Chapter Four · failure evidence
What Signal Thresholding & Edge Detection got wrong, from 84 dissertations
The records document widespread failure points when applying thresholding and edge detection methods across image segmentation, acoustic sensing, and time series monitoring. These failures stem primarily from sensitivity to noise fluctuations, non-uniform illumination, dynamic signal drift, and the inability of simple cutoffs to separate overlapping feature distributions. These records come from PhD theses at 29 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Fixed amplitude thresholds fail under baseline drift and overlapping signal distributions
Static threshold cutoffs in electrophysiology, acoustic, and kinematic time series fail when sensor baselines drift or signal-to-noise ratios change across recording sessions. They frequently trigger false positive alarms on normal background fluctuations while missing true low-amplitude events because target and noise distributions overlap.
Tried and failed
fixed voltage threshold spike detection applied to long extracellular electrophysiology recordings. Outcome: unstable. Reason: signal-to-noise ratio drifted over time across extended recording sessions
Tried and failed
tight amplitude consistency threshold between paired channels applied to signal event filtering and selection. Reason: overly strict matching threshold filtered out genuine high-amplitude events due to larger variance at high signal levels
Tried and failed
single sensor thresholding for event detection applied to fetal movement detection from acoustic signals. Reason: high false positive rates caused by spectral overlap between target signals and background noise
Multi-modal approach to fetal movement detection using a wearable heterogeneous sensor system · Imperial
Tried and failed
amplitude thresholding for transient event detection applied to live audio dynamic effect triggering. Outcome: unstable. Reason: narrow margin between missed dynamic peaks and false positives from unaccented signals causes high sensitivity to thresholding
Tried and failed
high probability threshold in neural classifier applied to rare acoustic event detection in speech. Outcome: no signal. Reason: conservative decision thresholds severely suppressed true positive detection rates for sparse acoustic events
Tried and failed
single-threshold power segmentation applied to noisy waveform event detection. Reason: missed low-amplitude signals while falsely triggering on noise artifacts and debris
Microfluidic Platforms for High Throughput Quantitative Cell Mechanotyping · Georgia Tech
Tried and failed
adaptive threshold tracking via peak mean estimation applied to real-time spike detection. Outcome: unstable. Reason: noise peaks reduced estimated peak values and thresholds, creating positive feedback instability without frequent resets
Tried and failed
threshold-based alerting on continuous time-series data applied to continuous physiological vital sign monitoring. Reason: Excessive false-positive alert rates due to high sensor noise and normal physiological fluctuations.
Tried and failed
thresholding average spectral band power applied to binary classification of brain states. Outcome: no signal. Reason: substantial overlap in empirical probability density functions between target classes
Employing Intracranial EEG Data to Decipher Sleep Neural Dynamics · Virginia Tech
Tried and failed
threshold-based electromyography state machine controller applied to wearable movement assistance. Outcome: did not generalise. Reason: fixed thresholding caused frequent false positive activations across varying task postures and movement heights
Assisting and Evaluating Upper Extremity Movements with Wearables Systems · Harvard
Tried and failed
phase-space threshold despiking applied to unsteady velocity time series. Reason: non-steady flow conditions caused the algorithm to over-filter true transient wave signals as spikes
Characterization of Low-Frequency Ship Wake Along the Margins of Confined Channels and Connected Waterways · Georgia Tech
Considered and rejected
Considered and rejected: Rejected using the published 4.0–4.5 SD threshold (from Farrell et al. 2024) for dentate spike detection because it resulted in an abnormally low event count and missed visually verified spikes.
Neuronal and network responses in the dentate gyrus to salient and ethologically relevant stimuli · UT Austin
Considered and rejected
Considered and rejected: Rejected single-threshold spike sorting / single-unit detection because it limits detected spike yield and inadequately captures continuous multi-channel neural population dynamics over 8-hour recordings.
Neural Population Dynamics in Porcine Stellate Ganglion in Normal and Heart Failure States · DalSpace
Considered and rejected
Considered and rejected: Rejected standard amplitude voltage thresholding (0.5 to 20 uV) for burst suppression segmentation due to vulnerability to noise, short low-amplitude epochs, and inter-individual amplitude variation.
