Photorealistic rendering

In computer graphics, unbiased rendering refers to a rendering technique that does not introduce any systematic error, or bias, into the radiance approximation. Because of this, it is often used to generate the reference image to which other rendering techniques are compared. Mathematically speaking, the expected value of the unbiased estimator will always be the population mean, for any number of observations. Error found in an unbiased rendering will be due to variance, which manifests itself as high-frequency noise in the resultant image. Variance is reduced by ${\displaystyle n}$ and standard deviation by ${\displaystyle {\sqrt {n}}}$ for ${\displaystyle n}$ data points, meaning that four times as many data points are needed to halve the standard deviation of the error. This makes unbiased rendering techniques less attractive for realtime or interactive rate applications. Conversely, an image produced by an unbiased renderer that appears smooth and noiseless is probabilistically correct.

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