Unbiased rendering From Wikipedia
An example of an unbiased render using Indigo RendererIn 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 fact, they are often used to generate the reference image by which other rendering techniques are compared to. Mathematically speaking, the expected value of the unbiased estimator will always be the correct value, for any number of samples. 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 for n samples, meaning that four times as many samples are needed to halve 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.
A biased rendering method is not necessarily wrong, and it can still converge to the correct answer if the estimator is consistent. It does, however, introduce a certain bias error, usually in the form of a blur, in efforts to reduce variance and noise. It is important to note that an unbiased technique may not consider all possible paths. Path tracing can not handle caustics generated from a point light source, as it is impossible to randomly generate the path the directly reflects into the point. Progressive photon mapping, a biased rendering technique, can handle caustics quite well. PPM is also provably consistent, meaning that as the number of samples goes to infinity, the bias error goes to zero, and the probability that the estimate is correct reaches one.
Unbiased rendering methods include:
Metropolis light transport
Energy Redistribution Path Tracing
Some of the programs that support unbiased rendering are:
Indigo Renderer From Wikipedia
This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (January 2010)
A photorealistic image rendered with Indigo.
Developer(s) Glare Technologies
Stable release 2.4 / September 15, 2010; 6 months ago (2010-09-15)
Operating system Linux, Mac OS X and Microsoft Windows
Type Rendering system
License Proprietary commercial software
A render demonstrating Indigo's realistic light simulation
Indigo Renderer is a 3D rendering software that uses unbiased rendering technologies to create photo-realistic images. In doing so, Indigo uses equations that simulate the behaviour of light, with no approximations or guesses taken. By accurately simulating all the interactions of light, Indigo is capable of producing effects such as:
Depth of field, as when a camera is focused on one object and the background is blurred; Spectral effects, as when a beam of light goes through a prism and a rainbow of colours is produced; Refraction, as when light enters a pool of water and the objects in the pool seem to be “bent”; Reflections, from subtle reflections on a polished concrete floor, to the pure reflection of a silvered mirror; Caustics, as in light that has been focused through a magnifying glass and has made a pattern of brightness on a surface.
Indigo uses methods such as Metropolis light transport (MLT), spectral light calculus, and virtual camera model. Scene data is stored in XML or IGS format.
Indigo features Monte-Carlo path tracing, experimental support for bidirectional path tracing and MLT on top of bidirectional path tracing, distributed render capabilities, and progressive rendering (image gradually becomes less noisy as rendering progresses). Indigo also supports subsurface scattering and has its own image format (.igs).
Indigo was originally released as freeware until the 2.0 release, when it became a commercial product.
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