Digital Distortion Research Articles

Geometric distortion on video see‐through head‐mounted displays

AbstractVideo see‐through (VST) head‐mounted displays (HMDs) reconstruct the physical world using outward‐facing cameras and depth sensors. One of the major challenges for VST HMDs is the geometric distortion of the physical pass‐through content. In this study, we present the experimental setup and metrology for VST geometric distortion measurement on single‐camera and dual‐camera VST HMDs. The VST geometric distortion is compared to the digital distortion by the HMD. Finally, we investigate the impacts of camera misalignment and depth distance on VST geometric distortion without and with angular‐based distortion correction. The results demonstrate that camera misalignment with respect to the eye position is the primary root cause for the distortion. Dual‐camera setup is necessary to minimize the VST geometric distortion by placing the cameras close to the eye positions. Although distortion correction can partially mitigate VST geometric distortion in a 2D plane, it remains a challenge for VST distortion correction at multiple depth distance in the 3D space. The method and findings presented of this study may provide guidelines for evaluation of spatial accuracy on VST HMDs and hardware design.

Digital distortions arising when encoding regulation

Digital distortions arising when encoding regulation

Digital distortions and interpretive choices: A cartographic perspective on encoding regulation

Rules as Code (RaC), which encompasses the conversion of legal and regulatory rules into computer code, is gaining traction internationally. This article analyses ‘digital distortions’ in RaC, which refer to disconnects between regulation and code that arise from interpretive choices in the encoding process. We contend that Boaventura de Sousa Santos’ ‘symbolic cartography of law’ provides valuable concepts for understanding digital distortions in encoding regulation. Specifically, we argue that the cartographic concepts of scale, projection, symbolisation and orientation highlight distortions that can arise from choices involving the documentation to code, logics to follow, languages to use and coded outputs to present. We demonstrate how these distortions arose in our attempt to convert the ePayments Code, an Australian voluntary code of conduct for consumer electronic payment transactions, into machine-executable code. The article concludes by underscoring the importance of greater awareness of interpretive coding choices and their implications for diverse users of digitised regulation.

Sailing on Encrypted Seas: The Archive and Digital Memory in African and Diasporic Futurism

Digitization has commonly been marketed as a predictive technology that can enable humanity to intercede into the future. This faith in digital media’s prophetic powers, however, obfuscates the fact that digitization is unavoidably stuck in the past. In effect, digitization transforms the past into highly mutable and volatile data sets that are persistently rewritten by computer’s memory refresh circuits. While some lament this temporal incongruity as problematic to the archival process, African and diasporic futurist artists are utilizing digital distortion as an opportunity to emplace the archival process within the sea and reimagine the archive as an impermanent, transitory, and fluid practice that has the capacity to usher in a more culturally and scientifically nuanced understanding of memory. This article explores the capacity of the sea to reorientate digital humanities scholarship around the cyclical interplay between machinic, environmental, and human social systems and craft historiographical methods around envisioning a viable future for humanity.

GNSS Signal Distortion Estimation: A Comparative Analysis of L5 Signal from GPS II and GPS III

The nonlinear navigation payload transmission channel introduces errors at a system level, resulting in a distortion of the received signal and affecting differential positioning users. This work models the transmission channel of the navigation payload and uses the joint estimation algorithm to calculate the digital distortion and analog channel response of the transmission channel from the received signal. On the above basis, the algorithm and model are verified by GPS-L5 measured data, and the channel characteristics of GPS II and GPS III are deeply analyzed. The results show that the existing GPS IIF satellites have a digital distortion, which is negligible in GPS III satellites. Regarding the analog channel response, GPS III has better amplitude and group delay consistency than GPS II. Lastly, the ranging bias caused by the transmission channel of the navigation payload is provided to the user for reference, and GPS III is improved by approximately 0.02 m compared with GPS II. This study provides support for adjusting the satellite signal pre-distortion and enriches subsequent GNSS signal quality assessment work; it can also be used as a reference for differential positioning users.

Ultra-compact 3D-printed wide-angle cameras realized by multi-aperture freeform optical design.

