[Arnold] Tips for reducing noise when rendering interior scenes with indirect lighting


Indirect lighting of interior scenes can be a challenge, but there are some things you can do. In this post, we’ll give you some quick tips, but you can find more detailed information on support.solidangle.com, both for interior lighting and for troubleshooting noise.

Avoid the Skydome and use a Sky background and Quad lights

Instead of using a Skydome light, use a Sky for the background and quad lights for the light coming in through the windows. The quad lights should just barely cover the entire window.

If there’s anything visible outside the window, you may want to put a spot light on them. Just be careful not to let the spot light go into the room.

Use a distant light to simulate beams of light coming into the room

A distant_light is an easy-to-use option that perfectly matches sun light.

Spot lights don’t produce realistic sun beams since the beams look like they’re expanding, which sun beams don’t do. Moving the spot light further back, and also making sure it’s no larger than it needs to be to illuminate the window, will reduce noise and make it look more realistic.

Don’t put lights too close to the windows

If a light is too close to the window, that means the light hitting the window area is significantly more concentrated and so much brighter than the light hitting the far side of the room and so this produces more noticeable noise.

Make sure your materials are physically based

For example, don’t shade the room Standard shaders with a Diffuse weight of 1, and Diffuse color full white (1 1 1). I don’t think there’s any material known to man that is this reflective. Lowering the Diffuse weight to 0.7 will roughly match white paint and it will also get rid of noise. If it’s too dark, then try increasing the intensity of the lights, increase the number of diffuse bounces, or increase the camera’s exposure.

For a richer look, avoid fake lights inside the room

Consider getting rid of any fake lights you may have inside the room, and instead increase the number of diffuse and glossy bounces in order to get an even more realistic look, not to mention make the lighting easier. Doing that does increase render times, unfortunately, but does give a richer look.

hat tip: Thiago

Getting an Arnold log from Royal Render


I’ve had a few cases where people weren’t sure how to get the Arnold log from Royal Render. The Arnold log is pretty important, at least for me, so here’s how to get it.

First, when you submit the job, set the log verbosity in rrSubmitter. You can do that in the Override section, but note that the verbosity levels in the Verbose list don’t match up with the newer MtoA verbosity levels. To get a Debug log, you’ll have to set the Verbose to Progress.
rrSubmitter_w_spotlight

rrSubmitter_Override

You can view the log in rrControl:
rrControl_Log_Files

[kick] [ass] reading from stdin


Some customers have reported a problem using a render manager (Muster, Tractor, Deadline) to render jobs with kick, typically via a wrapper script. The problem is that kick tries to read from STDIN instead of loading the specified ASS file. In the log, you’d see this:

00:00:00     0MB         | [ass] reading from stdin ...

A workaround is to add the -nstdin flag (Ignore input from stdin) to the kick command line.

Rayswitching shadow rays


The ray_switch node lets you evaluate different shading trees for different ray types. In general, it’s used to provide a simpler shading tree for secondary rays, such as diffuse, glossy, or shadow rays. So when a camera ray hits the object, you can do one thing, but when a secondary ray hits the object, you can do another, simpler thing 🙂

For shadow rays, it’s not the color that matters, but whether the object blocks the shadow ray from a light. For example, if an object is opaque, then it doesn’t matter whether ray_switch returns red or blue or green or yellow for the shadow rays: the object is still opaque and blocking the light. So, you could use a ray_switch.shadow to plug in a simple standard shader that provides just the opacity mask.

ray_switch_shadow_opacity

[SItoA] Disabling camera motion blur


Starting with version 2.8, SItoA no longer supports the Softimage motion blur property. Instead, you use the Arnold Parameters property to control transformation and deformation motion blur.
arnold_parameters_motion_blur

However, you cannot add an Arnold Parameters property to a camera (at least not using the SItoA custom menus, which will tell you that a camera is “is not a valid Object to add Arnold Parameters to”). Here’s a couple of ways to work around that:

  • Create an Arnold Parameters property on a polygon mesh, and then in the Explorer, drag that property to your Camera.
  • Select your camera and run this Python snippet:
    cam = Application.Selection(0)
    cam.AddCustomProperty( "Arnold_Parameters" )
    

Creating object mask AOVs that include opacity


  • Create a custom RGB AOV.
  • Use aiWriteColor to write the object mask to the custom AOV. The Input color of the aiWriteColor is the mask color, and you have to enable Blend to get the opacity blended into the Input.
    mask_opacity_aiWriteColor
  • Connect the Out Color of the aiWriteColor to the Color of a Standard shader. That sends the aiWriteColor beauty to the Standard.
    mask_opacity_Nodes
  • Make sure Enable AOV Composition is turned on in the Render Settings.
    EnableAOVComposition

I don’t think this set up works if you plug a Standard into the beauty of the aiWriteColor (eg Standard > aiWriteColor > Standard). With that set of connections, I could never get the opacity right in both the Beauty and the Mask AOVs.