HDR setup in vray - is this correct?

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  06 June 2013
HDR setup in vray - is this correct?

I'm using my own HDR plugged into a dome light - problem I had with it was it's low intensity compared with any online tutorials:

Would this be a correct setup?
- Plug HDR in dome light and env.
- Use reference photograph i.e. single tile from panorama with known camera metadata
- Set vray physical camera to those settings.
- Adjust overall multiplier (inside VRayHDR) to get image to look like the same exposure in viewport
- Adjust render multiplier to get HDR exposure to look correct in render.

Insert sun pretty much using 1.0 multiplier, or target light with multiplier set to 16,384


Doing the above resulted in

VrayHDR multipliers: Overall 7.0, Render 6000! (I'm assuming that translates to 7x6000 = 42,000 = approx. 15stops which surprises me as I captured a fair amount of dynamic range - though the sun was clipped quite a lot but I'd be surprised if it was by 15 stops.)

And for the target light multiplier: (1x2)^14 = 15stops = 16,384
  06 June 2013
turns out that whilst I had exposure control off, mr was still selected in exposure control which meant that the Physical scale was still active.

Set to exposure none - the HDR behaves more as expected.

Overall multiplier 6, render multiplier 18

Anyone know how you'd pick an appropriate direct light intensity for this without eyeballing it?
  06 June 2013
Your light intensity should be.... 1.
  06 June 2013
Any chance you could elaborate on that? A direct light isn't as intense as say a sunlight.
  06 June 2013
I assumed you mean the intensity of your dome light that the HDRI is applied to. In that case all your intensity is taken care of by the map and is baked into the texture. So you'd just want to use an intensity of 1 on the dome light as a result.

Personally, I never mess with "render multiplier" just "overall". To each his/her own.

In terms of matching a 2nd direct light without eyeballing, you could always crop the main light source in your HDRI and map it to the texture slot of a plane light, otherwise the intensity doesn't matter too much if you're compositing in post anyway. (The above would slow down and noisy up the renders quite a bit....)

Last edited by Diffus3d : 06 June 2013 at 11:48 PM.
  06 June 2013
Yeah the dome is set to 1 but I was wondering about the separate direct light intensity simulating the sun. You're right that this could be dealt with during comp but I'm just trying to learn how to get the correct intensity if using a direct light - perhaps though it's not that important and I should just wing it.
  06 June 2013
Ok... that makes things a bit clearer.

We know the sun/sky is 'physically correct', so in my pipeline, that's the first thing I expose to. Then, I adjust the dome HDRI intensity as needed. Personally, I never adjust the sun intensity settings as they are supposed to be accurate and therefore it's the 'known' in my equation.

So I would basically work in the opposite direction than you did, start with sun and exposure, then add your HDRI around it. I did a lot of work for Nike at my last job and this is how we did it, and it went very quickly.
  06 June 2013
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