Anomaly Detection with Transformers in Face Anti-spoofing (2023)
Conference Proceeding
Abduh, L., Omar, L., & Ivrissimtzis, I. (2023). Anomaly Detection with Transformers in Face Anti-spoofing. . https://doi.org/10.24132/JWSCG.2023.10

Transformers are emerging as the new gold standard in various computer vision applications, and have already been used in face anti-spoofing demonstrating competitive performance. In this paper, we propose a network with the ViT transformer and ResNe... Read More about Anomaly Detection with Transformers in Face Anti-spoofing.

Exploring the Potential of Immersive Virtual Environments for Learning American Sign Language (2023)
Conference Proceeding
Wang, J., Ivrissimtzis, I., Li, Z., Zhou, Y., & Shi, L. (2023). Exploring the Potential of Immersive Virtual Environments for Learning American Sign Language. In Responsive and Sustainable Educational Futures: 18th European Conference on Technology Enhanced Learning, EC-TEL 2023, Aveiro, Portugal, September 4–8, 2023, Proceedings (459-474). https://doi.org/10.1007/978-3-031-42682-7_31

Sign languages enable effective communication between deaf and hearing people. Despite years of extensive pedagogical research, learning sign language online comes with a number of difficulties that might be frustrating for some students. Indeed, mos... Read More about Exploring the Potential of Immersive Virtual Environments for Learning American Sign Language.

Developing and Evaluating a Novel Gamified Virtual Learning Environment for ASL (2023)
Conference Proceeding
Wang, J., Ivrissimtzis, I., Li, Z., Zhou, Y., & Shi, L. (2023). Developing and Evaluating a Novel Gamified Virtual Learning Environment for ASL. In Human-Computer Interaction – INTERACT 2023: 19th IFIP TC13 International Conference, York, UK, August 28 – September 1, 2023, Proceedings, Part I (459-468). https://doi.org/10.1007/978-3-031-42280-5_29

The use of sign language is a highly effective way of communicating with individuals who experience hearing loss. Despite extensive research, many learners find traditional methods of learning sign language, such as web-based question-answer methods,... Read More about Developing and Evaluating a Novel Gamified Virtual Learning Environment for ASL.

Bivariate non-uniform subdivision schemes based on L-systems (2023)
Journal Article
Gérot, C., & Ivrissimtzis, I. (2023). Bivariate non-uniform subdivision schemes based on L-systems. Applied Mathematics and Computation, 457, Article 128156. https://doi.org/10.1016/j.amc.2023.128156

L–systems have been used to describe non-uniform, univariate, subdivision schemes, which offer more flexible refinement processes than the uniform schemes, while at the same time are easier to analyse than the geometry driven non-uniform schemes. In... Read More about Bivariate non-uniform subdivision schemes based on L-systems.

User-Defined Hand Gesture Interface to Improve User Experience of Learning American Sign Language (2023)
Book Chapter
Wang, J., Ivrissimtzis, I., Li, Z., Zhou, Y., & Shi, L. (2023). User-Defined Hand Gesture Interface to Improve User Experience of Learning American Sign Language. In C. Frasson, P. Mylonas, & C. Troussas (Eds.), Augmented Intelligence and Intelligent Tutoring Systems: 19th International Conference, ITS 2023, Corfu, Greece, June 2-5, 2023, Proceedings (479-490). Springer Verlag. https://doi.org/10.1007/978-3-031-32883-1_43

Sign language can make possible effective communication between hearing and deaf-mute people. Despite years of extensive pedagogical research, learning sign language remains a formidable task, with the majority of the current systems relying extensiv... Read More about User-Defined Hand Gesture Interface to Improve User Experience of Learning American Sign Language.

Big data for human security: The case of COVID-19 (2022)
Journal Article
Cárdenas, P., Ivrissimtzis, I., Obara, B., Kureshi, I., & Theodoropoulos, G. (2022). Big data for human security: The case of COVID-19. Journal of Computational Science, 60, Article 101574. https://doi.org/10.1016/j.jocs.2022.101574

The COVID-19 epidemic has changed the world dramatically since societies are changing their behaviour according to the new normal, which comes along with numerous challenges and uncertainties. These uncertainties have led to instabilities in several... Read More about Big data for human security: The case of COVID-19.