Simultaneous realization of ultra-large field of view (FOV), large lateral image size, and a small form factor is one of the challenges in imaging lens design and fabrication. All combined this yields an extensive flow of information while conserving ease of integration where space is limited. Here, we present concepts, correction methods and realizations towards freeform multi-aperture wide-angle cameras fabricated by femtosecond direct laser writing (fsDLW). The 3D printing process gives us the design freedom to create 180° × 360° cameras with a flat form factor in the micrometer range by splitting the FOV into several apertures. Highly tilted and decentered non-rotational lens shapes as well as catadioptric elements are used in the optical design to map the FOV onto a flat surface in a Scheimpflug manner. We present methods to measure and correct freeform surfaces with up to 180° surface normals by confocal measurements, and iterative fabrication via fsDLW. Finally, approaches for digital distortion correction and image stitching are demonstrated and two realizations of freeform multi-aperture wide-angle cameras are presented.

Swapping Gender is a Snap(chat)

In May 2019 the photographic cellphone application Snapchat released two company-generated image filters that were officially dubbed “My Twin” and “My Other Twin,” though users and media labeled them as feminine and masculine, respectively. While touted in most commentary as a “gender swap” feature, these digital imaginaries represent a unique opportunity to consider what features contribute to classification of faces into binary gender buckets. After all, the commonly considered “male” filter makes various modifications—including a broader jaw and addition of facial hair—to whichever face is selected in the photograph. It does not ask and cannot detect if that face belongs to a man or woman (cis- or transgender) or to a non-binary individual. Instead, the augmented reality that it offers is a preprogrammed algorithmic reinscription of reductive gendered norms. When interacting with a novel face, humans similarly implement algorithms to assign a gender to that face. The Snapchat “My Twin” filters—which are not neutral, but rather human-designed—offer an analyzable projection of one such binarization, which is otherwise rarely articulated or visually recreated. Here I pair an ethnographic exploration of twenty-eight transgender, non-binary, and/or gender diverse individuals’ embodied experiences of facial gender legibility throughout life and with digital distortion, with a quantitative analysis of the “My Twin” filter facial distortions, to better understand the role of technology in reimaginations of who and what we see in the mirror.

Brightfield, fluorescence, and phase-contrast whole slide imaging via dual-LED autofocusing.

Whole slide imaging (WSI) systems convert the conventional biological samples into digital images. Existing commercial WSI systems usually require an expensive high-performance motorized stage to implement the precise mechanical control, and the cost is prohibitive for most individual pathologists. In this work, we report a low-cost WSI system using the off-the-shelf components, including a computer numerical control (CNC) router, a photographic lens, a programmable LED array, a fluorescence filter cube, and a surface-mount LED. To perform real-time single-frame autofocusing, we exploited two elements of a programmable LED array to illuminate the sample from two different incident angles. The captured image would contain two copies of the sample with a certain separation determined by the defocus distance of the sample. Then the defocus distance can be recovered by identifying the translational shift of the two copies. The reported WSI system can reach a resolution of ∼0.7 µm. The time to determine the optimal focusing position for each tile is only 0.02 s, which is about an 83% improvement compared to our previous work. We quantified the focusing performance on 1890 different tissue tiles. The mean focusing error is ∼0.34 µm, which is well below the ± 0.7 µm depth of field range of our WSI system. The reported WSI system can handle both the semitransparent and the transparent sample, enabling us to demonstrate the implementation of brightfield, fluorescence, and phase-contrast WSI. An automatic digital distortion correction strategy is also developed to avoid the stitching errors. The reported prototype has an affordable cost and can make it broadly available and utilizable for individual pathologists as well as can promote the development of digital pathology.

The Golem In The Machine: FERPA, Dirty Data, and Digital Distortion in the Education Record

Like its counterpart in the criminal justice system, dirty data—data that is inaccurate, incomplete, and or misleading—in K-12 education records create and catalyze catastrophic life events. The presence of this data in any record suggests a lack of data integrity. The systemic problem of dirty data in education records means the data stewards of those records have failed to meet the data integrity requirements embedded in the Family Educational Rights and Privacy Act (FERPA). FERPA was designed to protect students and their education records from the negative impact of erroneous and misinformation rendered from the “private scribblings” of educators. The legislative history of FERPA indicates that legislators were concerned about the harm to students’ education and structure of opportunities based on misinformation in secret files created and kept in schools. Dirty data created, collected, and processed as accurate and reliable, notwithstanding the disproportionate impact of school discipline, on marginalized students in general, and Black children specifically, is exactly the kind of harm that FERPA was intended to prevent. This Article demonstrates (1) How educational inequities linked to dirty data violates FERPA and (2) How FERPA should be enhanced to prevent dirty data harms at the point of collection and creation. Additionally, this Article outlines the concept of dirty data and data integrity requirements embedded in FERPA and proceeds to examine the phenomenon of dirty data and student harm in historically marginalized students’ education records, starting at the point of creation and collection. While several Articles have examined the failure of FERPA, none of the prior scholarship has analyzed FERPA’s connection to dirty data in the education record related to racial discrimination. This Article introduces a two-step process that would require input validation in the educational record context through (1) substantive content and input validation and (2) a reasonable inference review. Additionally, this Article introduces an accounting of disclosures to law enforcement requirement.

