HDRI - theory?

[CliveG]

Is it just me....

 

I've tried to do some simple tests using the HDRI dome light lighting methods in an effort to add more lighting character to my scenes. I've also played with the Gamma to increase the lighting effect of the HDRI.

 

Rather than do little test scenes, I've taken some of my finished scenes and added a Vray Dome light with HDRI to test. Admittedly I do mainly interior scenes, but have tried this on scenes with a good contribution of exterior light (big atriums etc.)

 

My conclusions so far are that I seem to be better off just using a Vray Sun and sky combo due to the longer render times that seem to happen when I involve an HDRI, either in combination or on it's own in providing the exterior light in a scene.

 

It seems that the quality of the HDRI itself has a big effect on the quality of the final image, a smaller or perhaps less well produced HDRI (perhaps 60k) results in a grainy or noisy render for me, whereas simply swapping that HDRI to a higher quality HDRI (280k) will cure the grainy / noisy results without changing render settings at all. (on a 1800x1350 pixel render)

 

In a few cases using HDRI has more than doubled the render time and to my eye (?) has just resulted in just a different colour light than the Vray Sun / Sky combo - a result that could be easily replicated with photoshop, especially in the time saved not using HDRI.

 

I don't want to give up on the HDRI lighting but am curious whether my tests are a fair reflection on IBL or whether the HDRI / dome is better suited to exterior work or maybe I should change my approach?

 

Any advice?

Oh and sorry for long post!

[Stephen Thomas]

Using the HDRI in a dome light will give you more noise to deal with, but better defined shadows. Using it in the environment slot can speed things up and make it less noisy, but at the expense of the sharper shadows.

 

Another approach is to use the sIBL plugin which automatically creates a small blurry version of your HDRi used inconjuction with a direct light to light your scene plus a larger one for reflections. The nice thing about this approach is that it automatically loads all your maps in for you and links them to a visible sphere within your scene so you can control the rotation of your HDRi via the sphere and see instant feedback in the viewport.

 

http://hdrlabs.com/sibl/

[notamondayfan]

I must admit 9 times out of 10 I find HDRIs more a hindrance than anything else. They add to render times and aren't flexible enough, and often require other work-arounds to get nice results. Sometimes I use HDRIs purely for reflections, but then again I'll generally re-do the reflections in post anyway.

[Tommy L]

Dont believe the nay-sayers, HDRI is awesome. This tutorial may help you:

http://www.zwischendrin.com/tutorials/hdr_scene_setup_tutorial.pdf

[Scott Schroeder]

I have to agree with Tom, they are extremely powerful. I used to think HDRI's were annoying and a hindrance as well. Then I was visited by the HDRI ghosts one night and I learned two very important things. One, learn how to actually use them. And two use good HDRI's for lighting and for backplating.

 

The subtle color differences that a HDR image gives you in your lighting cannot be faked. Even a perfect blue sky at noon HDRI will look better than your basic Vray Sun/Sky setup.

 

Some good free HDRI's can be found here: http://www.openfootage.net/

[CliveG]

OK if I persevere... what about using a blurry lower quality HDRI for the lighting and a sharper higher res version in the environment or reflections slot to provide crisper reflections that marry up with the lighting component.

 

Is this a mechanism for cutting the render times and the noise or is it going to be just down to meticulous adjustment of render settings to overcome the grainy results?

 

Otherwise for a predominantly interior shot, it's hardly worth the extra hour or two for the small difference it seems to provide to the overall lighting character?

[Nic H]

how long is too long for a final render?

we dont bother with the blurry hdri for light and the hi res one for relfections now

i think it can look much better than a sun sky system - of course it depends what look you are going for.

 

its very easy to troubleshoot noise with a HDRI - increase the sub divs and AA