Faster opacity maps

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  02 February 2013
Faster opacity maps

During the last few projects, I checked my scenes throughly to find out which scene elements increase the rendering time at most.

It turns out that opacity or cutout maps take a great deal of time to calculate, and if there are several objects behind each other like tree leaves or billowing smoke, rendering of that single material takes more time than the entire scene.

You know in softwares like particle illusion, such effects can even be previewed in real time with even better quality.

I'm rendering the breath of a 3d character like in cold weather. Entire scene renders in 20 seconds but when this quad faced particles with opacity maps are present it takes 2-3 minutes.

I wonder if there is a faster way to render such effects in 3DS Max.
  02 February 2013
What renderer?
With Vray it helps a great deal to disable filtering for the opacity bitmap.
  02 February 2013
I use Mental Ray. It is sometimes unexpectedly* slow.

*Rendering time varies greatly even when a portion of scene is overexposed or just very very dark.
  02 February 2013
Are you using Area-lights+shadows?
Maybe try to exclude them from casting shadows if possible.
  02 February 2013
In both MR and VRay there are ways of having different maps for the shadows vs for the material. Often it's the shadows which cause problems with opacity maps, so if you swap out the map for the shadows with a significantly lower resolution version of the same thing, you cna often make enormous savings and often you won't be able to tell a difference. On Vray you do this using a VRay Over-ride material and if the 'Shadow' slot you have the same material but with lower-resolution maps. For MR, it's in the Mental Ray Connection bit of materials.

  02 February 2013
I even completely turn off shadow casting and receiving of these objects.
On a scene with trees a 4 minute render dropped down to less than 2 minutes just by turning off cutout maps of leaves.

In the latest project, opacity mapped particles are completely excluded from shadow operations, both casting and receiving. Still very slow just being transparent and many objects coming one over the other.

I guess there is no way else.

addition: I also used a very small resolution of the leaf bitmap - like 32x32- nothing changes even due to such resolution
  02 February 2013
I'll be keeping an eye on this thread as I've been leaning towards geometry leaves for improved render speed but they have their downsides.
  02 February 2013
Originally Posted by MisterS: I'll be keeping an eye on this thread as I've been leaning towards geometry leaves for improved render speed but they have their downsides.

If you have leaf geometries that have leaf shape instead of opacity or cutout maps, they're definitely going to be rendering faster. On my geometry trees leaves are achieved by cutout maps. As I've mentioned, I thought I could gains some speed by reducing the resolution, These are very tiny trees at a distance. Literally nothing changed, in terms of rendering time, by dropping the resolution from 512x512 to 32x32.

But when I just turned off the cutout map, buckets that were used to get stuck more than 20 seconds over the trees, were just rendering like a flat surface.

I encourage the use of geometry trees with proxies.
  02 February 2013
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