VIZARD II: VIZARD II: A Reconfigurable Interactive A Reconfigurable Interactive Volume Rendering SystemVolume 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‡

WSI/GRIS, University of Tübingen

09/02/2002

OverviewOverview

• Motivation

• Features

• System

• RPU

• Results & Future Work

• Acknowledgments

WSI/GRIS, University of Tübingen

09/02/2002

MotivationMotivation

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)

WSI/GRIS, University of Tübingen

09/02/2002

MotivationMotivation

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)

WSI/GRIS, University of Tübingen

09/02/2002

OverviewOverview

• Motivation

• Features

• System

• RPU

• Results & Future Work

• Acknowledgments

WSI/GRIS, University of Tübingen

09/02/2002

FeaturesFeatures

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

WSI/GRIS, University of Tübingen

09/02/2002

FeaturesFeatures

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

WSI/GRIS, University of Tübingen

09/02/2002

FeaturesFeatures

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]

WSI/GRIS, University of Tübingen

09/02/2002

OverviewOverview

• Motivation

• Features

• System

• RPU

• Results & Future Work

• Acknowledgments

WSI/GRIS, University of Tübingen

09/02/2002

SystemSystem

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.

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)

DIMM0

DIMM1

DIMM2

DIMM3

32x32x32 Voxel fit into Caches of 4 DIMMs --> ideal access time (e.g. 10ns)

SystemSystem

Replication

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

SystemSystem

WSI/GRIS, University of Tübingen

09/02/2002

PCI Interfac

e

System bus

PCI bus

Ray casting

DIMMXilinx

Virtex

SRAM

PCI card (long!)

SystemSystem

DSP

SDRAM

Ray Setup

Host

com

pu

ter

WSI/GRIS, University of Tübingen

09/02/2002

DIMMs

Reconfigurable chip (FPGA)DSP

PCI interface chip

Power supplyand converters

SRAM

SystemSystem

WSI/GRIS, University of Tübingen

09/02/2002

OverviewOverview

• Motivation

• Features

• System

• RPU

• Results & Future Work

• Acknowledgments

WSI/GRIS, University of Tübingen

09/02/2002

RC

RPU

Central unit of VIZARD II is the RPU:

AU

DIMMs

TIU

SU

bandwidth iscritical

RPURPU

CU

SRAMs

Com

bin

e

BU

High frequency is challenging

Sample props /pre-integration

WSI/GRIS, University of Tübingen

09/02/2002

Compositing @ 100 MHz is a challenge:

Opacity: Ai+1 = Ai + (1-Ai) * As

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: CompositingRPU: Compositing

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: CompositingRPU: Compositing

RC BU

WSI/GRIS, University of Tübingen

09/02/2002

OverviewOverview

• Motivation

• Features

• System

• RPU

• Results & Future Work

• Acknowledgments

WSI/GRIS, University of Tübingen

09/02/2002

ResultsResults

Physical Design (~2 million gates)

Memory-Controller(s)

CU & SU BU

RC & AU TIU

DS

P-I

/O

WSI/GRIS, University of Tübingen

09/02/2002

ResultsResults

WSI/GRIS, University of Tübingen

09/02/2002

ResultsResults

DEMO

WSI/GRIS, University of Tübingen

09/02/2002

ResultsResults

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)

WSI/GRIS, University of Tübingen

09/02/2002

ResultsResults

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

WSI/GRIS, University of Tübingen

09/02/2002

Future WorkFuture Work

On-chip ray setup: Remove current bottleneck of system

Space Leaping: “Content based” real-time check of

contributing 163 subcubes (50x per second) [Meissner et al. VG2001]

Non-photorealistic rendering: Technical drawings

WSI/GRIS, University of Tübingen

09/02/2002

OverviewOverview

• Motivation

• Features

• System

• RPU

• Results & Future Work

• Acknowledgments

WSI/GRIS, University of Tübingen

09/02/2002

AcknowledgementsAcknowledgements

Work:

•Fellows and many many students

Funding:

•German Research Council (DFG), grant 382

WSI/GRIS, University of Tübingen

09/02/2002

ConclusionConclusion

Graphics

Hardware