Buzzing GI

[David Sander]

Hey all,

I have been building landscapes in EI for a feature I'm working on. One shot calls for a landscape soft-lit, as if by sunlight though medium to heavy clouds. I struck on the idea of making up an HDRI image and just using Global Illumination to light the scene, no lights at all. After a few practise runs to make sure my geometry was all looking okay, and dealing with a pesky anti-aliasing issue, I thought I had it done. The landscape does not move. The camera flies over the top of it. That is all.

After a lengthy overnight render, I find there are areas that are buzzing or shimmering, as if I have noise turned up to 11. I have high polygon-count trees in the scene, and it looks like they're covered in ants. Add to that there's an odd strobing effect with shadows being cast, like a moire pattern. I haven't varied my skymap resolution yet (1000 x 500 pixels), that is my next thought, but other than that I'm wondering if there's some solution that's not going to result in a week-long render. Can I "bake" the scene with that light? Is there some simpler solution?

David

[interstellar]

Hi David,

When I render an object that has a procedural shader, the details shimmer if the "density" of the shader is set too high. That also happens near the edges of round objects where perspective causes the shader's details to crowd together. Shimmering also happens when the scene is rendered at the default anti-aliasing and sampling levels of 4x4 and 1x1.

However, I don't use GI so my thoughts might not apply to your situation.

Joe

[Tomas Egger]

Ola David,

Please, have enabled only one group in the project window which you have problems to render tests and use these settings:

More Primary Rays, Higher Color Tolerance help with shadows flick.

The last move here is decrease the Sampling Area from 8x8 to 4x4. (only if necessary, since it slow down the render changing the Sampling Area).

Please, dont use Procedurals, try to use bitmap textures, procedurals flicks more.

To improve AA as Joe wrote:

You need to use the contextual menu on the group info window and change the Sampling to 2x2.

And in the render window, change to 8x8 / 2x2.

Hope that helps.

Thanks

Tom

[David Sander]

Okay, I've been through this a few times now, altering the settings as advised above and so on, then re-rendering and testing (pushing my renders up from 6 minutes a frame to 55 minutes a frame in the process). I pared back the project to render just a luminance pass, which would incorporate the shadows etc and leave textures and so on to other render passes (likely in Phong, as there's no need to raytrace textures).

However, even in just a luminance pass, with no textures (except the GI map), transparencies, specular, transmission or anything else, just geometry, I'm still getting shimmering shadows. This is frustrating the hell out of me, and now I'm looking to have to render the cast shows as a texturemap and apply that via a projection camera as another texture, because I can't bake the shadowmap into the scene. from a practical perspective the shadows need to be calculated just the once - there's nothing moving in the scene except the camera. Even with multiple processors, 55 minutes per frame on a 60 second shot is a real time-hit, and I've already lost a week troubleshooting shimmering shadows.

Has anyone additional wisdom they can impart here?

David

[Tomas Egger]

Ola David,

The problem was simple, but hidden..

My Tip: Always try to simplify the project and minimize it to find the basic issue you want to solve.

The render hit here are your trees (2 million polys) and the problem is not the GI, its the diffuse maps textures on the leafs only.

Looking your project I saw:

1) All leafs textures had the “Live Material” turned off.

2) All leafs textures had no Samples.

3) Last Detail and really important, turn off the transparency maps on all leafs, I know, this is not correct, but in your case, its better.

but it will make the “flick” disappear, using Trees which doesnt need “transparency” map will avoid this issue, Trees with modeled leafs, like Triangles.

Since your Trees are really small, you will not need to change them and they will not flick now.

The result rendering using Phong:

War_Trees_No_Samp.mov

So, changing these parameters:

1) Live Material ON

2) Add Samples, you can use the default samples, like 5.0.

The result will be this:

War_Trees_Textures.mov

Projs Attached :)

Projs.zip

Now you can lower the GI settings and minimize the AA (4x4 1x1) since the problem was no GI related, you will have a faster render with better quality.

Thanks

Tom

[David Sander]

That's great! Thank you!

I'm still struggling with the buzzing/shimmering shadows issue (my current tests are without trees entirely), but it appears that might be resolved with an upgrade to 9 (whenever that might be possible).

[David Sander]

Determined a compromise on this, creating a two-pass pre-comp for a luminance pass. The first pass relied on a simple Global Illumination white sky colour to create a general shadow effect; and then rendering a second pass in Phong shading of a buffer shadow pass for shadows being cast from a specific light source (in this case the sun). As the scene is supposed to be misty early morning light, I've adjusted and softened the transparency of the buffer shadow accordingly in my After Effects comp. I had originally achieved the same effect with a single pass using a skymap and applying that as a GI light source, but on animating, its shadows shimmered and buzzed, regardless of anti-aliasing settings and blurs applied to the texturemap. Here's hoping EIAS 9 allows the burning in of a GI map onto a scene!