Image Based Lighting [HDRI]

[Peter M. Gruhn]

This totally belongs in Mental Ray. Sorry.

(Hey, they both begin with 'M'.)

 

My plan is to:

 

- create a scene in Max

- generate panorama

- save as HDRI

- use HDRI to light new scene

 

My plan is sorta working. All the steps are there and I'm getting HDRI lit type results. I have two obvious troubles which I think are one.

 

- too much contribution from trees and grass. my matte material looks a little reflective.

- no strong contribution from the sun

 

On a lark I've got (even as we speak) a render going in Maxwell using the same image (loaded directly into the Renderer UI tab so w/o the exposure control on Max's loading) and it is giving a very similar result AND the camera has to be cranked for a wide and long exposure. This is supposed to be outside.

 

So it really looks like my problem isn't "can't set up the renderer to do it right" (I should have a test w/ a third party HDRI, tons of them) which I did worry about ("Am I setting the exposure correctly on import?") and instead is "can't make a proper HDRI to start with." The sun just isn't that much brighter than the trees. And this is was evidenced in Max adjusting HDR exposure. Pull the white point close to the sun and just a touch beyond and the trees would start clamping. Now I don't know about you but I've never seen a tree almost as bright as the sun.

 

So, what might I be doing wrong for getting a proper HDRI out?

 

- I'm using Mental

- I'm using a daylight system with mr_ sun and sky

- I tried boosting sun disk intensity on the sky as high as it would go.

It may have.. had an effect.

- I've set the frame buffer to [lots of] bits

- I save using the bottom option as recommended ('regular rgb' or some such language)

 

What dont' I get? My googlef-fu is down. You are my only hope.

Edited January 3, 2009 by Peter M. Gruhn
wrong forum

[STRAT]

ibl isn't hdri specifically

[cristiancol]

Whats the diference betwen IBL and HDRI, I suposed both was the same

[STRAT]

image based lighting is lighting your scene with an image. this image can be either a conventional picture or an HDR picture. 2 different things.

[Crazy Homeless Guy]

On another note, it is my understanding that FG doesn't handle IBL or HDRI well. It doesn't sample the environment enough to get the detail from the image. I don't know this for a fact, just what I have read. On the other hand, Irradiance Particle and Importons work very well with HDRI files. There are controls for how many samples are taken from the environment. This means that you should be able to get highly accurate results from HDRI.

 

The only problem with IR is that it isn't fully supported in Max yet, and even the version that is supported in Maya, doesn't support transparency in materials. Which can be quite a problem when it comes to glass. I am keeping my fingers crossed that Max2010 has full support of this.

 

http://www.mrmaterials.com/jeffs-blog/91-irradiance-particles-hdrs-and-you.html

[Peter M. Gruhn]

The only other problem is that I'm on Max 9 and whatever Mental that means ;-).

 

But looking around the web a bit did get me to believe that you can't really get strong shadows from IBL at this day and age.

 

Be that as it may (can somebody move this to Mental Ray?) my real problem is getting a proper exterior panorama with a really bright sun.

[Crazy Homeless Guy]

Correct, HDRI lighting is generally for environmental light. Typically you use an HDRI for environmental light, and then a subsequent light source to represent the sun location, and cast shadows, and increase the intensity where the light strikes. The subsequent light source typically needs manually matched to the location of the sun in the HDRI map. This makes the scene feel natural.

 

However, look at this link... This scene is lit with Irradiance Particles, and a HDRI map. At least I think there is only an HDRI map. Because IR has emphasize on enviromental sampling, the shadows cast from the HDRI map are greatly improved when compared to solution that Final Gather creates, or solutions that are generated by the current Vray lighting algorithms.

 

The solution shown in the example were created with MR 3.7, but I think the later stages of 3.6.X can do this also, as long as you use the Ctrl.Ghost shaders.

 

http://forum.lamrug.org/viewtopic.php?f=1&t=1608#p7102

Edited January 4, 2009 by Crazy Homeless Guy