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Ringing artifacts

Ringing artifacts, also known as the Gibbs phenomenon, are spurious oscillations or ripples that occur near sharp transitions or discontinuities in signals, arising from the approximation of functions using finite Fourier series or transforms in digital signal processing.^[1]^[2] These artifacts manifest as wavy patterns or "ghosting" effects, with the overshoot typically reaching about 9% of the jump discontinuity height, and their severity decreases with distance from the transition but persists regardless of the number of terms used in the approximation.^[3] In image processing, ringing appears as alternating bright and dark bands around high-contrast edges, commonly introduced by lossy compression algorithms like JPEG, aggressive sharpening filters, or reconstruction from undersampled data in techniques such as MRI or deconvolution.^[1]^[4] For instance, in magnetic resonance imaging (MRI), they present as parallel lines adjacent to boundaries like the skull-brain interface, resulting from finite k-space sampling and inverse Fourier transformation.^[2] Mitigation strategies include increasing sampling resolution, applying low-pass filters, or using advanced deringing algorithms based on sparse representations or variational methods.^[1]^[5] In audio signal processing, ringing manifests as damped oscillations or echo-like artifacts following transients, such as percussive sounds in drums or piano attacks, primarily caused by the impulse response of digital filters like equalizers or anti-aliasing filters in digital-to-analog converters.^[6] Pre-ringing (before the transient) and post-ringing (after) can occur, often in ultrasonic frequencies during resampling, and are reduced by employing minimum-phase filters or higher sampling rates to preserve transient fidelity.^[6] Overall, ringing artifacts degrade perceptual quality across domains—from visual distortions in compressed media to audible "smearing" in sound reproduction—and remain a fundamental challenge in bandlimited signal reconstruction, prompting ongoing research into adaptive suppression techniques.^[7]^[1]

Fundamentals

Definition

Ringing artifacts refer to unwanted oscillations or ripples that manifest as spurious signals near sharp transitions or discontinuities in processed signals, images, or audio.^[8] These distortions arise from limitations in representation techniques, appearing as repetitive waves or halos adjacent to edges or abrupt changes.^[9] They are primarily associated with the Gibbs phenomenon, which occurs in Fourier-based approximations where a finite number of harmonics fails to accurately reconstruct discontinuities, leading to overshoots and oscillations.^[10] This phenomenon, first described in the context of Fourier series convergence, underpins the oscillatory nature of ringing in various transform-based processing methods.^[11] Unlike random noise, which is stochastic and uniformly distributed across the signal, ringing artifacts are periodic and localized, exhibiting structured, deterministic patterns confined to regions of high contrast.^[12] Historically, these have been termed Gibbs ringing, truncation artifacts, or spectral leakage artifacts, reflecting their origins in frequency truncation and windowing effects.^[9] Such artifacts commonly appear in domains like digital imaging and audio signal processing.^[2]

Contexts of Occurrence

Ringing artifacts manifest across multiple technical domains in digital signal processing (DSP), where they arise from band-limiting or filtering operations that approximate discontinuous signals.^[13] In image compression, such as JPEG or HEVC standards, these artifacts appear as oscillatory halos or ripples around sharp edges due to the truncation of high-frequency components during transform coding and quantization.^[14] Similarly, in magnetic resonance imaging (MRI), Gibbs ringing—also termed truncation artifact—presents as parallel lines adjacent to high-contrast boundaries, like the cerebrospinal fluid-spinal cord interface, stemming from finite k-space sampling in the Fourier reconstruction process.^[2] In audio encoding, particularly perceptual coding schemes like MP3, ringing manifests as pre-echo (sound preceding transients) or post-echo (lingering after transients) in block-based compression, where short attack times smear impulsive signals such as percussion strikes across frame boundaries.^[15] For oscilloscope signal measurements, ringing appears as overshoots and oscillations near voltage transitions in high-speed waveforms, induced by the instrument's band-limited response when capturing fast edges, as seen in time-domain reflectometry (TDR) or eye diagram analysis.^[11] Hardware contexts involving analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) exhibit ringing due to finite sampling and reconstruction filtering; for instance, the sinc interpolation in DAC output stages introduces oscillatory transients around step changes, amplifying with steeper filter roll-offs.^[16] In modern applications, super-resolution techniques in AI-generated images often produce ringing near enhanced edges, as neural networks struggle to reconstruct high-frequency details without introducing Gibbs-like oscillations, particularly in medical imaging upscaling.^[17] Likewise, high-speed printed circuit board (PCB) signal integrity analysis reveals ringing in simulations of transmission lines, where discontinuities like vias cause resonant overshoots in gigahertz-range signals, impacting data rates beyond 10 Gbps.^[18]

Causes

Gibbs Phenomenon

The Gibbs phenomenon refers to the oscillatory overshoot and ringing that occur in the partial sums of the Fourier series of a piecewise continuously differentiable periodic function near points of jump discontinuity.^[19] This behavior manifests as persistent ripples on either side of the discontinuity, where the approximation exceeds the true function value before settling toward it.^[20] The phenomenon was first described by Henry Wilbraham in 1848 in a paper examining the convergence of Fourier series for discontinuous functions. It was independently rediscovered and popularized by J. Willard Gibbs in 1899 through his analysis of Fourier series convergence, following earlier experimental observations by Albert Michelson in 1898 using a harmonic analyzer. Although the effect bears Gibbs's name, Wilbraham's earlier work highlighted the non-uniform convergence near discontinuities, laying the groundwork for later mathematical scrutiny.^[19] A key characteristic is that the amplitude of the ringing approaches a fixed overshoot of approximately 9% of the jump height, independent of the number of terms in the series, with the oscillations decaying slowly as one moves away from the discontinuity.^[19] For the classic example of a square wave with a jump discontinuity at x = 0, the partial sum S_N(x) exhibits oscillations whose maximum height near the discontinuity is given by

