FOG

I have a scene were I need some rolling fog, slow/dense fog. I have tried doing it in 3D and it does look very nice but the render time is not worth the image. I was thinking of doing this in PI3 but not quite sure how to go about getting a nice slow rolling dense fog that I could use. Any help would be great. My scene is set up were the viewer is inside a car driving down the highway. The fog is light and then starts to get thicker, to the point were the viewer can not see more than 10 feet in front of them. So the fog would need to be slow enough that the fog does not look like it is flying past the car but enough to see that the car is moving thru the fog and that there is some change in the fog so it does not look so flat (2D). I hope this makes some since. Thanks a million.

Dave

I love when Paul posts clips, because he always goes to the trouble of adding sound, and making a polished sample.

He could have just shown the fog emitter in action, but he put it in context! Nice job!

Alan.

http://www.allbetsareoff.com/pIllusion/Fog_3D.mov

Check it out. pIllusion and Fog 3D in After Effects.

Aharon Rabinowitz
arabinowitz@yahoo.com
http://www.allbetsareoff.com

It would be hard to teach this in detail, if you don't use AE or 3D, but I'll try...

In addition to Alpha Channel and color (RGB) info, many 3D applications (like Maya or Max) let you save information which can give you deeper control over your rendered images. The RLA or RPF image format can contain several extra channels, such as Z-Depth, Camera position data, Object ID’s... and many more.

Basically, you set up your image/animation in a 3D program and make sure that the format you are outputting your images in CAN and DOES contain the channels you want to use. Z-depth, which is probably the most often used channel, tells AE how far away each object in the image is from the camera. From there certain 3D-based effects can be applied.

When you import a file containing these extra channels, After Effects will automatically interpret the data, knowing what channels can be found in the image files.

The fog 3D effect creates a z-depth-based fog effect, by taking a color that you pick, and blending it with the 3D image/sequence you've rendered. the blending is based on how far the object's are from the camera. The further away they are, the stronger the color blend.

The problem is that on it's own, the effect looks too fake, that is, it just fills it up with color, but no texture.

However, using a greyscale smoke image sequence I made in pIllusion (an area emitter of smoke filling the screen), you can get something that looks a lot more real by telling AE to use that image as a matte for the Smoke effect, giving it texture.

All of it is composited in After Effects.

So, for this effect you need:

- A 3D image rendered with the Z-Depth Channel embedded.
- After Effects Production Bundle (for 3D Channel Effects)
- pIllusion to render the smoke particles

Hope this helps.




Aharon Rabinowitz
arabinowitz@yahoo.com
http://www.allbetsareoff.com

Like I said this would be a tough one. I strongly suggest you get trish and Chris meyer's books "Creating Motion Graphics with After Effect" vol 1 and 2. In volume 2, 3D compositing of this nature is xplained in detail. It's how I learned this stuff.

Anyway, choose the pIllusion render as your Gradient Layer (Make sure it is in the comp, and the video switch (eyeball) is set to off).

To fog an infinate BG (i.e., not items in certain areas of the shot) choose "Foggy Background" from the options in the effect. You need to have no Alpha channel in your picture for this to work, or AE won't be able to add fog to the infinate BG, since it isn't present (with an alpha channel, the empty BG areas get cut out).

For emitters, try "smokey variation 2" (in the pI3 smoke library) and make it an area emitter.

FYI, the Z-Depth channel is not anti aliased, you may want to consider rendering at twice the size so that the Z-Depth comes in clearer.

Again, if you want to use AE like a pro, get Trish Meyer's books. There will almost never be a question they can't answer - and I've come up against some pretty obscure problems that she knew about, especially when dealing with 3D.


Aharon Rabinowitz
arabinowitz@yahoo.com
http://www.allbetsareoff.com

Aharon,

Sorry last question about this I promise. You said make the PI emitter an area emitter. How do you change the emitter to a area emitter?

Dave

Thanks to everyone’s reply. I have been playing with several different ways of pulling this effect off. I know from some test that fluid effects although look great in Maya are a really render time pain in the butt. I will look towards PI3 and z depth rendering after looking at some of the examples. IF I have any more problems I know and hope you guys can help. Once again thanks for the help.

Dave

I'll post a little something once I complete it.