Rendering a world position pass with Arnold

You can use the Arnold_Point AOV to create a world position pass (an AOV is the Arnold equivalent of a render channel). Here’s the Arnold_Point render channel in the render region:

A world position pass (aka a position map), is an image where each pixel’s R, G, B colour values represent the x, y, z coordinates of the corresponding vertex, in 3D world space.

If you loaded the rendered position map into the FxTree, or Composite, you can see that the RGB values correspond to the XYZ position coordinates:



Arnold – Rendering shapes distributed along strands

Arnold always renders shapes as if they were lofted along the strand. It doesn’t matter whether you clear the Loft Shape along Strand checkbox in the Create Strands PPG, the shape will always be lofted in the render, like this:

If you want your instance shapes to be distributed along the strands, you could use a second point cloud to put the shapes along the StrandPositions:

If you find this slows down your viewport, change the Particle Display to points.

Glossy reflections in the Arnold standard shader

In the Arnold standard shader, you use specular reflections when you want glossy reflections. There’s direct specular (the “classical” specular hightlight) and indirect specular (glossy/blurry reflections), and both are part of the same BRDF behaviour. In this screenshot, direct specular (Direct Scale) is turned off, so you see only the indirect specular reflections. The Roughness makes those reflections glossy.

So what’s up with the separate Reflection/Refraction tab? Well, that tab gives you an alternate way to do sharp, mirror reflections (with no blurring or glossiness). However, with Specular, you can get pretty much the same thing by setting the Roughness to 0:

Finally, since I mentioned the direct specular, here’s the shaderball with just the direct spec:

Might as well…change the default scene renderer

Goodbye for now, mental ray. Arnold is now my default scene renderer 🙂

File > Preferences > Rendering

Now everytime I start Softimage or create a new scene, Arnold will be the scene renderer. And I’ll have an Arnold light by default (Arnold doesn’t support the default Softimage lights).

And you’ll have all the Arnold render channels.

The SItoA addon includes some events for setting up new scenes when Arnold is the default renderer.

A procedure couldn’t be found in library

When you get an error like this

A procedure couldn’t be found in library Addons\SItoA\Application\bin\nt-x86-64\sitoa.dll. The library will not be loaded.

it usually doesn’t mean that Softimage couldn’t find the DLL (sitoa.dll in this case).

Typically, this error is caused by a missing DLL dependency, or the wrong version of a dependent DLL. You can use Dependency Walker and Process Monitor to track down what’s going wrong. A “DLL dependency” or “dependent DLL” is another file that sitoa.dll depends on. When Softimage loads sitoa.dll, that other DLL isn’t found, or if it is, it’s the wrong version. And so you get the error.

Tip – UI color widgets have a visual cue for gamma correction

In the Display > Color Management preferences, you can turn on gamma correction for UI widgets like the color chip. On the PPG, there’s a visual cue (a “dotted highlight”) that tells you whether gamma correction is on.

Gamma-corrected color widget:


Regular color widget (no gamma correction):


Also, you can right-click the color chip to toggle gamma correction on and off for that specific widget.

This is all in the docs, but I have to admit I found that out only after I noticed this on my own. Too bad, because if I had known this, I would have figured out sooner why my color chips looked so “faded”:


(because at some unknown point in time I had enabled the display of gamma correction for UI widgets, and then set the Profile Source to “From LUT File”)

Introduction to Arnold

I see the October term at fxphd includes ARN101: Introduction to Arnold. The course uses Softimage (yay!) and you get access to Arnold.

I’ve never tried fxphd. It’s not exactly cheap ($359 US for 3 courses, $399 US for 2 courses) so I assume it must be pretty good 😉

ARN101: Introduction to Arnold
Professor: Ulf Lundgren
Software Version:
Original Run Date: October 2012
This course is targeted at anyone who may already be familiar with rendering and lighting but who wants to move over to Arnold; or just wants to know how Arnold can help in production.

Taught by Ulf Lundgren, the goal of the course is to get you up to speed in Arnold and help you understand the differences when using Arnold compared to other Render engines. Prior experiences of rendering and lighting is a plus but not necessary since this course should still help you get on your way to amazing renders.

Workflow, rendering optimization, basic shaders, usefull lighting riggs, sss, volumetrics, linare workflow, Aov and practical work-flow tools might not sound all that sexy but you’ll come to love the results. Furthermore this course is designed to mix more theoretical classes with in-depth case studies of Arnold working on real projects, giving a better understanding of how to use Arnold in production. This course gives you a very good understanding of how to do both full CG projects as well as taking you through all the steps of a production for using Arnold to integrate CG into a live action plate.

Even though the course is using Softimage as it’s main application all the classes are kept generic and should be as relevant for any implementation of Arnold; be it Maya, Softimage or feature implementations in Houdini or Light Wave. No knowledge of Softimage should be needed. Course members will be able to have access to the the Arnold renderer software, thanks to a partnership with Solid Angle.

Ulf Lundgren is a VFX supervisor and director at Lost Liner Productions in Stockholm Sweden. He’s worked on a number of international feature films and well known commercials like Harry Potter 1 and 2, Golden Compass, James Bond Die another day and Xbox Mosquito before starting his own studio and tackling the Swedish movie scene of ghosts and Zombies.

class syllabus

Class 1: A brief history of Arnold and how it integrates into a production workflow and the good vs bad when comparing Arnold with other renderers.
Class 2: How to setup and render with a linear workflow using color managment in Arnold, followed by and an in depth look at all the types of lights Arnold has to offer.
Class 3: An in depth look at shading with Arnold and how to use the different types of shaders in production.
Class 4: An in depth look at render effects and settings and learn how to export ASS files to do batch rendering of sequences using kick.
Class 5: Shading for production, a case study of how to create shaders for all objects in a scene.
Class 6: Working efficiently with Arnold, optimizing renders and setting up a good workflow.
Class 7: Case studies of how to do lighting and shading in a full CG productions.
Class 8: A case study of how to do lighting and shading for live action integration. Part 1. Using lightprobes and other on-set data to better integrate the CG elements into the plate.
Class 9: A case study of how to do lighting and shading for live action integration. Part 2. Rendering with AOV’s and how to best use them in compositing.
Class 10: Wrap up any questions from the forums.