ighting in 3D computer graphics has come a long way since the early days. In the beginning there were simple point lights, then came different types of shadows, followed by area shadows (faking area lights) and ultimately true area lights arrived at the 3D scene. But it was the introduction of radiosity and global illumination that really refined 3D CG lighting, by enabling the simulation of reflected light. Still, there was more to come. Although you could already achieve a lot with area lights and reflected light, bitmap-based lighting introduced the possibility to derive light color and intensity from any desired bitmap. An ideal application for this technique is of course the simulation of environmental light, creating realistic diffused light that comes from all angles, causing evenly scattered lighting with nice subtle shadows. Combined with a bright light source like a sun or a lamp (for clean-cut shadows), you can achieve quite a realistic lighting result.

There was yet one flaw left: the dynamic range of the images used for bitmap-based lighting was too limited to yield truly realistic results. The subtle shades from the real world could not be captured in the limited value range of a standard bitmap. One day 3D CG techniques pioneer Paul Devebec developed a new bitmap format he baptized as "High Dynamic Range Imaging". The bitmap format involved a combined series of the same image with different exposures. This results in one image bearing a much higher range of value information per pixel and thus being closer to the dynamic color range of the real world.

A collection of 3D marbles, rendered with a normal bitmap for the environment lighting.

The same collection of marbles, rendered with a HDRIbase High Dynamic Range Image as the environment. The improvement in light dynamism is clearly noticeable.

The Germany-based company Sachform, founded by 3D freelancer Jan Häusle, created an impressive series of high quailty spherical panorama photos, covering the complete viewing angles from 0 to 360 degrees in all directions. The seamlessly looping environment photos were taken at several different light exposures in order to prepare them for being combined into a high-resolution HDRI bitmap of 3000 x 1500 pixels. The resulting two image collections by the name of HDRIbase are for sale independently or bundled at www.sachform.de. Each collection offers 40 different environments.

One of HDRIbase's many environmental High Dynamic Range Images

A rendered result using the above HDRI bitmap as the environment. Notice the correct color ambience caused by the HDRI environment, next to the realistic feel of the diffuse lighting.

A very important feature of the HDRIbase environments is the exclusion of the photographer and/or the equipment. In a 360 degrees snapshot it's hard to avoid capturing at least the necessary photo equipment along with the imagery. But Sachform has properly eliminated that disturbing element from the images. HDRIbase is divided into two categories: achitecture and nature. Architecture includes a number of indoor environments, ranging from a bathroom to the lobby of a building. Next to the indoor scenes, the architecture category also offers a range of outdoor environments including architectural elements. Nature, as you might expect, offers a variety of beautiful outdoor scenery. All HDRIbase environments come in two shapes: a color and a greyscale variant. The greyscale version is very useful for neutral lighting, in case you don't want the HDRI colors to influence the ambience of your scene.

An example of how two different HDRI environments surrounding the same scene can make a significant difference in overall light color tinting.

HDRI IN PRACTICE
So how do you include a HDRI bitmap in your favourite piece of 3D software? Well, first of all your 3D software needs to support HDRI bitmaps. These bitmaps come in the shape of several different formats. The most important formats are HDR (supporting the Radiance lighting simulation system) and the currently rapidly rising star is the flexible OpenEXR format, developed by special effects veteran Industrial Light & Magic. HDRIbase offers its two environment collections in both the HDR and the OpenEXR format. At the time this review is written not many 3D packages support OpenEXR yet, but most major 3D packages do already support HDR. The U.S. company Splutterfish (known for their Brazil renderer) has released a free OpenEXR loader for 3ds Max. Talking about Max: the major plug-in renderers Brazil, FinalRender and VRay already support HDRI lighting, for use with their global illumination engines. The renderers allow you to use a HDRI bitmap as an object's texture or to simply put a HDRI bitmap in the Max environment map channel and derive the scene's lighting from the surrounding pixels of the bitmap. For adjustments or conversions of HDRI bitmaps, make sure you download and install Paul Devebec's free HDRI tool HDR Shop. It's a useful companion for your HDRI needs, at least until Photoshop will support it.

THE BOTTOM LINE
Sachform has created a range of very useful image data for any modern-day 3D artist, architectural visualiser, etcetera. HDRIbase is a valuable toolset of high quality images prepared for lighting, reflection and refraction purposes. The only thing one would want to shout to Sachform is: "We want more!"

Metin Seven

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