Adaptive Sampling in the Age of Unbiased Rendering
Physically accurate spectral based rendering, like it is offered by finalRender, uses unbiased rendering methods to create realistic and physically accurate rendering results. No other rendering method is able to recreate physically correct real world effects like diffraction, interference and dispersion or even calculate radiation based effects.
Unbiased rendering, while physically accurate, suffers from higher levels of noise in the final rendering when compared to old school biased rendering approaches. In simple terms unbiased rendering can be described:
As long as you shoot an unlimited amount of random rays at a scene, the rendering will converge to what we see in the real world. However, to get the exact and error free rendering result as we see it in mother nature, an unlimited amount of rays would be needed.
I'm sure we all agree "unlimited" is not realistic to achieve within a normal life time of a human. Thanks to modern GPU and CPU advancements the amount of rays we can use in our renderings is steadily increasing, and so is the scientific progress on algorithms and theories behind unbiased rendering. Adaptive sampling is meant to help accelerate the rendering process by controlling when and where calculations happen at render time. It is the go to method to get more speed or higher quality out of a renderer. However, such speedups usually come at a cost and generally speaking adaptive sampling always bares the risk of introducing bias into any kind of rendering calculation and bias means the willful introduction of error in exchange for a possible increase in rendering speed.
Great care was taken to bring adaptive sampling methods to finalRender without introducing any bias in rendering. finalRender stays true to its physically accurate unbiased approach of spectral based rendering, even when adaptive sampling is turned on. This is possible because of how finalRender interprets adaptive sampling, calculated pixels are never changed or interpolated. The only thing finalRender does in its adaptive process is to skip processing for certain pixels that fall within a threshold. To overcome the bias pitfall, finalRender allows to recalculate any pixel after several passes even those pixels that have been skipped before so they can fall back into the threshold and become processed for some passes until ruled to be fully converged. finalRender works within a complex "feedback loop" to generate the most realistic and physically correct rendering result in the least amount of time.
The renderings shown above have been created with finalRender Subscription Drop 1, a new release of finalRender expected to ship very soon. This new release will incorporate adaptive sampling as it is outlined in this article. For more information visit http://www.cebas.com/finalRender
