How many of you use GI for rendering cars?

[ThirdEye]

my humble opinion is GI is basically useless with cars, raytracing (or even better environment mapping) and area lights do a good enough job and you save a lot of rendertime.

[Sully]

I was browsing the internet using my best mate google the other day and came across some interesting pics of photographers car lighting setups, It seems that hardly use any direct light to light the car, the technique they use is to cast light onto the white cards surrounding the vehicle and use the white spots as reflections and also the indirect light coming off the white boards, this it makes perfect sense for rendering cars as you will get a very soft diffuse light as well as nice gradiating reflections.. IVe always used a pure white material applied to a plane to replicate this effect no wonder my studio renders always look bollocks.. Im gonna try to simulate this method using gi and see what kind of results I can get, it should be possible to get almost the same result as in the pics I got with the right settings in Mentalray..I will post my progress here..

[CaptainObvious]

I don't render cars, but if I did, I would use global illumination. First I'd set the car up in an environment. Either using an HDRI if it's an exterior shot, or using white luminous polygons and sweepbacks or whatever they're called if it's a studio shot. Then I'd turn on global illumination with some kind of irradiance caching method. Irradiance caching does tend to reduce the amount of detail the lighting brings out, compared to area lights, but a car has very low diffuse anyway, so it doesn't matter all that much. In fact, rendering with irradiance caching ("final gathering" in some applications) with a few light boxes is usually faster than rendering with area lights with enough samples to be noise-free.

[Morph106]

guys, I just wanted to say thanks for talking about stuff I know nothing about and is whimsically available when hunting through massive-mofo-forums like this one.

I appreciate learning different things here and there!

[JamesArndt]

Morph,

Well it all sounds real technical I know...but if your familiar with working in 3D at all in any program the explanation is rather simple. They are talking about methods to light a scene with a vehicle in it and to also not only light the car, but to produce some very nice reflections on the body of the vehicle. They are discussing the (GI) Global Illumination method which is basically a checkbox in the Mental Ray global render settings, and it uses objects, such as polygon planes as light sources. Of course if you do use a polygon plane to light something in a scene using GI, then you must push up the Incandescence of that material so it will indeed "glow" and light the scene. Usually they will use several of these polygon planes with incandescence turned up and Global Illumination turn on. The other method I think I heard on here was just using Area Lights in the same fashion as the GI Solution. People will always look for cheaper ways to render rather than using all out GI. My opinion is that if it is indeed a still frame and high resolution, why not go all out and use full GI!? The other method Sully mentioned is really a form of "bounce lighting" that film people and professional photogs have been using for ages with using umbrellas, reflectors or just plain white boards that reflect a dull light onto something. Finally discussed was using an HDRI image to cast lighting onto a vehicle. It's basically a High Dynamic Range Image that is taken specially and put together to incorporate all the different level of exposures (lightness and darkness) into one big image. Your program of choice will look at this image at render time and if you have decided and checked that you are using Image Based Lighting, it will light the scene based on the data in the image....I think its actually areas of the image that are overexposed on the image will light the vehicle brightly and underexposed areas will put it into shadow....it's pretty realistic looking, just like the GI solution. Of course if you search there are many tricks to duplicate this without using the real thing and it's not as computationally expensive. I hope I made this all clear for you and they aren't speaking jarble to ya anymore. Believe me I know, it's hard if your new to some of this stuff. I was not too long ago and I am very new to other things being a student at Full Sail myself right now.

[Arrrgh4life]

I dont do car renderings, but from what I know, it seems like using final gather making some planes to emit lights from could work well. That and/or an enviorment map, depending if its a studio or outdoor rendering. I have seen studio renders done just by making an HDR image of some white squares on a grey background. GI would probably not be worth the extra rendering times.

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