]

9. WSI/GRIS, University of Tübingen 09/02/2002 Overview Motivation Features System RPU Results & Future Work Acknowledgments

10. WSI/GRIS, University of Tübingen 09/02/2002 System Memory interface: Trilinear interpolation requires eight Voxels in parallel. Ideally, one would like to have eight memory devices For more flexibility, use exchangeable DIMMs instead of single SDRAM devices DIMM modules are large in physical size and come in 64 data bits, thus use four – eight would not fit anyway - and store two voxel values ( 32 bit each ) in one entry.

11. WSI/GRIS, University of Tübingen 09/02/2002 Cubic memory organization: Volume is partitioned in sub-cubes and stored in linear memory (4 DIMMs, 64 bit) DIMM 0 DIMM 1 DIMM 2 DIMM 3 32x32x32 Voxel fit into Caches of 4 DIMMs --> ideal access time (e.g. 10ns) System Replication

12. WSI/GRIS, University of Tübingen 09/02/2002 Non blocking access using prefetching: Delay of page x-ings can be overlapped in time. [Doggett et al. HWW1999] Time No Yes System

13. WSI/GRIS, University of Tübingen 09/02/2002 PCI Interface System bus PCI bus Ray casting DIMM Xilinx Virtex SRAM PCI card (long!) System DSP SDRAM Ray Setup Host computer

14. WSI/GRIS, University of Tübingen 09/02/2002 DIMMs Reconfigurable chip (FPGA) DSP PCI interface chip Power supply and converters SRAM System

15. WSI/GRIS, University of Tübingen 09/02/2002 Overview Motivation Features System RPU Results & Future Work Acknowledgments

16. WSI/GRIS, University of Tübingen 09/02/2002 RC RPU Central unit of VIZARD II is the RPU: AU DIMMs TIU SU bandwidth is criticalRPU CU SRAMs Combine BU High frequency is challenging Sample props / pre-integration

17. WSI/GRIS, University of Tübingen 09/02/2002 Compositing @ 100 MHz is a challenge: Opacity: A i+1 = A i + (1-A i ) * A s Inverse, multiply and subsequent Add of two 16 bit values is not feasible in 10ns Use Threading: One compositing unit, multiple processed rays [Hesser VG ’99] RPU: Compositing

18. WSI/GRIS, University of Tübingen 09/02/2002 Iteratively process n rays instead of one: >= Eight rays allow frequency of 100 MHz + Better memory efficiency (overall less page x- ings) + Higher efficiency of early ray termination (overall pipeline latency is “divided” by number of rays)  Use early ray group termination RPU: Compositing RCBU

19. WSI/GRIS, University of Tübingen 09/02/2002 Overview Motivation Features System RPU Results & Future Work Acknowledgments

20. WSI/GRIS, University of Tübingen 09/02/2002 Results Physical Design (~2 million gates) Memory-Controller(s)CU & SUBU RC & AU TIU DSP-I/O

21. WSI/GRIS, University of Tübingen 09/02/2002 Results

22. WSI/GRIS, University of Tübingen 09/02/2002 Results DEMO

23. WSI/GRIS, University of Tübingen 09/02/2002 Results VIZARDII VolumePro TexMap Pipelines,@MHz 1@50 4@250 4@300 Speed 3-7 >= 30 <=10 Perspective yes (no) (yes) Precision 16 12 8-10 iso-surface yes no (yes) Pre-integrated yes no (yes) ERT & Co yes yes (no)

24. WSI/GRIS, University of Tübingen 09/02/2002 Results Flexibility: Dual use of the same board!!! Philips Research developed a design for volume reconstruction from projected images (C-arm CT, currently at 50 MHz) 1. Reconstruction in 1 min (SW > 30 min) 2. Subsequently interactive volume rendering of reconstructed data

25. WSI/GRIS, University of Tübingen 09/02/2002 Future Work On-chip ray setup: Remove current bottleneck of system Space Leaping: “Content based” real-time check of contributing 16 3 subcubes (50x per second) [Meissner et al. VG2001] Non-photorealistic rendering: Technical drawings

26. WSI/GRIS, University of Tübingen 09/02/2002 Overview Motivation Features System RPU Results & Future Work Acknowledgments

27. WSI/GRIS, University of Tübingen 09/02/2002 Acknowledgements Work: Fellows and many many students Funding: German Research Council (DFG), grant 382

28. WSI/GRIS, University of Tübingen 09/02/2002 Conclusion Graphics Hard ware