How to create an "Atmosphere Pass"

[Scratch]

Hey Folks,

I was wondering how to achive such a atmosphere renderpass (see attachment).

I searched a bit around and found an "atmosphere object" (sop) with an example in the help, using a "v_lit_fog" shader.

I also thought about taking the zdepth pass as a mask for a solid (in comp).

A friend of mine suggested me to use a volume (cube -> create volume) and use a VolumeVOP (ramp) to control its density until it looks nice)

I'm not quite sure in wich direction I should go. Can you give me any hints?

Thanks in advance for your time and help!

[nFrame]

we typically use a depth pass for this. invert it, screen it, and curve it to look nice. maybe tonemap it a bit

I don't really see a need for a volumetric solution, I guess it depends on style and artistic directions. i.e. do you need to see air/dust particle pass by the camera lense? even then, they're are less expensive solutions.

[Scratch]

Thanks for your answer!

In the meantime, i checked both, the atmosphere object (got it to work ) and the zdepth pass solution you mentioned. Here is my comparison:

Atmosphere object (see attatchment):

+ volumetric shadows

+ (more) physical correct

- expensive in terms of rendertime

ZDepth-Path

+ easy to use

+ some kind of fake

+ cheap in terms of rendertime

- no volumetric Shadows

I ended up using the ZDetph as suggested by nframe because it is quick and sufficiant for my needs (and because I do not have the resources to devote lots of renderpower to this).

Thanks alot for taking the time to answer!

cheers

Philipp

Edited March 21, 2013 by Scratch

[nFrame]

since you have the z-pass, now throw some deep focus in there with some depth of field!

[jim c]

This is what I've done in the past. Make a new take, call it "atmo" or something like that. Add the matte (http://www.sidefx.com/docs/houdini12.1/nodes/obj/geo - Matte shading ) object property to the take, and turn all your geo objects matte property to true. For the main take, obviously this will be false, and then you can turn off the atmo object. Also consider fiddling with your mantr ROP's volume settings in the Samples tab to increase your speed. Render both, composite as needed.

[Scratch]

Exactly the workflow how I ended up doing it! Thanks for your reply jim c!

[muzaffer]

Could you share your hip file,

thanks

[Scratch]

Hey,

I can't post my hip-file because the scene is too heavy for that, but the exact same technique i used is described in an example scene which is coming along with houdini by default.

http://www.sidefx.com/docs/houdini12.1/nodes/obj/fog

You can not load or launch it from the web, but when you open up the exact same help-side from inside houdini, it works (windows)

In addition, this is the help-card of the shader I use in conjunction with the atmosphere object:

http://www.sidefx.com/docs/houdini12.1/nodes/shop/v_litfog

Hope that helps!

[TomRaynor]

There are so many nice little example hip files in the help, gotta love sidefFX for doing that. Cheers for sharing Philipp, hope the dragon is coming on well, post some stuff when you get some renders.

[Scratch]

Hey Tom!

I will for sure post everything when it is finished, just gimme a little bit more time, I'm are nearly there!

[muzaffer]

thanks for sharin, will check them