New to MR. Trouble getting strong Bounce light

[Patrick Sirk]

I primarily do daylight exteriors. I use an Hdri skydome and a spotlight with an angle of 179 degrees to simulate a direct sunlight. My spot emits photons. However, I just can't seem to nail the strength of the bounced lighting. To my eye, I simply do not see enough bounce from the ground plane or brightly lit surfaces.
This is what I've tried: Low exponent values (.1 - .9). High photon intensity 16000, 32000. The problem is that I get really hot spots around the dense photon areas, far hotter than any "normal" value in the render. It is as if energy is being added where the light is bouncing which is physically impossible.
I need to match some renders I did with Brazil which my producers are thrilled with but I must use MR in Maya because of heavy animations of both charcters and cameras. Any help here would be a life saver.
Pat Sirk

[bart]

So you used diagnostic photon to see the density?

When you say a spotlight of 179 degrees do you mean almost a full hemisphere? That will be a lot of photons required.
How many photons for the light?

What are the materials on the bounce surfaces?
Do they have appropriate photon shaders?

Does the HDRI skydome emit photons?

Are you using final gathering (FG)?

How many bounces on average do you want?
Consider using FG only with secondary diffuse,
if less than 3 and you are in Maya 6.5

[bart]

Keep in mind that high intensity with low photon count leads to sporadic hot spots.

For each light, a photon contains intensity/photons amount of energy. More photons spreads the energy out.

[Patrick Sirk]

Thanks for the reply, Bart. Your response indicates that I really don't know all the tools that I should be using. (I use Maya 6.1). I'm using a Spot with an angle of 179 (yes almost hemispherical) because I'm told MR does not like directional lights.

The spot is emitting 5000 photons with Intensity at 20000 and exp. at .6

Max Photon Depth is at 8

I am using FG (2000 rays)

The HDRI dome is emitting Phots but not "light" (I haven't seen much difference between having Photons on or off which confuses me)

None of my materials have any photon shaders applied..How importnt is this? Should I disable all Maya shaders to do this? How do I do this?

[Patrick Sirk]

OK...I just realized that Irradience color can go beyond 1.0 and that it is not dirclt linked to "Irradience". Already getting closer to the results I want.

[bart]

And for a hemisphere that needs to spread all over a scene, 5000 photons is a very small number.

[bart]

In comparison, for FG that sounds like a lot of rays.
However, it is scene dependent.

Personally, I'd try some lighting tests with FG only at around 100 to 200 rays, or 200 to 400 in Maya 6.0.1.

You'd probably want to increase the number later, but for getting a feel of the lighting in the room, interactively, that would do.

[bart]

Emitting photons without photon shaders doesn't do you any good.
I suspect there may be some default photon shader behavior happening.

Some tips.

GI and caustics use photons. FG does not.
Photon tracing happens in the front part of the render.
It shoots photons and the photon shaders on the materials store photons into the photon map.

FG points are mostly created ealier in a pre-processing phase.

Later, in the ray tracing phase, the indirect illumination calculation in a material uses illumination from the photon map for GI and causics, and illumination from nearby FG points for FG.

I believe the irradiance factors affect all indirect illumination.

[Patrick Sirk]

excellent, I'll dive into a new series of tests and let u know...Most helpful...thanks a million Pat Sirk