What’s the difference between biased and unbiased render engine?

LadyInTheMistWith 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?


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.


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


10 Responses to “What’s the difference between biased and unbiased render engine?”

  1. Larry October 14, 2012 at 4:07 am #

    That is a very interesting and worth-my-time explanation. Thanks I appreciate it.

  2. Mark October 14, 2012 at 8:28 pm #

    Thanks for the info. I appreciate the education. So if I got this right reality 2.1 is unbiased and DAZ and poser renders are biased.

    • willi October 16, 2012 at 7:53 am #

      Hey, yes Reality is part of the unbiased story for DAZ, however Reality is a plug in that makes the unbiased Lux render engine co-work with DAZ Studio, so Reality in it self is not a render engine…

  3. 3D bad boy October 3, 2014 at 10:30 am #

    Nice, clear explanation!

    (“Subtle”, not “suddle”) 😉

    • Val Cameron November 9, 2014 at 11:18 pm #

      Thanks, yepp, you’re right it IS subtle! 😉

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  5. Lancer Kind February 7, 2016 at 7:35 am #

    Never mind that other guy, he’s a spammer.
    Another aspect of biased rendering is it allows for adding a style, such as Pixars toy looking characters with shiny plastic bodies. In the last two years, GPUs have gotten good enough to do very good real actively quick unbaised rendering. Our film, Miss Wisenheimer and the Aliens uses in biased. (Trailer on YouTube.) I think it takes more courage with unbaised because you are saying you can make a scene appear realistic, where with biased, stylisations are admission of not being realistic–yet cool or interesting due to the style. It takes more courage and risk to say, we are showing reality. The audience’s minds may not accept the verisimilitude.

  6. Charleton June 26, 2017 at 11:36 pm #

    The information in this article isn’t correct.

    Unbiased rendering engines can still have quality controls. Arnold is an unbiased renderer, and you have several controls for quality; number of camera rays, number of bounces, number of shadow / sss / GI / refraction rays, etc.

    An Unbiased renderer is a renderer that mathematically cannot return a result for a rendering operation that is anything except the mean of all the results calculated for that operation. This means that even though there are discrepancies in the image as it renders (render noise) all the rendered pixels are the results of the average of the calculations for the area they cover. You can still have a low-quality image with lots of noise, but the values in the noise will are strictly representitive of the observed scene.

    A Biased renderer can return results that are outside the average result, and as such must be multisampled or “biased” towards the surrounding result data, so the average ends up being closer to the “reality” of the scene.

    • Val Cameron July 4, 2017 at 2:14 pm #

      You’re absolutely right, thanks for correcting!

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