Maskless lithography based on oblique scanning of point array with digital distortion correction

The oblique scanning of a rectangular array of ultraviolet (UV) spots provides a feasible means of realizing maskless lithography with well-controlled UV exposure. In such a method, the UV light is modulated by a digital micromirror device (DMD), collected by a microlens/pinhole array, and then projected onto a photoresist (PR) layer for UV patterning. However, the strict requirements imposed on the optical distortion of the image projection system pose a significant technical challenge. Accordingly, the present study proposes a method for improving the UV patterning accuracy by using an empirically-derived distortion model to adjust the working DMD images. The patterning errors caused by optical distortion are then further reduced by adjusting the tilt angle of the oblique scanning process. The experimental results show that the proposed method yields a significant reduction in the UV patterning error. Consequently, it provides a practical solution for performing maskless lithography without the need for a high-quality image projection lens system.

An algorithm for glare detection via photometric, colorimetric, and global positioning features

Biological and automated vision systems which use digital video for navigation depend on the video to be of sufficient quality in order to extract reliable information that can inform the guidance and/or other decision-making processes. Although systems are available for detection and mitigation of digital distortions (e.g., compression, packet loss), detection and mitigation of natural distortions such as glare, rain, and fog have received much less attention. In this paper, we address the issue of glare detection in a single captured frame. We propose an algorithm which uses a combination of simple and efficient photometric, colorimetric, and GPS features to detect the location and spatial extent of glare within captured images. Specifically, feature maps using lightness, saturation, contrast, and color distance are computed, combined, and then, refined based on the sun's predicted location from the GPS information. In addition, we present a new ground-truth database for glare detection, in which the location, extent, and severity of glare was rated by human subjects for a collection of images. Testing on our ground-truth database revealed that the proposed algorithm can reliably detect the locations and spatial extents of glare sources in a variety of images based on subjective ratings and well-known quantitative measures.

Detection and Classification of GNSS Signal Distortions Based on Quadratic Discriminant Analysis

Satellite signal distortions, or so called “evil waveforms” (EWFs), may cause severe distortions of the cross-correlation function in receivers. Undetected EWFs could result in large range errors and threaten the integrity of Global Navigation Satellite System (GNSS). Analog distortion and digital distortion are two classical types of signal distortions. With the advent of modernized GNSS signals, more failure types are considered to cover potential EWFs of Binary offset carrier (BOC) modulated signals, such as code-only distortion and subcarrier-only distortion. Different failure types affect the correlation functions and the tracking precision in different ways. Therefore, it is useful to identify the failure type of a detected distortion. Conventional multi-correlator method can detect signal distortions; however, it is infeasible to identify the failure types. We developed a novel multi-correlator method based on Quadratic Discriminant Analysis (QDA). The QDA-based method also uses correlation-domain detection metrics but performs distortion type classification by supervised learning algorithm. Experimentally measured results on Beidou B1C data signals are presented, which show the effectiveness and robustness of proposed method. Compared with conventional multi-correlator method, the QDA-based signal quality monitoring (SQM) method shows better performance on detecting EWFs and provides an extra capability to identify the failure types accurately.

