Search Results for author: Symeon Papadopoulos

Found 44 papers, 23 papers with code

Sum of Group Error Differences: A Critical Examination of Bias Evaluation in Biometric Verification and a Dual-Metric Measure

no code implementations23 Apr 2024 Alaa Elobaid, Nathan Ramoly, Lara Younes, Symeon Papadopoulos, Eirini Ntoutsi, Ioannis Kompatsiaris

Biometric Verification (BV) systems often exhibit accuracy disparities across different demographic groups, leading to biases in BV applications.

Fairness

Fusion Transformer with Object Mask Guidance for Image Forgery Analysis

no code implementations18 Mar 2024 Dimitrios Karageorgiou, Giorgos Kordopatis-Zilos, Symeon Papadopoulos

In this work, we introduce OMG-Fuser, a fusion transformer-based network designed to extract information from various forensic signals to enable robust image forgery detection and localization.

Image Forensics Image Forgery Detection

Leveraging Representations from Intermediate Encoder-blocks for Synthetic Image Detection

no code implementations29 Feb 2024 Christos Koutlis, Symeon Papadopoulos

The recently developed and publicly available synthetic image generation methods and services make it possible to create extremely realistic imagery on demand, raising great risks for the integrity and safety of online information.

Image Generation Synthetic Image Detection

RED-DOT: Multimodal Fact-checking via Relevant Evidence Detection

1 code implementation16 Nov 2023 Stefanos-Iordanis Papadopoulos, Christos Koutlis, Symeon Papadopoulos, Panagiotis C. Petrantonakis

Online misinformation is often multimodal in nature, i. e., it is caused by misleading associations between texts and accompanying images.

Fact Checking Misinformation +1

FairBranch: Fairness Conflict Correction on Task-group Branches for Fair Multi-Task Learning

1 code implementation20 Oct 2023 Arjun Roy, Christos Koutlis, Symeon Papadopoulos, Eirini Ntoutsi

The generalization capacity of Multi-Task Learning (MTL) becomes limited when unrelated tasks negatively impact each other by updating shared parameters with conflicting gradients, resulting in negative transfer and a reduction in MTL accuracy compared to single-task learning (STL).

Fairness Multi-Task Learning

Mitigating Viewer Impact from Disturbing Imagery using AI Filters: A User-Study

no code implementations19 Jul 2023 Ioannis Sarridis, Jochen Spangenberg, Olga Papadopoulou, Symeon Papadopoulos

This paper presents a user study, involving 107 participants, predominantly journalists and human rights investigators, that explores the capability of Artificial Intelligence (AI)-based image filters to potentially mitigate the emotional impact of viewing such disturbing content.

Towards Fair Face Verification: An In-depth Analysis of Demographic Biases

no code implementations19 Jul 2023 Ioannis Sarridis, Christos Koutlis, Symeon Papadopoulos, Christos Diou

This paper presents an in-depth analysis, with a particular emphasis on the intersectionality of these demographic factors.

Face Recognition Face Verification +2

The 2023 Video Similarity Dataset and Challenge

1 code implementation15 Jun 2023 Ed Pizzi, Giorgos Kordopatis-Zilos, Hiral Patel, Gheorghe Postelnicu, Sugosh Nagavara Ravindra, Akshay Gupta, Symeon Papadopoulos, Giorgos Tolias, Matthijs Douze

The problem comprises two distinct but related tasks: determining whether a query video shares content with a reference video ("detection"), and additionally temporally localizing the shared content within each video ("localization").

Copy Detection Video Similarity

VERITE: A Robust Benchmark for Multimodal Misinformation Detection Accounting for Unimodal Bias

2 code implementations27 Apr 2023 Stefanos-Iordanis Papadopoulos, Christos Koutlis, Symeon Papadopoulos, Panagiotis C. Petrantonakis

Multimedia content has become ubiquitous on social media platforms, leading to the rise of multimodal misinformation (MM) and the urgent need for effective strategies to detect and prevent its spread.

