RayTracing: Aliasing Vs Antialiasing

Tour theoretical line on screen

To generate a synthetic image, such as those used in films as Avatar, can produce unwanted effects or "artifacts" that impoverish the image. One such effect is called "Aliasing”.

Aliasing occurs mainly in lines and edges of straight lines, having a shape "sawtooth" that breaks the continuity.

Suppose you want to represent one of these lines on a screen composed of a set of points or pixels of equal size.

The rendering algorithm to calculate the points of the screen that light up to get the image of the line.

The line features a sawtooth shape

A first solution is to identify those pixels that are crossed by the line, namely, those who "plays" to be projected onto the image plane (computer screen).

This technique can be very simple for high quality images, but does so without exhibition that seeks to delve into more complex solutions.

This solution generates a ladder-shaped pattern that breaks the continuity of the line, and reminiscent of the toothed form a wood saw. This is the effect of aliasing.

Aliasing Effect

To minimize this, can be illuminated at different intensities, depending on "the straight line intersects", and create a blur effect in the points near.

By making the pixels small enough, lines are obtained acceptable

• The aliasing is thus defined as a distortion of the information originating sampling a low frequency image (subsampling).
• By smoothing techniques (eg supersampling) this effect can be compensated. These techniques are called "antialiasing”.
• Sampling frequencies liitan these effects are known as "Nyquist frequency

Here you have a collection of images that compare visually the same scene rendered using a simple ray tracing of three levels of recursion, and applying a technique supersampling to reduce aliasing of lines. First image is presented in “gross” and then “refined”

For an introduction to image synthesis can be found What is Ray Tracing? Introduction to image synthesis

Explanations on the effect of aliasing and antialiasing techniques can be documented in the references

When the patterns are straight, this effect is accused much, as in the following example soil

In curves is less visible forms, but creates the impression of a tarnished image

In composite images, creates areas of visual attraction, degrading the quality of the set

By introducing very bright forms that direct our attention to minimize visual impact, although there is similarly if sensitive regions is focused on
References

Image Synthesis