Opacity maps in MR.

[Crazy Homeless Guy]

I have a question about the best way to deal with opacity maps in Mental Ray. Recently I completed a project where I used a lot of 2d mapped trees and bushes. Most of them rendered without to much of a problem, but in a few places the render engine slowed to a crawl, especially on the FG calculations. When setting up the tree planes, I didn't do anything special, like exclude from FG calculations, but maybe I should have. Not sure if that would have helped.

 

I also used an opacity for a perforated metal screen on this project. It really does not seem like an efficient method for handling it.

[blowback]

Hey Travis,

 

I really like some of that grass ..... is that 2d map as well. I am rendering something as we speak that is griding to a crawl ......I am wondering if thats the case? I used 2d maps with particle system to create the grass. I also use vray but I am sure the principals are the same. sorry not much help....just more questions.

[Crazy Homeless Guy]

The grass is hair and fur. The 2d maps are the bushes and palm trees to the left of the sidewalk. All GI engines struggle with opacity mapped objects. If the 2d maps with the particle system have opacity, then that is most likely what is slowing your scene. Simple turn off the opacity map, and render it. Does it speed up dramatically?

[blowback]

It's rendering @ home. I like were the rendering was going this morning so I want it to finish first then I can test the settings. That hair & fur looks great. I can't seem to get mine to work without slaughtering my render times. I will end up xrefing a piece in front of my camera ...... not the best way to work:rolleyes:

[Crazy Homeless Guy]

yes, it can be memory intensive. i rendered the hair and fur grass out in a separate pass, and comped them together. the pass with the hair and fur took 4 to 5 hours at 3500 pixels wide, and consumed 5 gigs of ram. here is a thread i started last week on it...

 

http://www.cgarchitect.com/vb/31082-field-grass-using-hair-fur.html

[Justin Hunt]

For things like the trees use "Cutout", its opacity on steroids. Basically it applies a pass through instruction so rays do not see , and affect the areas being cut out by the map. Render quickly and is less intensive on calculations

 

jhv

[Crazy Homeless Guy]

I went back and double checked to see how it was set up, and for some reason I had used a standard material with an opacity map on the bushes. I will switch it when I get a chance, and see how it effect the time. Thanks.