In this tutorial I’ll explain some things you can do sto help optimize your scenes for iray. I believe these tips are standard fare for many of the GPU rendering applications. Read on for the details.For this “tutorial” I will be using an architectural test scene created by Mark Galbraith in a thread at the Vizdepot (thanks).
Upon starting with iray you may be tempted to simply load some of your mental ray scenes in iray and hit the make pretty button. That may work, provided you didn’t use shaders, materials, or features not supported by iray. However you may be able to make some adjustments to your mental ray scenes in order to get less noise in your iray renders.
First tip: Direct light + no glass = less noise. What that means is that a scene with light sources outside the windows and no glass in the windows will produce less noise within the same render time as a scene with visible glass and lit by the environment.
In this render the scene is lit by the scene environment (mr Physical Sky) without any portal lights outside the windows and the window glass is visible:
This is the same scene with the window glass hidden:
While the scene with glass is more realistic in that the glass provides that subtle green/blue tint as you’d expect to see, it also needs more time to clear noise than the non-visible glass version. The non-visible glass version is also brighter, but again that’s to be expected since the glass had a subtle tint to it. I could have easily adjusted the exposure to make the glass version brighter…or rendered out to HDR/EXR format and adjusted the exposure “real-time” in post.
Up next I placed portal lights outside the windows (4 of them) and configured them to be visible and use a color instead of the scene environment. Here’s the visible window glass version:
And here’s the version with the window glass hidden:
You’ll notice a big difference in these from both the visible glass and hidden glass renders and the environment lit versions from earlier. There’s far less noise in the non-visible glass, visible portal lights outside windows version. So, if you can get by with hiding the window glass in your scenes you may find placing lights outside the windows of your interior scenes provides quicker renders by eliminating noise faster.
Next, since self-illuminated objects work so well in iray I wanted to see if there was any difference between lighting a scene with a photometric light vs. self-illuminated geometry. Here’s the scene lit with a single photometric light source:
And the same scene without any light sources, and illuminated by a 3″ piece of geometry with a self-illuminated material applied:
I was a bit surprised by this one. I thought there would be more noise in the self-illuminated material version, but they are fairly similar in terms of noise/grain! So, it seems there’s not a lot of extra noise/grain when using self-illuminated geometry.
All the renders used in this blog entry were set to use the same amount of time, 15 minutes with a full resolution of 1920 x 1080 using a Quadro5000 + i7 960 CPU. Since scaling the images down reduces the noise I have uploaded the full resolution images HERE for easier comparison.