Using Quantitative Electroencephalogram to Predict Neurological Recovery after Resuscitation from Cardiac Arrest · JScholarship
Considered and rejected
Considered and rejected: Rejected using only time-domain thresholding for zebrafish seizure detection due to susceptibility to movement artifacts and lack of frequency sensitivity.
Tried and failed
amplitude-threshold signal detection applied to audio vocalization segmentation. Outcome: worse than baseline. Reason: amplitude thresholding failed to robustly capture syllables compared to deep learning and spectral methods
Tried and failed
energy thresholding on acoustic echoes applied to foliage gap detection in sonar. Outcome: did not generalise. Reason: energy levels varied significantly across outdoor sites, causing high miss and false-alarm rates
Solutions to Passageways Detection in Natural Foliage with Biomimetic Sonar Robot · Virginia Tech
Tried and failed
single-threshold crossing time encoding applied to noisy acoustic echo classification. Outcome: did not generalise. Reason: single threshold lacked sufficient dynamic range to capture complex acoustic clutter in real-world environments
Solutions to Passageways Detection in Natural Foliage with Biomimetic Sonar Robot · Virginia Tech
Tried and failed
heuristic amplitude thresholding applied to audio signal speaker discrimination. Outcome: no signal. Reason: focal and non-focal signal amplitude distributions overlap heavily
Tried and failed
magnitude thresholding of kinematic sensor signals applied to impact event detection and validation. Outcome: no signal. Reason: linear and angular thresholds poorly distinguished true impacts from false positives, explaining minimal peak acceleration variability
Tried and failed
tuning voice activity detection energy threshold applied to infant audio diarization. Outcome: no signal. Reason: energy threshold adjustments did not significantly alter or improve system performance on infant vocalizations
Towards Automatic Analysis of Audio Recordings from Children with Autism Spectrum Disorder · Georgia Tech
Tried and failed
threshold-based cosine similarity classification applied to directional fault discrimination in microgrids. Outcome: did not generalise. Reason: metric exceeded threshold for reverse fault conditions, causing false positive forward fault declarations
Protection and Cybersecurity in Inverter-Based Microgrids · Virginia Tech
Tried and failed
fixed threshold offset baseline compensation applied to ultrasonic structural damage detection. Outcome: did not generalise. Reason: temperature shifts exceeding the offset tolerance degraded detection sensitivity, causing unacceptable false negatives
The temperature effect on guided wave based structural health monitoring of composite structures · Imperial
Global and Otsu thresholding fails on non-uniform illumination and non-bimodal distributions
Automated global thresholding methods like Otsu fail when image histograms lack a clean bimodal distribution or exhibit unimodal and multimodal profiles. Variations in illumination, background clutter, and surface reflections lead these algorithms to misclassify bright backgrounds as objects or lose low-contrast targets.
Tried and failed
Otsu thresholding applied to image segmentation with complex textures. Outcome: did not generalise. Reason: Global thresholding failed to separate foreground from background in complex road texture scenes
Driver lane change intention inference using machine learning methods. · Cranfield
Tried and failed
intensity thresholding and Otsu segmentation applied to phase-contrast x-ray computed tomography images. Reason: phase contrast fringe artifacts and low attenuation contrast obscured feature boundaries
Tried and failed
Otsu global thresholding segmentation applied to sparse particle imaging. Reason: Lack of distinct bimodal intensity histogram distribution when particles are small or sparse relative to background
Tried and failed
running average background subtraction with Otsu thresholding applied to real-world video motion decomposition. Outcome: did not generalise. Reason: vulnerable to noise, illumination changes, and static reference frame objects
Wavelet-based image and video super-resolution reconstruction. · Cranfield
Tried and failed
standard Otsu thresholding segmentation applied to fluorescence microscopy images. Reason: pixel intensity distributions are non-Gaussian without log transformation
Development and application of deep learning and spatial statistics within 3D bone marrow imaging · Imperial
Tried and failed
standard Otsu thresholding without contrast shifting applied to unimodal image segmentation. Reason: incorrectly classified bright foreground pixels as background on unimodal intensity distributions
Tried and failed
Otsu thresholding for optical liquid level sensing applied to fluid reservoir volume monitoring. Reason: bubble formation, surface films, and variable background lighting corrupted threshold segmentation
Toward a deeper understanding of concentrated electrolyte effects in redox flow batteries · Oxford
Tried and failed
global Otsu thresholding for image binarization applied to foreground object segmentation. Reason: bright background regions were misclassified as foreground due to non-uniform intensity distribution
An image processing technique for erosion analysis on compressor blade geometry · Virginia Tech
Tried and failed
Otsu thresholding for object segmentation applied to multispectral satellite vehicle motion tracking. Reason: Failed to separate targets from background and failed entirely on low-reflectance dark targets
Applying deep learning to satellite imagery for emission inventory development · Imperial
Tried and failed
Otsu thresholding on estimated depth maps applied to aerial canopy segmentation. Reason: Multimodal depth histograms across wide depth ranges prevented reliable optimal threshold selection
Application of deep learning-based monocular depth estimation in forest canopy studies · Iowa State
Tried and failed
direct multi-level Otsu thresholding without local masking applied to multi-scale feature edge segmentation. Reason: peak shoulders in the global intensity histogram caused misclassification of adjacent multi-scale boundaries
STL NEMS fabrication, design, and inspection · Imperial
Lost to a baseline
Otsu thresholding achieved lower mIoU (0.19 on grape, 0.59 on hemp) compared to DeepLabv3 (0.85) and SAM*ExG (0.95).