\frac{1}{2} + \frac{1}{\pi} \int_0^\pi \frac{\sin t}{t} \, dt \approx 1.089

times the half-jump value, where the integral evaluates to the sine integral \mathrm{Si}(\pi) \approx 1.85194.^[20] This overshoot persists in the limit as N \to \infty, illustrating the failure of pointwise convergence at the discontinuity despite uniform convergence elsewhere for smooth functions.^[21] The Gibbs phenomenon underscores a fundamental limitation in Fourier analysis: it is inherent to any band-limited approximation of functions with sharp transitions, such as ideal low-pass filters, where truncating high-frequency components inevitably introduces these oscillations.^[22] This property explains why exact reconstruction of discontinuous signals requires infinite bandwidth, impacting applications in signal processing where finite representations are unavoidable.^[19]

Filter Impulse Responses

The impulse response of an ideal low-pass filter is given by the sinc function, expressed as h(t) = \frac{\sin(\pi f_c t)}{\pi t}, where f_c is the cutoff frequency.^[23] This continuous-time response exhibits infinite-duration oscillations, or ringing, that decay inversely with time, arising from the abrupt discontinuity in the filter's frequency response at the cutoff.^[24] In discrete-time systems, finite impulse response (FIR) filters approximate this ideal sinc function by truncating it to a finite length, which introduces approximations that manifest as truncated ringing in the time domain.^[25] This truncation preserves the oscillatory nature near the filter's edges but limits the duration of the ripples, often exacerbating localized artifacts around sharp signal transitions. High-pass and band-pass filters exhibit similar ringing behaviors due to their oscillatory impulse responses, particularly at the cutoff or center frequencies, where the frequency response discontinuities lead to prolonged oscillations in the output.^[26] In image compression schemes like JPEG, quantization of discrete cosine transform (DCT) coefficients effectively imposes band-limiting, which triggers Gibbs-like ringing effects along high-contrast edges.^[27] Non-ideal filters with smoother roll-off characteristics in the frequency domain reduce the amplitude and extent of ringing compared to brick-wall designs, though they cannot fully eliminate the phenomenon inherent to band-limiting operations.^[16]

Analysis

Time Domain Characteristics

In the time domain, ringing artifacts manifest as alternating positive and negative peaks that are symmetric around sharp edges or transients in signals and images. These oscillations arise prominently in the response to abrupt changes, such as step inputs or discontinuities, creating ripple-like patterns that extend away from the transition point. The peaks typically exhibit a sinusoidal character, reflecting the underlying frequency content of the filter involved.^[8]^[28] For signals processed through bandlimited filters, ringing appears as damped sinusoids oscillating at approximately the filter's cutoff frequency immediately following a step input. The decay of these oscillations is characteristically slow, following an inverse-time envelope rather than a rapid exponential falloff, leading to prolonged ripples that can span multiple cycles. This behavior is caused by the sinc-like impulse responses of ideal filters, which introduce these persistent waves.^[8] In contrast to physical signals, where oscillations are naturally attenuated by damping mechanisms like friction or resistance, ringing artifacts in digital or filtered systems persist indefinitely without such inherent decay, potentially distorting the signal for extended durations.^[28] The severity of ringing is quantified through metrics such as peak overshoot percentage, which measures the maximum deviation beyond the steady-state value (often around 9% for the Gibbs phenomenon in square wave approximations), and ringing duration, defined as the time required for the response to settle within 1% of the final value.^[29] For the step response of an ideal low-pass filter, the ringing component can be approximated asymptotically as

\frac{1}{\omega_c t} \cos(\omega_c t),

where \omega_c is the cutoff angular frequency; this term highlights the 1/t decay modulating the sinusoidal oscillation at the cutoff frequency.^[30] Such characteristics emphasize the artifact's origin in mathematical truncation rather than physical processes, making it a key indicator of insufficient bandwidth or abrupt filtering.^[8]

Frequency Domain Characteristics

Ringing artifacts in the frequency domain stem from the presence of discontinuities in the time-domain signal, which generate theoretically infinite high-frequency content in the spectrum. Band-limiting this content through truncation, as occurs in practical filtering or sampling processes, results in ripples within the passband and stopband of the frequency response, distorting the ideal rectangular shape of a low-pass filter. This truncation effectively multiplies the ideal infinite sinc impulse response by a rectangular window in the time domain, leading to a convolution in the frequency domain that spreads spectral energy.^[31] The Gibbs phenomenon manifests in the frequency domain as this convolution of the ideal frequency response with the sinc function derived from the truncation window, producing prominent side lobes that leak energy across frequency bands. For a rectangular window, the first side lobe level is approximately -13 dB relative to the main lobe peak, with subsequent lobes rolling off at about 6 dB per octave; this fixed side-lobe structure arises from the abrupt discontinuities at the window edges. The discrete-time Fourier transform (DTFT) of the rectangular window approximates a sinc function, whose envelope decays as $1/\omega, contributing to the persistent leakage even as the main lobe narrows with increased window length.^[32]^[33] The frequency response of a truncated sinc filter, given by the convolution of the ideal rectangular spectrum with the window's transform, exhibits ripples whose amplitude remains largely independent of the truncation length N for a rectangular window, though the spacing between ripple peaks scales inversely with N. In mathematical terms, for an ideal low-pass filter with cutoff \omega_c, the truncated response is:

