View Full Version : HDRI and Nostrils.

01 January 2004, 07:20 PM
Hi all,

I've just started learning about rendering with Mental Ray using XSI. I've done testing with Brazil R/S in Max and don't recall having the difficulties that I'm having now in XSI in regards to overly bright nostrils.

I've tried setting up HDRI lighting both in the render pass and as actual sphere geometry... I've even tried removing the bottom half of the sphere and shifting it up in hopes that no rays would hit the underside of the nose.

I've positioned different color grids in different directions in hopes of pulling light out of that area using final gathering.

Is it final gathering that is causing these problems?

Activating final gathering is the only way to render image based lighting in XSI right?

I haven't tinkered much with global illumination yet because i've been trying to isolate the problem and resolve it just using HDRI w/ Final Gathering.

Here's a pic showing only HDRI lighting w/ FG.

Any help would be appreciated. Thanks


01 January 2004, 10:19 PM
I've noticed that the brightness changes depending on the render size, I went to a single window with a large render region and the problem was not as noticable.

Food for thought.

01 January 2004, 07:16 AM
it looks to me as if you don't have shadows turned on

01 January 2004, 05:14 PM
All the light in this render is coming from an HDRI environment dome... can you cast shadows just using the dome without the help of any standard lights?

Even if I do add some point lights or better yet, area spot lights... the shadows that are cast still aren't enough to override the illumination in the nostril area that is caused by the HDRI environment.


01 January 2004, 06:32 PM
That's because you're using too high FG radius values. Decrease them a lot, like 0.01/0.1, and increase the Accuracy considerably, like 2000.


01 January 2004, 04:51 AM
Those FG settings definitely have something to do with it.

Also, it seems the size of the model in XSI has some bearing on it as well. Maybe it would help more to understand what those radius measurements actually stand for.

I've read some tutorials and interviews from you Bernard, they've prooved very insightful, just as this comment was.

As the topic shifts from modeling to lighting and rendering over at my focused critique thread, I'd like to invite you and anyone else interested in learning more about XSI's rendertree setup with regards to realistic skin and SSS.

Thanks in advance.

01 January 2004, 05:29 AM
Plug the dirtmap shader into your radiance input. Voila! (some settings may need to be teaked).

01 January 2004, 10:04 AM
be sure that you default light is seted to 0.
you can also use Light Rig, to produce a light dome from hdr image.

01 January 2004, 10:41 AM
although the hdri image is lighting your scene the lights are providing the intensity map so they do matter where they are placed and whether or not they have shadows turned on.

01 January 2004, 03:42 PM
Alphatron >> not quite following you on the dirtmap shader. I'm sorry, i'm pretty new to the xsi rendertree... where is the dirtmap shader accessed from? and which radience input are you speaking of?

Currently my HDRI image is setup through the environment shader of my default renderpass. Are you speaking as if my HDRI map were on a piece of geometry (dome) instead?

Saturn & Quid >> Yea, my default light is set to 0, and my scene ambience is down as well. I was aware that a light was required in order to kick off the image based lighting... but I didn't know that it's position or settings were important! Thanks Quid, I'd yet to hear that one on any tutorial page. When you say intensity map... are you saying that with lights turned to 0, you can actually specify where shadows should be cast from your image based lighting? and if so, would it be important to no use point lights and only area lights so you'd get softer shadows?

The plot thickens.

01 January 2004, 06:23 PM
What Id suggest would be to set up a simple scene like grid and a torus and a spot. Set up your image based pass and play with the scene so you can see subtitle changes on a simple version. Be sure to keep the diffuse component on, on the lights you have set to cast shadows and they must have an intensity that is greater than zero. And get rid of the default light. You can turn down the final gathering settings in the environment shader node, in your hdri pass to get the effect you want. To gain even better control of your shadows, render out shadow passes and then you can have a ton of control over the blurring which can be done while compositing.

and the dirtmap shader can be found at it was created by bigmuh

01 January 2004, 05:09 PM
Is it necessary to setup standard lights in order to get any specularity? Is there any way to specify some sort of source point for an HDRI environment (possibly through a greyscale map or something) that could be used to generate specular highlights without having to add additional standard lights?

01 January 2004, 07:52 PM
Im not quite sure that I follow... But as far as I know, and I may be wrong, you need to have a light in the scene with its specular box checked in order for objects in the scene to have specular highlights. If you want more independent control of them, then why not render out the hdri pass separate and then create a highlight pass separately. Just an idea.

01 January 2004, 07:58 PM
Yea, I like the idea of the specular pass also, and that will probably done regardless, but my question really is... are specular highlights caused on objects by the brightest spots in the HDRI image? I was under the impression that you could only get diffuse lighting out of an image based light.

I might be completely wrong about this, but I thought standard lights were necessary to achieve specular highlights due to their placement in the scene... as opposed to an HDR environment which is basically coming from everywhere.

01 January 2004, 09:32 PM
Ah I see what you mean now. I think that you're right the specular only comes from lights in the scene. Somebody please correct me if that's wrong. But I am pretty sure that's the case.

If you do the hdri pass and the specular pass separate, but for the specular pass you use the same hdr image to generate a light rig which you can then use to drive and tweak the specular any way you want, then I think you can get what you're looking for in a composite.

01 January 2004, 09:47 PM
Thanks Quid, how might I go about generating a light rig from an HDR environment? My light is currently coming from the environment shader of the HDRI render pass at the moment.

01 January 2004, 11:23 PM
You create it from the left toolbar, choose Get > Light > Light Rig from Image.

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