Underwater rendering

[Deflaminis]

Hello all, thanks for peeking in.

There is a new lighting challenge at CGTalk that is an underwater scene. There is some interesting discussion going on in the thread currently. http://forums.cgsociety.org/showthre...=185&t=1061572

One of the poster's mentioned Snells Window (http://en.wikipedia.org/wiki/Snell's_window). I was wondering what some best practices would be here for getting the most realistic underwater render possible. I realize post work can really cut down time and effort, but I was hoping for any tips or advice on doing most of it in renderer.

I've been using vray for work for almost 8 years now, and to be honest I've only rendered on the top side of water, not under. So I really don't know where to begin. Thanks for any ideas!

EDIT: Added a question: Would you create a volume to put the camera in (like a box or something) or should the water just be a plane? If it's just a plane, how does that work? If not, also.. would you want to use the VrayMtl translucency? Thanks for any help!

Best Regards,
AJ

[Deflaminis]

C'mon guys! Someone has some insight here! Is the question too broad?

[anchovy]

C'mon guys! Someone has some insight here! Is the question too broad?

To get an optical manhole just take 1/the ior. 1/1.34 = 0.7462686567164179. try that. And yes as you are in the medium I would just have the surface as a plane.

Here is a quick test using the above water material with displacement, Hdr lighting and Vrayenvironment fog.



-Michael

[super gnu]

-ive done some murky underwater animation in the past. a box for the water volume with the normals flipped. displaced plane for the seabed, some pointcached wavy seaweed dotted around.

i used the "blend" aa filter. looks just right in an underwater setting.

a few particle systems for debris and plankton etc, and a direct light, with a looping "caustics generator" map and vray env. fog for those lovely caustic rays. some motion blur and depth of field, then a blurred moonlit hdri in the env slot.


the scene was focused mainly on the sea bed.. ill see if i can dig out some stills but it was a long time ago.

[Richb]

You've got me hooked on trying to achieve this 'optical manhole'/snell's window thing now Deflaminis, I'll post my findings

I've got my water's ior set to .75 and while I am getting an awesome looking underwater render, snell's window is eluding me. I don't really want to try any fake's, I'm going to let Vray seduce me with it's accuracy (or so I hope)

[vlado]

I've got my water's ior set to .75

In that case make sure that the normals of the water surface point down (towards the camera).

Best regards,
Vlado

[Richb]

Cheers Vlado, the normals are indeed pointing towards the camera, still can't get Vray to show me Snell's window, can get it in Maxwell/FryRender but not quite cracked it in vray as yet, the atmospherics, caustics and dispersion look amazing though (will post something at a later date)

There's a link with some info here in case anybody wants to see what happens in reality



taken from: http://www.camerasunderwater.co.uk/refraction

[vlado]

Works fine for me... I didn't flip the normals on the surface though, I just wrapped the camera in a bubble with inverted normals and kept the material IOR to 1.33



snell.zip

Best regards,
Vlado

[Richb]

When in doubt, ask Vlad!

That's awesome thanks for your help on that, and the scene file

Just out of curiosity, could you explain the logic behind placing the camera inside a bubble/sphere? It works perfectly but I probably wouldn't have ever considered this approach

Thanks Again

[vlado]

Because of the fog color that I used in the VRayMtl material, which is the same material on both the bubble and the water surface; otherwise V-Ray won't know when to start and stop the fog. It also helps V-Ray to compute the correct IORs. Think of it like a real-world underwater camera case

Best regards,
Vlado

[Richb]

Perfectly understandable logic, remembering that underwater camera's are indeed wrapped in a bubble (it's always the little things that count)

Thanks again, I'm sure many people will find this really helpful

Ant

[anchovy]

Thanks for the sample scene Vlado, so simple...

-Michael

[Deflaminis]

Wow step away for a weekend and there is 2 pages of posts! (My face is red.)

Thank you all for posting, I'll have some time here Wed to play with this a bit and learn more about things in this regard. Thank you all again for posting.

EDIT: To make sure I understand how Vlado got what he did, it's basically a sphere object around the camera, inside the box volume?

anchovy: That's pretty amazing, this might seem like a lame question but how did you know to do that?

[anchovy]

anchovy: That's pretty amazing, this might seem like a lame question but how did you know to do that?

I did a number of underwater shots when I was a TD at the Orphanage. We used Brazil there but the premise is the same. I admit I like Vlados suggestion and I want to try it here in a bit.

-Michael

[Richb]

It works as well as Vlado's image suggests, little bit of noise or displacement on the water and some objects above it (and HDR environment of course) and it really comes to life. Just adding a seabed to my scene which should reflect beautifully in the area outside of snell's window, with some caustics as well this should turn out nicely

Ant