Multidisciplinary strategies for grapevine disease monitoring in the age of digital viticulture · Cornell
Lost to a baseline
For wide-spaced hemp segmentation, Otsu thresholding (0.59 mIoU) and DeepLabv3 (0.80 mIoU) lost to ExG alone (0.93 mIoU) and SAM*ExG (0.95 mIoU).
Multidisciplinary strategies for grapevine disease monitoring in the age of digital viticulture · Cornell
Considered and rejected
Considered and rejected: Rejected global and adaptive threshold-based segmentation baselines (e.g., Otsu's method) because histogram-based thresholding inherently fails to distinguish root from non-root foreground noise.
ITErRoot: High Throughput Segmentation of 2-Dimensional Root System Architecture · HARVEST
Considered and rejected
Considered and rejected: Rejected using single global image thresholding (Otsu) for water extraction due to variable water turbidity and depth
Spatializing Coupled Human and Natural System (CHANS) · OpenBU
Considered and rejected
Considered and rejected: Rejected global Otsu thresholding alone due to uneven illumination and shadow gradients causing missed bubbles near walls.
Developing Algorithms for Bubble Identification and Tracking for the PICO-40L Dark Matter Experiment · Queens University Institutional Repository
Considered and rejected
Considered and rejected: Rejected using Otsu or Huang bimodal thresholding algorithms for segmenting CLSM stacks of nitrocellulose membranes because the images lacked a distinct bimodal gray value distribution.
Principles behind membrane features and sensitivity of lateral flow assays · Leibniz Universität Hannover Repository
Considered and rejected
Considered and rejected: Rejected purely automated thresholding (Otsu/RenyiEntropy) for final segmentation because overestimation and rigidity included background and cell bodies instead of true synaptic puncta.
Considered and rejected
Considered and rejected: Global Otsu thresholding across the full image was rejected due to non-uniform background illumination; local Otsu within YOLO bounding boxes was used.
A Synthetic Image Generation and Deep Learning Framework for Entrained Droplet Detection · Virginia Tech
Tried and failed
global and adaptive intensity thresholding applied to image segmentation with non-uniform illumination. Reason: produced false detections in bright regions and failed under non-uniform illumination
Advanced Experimental Characterization of Bubbly Flows in Rectangular and Rod-Bundle Geometries · Virginia Tech
Sensitivity threshold tuning creates an intractable trade-off between false alarms and signal loss
Choosing rigid statistical or anomaly thresholds creates a dilemma where low thresholds capture background measurement noise and cause false positive detections. Conversely, raising thresholds causes fragmentation of continuous structures, clips valid signal tails, and eliminates low-amplitude observations.
Lost to a baseline
In Case 1 step detection, the standard deviation (SD) thresholding baseline missed 2 of 4 small steps, and MAD caused false alarms on noise spikes compared to the proposed unimodal Rosin thresholding.
