View Full Version : rim light question.

08 August 2002, 04:15 PM
I've asked this question in the Lightwave section, but the more I think about it, the more I realise it's not a app specific thing.

What nifty tricks do all of you use to get good back or rim light effects. I've tried gradients in the luminosity channel but this doesn't look right because it effects all areas of a model, not just the edge.

here is the thread if you don’t understand what I'm after.

08 August 2002, 04:23 PM
faloff, translucency or... subsurface light scattering .

08 August 2002, 04:38 PM
Yeah, falloff.

08 August 2002, 04:55 PM
Falloff effects the whole object. I've tried this method, and it doesn't work.
Here is an image of what I need. There is only one light from behind. The light almost bends around the object to create a nice bright rim light. (the AA is a bit low in this image)

I suppose SSS is the way to go. I just wonder what other people used before SSS was around.

08 August 2002, 07:32 PM
Well, I'll say, you have to know what is this light (not the directly reflected, but the secondary).The light does not bend in the air. If it travels from inside the translucent parts skin,hair etc and is refracted it's SSS ;if it's bounced it's radiosity.. I think people used to cheat with their own lightning setup when there was neither.No other way I guess.

08 August 2002, 01:27 AM
Werner. What you need to do is create an array of rimlights behind your subject. Space them a littl way apart so they act as a single light source covering a broad area, say 1 or 2 metres across if you're lighting a human sized object. Why? This is what photographers do. They use things called soft boxes, which are used for soft even illumination, and are great for rimlighting.

This is what you do when you don't want to wait around for subscatsufaces or whatever to render.

08 August 2002, 08:00 AM
Thanks for all the help. I've played around with area lights in Lightwave, and it works very well. It renders way faster than SSS as well. I'm busy reading up on the 3-point light setup. Why re-invent the wheel? :bounce:

thanks again.

08 August 2002, 11:17 AM
I dont know how the faloff works in Lightwave but in max you can select it to effect Shadow/light and then shoose a second falloffmap in the light part of the first and you will get a result that the rim is only visible where you cast a ligth and the part thats in shadow is just that, in shadow. This tecnique is allso very usefull for wet surfaces that arenīt effected by direct light like inside the mouth.


hope my ramblings help you a bit.

08 August 2002, 06:07 PM
hey werner...

I know you aren't using maya...and I don't know how lightwave works...but here's a tutorial on how to make a backlight shader in maya, by Emmanuel Campin...maybe you can use it to relate in lightwave somehow..

09 September 2002, 03:50 PM
The physical way to get that effect would be to have one huge light behind the object in question. Meaning the light has a dimension to it. Usually you'd think an arealight would do this but most often the arealights in 3d packages are not true arealights, they are only areashadows. The shadows are soft but the light itself still comes from a point source so it the distribution isn't across a large surface.

If you can get hold of a plugin that does true arealights you can get that effect. I don't know what might do it for lightwave but for max you'll have Brazil (release version), finalRender Stage-1, Mental Ray and Renderdrive/Pure. Not sure about Vray.

Otherwise you will have to fake it with falloff materials or arrays of lights.


09 September 2002, 11:33 PM
Here, we use a custom RenderMan shader. Basically, it uses a modified diffuse shading model that supports brighting the edge of an object opposite the incoming light direction.
Very simple, yet effective.

A similiar shader can be found in the latest RMan SIGGRAPH coursenotes. It works with all current RMan implementations, including the free ones like 3Delight or AQSIS. Through LightMan by Tim Dapper, you should be able to use it from Lightwave too.


09 September 2002, 01:20 PM

I also built a backlight shader in Maya :


09 September 2002, 01:22 PM
sorry, the right url is :

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