what's a good way to create smog?

[dpcaltdcah]

I've got max design 2009 with vray. I want the amount of smog/fog to increase based on the distance from the camera as you look out over a city...

 

I assume I can either do it within max or in post using a z-depth pass in after effects/photoshop but I've never done that before so I don't really know where to start or which is a better idea.

[Chad Warner]

You could always add a fog to your camera. It's in the rendering menu under environment then atmosphere. Bsically you attach it to your camera and then set the near and far distances. I can't remember if it's been fixed or not, but it used to be that I would put a vraycolor map in the color slot and crank the rgb multiplier value super high in order for the fog to show up (if you're using vray cameras and lights).

 

Also, if you check "exopnential" you can vary the intensity of the fog based on the near and far distances.

[ruskie77]

I always do my smoke/fog in post, because you have a lot more control.

 

you're right about doing a zdepth pass. when you get your "beauty" pass into Photoshop, add a new layer with clouds in, change the layer blend mode to screen/overlay, or whatever works best with your image, the drop the z-depth in as a layer mask on the clouds. tweak the contast of the alpha with levels, curves or threshold to adjust the depth and density of the fog... if it appears a bit wrong, try inverting your alpha.

 

what renderer are you using?

[WAcky]

Yeah I've seen it done very well with the z-depth pass. I saw it used to implement a blueish haze which looked great.

[Nic H]

use vray fog?

works with vray cams properly, and its controlled with an atmospheric gizmo.

 

what i do is turn on 'material overide' with a pure black flat light material. and then render that, and comp over using screen mode to knock out the black.

 

it is a quick a dirty way, but more flexible than doing in render as people always seem scared of excessive fog!

[Stephen Thomas]

If you are using vray proxies for trees then ZDepth will not work correctly. The way around it, as mentioned above, is to use fog instead. I find by far the simplest way is to use a standard 'fog' environment effect and change it to 'layered' type, making sure to set the top and bottom values depending on the height of your scene. If you want a standard ZDepth then use a white vray light material override and a black fog. Or if you want the opposite with black foreground and white in the distance to create mist then use the opposite colours. Always keep your environment (background) colour the same as your fog.

 

Also make sure you check the box in your light material that says 'emit light on back side'. This will stop any flipped or single sided faces showing up black.

[Nic H]

how come zdepth doesnt work with proxies?

do you mean the render element zdepth.

[Stephen Thomas]

Yeah, I meant the standard max ZDepth obviously wouldn't work with vray proxies. I've never been able to get the VrayZDepth render element to work but maybe I'm doing something wrong?

[Stephen Thomas]

Okay, just tried it and seems to work fine! I guess they must've fixed it.

[Nic H]

hmm thats strange. all you do is tick it like any other element and enter you near / far distance in the elements rollout down the bottom.

 

sometimes it can be used as its aliased, and you need to do a falloff override material instead to get smooth edges.

[Stephen Thomas]

I used to always have problems with it in the past so always just went with the max one. Just ignore the above then!

[dpcaltdcah]

thanks everyone, I used fog for the time being and it looked ok. has anyone used the zdepth method for animation?

[Stephen Thomas]

Yes, I've used both Vray environment fog directly in the render and ZDepth pass in animations and both work really well. The benefit of having the seperate pass though is that as well as just putting your ZDepth sequence over the top with a screen blending mode for example, you could also use it as a mask for other effects such as colour corrections or depth of field. For large masterplans it definitely helps give a sense of scale if things blur a little towards the background.

 

And like I said you can also use it as an alpha for effects such as reducing the contrast or saturation of distant areas, or colour becoming more blue towards the horizon. All these things help sell the perspective and give realism to your scenes.

[dpcaltdcah]

thanks! we're working with the entire city of chicago and our far away bldgs tend to just be gray boxes so we can only get so realistic. but it helps make that far away stuff less noticeable. I might try it with dof too, that's a good idea.