Tried and failed
standard t-test on thresholded candidate regions applied to signal detection in noisy images. Reason: thresholding introduces severe positive selection bias and false positives
Automated Tracking of Mouse Embryogenesis from Large-scale Fluorescence Microscopy Data · Virginia Tech
Tried and failed
global intensity thresholding for image preprocessing applied to fractal dimension estimation. Reason: high thresholds fragment structural components while low thresholds retain noise and debris
Tried and failed
strain thresholding for crack segmentation applied to surface crack detection in stone masonry. Outcome: worse than baseline. Reason: boundary noise and artifacts produced high false positive rates and fragmented crack maps
Damage Assessment of Stone Masonry Piers Using Imaged Surface Cracks · EPFL
Tried and failed
histogram skewness thresholding for object detection applied to low resolution time lapse culture images. Reason: prone to background noise at low resolution leading to high false positive rates
Quantification of Aggregate Formation in Prochlorococcus · MIT
Considered and rejected
Considered and rejected: Using a fixed percentage threshold for Mahalanobis distance outlier removal was rejected because it generalizes poorly across individual sensors compared to probability-based thresholds.
Security and Reliability in Pervasive Computing · IRIS - POLITO - prod
Considered and rejected
Considered and rejected: Fixed geometric thresholding for crack detection was rejected in favor of unsupervised anomaly detection due to sensitivity to manual parameter tuning across scenes.
3D Segmentation and Damage Analysis from Robotic Scans of Disaster Sites · Georgia Tech
Tried and failed
wavelet threshold denoising applied to acoustic signal preprocessing. Reason: low thresholds left residual noise while higher thresholds removed essential decomposed signal features
Soft Wearable Acoustical Sensing in Disease Autodiagnoses · Georgia Tech
Tried and failed
Low statistical anomaly threshold for peak detection applied to sediment core storm event identification. Reason: Low standard deviation thresholds identified false positives caused by background measurement noise
Environmental drivers of coastal evolution · Woods Hole
Tried and failed
Optimizing momentum thresholds for rest-frame subjet clustering applied to High-energy boosted particle identification. Outcome: worse than baseline. Reason: Strict thresholds degraded overall significance rather than improving signal sensitivity at high energies
Search for heavy resonance decaying into a photon and a Higgs bosonwith the ATLAS detector at the LHC · Iowa State
Tried and failed
low statistical threshold anomaly detection applied to sediment core grain size anomalies. Outcome: no signal. Reason: background signal noise caused false positive anomaly detections at lower standard deviation thresholds
Considered and rejected
Considered and rejected: Rejected automated SNR-threshold filtering for cleaning distant wildlife seismic labels because it mistakenly discards valuable low-amplitude signals.
Inference and machine learning across the spatial scales in geophysics · Oxford
Considered and rejected
Considered and rejected: Applying soft thresholding rather than hard thresholding as default in reconstructions (soft thresholding reduced signal amplitude and distorted discontinuities).
Statistical Analysis of Audio Signals using Time-Frequency Analysis Statistische Analyse von Audiosignalen mittels Zeit-Frequenz-Analyse · open_UMR Marburg DSpace 10.0
Considered and rejected
Considered and rejected: Using variable thresholds (based on empirical standard deviation of omc residuals over recent epochs) for observation exclusion was rejected for general use because thresholds become too tight under low noise, erroneously rejecting valid observations.
Towards instantaneous PPP convergence using multiple GNSS signals · DSpace-CRIS at TU Wien
Considered and rejected
Considered and rejected: Rejected lower event detection thresholds (1.5σ and 2σ) for core D90 anomaly identification to prevent noise from being classified as storm layers.
Environmental drivers of coastal evolution · Woods Hole
Tried and failed
flat threshold zero suppression on waveform signals applied to photodetector pulse energy reconstruction. Reason: clipping signal tails distorted energy measurements and introduced artificial position-dependent energy losses
Toward Tonne-Scale NEXT Detectors: SiPM Energy-Tracking Planes and Metalenses for Light Collection · Harvard
Tried and failed
threshold-based grain segmentation applied to low-misorientation electron backscatter diffraction data. Reason: measurement noise caused unrealistic over-segmentation below low threshold angles
Dynamic grain growth and subgrain evolution in an interstitial-free steel · UT Austin
Simple thresholding fails to separate touching objects and overlapping feature boundaries
Intensity, color, and geometric edge thresholding struggle when distinct physical structures touch, overlap, or share similar radiometric values with reflective surroundings. In these scenarios, thresholding merges adjacent entities into single connected components or breaks continuous features into fragmented artifacts.