H(\omega) = \frac{1}{2\pi} \int_{-\pi}^{\pi} \operatorname{rect}\left(\frac{\theta}{2\omega_c}\right) \cdot \frac{\sin\left(N(\omega - \theta)/2\right)}{N \sin\left((\omega - \theta)/2\right)} \, d\theta

where the Dirichlet kernel approximates the sinc for large N, leading to oscillatory deviations from the ideal flat response near the band edges.^[31] Spectral leakage occurs because finite observation windows in the discrete Fourier transform (DFT) cause energy from a true frequency component to spill into adjacent bins, particularly pronounced for signals with components near bin boundaries. This leakage is a direct consequence of the window's non-ideal frequency response, manifesting as ringing during inverse transformation back to the time domain.^[34]^[35] In DFT and FFT implementations, zero-padding the signal—appending zeros to increase the transform length—interpolates the underlying DTFT, thereby reducing discretization artifacts like scalloping loss but failing to eliminate the core spectral leakage or associated ringing, as the window's side lobes persist.^[36] These frequency-domain imperfections correspond to the temporal ripples observed in the time domain.

Mitigation

Filter Design Improvements

To minimize ringing artifacts inherent in filter designs, particularly those arising from sharp frequency cutoffs, engineers often employ filters with smoother roll-off characteristics instead of ideal brick-wall responses. Ideal low-pass filters, which abruptly transition from passband to stopband, exhibit pronounced ringing due to the Gibbs phenomenon in their time-domain impulse responses. In contrast, Butterworth filters provide a maximally flat passband response with a gradual roll-off, reducing the amplitude of these oscillations by distributing energy more evenly across frequencies. For instance, a higher-order Butterworth filter sharpens the transition while limiting ringing duration, though it may amplify oscillation amplitude if not balanced properly. Chebyshev filters further optimize this by allowing controlled ripple in the passband or stopband to achieve steeper roll-offs with less overall ringing compared to the ideal case, trading minimal distortion for reduced sidelobe effects.^[37]^[38] A primary linear method to suppress ringing in finite impulse response (FIR) filters involves applying windowing functions to the ideal sinc impulse response, which otherwise produces infinite sidelobes leading to persistent oscillations. Windowing tapers the filter coefficients to zero at the edges, lowering sidelobe levels in the frequency domain and thereby attenuating the ripples associated with ringing. Common windows include the Hamming, Blackman, and Kaiser types; for example, the Hamming window reduces sidelobes to approximately -43 dB, significantly mitigating Gibbs ringing at the cost of a wider transition band. The windowed sinc filter is defined as

h = \mathrm{sinc}\left(\frac{n - M/2}{M}\right) \cdot w,

where M is the filter length and the Hamming window is given by

w = 0.54 - 0.46 \cos\left(\frac{2\pi n}{M}\right), \quad 0 \leq n \leq M.

This approach trades filter sharpness for lower ripple amplitude, with unwindowed sinc filters exhibiting more severe ringing near discontinuities.^[25]^[39] Infinite impulse response (IIR) filter designs can reduce the effective length of ringing by placing poles farther from the unit circle to enable faster exponential decay in the impulse response, though this may require higher orders or compromise sharpness compared to FIR equivalents. This pole placement allows for efficient approximation of desired frequency responses with shorter effective lengths, minimizing transient oscillations. However, IIR filters risk instability if poles lie outside the unit circle, necessitating careful design constraints such as bilinear transformation from stable analog prototypes to ensure bounded outputs.^[40]^[41] Optimal filter design requires balancing multiple tradeoffs to curb ringing without excessive performance loss: passband flatness to preserve signal integrity, stopband attenuation for effective noise rejection, and transition width to control sharpness versus ripple extent. Narrower transitions exacerbate ringing, while wider ones reduce it but may allow unwanted frequencies to leak through; thus, the design selects parameters like order and window type to meet specifications while keeping oscillations below perceptible thresholds.^[42]

