Tech Thursday: The Right Light
There are two main topics to cover: Radiosity, or Global Illumination (GI) and High Dynamic Range Images (HDRI). These two technologies work together to dramatically improve the ability of 3d rendering software to achieve realistic light and shadow, which, as you'll see, is by far one of the most important parts of a good image. First, though, lets do a little history.
It all started in the early nineties, when some computer graphics programs, notably the Institute for Creative Technologies at Stanford University began work on a novel method for lighting a scene using an existing real life lighting scenario, or "light space". Think of it like trying to transport the current lighting configuration of your room -- with floor lamps, a chandelier, and even the light from your computer monitor -- into your 3d program. Their solution was to use a panoramic image of the room, captured at the point where the product should appear. This panorama was obtained either by stitching lots of camera images, or by using a few captured by a mirror ball, or a super-wide-angle lens. But the real trick came when they wanted to describe the full range of brightness in the scene, from under the desk, where there's very little light, to staring straight at the lightbulb for maximum light. If they could capture all this information, then you would have a full description of the lighting in the scene at that point.
But, there was a problem. You know that if you take a picture straight at a bright light, and then with the same exposure settings, take a picture of the under-the-desk, you'll get one picture which is really blown out, or one that is really dark, or both. There is no way to capture that high of contrast, called a "dynamic range" of on film, let alone on a digital camera. So, in order to solve the problem, they developed a new file format which included all the information from a series of images taken at different exposure settings and merged. This was the HDRI or High Dynamic Range Image. HDRI's are pretty complicated to create, since you not only need to take a series of pixel-matching panoramas, but also learn new software to stitch them together. But, if you're interested in looking into it, HDRI Shop is the tool of choice for creating and editing them. Otherwise, take a look at these great panoramas from Vienna.
At the same time, rendering programs and computers were becoming powerful enough that they could run the millions of calculations needed to solve more complex lighting problems. The first one of these to be implemented was a global illumination renderer. In order to simulate the complex lighting from all directions that the sky, or a very nice studio softbox would produce, GI renders hundreds of light sources arranged around an object. Images like this one are created in this way.
Even more power-hungry, is the "Holy Grail" of these lighting solutions: radiosity rendering. Rather than simply looking out from the camera to see what light gets picked up, a radiosity system actually emits packets of light from each light source which bounce around the room, getting absorbed, reflected, and even color-shifted by the objects they hit until they reach the camera. Without radiosity, the red tint of a dark room lit only by light reflected off a half-open red door would not be rendered. When you combine a GI rendering with Radiosity and an HDRI light map, you get the potential for some of the most realistic lighting and shadows you can find.
So, how are you going to get started in this stuff. First off, you need a renderer that can handle it -- Brazil, 3ds MAX, Lightwave, and Maya all have these capabilities in their latest versions.
Second, you need some HDRI Files. If you're so inclined, you can make your own. We would recommend that you start by digitizing your favorite studio lighting setups. Imagine being able to photoshop a 3d prototype and the final item next to each other and have the lighting match perfectly. Or, you can buy yourself a set of "pro-quality" image maps on CD. HDRImaps.com and HDRI-studio.com have some pretty nice selections, but the prices are steep. Otherwise, you can find good files at the Vienna site mentioned above, or at Paul Debevec's Site. Paul is one of the pioneers of this sort of rendering, and his research projects will open your eyes to entirely new ways of looking at color and spatial information -- a definitely worthwhile read.
Third, you need to know how to setup the scene. There are all kinds of web tutorials which have done this job better than we ever could, so here are a selection :
--More in-depth HDRI explanation
--A tutorial for HDRI and GI in Brazil
--HDRI in Max 6 with no plugins needed
--Complicated looking tutorial for Maya
--HDRI in Lightwave
We don't mean to make you all experts overnight with this stuff. But lighting isn't often emphasized in classes that teach ID 3d modeling, and you definitely could have missed this stuff. So now you've got a head start to learn as much as you need to make some really awesome renderings. Good luck guys.
Copyright 2004-2006 Dominic Muren and IDFuel Team