Ray Tracing Gallery

To cast or not to cast?What's new?Ray TracingMinimumTeapotContact


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To cast or not to cast?

Since I got my hands on a reasonable microprocessor I made some experiments with raytracing. At that time it was a Motorola 68000 clocked at 8 MHz and I was running the PRT ray tracer (or was it DKB Trace?). I now use Persistence of Vision on a 1.7 MHz Pentium IV microprocessor.

Bellow are some renderings of scenes I created over the years. I'll try to dig old scenes, and show them here.

I am the author of all the pictures showcased on this document. They are licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 2.0 France License. If you want to use any of the this material in a way that is prohibited by this license free free to contact me to discuss your plans.

What's new?

2005-09-07
A rendition of the classic Utah Teapot was added.
2005-08-30
This is the first inception of this gallery.

Minimum (2005)

1,000 × 1,000 pixels
(PNG, 609,683 bytes)

This image is available as a poster at Zazzle.

Creative Commons License

This scene was conceived for the July–August 2005 round of the Internet Raytracing Competition. This session's topic was minimalism:

Extreme simplification of form, action, or concept. Any thing, process, or idea that has been trimmed down to its barest essentials. Either your entry can be minimalist, or can be a depiction of something “minimal”, or both.
I like the works of some minimalist artists, are they expressing themselves through sculptures (Constantin Brâncuşi), or music (Steve Reich). The usually simple shapes of this kind of works led me to think that I could eventually throw enough craft and computation power to compete at the IRTC. The result was the scene titled minimum, it is a minimalistic and surrealist rendering that was simple to build as it is based on an idea that was already developed in print.

Here is some excerpts of the companion file that was submitted to the contest along the image:

This image is an evolution of a design I used as a unique seasons greetings card. That card was sent to a friend following a discussion we had about how I use the word "minimum" to evaluate some qualities or defects of non-decorative type faces. The greetings card had that word set almost as it is in the present image, it also had a signature.

[...]

We're dealing here with raytracing so I could not only lay a flat word on a plane, it had to protrude somehow in order to cast shadows. These are deep shadows, that's a deliberate choice at they permit to render the word with a maximum effect on the viewer using only a very limited number of features on the image.

[...]

Povray version 3.6 was used to render the image. The word is just a Povray text object using the Bubbleboy type face as geometry source. This type face was designed by Jakob Fischer. Unfortunately that font file missed some of the tables used by Povray to access glyphs. I had to regenerate the font file using FontForge. I also had to make a minor change to the font: the designer did align all curved letters on the baseline. Designing letters this way generates unwanted visual effects: the word appeared unevenly aligned, it looked as if the U letter was shifted upward. Again FontForge was used to tailor the font. The font was specially chosen for that scene from the set of freely available fonts of the DaFont repository.

The lighting is very simple: just one spherical area light. I made some tests with a second source to lighten the shadows. That move revealed itself as a bad one as it lessened the effect of the picture even when that second light was configured to cast no shadows.

The scene use radiosity even if the influence on the picture is barely visible. That effect is nevertheless important as it creates a lighting difference between the top of the letters and the underlying plane. Without radiosity the top curves appears to blend with the background and that's not desirable.

Initially the background plane had just a plain white pigment. When the image was rendered at higher resolutions, the different shades of gray appeared as concentric circles due to the limited number of grays representable using 8-bit numbers. That was not acceptable. However there is an easy trick to overcome this limitation: add some noise. This tricks the eye and the brain to see more shades of gray than there actually is in the image. Several texture tests were made and I settled for a agate-based normal perturbation for both the text and the supporting plane: this looks almost as paper illuminated by a skimming light. Considered the origin of the scene idea I thought that was a bonus.

[...]

The area light is another source of intensive computation. I wanted the scene to have absolutely smooth penumbras to contrast the sharpness of the word and the deep shadows between the letters legs. The smoothness of penumbras is directly related to the number of sub-samples used for the area light. Unfortunately the smoothness is also an inversely related to the rendered image size: when penumbras surface raises, one must also raise the number the area light sub-samples to avoid banding effects.

The exact rendering time is unknown as I rendered the same scene three times with decreasing resolutions, each one benefiting from the radiosity calculations accumulated by the previous run. The image submitted to the contest was the last being rendered. Another source of imprecision on the rendering time is Povray itself because of a feature I view as a bug: it reports wall clock durations!

Teapot (1997)

800 × 364 pixels
(PNG, 230,732 bytes)

This image is available as a poster at Zazzle.

Creative Commons License

No descent ray tracing gallery should be without a scene showing a teapot but no common teapot will suffice, only the Utah Teapot is acceptable. This kitchen utensil has reached an iconic status as it was the first model widely available to synthetic imaging researchers at a time when 3D modelers were not yet invented.

The scene I set the teapot in is really simple: it is a box. To enhance the iconic value of the picture I textured the environment with a plain dull checkered tile and made all objects slightly reflective. Both of these qualities were also common in early ray traced images. I don't remember where I got the dataset here represented nor what format it was in but I do remember that I had to write a quick program to convert it to the rayshade syntax.

The picture shown here was obtained using rayshade. It was re-rendered especially for this gallery as the file I kept was not anti-aliased. This was done on an 1.7 GHz Pentium IV host with the anti-alias settings at their maximums, it took 34 minutes for the 800 × 364 pixels. The image available in print at Zazzle spent 20 hours and 52 minutes of CPU time at a resolution of 5,500 × 2,500 pixels.

A few word should be said about the picture aspect ratio. When this scene was modeled I was fascinated by large format cinematography. I had the chance to view in their original format in a wonderful Paris theater many of the films that were produced on 65 mm negatives. Among theses, three chef d'œuvre stand out: 1. 2001: A Space Odyssey by Stanley Kubrick (1968); 2. Playtime by Jacques Tati (1967); and 3. Baraka by Ron Fricke (1992). The cinematographic processes used by those films are unsurpassed and as a tribute I decided to use the 2.2 aspect ratio of the Todd-AO process.

Contact

Questions, bug reports, advices, etc. are welcome. Please mail your queries to < irtc at phoe dot frmug dot org >. Note that things such as HTML e-mails, word documents, etc. will be blindly discarded. Patches sent as unified diffs are preferred over any other format.

If you value your privacy you can send OpenPGP-crypted mails, the author's key whose id is 0606CEF7 is available on public keyrings such as the MIT PGP Public Key Server or directly here. Be sure that the fetched the key you obtained has the following fingerprint:

79C9 10C8 9C3A 3F35 482F  06D6 150B A8BB 0606 CEF7


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      4.0!Valid CSS! Bertrand Petit <irtc \at phoe \dot frmug \dot org>
2005-09-07