Post-Processing Techniques

Post-processing techniques for ringing artifacts focus on suppressing oscillations in signals or images after initial acquisition or compression, targeting remnants of phenomena like the Gibbs effect without altering upstream processes. De-ringing filters, such as those using adaptive median operations, dampen periodic ripples by selectively smoothing oscillatory regions while preserving sharp transitions. These filters adapt to local signal characteristics, applying median-based smoothing only where oscillations exceed thresholds derived from neighborhood statistics, thereby minimizing edge degradation. Morphological operations, including adaptive directional morphological filters (ADMF), further enhance this by employing erosion and dilation in edge-aligned directions to erode ringing halos around discontinuities in compressed images like those from JPEG-2000, achieving perceptual quality improvements without introducing blur.^[43]^[44] Wavelet-based denoising represents another cornerstone of post-processing, where the signal is decomposed into wavelet coefficients, and thresholding is applied to suppress high-frequency components responsible for ripple-like artifacts. This approach exploits the sparsity of wavelet representations to attenuate Gibbs-induced ringing by setting small coefficients near edges to zero or shrinking them adaptively, often using soft-thresholding functions tuned to noise levels. A notable method reverses the standard wavelet denoising pipeline to explicitly target and reconstruct ringing-free subbands, reducing artifact visibility in denoised images while maintaining overall fidelity. Such techniques are particularly effective in transform-coded signals, where they mitigate ripples originating from truncated basis functions.^[45]^[46] Advancements in machine learning have introduced convolutional neural networks (CNNs) trained on datasets of artifact-affected and clean images for targeted de-ringing via inpainting and restoration. Post-2018 developments, especially in super-resolution and video compression, leverage deep architectures like sub-layered deeper CNNs (SDCNN) to predict and correct ringing in block-based codecs such as HEVC, using strided convolutions for efficient feature extraction and mean squared error optimization during training. These models outperform traditional filters by learning contextual patterns, yielding bit-rate reductions of up to 4.1% and PSNR gains of 2-3 dB on benchmark sequences. Recent advancements as of 2023 include attention-based CNNs for Gibbs-ringing suppression in MRI.^[47]^[48] In MRI applications, parallel imaging accelerates k-space sampling to undersample high frequencies less severely, reducing truncation ringing, while direct k-space filtering applies low-pass attenuation to suppress Gibbs artifacts, though it risks over-smoothing. CNN variants trained on simulated ringing further refine MRI reconstructions, eliminating artifacts with minimal structural loss.^[49]^[50] A key trade-off in these post-processing methods is the balance between artifact suppression and preservation of fine details, where aggressive filtering can induce blurring, as quantified by metrics like peak signal-to-noise ratio (PSNR) and structural similarity index (SSIM). For instance, wavelet thresholding may reduce ringing by 20-30% in PSNR terms but requires careful parameter tuning to avoid low-frequency attenuation, while CNN-based approaches demonstrate superior SSIM scores (e.g., 0.95+ on compressed videos) yet demand computational resources for inference. Effectiveness is evaluated through such metrics on standardized datasets, ensuring ringing reduction enhances perceptual quality without compromising diagnostic or visual utility.^[47]^[48]^[45]

Examples

In Image Processing

In JPEG compression, ringing artifacts manifest as halo-like oscillations around sharp edges and high-contrast boundaries, resulting from the quantization of Discrete Cosine Transform (DCT) coefficients in 8x8 pixel blocks.^[51] The process involves dividing the image into blocks, applying the DCT to convert spatial data to frequency domain, and then quantizing coefficients—particularly truncating high-frequency ones—to achieve compression ratios, which introduces Gibbs-like ripples due to the abrupt cutoff in the frequency spectrum.^[52] These artifacts become more pronounced at higher compression levels, such as 25:1 or above, where the loss of fine details leads to visible wavy distortions decaying outward from edges, often appearing as spurious bright or dark rings.^[51] In magnetic resonance imaging (MRI), the Gibbs ringing artifact arises from the truncation of high-frequency components in k-space during Fourier transform reconstruction, producing parallel lines or oscillations adjacent to tissue boundaries.^[2] This occurs because MRI data acquisition inherently band-limits the signal by sampling a finite k-space extent, leading to incomplete representation of sharp intensity transitions, such as those between cerebrospinal fluid and brain tissue in axial scans.^[9] The artifact typically appears as symmetric overshoots and undershoots—up to 9% of the edge height—parallel to discontinuities, potentially mimicking pathologies like syrinx in spinal images if not recognized.^[53] Caused by the same band-limiting effects as in other transform-based processing, these ripples decay with distance from the edge but can degrade diagnostic accuracy in high-contrast regions.^[9] Neural network-based super-resolution upscaling can introduce ringing artifacts around edges if the model lacks sufficient regularization, as the networks amplify high-frequency details from low-resolution inputs without fully capturing natural image priors.^[54] For instance, convolutional neural networks like SRCNN may generate overshooting oscillations in reconstructed high-resolution images, particularly in textured or edged areas, due to over-reliance on learned patterns that extrapolate frequencies beyond the input's bandwidth. Regularization techniques, such as total variation penalties or perceptual loss functions, are essential to suppress these wavy halos and ensure smoother transitions. Visually, ringing in these image processing contexts appears as decaying ripples or wave-like patterns emanating from high-contrast areas, such as object silhouettes or tissue interfaces, with amplitudes diminishing exponentially away from the edge.^[9] In compressed or upscaled images, these distortions often resemble faint echoes or fringes, contrasting with the uniform texture of surrounding regions. Ringing artifacts are quantifiable using metrics such as the ringing measure (RM), which helps evaluate artifact severity across processing pipelines, with lower values indicating reduced visible distortions in applications like JPEG or MRI reconstruction.^[55]