Misinformation

FLAC: Fairness-Aware Representation Learning by Suppressing Attribute-Class Associations

1 code implementation27 Apr 2023 Ioannis Sarridis, Christos Koutlis, Symeon Papadopoulos, Christos Diou

To overcome these limitations, this work introduces FLAC, a methodology that minimizes mutual information between the features extracted by the model and a protected attribute, without the use of attribute labels.

Age/Bias-conflicting Age/Unbiased +13

Improving Synthetically Generated Image Detection in Cross-Concept Settings

1 code implementation24 Apr 2023 Pantelis Dogoulis, Giorgos Kordopatis-Zilos, Ioannis Kompatsiaris, Symeon Papadopoulos

New advancements for the detection of synthetic images are critical for fighting disinformation, as the capabilities of generative AI models continuously evolve and can lead to hyper-realistic synthetic imagery at unprecedented scale and speed.

Graph Neural Network Surrogates of Fair Graph Filtering

no code implementations14 Mar 2023 Emmanouil Krasanakis, Symeon Papadopoulos

Graph filters that transform prior node values to posterior scores via edge propagation often support graph mining tasks affecting humans, such as recommendation and ranking.

Fairness Graph Mining

Synthetic Misinformers: Generating and Combating Multimodal Misinformation

1 code implementation2 Mar 2023 Stefanos-Iordanis Papadopoulos, Christos Koutlis, Symeon Papadopoulos, Panagiotis C. Petrantonakis

To address this, we perform a comparative study on existing and new Synthetic Misinformers that involves (1) out-of-context (OOC) image-caption pairs, (2) cross-modal named entity inconsistency (NEI) as well as (3) hybrid approaches and we evaluate them against real-world misinformation; using the COSMOS benchmark.

Misinformation

Design-time Fashion Popularity Forecasting in VR Environments

no code implementations14 Dec 2022 Stefanos-Iordanis Papadopoulos, Christos Koutlis, Anastasios Papazoglou-Chalikias, Symeon Papadopoulos, Spiros Nikolopoulos

To this end, we develop a computer vision pipeline fine tuned on fashion imagery in order to extract relevant visual features along with the category and attributes of the garment.

Image Classification Popularity Forecasting +1

A Multi-Stream Fusion Network for Image Splicing Localization

no code implementations2 Dec 2022 Maria Siopi, Giorgos Kordopatis-Zilos, Polychronis Charitidis, Ioannis Kompatsiaris, Symeon Papadopoulos

In this paper, we address the problem of image splicing localization with a multi-stream network architecture that processes the raw RGB image in parallel with other handcrafted forensic signals.

Leveraging Large-scale Multimedia Datasets to Refine Content Moderation Models

no code implementations1 Dec 2022 Ioannis Sarridis, Christos Koutlis, Olga Papadopoulou, Symeon Papadopoulos

The sheer volume of online user-generated content has rendered content moderation technologies essential in order to protect digital platform audiences from content that may cause anxiety, worry, or concern.

MINTIME: Multi-Identity Size-Invariant Video Deepfake Detection

1 code implementation20 Nov 2022 Davide Alessandro Coccomini, Giorgos Kordopatis Zilos, Giuseppe Amato, Roberto Caldelli, Fabrizio Falchi, Symeon Papadopoulos, Claudio Gennaro

In this paper, we introduce MINTIME, a video deepfake detection approach that captures spatial and temporal anomalies and handles instances of multiple people in the same video and variations in face sizes.

Classification DeepFake Detection +1

AdaCC: Cumulative Cost-Sensitive Boosting for Imbalanced Classification

1 code implementation17 Sep 2022 Vasileios Iosifidis, Symeon Papadopoulos, Bodo Rosenhahn, Eirini Ntoutsi

Class imbalance poses a major challenge for machine learning as most supervised learning models might exhibit bias towards the majority class and under-perform in the minority class.

Classification imbalanced classification

VICTOR: Visual Incompatibility Detection with Transformers and Fashion-specific contrastive pre-training

1 code implementation27 Jul 2022 Stefanos-Iordanis Papadopoulos, Christos Koutlis, Symeon Papadopoulos, Ioannis Kompatsiaris

For fashion outfits to be considered aesthetically pleasing, the garments that constitute them need to be compatible in terms of visual aspects, such as style, category and color.

