Radiance vs. YouNameIt

1   Introduction

Q: What is Radiance?

A: Instead of describing in my own words what Radiance is, let me provide the information, where to find it, and which documents or which book you should read.

Rendering with Radiance The Art and Science of Lighting Visualization By Greg Ward Larson and Rob A. Shakespeare, with contributions from Peter Apian-Bennewitz, Charles Ehrlich, John Mardaljevic, and Erich Phillips Copyright © 1998 by Morgan Kaufmann Publishers You can order the book e.g. via Amazon, but to get started you might just want to download and install the software to start experimenting with it. There are pre-compiled executables for Mac OS X, but I didn't have a problem to compile them myself from the source code provided there (same for Linux).

Q: Why Radiance vs. YouNameIt ?

A: It's basically a comparison of Radiance with other renderers which are able to render a scene with global illumination (GI). Radiance is around for a long time but still can be used to describe a scene and accurately simulate how incoming light (e.g. from the sun and other light sources) will illuminate it. You will also realize that there wouldn't be HDR imaging (HDRI) around without this renderer and people who discovered it's usefulness. The HDRI Handbook was written by a friend of mine and is available in several languages.

Q: What can we learn here?

A: First of all about rendering in general, but more from a user perspective (in contrast to teaching you how to write your own renderer). I will also provide little tools for reading the Radiance scene description for some simple examples (scenes shipping with the book) and to convert them into other scene descriptions (either to bring them into a modelling system, or to convert directly to a file which can be rendered with another renderer).

2   Simple Scene

From the Radiance book web site you can download chapter 1 as a PDF file and there are also several compressed files (scene[0-2].tar.Z) which contain the three scenes I will talk about. Please read and compare with chapter 1.3 (called 'Scene 0 Tutorial' ).

As you can see in the screenshot above I do use Houdini from Side Effect Software as one of the modelling systems to experiment with alternative renderers. But let's first focus on some commands and images described in the tutorial mentioned above.

2.1   Radiance

The scene is as simple as it can get for global illumination. The tutorial starts with two spheres, one which we will look at, the other one to illuminate the scene (acting as a light source). So here are the three commands I used the render the image below:

% oconv room0.rad > test.oct
% alias rview /usr/local/bin/rview
% rview -vp 2.25 .375 1 -vd -.25 .125 -.125 -av .5 .5 .5 test.oct

The scene isn't that impressive yet, but let's shortly describe what's going on. The first command takes the scene description and converts it to an octree (an acceleration structure for the renderer). The second command isn't really necessary if your system finds the command rview, which comes with the Radiance installation, first. Unfortunately on my computer it finds a command with the same name first, which actually starts Vim . The interesting bit of the third command, which starts an interactive viewer, is that the scene description itself does not contain a camera. So your view point (option vp) and the view direction (option vd) are specified via the command line (or will be read via a file). The tutorial in the book actually has some more intermediate steps but I will omit them here. Basically it explains the usage of genbox, a generator program to create a simple box, adds two boxes to the scene (the inner box acts as a table, the outer box as the room we are in), adds a rod to connect the light source to the ceiling, changes materials and re-renders a couple of times by re-creating the octree and starting the interactive viewer. The following example reads the view point and direction from a file:

% oconv room3.rad > test.oct
% rview -vf default.vf -av .5 .5 .5 test.oct

After adding a window by cutting a whole into one of the walls of the outer box the tutorial describes how to use the special-purpose generator gensky . It also defines a window material which lets sun light into the room (see bright spot on the floor):

% gensky 3 20 10 -a 40 -o 98 -m 105 > sky.rad
% oconv sky.rad outside.rad window.rad room.rad > test.oct
% rview -vf default.vf -av .5 .5 .5 test.oct

But beside the visibility of the window and the sun light cast on the floor within the glass sphere the picture looks still pretty much the same. We need to modify the rendering commands to use another description of the window's glass material, which actually makes it act like a secondary light source.

% oconv sky.rad outside.rad srcwindow.rad room.rad > test.oct
% rview -vf default.vf -av .5 .5 .5 test.oct

Now we see some extra shadows cast on the wall and the sun light contributes to the illumination of the room.