In Audio and Signal Processing

In audio signal processing, ringing artifacts manifest as pre-echo distortions in perceptual coding schemes like MP3, where lookahead buffering inadequately handles transients, leading to audible oscillations preceding sharp attacks such as those in cymbals.^[56] This occurs because block-based transforms, such as the modified discrete cosine transform (MDCT), spread quantization noise across the entire block when a transient falls near its end, following a low-energy region; for instance, in MPEG-1 Layer III, long blocks of 1152 samples (~26 ms at 44.1 kHz) or short blocks of 384 samples (~8.7 ms) fail to resolve attacks within the auditory system's temporal resolution of about 2-5 ms, resulting in unmasked noise that smears backward into silence.^[57] Adaptive techniques, like switching to shorter blocks upon detecting transients via lookahead, mitigate this by confining noise to the attack's vicinity, where it can be masked by post-masking effects.^[56] In electrical signal measurements, ringing artifacts appear as Gibbs phenomenon-induced oscillations on oscilloscope displays of high-speed waveforms, arising from finite FFT resolution that truncates higher harmonics in signals like those on PCB traces.^[28] For example, when capturing fast rise-time edges in digital signals exceeding 1 GHz, the oscilloscope's band-limiting—whether analog filtering or digital signal processing—approximates the discontinuous waveform with a finite Fourier series, producing spurious ripples up to 9% overshoot near transitions; this artifact mimics true signal integrity issues like reflections but dissipates within one period of the cutoff frequency.^[28] Distinguishing it requires ensuring the instrument's bandwidth is at least three times the signal's knee frequency or 1/rise time to minimize truncation effects.^[11] Filter ringing in audio and signal processing is exemplified by the output of a high-pass filter to a square wave input, where the response exhibits decaying sine-like oscillations centered at the cutoff frequency due to the filter's resonant poles.^[58] In a second-order high-pass filter with quality factor Q > 0.707, the step-like transitions of the square wave excite these poles, causing overshoot and ringing that persists for several cycles before settling, particularly evident when the input frequency is below the cutoff, blocking DC while passing harmonics.^[59] This time-domain ripple, akin to the broader analysis of transient responses, can introduce distortion in audio equalizers or anti-aliasing stages if the Q is too high.^[60] A practical mitigation in digital-to-analog converters (DACs) involves oversampling, which reduces ringing duration by shifting spectral images to higher frequencies and enabling gentler analog reconstruction filters with wider transition bands.^[61] For instance, 4x or 8x oversampling in delta-sigma DACs allows low-order filters (e.g., first- or second-order) that exhibit minimal Gibbs ringing compared to sharp Nyquist filters, shortening oscillation tails from tens of samples to under 10 μs while preserving audio fidelity above 20 kHz.^[62] From an auditory perception standpoint, ringing artifacts below 20-30 ms in duration are often masked by temporal pre-masking effects, rendering them inaudible in natural listening but detectable as smearing in spectrograms of compressed audio.^[63] Pre-masking, effective up to about 20 ms before a transient, leverages the ear's integration time to hide low-level oscillations preceding attacks, though longer pre-echoes in low-bitrate coding exceed this threshold and become perceptible.^[64]

Overshoot and Clipping

Overshoot refers to the phenomenon in signal processing where a signal temporarily exceeds its steady-state value following a sharp transition, such as in the step response of a bandlimited system. This initial peak arises due to the system's inability to instantaneously reach equilibrium, often manifesting as an amplitude deviation before settling. In the context of the Gibbs phenomenon, which occurs in the partial summation of Fourier series for discontinuous functions, the overshoot is characteristically limited to approximately 9% of the jump discontinuity height, regardless of the number of terms included. The overshoot is quantified as approximately 9% of the jump discontinuity height, or \frac{\text{peak} - \text{final}}{\text{jump height}} \times 100\%, where the jump height is the size of the discontinuity.^[24]^[65] This overshoot frequently precedes ringing artifacts, as the excess energy in the initial peak excites oscillatory modes in the system's impulse response, leading to subsequent damped oscillations around the steady-state. In filter designs, particularly low-pass filters, the step response exhibits this pattern where the overshoot directly contributes to the onset of ringing by amplifying transient ripples near edges or transitions. Both overshoot and ringing stem from band-limiting effects that truncate higher-frequency components necessary for sharp signal changes. Clipping occurs when a signal's amplitude is hard-limited by a threshold, such as in amplifiers or analog-to-digital converters (ADCs), resulting in flattened peaks that introduce artificial discontinuities into the waveform. These discontinuities act as new sharp transitions, generating secondary ringing artifacts as the signal propagates through subsequent processing stages, where band-limiting exacerbates the oscillations. In practical systems, clipping not only distorts the primary waveform but also intensifies existing overshoot by pushing the signal into nonlinear regimes, thereby worsening both phenomena in devices like ADCs where dynamic range limitations are common.^[66]^[4] The interconnection between overshoot and ringing is evident in their causal relationship, where overshoot serves as the trigger for ringing in underdamped responses, while clipping amplifies the severity of both by creating additional distortion sources. In control systems, the step response of second-order systems typically demonstrates overshoot followed by ringing, with the oscillations decaying over the settling time as the system stabilizes. This pattern underscores the distinct yet linked roles of these amplitude distortions in overall signal integrity.^[67]^[68]

