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aliasing

  1. Incomputer graphics and video, aliasing refers to unwanted effects in computer-generated graphics that occur due to inadequate sampling techniques. These effects can be seen in the staircase gradient in color transitions of bitmap graphics and in the jagged curves in fonts, curves, circles, and so on. Aliasing occurs especially with oblique or curved lines and is more disturbing the lower the sampling rate.
    Circle display without and with anti-aliasing

    Circle display without and with anti-aliasing

    All measures to prevent these effects are called anti-aliasing. This is software that calculates color gradients, background colors and edges and smoothes them so that color transitions appear continuous and the edges of fonts, edges and curves appear smooth again.
  2. For audio, aliasing is apparent frequencies that occur during A/D conversion and are above half the sampling rate. These apparent frequencies, or noise, can occur when multiple samples are represented by the same value or when the sampling rate does not satisfy the sampling theorem.
    Alias effect when undersampling a sinusoidal signal

    Alias effect when undersampling a sinusoidal signal

    In such an "undersampling" the amplitude frequency responses overlap. Aliasing is avoided by multiplying the sampling frequency or by oversampling.
Informations:
Englisch: aliasing
Updated at: 15.03.2009
#Words: 179
Links: graphics, video, computer, sampling, color
Translations: DE
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