Thanks for visiting! This site is a brief portfolio of my work into global illumination and realistic image synthesis.

The following is a case study of a simple scene with a short description of each step of the design process. This example is designed to demonstrate various types of complex light transport including caustic and sub-surface scattering. Specifically, a novel photon mapping approach developed as part of my research is used to achieve high quality global illumination.

Update: The image was chosen as the winner of the 2009 Computer Graphics Forum cover competition and will appear on the front of all this year's issues of the journal.

 

The finished render
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Modeling in 3ds Max
The original concept of the scene was to highlight a contrast between the elegant, minimalist geometry of a glass sphere and the complex, organic surface of a leaf. A texture map was created by scanning in a real leaf and applying colour correction and post processing in Photoshop. Red highlights were then selectively added to create a more visually pleasing, analogous colour palette. A garment mesh was used for the leaf surface, perturbed using a fractal noise function and curved inward to suggest fragility and decay.


The finished diffuse texture map
 
The scene in a 3ds Max viewport


Designing the Materials
After creating the basic geometry in Max the materials were specified using Igneus' XML-based scene definition language. The glass sphere was rendered using a shader which ray traces dielectrics; in this case, glass. Igneus is also capable of handling more complex effects such as dispersion which accurately simulates materials such as diamond. However, we found that a basic model of refraction produced the best result with less visual distraction.


Direct illumination only
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Igneus's SSS model
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The organic material that makes up the leaf proper required a more complex shader since light needed be both be reflected and scattered below the surface. The fact leaves are so thin meant that a special shader had to be created to handle scattering through a film interface. The render above shows the result rendered using direct illumination from a large area light. In this state, several components of the illumination integral are missing which makes the render seem synthetic and unrealistic.

 

Adding Global Illumination
The next step was to introduce global illumination to add depth and realism to the scene. I used a specially designed two-pass photon mapping technique to achieve these effects.


Relaxed photon map
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Caustics only
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The above render is an isolated caustic illumination pass showing light that has been transmitted specularly then reflected diffusely (known as SDS illumination). The soft glow below the leaf and the focused caustic from the ball are both rendered using illumination stored in the caustic photon map. After casting 3,000,000 photons, we processed the resulting map using our new technique. By relaxing the photons into a distribution with a blue noise spectral signature, we were able to achieve high quality radiance estimates using comparatively few photons. This approach allows both high- and low-frequency caustics to be rendered with virtually zero variance.

 

The Finished Image
By compositing the previous two passes together, we obtained the final, finished render. Notice how the translucent leaf transmits light that has been scattered into the surface, reflected off the background plane, then bounced out again. A Reinhard tone mapping operator was applied to even out the luminosity across the image, creating a more natural, even feel to the illumination.

 

Alternative Versions
This second scene was created after the orginal's submission and uses a more decayed version of the texture together with a broken and eroded glass sphere. The surface of the glass has been roughened causing the caustic to appear blurred and diffused. Subtle depth of field blur has also been applied to give a macro lens-like effect. Some post-processing in Photoshop helped to bring out the vivid oranges and yellows around the veins in the leaf that were lost by the Reinhard tone mapping.


Decayed leaf
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About Me
My name is Ben Spencer. I'm a postgraduate student currently completing the final year of a PhD in computer graphics at Swansea University. The focus of my research has been global illumination and physically-based rendering, specifically enhancement of the popular photon mapping algorithm developed by Henrik Jensen. I have also explored the fields of computational fluid dynamics and its potential for rendering effects such as smoke and fire, as well as complex flow visualisation using streamlines.

I am interested in all aspects of computer graphics including graphic design, non-photorealistic rendering, compositing, image processing, visalisation and on- and off-line rendering. My ultimate ambition is to work in the VFX industry in research and development, helping extend the techniques and technologies used to realise cinematic special effects.

To further explore the techniques behind these images, please visit my research homepage where electronic copies of my papers are available to download together with a short biography.