Tried and failed
unmasked edge detection and global thresholding applied to in-situ fluid filament optical imaging. Outcome: no signal. Reason: severe background optical noise obscured accurate boundary extraction
Development of process control and material for micro/nano-scale electrohydrodynamic inkjet manufacturing · Iowa State
Lost to a baseline
Canny Edge Detector removed crystallographic RGB orientation/texture data and required sensitive manual trial-and-error tuning of hysteresis thresholds (tested 125 and 50) compared to proposed methods.
New Computational Methodologies for Microstructure Quantification · Virginia Tech
Considered and rejected
Considered and rejected: Rejected simple scalar intensity thresholding for interface identification because laser power fluctuations and secondary fluorescence halo effects cause false edge detections.
Considered and rejected
Considered and rejected: Rejected using standard thresholding/watershed image processing for HSV due to varying contrast, rough background textures, and turbulent wakes.
Investigation of Separate Effects of Surface Condition on Subcooled Flow Boiling Heat Transfer · MIT
Tried and failed
Okubo-Weiss parameter thresholding applied to vortex and eddy boundary detection. Reason: Fragmented features into non-core filament strips causing high false-positive detection rates
Characterization of Hydrodynamics Impacting Renewable Energy · Georgia Tech
Tried and failed
per-channel thresholding for boundary detection applied to noisy microstructure image segmentation. Reason: per-channel tolerance produced excessive false-positive boundaries in complex textured regions
New Computational Methodologies for Microstructure Quantification · Virginia Tech
Considered and rejected
Considered and rejected: Rejected using single grayscale intensity thresholds on RGB imagery due to errors from fluctuating solar lighting, adopting multispectral calibrated reflectance panels and downwelling sensors instead.
Tried and failed
binary thresholding on continuous field data applied to segmenting interacting fault structures. Reason: biases segment length and merges distinct adjacent structures
Understanding fault evolution using numerical models and seismic data observations · Imperial
Tried and failed
color thresholding and skeletonization applied to overlapping root system segmentation. Reason: heuristic segmentation failed to separate complex overlapping structures from background
Tried and failed
HSV color thresholding for surface segmentation applied to white markings on reflective metallic surfaces. Reason: High-reflectance metallic regions overlapped with white marker HSV values, causing false-positive point segmentation
Development of 3D image processing techniques and testing procedures for a perceptive robotic grinding system · Iowa State
Tried and failed
Color thresholding and connected component analysis applied to segmenting overlapping objects in unconstrained layouts. Outcome: did not generalise. Reason: Touching and overlapping instances merged into single connected components without rigid spacing constraints
Modular Computer Vision Pipelines for Monitoring Lettuce Growth in Greenhouses · Cornell
Tried and failed
thresholding time-domain angle deviation for echo rejection applied to broadband acoustic split-beam angle estimation. Outcome: did not generalise. Reason: introduces false rejection bias against broadband single echoes exhibiting resonant scattering phase distortions
Broadband Acoustic Characterization of the Deep Scattering Layer · MIT
Considered and rejected
Considered and rejected: Rejected using fixed minimum/maximum angle threshold heuristics (e.g. 45°) for overlap classification, opting instead for steerable-filter path segmentation.
Automated image-based analysis methods for filament networks structures in two and three dimensions · IRIS - UNITN - prod
Considered and rejected
Considered and rejected: Thresholding pixel values alone for laser line extraction (lacked repeatable precision required for structured light sensing, necessitating regional segmentation / binary image conversion).
Volumetric flow monitoring of biomass through an industrial grinder · Iowa State
Acoustic speckle and imaging artifacts disrupt gradient and edge detection
Coherent imaging systems introduce speckle noise, fringe artifacts, and phase contrast distortions that obscure actual physical boundaries. Conventional intensity thresholding and gradient-based edge detectors misinterpret these interference patterns as real edges, causing false wall classifications and broken contours.
