1. Smart Hardware-Accelerated Volume Rendering Stefan Roettger Stefan Guthe Daniel Weiskopf

2. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Overview Current State of the Art in Direct Volume Rendering What can be improved? Segmentation HW Raycasting

3. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Direct Volume Rendering 3D Slicing Approach (Akeley) Pre-Integration (Roettger ‘00, Engel ‘01) Material Properties (Meissner ‘02) Hardware-Accelerated Pre-Integration (Roettger ‘02, Guthe ‘02) Volume Clipping (Weiskopf ‘02)

4. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen What is missing? From a medical point of view: Pre-integration is difficult to apply to segmented medical data Pre-integration quality is still not good enough 8 bit frame buffer produces artifacts

5. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Pre-Integration Ray integral depends on three variables: S f, S b, and l, where l is assumed to be constant Pre-compute a table for all combinations of S f and S b and store in 2D dependent texture

6. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Volume Clipping Use additional 3D clip volume C(x,y,z) Iso surface defines clip geometry Adjust S f, S b, and l according to clip volume for the case C f <0.5<C b w = |C b -0.5 |/|C b -C f | S’ f = (1-w)*S b +w*S f l’= l*w C=0.5

7. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Pre-Integrated Segmentation Segmentation of two materials Define second transfer function In the pixel shader: Make a lookup in TF1 for the blue area Blend with the lookup in TF2 for the grey area C=0.5

8. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Quality Comparison with naive clipping with correct adjust- ment clipped Bonsai

9. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Supersampling Quality

10. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Supersampling Quality

11. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Supersampling Quality

12. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Supersampling Quality

13. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Supersampling Quality

14. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Supersampling Quality

15. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Drawback of Pre-Integration Linear interpolation assumed in slab But in fact the interpolation is trilinear Inside the slab one may cross a voxel boundary Lighting is also non-linear Conclusion: For superior quality one needs at least 2-times, better 4-times oversampling

16. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Ray Casting Supersampling is slow, but fortunately we do not need to supersample everywhere Define importance volume which tells where to sample more precisely Depends on 2nd derivative of scalar volume and 1st derivative of TF Perform adaptive ray casting on the graphics hardware

17. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Hardware-Accelerated Ray Casting Can be done on the ATI Radeon 9700 with multiple floating point render targets: Need to process all pixels at once Cannot exploit ray coherence Early ray termination by hierarchical Z-test Adaptive sampling includes space leaping Stop if all pixels are terminated (asynchronous occlusion query)

18. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Hardware-Accelerated Ray Casting Store ray parameter to determine actual position Complete PS 2.0 code given in the paper

19. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Quality Comparison 4-times oversampling 8 bit frame buffer HW ray casting full floating point RT

20. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Performance Same performance as 4 times over-sampling But much better quality (about 2s/frame)

21. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen ANTSCD: Bonsai Examples Note: Raw data of all three Bonsai is available on my homepage

22. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Conclusions With respect to quality HW Raycasting is superior to the traditional slicing approach By reducing the number of adaptive samples interactive frame rates can be achieved easily without compromising quality Now switching to Stefan Guthe who has preparerd THE LIVE DEMO

23. Smart Hardware-Accelerated Volume Rendering - VisSym ‘03, Grenoble Stefan Roettger, University of Erlangen - Stefan Guthe, University of Tübingen Fin Thanks for your attention! For further reading see my home page: GoogleBeHappy: ”Stefan Roettger”