Signal analysis of the first GPS III satellite

The signal-in-space of the first GPS Block III spacecraft is analyzed based on radio frequency measurements collected with a 30-m high-gain dish antenna as well as data from geodetic GPS receivers. The spectral properties and modulation characteristics are discussed with focus on the L1 band, which employs a novel interlaced majority voting technique for combination of the C/A, P(Y), and L1C data + pilot signal components. Compared to the preceding generation of Block IIF satellites, a modified shaping of the L1 transmit antenna gain pattern is found, which results in lower carrier-to-noise density ratios at mid to high elevations. Along with this, use of a separate transmission chain for the military M-code signal is evidenced through the analysis of in-phase/quadrature signal components and the derived transmit antenna gain variations. A high level of signal purity is demonstrated on all frequencies, which can be attributed to the use of a new, mostly digital, signal generation unit. Maps of code bias variations for selected signals are presented to quantify the achievable user tracking performance as a function of user receiver parameters. For the L5 signal, a notable reduction in digital distortions is obtained with respect to the Block IIF satellites, whereas analog distortions are found to be of similar magnitude. Thermally induced L5 phase variations found in the Block IIF satellites are no longer observed in GPS III. Using triple-frequency phase observations, a sub-centimeter consistency of the L1, L2, and L5 carriers is demonstrated.

Quality monitoring and biases estimation of BOC navigation signals

Many safety-critical applications that utilize the global navigation satellite system (GNSS) demand highly accurate positioning information, as well as highly integrity and reliability. Due to GNSS signals are easily distorted by the interferences or disturbances, the signal quality monitoring (SQM) is necessary to detect the presence of dangerous signal distortions. In this paper, we developed an SQM software for binary offset carrier (BOC) modulated navigation signals. Firstly, the models of BOC signal with ideal and distortion are presented respectively. Then the architecture of SQM software is proposed. Moreover, the effect of the white gaussian noise (WGN) and the front-end filter on the correlation peak of the receiver is analyzed. Finally, the biases induced by the signal distortion are evaluated. The experiments simulate the relationships between the code phase shift and the normalized correlation value in the case of the signal digital distortion and the analog distortion. The simulation results demonstrate that the proposed SQM method can effectively monitor the signal distortion and accurately estimate the correlation peak deviation caused by the distortion.

Digital Distortion Through Co-creation

Co-creation is changing the way that the end-user and the manufacturing knitting industry engage with design of knitted products. This is in part due to the change in technological interfaces and capabilities but also due to the knitting technology becoming more available through open source portals and designers having gained a greater understanding of what knitted technologies such as seamless knitting—can do. The technological capabilities of seamless knit have been designed to use a traditional body shape that dictates a recognized silhouette during the development of outputs. Through creative practice this paper discovers alternative design possibilities when the technology is hacked to distort this archetypal body shape; new design outputs and textiles emerge. New methodologies for textile design approaches are also discussed through this article when new methods of creation which ignore the pre-programmed body form are introduced, and therefore new ways of discussing design development processes are revealed. This practice-led research focuses on the investigation of non-conventional body shapes utilizing the Wholegarment® knitwear technology as a material essential to the design development process. The design methodology developed combines the machine and designers as co-creators throughout the practice; resulting in distortion of mass manufactured silhouettes. This approach extends beyond the normal boundaries set by the digital interface generating possibilities for extreme knitted textile forms. This article outlines through practice some of the technological issues to overcome before full integration of co-creation by the end-user would be possible using seamless knit technology.

Digital Cancellation of Harmonic and Intermodulation Distortion in Wideband SAW-Less Receivers

This brief presents a digital distortion equalizer that compensates for the effects of both the harmonic mixing and intermodulation products in wideband surface acoustic wave (SAW)-less receivers. A mathematical framework is derived for analyzing signal distortion in the presence of harmonic and out-of-band interferers. This framework models a ${K}$ -path SAW-less ${M}$ -phase receiver, which provides sufficient front-end observations to cancel the distortion products. An adaptive minimum mean-squared error (MMSE) digital equalizer is employed to estimate the desired signal in the presence of distortion products. The MMSE equalizer jointly accounts for distortion products as well as correlated noise of the two paths. A dual-path 4-phase receiver fabricated in 130 nm CMOS process has been used to validate the distortion compensation scheme.

Joint Rate and Resource Allocation in Hybrid Digital–Analog Transmission Over Fading Channels

