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Aliasing refers to artifacts that occur in a rendered 3D image when the scene has not been sampled enough to accurately represent it in pixels. Because it depends more on contrast and image detail than image size, it can occur at any resolution. One of the most common aliasing artifacts is “jaggies” — or jagged edges — on rendered objects (shown below), especially where the edges are curved or diagonal.
These images were rendered from the same model (right). The first image (A) is rendered with no antialiasing. Notice the jagged edges (aliasing) along the sphere’s surface. The second image (B) uses antialiasing to achieve a smoother-looking curve without changing the sphere’s geometry.
Another common aliasing artifact is “popping,” which occurs when an object — or part of one — is small enough to intermittently fall between sampling rays. As a result, it “pops” in and out of view as it moves across the scene. Moiré patterns, which create a shimmering effect in distant regions of high-detail textures or surfaces, are another common artifact.
Fortunately, aliasing can be visually curbed by antialiasing. Antialiasing is a method of smoothing out rough or jagged edges of images, and other aliasing artifacts, to produce a more polished look. It uses a mathematical process that subsamples each pixel, then averages the values of neighboring samples to get the final pixel color. Further sampling occurs when the difference between samples exceeds a defined threshold. As a result of these calculations, antialiasing can increase rendering time dramatically.
Setting Min Level and Max Level Options
The Aliasing parameters describe the number of samples taken to compare surrounding color values that are averaged to define the color of a pixel.
The main sampling controls are the Min Level and Max Level sliders. These options determine the minimum and maximum sample rate. Each pixel is sampled at least 2^min x 2^min times and at most 2^max x 2^max times (2^n in each direction).
If the Min Level is zero, each pixel is sampled at least once. Positive values increase the sample rate and negative values reduce the sample rate to less than one initial sample per pixel (known as infrasampling). For example, if the Min Level is set to one, each pixel is sampled at least four times, if the Min Level is -1, at least one sample is taken for every four pixels (a 2-by-2 pixel square).
It is recommended to set Max Level values larger than or equal to Min Level + 2; the difference should not be higher than 3. This limitation is meant to limit the amount of memory required and thus optimize performance.
Typical values for Min Level and Max Level are -2/0 for low-quality preview rendering, -1/1 for medium-quality rendering, and 0/2 or 1/3 for high-quality renders.
Use the Min and Max Level options only to set a hard sampling limit. These options offer simple control over rendering quality. For finer control over quality, use Sampling Contrast which deals more gracefully with high-contrast cases where the Min and Max Level technique can leave behind aliasing due to the hard cutoff.
For more information, see.
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