The rest of the tutorial is about how to automate the rendering process and adding a simple outdoor scene which should have an impact on the indoor scene. Here is the first command using an outside ground plane and a nearby building with one indirect bounce for the light coming through the window.

% rad -o x11 inter.rif

As you can see the shadows which do not come from the indoor spherical light source are much more diffuse, but the rendering time goes up a lot. To compensate for that there is another RIF file, which does not use interreflections but uses a program called mkillum "to create a modified window file that uses calculated data values to define its light output distribution."

% rad -o x11 illum.rif

But this looks pretty similar to the result we had using no outdoor scene. So let's use mental images' imf_diff program to visualize the difference between those two images:

On the left side you see the difference in absolute color values (which is hard to see), on the right side there is a false color representation, where blue to green indicates only small differences, whereas red to white means huge differences (see histogram on top). Let's do the same for the diffuse shadows vs. the hard shadows created by the different RIF files:

For convenience here is a little text file (called render_scene0_book.txt ) which can be used to render all examples coming with chapter one from a shell by simple “sourcing” it. Simply save it in the scene0 folder you downloaded above (once you uncompressed and “un-tarred” the scene0.tar.Z file). It prints a single echo line what you can expect from the rendering (done with the interactive viewer rview):

% source render_scene0_book.txt

There is another text file (called render_scene0_filt.txt )) which is used to re-render two images (one using inter.rif, the other using illum.rif) in higher resolution and scale them down, essentially filtering them to avoid aliasing.

% source render_scene0_filt.txt

Here are the resulting images:

Here some simple tests regarding tonemapping and how renderers deal with overexposed images. The following text file (called render_scene0_cams.txt )) was used to generate images from the same scene from different camera views:

% source render_scene0_cams.txt

Here are the resulting images:

2.2   Arnold

2.3   Cycles

2.4   Maxwell

Be careful to export vertex normals (e.g. with OBJ files) for smooth objects (like the sphere) before you bring in the geometry in Maxwell's Studio application.

2.5   Indigo

2.6   Luxrender

The first image was rendered without the window glass. For the other images architectural glass was used.

2.7   Vray

2.8   Lagoa

2.9   Mitsuba

2.10   Octane Render

2.11   iray

2.12   Mantra

For Mantra you can use primitives (like a sphere or tube) instead of polygons or NURBS. For light emitting geometry that seems to make a huge difference, as you can see in the following images (The first uses imported OBJ files, the second one uses primitives):

After setting up a daylight system and a portal for the window the result looks like this:

2.13   Povray

2.14   mental ray

2.15   Yafray

TODO: Ask on forum how to tweak some render parameters and material settings to get good results.

3   Changing Lights

3.1   Radiance

Using *.rif files improved the quality of the resulting Radiance images a lot (in comparison to the settings mentioned in the Radiance book).

3.2   Arnold

To render more efficiently with Arnold I replaced the light emitting spheres behind the lenses (lights on the wall) with point lights using the same radius. The light emitting disks (ceiling) were replaced by disk lights. The light emitting objects were rendered separately (without GI) and composed over the GI image (otherwise the disks would not be visible).

Using point and spotlight instead of light emitting geometry saves a lot of rendering time. The point lights could use a radius as well, but this should be closer to what Radiance does. The left image renders in about an hour, the right one in approx. 15 minutes.

3.3   Cycles

3.4   Maxwell

3.5   Indigo

3.6   Luxrender

Using my own exporter for Luxrender:

The second image uses linear tonemapping (ISO 640, shutter 0.067, f-stop 5.6, gamma 2.2). The weights for bulbf and lens are 100 and 10.

3.7   Vray

To render more efficiently with Vray I replaced the light emitting spheres behind the lenses (lights on the wall) with point lights using the same radius. The light emitting disks (ceiling) were replaced by (square) area lights. The light emitting objects were rendered separately and composed over the GI image (otherwise the disks would be visible as squares).

