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Rendering fog with VRay
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Rendering fog with VRay // Archive: Tech Forum
Post by Burisman // Jan 5, 2007, 6:35am
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Burisman
Total Posts: 128
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Hello guys, this is my first post, so I take the risk of asking a stupid question, but I can't figure it out. When I switch over to the VRay renderer in TS7, my painstakingly designed fog-settings disappear. All the objects render fine, but no fog. So I suppose fog belongs to the built-in renderer. Is there a way of rendering fog with VRay? I can't find it in the pdf that comes with the renderer. The tutorials treat great features like caustics, and GI, but, to my knowledge ... no fog. I haven't the foggiest idea where to go next. |
Post by TomG // Jan 5, 2007, 6:39am
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TomG
Total Posts: 3397
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Post process effects such as fog and depth of field depend on the render engine. Fog and DoF are currently only for Lightworks, as are volumetrics.
My suggestion would be post process. A V-Ray render for the actual image, then a Lightworks render using the built in multipass rendering in tS7. You can just remove all shadows, paint your objects single simple color etc for this, as what you want is the depth information only. So in this case the rendered image doesnt count, you want the z-buffer info only in the resulting PSD.
You can then use this depth / distance info to create fog by using it as a layer mask in Photoshop. More powerful than straight fog too, as you can apply noise etc and get tendrils, grain, and whatever other effects you want to the fog, all without re-rendering!
While it does require the one extra render pass, it brings many advantages. For professional productions, from images to movies, more than one render pass is nothing surprising or unusual either, it's not cheating, nor does it mean it's broken :)
HTH!
Tom |
Post by Burisman // Jan 5, 2007, 6:44am
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Burisman
Total Posts: 128
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Dear TomG, Thanks! I realized that I was talking about advanced volumetrics, not simply 'fog' when I read your answer. I will take your recipe and try to brew something with it. Thanks for your very fast and clear answer.
;) |
Post by Bobbins // Jan 5, 2007, 8:03am
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Bobbins
Total Posts: 506
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Depending on your scene you might also be able to use semi transparent planes to add the effect. Set a large plane perpendicular to the camera and paint it with a semi transparent texture. Repeat, but put the next plane further away from the camera and so on. As different objects are seen through different numbers of semi transparent planes, they will appear progressively more dim in the distance. You'll likely have to increase the ray depth limit for the renderer for this to work.
The technique is used in real miniature models for film work using semi-opaque panes of glass and it is equally valid in CG. |
Post by TomG // Jan 5, 2007, 8:51am
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TomG
Total Posts: 3397
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The planes would be good for animation - you could animate the fog, either by moving the planes and / or the texture or transparency map on them.
It would also remove the need to batch process the image files as the two render pass approach would need.
As usual, there's more than one way to skin a cat as they say (not sure why cats get singled out for that treatment), and there are many ways to achieve an end result!
HTH!
Tom |
Post by Burisman // Jan 5, 2007, 10:40am
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Burisman
Total Posts: 128
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Thanks Bobbins, this sounds really promising and refined! I will explore both the techniques as suggested by TomG and you. Might take some time to figure it all ou, but I will post the result as soon as it is presentable. Many thanks for your clear suggestion.
Eelco :) |
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