Antialiasing Settings

Contains controls that set how antialiasing is performed for ray traced images. The Antialiasing section of the Ray Tracing dialog box is expandable/collapsible via the arrowhead icon to the left of the section title.


Ray Tracing dialog box with Antialiasing section expanded.

In most cases, selecting a preset setting from the Quality option menu should be adequate. To use settings other than one of the presets, you can choose Custom. Before manually changing these values, however, you should become familiar with the following material.

Antialiasing improves image quality by reducing jagged edges. For example, you might find a red region in part of a pixel and a green region in another part. Antialiasing examines different parts of a pixel and combines the values to achieve a smooth image.

MicroStation uses an adaptive antialiasing technique.

A small number of initial samples is taken in a pixel (determined by the Samples Min setting in the More Ray Tracer Settings box).
How much the samples vary from each other is determined.
If the variance exceeds the Contrast Threshold, another sample is taken and the variance is re-evaluated.
This procedure is repeated until the variance between the samples is acceptable, or until the maximum number of samples is reached (determined by the Samples Max setting).
When done, all the samples are combined into a final pixel value.

Improve antialiasing image quality by doing the following:

Take a larger number of initial samples.
Allow a larger number of total samples.
Lower the threshold at which sampling stops.

Quality

Used to set the number of Samples taken during antialiasing calculations. Choosing any of the following options: Very Low, Low, Medium, High, Very High, automatically sets the values for Samples, Min and Max. Choosing Custom lets you manually edit the values for Min and Max Samples.

Samples: Min

Sets the minimum number of samples taken per pixel during antialiasing. This can be an integer from 2–64.

Key-in: RAYTRACE SET MINSAMPLES value

As a rule of thumb, to determine the minimum time to render an antialiased image, take the amount of time taken to ray trace the view without antialiasing and multiply by the value for Min.

Samples: Max

Sets the maximum number of samples taken per pixel during antialiasing.

No more than this number of samples are taken for any pixel during ray tracing. In general it is rare that this many samples are taken.

Key-in: RAYTRACE SET MAXSAMPLES value

Contrast Threshold

Sets the degree of antialiasing for a given pixel. When the contrast between all the samples of a pixel exceeds this value, more samples are taken. When the contrast drops below this value, or when the maximum number of samples is reached, antialiasing is stopped for the pixel.

The default value of 0.1 is adequate in most cases. This can be a floating-point number between 0.001 and 1.0 — a lower value achieves a higher degree of antialiasing and results in longer rendering times. A higher value will often result in fewer samples being taken per pixel, leading to shorter rendering times with some loss in image quality.

Key-in: RAYTRACE SET CONTRAST Value

In mathematical terms, contrast is defined as the ratio of variance of the samples within the pixel to the average value of the pixel. This means that the more samples differ from the average value of the pixel, the higher the contrast within the pixel. For example, a contrast of 0.1 means that there is a 10% variance between the samples of the pixel. A contrast threshold of 0.1 implies that more samples need to be taken if the current samples vary by more than 10% from the average of the pixel.

Jitter Samples

If on, antialiasing samples are taken in a non-uniform manner.

This can be used to create a softer image, and is especially useful for still images. It helps reduce moiré patterns introduced by fixed-grid sampling of high-frequency (noisy) images. A good example is a checkerboard disappearing into the distance.

If off, each antialiasing sample is taken on a fixed grid.

Key-in: RAYTRACE JITTER

Key-in: RAYTRACE SET JITTER [ON | OFF]

Since using jitter is similar to adding noise to an image, horizontal and vertical edges in an image may become slightly ragged. Turning off Jitter Samples reduces this effect.

Usually, Jitter Samples should be turned off when creating animations to prevent temporal aliasing, where elements “pop” in and out from frame to frame.