Left:

1. Color mapping: Gamma 2.2, Linear workflow, Clamp output
2. Image sampler: Adaptive subdivision (min -2, max 3), Object outline, Normals (0.05), Randomize samples
3. Global Illumination: Primary engine (Light cache), Secondary engine (Light cache), Limit ray distance (40)
4. Light Cache: Subdivs (1000), Sample size (0.01), World, do not store direct light, Filter Nearest

Tracing 62500 (250x250) image samples for light cache in 8 passes.

Light cache contains 416 samples (Sample size 1.0)

Light cache contains 4595 samples (Sample size 0.1)

Light cache contains 10253 samples (Sample size 0.01)

Tracing 250000 (500x500) image samples for light cache in 8 passes.

Light cache contains 9238 samples (Sample size 0.1)

Light cache contains 37687 samples (Sample size 0.01)

Light cache contains 41988 samples (Sample size 0.001)

Tracing 1000000 (1000x1000) image samples for light cache in 8 passes.

Light cache contains 14840 samples (Sample size 0.1)

Light cache contains 130139 samples (Sample size 0.01)

Light cache contains 162845 samples (Sample size 0.001)

Use light cache marked with bold font and filter it: Filter Nearest 1000 Samples, Pre-filter 100

Right:

1. Color mapping: Gamma 2.2, Linear workflow, Clamp output
2. Image sampler: Adaptive subdivision (min -2, max 3), Object outline, Normals (0.05), Randomize samples
3. Global Illumination: Primary engine (Light cache), Secondary engine (Light cache), Limit ray distance (40)
4. Light Cache: Subdivs (1000), Sample size (0.01), World, do not store direct light, no filters

The three round lights were rendered separately and composited above the square area lights, because V-Ray doesn't support disk lights.

3.8   Lagoa

3.9   Mitsuba

3.10   iray

3.11   Mantra

3.12   Povray

4   The Art Gallery

I added a grey ground object outside of the building which wasn't in the original scene description because different renderers did react differently to the daylight simulation outside of the building. Some do only simulate the sky color, other allow to define a ground color. In any case what would you expect if you look through a glass door or window and there is nothing outside? So, to make the rendered images more consistent I added a geometry outside with a grey material.

4.1   Radiance

For longer rendering times it's handy to know that you can send the process into the background and ask on demand for a status report. First you use the ampersand to send the process to the background. Then you have to find out the process number of the rpict command (not the rad command). Once you got the process ID (PID) you can use the kill command with an option (to continue) to get a status report. For example:

% rad scene2n.rif &
% ps -ef | grep rpict
PID
% kill -CONT PID

4.2   Arnold

4.3   Cycles

4.4   Maxwell

1. ISO: 800, 1/Shutter: 250.0, Burn: 0.2, Monitor Gamma: 2.2, Intensity: 1.0
2. ISO: 400, 1/Shutter: 250.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 10000.0
3. ISO: 800, 1/Shutter: 125.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 1.0
4. ISO: 800, 1/Shutter: 500.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 10000.0
5. ISO: 800, 1/Shutter: 30.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 10.0
6. ISO: 100, 1/Shutter: 1000.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 1.0
7. ISO: 800, 1/Shutter: 10.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 1.0
8. ISO: 100, 1/Shutter: 1000.0, Burn: 0.8, Monitor Gamma: 2.2, Intensity: 1.0

The sign at the wall uses kind of a gold material but it allows to change the color (which was used in the original Radiance scene).

4.5   Indigo

For the tapestry glass pieces I had to export the scene from Blender 2.57b and adjust the medium (not the material) settings within Indigo (3.0.14). To get the right colors I used the color within Blender (using the original color values), switched to HSV and adjusted the value to 1.0. The resulting RGB values were inverted for Indigo's medium settings and the brightness was adjusted to 200 (for all glass medium settings).

