render question

[danteprojetos]

I am rendering a scene in mental ray, and i'd like to keep the rpc's that are in the scene, but unfortunately mental ray doesn't support it yet.

 

My question is, How can I render only the rpc, but with the entourage affecting them?? If i manage to do that, all I have to do is to composite the rpc's in the rendered scene.

 

Thanks in advance !

[Ras]

Hi

 

I´d suggest that you put all the RPC´s in a seperate layer and turn it off. Then you select the rest of the geometry, right click, properties and remove the tick under "visible to camera" (you might have to turn "by layer" to "by object first).

Then you turn on the RPC layer and again you´ll se everything in your viewport but when you render only the RPC´s will render. But the rest of the obejcts will still affect the scene with shadows etc.

 

Hope that helps.

[Bugga_Guy]

Basically what you need to do is create 2 files. When you are confident in your overall model for a final render, make a duplicate file insert RPC's then apply a - MATTE/SHADOW texture to everything but the RPCs. What this does is makes everything black, so when you render all you will see are just RPCs, which make it easy to composite to your rendering of your model. What is the benefit you ask? IT isolates objects, but render with interaction of the scene too - So for example an object is infront of RPC, it will nicely render a black object infront of the RPC for easy compositing - especially if you take advantage of the alpha channel.

[danteprojetos]

Wonderful!! both solutions worked !!!!

 

Thanks a lot!!!!!!!!!!

 

By the way, i've been meaning to ask this question for a long time

 

Bugga guy,

 

How can I use the alpha channel and what is the use for it?

[Bugga_Guy]

danteprojetos,

 

Alpha channels are transparentcey information store in an image file. Only cetain file types have the ability to store them - most popular is the TGA - or Targa File. In these files like TGA's it store R(red)G(green)B(blue) Colours and an alpha channel. If you study an alpha channel - it looks like a black and white shiloutetted image, what is this you ask? Well, basically how a Alpha channel works is anything that is black is transparent (or negative space) and whatever anything is white is positive space (or the actual object), anything that is grey is semi transparent (or ghosted) the darker the grey the more transparent the object is in the image file - visa vera when the grey is lighter. Saving a TGA file automatically save the Alpha channel information so all you have to do is put it in photoshop and access the alpha channel - do a google search on this I am sure you will get tons of tutorials.

 

Alpha channels are great when you want to do post production work/compositing. Instead of rendering everything all at once, you can render certain items then assemble them in post production software.

 

Here is a website that talks about alpha channels alittle more:

 

http://www.am-guide.com/TinCan/AM_&_Alpha.htm

[danteprojetos]

Great info Bugga Guy!!!

 

Thank you very much!!!!