Truncation and Spectral Leakage

Truncation artifacts in ringing occur when the frequency domain representation of a signal is limited to a finite extent, such as in a truncated Fourier series or a cutoff in k-space during data acquisition. This finite resolution causes energy from higher frequencies to leak into the reconstructed signal, manifesting as oscillatory ringing patterns in the time or spatial domain near sharp transitions or discontinuities. In magnetic resonance imaging (MRI), this effect is synonymous with the Gibbs phenomenon, where the partial summation of Fourier components fails to converge uniformly at jump discontinuities, producing spurious oscillations adjacent to high-contrast interfaces like tissue boundaries.^[69]^[9] Spectral leakage represents the underlying mechanism of this truncation-induced ringing in discrete systems. When a non-periodic signal is processed using the discrete Fourier transform (DFT), the finite observation interval implicitly applies a rectangular window, which convolves the true spectrum with the transform of that window—a sinc function. This convolution spreads the spectral energy across adjacent frequency bins, creating ripples or sidelobes in the frequency domain that translate to ringing artifacts in the time domain. Unlike broader ringing artifacts arising from filter impulse responses or general processing, truncation specifically results from the limited frequency resolution imposed by finite sampling, where the abrupt cutoff acts as an ideal low-pass filter with poor stopband attenuation. The frequency response of the rectangular window, given by

W(\omega) = \frac{\sin(\omega N / 2)}{\sin(\omega / 2)} e^{-j \omega (N-1)/2},

where N is the window length, exhibits sidelobes whose amplitudes contribute significantly to the leakage error; for the rectangular window, the highest sidelobe level is approximately -13 dB, equivalent to about 22% of the main lobe amplitude.^[70] This truncation and spectral leakage are ubiquitous in sampled digital systems, including audio processing, imaging, and communications, as they stem from the fundamental assumptions of the DFT. While zero-padding can partially alleviate ringing by increasing the effective frequency resolution and reducing the prominence of sidelobes, it does so at the expense of higher computational demands without altering the underlying window spectrum.

