A cave system for interactive modeling of global illumination in car interior
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A Cave System for Interactive Modeling of Global Illumination in Car Interior. Kirill Dmitriev, Thomas Annen, Grzegorz Krawczyk, Rafal Mantiuk, Karol Myszkowski, and Hans-Peter Seidel Max-Planck-Institut f ür Informatik, Saarbrücken, Germany. Karol Myszkowski. High Dynamic Range.

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A Cave System for Interactive Modeling of Global Illumination in Car Interior

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A Cave System for Interactive Modeling of Global Illumination in Car Interior

Kirill Dmitriev, Thomas Annen,

Grzegorz Krawczyk, Rafal Mantiuk,

Karol Myszkowski, and Hans-Peter Seidel

Max-Planck-Institut für Informatik,

Saarbrücken, Germany

Karol Myszkowski

High Dynamic Range

Human eye adjusts comfortably up to 12 orders of magnitude

and can see simultaneously up to 4 orders of magnitude

HDR Pipeline: Acquisition

  • Global illumination

  • Products: HDR cameras

    • Lars III (Silicon Vision), Autobrite (SMal Camera Technologies), HDRC (IMS Chips), LM9628 (National), Digital Pixel System (Pixim)

  • Technology [Nayar 2003]:

    • Trading-off spatial resolution

      • Multiple sensor elements within pixel

      • Spatially varying pixel exposures

      • Mosaicing with spatially varying filter

    • Trading-off temporal resolution

      • Multi-exposure LDR capture

    • Multiple image detectors (beam splitters)

    • Smart pixels

HDR Pipeline: Storage

  • Several formats for still images

    • Radiance

    • OpenEXR (new industrial standard)

    • logLuv tiff

    • HDR JPEG


HDR Pipeline: Display

  • LDR displays: luminance compression required

    • Solution: tone mapping

    • Important factors in tone mapping selection

      • Dynamic range of display device

      • Video display conditions

        • Background lighting

      • Application

        • Just nice looking video

        • Visually plausible results

        • Optimizing visibility of details

        • Improving contrast …

  • HDR displays start to appear

    • Sunnybrook Technologies and University of British Columbia

HDR Pipeline: Applications

IMS Chips

Realistic Image Synthesis

Light Reflection

Light Transport


Visual Display

Display Observer















Greenberg et al. Siggraph’97. Cornell University

Acquisition: Materials

  • Shift variant Bi-directional Reflectance Distribution Function (BRDF)

    • Lensch et al.

  • Transluscency

    • Goesele et al.

Acquisition: Luminaires

  • Luminaire spatial power distribution (Goesele et al.)

    • Near field photometry

    • Emitted energy represented as 4D light field

      • Relevant for light sources installed in the car interior


VR: rendering

Acquisition: Luminaires

  • Natural lighting

    • Light probes and multi-exposure techniques

    • SpheroCam from Spheron VR

    • Emitted energy represented as an environment map

      • Relevant for external car illumination

Light probe

VR: rendering

Paul Debevec

Lighting Simulation + Rendering

1) Photographs of mirror sphere at varying exposure times

3) Use as light source in Monte

Carlo radiosity algorithm

2) High-dynamic

range environment map

Philippe Bekaert

Our Goal

  • CAVE system for car interior rendering

    • Real-time lighting simulation

    • Dynamic real world lighting

      • HDR video environment maps

    • Free observer position

      • Head tracking

  • Special focus:

    • Predict impact of quickly changing lighting conditions on the visibility of information displayed at the LCD panel

      • Precise modeling of light reflections from the LCD panel

      • Predicting effective contrast and information readability for various viewing angles

      • Taking into account light adaptation conditions for the human eye

Requirements for Rendering Algorithm

  • 5x2 full screen resolution frames at interactive rates

  • LCD panel illumination must be computed precisely

  • Higher error tolerance for the car interior illumination

    • Only low spatial frequencies in reconstructed lighting acceptable

  • Distant lighting assumption holds

    • HDR environment maps acceptable

  • Lighting can change quickly

    • Relying on temporal coherence between frames impractical

  • Car interior geometry static

Rendering Algorithm Selection

  • Requirements

    • Exploit all computational resources available in the CAVE: 20 CPUs + 10 GPUs

  • Rendering solution

    • Use Precomputed Radiance Transfer method for car interior: 10 GPUs + 10 CPUs

    • Use Final Gathering for the LCD panel: 10 CPUs

Spherical Harmonics

  • Spherical Harmonics:

    • Orthonormal basis over the sphere

    • Analogous to Fourier transform

  • Projection:

  • Reconstruction:

  • Integration:

Incident Light



Rendering Equation


Jan Kautz

into SH

into SH

light function:


Precomputed Radiance Transfer

"light vector"

