Should your renderer be biased or unbiased?

I’m happy to say that this is not another article about workplace bias.  Rather, it is about rendering images from a 3D or CAD program.  Rendering your 3D scenes can often be a complex task, and the advent of “unbiased” renderers promises to simplify that task.  Does that promise hold true? 

Unbiased Rendering

An “unbiased” renderer is designed to be as physically accurate as possible. Although there is no such thing as “physical” in the CG world, the goal for an unbiased renderer is to calculate the path of light through the scene as accurately as possible. Hopefully, this introduces little or no “bias” to the image. Images rendered this way will usually come out a bit “noisy” at lower quality settings, but given enough time, they converge on a physically “accurate” result.  Some examples of unbiased renderers are Arnold, Maxwell, and Keyshot.

The classic unbiased renderer has just a few controls. Many, such as Autodesk’s ART Renderer, simply have a quality slider. Slide it to the right to get more quality (and longer render times) or slide it to the left for faster render times (and lower quality). This can be augmented by noise-reduction controls that can smooth out the images while keeping render times short. 

Biased Rendering

A “biased” renderer is allowed to take shortcuts in the name of efficiency and to manipulate images purposely in order to achieve a desired look.   Instead of calculating every single photon of light through the scene, a biased renderer takes a more strategic approach, leaving out parts of the solution in the interest of time. In the right hands, this can result in much faster render times while maintaining quality. A good render artist can also tweak the settings to change the look of the final images. Some examples of biased renderers are V-Ray, Mental Ray, and Renderman.

Which to Choose?

Both methods are equally viable and can produce excellent results. One way to think of the differences is that the unbiased renderer is something like a Polaroid, while the biased renderer is more like film.  A Polaroid is easy to develop, but pretty much comes out only one way, whereas film can be manipulated in all sorts of ways - both in film processing as well as in the darkroom.

As with most things, there is no firm dividing line between the two. Many unbiased renderers can have a lot of controls, while biased renderers, such as V-Ray, can be configured to operate in an “unbiased” way.  So, there is a lot of grey area.  For most people, the choice of render image will boil down to couple of key decisions.

Speed: Typically, the brute force methods used by unbiased renderers will make them slower than a biased renderer. With computing costs dropping, this may or may not be a big issue. Additionally, you also have to consider the amount of time it takes an artist to set up a render. If an artist takes more time to set up a biased renderer, yet it renders faster, is that a time savings?  Maybe, maybe not.

Ease of Use: The user interface of any renderer plays a big role in how easy it is use. Unbiased renderers are typically simpler to set up, which puts rendering into the hands of more people. This can allow the visualization process to happen closer to the source. An engineer or architect might be able to quickly toss off a render, where previously, a dedicated rendering guru may have been needed.

Features: Biased renderers, by nature, have more control, and thus more “features”.  For some organizations, the ability to dig deeper into rendering technology may be a big benefit. A larger visual effects studio may want to have that level of control, while a small architect’s office would be happy with an out-of-the-box solution. 

While each organization is different, the simplicity of an unbiased renderer can appeal to smaller shops where rendering is just one of many tasks for an artist. The learning curve is relatively small, and acceptable results can be had with little fuss. In larger, more dedicated facilities, biased renderers can be fine-tuned for both speed and quality. This additional degree of control can make or break a large project.

And before anyone asks, I like both types of renderers and have used quite a few of each. So, on that front, I am decidedly "unbiased".