Binary Classification Recommendation Systems

MemeTector: Enforcing deep focus for meme detection

1 code implementation26 May 2022 Christos Koutlis, Manos Schinas, Symeon Papadopoulos

To this end, we propose a methodology, called Visual Part Utilization, that utilizes the visual part of image memes as instances of the regular image class and the initial image memes as instances of the image meme class to force the model to concentrate on the critical parts that characterize an image meme.

InDistill: Information flow-preserving knowledge distillation for model compression

1 code implementation20 May 2022 Ioannis Sarridis, Christos Koutlis, Giorgos Kordopatis-Zilos, Ioannis Kompatsiaris, Symeon Papadopoulos

In this paper we introduce InDistill, a model compression approach that combines knowledge distillation and channel pruning in a unified framework for the transfer of the critical information flow paths from a heavyweight teacher to a lightweight student.

Knowledge Distillation Model Compression

The MeVer DeepFake Detection Service: Lessons Learnt from Developing and Deploying in the Wild

no code implementations27 Apr 2022 Spyridon Baxevanakis, Giorgos Kordopatis-Zilos, Panagiotis Galopoulos, Lazaros Apostolidis, Killian Levacher, Ipek B. Schlicht, Denis Teyssou, Ioannis Kompatsiaris, Symeon Papadopoulos

Enabled by recent improvements in generation methodologies, DeepFakes have become mainstream due to their increasingly better visual quality, the increase in easy-to-use generation tools and the rapid dissemination through social media.

DeepFake Detection Face Swapping

Multimodal Quasi-AutoRegression: Forecasting the visual popularity of new fashion products

no code implementations8 Apr 2022 Stefanos I. Papadopoulos, Christos Koutlis, Symeon Papadopoulos, Ioannis Kompatsiaris

We employ the product's target attributes time series as a proxy of temporal popularity patterns, mitigating the lack of historical data, while exogenous time series help capture trends among interrelated attributes.

Image Captioning Image Classification +4

p2pGNN: A Decentralized Graph Neural Network for Node Classification in Peer-to-Peer Networks

1 code implementation29 Nov 2021 Emmanouil Krasanakis, Symeon Papadopoulos, Ioannis Kompatsiaris

In this work, we aim to classify nodes of unstructured peer-to-peer networks with communication uncertainty, such as users of decentralized social networks.

Node Classification

Leveraging Selective Prediction for Reliable Image Geolocation

no code implementations23 Nov 2021 Apostolos Panagiotopoulos, Giorgos Kordopatis-Zilos, Symeon Papadopoulos

In this paper, we define the task of image localizability, i. e. suitability of an image for geolocation, and propose a selective prediction methodology to address the task.

Fake News Detection

pygrank: A Python Package for Graph Node Ranking

1 code implementation18 Oct 2021 Emmanouil Krasanakis, Symeon Papadopoulos, Ioannis Kompatsiaris, Andreas Symeonidis

We introduce pygrank, an open source Python package to define, run and evaluate node ranking algorithms.

A Survey on Bias in Visual Datasets

no code implementations16 Jul 2021 Simone Fabbrizzi, Symeon Papadopoulos, Eirini Ntoutsi, Ioannis Kompatsiaris

Hence, this work aims to: i) describe the biases that might manifest in visual datasets; ii) review the literature on methods for bias discovery and quantification in visual datasets; iii) discuss existing attempts to collect bias-aware visual datasets.

DnS: Distill-and-Select for Efficient and Accurate Video Indexing and Retrieval

1 code implementation24 Jun 2021 Giorgos Kordopatis-Zilos, Christos Tzelepis, Symeon Papadopoulos, Ioannis Kompatsiaris, Ioannis Patras

In this work, we propose a Knowledge Distillation framework, called Distill-and-Select (DnS), that starting from a well-performing fine-grained Teacher Network learns: a) Student Networks at different retrieval performance and computational efficiency trade-offs and b) a Selector Network that at test time rapidly directs samples to the appropriate student to maintain both high retrieval performance and high computational efficiency.

