Is HDRI lightning physically incorrect?

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Hello everyone

When using HDRI as an environment just for the background with Skylight and direct light for the sun, everything is OK. But when HDRI is used in Skylight to illuminate the scene ("Use Scene Environment") then i have "problems".

HDRI of clear sky in the noon, sky is blue. Since it is noon everything should be illuminated with the (almost) white light from the sun, but instead everything turns blue (like it is illuminated with blue light). I guess FG is picking up all that blue sky.

More importantly (color can be fixed with whitepoint), the lightning is quite weak. I could pass it through Gamma & Gain but, again, where is physically correct in that case?

 

What i'm asking is, is that normal behavior? If yes, then HDR images can be successfully used for lightning just in special condition (sunset, sunrise). Am i right, or am i doing something wrong?

 

Thanks in advance!

[Crazy Homeless Guy]

Not sure about your direct problems, but 99.7% of HDRI usage is artistic interpretation.

[marius e]

I think what that blue is, is a not so good quality HDR image, I also have some of those, they have an intense blue on the sides, not quite sure why, but I do not use those because of that reason. THat blue then gets reflected throughout your scene. You need some without that intense blue, just a gray instead.

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Not sure about your direct problems, but 99.7% of HDRI usage is artistic interpretation.

 

Oh, then i must have mixed up HDRI with something else (i'm still learning). Don't know why i thought they give physically correct illumination.

 

Thanks!

 

 

I think what that blue is, is a not so good quality HDR image

 

You are right, it is quite small.

[RyderSK]

Oh, then i must have mixed up HDRI with something else (i'm still learning). Don't know why i thought they give physically correct illumination.

 

Thanks!

 

 

 

 

You are right, it is quite small.

 

 

You missunderstood what he said.

 

The HDRi DOES give you physically correct result. Neither HDRi being small is a problem. You should learn more about the approach in some tutorials (there aren;t many for Mental ray though, since HDRi for archviz lighting is definitely it's weak spot).

 

Some tips though, if you use small blurred HDRi (like in sIBL setup) then you will only get weak diffuse lighting and need a direct light to it too (either direct or sun). If you use high-rez HDRi map, and it has visible sun spot, and if it's quality map, then you can tweak gamma (lower than 1, the lower the sharper the shadows will be) for higher illumination of the "sun" in map.