volume fog lights (God rays)

[bazuka]

here is it after few min of playing



check the render time at the bottom

[aweidenhammer]

When I say "this method is fast" I don't mean turning up the color value. I mean the setup:

spotlight+animated casutic map projection
I was using the ole BF+LC method.

increasing the "color" over 1 isn't speeding anything up, just enhancing the shafts of light visually, if you don't see enough contrast.

[pg1]

Any chance of the scene?
I have setup something but no where near as fast rendertime, quad core, vray 1.5, 1280x720

[bazuka]

i forgot to say i have q6600 8gb ram

[pg1]

@ bazuka
well at least I know its possible
you on vray 2.0?

[bazuka]

no im on 1.5 and as u can see max 2009

[pg1]

got the rendertimes way down, 7 mins a frame at HD. Not sure what I did wrong before but I rebuilt the scene and the render times were much lower. Thanks for the inspiration to keep at it.

[bazuka]

ill have to think about sharing the scene

[aweidenhammer]

Most likely, the rendertime is too high because you are using a fully adaptive setup? Turn your adaptive amount down a bit... like to .95 If you have it at 1, the dmc sampler will do all the work at reducing the noise. fog this heavy will need something like 128 or 256 samples to render clean. So your dmc sampler trying to sample that high is inefficient... plus you prob have the dmc samples limited to something much lower anyway, so you'll never get rid of fog noise that way.

set the adaptive amount to .95 and tell fog to have 128 or 256 samples... you'll get much faster renders and cleaner fog.

Andrew

[ricorio]

Hi there,

I am trying to setup an underwater scene ... atm just a simple plane (floor), above the floor a sphere and env fog as an environment shader.
If the spot light is close to the sphere I can see the difference between the dark/light rays very clear. If I move my spotlight further away (in order to light the whole ground plane) the difference in the shading of the volume disappears.
The fog underneath the sphere has more or less the same color then the fog which is not in the shade of the sphere. No GI untill now.

So how can I light my whole floor plane and still get good seperation in the volume shading regarding shadow casting objects?

Thanks a lot

Rico

[Svetlozar Draganov]

Can you send a sample of the scene you are working on?

[ricorio]

env_fog_shadow_strength.zipHey Svetlozar,

here is a scene where I keyframed the spot light

frame 1 (close to the object) -> good differentiation in the volume shadow

frame 2 (spotlight futher away to light the whole floor plane) -> very very little differentiation between shade and light.

Thanks a lot

Rico

env_fog_shadow_strength.zip

[Svetlozar Draganov]

The position of the light is not so important, the shadow under the sphere is barely visible because the shaded volume is much smaller than unshaded one and when vray interpolate those values the the colors are almost identical. Here is one example with the light far away but with environment fog placed on box.

Increasing box-width parameter with make the shadows more close to the illuminated fog and vice versa.
Scene==>cg.zip

[ricorio]

Thanks alot for your explenation!

So if I understand you correct you are saying ... :
the more illuminated fog in relation to shadowed fog the less visible difference in color values.
Well that maybe correct in a physical way but can I somehow control the color value difference (illum/shade).

I can't mess with the size of my fog box and not with the spot light because they both need to encompass my scene.
So I don't see a way to change the ratio beween the illuminated and shadowed fog.

I tried to boost the color of the fog and counteract on this with the iso of a physical cam ... but this way I loose the gradients in the shading of the objects.
I put the shadows color value in the spot light to -5 which is boosting the difference in the color between shaded and illuminated fog but also gives me a really drastic lighting.

Well in most underwater reference pictures the the difference is barly visible anyway.
But I still think it would be nice to have control over that value.

Cheers

Rico

[Svetlozar Draganov]

We are sorry to inform you but there is no way to control the contrast between the illuminated and shaded part of the fog.
You have to separate the scene on separate passes and render a few versions of the environment fog with different size of the fog-width and then compose them in a way to get the effect you are looking after.