Faking indirect light (GI) on an animated object - Need a simpler solution

[SaCCo]

Hi there

I need a way to fake GI on a animated object.

The problem is.
When doing object animations in an interior scene which is primarily lit by indirect light coming from the out side, Its very hard (not to say impossible within realistic render times 3-10 mins a frame on a dual quad) to get rid of flickering - even in high animation Irradiance map mode, blended over two or three frames and using a default 1000 subdivs Lightcache.

My solution to this is that I am willing to sacrifice realism on the animated object by faking the indirect light.

In details this can be done with the following technique (in a lock down camera scene)
First I select the animated object and in its vray properties I disable GI receive, GI generate and GI visible.
Next I simulate GI for the surrounding scene and "freeze" the solution by loading it from file.

Now the scene appears okay, but the animated object is black unless hit by direct light.

I can then use a Vray lightmaterial on the "black" animated object and crank up the multiplier just enough to fake light coming from its surroundings.
The downside to this is that direct light no longer shades the surface and I loose almost all of my material properties like reflection etc.

To solve this I can do a blend material where I separate which material to be used when the surface is hit by direct light and when not hit by direct light.
I use a lightmaterial as root and a default vray material coating, controlled by a falloff (set to light/shadow mode)

Now the problem is that if I need an overall reflection on the object - I then need to add a new vray Material coat on top, which is reflective controlled by a falloff with a IOR index.

All this works, but the material I end up with gets quite complex and hard to control.

Any suggestions on how to achieve the same effect in a simpler way?

[vlado]

There are several approaches to this.

One thing you can do, is calculate the light cache for your scene, without the moving object; save this into a file and then set the light cache mode to load that file. Next, you can render your object with brute force GI for the primary engine, and the loaded light cache for the secondary engine. This will cause the object to correctly pick up GI from its surroundings. Then you can composite the object into your pre-rendered background.

Another thing to do with a similar result is to put a spherical camera roughly where your object is, and render a 360 degrees HDR view of the scene; then you can use the HDR inside a V-Ray dome light to illumate your object.

Best regards,
Vlado

[SaCCo]

See post below

[SaCCo]

Hi Vlado thanks for answering

One thing you can do, is calculate the light cache for your scene, without the moving object; save this into a file and then set the light cache mode to load that file. Next, you can render your object with brute force GI for the primary engine, and the loaded light cache for the secondary engine. This will cause the object to correctly pick up GI from its surroundings. Then you can composite the object into your pre-rendered background.
Vlado

In this solution I would not be able to get reflections from the objects surrounding. (unless, I do the spherical HDR map thing)

Another thing to do with a similar result is to put a spherical camera roughly where your object is, and render a 360 degrees HDR view of the scene; then you can use the HDR inside a V-Ray dome light to illumate your object.
Vlado

This solution works with both light and reflections on the animated obejct, but problems will appear when the object moves arround coners inside the building or in generel far from its original origin.

I was hoping not comp any elements in post and have everything happen in the render.

Basicly what I need is a vray light material that can be lit by direct light, when the dirrect light is brighter than the self illumination light level.

Does this make any sense?

[vlado]

Well, there is no ready material to do exactly what you want; I suppose the solution that you have now is the only one you can do for the moment.

Other than that for the spherical HDRI approach, you can also use animated HDRI's from several locations on the object's path and blend between them based on how close the object is to the HDRI's original location.

Best regards,
Vlado

[bob-cat]

Maybe this is to simple, but, why don't you throw a heap of spots around to fake the GI for the animated object?

Select the spots to include only the animated object?

I guess this is what Vlado is meaning but using a vray dome light with the HDRI which sounds like a lot better idea.

[percydaman]

I second the mapped domelight. I think that should work pretty well.

[pixelstudio]

dunno if you can use this, but cannot you exclude the moving objects from the GI sollution (to avaoid flichering).
then compose the excluded objects of a diffuse, and a dirtmap. with some self illumination..

[SaCCo]

I agree that Dome HDR light should work quite well.

But by experience, I have learned that when doing photo real or complex animations, render passes often falls short due to the lack of "communication" between the separate passes FG/BG (reflections, light etc.). So I end up with more problems than I solve.

Anyways
Its a matter of personal believe, and I believe in "if it works in the camera - it works".
That is, you don't end up with unpredicted problems later in the process.

The method I came up with also works quite well, especially when I use a dirt map in the "diffuse" slot of the Light material, but it seems to get unnecessary complicated, which is a considerable downside.