References

[1]
Ringing analysis | Laboratory of Mathematical Methods of Image ...
Ringing effect so known as Gibbs phenomenon in mathematical methods of image processing is the annoying effect in images and video appeared as rippling ...
[2]
Gibbs and truncation artifacts | Radiology Reference Article | Radiopaedia.org
### Summary of Gibbs and Truncation Artifacts
[3]
Gibbs Phenomenon (Eitan Tadmor) - UMD MATH
A method to reduce the Gibbs ringing artifact in MRI scans while keeping tissue boundary integrity. IEEE Transactions of Medical Imaging 21(4) (2002) 100-114 ...
[4]
RingingArtifacts - Scientific Volume Imaging
Ringing is an image artifact that may appear when Doing Deconvolution under certain conditions. It produces dark and light ripples around bright features of an ...
[5]
Ringing and Blur Artifact Removal in Image Processing Applications
In this work we present an effective ringing and blur artifact removal method to produce ringing free deblur images.
[6]
What Is Ringing in Audio (Artifacts)? [Definitive Guide]
Aug 2, 2025 · Audio ringing is an artifact that emerges from the output of audio filters, triggered by the input signal. These artifacts manifest as damped ...What is ringing audio · How digital filter works · Interpreting ringing in relation...
[7]
[PDF] An Adaptive Approach to Gibbs' Phenomenon
In digital signal processing it commonly appears as ringing artifacts near instantaneous transitions that can cause unwanted echos in acoustics [8] or ...
[8]
Ringing Artifact - an overview | ScienceDirect Topics
'Ringing artifact' refers to the oscillations or unwanted ripples that occur in a signal or image due to the choice of a specific model or interpolation ...
[9]
Gibbs artifact? - Questions and Answers in MRI
Gibbs artifacts (also known as truncation, ringing, or spectral leakage artifacts) typically appear as multiple fine parallel lines immediately adjacent to ...<|control11|><|separator|>
[10]
Gibbs Ringing in Diffusion MRI - PMC - NIH
Aug 10, 2015 · The Gibbs ringing artifact arises because the Fourier series cannot represent a discontinuity with a finite number of harmonics. A sharp cut-off ...
[11]
How to Avoid Gibbs Ringing Artifacts in Measurements
Jun 29, 2021 · As a robust rule of thumb, to avoid the Gibbs ringing artifact, make sure the bandwidth of your measurement is at least as high as 1/RT of the signal.
[12]
In image processing, what is the difference or relationship between ...
Oct 13, 2018 · The difference is that noise may obscure features in an image, while artefacts appear to be features but are not.Missing: ringing distinction
[13]
Performance evaluation of a perceptual ringing distortion metric for ...
This paper evaluates a perceptual impairment measure for ringing artifacts, which are common in hybrid MC/DPCM/DCT coded video, as a predictor of the mean.
[14]
MP3 codec: pre- and post-echo test - ResearchGate
The third test has been performed as pre- and post- echo test. Encoders often doesn't work properly leaving/adding some artifacts before and after original ...
[15]
How the Gibbs Phenomenon Produces Measurement Artifacts | Blog
Sep 10, 2021 · To summarize, Gibbs ringing is entirely an artifact of your measurement instrument and Fourier/Laplace transform operations on bandlimited ...
[16]
An Unsupervised Framework for Joint MRI Super Resolution and ...
Feb 6, 2023 · Therefore, MRI images often suffer from low spatial resolution and Gibbs ringing artifacts. Previous studies tackled these two problems ...
[17]
What Causes Gibbs Signal Ringing in High-speed Channel ...
Sep 10, 2021 · Convolution and transform operations can produce Gibbs ringing, where a transient oscillation appears in a predicted signal response.
[18]
[PDF] ON THE GIBBS PHENOMENON AND ITS RESOLUTION 1 ...
Nov 29, 2024 · The Gibbs phenomenon is the inability to recover point values of a nonperiodic, but otherwise smooth, function from its Fourier coefficients.
[19]
https://www.math.pku.edu.cn/teachers/litj/notes/numer_anal/SIAMRev_39_644.pdf
[20]
Fourier series and the Gibbs phenomenon - AIP Publishing
May 1, 1992 · The occurrence in Fourier series of an overshoot effect near function discontinuities, called the Gibbs phenomenon, is discussed from a ...Missing: definition | Show results with:definition
[21]
[PDF] Filters, mollifiers and the computation of the Gibbs phenomenon
The Gibbs phenomenon is spurious oscillations around edges of piecewise smooth functions, causing loss of accuracy in Fourier projections.
[22]
The Ideal Lowpass Filter
An ideal lowpass filter has a gain of 1 below a cut-off frequency and 0 above, with a sinc function impulse response, but is not practically realizable.<|control11|><|separator|>
[23]
Gibbs Effect - an overview | ScienceDirect Topics
The discontinuous nature of the ideal low pass filter causes ringing to occur in the filtered output. This phenomenon is known as the Gibbs effect.<|control11|><|separator|>
[24]
FIR Filter Design - MATLAB & Simulink - MathWorks
This example shows how to use windowing, least squares, or the Parks-McClellan algorithm to design lowpass, highpass, multiband, or arbitrary-response filters.
[25]
Filters: When, Why, and How (Not) to Use Them - ScienceDirect
Apr 17, 2019 · The oscillatory response of a filter to an impulse-like input is informally called “ringing” and may occur in all filter types (low-pass, band- ...
[26]
https://www.sciencedirect.com/science/article/pii/S0896627319301746
[27]
Gibbs Effect
This overshoot and ringing is known as the Gibbs effect, after the mathematical physicist Josiah Gibbs, who explained the phenomenon in 1899.
[28]
[PDF] CHAPTER 8 ANALOG FILTERS
The impulse response of a filter, in the time domain, is proportional to the bandwidth of the filter in the frequency domain. The narrower the impulse, the ...
[29]
Understanding Gibbs Phenomenon in signal processing
Apr 6, 2010 · Gibbs phenomenon is a phenomenon that occurs in signal processing and Fourier analysis when approximating a discontinuous function using a series of Fourier ...Missing: band- limited<|control11|><|separator|>
[30]
[PDF] Windowed-Sinc Filters
For instance, the Hamming window results in a passband ripple of 0.2%, and an identical stopband attenuation (i.e., ripple in the stopband) of 0.2%.
[31]
Side Lobes - Stanford CCRMA
radian, and the side-lobe level is 13 dB down. Since the DTFT of the rectangular window approximates the sinc function (see (3.4)), which has an amplitude ...
[32]
Rectangular Window Side-Lobes | Spectral Audio Signal Processing
radian, and the side-lobe level is 13 dB down. Since the DTFT of the rectangular window approximates the sinc function (see (3.4)), which has an amplitude ...
[33]
[PDF] Fast Fourier Transforms explained - Pico Technology
The Gibbs phenomenon can be seen as the ringing effects in the above waveform. ... This “smearing” of the frequency spectrum is known as spectral leakage.Missing: artifacts | Show results with:artifacts
[34]
[PDF] Spectral Leakage and Rethinking the Kernel Size in CNNs
Often referred to as spectral leakage, such windowing artifacts are closely related to the Gibbs phenomenon [13] or ringing artifacts in digital image ...
