Strange Light Leaks - Vray Region Render Behavior

[ajroane]

I'm working on a simple massing study, and I'm stuck on what I thought would be a very easy problem to fix. The model is lit with a bitmap in the Vray environment slot, and there are several Vray plane lights in the interior. If I render with only my environment, then everything looks as you would expect. When I turn on my interior lights, I get some strong light leaks showing up on the exterior roof plane of the model. While troubleshooting, I turned on the region render in the Vray frame buffer, and I thought the problem had been fixed. Then I turned off the region, and rendered the whole image, only to find the problem was visible again. Has anyone else had this issue? Any suggestions as to a fix? I am using Vray 1.5 sp6, and Max 2012.
Thanks,
Andrew

[Neilg]

Are you using IR/LC?

It could be a number of things. try these.
check the geometry, make sure it overlaps/is welded
turn on 'check sample visibility' in the IR map
turn your IRmap settings up
change your light cache filter values and pre-filter. it may be blurring the samples from one side with the other
check your lights, set them up differently. point them all down/etc, whatever. I dont know how you've got it set up now.

[ajroane]

Thanks, I appreciate the suggestions.
- Yes, I am using IM/LC, and my settings for both are already quite high. The problem seems to come from the LC. If I turn off LC, and use only the IM primary bounce, then the light leaks do not appear.
- I have already tried adjusting the LC Pre-filter and Int. samples. Adjusting these values did help clear up the region render, but this does not help the overall render.
- The scene is extremely simple. Extruded splines, sweeps and one Vray plane. All of my lights are pointing down, and all are set to only affect diffuse; affect specular and reflections are turned off for the lights.
- The problem still persists with a flat grey override material applied to the scene.
- Overlapping the geometry doesn't help. I guess I could try welding pieces together, but such a simple scene shouldn't require such effort, IMO. I may as well revert to radiosity, if that's the case.
- My main question is about why the region render shows the image correctly, when the overall image does not. This discrepancy makes it very difficult to troubleshoot render settings. I thought I had the problem solved, but I was troubleshooting the image using the region render. Unfortunately, rendering the entire view does not yield the same result as the region. The areas within the region, and out, are both rendered with the same settings, as shown in my attached image. But the results are very different.
- Sorry for the wordy reply.
Thanks,
Andrew

[ajroane]

Hit the reply button twice.

[Morbid Angel]

I think the lightcache may be finer for a smaller region then for a large image. See if you reduce your lc sample size and see if it helps. Also light leaks can occur if the geometry is not properly shelled.

[Bruce Hart]

have you tried turning off "store direct light" in the LC? That region render is interesting. I thought the light cache would be using a sample size that was a small fraction of the overall screen size, but perhaps it is finer as mentioned above?

[vlado]

You could try turning off the "store direct light" option for the light cache and/or turn on the retrace option.

Best regards,
Vlado

[Svetlozar Draganov]

In addition you can turn on Retrace Threshold in Light Cache option and also you can set Secondary Rays Bias to 0.1 from Global Switches window.
You can also send this scene to vray@chaosgroup.com - and we will try to find out what cause these leaks.

[MoonDoggie]

I believe when you region render vray calculates a percentage of the light cache subdivs based on how big your region is. It will put samples in different spots because of this. (correct me if I'm wrong Vlado). Try using the retrace option as suggested by vlado.

[ajroane]

Thanks guys, your input is appreciated. I'm sending some more test renders right now. I'll let you know what I find.
Is the LC Retrace Threshold option new to 2.0? I can't find that option in my LC settings, still using 1.5.
Thanks,
Andrew

[3DMK]

Is there any reason you can't use brute force & LC.....????
It will take longer to render but you will get rid of any light leaks.....and a bonus is that it will look more realistic.

hope this helps

[ajroane]

Result of my tests from last week. I ended up cloning out the problem areas in Photoshop.

@3DMK - I work out of habit, I guess. I have always used IM/LC. I have done some tests with BF/LC in the past, but haven't been dedicated enough to get good results.
Still curious about the retrace option; is that only available in Vray 2.0?
Thanks,
Andrew

[tashko.zashev]

Hi Andrew,
The retrace option is available only for the versions after V-Ray 2.0.
Maybe you can try also IM/BF combination for this scene.