Quality perception and discrimination thresholds in quantised triangle meshes (2021)
Conference Proceeding
Almutairi, A., Saarela, T., & Ivrissimtzis, I. (2021). Quality perception and discrimination thresholds in quantised triangle meshes. . https://doi.org/10.1117/12.2604720

At certain stages of the graphics pipeline, and most notably during compression for transmission and storage, triangle meshes may undergo a fixed-point arithmetic quantisation of their vertex coordinates. This paper presents the results of a psychoph... Read More about Quality perception and discrimination thresholds in quantised triangle meshes.

From Farey fractions to the Klein quartic and beyond (2021)
Journal Article
Ivrissimtzis, I., Singerman, D., & Strudwick, J. (2021). From Farey fractions to the Klein quartic and beyond. Ars mathematica contemporanea (Spletna izd.), 20(1), 37-50. https://doi.org/10.26493/1855-3974.2046.cb6

In a paper published in 1878/79 Klein produced his famous 14-sided polygon representing the Klein quartic, his Riemann surface of genus 3 which has PSL(2,7) as its automorphism group. The construction and method of side pairings are fairly complicate... Read More about From Farey fractions to the Klein quartic and beyond.

Early Fault Diagnostic System for Rolling Bearing Faults in Wind Turbines (2021)
Journal Article
Xu, L., Wang, Q., Ivrissimtzis, I., & Li, S. (2022). Early Fault Diagnostic System for Rolling Bearing Faults in Wind Turbines. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 5(1), Article 011004. https://doi.org/10.1115/1.4051222

The operation and maintenance costs of wind farms are always high due to high labor costs and the high replacement cost of parts. Thus, it is of great importance to have real-time monitoring and an early fault diagnostic system to prevent major event... Read More about Early Fault Diagnostic System for Rolling Bearing Faults in Wind Turbines.

Colour Processing in Adversarial Attacks on Face Liveness Systems (2019)
Conference Proceeding
Abduh, L., & Ivrissimtzis, I. (2019). Colour Processing in Adversarial Attacks on Face Liveness Systems. In F. P. Vidal, G. K. . L. Tam, & J. C. Roberts (Eds.), Proceedings of Computer Graphics and Visual Computing 2019 (CGVC) (149-152). https://doi.org/10.2312/cgvc.20191272

In the context of face recognition systems, liveness test is a binary classification task aiming at distinguishing between input images that come from real people’s faces and input images that come from photos or videos of those faces, and presented... Read More about Colour Processing in Adversarial Attacks on Face Liveness Systems.

Using theoretical ROC curves for analysing machine learning binary classifiers (2019)
Journal Article
Omar, L., & Ivrissimtzis, I. (2019). Using theoretical ROC curves for analysing machine learning binary classifiers. Pattern Recognition Letters, 128, 447-451. https://doi.org/10.1016/j.patrec.2019.10.004

Most binary classifiers work by processing the input to produce a scalar response and comparing it to a threshold value. The various measures of classifier performance assume, explicitly or implicitly, probability distributions Ps and Pn of the respo... Read More about Using theoretical ROC curves for analysing machine learning binary classifiers.

Trivalent expanders, $(Delta – Y)$-transformation, and hyperbolic surfaces (2019)
Journal Article
Ivrissimtzis, I., Peyerimhoff, N., & Vdovina, A. (2019). Trivalent expanders, $(Delta – Y)$-transformation, and hyperbolic surfaces. Groups, Geometry, and Dynamics, 13(3), 1103-1131. https://doi.org/10.4171/ggd/518

We construct a new family of trivalent expanders tessellating hyperbolic surfaces with large isometry groups. These graphs are obtained from a family of Cayley graphs of nilpotent groups via (Delta–Y)-transformations. We study combinatorial, topologi... Read More about Trivalent expanders, $(Delta – Y)$-transformation, and hyperbolic surfaces.

A Perceptual Difference Scaling Study on Quantized 3D Models (2018)
Presentation / Conference
Almutairi, A., Saarela, T., & Ivrissimtzis, I. (2018, December). A Perceptual Difference Scaling Study on Quantized 3D Models. Paper presented at ACM Symposium on Applied Perception, Vancouver, Canada

Single Image Watermark Retrieval from 3D Printed Surfaces via Convolutional Neural Networks (2018)
Conference Proceeding
Zhang, X., Wang, Q., & Ivrissimtzis, I. (2018). Single Image Watermark Retrieval from 3D Printed Surfaces via Convolutional Neural Networks. In G. Tam, & F. Vidal (Eds.), Computer Graphics & Visual Computing (CGVC) 2018 : Eurographics UK Chapter proceedings (117-120). https://doi.org/10.2312/cgvc.20182019

In this paper we propose and analyse a method for watermarking 3D printed objects, concentrating on the watermark retrieval problem. The method embeds the watermark in a planar region of the 3D printed object in the form of small semi-spherical or cu... Read More about Single Image Watermark Retrieval from 3D Printed Surfaces via Convolutional Neural Networks.

