Irradiance Particles, HDRs and you

[TheAllusionist]

Written by Jeff Patton Tuesday, 09 September 2008 08:00

Ever wanted decent shadows from your image based lighting scenes (HDR)? Well, it's possible if you use Irradiance Particles in 3ds Max/Design 2009. Read further to find more information & files.
I'm sure by now you've seen the posts on using Importons & Irradiance Particles in 3ds Max 2009. So in this post I'll assume you've already installed the required shaders. If not, then you'll want to go here first:
CGTalk - Importons and Irradiance Particles
Once you have installed the items provided in that link all you need to focus on is the Irradiance Particles. In a nutshell, you'll disable the default lighting, assign your .HDR to your environment as normal then activate Irradiance Particles and enable the Environment Evaluation option and finally tune the ray settings to suit your scene.
Example:

The render above is not using the interpolation option on the Irradiance Particles. Therefore it'll be a bit more accurate, but will also have more grain which will require higher samples and that means longer render times.
So, you may want to use interpolation to help keep render times down by sacrificing a bit of accuracy. In the following render I used Interpolation:

I used one of the default .HDR's that shipped with 3ds Max 2009. While I simply plugged the HDR into the environment (I probably wrapped it in a gamma/gain shader as well), you may want to consider using the environment/background switcher to use a low-res version of the HDR for the lighting & the higher resolution version for reflections.
Doing so will allow you to use lower samples, but a small blurry HDR will also not provide as much lighting detail as a high resolution version. So as with most everything, it boils down to a trade off between accuracy and render times.

Test scene: http://jeffpatton.net/Blog-images/IP-HDR01.rar

Notes: For a detailed explanation of the Importons & Irradiance Particles settings, see the "ctrl_ghost_settings_v1.2.txt" file that comes with the shaders.
I noticed that when I saved the file, restarted 3ds Max and reopened the file, often the Importons option would be enabled...even though I had it disabled. So if it's enabled when you open this scene you can turn it off or leave it on, doesn't really matter for this scene since there's no active lights. Speaking of lights in the scene, you'll see a disabled skylight...that's simply to ensure the default lighting is off.
Don't forget you can save the IP calculation by entering a save to path in the "File" box of the IP settings.


Actual Blog Entry:
Irradiance Particles, HDRs and you