Energy preservation mode - RGB??

[RichardBlank]

I know there must be a good reason for this option.
When, typically, would you like to set the energy preservation mode to RGB?
I find it a bit hard to control the colors when I turn this option on.

[trixian]

I think the monochrome mode is for making caustics and refractions single coloured, and is maybe a nanosecond cheaper to compute.

[CCS]

Actually, I believe it has to do with reflections (also called specular). I read a good paper on it once upon a time, but can't locate it now.

In many materials (like plastic), reflected light sources are the same color as the light source. With metals (and other materials, perhaps?), the reflected light source is influenced by the color of the metal. Reflected environment is also influenced, but to a lesser degree. Shine a light on your coffee mug, then on a brass doorknob to see the difference.

I'm pretty sure the energy preservation mode allows you to make that distinction.

[trixian]

Could be, but you achieve the same monochrome reflection effect by tinting your reflection colour to any hue. The more saturated the more the reflection loses its colour variety.

[RichardBlank]

I just did some tests with caustics, reflections and refractions and it do not have any influence on the rendering except that the RGB took 33 sec and the MONO took 26 sec.
It has to do something with the relationship between diffuse reflections, specular reflections and refractions.

I just wonder when you're supposed to use RGB? And why it's default?

Richard

[CCS]

Or... we could look at the help.

Energy preservation mode - determines how the diffuse, reflection and refraction color affect each other. VRay tries to keep the total amount of light reflected off a surface to be less that or equal to the light falling on the surface (as this happens in the real life). For this purpose, the following rule is applied: the reflection level dims the diffuse and refraction levels (a pure white reflection will remove any diffuse and refraction effects), and the refraction level dims the diffuse level (a pure white refraction color will remove any diffuse effects). This parameter determines whether the dimming happens separately for the RGB components, or is based on the intensity:

RGB - this mode causes dimming to be performed separately on the RGB components. For example, a pure white diffuse color and pure red reflection color will give a surface with cyal diffuse color (because the red component is already taken by the reflection).

Monochrome - this mode causes dimming to be performed based on the intensity of the diffuse/reflection/refraction levels.

Sounds like my assumption was wrong...
Where then would you specify whether the material color should influence the reflection's color? Another thread, I suppose.

[RichardBlank]

That says a little more, but it does not answer my question...