Physically based Renderers

"Rendering is a fundamental component of Computer Graphics. At the highest level of abstration, rendering is the process of converting a description of a 3d scene into an image."

Matt Pharr, Greg Humpreys in Physically Based Rendering book.

Attempt to simulate reality. And at marketing and sales depts one of the primary goals for promoting a renderprogram.

In this site we suggest that 'physically based renders' tries to live up to the fact that physical laws are used and respected. Nothing more, but nothing less either.

Physically Based Rendering (pbrt) is based on the ray-tracing algorithm. Ray-tracing is an elegant technique that has its origins in lens making:

Carl Friedrich Gauss traced rays through lenses by hand in the 19 th century.


Carl Friedrich Gauss, painting by C.A. Jensen (1792&endash;1870); in the Archiv der Georg-August-Universität, Göttingen, Germany.
He taught himself to read and count by the age of three.


Gaussian Ray Tracing Technique

Carl Friedrich Gauss invented a ray-tracing technique.
A positive lens with two focal points both giving real and virtual images.
He worked both on the physics and the mathematics sides.

An early by-product of fieldwork was the invention of the heliotrope by Gauss, an instrument for reflecting the sun's rays in a measured direction. Meditating on the need for a beacon bright enough to be observed by day, Gauss hit on the idea of using reflected sunlight. After working out the optical theory, he designed the instrument and had the first model built in 1821.

Sunflow rendering


The basic three (3) rules for pbrt


1. I should be complete

2. it should be illustrative

3. it should be physically based


4. see further on

4b. see further on

Complete and Illustrative (1 & 2) gives a tension between those two goals.

The physically based (not mentioning physically correct) renderings are the ones that uses the laws of physics, with their mathmatical expressions.

If different physically based lighting algorithms in pbrt gives different results (!) for the same 3D scene, or gives different outputs with different 'all' physically based render programs, then there must be one or more errors in them. Perhaps it is better to talk about the intension to work following the physically based laws.

The fourth rule is efficiency it is clearly important for stills in high resolution. But even more important in animations because there must be at least 25 frames to produce one second footage and they all to be rendered as stills in a reasonable time.
An add-on is 4b. where we speak about stability. The floating point precision must be repeatable within certain bounderies. And the software must be capable to use a high demand of complexity and large 3D models. The software must behave steady and robust in the compatible platform's with the right hardware).



"In computer graphics, ray tracing is a technique for generating an image by tracing the path of light through pixels in an image plane. The technique is capable of producing a very high degree of photorealism; usually higher than that of typical scanline rendering methods, but at a greater computational cost."



Rendering in Photorealistic modus is to create a 3D scene that is indistinguishable from a photograph. Indistinguishable is just a word, that could be interpreted by human eyes. Every other person can see and interprete such a comparison differently.

So a 'good' ilustration will be the best result to get. There must be some sort of machine discrimination that could be performed and giving the final answer to good, bad and medium illustrations and their differences, regarding physically based or photorealistic renderings. Some progress on this field is on their way, but it seems to be a long windy road.

Book Physically Based Rendering

Physically Based Rendering, Second Edition describes both the mathematical theory behind a modern photorealistic rendering system as well as its practical implementation. A method known as "literate programming" combines human-readable documentation and source code into a single reference that is specifically designed to aid comprehension. The result is a stunning achievement in graphics education. Through the ideas and software in this book, you will learn to design and employ a full-featured rendering system for creating stunning imagery.

This new edition greatly refines its best-selling predecessor by streamlining all obsolete code as well as adding sections on parallel rendering and system design; animating transformations; multispectral rendering; realistic lens systems; blue noise and adaptive sampling patterns and reconstruction; measured BRDFs; and instant global illumination, as well as subsurface and multiple-scattering integrators. These updates reflect the current state-of-the-art technology, and along with the lucid pairing of text and code, ensure the book's leading position as a reference text for those working with images, whether it is for film, video, photography, digital design, visualization, or gaming.

The author team of Matt Pharr, Greg Humphreys, and Pat Hanrahan garnered a 2014 Academy Award for Scientific and Technical Achievement from the Academy of Motion Picture Arts and Sciences based on the knowlege shared in this book.The Academy called the book a "widely adopted practical roadmap for most physically based shading and lighting systems used in film production."


* The book that won its authors a 2014 Academy Award for Scientific and Technical Achievement from the Academy of Motion Picture Arts and Sciences

* New sections on subsurface scattering, Metropolis light transport, precomputed light transport, multispectral rendering, and much more

* Includes a companion site complete with source code for the rendering system described in the book, with support for Windows, OS X, and Linux: visit

* Code and text are tightly woven together through a unique indexing feature that lists each function, variable, and method on the page that they are first described


Resources with the book

Depending on your interests, you may find Luxrender useful: it's a sophisticated physically-based rendering system, originally forked from pbrt. Its goals include physical correctness, building a strong community of users and developers, and providing good support for exporting scenes from applications like Blender.

The Mitsuba renderer may also be of interest: it is a GPL-licensed physically-based rendering system. It features implementations of a number of state-of-the-art light transport algorithms.

Sanmiguel straatje, diverse render afbeeldingen


Scenes with big numbers and counts

How 10.7 million triangles are converted to 2.5 million.


this scene was modeled by Guillermo M. Leal Llaguno of Evolución Visual, based on a hacienda that he visited in San Miguel de Allende, Mexico. The scene was modeled in 3ds Max and exported to the pbrt file format with a custom script written by Guillermo. The scene features just over 2.5 million unique triangles and has a total geometric complexity of 10.7 million triangles due to the use of object instancing; the pbrt files that describe the scene geometry require 620 MB of on-disk storage. There are a total of 354 texture maps, representing 293 MB of texture data.



Content website

  • Introduction
  • Render systems
  • Software & API's
  • Background info
  • Render programs with links
  • Hardware

On this site you see a small preview of the current market august 2015. Where there are strong advocates to use GPU in stead of GPU, but beware of the consequences and try to come to a decision before buying the software of your choice. Beware that prices, type numbers, specifications and even brands may change in the course of time.

Most of this site is in Dutch language

but 35 % is in English, so if you skip the Dutch parts, perhaps you see information that's interest you.

Of course there are fairly good translators on the internet, to translate the textpages in order to read the full contents in your language.

Remarks and add ons? Please send an E-mail with Subject: "Render zone".