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View Full Version : maya 4.5 MR: how to do a white void


lossy
05-12-2003, 11:37 PM
I need a white void for a school project, and nothing I've tried works. I've tried changing the environment color in the camera to white, but that washes out the entire scene for some strange reason. Using a sphere and a plane with a white shader leaves a wierd shadow at the edge of the sphere. Leaving the background black and using a plane at the base (need shadows for scene objects), turing off all renderability except receive shadows (and various other combos), and then compositing into After Effects also doesn't work (made sure alpha channel was on and imported premultiplied).

I may have to use traditional lighting techniques anyway, since another problem I'm having is WAY to much reflected light from the ground plane, making the bottom of my objects totally washed out.

Any suggestions?

DesignDawg
05-13-2003, 01:17 AM
You can't make the environment white by itself if you are raytracing, because it reflects the environment (background)color. So, that's where you are getting the "washing out" of your scene probably. Just use a "use background" shader for your floor and leave the background black. Then composite in After Effects onto a white comp.

I have a client that has a "white void" campaign... Done lots of spots that way.

Ricky

Jozvex
05-13-2003, 01:17 AM
It's certainly tricky if you're using Final Gather, but don't forget that you can control how much effect FG has on each shader by adjusting their Irradiance Colour in the Mental Ray section (of the shader).

I managed to do it using white fog (via a MRay volume shader attached to the camera) for the background, and just a white lambert plane for the floor.

I've attached the render I got. If you have Maya 5 I could send you the scene if you want, but if you don't and need more of an explanation, just say so!

:wavey:

lossy
05-13-2003, 03:01 AM
hey thanks for the suggestions guys, I appreciate it. I'll experiment and respond with any results/problems I encounter just as soon as my schedule allows.

Chappo
05-13-2003, 11:34 AM
Could you explain more to me Jozvex :)

Render looks very nice, could be usefull for easy model experiment rendering

Could you give a little more detail on settings ??

How long did it took to render anyway.

FG seems to be very slow here - compared to GI or anything else.


Thanks

elvis75k
05-13-2003, 12:00 PM
www.arteascuola.it

The zero-room-style rendering is very simple if you use mental ray: turn off default light - (you donět need any light to do this efx) go in the environment color and set it to middle gray (...). Make a plane and apply to him a lambert with the second gray find in the colour preset as a colour, and full white to ambientColour. Set mental ray Preview_Final_Gathering and turn off global illumination. Start with a low value of points and set the minimum and the maximum to 0.20 - 2.00. Of course create a sphere or what you want (...) with a different shader....

I've done that with mr using final gathering_ Not really full size 'couse of image compression and webspace problems...
It may be usefull...
Take-a-look.

TiKiMoN
05-13-2003, 03:38 PM
I tried attaching a MR volume shader to a persp camera's background color, and the button to create a new color shader was disabled, so I couldn't do it. (using Maya 4.5) Can I do it in 4.5??

Gremlin
05-14-2003, 06:32 AM
jozvex needs to stop explainin' and start makin' those damn tutorials on his website. you bastage, hurry up and make em!!
Cheers,
:beer:

Jozvex
05-14-2003, 12:06 PM
Eeek, I had work today so I wasn't here to answer questions!

Originally posted by Chappo
Could you explain more to me Jozvex :)

Render looks very nice, could be usefull for easy model experiment rendering

Could you give a little more detail on settings ??

How long did it took to render anyway.

FG seems to be very slow here - compared to GI or anything else.


Thanks

It only took 7.46 seconds to render! My computer is an AMD
Athlon XP 1800+ (1.53 ghz) with 768 meg of DDR RAM.

Scene details:

*In the scene there are a poly sphere, a poly plane and a point light.

*The plane has a lambert material with the colour set to full white and the diffuse set to 1.

*The sphere has a lambert material with the colour set to blue and diffuse set to 0.5 (because it was too bright on the default 0.8).

*The point light has raytraced shadows turned on and the intensity set to 0.5 (because most of the light is from the FG).

*The environment colour is set to full white.

*In the render globals, the quality is set to Production and FG was turned on with 600 Final Gather Rays. The Min and Max Radius values are just left on the default 0, 0.

Now, if you create what I've just listed, it will render WAY too bright. The last thing to do is adjust the Irradiance Color values for both the lambert materials. The Irradiance Color sets how much the material will be affected by things like FG and GI. The Irradiance Color setting is found in the Mental Ray section of each shader.

*For my scene I had the Irradiance Color for the sphere set to 0.5 (middle grey). And for the plane 0.275 (about a third of the slider).

Those values were just determined by adjusting and re-rendering, hehe nothing mathematical or anything. :) All it does it lessen the FG effect.

Then, about the fog....I can't remember why on earth I put that in there. Turns out you don't need it at all. :shrug:

But I'll explain it anyway because it's cool. What you do is put an Mib_Volume shader into the 'Volume Shader' slot of your camera. The 'Volume Shader' slot is found in the Mental Ray section of your camera (go to View > Camera Attribute Editor).

Once you put it in there, you choose a colour for the fog, then set the Max value to the distance from the camera at which you want the fog to be solid.....I think. Mine was set to 85.

