PDA

View Full Version : A few MRay questions...


BlurFrame
07-19-2011, 06:47 AM
Hi guys,
I have a few mental ray questions for a small project that I am working on, I couldn't find proper answers to these from google, I have already setup Glow and FG. I'd rather just have one render from Maya and be done with it. Wish to do minimal compositing on this one,

* Is there a way to render FG , Glow and AmbOcc together in one final render. All tutorials I have found to render AmbOcc tell me to apply a new shader or setup a renderpass, so is there no way to render AmbOcc+FG in one render.

* If not, how do I render Glow in seperate passes, I have a lot of objects with different glows

* I have a light coming from an opening in a room which has volumetric 'God rays'. Is partiVolume setup the only way to do this.

* Which motionVector pass should I go for, 2D or 3D, the blur doesn't need to be accurate but also shouldn't look wonky. How do I composite this pass.

* Any tips you can give me about compositing depth pass with motionVector pass would be great.

* Finally how do I make shader for an object that looks like the images below. I have a Lambert shader with Incandescence and glow which works fine until I turn on FG. With FG it goes a pink shade and I cant get the saturated red colour working at all...I am using a high FG diffusion and low point density. Actually it looks exactly as the reflection of the lamp on the white floor in the image below

http://img220.imageshack.us/img220/885/nicholasfurrowredlight2.jpg (http://img220.imageshack.us/i/nicholasfurrowredlight2.jpg/)

Uploaded with ImageShack.us (http://imageshack.us)

http://img845.imageshack.us/img845/9028/redlight470x400.jpg (http://img845.imageshack.us/i/redlight470x400.jpg/)

Uploaded with ImageShack.us (http://imageshack.us)

This is a simple animation project with decent shading but no real textures. I am not going for a photoreal look, just suggestive stuff.

Thanks a lot.

kiryha
07-19-2011, 08:42 AM
> Is there a way to render FG , Glow and AmbOcc together in one final render
yes, but i would strongly advice you to do glow in post- much more benefits, than dificulties.

Since you use MR, you should use ONLY MR shaders (no lambret, blinn etc). Use mia_material_X_passes for all object in scene, its amazing material which give you awesome results easy. Also, very important to work in Linear color space (LWF), its very easy to setup:
http://www.djx.com.au/blog/2010/03/07/maya-linear-workflow-in-two-steps/

Turn on FG in render globals- you will render with FG, turn on AO in shader (mia_material_X_passes )- you will render with AO. Glow- for post.

>how do I render Glow in seperate passes, I have a lot of objects with different glows
You will need to output masks for objects, or for materials for creating separate glow effects for different objects(or materials). It could seems complex, but it doesn`t, you can get deeper to this topic later, after u will satisfy with you render.

> Which motionVector pass should I go for, 2D or 3D, the blur doesn't need to be accurate but also shouldn't look wonky. How do I composite this pass.
2D motion vector (2d mv toxic). Compositing way relay on comp application. You will never get same result with MV as with rendered motion blur, but in most cases it should look good.

>Any tips you can give me about compositing depth pass with motionVector pass would be great.
Later, when you will get first result of doing it. A lot deppends on you scene, camera, etc. There is no way to do it math correctly, but in most cases cheating will works fine.

> Finally how do I make shader for an object that looks like the images below.
Use mia_material_x_passes with mia light surface connected to additional color.

Read grate article about architectural shader in maya docs for quick start with mia_material.
http://www.mentalimages.com/fileadmin/user_upload/PDF/arch_and_design.pdf

BlurFrame
07-19-2011, 11:18 AM
Wow man, I had no idea, I have stayed away from lighting and rendering for a long time. Thanks for the links, I will look into them soon.
For my scene I have all the shaders already setup, a lot of them are layered and it took me two days just to get the diffuse levels and colours adjusted with the FG.
Converting all of them to mia shaders is gonna take a while, I will do it if I have time.
I will try the mia shader for the light effect that I want.
I was looking to do FG+AO+Glow all in one pass, I guess I will have to setup different passes. I am using AfterEffects and I think it has a filter for the glow.

So most things are set for now, except Depth pass and MotionVector, does applying motionblur on the depth pass before using it for DOF in comp work fine...

The pdf was an eye opener for me, I will get a lot of control with mia shaders, for all future projects I will be using them.

Thanks for the quick reply.

MasonDoran
07-19-2011, 12:21 PM
Glow is a post render effect, which is why it is not in the render passes.

FG will use AO in the calculations by default if you turn on AO in the MIA shaders and enable it in the render globals.

BlurFrame
07-19-2011, 02:21 PM
Thanks MasonDoran and kiryha, I played around a bit with my shaders and have made the lamp shader work, I added a specular layer on top of a surface shader and it looks good enough. Tried bumping the colour value and saturation beyond 1 and it works fine with FG, needs tweaking tho.

For the God rays I am just rendering a spotlight with lightFog and depthMap shadows from Maya software render. Will comp it in and it should be not bad.

I knew the glow was post effect, just couldn't remember how to render the glow in alpha, used to do it sometime back. Figured it out now, I apply UseBackground shader on all objects except the glowing ones and I get good glow renderPass in alpha channel.

Sweet, fast approximate results.

Now only if someone who has experience comping MotionVectors with depthPass for DOF can give me a few guidelines, it would be great.

Thanks again guys :)

kiryha
07-19-2011, 04:11 PM
Rendering motion vectors and depth path is not a problem. Problem to get DOF and MB on compositing stage, cos result of any of this post operation destroy data for another. Just do it and if result will good for you- its OK, if not- than ask.

BlurFrame
07-19-2011, 04:24 PM
I will do a test and see how it goes.

CGTalk Moderation
07-19-2011, 04:24 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.