Computational Efficiency Knowledge Distillation +2

Audio-based Near-Duplicate Video Retrieval with Audio Similarity Learning

1 code implementation17 Oct 2020 Pavlos Avgoustinakis, Giorgos Kordopatis-Zilos, Symeon Papadopoulos, Andreas L. Symeonidis, Ioannis Kompatsiaris

For the robust similarity calculation between two videos, we first extract representative audio-based video descriptors by leveraging transfer learning based on a Convolutional Neural Network (CNN) trained on a large scale dataset of audio events, and then we calculate the similarity matrix derived from the pairwise similarity of these descriptors.

Retrieval Transfer Learning +1

Investigating the Impact of Pre-processing and Prediction Aggregation on the DeepFake Detection Task

no code implementations12 Jun 2020 Polychronis Charitidis, Giorgos Kordopatis-Zilos, Symeon Papadopoulos, Ioannis Kompatsiaris

In this paper, we propose a pre-processing step to improve the training data quality and examine its effect on the performance of DeepFake detection.

DeepFake Detection Face Swapping

ViSiL: Fine-grained Spatio-Temporal Video Similarity Learning

1 code implementation ICCV 2019 Giorgos Kordopatis-Zilos, Symeon Papadopoulos, Ioannis Patras, Ioannis Kompatsiaris

Subsequently, the similarity matrix between all video frames is fed to a four-layer CNN, and then summarized using Chamfer Similarity (CS) into a video-to-video similarity score -- this avoids feature aggregation before the similarity calculation between videos and captures the temporal similarity patterns between matching frame sequences.

ISVR Retrieval +2

Brenda Starr at SemEval-2019 Task 4: Hyperpartisan News Detection

no code implementations SEMEVAL 2019 Olga Papadopoulou, Giorgos Kordopatis-Zilos, Markos Zampoglou, Symeon Papadopoulos, Yiannis Kompatsiaris

In the effort to tackle the challenge of Hyperpartisan News Detection, i. e., the task of deciding whether a news article is biased towards one party, faction, cause, or person, we experimented with two systems: i) a standard supervised learning approach using superficial text and bag-of-words features from the article title and body, and ii) a deep learning system comprising a four-layer convolutional neural network and max-pooling layers after the embedding layer, feeding the consolidated features to a bi-directional recurrent neural network.

FIVR: Fine-grained Incident Video Retrieval

1 code implementation11 Sep 2018 Giorgos Kordopatis-Zilos, Symeon Papadopoulos, Ioannis Patras, Ioannis Kompatsiaris

To create the dataset, we devise a process for the collection of YouTube videos based on major news events from recent years crawled from Wikipedia and deploy a retrieval pipeline for the automatic selection of query videos based on their estimated suitability as benchmarks.

Benchmarking Retrieval +1

A Two-Level Classification Approach for Detecting Clickbait Posts using Text-Based Features

1 code implementation23 Oct 2017 Olga Papadopoulou, Markos Zampoglou, Symeon Papadopoulos, Ioannis Kompatsiaris

The detector is based almost exclusively on text-based features taken from previous work on clickbait detection, our own work on fake post detection, and features we designed specifically for the challenge.

Clickbait Detection Fake News Detection +2

A Physical Metaphor to Study Semantic Drift

no code implementations3 Aug 2016 Sándor Darányi, Peter Wittek, Konstantinos Konstantinidis, Symeon Papadopoulos, Efstratios Kontopoulos

By using term distances as a measure of semantic relatedness vs. their PageRank values indicating social importance and applied as variable `term mass', gravitation as a metaphor to express changes in the semantic content of a vector field lends a new perspective for experimentation.

Bridge Bounding: A Local Approach for Efficient Community Discovery in Complex Networks

1 code implementation5 Feb 2009 Symeon Papadopoulos, Andre Skusa, Athena Vakali, Yiannis Kompatsiaris, Nadine Wagner

There are numerous techniques adopting a global perspective to the community detection problem, i. e. they operate on the complete network structure, thus being computationally expensive and hard to apply in a streaming manner.

Data Analysis, Statistics and Probability Physics and Society

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