Mental ray interior render problem 1 skylight

[JeffPatton]

I have just one light in the scene, thats a skylight with a HDRI map on it.

When I render the scene with GI 100000ph and FG 500ph the scene becomes realy dark. black almost. render time is acceptable

When i render with only FG 7500ph the scene is nicely lighted. but the render time is horrible.
The skylight does not emit photons, therefore it only works with FG. If you must use a HDRI to light your scene, you should try using only FG and increase the FG bounces. However it would be more efficient to use a regular sunlight setup (a photon emitting light), and some secondary fill lighting.

[Willem]

Hey Jeff,
Thanks for your reply.
What you mean is when I use FG 7500ph. I should increase the amount of bounces?
Now I use 8 bounces.

Strange thing is, when rendering the perspective/camera view the scene looks nice. (with FG 7500ph and 8 bounces.)
But when I render to texture. the lightmap doesn't look like the lighting in the perspective/camera render.

Still rendering the new bouncing settings ..

Willem

[JeffPatton]

What you mean is when I use FG 7500ph. I should increase the amount of bounces? Now I use 8 bounces.
I'm not sure. When you say 7500ph do you mean 7500 FG samples or 7500 GI photons? If it's FG samples, that's really high. You may want to consider using a blurred HDRI. You would lose a bit of shadow detail, but you would be able to use a lower FG sample setting.

Afraid I'm not very experienced with baking the lighting solution. So hopefully someone else will have some helpful info for you on that.

[Willem]

Oke back again,
Just rendered the scene from perspective view.
FG 7500 samples and bounces 40.
Just a simple preview render costs 20 minutes to render.
And the result isn't that great. Well, I see the potential when rendering the full FG, but that costs me 5 hours or more!
The main problem still, is the render time, and the quality of the render to texture output.

I assume that the quality of the render from the render to texture is the same as the perp./cam view.
but that isn't?

even when the rendertime is much longer.

Last night I made 2 renders GF 75000 samples, and FG 100000 samples, bounces both on 8.
now difference between those renders.

Do you think the amount of bounces will increase the quality of those renders? and not the FG setting?

or can I change things by filling in the size of the samples in FG? the Higher the size the more blurry it is, but the more realistic. How can I test this without waiting minutes for a simple testrender?

(its not I don't want to wait, but the scene isn't that complex. at least the viewport I am rendering. there still the rest of the house that isn't yet on screen.)

I want to make 1 lightmap of the innerwalls, so when putting this object into our realtime engine, the mentalray lighting is mapped on the object.

I assume/ it looks like the quality of the mapsize I am rendering to is enherith to the amount of FG samples?

What am I doing wrong?

Willem

[Willem]

FG samples idd. sorry for the confusion.

Ok 7500 samples is to high.
But when decreasing this amount the darker the scene becomes.
Even with 40 bounces.
I already blurred the HDRI,
and set the output rgb level value to 6,5 and the output amount to 5,5.
but rendering is going faster thats one problem fixed.:thumbsup:

Willem

[JeffPatton]

40 FG bounces with 7500 FG samples...the only reason I can imagine that your computer didn't explode was because you had used the default FG trace depth settings. :)

I'll just throw some info out here. If you're already aware of these items, sorry, but I didn't know.

1) FG max bounces will only go as high as the FG trace depth settings will allow. For example if you have the default setting of 5 for the max reflections,refractions and depth...but put 10 for the max bounces...you will only get 5 bounces.

2) If you enable GI, FG bounces will equal 1.0 regardless of what you set it to. It's ignored (unless that was changed in ver.8?)

Again, I'd really urge you to consider a GI solution instead of the HDRI route. It's very difficult & inefficient to illuminate an interior with a HDRI.

[dprgb]

Yeah, only skylight to light a room probably isn't the best way to do it. Try putting a mental ray area light the size of the window in one of the window openings. Then use photons and GI to get the interior lighting.

You might also just want to try using the ambient occlusion shader, but for 'realism' GI/photons is the only way to go.

[Willem]

Ok thanks both!

:Jeff: idd the depth was 5 idd. didn't know that affected the global bounces.. thanks!

I just made a render with FG 100 samples and bounces/depth 10. rendertime was 20 minutes.
not that bad.
but I think this isn't enough for texture baking.
maybe I have to put some area light in the windows instead..
and only use the skylight for the exterior texture rendering.

[AnthonyC]

Hi Willem,

Just a thought, but have you tried experimenting with the exposure settings to lighten up the scene?

Good luck,

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