Large scale underwater scene renders almost black

[JuhaHo]

I'm working on a large scale underwater scene - or actually it's partially underwater. When rendering, everything is way too dark probably due to distance. I couldn't fine the parameters that helps extension of underwater visibility. On rendering only visible thing is partial VRayPlane. The teapot is located at the point of interest.

The other thing; is it possible to cancel the IOR 1.33 effect? I don't want to distort the camera in order to match the underwater rendering to surface rendering.

[georgi.zhekov]

Hey,

When rendering underwater the things that will influence your renders are:

- the lighting - how strong your lights are
- the liquid shader - if you have the Underwater Goggles option turned on a surface gets automatically added in front of the camera, using the same material that is assigned to the Simulator, and this way mimics the effect of real life underwater goggles. This way the ocean volume receives the Fog color from the material assigned to the Simulator, and the field of view shrinks when the index of refraction of the material is above 1. So if your fog color of the V-Ray Material is too dark or has a high multiplier the render can become too dark

You can find how the Underwater goggles option affects the rendering here - https://docs.chaosgroup.com/display/...erwaterGoggles

So try disabling the Underwater goggles and it should look brighter and without the refraction of the liquid material.

[JuhaHo]

Thanks Georgi,

I disabled the underwater goggles option and this is what I get;

[georgi.zhekov]

Yes, this happens because the ocean surface is generated only in the camera view, which can lead to problems when using camera motion blur, using reflections, using refractions with Underwater Goggles enabled, or when the ocean casts shadows on objects underwater.

For such cases you need to use the Off-screen margin option in the Rendering rollout of the simulator. It allows you to extend the ocean further from the borders of the camera view in order to solve such issues. The value is a percentage of the image size. So start increasing it gradually as if you enter a large value it will consume a lot of memory.

[JuhaHo]

OK, here's another comparison Goggles on vs off. Goggles on on the right side begins to look underwater when I reduce the intensity value to 0.001. However the distortion is there like it's seen on far right, the viewport view. I think this would look good enough, if I could cancel the distortion. On far left can be seen what happens if I turn of the goggles, which don't look good at all.

So I'm looking for the looks in the middle with caustics and all, but without lens distortion. So what I need to do to cancel the distortion without losing the underwater looks?

[georgi.zhekov]

Then keep the Underwater goggles on and lower the IOR of the liquid material.

Cheers!

[JuhaHo]

I still don't get it. I opened and examined the Chaos underwater goggles example scene. Here's a comparison. As soon as I lower the seabed object out of camera window, the scene turns black like outer space. I have my own scene objects nicely rendered, but the tricky part is to render the water itself other than black.

[Ivaylo Katev]

The black rendering of the far underwater objects is related to the fog color of the material. There is a multiplier of this value, otherwise would be impossible to adjust the color in cases of almost purely transparent materials (like the water)

[georgi.zhekov]

As Ivaylo said, adjusting the Fog multiplier for the water material should do the job.

[JuhaHo]

Here's screenshot of the fog settings.In my scene, adjusting the fog settings are affecting only the color and visibility of the submerged objects, not the water itself which is always black (RGB 1,1,1). Do we need a back plate for underwater scenes.

In fact while writing this, I the seabed of Phoenix underwater sample to be a back plate I got following results. However, when turning the V-Ray infinite plane to be back plate didn't work at all. It's all black (RGB 0.0.0) apart from submerged geometry.

[georgi.zhekov]

Ah I got what you mean. The places where there is no geometry behind, will render black indeed. This is due to the way the fog color of the V-Ray material works.
The easiest solution would be to place a large box far back to act as a background.

[Ivaylo Katev]

The real water is not totaly black because it has small diffuse component, i.e. it acts like thin smoke. To achieve the same effect you have to add some dummy volumetric object with constant opacity, but keep in mind that this may increase the render times. On the other hand you can get the "god rays" effect as a bonus, if you need it

[JuhaHo]

Thanks again,

I created a trumpet look alike cylinder surrounding my underwater scene. It was much better, but I'm not even close to what I'm looking for. I think the effect can't be achieved with underwater goggles. I will try next V-Ray fog. Do I need an atmospheric helper if I want to add some variation depending on the depth?

[Ivaylo Katev]

I think without variation will be fine.

[Svetlin.Nikolov]

Hey, JuhaHo , indeed when there is no geometry behind the ocean fog, V-Ray understands that the fog color should continue building up infinitely, so it becomes this dark.

If you want to have varying density, the environment fog would indeed be a better choice - the vraymtl's fog can't be mapped with different densities in depth.

Still, how does it look with your own cylinder geometry?