image based lighting tips needed

[wannabeArtist]

Hello,

I'm trying to get as photo realistic renders from my car model as possible and I thought I'd try setting up a HDR image for an environment and using FG for lighting the scene.
Now, I don't know even if this is the best way to do it, please correct me if I'm on the wrong track with this setup!

Anyhow, so far my renders are a little dissapointing. As soon as I added the HDR environment, the colors started to look really washed out.
What would help to solve this? Or is my HDR sunrise not the best choice for this?

I'm have tried changing the gamma and exposure value for the hdr image, as well as the various settings of the simple tone mapping lens shader I have in my camera, but so far with very little improvements.

The scene has a single light, with the intensity at 0, and there should be no ambient light either (ambience). Most of the render settings are at their default values, except FG is turned on off course.

Yet my renders look like this (the rubber on tire should be black or at least much darker) - any tips?

[Letterbox]

Hi,

looks like mr sun & sky, change the light back to .75, and make sure its pointing downwards, thats 'noon', it looks like its point along the ground plane which is much "later" in the day. ie Dusk.

Cheers
Terry

[Rork]

A great tool to have, and to see how things can be set up lighting wise with HDRI's, is Kel Solaar's excellent sIBL_GUI For XSI.

Browse xsibase or here on threads, or go here:
http://www.hdrlabs.com/cgi-bin/forum/Ya ... 1221392511


rob

[wannabeArtist]

Terry,

Thanks, I will try to put back some of the direct lighting (It was at 0 in that render).

Although it's showing washed out colors, it's kind of a low light scene with that HDR image I used -it was actually a sunrise (man, I had to get up early to take those shots!). But, yeah, probably I should go with a brighter image for starters.

Rob,

Thanks for the link! I watched the screen cast and will definitely give it a try as soon as I get a little better understanding of how this works. Seems like a lot of things are nicely automated there.



Just a quick additional question: am I supposed to combine things like physical sun and "light" retrieved from the image set as environment for the render pass - or are these mutually exclusive?

I got a card full of some fresh makings for a new hdr panorama - I'll see tomorrow if that works out better than that sunrise picture

[Rork]

An HDRI will give you environment lighting, but no shadows.

So in case of a sun, spotlights, neon etc., yes, you need additional lights to create the shadows generated by the sun or artificial lighting.

rob

[shushens]

If you want an easy way out, it should not be so hard.

First of all, Initialize sky shader and replace the usual soft light shader with the physical sun shader.

Then position the sun pretty close to the ground at a small angle with the X axis so that it actually looks kinda like dawn.

The sky will not be an issue in here because you are going to use the HDRI. So just get rid of the physical sky shader and bring in the HDRI. Make sure the colour profile of the image is set to 'linear'. Then activate gamma correction for render region and take a render.

The physical sun will blow everything out if you do not turn down the multiplier. Since it is dawn, 0.001 will be more than enough. Actually, this should not be. Multiplier should be 1 or at least 0.85. But the photographic exposure control shader in XSI cannot accept luminocity value in Lux, so if you raise the cd/m^2 too high, you will lose HDRI contribution, and if you don't, sunlight will blow everything out. I tried asking around what the solution could be. Never found any.

On its own, HDRI lighting alone should not give you bright normal render. If you try to raise the exposure to get such renders, certain regions will be blown out. So your render is perfectly alright. As soon as you got that dusklike result, your HDRI's job was done. The rest you have to do with direct lights, polypatches, etc.

After doing all this, if you find that tyre still looks washed out, then it's because of some other property of the material like specularity. If all else fails, lower the radiance.

Or you can try smart IBL like Rork suggested, but I personally like to do things manually. I do download their archives and use the HDR images therein though hehehehe.

[wannabeArtist]

Thanks for the tips!

I've been pretty much relying on sIBL (http://www.hdrlabs.com/sibl/index.html) since Rob posted the link to their site. Most of the lighting magic works out of the box and I really like their images too - actually I'm planning to shoot some of my own panoramas in near future