View Full Version : Image Based Lighting

Richard Hebert
01-06-2011, 01:29 PM
When using IBL how are specular highlights achieved without using CG Lights? I've seen some very nice renders complete with specular "hotspots" yet the caption indicates that only IBL was used without the help of CG lights. Any input would really be great on this topic.

Thanks as always,

01-06-2011, 05:59 PM
The surfacing nodes such as Delta, conductor, carpaint etc are energy conserving nodes and will produce what you are after. Specular highlights are simply reflections and these nodes will create the specular effect in the same way. The downside is a considerable render hit.

Here's a car I built a while ago that is purely lit by an HDR image, no lights what so ever.

01-06-2011, 06:19 PM
You need to model your light sources to give the surface something to render, this will show up as a 'hotspot' which in real life is just a reflection of a light source.

Richard Hebert
01-06-2011, 06:29 PM
Thanks for the responses guys. I'm new to HDRI's and Floating Point image technology and I was wondering if one of you might be able to direct me to a site that may explain some of the finer points of these formats from an artistic perspective rather than scientific. I'm looking online but can't make heads or tails out of graphs and curves as it relates to creating photoreal imagery. Thanks for examples btw.


01-06-2011, 06:41 PM

This would be a good place to look for tutorials. Nicholas Boughen is very good at lighting and it maybe worth looking ibto his tutorials to see if they cover what you are after. There are also many very knowledgeable people on this site that will be able to offer a great deal of help so don't be afraid to ask.

Richard Hebert
01-06-2011, 06:46 PM
Thanks Crash, we'll do.

01-06-2011, 06:55 PM
Here's the nodal setup I used for my car paint. With just a single HDR image used in Imageworld to light the scene.

01-07-2011, 08:02 AM
Here's my car paint shaders..

the simpler (faster to render) http://www.presetcentral.com/preset/79/
and more complex http://www.presetcentral.com/preset/419/ but more physically correct.

The thing you have to realise is that 'specular' is a big fake. It's a simulation of specular reflection bloom, which you get when surfaces reflect. Spec is a good fast simulation of the way in which light reflects of objects from small and extremely bright sources of light. However all they ever reflect is a 'disk'. Take a look at a real world surface and look at the 'specular' you will see it's just a reflection, usually irregular and colourful. Only the sun has a genuine disk shape like that :) Also specular doesn't reproduce other reflections of the scene, only the lights. Those light sources are ultra-bright, so they reflect strongly even on incredibly un-reflective surfaces.

With an HDR sphere you are capturing the full environment, including luminosity several orders of magnitude higher than the 0-255 brightness of regular images. This means that even with extremely low reflectivity values, objects can exhibit bright specular highlights for 'light sources', which wouldn't work at all for low dynamic range images. You can simulate the effect by using ultra-bright geometry (with luminosity values above 100%). I often use values in the 700-1000% range!

To get the most realistic results out of HDR you really need to render in linear colour space (which is much easier in LW10) as HDR's look 'wrong' in normal sRGB colour space in Lightwave. Most people incorrectly modify the HDR to have a 2.2 gamma modification, whereas it's the other way round, you leave it be and then modify the display space of the final render (which in most image editing/compositing apps is automatic nowadays).