Aliasing

aliasaliasedtemporal aliasingaliasesaliasing artifactaliasing artifactsaliasing distortionanti-aliasingare physically equivalent to vectors inside itdigital aliasing
In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled.wikipedia
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Spatial anti-aliasing

anti-aliasinganti-aliasedantialiasing
For spatial anti-aliasing, the types of anti-aliasing include fast sample anti-aliasing (FSAA), multisample anti-aliasing, and supersampling.
In digital signal processing, spatial anti-aliasing is a technique for minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution.

Digital audio

digital musicdigitalaudio
Aliasing can occur in signals sampled in time, for instance digital audio, and is referred to as temporal aliasing.
Analog signals that have not already been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the aliasing distortion that is caused by audio signals with frequencies higher than the Nyquist frequency (half the sampling rate).

Supersampling

supersampledantialiasingfull-scene anti-aliasing
For spatial anti-aliasing, the types of anti-aliasing include fast sample anti-aliasing (FSAA), multisample anti-aliasing, and supersampling.
Supersampling is a spatial anti-aliasing method, i.e. a method used to remove aliasing (jagged and pixelated edges, colloquially known as "jaggies") from images rendered in computer games or other computer programs that generate imagery.

Anti-aliasing filter

anti-aliasinganti-aliasing (AA) filteroptical low-pass filter
Aliasing is generally avoided by applying low pass filters or anti-aliasing filters (AAF) to the input signal before sampling and when converting a signal from a higher to a lower sampling rate.
Since the theorem states that unambiguous reconstruction of the signal from its samples is possible when the power of frequencies above the Nyquist frequency is zero, a real anti-aliasing filter trades off between bandwidth and aliasing.

Moiré pattern

moirémoiremoire pattern
It can also occur in spatially sampled signals (e.g. moiré patterns in digital images); this type of aliasing is called spatial aliasing.
Moiré patterns are often an artifact of images produced by various digital imaging and computer graphics techniques, for example when scanning a halftone picture or ray tracing a checkered plane (the latter being a special case of aliasing, due to undersampling a fine regular pattern).

Reconstruction filter

filteringFiltering by reconstructionmultivariate interpolation kernels
Suitable reconstruction filtering should then be used when restoring the sampled signal to the continuous domain or converting a signal from a lower to a higher sampling rate.
The sampling theorem describes why the input of an ADC requires a low-pass analog electronic filter, called the anti-aliasing filter: the sampled input signal must be bandlimited to prevent aliasing (here meaning waves of higher frequency being recorded as a lower frequency).

Sampling (signal processing)

sampling ratesamplingsample rate
In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled. If a piece of music is sampled at 32000 samples per second (Hz), any frequency components at or above 16000 Hz (the Nyquist frequency for this sampling rate) will cause aliasing when the music is reproduced by a digital-to-analog converter (DAC). See Sampling (signal processing), Nyquist rate (relative to sampling), and Filter bank.
That fidelity is reduced when s(t) contains frequency components whose periodicity is smaller than two samples; or equivalently the ratio of cycles to samples exceeds ½ (see Aliasing).

Nyquist frequency

Nyquist limitNyquistN/2 different frequencies
If a piece of music is sampled at 32000 samples per second (Hz), any frequency components at or above 16000 Hz (the Nyquist frequency for this sampling rate) will cause aliasing when the music is reproduced by a digital-to-analog converter (DAC).
It is sometimes known as the folding frequency of a sampling system.

Analog-to-digital converter

ADCanalog to digital converteranalog-to-digital conversion
Audio signals are sampled (digitized) with an analog-to-digital converter, which produces a constant number of samples per second.
The SNR of an ADC is influenced by many factors, including the resolution, linearity and accuracy (how well the quantization levels match the true analog signal), aliasing and jitter.

Wagon-wheel effect

wagon wheel effect
In video or cinematography, temporal aliasing results from the limited frame rate, and causes the wagon-wheel effect, whereby a spoked wheel appears to rotate too slowly or even backwards.
In these recorded media, the effect is a result of temporal aliasing.

Nyquist rate

Nyquist sampling rateNyquist limitNyquist
See Sampling (signal processing), Nyquist rate (relative to sampling), and Filter bank.
And 2B is called the Nyquist rate for functions with bandwidth B. When the Nyquist criterion is not met (B > ½ f s ), a condition called aliasing occurs, which results in some inevitable differences between x(t) and a reconstructed function that has less bandwidth.

Distortion

distortedharmonic distortiondistort
It also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal.
Other forms of audio distortion that may be referred to are non-flat frequency response, compression, modulation, aliasing, quantization noise, wow and flutter from analog media such as vinyl records and magnetic tape.

Undersampling

bandpass samplingundersampled
Undersampling, which creates low-frequency aliases, can produce the same result, with less effort, as frequency-shifting the signal to lower frequencies before sampling at the lower rate.
When one undersamples a bandpass signal, the samples are indistinguishable from the samples of a low-frequency alias of the high-frequency signal.

Nyquist–Shannon sampling theorem

sampling theoremNyquist-Shannon sampling theoremNyquist theorem
is met for the highest frequency component of the original signal, then it is met for all the frequency components, a condition called the Nyquist criterion.
When the bandlimit is too high (or there is no bandlimit), the reconstruction exhibits imperfections known as aliasing.

Multisample anti-aliasing

MSAAanti-aliasedanti-aliasing
For spatial anti-aliasing, the types of anti-aliasing include fast sample anti-aliasing (FSAA), multisample anti-aliasing, and supersampling.

Signal reconstruction

reconstructreconstructionPixel filtering
When a digital image is viewed, a reconstruction is performed by a display or printer device, and by the eyes and the brain.

Whittaker–Shannon interpolation formula

interpolation/sampling theoryreconstructingsinc interpolation
But the fidelity of a theoretical reconstruction (via the Whittaker–Shannon interpolation formula) is a customary measure of the effectiveness of sampling.
(See Aliasing.)

Jaggies

jaggednessjagginessjaggyness
"Jaggies" is the informal name for artifacts in raster images, most frequently from aliasing, which in turn is often caused by non-linear mixing effects producing high-frequency components, or missing or poor anti-aliasing filtering prior to sampling.

Stroboscopic effect

stroboscopicstrobe effectstroboscopically
The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous motion is represented by a series of short or instantaneous samples.

Wave field synthesis

sound field synthesiswave fieldWFS
Spatial aliasing, particular of angular frequency, can occur when reproducing a light field or sound field with discrete elements, as in 3D displays or wave field synthesis of sound.
There are undesirable spatial aliasing distortions caused by position-dependent narrow-band break-downs in the frequency response within the rendition range.

Sawtooth wave

sawtoothsawsaw wave
Six sawtooth waves are played in succession, with the first two sawtooths having a fundamental frequency of 440 Hz (A4), the second two having fundamental frequency of 880 Hz (A5), and the final two at 1760 Hz (A6).
If the waveform is digitally created directly in the time domain using a non-bandlimited form, such as y = x - floor(x), infinite harmonics are sampled and the resulting tone contains aliasing distortion.

Wavelength

wavelengthswave lengthsubwavelength
Waves must be sampled at more than two points per wavelength, or the wave arrival direction becomes ambiguous.
This produces aliasing because the same vibration can be considered to have a variety of different wavelengths, as shown in the figure.

Signal processing

signal analysissignalsignal processor
In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled.

Artifact (error)

artifactartifactsartefacts
It also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal.