Problems With GI

# 1 05-10-2012 , 06:35 AM

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Hello everyone. After following lessons on Mental Ray by Digital Tutors. I've been trying to work on this scene known as FourScripts from 3drender.com

I've worked with manual lights in Maya. It's just mental ray I'm not much used to.

So following are the issues I'm having.

1> First of all I'm using AreaLight as my photon emitter but unable to make GI behave the way I've followed from the tutorials and their practical scene files. As you can see from the image that the photon distribution is not satisfactory.

**I'm just following the setup not the exact attribute settings.**

2> The second thing is when I use Area Light with Use Light Shape attribute turned on the photon distribution gets more even.

Settings are as follows:-
user added image

Photon Distribution:-

Also these are Maya Lambert Material and I've tried with Mia_Material too but that didn't help.

Any help would be great. Thanks

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# 2 05-10-2012 , 05:19 PM

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You're trying to light a scene with just GI, and an area light? While this is possible is not IMO a very good way to do it. In fact I can tell by your shot your not using an exposure node on the camera which is why you have the hot spot in the window.

Your going to run into huge problems lighting a scene this way. The scene below was set up in less than 5 minutes and while not a great example of lighting it's the starting point of a GI based workflow, that you can then add to.

I'll include the scene file. Follow this method and you'll run into far far less problems. Whats more doing it the right way will get you from nothing to the overall lighting in the scene below in 5 minutes. leaving you more time to work on the additional lighting tweaks and materials that can really make your scene shine.

Good luck
https://simplymaya.com/development/basic_lights.rar

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# 3 05-10-2012 , 07:23 PM

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@David
Thanks a Lot Sir user added image

.

Actually I was not trying to Light the entire scene with GI alone. I've already gone through the exact setup as you've suggested.

But the thing is that I need to have an independent control over the photons. So I removed the "Mia_Portal_Light" from "Photon Emitter". You were absolutely right about me not using any exposure settings for camera.
Accidentally I've removed it when trying to see the GI distribution in isolation, Stupid me .

Anyway here's the deal with GI :- Now when I've independent control over GI. I still cannot setup to get satisfactory result. I mean when using portal light you've to stick with "Use Light Shape" Turned On Which according to me gives a more washed out GI distribution. Maybe I might be wrong on this. But please help me out.

Here's the screen shot with just the area light(on visible window)turned on with "Mia_Portal_Light" as light shader and GI.

I'm having another problem with the scene file. It's having this object which disappears every time I open the scene. And only shows up when I try to manipulate it. The huge problem is that if I don't make that object appear by manipulating it. It will cause maya to crash when rendered in mental ray using my setup. Please download the file from the link below and you'll know what I mean.

By the way the object name is "Wall1". The Culprit. user added image

https://www.megafileupload.com/en/file/369636/a-rar.html

Thanks again.

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# 4 06-10-2012 , 08:57 AM

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Something is up with that last link because it isn't working. Anyway what do you mean "washed out"?

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# 5 06-10-2012 , 09:11 AM

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Something is up with that last link because it isn't working. Anyway what do you mean "washed out"?

Originally Posted by GecT

Sorry, that the link has gone bad.

But it's basically the same scene file uploaded by Sir David. I've just removed the "Mia_Portal_Light" from both the area lights Photon Emitter in order to have manual control over the GI photons. But the problem is that I feel the GI distribution is not working well with the scene as you can make out from this screen shot. GI turned on for just one area light which is visible in the render.

And by "Washed Out" I mean that you get different results of GI distribution when Use Light Shape is off and on. And I'm talking about the latter when the Use Light Shape is On. Could you please explain.

Thanks

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# 6 06-10-2012 , 05:13 PM

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Turning on "use light shape" turns a Maya light into an MR light. Without photons even being involved Maya and MR area lights behave differently.

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# 7 06-10-2012 , 05:18 PM

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Turning on "use light shape" turns a Maya light into an MR light. Without photons even being involved Maya and MR area lights behave differently.

Originally Posted by GecT

Yes Mam, I agree. But could you please keep an area light in the visible window and enable it to cast GI photons. I really need to know the correct way of GI emission as from the results I'm getting it's not proper.

The scene is available with Sir David's post. If you could guide me it will be great help.

Thanks

Last edited by zestken; 06-10-2012 at 06:51 PM.

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# 8 06-10-2012 , 06:17 PM

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Don't know a lot of guys name Genny but ok lol.

Anyways I think you're on the right track when you disconnected the portal light from the area lights photon shader channel(I've never gotten good results with it plugged in there, just never looked right to me). In the following renders, fg acc 32, point density 0.1, 4 bounces and default GI settings. Light settings were, 'use light shape' on, 'visible' on, 'emit photons' on, photon intensity 80000(eyeballed it!), 'suppress all maya shaders' on, portal light plugged into 'light shader' channel only. Oh and turned on unified sampling, shouldn't make a difference with the issue at hand but thought I'd mention it anyway. Hopefully I didn't forget anything because I'm dead tired ugh!

Yep forgot something. Ao on mia materials, and some crucial tweaks to the exposure node to compensate for it being an interior shot.

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Last edited by GecT; 06-10-2012 at 06:21 PM. Reason: don't type while tired

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# 9 06-10-2012 , 06:58 PM

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Don't know a lot of guys name Genny but ok lol.

Anyways I think you're on the right track when you disconnected the portal light from the area lights photon shader channel(I've never gotten good results with it plugged in there, just never looked right to me). In the following renders, fg acc 32, point density 0.1, 4 bounces and default GI settings. Light settings were, 'use light shape' on, 'visible' on, 'emit photons' on, photon intensity 80000(eyeballed it!), 'suppress all maya shaders' on, portal light plugged into 'light shader' channel only. Oh and turned on unified sampling, shouldn't make a difference with the issue at hand but thought I'd mention it anyway. Hopefully I didn't forget anything because I'm dead tired ugh!

Yep forgot something. Ao on mia materials, and some crucial tweaks to the exposure node to compensate for it being an interior shot.

Originally Posted by GecT

Thanks a lot Mam. This is the kind of look I'm after. But could you do me a one last favor please? If you still have that scene could you just post a render with the area light just emitting GI photons from a camera angle similar to mine. This would answer the doubt I'm having.

Thanks again.

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# 10 07-10-2012 , 04:48 AM

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GI only, default settings. It looks as expected, blotchy and undefined shading in the corners.

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# 11 07-10-2012 , 06:21 PM

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GI only, default settings. It looks as expected, blotchy and undefined shading in the corners.

Originally Posted by GecT

The render is looking good enough for GI Photons. But still there's something wrong on my side. Ohk I'll have to work on it for more days to find out.

By the way nice blog. Please keep updating.

Thanks a lot. user added image

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