SH = (roughly/sometimes) Light probes = environment maps = cube maps
- Maps a direction to a color (or any value)
- Light probes can mean SH, which is an approximation and can store blurry stuff. It cannot store sharp (high frequency) details.
- Light probes can also mean environment maps / cube maps. They can handle sharp details.
PRT = Precomputed Global Illumination
- Need to read paper...
- Can store its results in some format... (paper mentions SH)
Irradiance map = filtered map of incoming radiance.
- Time saver.
- For diffuse stuff in image based lighting, you usually sum incoming light for a given direction, with each light 'beam' weighted by its angle. That's your irradiance.
- The summation is expensive, so we precompute a direction -> irradiance map.
- Usually looks like a blurred light probe.
- Stored in environment map, SH, etc...
Also I feel like that unless you're reading a paper, the terms 'SH', 'light probe', 'environment map', 'irradiance map' usually are used interchangeably.
Thanks for the information, I'm beginning to get a better grasp of the terminology. It sounds like I probably just need SH for now, and I'll use standard shadow mapping for my characters on top of that.
Spherical harmonics refers solely to the math/concepts behind storage, PRT is just the idea of calculating how light bounces around ahead of time. Technically speaking, boring old Quake 2 lightmaps are just as much PRT as are the fancypants spherical harmonics stuff that's in vogue today.
Thank you, that clears up a lot for me. So, to summarize, it sounds like to get the basic ambient indirect lighting I just need to do the steps by MJP. Just to make sure I'm understanding things now, it seems like both Unity and UDK are doing this, i.e. see this link http://udn.epicgames....html#Character lighting
there it looks like they are just doing an irradiance map as well? The DirectX SDK has an Irradiance volume sample from ATI that looks similar.