Tried and failed
classical edge detection and thresholding applied to ultrasound speckle vessel boundary tracking. Reason: speckle noise patterns disrupted edge detection and intensity thresholding
Measuring blood flow and pro-inflammatory changes in the rabbit aorta · Imperial
Tried and failed
intensity thresholding and adaptive segmentation algorithms applied to speckle-corrupted ultrasound image segmentation. Reason: acoustic speckle noise caused false vessel wall classifications and contour discontinuities
Forward-Viewing Ultrasound Guidance of a Robotically-Steered Guidewire for Peripheral Interventions · Georgia Tech
Tried and failed
sparse wavelet regularization using iterative shrinkage thresholding applied to ultrasound image reconstruction. Reason: Altered natural speckle patterns and improperly thresholded continuous linear intensity gradients.
Ultrasound Imaging: From Physical Modeling to Deep Learning · EPFL
Lost to a baseline
Threshold control, 2-D quadratic filtering, and CWM filtering failed to outperform standard median filtering on the phantom ultrasound data.
Median Filtering and Wavelet Filtering: A Study of Noise Eeduction in Prostate Ultrasound Images · TXST Digital Repository
Considered and rejected
Considered and rejected: Otsu thresholding directly on deconvolved PSD maps in favor of Canny edge detection with median boundary PSD thresholding due to vulnerability to noise
Ultrasound-based Noninvasive Monitoring Methods for Neurocritical Care · MIT
Considered and rejected
Considered and rejected: Rejected ISO50 global thresholding for XCT surface determination in favour of advanced local iterative thresholding due to systematic errors and inability to handle image artefacts.
Analysis of defects in additively manufactured lattice structures · University of Nottingham Repository
Left open by the authors
Problems the authors named and did not get to.
Left open
Develop an automated hyperparameter optimization method for automatic thresholding or SVD cutoff selection in 3D ultrasound super-resolution imaging. Blocker: None
Ultrafast 3-D ultrasound super-resolution imaging with a row-column array · Imperial
Left open
Develop an improved threshold selection method to replace Otsu's thresholding for multi-peak high-range depth maps in canopy segmentation. Blocker: None
Application of deep learning-based monocular depth estimation in forest canopy studies · Iowa State
Left open
Evaluate alternative thresholding-free methods for CAMs in weakly supervised CT and MRI medical image segmentation. Blocker: None
Label Efficient Deep Learning in Medical Imaging · Publikationssystem UB Tuebingen
Left open
Develop adaptive thresholding algorithms for Neural Dynamic Divergence error signals to detect seizure onset across diverse patient iEEG baselines. Blocker: None
QUANTITATIVE METHODS AND NEUROSTIMULATION MAPPING TO GUIDE PRECISION EPILEPSY THERAPIES · Penn
Left open
Correlate accuracies from the 100 trained EEG decoder instances and their ensemble average with speech reception thresholds to evaluate intelligibility prediction. Blocker: Requires the specific 100 trained decoder models and corresponding speech-EEG experimental dataset with speech reception thresholds.
Decoding auditory EEG responses to speech via deep neural networks · Imperial
Left open
Evaluate whether FFR-based neural network decoders correlate with and reliably predict speech intelligibility and speech reception thresholds. Blocker: Requires specialized EEG recordings with speech intelligibility and speech reception threshold measurements
Decoding auditory EEG responses to speech via deep neural networks · Imperial
Left open
Implement confidence thresholds or anomaly detection algorithms to reject false-positive gesture contractions during idle static states in MMG data. Blocker: Requires MMG sensor hardware setup or proprietary MMG gesture dataset collected in the thesis
Adaptive gesture recognition for human-robot interface using mechanomyography (MMG) · Imperial
Left open
Refine event detection algorithms and thresholds to match simulated earthquake outputs with empirical seismic recording conditions. Blocker: Lacks specific criteria or target observational datasets defining the empirical recording conditions
Left open
Implement and evaluate conditional soft thresholding on DWT decomposition detail coefficients instead of uniform thresholding for synthetic audio detection. Blocker: None
THE USE OF REGRESSION MODELS FOR DETECTING DIGITAL FINGERPRINTS IN SYNTHETIC AUDIO · Calhoun
Left open
Develop and implement advanced radio frequency interference mitigation algorithms for low-frequency synthetic aperture radar compensated phase history data. Blocker: Lack of specific algorithmic target or criteria beyond simple intensity thresholding
Utilising Synthetic Aperture Radar Data-dome Collections for Building Feature Analysis · Cranfield
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