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Micah-H
11-17-2010, 05:04 AM
Hello I am new Mental Ray. I had some questions about my first render.

http://img4.imageshack.us/img4/3569/gitest.jpg (http://img4.imageshack.us/i/gitest.jpg/)


-I have an area light and point light emitting photons.
-I tried a sss_fast shader for the lamp shade.

I am wondering about the grain mainly, what is a cause of this? number of photons? accuracy?

Could the shader be causing a problem.

Thanks any advice would be awesome.

ndeboar
11-17-2010, 05:15 AM
Why two lights? There is just one light source.

If you are emitting light from an area light, you need to increase your shadow ray samples, it'll help the grain.

Micah-H
11-17-2010, 05:40 AM
Hey

I was actually following this LINK (http://www.youtube.com/watch?v=EErZndeF5zI) and followed his two light technique.

I switched the scene to one light and see that it makes no difference.

http://img684.imageshack.us/img684/6820/gitest1.jpg (http://img684.imageshack.us/i/gitest1.jpg/)


I bumped the ray trace shadow rays to the max 40 and it still is grainy!!!

ndeboar
11-17-2010, 06:03 AM
if its a mental ray light, it might be tied to your high samples. Crank that up.

Micah-H
11-17-2010, 06:21 AM
sorry high samples of... photons?

man im ive moved passed tutorials and physics and just started to slide sliders and change values. nothing will fix the grain :banghead:

Ill just keep tweaking

ndeboar
11-17-2010, 06:30 AM
light: mental ray: high samples

If you use a mental ray light, these settings will override anything you change in the shadow rays.

If you find mental ray annoying, may i suggest V-Ray :)

Micah-H
11-18-2010, 11:28 PM
I would like to try vray, I dont have access, so for now I will learn mental ray.

I dont understand why your saying use a mental ray light.

-I turn on mental ray rendering
-and then I create a light

that is the only way I know to make light

from there I can have the light use raytrace/emit photons
then in my MR settings I adjust my GI and FG settings.

Micah-H
11-19-2010, 01:50 AM
so I know your not suppose to follow tutorials step by step, setting for setting, but I just did as an experiment, exactly duplicated settings. My render did not turn out nearly as nice, it was grainy, blown out, etc.

How important is my hardware in this test? Im using a pretty crappy computer and I am thinking that is the problem because I cannot solve these render problems.

Array
11-19-2010, 06:36 AM
so I know your not suppose to follow tutorials step by step, setting for setting, but I just did as an experiment, exactly duplicated settings. My render did not turn out nearly as nice, it was grainy, blown out, etc.

How important is my hardware in this test? Im using a pretty crappy computer and I am thinking that is the problem because I cannot solve these render problems.

Your computer hardware will have absolutely zero impact over the quality of your render, only your render time.

You have two different things going on in this scene, and those are area lights and photon mapping. A big part of lighting is learning how to isolate the various elements of your light rig in order to debug whatever may be causing an issue in your scene.

First thing that I would do in this scene is to turn off the photon mapping and fix the area light issues by turning up the number of shadow samples in your area light. Then I would worry about getting a nicer photon distribution.

In regards to your lights looking so blown out, turn up the falloff exponent of your light. A setting of 2.5 or 3.0 would be a good start.

Micah-H
11-20-2010, 06:12 PM
thanks Array
A big part of lighting is learning how to isolate the various elements of your light rig in order to debug whatever may be causing an issue in your scene.
So true, anyone can play with settings but unless you can debug, your not mastering anything.

So for this next round I switched the Ray trace shadows to Depth map shadows. and it instantly removed the grain. Added more photons into the scene. Switched the light to have some decay.

I didnt know what you meant by photon mapping?

http://img217.imageshack.us/img217/3559/photonmap.jpg (http://img217.imageshack.us/i/photonmap.jpg/)



http://img403.imageshack.us/img403/554/gitest3.jpg (http://img403.imageshack.us/i/gitest3.jpg/)

Array
11-22-2010, 06:53 AM
thanks Array

So true, anyone can play with settings but unless you can debug, your not mastering anything.

So for this next round I switched the Ray trace shadows to Depth map shadows. and it instantly removed the grain. Added more photons into the scene. Switched the light to have some decay.

I didnt know what you meant by photon mapping?

http://img217.imageshack.us/img217/3559/photonmap.jpg (http://img217.imageshack.us/i/photonmap.jpg/)



http://img403.imageshack.us/img403/554/gitest3.jpg (http://img403.imageshack.us/i/gitest3.jpg/)

That's looking much better already! I think that you set your decay a tad too high though. The base of your lamp should still look pretty bright.

Photon mapping is the algorithm that Mental Ray uses to calculate its 'global illumination'. Working with photon mapping entails finding a balance between the number of photons, photon radius, and filter size. You can also use Mental Ray's Final Gathering to smooth out your results.

Micah-H
11-22-2010, 06:16 PM
http://img97.imageshack.us/img97/5662/gitest4.jpg (http://img97.imageshack.us/i/gitest4.jpg/)

http://img190.imageshack.us/img190/8440/decayrate.jpg (http://img190.imageshack.us/i/decayrate.jpg/)

I dont see a place to change the value of the falloff or decay rate. I played with the intensity and it is reflected on the nearby box but not really on the ground.

I also tested the different values of the photon map. Here are different radius values.

http://img148.imageshack.us/img148/5012/gitestphotonradiussmall.jpg (http://img148.imageshack.us/i/gitestphotonradiussmall.jpg/)

http://img576.imageshack.us/img576/1776/gitestgiphotonradius.jpg (http://img576.imageshack.us/i/gitestgiphotonradius.jpg/)

http://img841.imageshack.us/img841/2763/gitestphotonradiuslarge.jpg (http://img841.imageshack.us/i/gitestphotonradiuslarge.jpg/)

I didnt find much of a difference with using a radius and fliter size verse leaving them at the default values.

Array
12-08-2010, 06:39 AM
Change the decay rate from linear to exponential.

tomdrum6
12-23-2010, 12:43 AM
do you need to use an area light? play around with other types, you can get more control from point and spot. Grain i have found can be from the shadow rays and depth limit, try increasing them in the light settings, if you want to use ray traced shadows again. For scenes like this, depth map is fine though.

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