VRaySun & LightMeter calibration

[Cesc Corbera]

Hello:

I want to use VRay to simulate natural light conditions in a real-life environment, inside a building. The plan is:

-To measure real light conditions in a open-space with a Sekonic 478D light meter, in sun (direct) and shadow (indirect).

-To create a similar open-space in 3ds, with a VRaySun/Sky and a VRayLightMeter.

-Configure the VRaySun with the same coordinates, date, time that the real measures.

-Calibrate the VRaySun intensity multiplier so that the VRayLightMeter gets the same values than the Sekonic.

-Use this configuration to run the renders inside the building, adjusting the VRayPhisicalCamera exposition according to the values of other VRayLightMeters placed inside the building.

Do you think this is gonna work? Is the VRayLightMeter precise enough?

In the renders parameters, I usually need to configure the primary bounce multiplier higher than 1, and color mapping in HSV exponential. This is going to be taken in consideration in the VRayLightMeter?

Thanks!

[Dariusz Makowski (Dadal)]

Interesting idea. Well I suppose u would just have to try and see if it works... Not sure how u will need to take in to account 2.2 gamma.

[Dave_Wortley]

3dsmax Design edition has tools in to do this, but not sure how they work with VRay.

[davision]

I'm won't pretend to be an expert on the VrayLightMeter but I'm fairly certain that it measures the actual light falling on the surface as calculated by Vray using physically correct GI settings.

Gamma is irrelevant since that's just a correction applied to final output and has nothing to do with light calculations. Same story for HSV exponential color mapping -- also unrelated to the underlying light calculations.

Increasing the bounce multiplier would no longer be physical correct and based on a quick test I did -- VrayLightMeter doesn't take into account any adjustment.

Actually, using the Lightmeter to take precise calculations and then using a non-default bounce multiplier for rendering seems to be self-defeating.

[Neilg]

I'm not sure why you wouldn't just skip a step and drop a sun/sky in then expose your cameras to the light meter. what's the need for real world calibration? the end result is going to be an image with an aesthetically pleasing amount of light and you're going to re-expose the camera for each shot anyway.