A user study on quantisation thresholds of triangle meshes (2017)
Conference Proceeding
Almutairi, A., Saarela, T., & Ivrissimtzis, I. (2017). A user study on quantisation thresholds of triangle meshes. In T. R. Wan, & F. Vidal (Eds.), Computer Graphics & Visual Computing (CGVC) 2017. Eurographics UK Chapter Proceedings, anchester Metropolitan University, United Kingdom, 14 – 15 September 2017. https://doi.org/10.2312/cgvc.20171283

We present the results of a user study on estimating a quantisation threshold above which the quantised triangle mesh is perceived as indistinguishable from its unquantised original. The design of the experiment and the analysis of the results focus... Read More about A user study on quantisation thresholds of triangle meshes.

Order-randomized Laplacian mesh smoothing (2017)
Conference Proceeding
Yang, Y., Rushmeier, H., & Ivrissimtzis, I. (2017). Order-randomized Laplacian mesh smoothing. In M. S. Floater, T. Lyche, M. Mazure, K. Mørken, & L. L. Schumaker (Eds.), Mathematical methods for curves and surfaces : 9th International Conference, MMCS 2016, Tønsberg, Norway, June 23 - June 28, 2016. Revised selected papers (312-323). https://doi.org/10.1007/978-3-319-67885-6_17

In this paper we compare three variants of the graph Laplacian smoothing. The first is the standard synchronous implementation, corresponding to multiplication by the graph Laplacian matrix. The second is a voter process inspired asynchronous impleme... Read More about Order-randomized Laplacian mesh smoothing.

Designing a facial spoofing database for processed image attacks (2016)
Conference Proceeding
Omar, L., & Ivrissimtzis, I. (2016). Designing a facial spoofing database for processed image attacks. In 7th International Conference on Imaging for Crime Detection and Prevention (ICDP 2016) : Madrid, Spain, 23-25 November 2016 ; proceedings. https://doi.org/10.1049/ic.2016.0073

Face recognition systems are used for user authentication in everyday applications such as logging into a laptop or smartphone without need to memorize a password. However, they are still vulnerable to spoofing attacks, as for example when an imposte... Read More about Designing a facial spoofing database for processed image attacks.

Reevaluating Reconstruction Filters for Path-Searching Tasks in 3D (2016)
Journal Article
Roberts, D., & Ivrissimtzis, I. (2017). Reevaluating Reconstruction Filters for Path-Searching Tasks in 3D. Computer Graphics Forum, 36(6), 291-302. https://doi.org/10.1111/cgf.12939

In this paper, we present an experiment on stereoscopic direct volume rendering, aiming at understanding the relationship between the choice of reconstruction filter and participant performance on tasks requiring spatial understanding such as 3D path... Read More about Reevaluating Reconstruction Filters for Path-Searching Tasks in 3D.

Resilience of Luminance based Liveness Tests under Attacks with Processed Imposter Images (2016)
Conference Proceeding
Omar, L., & Ivrissimtzis, I. (2016). Resilience of Luminance based Liveness Tests under Attacks with Processed Imposter Images. In V. Skala (Ed.),

Liveness tests are techniques employed by face recognition authentication systems, aiming at verifying that a live face rather than a photo is standing in front of the system camera. In this paper, we study the resilience of a standard liveness test... Read More about Resilience of Luminance based Liveness Tests under Attacks with Processed Imposter Images.

A 3D Steganalytic Algorithm and Steganalysis-Resistant Watermarking (2016)
Journal Article
Yang, Y., Pintus, R., Rushmeier, H., & Ivrissimtzis, I. (2017). A 3D Steganalytic Algorithm and Steganalysis-Resistant Watermarking. IEEE Transactions on Visualization and Computer Graphics, 23(2), 1002-2626. https://doi.org/10.1109/tvcg.2016.2525771

We propose a simple yet efficient steganalytic algorithm for watermarks embedded by two state-of-the-art 3D watermarking algorithms by Cho et al. The main observation is that while in a clean model the means/variances of Cho et al.’s normalized histo... Read More about A 3D Steganalytic Algorithm and Steganalysis-Resistant Watermarking.