With the vast amount of various render engines steadily growing each day, 3D artists are suddenly presented with the option to render using biased and unbiased approaches.

But what’s the difference and what should you chose?

First of all, let’s jump on the terms…

• Biased means that you have manual control over how the render engine interprets your scene, how well is casts the lighting, shadows and bouncing light calculations (radiosity / indirect lighting)–and other effects such as specularity. In other words, biased means “limited”–and you set the limit.
• An unbiased render engine will do the opposite. It will not settle for anything less than 100% correct  real world calculations, meaning no manual control.  An unbiased render engine will simply calculate ALL the data, even things you hardly see–those suddle small neuances that can make a real difference.

Now that we’ve cleared that up, what’s the deal?

Biased:

More control, superior render speed, since you can choose the quality you need for your projects. Another great detail is that you can often choose and therefore predict the render times. The downside is less realistic looking renders and at times, it doesn’t matter how much quality you throw in, since the approach is quite different to that of an unbiased render engine.

Unbiased:

No control of the quality, besides some adjustements that can be made during the rendering process, such as real camera adjustments, for instance exposure, film response and so on. Now, here’s the REAL differenece. An unbiased 3D image is never done. It will render forever, until you simply save it and call it done.

It’s a  different approach to rendering, since you can adjust the exposure and many other options live and interactive. It simply “catches” your 3D scene like a real camera, and you can then play with the settings while it’s rendering. However, you can NOT choose any quality settings or how deep it should calculate. It will simply do ALL the calculations. In other words, unbiased means “un-compromised”.

Unbiased render engines often produce exceptional render quality and a realism far superior to that of a biased render engine. Of course, the downside is that rendering speed is an issue.

A biased image can be set to render in 30 sec or 2 min. An unbiased can go on for 10 hours, 24 hours or more–depending when you think it looks good enough. Another downside of unbiased images, is that they may appear noisy until a certain quality is reached, while a biased image will have a lot less noise, if none.

There are ways of accelerating the rendering using your graphics cards processor(s), so called GPU’s–but then again, it’s a matter of additional cost, using a good graphics card. Another way of dealing with the inreased render times, is to use a render farm.

So, what you choose is a matter of control, render speed, cost and the results you need.

For superior quality, I always choose an unbiased render engine. For speed and control, I choose a biased one.

And there you have it… Make your renders shine!

– Val Cameron a.k.a. Waldemar B. / Dreamlight

Val Cameron