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Smoke, inside fog?

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Tim Vining
Smoke, inside fog?
on May 16, 2018 at 4:53:29 pm

Trying to show simple non-animating chimney smoke rising over a foggy city. It's a wide shot, so I tried first a smoke image with an alpha on a plane, but the alpha shows as a dark translucent box, and from what I have read, this still seems to be a known problem for over a decade with alphas & fog. I know about using a giant visible light to simulate the fog instead, but wondered if anybody had any other suggestions?

(For a bonus, can anybody explain why a visible light can play well with alphas, but fog can't, when this has been a known issue for years?)

Thanks--Tim



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Steve Bentley
Re: Smoke, inside fog?
on May 16, 2018 at 8:23:43 pm

Have you tried putting your "alpha" for the smoke in the transparency channel of the texture? (usually you have to invert it though - white is "clear" in the trani channel.)



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Tim Vining
Re: Smoke, inside fog?
on May 17, 2018 at 9:09:56 am

Yes, thanks, I did try that and it looked the same. How apparent the alpha/trans looks seems to depend somewhat on what is behind it. The landscape above the wall is dark, so the alpha seems to be very dark.





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Steve Bentley
Re: Smoke, inside fog?
on May 17, 2018 at 3:24:01 pm

I had this problem a while ago and did solve it. I'll try and dig up the file. But in the mean time, I remember fiddling with the matte object check box in the compositing tag or including a background plane that the camera couldn't see (or both)



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Tim Vining
Re: Smoke, inside fog?
on May 18, 2018 at 1:27:07 pm

Okay, thanks! I looked into the compositing tag and didn't find a solution, but I'll take your suggesting to look into it some more. A solution for this would be great--I'm embarking on an animated fantasy project, and that means lots of fog, mist & smoke!



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