Which Multiplier for VRayHDRI?

[JulianT_CD]

Hi guys,

pretty basic question I guess:

I want to load an HDRI image into the VRayHDRI node for use as a reflection and GI environment (not as a backplate). Am I always good leaving the VRayHDRI's "Overall Multiplier" at 1,0? Or how am I supposed to derive the correct multiplier value?

Say for instance, I have an HDRI where the hottest sun pixel has a value of 1.000. Changing the "Overall Multiplier" to e.g. 2.0 would change that pixel to a value of 2.000, right? Or is something more intricate going on behind the scenes?

Many thanks!

Julian

[Moriah]

If the hottest sun pixel has a value of 1.0, it's a pretty bad HDRI then. It should go way beyond 1.0, ideally in the 14 f-stops range. What i usually do is to check in photoshop if the HDRI has good enough dynamic range, and depending of the kind of illumination i want, i adjust the sun intensity. For example most HDRI's i have, the brightest spot has around 8 f-stops, so i manually paint it for it to have around 14 f-stops. You'll notice it behaves much better with default settings than without adjustment.

Changing the overall multiplier inside the vrayHDRI doesn't make the HDRI itself any better.

[short cirkuit]

yeah should be way more than 1 - check out the HDRIs by CG-SOURCE - they're my fav

[JulianT_CD]

If the hottest sun pixel has a value of 1.0, it's a pretty bad HDRI then. It should go way beyond 1.0, ideally in the 14 f-stops range. What i usually do is to check in photoshop if the HDRI has good enough dynamic range, and depending of the kind of illumination i want, i adjust the sun intensity. For example most HDRI's i have, the brightest spot has around 8 f-stops, so i manually paint it for it to have around 14 f-stops. You'll notice it behaves much better with default settings than without adjustment.

Changing the overall multiplier inside the vrayHDRI doesn't make the HDRI itself any better.

1.000 = one thousand Not 1.0. I know 1.0 wouldn't be enough. Sorry for the confusion.

So you never touch the VRayHDRI multiplier? All you do it manually correcting bad HDRIs and leaving good HDRI at their default settings inside VRayHDRI?


I usually dial an Exposure adjustment layer around two thirds of the slider down and if the sun remains visibly hot in a small area I deem the HDRI good enough. But how do I check precisely how many F-Stops an HDRI encompasses? Does the Exposure value directly translate to an F-Stop?

EDIT: I'm still using Photoshop CS6 Extended.

[svetlozar.draganov]

Hi guys,

pretty basic question I guess:

I want to load an HDRI image into the VRayHDRI node for use as a reflection and GI environment (not as a backplate). Am I always good leaving the VRayHDRI's "Overall Multiplier" at 1,0? Or how am I supposed to derive the correct multiplier value?

Say for instance, I have an HDRI where the hottest sun pixel has a value of 1.000. Changing the "Overall Multiplier" to e.g. 2.0 would change that pixel to a value of 2.000, right? Or is something more intricate going on behind the scenes?

Many thanks!

Julian

The easiest way would be to change the Overall Multiplier, and yes it will just multiple the pixel value by the value specific in Overall Multipler field.
Another options to change the intensity are the Output Map, Color Correction Map etc.

[JulianT_CD]

The easiest way would be to change the Overall Multiplier, and yes it will just multiple the pixel value by the value specific in Overall Multipler field.
Another options to change the intensity are the Output Map, Color Correction Map etc.

Ok thanks. And with good HDRIs, i.e. those with a high enough dynamic range, I don't need to touch the multiplier?

Also, how do I find out how many F-Stops my HDRI has?

[svetlozar.draganov]

Ok thanks. And with good HDRIs, i.e. those with a high enough dynamic range, I don't need to touch the multiplier?

It depends even with good HDRIs you might want to increase or decrease the intensity just a bit.

Also, how do I find out how many F-Stops my HDRI has?

I don't know actually.

[Moriah]

Also, how do I find out how many F-Stops my HDRI has?

You have to open them in Photoshop, since it's a 32-bit image, the color picker will be different and it will show a "f-stop" bar. If you color pick the center of the sun you'll see how many f-stops it has.

[JulianT_CD]

You have to open them in Photoshop, since it's a 32-bit image, the color picker will be different and it will show a "f-stop" bar. If you color pick the center of the sun you'll see how many f-stops it has.

Great, thanks a lot!