"transfer vector"

Such a dot product must be computed for each mesh vertex: n= 25

Jan Kautz

PRT for Arbitrary Meshes



Handling Two-Sided Geometry

  • Car geometry is two sided

    • Need to store SH coefficients for both sides and render geometry twice with back face culling

    • This leads to lower performance and twice larger memory consumption

  • Better store SH coefficients only for one side of geometry:

    • Only the rays going through the windows contribute to SH coefficients

    • User has to point out the mesh parts representing car windows

LCD Panel Modeling

  • Emission characteristic of the LCD-sandwich:

    • Spectral emission-function of the backlight

    • Transmission characteristic of the polarizer and other layers (e.g. BEF, d-BEF, LCF, rgb-filters, …)

    • Transmission characteristic of the LC-cell

    • Transmission of other optical elements – e.g. glass

  • Reflective characteristic in case of incoming light

    • Surface coating (e.g. AR/AG)

    • Reflection characteristic of the LCD sandwich


Incoming lighting




Computing LCD Panel Lighting

  • DIMOS or SPECTER systems can be used for lighting simulation within the LCD panel

    • We use just external spectral emissivity and reflectance data provided with a very high angular resolution

  • Algorithm

    • Cover geometry of LCD panel with texture

    • For each texel

      • Compute energy emitted in the observer direction

        • Use tabulated emissivity data

        • Modulate emissivity as a function of the displayed information

      • Compute energy reflected in the observer direction

        • Use the final gathering method

        • Improve performance using BRDF-weighted importance sampling

          • If traced ray hits the car window, query the environment map

          • If traced ray hits the car interior, query PRT data structures

System Architecture

Distributing the Computation

  • Use “Lightning” system that takes care of OpenGL synchronization between different PCs

  • LCD display computation is distributed in an asynchronous way

Camera parameters

Distributing the Computation

  • Use “Lightning” system that takes care of OpenGL synchronization between different PCs

  • LCD display computation is distributed in an asynchronous way

Broadcast the display image as it is ready

Tone Mapping in the CAVE

  • Visual adaptation is influenced by light projected on a small area around the center of retina

  • Head tracking enables precise estimation of the gaze direction

    • We assume that the adaptation is affected by scene luminances within the region of 10° surrounding the gaze direction

    • This region can be mapped to 1-3 walls in the CAVE

    • Luminance data within this region is collected and send to the master

  • Master computes common tone mapping parameters and broadcasts them to all computers in the cluster

    • There is a small delay in illumination update, but it is hidden by temporal adaptation model anyway

Rendering with Tone Mapping

  • 3 Passes:

    • Compute tone mapping parameters

      • Preview rendering of 128x128 HDR images for the CPU processing

    • Select visible geometry for tone mapping

      • Lighting OFF

      • Render geometry to z-buffer

    • Final rendering with tone mapping

      • Lighting ON

      • Use z-buffer test to tone map only visible fragments

Results (Car Interior Part)

  • Car model contains approx. 500K triangles

  • Preprocessing of SH coefficients takes about 100 minutes

  • Full model size with SH coefficients is about 60 MB

  • Rendering frame rate is about 10 FPS

    • For each frame current environment map is projected into SH basis and lighting in every vertex is computed

    • Full image tone mapping is applied

Results (LCD Panel Part)

  • One processor on each PC is busy with sending data to OpenGL

  • Another processor computes draft images (40 samples per pixel) of LCD panel and sends them to other PCs

  • Draft image display is available almost immediately after each head movement or environment maps rotation, converged image is computed in approx. 2 seconds


  • We proposed efficient global illumination and tone mapping solutions for CAVE VR applications involving static geometry and dynamic environment lighting

  • We successfully applied those solutions to the car interior modeling, efficiently utilizing all CPUs and GPUs resources on the CAVE cluster

  • We proposed an accurate algorithm for the LCD panel simulation and rendering based on measured BRDF and emission data.

Future work

  • Use HDR video stream as dynamic environment map lighting

    • Trivial to do, we are just waiting for a fish-eye lens suitable for our HDR camera

  • Use HDR display (0.05-3,000 cd/m2) to render the LCD panel with luminance levels similar to real world driving conditions

    • Display-in-display rendering problem

  • Consider recently proposed techniques for all frequency PRT lighting


  • We would like to thank the following people

    • Michael Arnold (Virtual Reality Center, DaimlerChrysler AG)

    • Thomas Ganz (Research & Technology Displays and Controls (RBP/BM), DaimlerChrysler AG)

    • Matthias Bues (VR Lab., Fraunhofer IAO)

Adaptive Logarithmic Tone Mapping

Tone Mapping: Time-Dependent Visual Adaptation

  • Light adaptation

  • Dark adaptation

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