In hybrid digital-analog (HDA) systems, resource allocation has been utilized to achieve desired distortion performance. However, existing studies on this issue assume error-free digital transmission, which is not valid for fading channels. With time-varying channel fading, the exact channel state information is not available at the transmitter. Thus, random outage and resulting digital distortion cannot be ignored. Moreover, rate allocation should be considered in resource allocation, since it not only determines the amount of information for digital transmission and that for analog transmission, but also affects the outage probability. Based on above observations, in this paper, we attempt to perform joint rate and resource allocation strategies to optimize system distortion in HDA systems over fading channels. Consider a bandwidth expansion scenario where a memoryless Gaussian source is transmitted in an HDA system with the entropy-constrained scalar quantizer (ECSQ). Firstly, we formulate the joint allocation problem as an expected system distortion minimization problem where both analog and digital distortion are considered. Then, in the limit of low outage probability, we decompose the problem into two coupled sub-problems based on the block coordinate descent method, and propose an iterative gradient algorithm to approach the optimal solution. Furthermore, we extend our work to the multivariate Gaussian source scenario where a two-stage fast algorithm integrating rounding and greedy strategies is proposed to optimize the joint rate and resource allocation problem. Finally, simulation results demonstrate that the proposed algorithms can achieve up to 2.3dB gains in terms of signal-to-distortion ratio over existing schemes under the single Gaussian source scenario, and up to 3.5dB gains under the multivariate Gaussian source scenario.

Glitching History: Using Image Deformance to Rethink Agency and Authenticity in the 1960s American Folk Music Revival

Tactics of glitching and deformance, which alter existing digital data into new outputs through the manipulation of underlying code, offer untapped possibilities for historical inquiry. A photograph of musicians Mississippi John Hurt, Doc Watson, and Sam Hinton at the 1964 Berkeley Folk Music Festival serves as a case study for discovering how glitching and deformance reveal previously undetected aspects of the historical record: when glitched, the photograph sparks a heightened awareness of how Hurt and Watson, forced to be carriers of a limiting racial and regional authenticity, also found ways to expand their freedom and agency within the constraints of early 1960s consensus liberalism in the United States. While most histories of the folk revival focus on its primarily white, middle-class audiences, if even to critique their actions, the glitched image aids us in accessing the experiences of Hurt and Watson more robustly. In this way, a digital distortion of a photograph paradoxically produces a more accurate interpretation of the history it captures, enabling a compelling intervention in historiographic debates about the folk revival and its post-World War II American context.

The IFFT-based SQM method against digital distortion in GNSS signals

Global navigation satellite systems (GNSS) signal deformations could threaten the position accuracy and integrity of GNSS, especially for safety critical applications. Digital distortion is an important kind of deformations caused by failures inside the baseband generation unit onboard the GNSS satellites. Multi-correlator technique, as a prevalent signal quality monitoring (SQM) method, was developed to reliably detect the signal anomaly and therefore protect airborne users from this integrity threat. However, the conventional multi-correlator technique is unable to estimate the degree of distortion quantitatively, while another SQM method, the chip domain observable, has a poor real-time capability so that it could not meet the stringent time to alarm requirements. To solve the above problem, we derived the spectrum form of the conventional Threat Model A first and proposed a IFFT-based SQM algorithm. This new method can perform SQM easily by analyzing the impulses after PSD division and IFFT: Detect the presence of digital distortion by judging whether there is an impulse after IFFT and estimate the degree of distortion by computing the offset of the impulse. The results show that the IFFT-based method can not only detect digital distortion real-timely but also estimate the digital distortion degree quantitatively.

Bundle Block Adjustment of Tilt-Shift-Based Multidigital Camera System by Rigorous Orientation Model

Thorough application research of multidigital camera system (MDCS) based on tilt-shift technology has commenced since its prototype system was finished. This letter aims to study mapping applications of tilt-shift-based MDCS with inertial measurement unit and differential global positioning system (IMU/DGPS) data. A rigorous orientation model with equivalent inner orientation elements (IOEs) and digital distortion model (DDM) is proposed to be used in the IMU/DGPS-assisted bundle block adjustment (BBA) for improving geometric accuracy. In this letter, the indoor control field and calibration devices developed by our research team were directly applied to construct equivalent IOEs and DDM of a virtual camera. Two sets of IMU/DGPS-assisted BBA experiments with and without our proposed model and ground control points (GCPs) are presented in this letter, as well as the positioning accuracies. The experimental results illustrate that the positioning accuracies of 53.9 and 46.2 cm in planimetry and height are separately improved to 24.9 and 37.5 with the use of our proposed model in the IMU/DGPS-assisted BBA process at a flight height of 1000 m, ground sample distance of about 20 cm, and no GCP, and the higher accuracies of 19.0 cm in planimetry and 13.6 cm in height are achievable with the help of few GCPs. Therefore, the BBA by the proposed rigorous orientation model is considered practical and feasible for improving mapping accuracies of tilt-shift-based MDCS.