1. Prescale: 4.0, Postscale: 1.2, Burn: 6.0
2. Prescale: 4.0, Postscale: 1.2, Burn: 6.0
3. Prescale: 4.0, Postscale: 1.2, Burn: 6.0
4. Prescale: 4.0, Postscale: 1.2, Burn: 6.0
5. Prescale: 4.0, Postscale: 1.2, Burn: 6.0
6. Prescale: 4.0, Postscale: 1.2, Burn: 6.0
7. Prescale: 1.0, Postscale: 1.2, Burn: 6.0
8. Prescale: 2.0, Postscale: 1.2, Burn: 6.0

4.6   Luxrender

1. Prescale: 1.0, Postscale: 1.2, Burn: 8.0
2. Prescale: 1.0, Postscale: 1.2, Burn: 6.0
3. Prescale: 1.0, Postscale: 1.2, Burn: 10.0
4. Prescale: 1.0, Postscale: 1.2, Burn: 6.0
5. Prescale: 1.0, Postscale: 1.2, Burn: 6.0
6. Prescale: 1.0, Postscale: 1.2, Burn: 6.0
7. Prescale: 1.0, Postscale: 1.2, Burn: 6.0
8. Prescale: 1.0, Postscale: 1.2, Burn: 6.0

Luxrender doesn't allow me to change the color of the “gold leaf” material. I tried to fake it with other materials but it's not a great success yet. For the “wave” object on the left I simply used the “gold” material, even though the original scene uses a different color. Same for the pipe color of the chairs and tables, where I used a chrome like material.

If you render a daylight only scene make sure that your light emitting geometry gets assigned a “matte” material, otherwise you still kind of render the light groups (even if you turn them off), and you rendering doesn't converge as fast as it could without the light emitting geometry.

4.7   iray

This scene was exported by my own Blender iray exporter, adjusted (some materials) within RealityPlayer, and rendered within view. I had to “tag” the PNG images within Gimp, otherwise the gamma correction is taking place twice.

TODO: Rerender the unfurled object because it's tip (geometry) was modified.

4.8   Mantra

You can adjust the brightness etc. in Houdini's ImageViewer , but unfortunately there is no tonemapper you can use. Therefore I saved the image in Radiance's HDR format and converted it first to TIFF, manipulating the exposure, and later I converted it from TIFF to PNG:

% ra_tiff -e -2 scene2_mantra.hdr scene2_mantra.tiff
% imf_copy scene2_mantra.tiff scene2_mantra.png

As a result of this conversion you see the ground color of Houdini's Environment Light. Basically you should see the “ground” with other renderers too (and iray shows it, but I selected a grey ground color, so the room doesn't pick up too much of the ground color by color bleeding).

The second image is rendered with Mantra's IPR.

4.9   Povray

5   The Conference Room

LBL Building 90 Third Floor Conference Room by Anat Grynberg and Greg Ward, Windows and Lighting Program, Lawrence Berkeley Laboratory, Berkeley, California.

This model was created over a period of three weeks by painstaking measurements and many vi editing sessions. The real conference room looks very similar to the Radiance renderings as a consequence, and we would be interested to compare results to other rendering techniques if you have them.

Please do not use this model for any purpose without giving proper credit.

5.1   Radiance

5.2   The Geometry

Imported by the Radiance importer for Blender (written by myself) and rendered with 3Delight (using the defaultsurface shader - the Arnold utility shader's ndoteye shade mode would render pretty much the same).

5.3   Arnold

5.4   Luxrender

5.5   Indigo

6   The Bathroom

6.1   Radiance

6.2   Arnold vs. 3Delight

6.3   Indigo vs. Luxrender

7   The Ice Cream Store

7.1   Radiance

7.2   Arnold

7.3   Luxrender

7.4   Indigo

8   The Theater

Candlestick Point State Recreation Area (SRA) Community Theater (unbuilt)

Copyright 1989, University of California Regents.

• Design: Mark Mack Architects
• 3D Model: Charles Ehrlich and Greg Ward
• Renderings: Charles Ehrlich and Greg Ward

Acknowledgements: This work was conducted as a research project during the Architecture 239X course taught by Kevin Matthews formerly at UC Berkeley, College of Environmental Design. His assistance and guidance was critical to the success of this study.

8.1   Radiance

8.2   Arnold

8.3   Luxrender

8.4   Indigo

9   The Townhouse

10   Using Materials and Textures

10.1   Maxwell

10.2   Indigo

1. Linear tone mapping with scale 0.05