That's all you wanted to know right?

And Gremlin, I can't resist answering these questions!!! I'll finish the FG tutorial tomorrow.........maybe. :scream:

Chappo
05-14-2003, 07:05 PM
Aah, thank you for replying Jozvex

Have been following your scene setup and it works very nicely.
Understand now why most of my FG setup is overlit.
I usually thought i had to turn off my default light when using FG.


Can't wait to see your tutorials on your site :)


Thanks again


Chappo

lossy
05-15-2003, 11:34 PM
Thanks to Jozvex, you're advice really worked. I tried using a "use background" shader on my floor plane, but for some reason MR seemed to freeze up (I was on 15 minutes for a 320 X240 preview and it hadn't even started yet!).

Here's my result so far (fruit is for a juice box commercial):

Now I just need to figure out how to smooth out the shadows a bit (seem grainy) and get them to look softer (have area light and ray traced shadows turned on) other than I'm on the right track now.

Jozvex
05-16-2003, 12:21 AM
Hey that looks great!

Did you use a displacement map for the lumps on the rasberry? Looks very nice.

What sort of area light did you use? The normal Maya one or did you turn on the Mental Ray Area Light section of a normal light?

lossy
05-16-2003, 05:13 AM
Thanks! My teacher/project manager was pleased as well.

I used the area light in the mental ray section of a point light. The rasberry is actually made up of many NURBS spheres, no displacement there (took longer to model but render time is less). I think the rasberry looks the best, however I can't take all the credit for it, as one of the other modelers on our team was in charge of it.

All in all I'm pretty pleased, though I need to play with the orange's shader to get it to not look so flat.

What I really want now is to figure out how to get difuse shadows that don't have either a hard edge or graininess at the edges. Turning off ray-traced shadows yields gives undisireable results (blockiness, etc).

Jozvex
05-16-2003, 06:57 AM
Cool,

Well for the shadows, I'd use the sphere area type. Then by scaling the light (just like scaling anything else) you can control how fast and how much the shadow diffuses. The larger the area light, the more the shadow diffuses.

And to make it not grainy you turn up the area light samples. I think the default is 3, 3? Try turning it up to something like 5, 7.

That means it will sample the shadows a minimum of 5 times, up to a maximum of 7 times on parts that need more.

lossy
05-17-2003, 01:02 AM
Again thanks for the tip. I adjusted the area light samples, but I found that I had to jack them up all the way to 15 to get anything halfway descent (and that is STILL grainy to my eyes), and that increases render time from 5-6 min to 18! Unfortunately, our school won't have a render farm untill fall so that is not acceptable. I'll post a pic as soon as I get home (at work now).

There are also "low sample" boxes...do you know the difference between these and the others? I tried adusting the number of rays under the shadow section of the MR render globals also, but that didn't seem to do anything. Perhaps MR in 4.5 just doesn't handle shadows well.

I'll try and play with depth map shadows in the mean time instead of raytraced, and see if I can't get good results using that route.

lossy
05-22-2003, 07:28 PM
This image is my latest attempt with depth map shadows (difuse shadows with ray tracing is ridiculously slow). However, in order to get rid of artifacting in the caustic color bleeding, I had to increase final gather rays to 3000, which produces render times at 20-30 minutes on a PIII 866 machine.

>> Also, notice the sharp diagonal edges on the shadows, anyone know what is causing them? I have depth map sampling set at 200, and have played with various resolutions. Radius for both GI and FG are set at the default 0 settings.

In addition to getting rid of the sharp diagonal shadows and (hopefully) reducing render times, does anyone know of a way to eliminate the ground plane's shadows and caustic reflections so I can do a seperate shadow pass? Since we like the look of the fruit itself with MR, we want to use just that and fake caustics/GI with an addition shadow pass using more traditional methods in an attempt to reduce render time. Any insight would again be appreciated, as I have again hit a wall in my progess.

lossy
05-22-2003, 07:28 PM
sorry, double posted

playmesumch00ns
05-22-2003, 08:54 PM
Have you tried using a spotlight centred round the objects rather than a pointlight? After all you only want shadows where the fruit is, not everywhere else.

As I understand it, mr makes intelligent depth maps, so it shouldn't needlessly be generating shadow maps where there's no objects, but I think it should still help your render time

andrewjohn81
06-27-2003, 08:49 PM
I took the advice of several people and used the Use Background shader to accomplish a white void. When using final mental ray with final gather the shadows do not work. I looked it up, and this is already known. Final gather does not interact with Use Background, unless I am reading that wrong. I am just a student, and am fairly new, but I usually understand things pretty good.

Is there a work around to get a white void using final gather while still having nice ground shadows?

I would prefer to use a simple light or two to get some good specular values as well, but that usually blows everything to white unless I am really careful. I'm still not good at judging the values I should use. If anyone has tips on that I would appreciate it as well.

Jozvex
06-28-2003, 02:06 AM
Back on the first page of this thread in my really long post with all the * points, I explained a way of doing it without the Use Background shader.

And maybe if you read my Final Gathering tutorial you'll understand more about it?

www.geocities.com/jozvex/tutorials/fg.html

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