[35]
The Rectangular Window | Spectral Audio Signal Processing
First side lobe only 13 dB down from the main-lobe peak. Side lobes roll off at approximately 6dB per octave. A phase term arises when we shift the window ...
[36]
10.2. Convolutional Filtering — Digital Signals Theory - Brian McFee
These oscillations produce audible artifacts, known as ringing, when h is convolved with a signal. The example below demonstrates this, using an audio clip of a ...
[37]
Reducing coherent filtering artefacts in time‐domain operational ...
Mar 21, 2022 · This filtering introduces filtering artefacts into the data due to the non-ideal filter response and is well understood for impulse excitation.
[38]
[PDF] Chapter 4 – Design of FIR Filters
FIR filters can be designed using impulse response truncation (IRT) or windowing techniques. IRT involves truncating the impulse response, and windowing can ...Missing: ringing artifacts
[39]
(PDF) Digital -Varying Notch IIR Filter With Transient Suppression
Aug 6, 2025 · Instead of keeping a fixed pole and zero configuration, the filter starts with a gentler configuration (to produce a fast decay) and then ...
[40]
10.3. Filter Design and Analysis — Digital Signals Theory
High stop-band attenuation. The filter stops frequencies when it should. · Small pass-band ripple. Passing frequencies aren't too distorted. · Narrow transition ...
[41]
Morphological de-ringing filter design for JPEG-2000 - ResearchGate
Aug 6, 2025 · In this paper, an adaptive directional morphological filter (ADMF) to reduce ringing artifacts is presented. Compared with the previously ...
[42]
[PDF] Adaptive Non-linear Filtering Technique for Image Restoration - arXiv
This paper considers application of median- based algorithms for removal of impulses, strip lines, drop lines, band missing, and blotches while preserving edges ...
[43]
https://www.researchgate.net/publication/283613868_Morphological_de-ringing_filter_design_for_JPEG-2000
[44]
https://arxiv.org/pdf/2204.09302
[45]
[PDF] Machine Learning based Post Processing Artifact Reduction in ...
The lossy compression techniques produce various artifacts like blurring, distortion at block bounders, ringing and contouring effects on outputs especially at ...
[46]
[PDF] Review: Noise and artifact reduction for MRI using deep learning
Feb 28, 2020 · Lack of high-frequency signal leads to Gibbs artifact, which is also called truncation, or ringing artifact. Simple k-space do- main filtering ...Missing: post- | Show results with:post-
[47]
https://arxiv.org/pdf/1912.13100
[48]
[PDF] Digital Image Processing - CL72.org
Gonzalez and Richard E. Woods to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act ...
[49]
https://doi.org/10.1002/mrm.27894
[50]
Development and evaluation of a deep learning model for multi ...
Background: Gibbs artifacts frequently occur as a result of truncation in the frequency domain (k-space). Gibbs artifacts can degrade image quality and may be ...
[51]
A lightweight large receptive field network LrfSR for image super ...
Apr 11, 2025 · It is noteworthy that reconstruction-based techniques often produce HR images with sharp, yet undesirable edges, as well as ringing artifacts, ...
[52]
Deep unsupervised learning for image super-resolution with ...
A sub-pixel convolutional layer is operated on the top of the generator to upscale the inputs, and the standard convolutions are all implemented in the LR space ...
[53]
A ringing metric to evaluate the quality of images restored using ...
RM [18] is employed to measure the ringing artefacts in the restored images. ... Quality evaluation of an image is an important task in image processing ...
[54]
Measurement of ringing artifacts in JPEG images - ADS
In this paper, we propose a no-reference method to measure the visual impact of ringing artifacts for JPEG images. Unlike previous work, we perform a global ...
[55]
Pre-Echo Distortion - AES Audio
Pre-echoes mainly appear as disturbing artifact if transient signals (castanets, triangle) are coded. Pre-echoes are most audible if the attack is preceded by ...Missing: MP3 cymbals
[56]
[PDF] Perceptual Coding of Digital Audio - MP3-Tech.org
An artifact known as “pre-echo” distortion can arise in transform coders using perceptual coding rules. Pre-echoes occur when a signal with a sharp attack ...Missing: cymbals | Show results with:cymbals<|separator|>
[57]
Is Your Op Amp Filter Ringing? Look at Q! - Texas Instruments
A Q greater than 0.5 indicates a lower rate of energy loss relative to the stored energy in the filter. At the output of these filter systems there will be a ...
[58]
[PDF] Decompensated Amplifier Stabilization Circuit - Texas Instruments
The silver peaking in the Frequency Response and ringing in the Square-Wave Response are signs of < 45° of phase margin and instability. Simulation and ...
[59]
[PDF] MT-017: Oversampling Interpolating DACs - Analog Devices
The high oversampling rate moves the image frequencies higher, thereby allowing a less complex lower cost filter with a wider transition band. In addition, ...
[60]
Filter ringing - Troll Audio
Aug 26, 2018 · We have demonstrated that ringing effects from oversampling filters can be eliminated by leaving a small margin above the highest frequency in a recording.<|separator|>
[61]
Auditory Masking - SIEMENS Community
Aug 29, 2019 · Pre-masking can only occur about 20 milliseconds before the masking sound starts. This phenomenon is usually ignored as it is very brief and ...
[62]
Lossy audio compression: principles, methods, misconceptions
Jun 8, 2025 · MP3 has issues at 128 kbps and 192 kbps with transients. At 192 kbps, the pre-echo is so quiet that it can easily be masked by the noise in the ...Missing: post- | Show results with:post-
[63]
[PDF] Lecture 9: Dynamics of Response: Complex Poles - Matthew M. Peet
Definition 2. The Percent Overshoot, Mp is the peak value of the signal, as a percentage of steady-state.Missing: processing | Show results with:processing
[64]
Oscillations, Clipping, and Ringing in Amplifier Stability Analysis | Blog
Mar 8, 2021 · Clipping: When driven too high with negative feedback, or when positive feedback dominates, the amplifier can saturate and will clip. This is ...
[65]
What is the Significance of Signal Overshoot and How is it Reduced?
Feb 5, 2020 · Signal overshoot is when a signal exceeds its target value, often undesired. It can be reduced by using damping resistors.
[66]
Step Response - an overview | ScienceDirect Topics
The two most important parameters of a filter's step response are the overshoot and ringing. Overshoot should be minimal for good pulse response.
[67]
Characteristic features of MR truncation artifacts | AJR
Ring artifacts (Gibb phenomenon) occurring near highly contrasting interfaces represent but one manifestation of truncation artifacts visible on MR images.
[68]
[PDF] On the Use of Windows for Harmonic Analysis
Jan 1, 1978 · I. INTRODUCTION. HERE IS MUCH signal processing devoted to detection and estimation. Detection is the task of determiningif.