Publications
Background segmentation in multicolored illumination environments
Nikolas Ladas, Paris Kaimakis, Yiorgos Chrysanthou
The Visual Computer, Oct 2020
We present an algorithm for the segmentation of images into background and foreground regions. The proposed algorithm utilizes a physically based formulation of scene appearance which explicitly models the formation of shadows originating from color light sources. This formulation enables a probabilistic model to distinguish between shadows and foreground objects in challenging images.
Adult2Child: Motion Style Transfer using CycleGANs
Yuzhu Dong, Andreas Aristidou, Ariel Shamir, Moshe Mahler, Eakta Jain
Presented at: ACM SIGGRAPH Conference on Motion, Interaction, and Games, MIG'20, Oct 2020
This paper presents an effective style translation method that tranfers adult motion capture data to the style of child motion using CycleGANs. Our method allows training on unpaired data using a relatively small number of sequences of child and adult motions that are not required to be temporally aligned. We have also captured high quality adult2child 3D motion capture data that are publicly available for future studies.
Using Epistemic Game Development to Teach Software Development Skills
Christos Gatzoulis, Andreas S. Andreou, Panagiotis Zaharias, Yiorgos Chrysanthou
International Journal of Game-Based Learning (IJGBL), 10(4), Oct 2020
MotioNet: 3D Human Motion Reconstruction from Monocular Video with Skeleton Consistency
Mingyi Shi, Kfir Aberman, Andreas Aristidou, Taku Komura, Dani Lischinski, Daniel Cohen-Or, Baoquan Chen
ACM Transaction on Graphics, 40(1), Article 1, Sep 2020
Presented at: SIGGRAPH Asia 2020
MotioNet is a deep neural network that directly reconstructs the motion of a 3D human skeleton from monocular video. It decomposes sequences of 2D joint positions into two separate attributes: a single, symmetric, skeleton, encoded by bone lengths, and a sequence of 3D joint rotations associated with global root positions and foot contact labels. We show that enforcing a single consistent skeleton along with temporally coherent joint rotations constrains the solution space, leading to a more robust handling of self-occlusions and depth ambiguities.
Salsa dance learning evaluation and motion analysis in gamified virtual reality environment
Simon Senecal, Niels A. Nijdam, Andreas Aristidou, Nadia Magnenat-Thalmann
Multimedia Tools and Applications, 79 (33-34): 24621-24643, Sep 2020
We propose an interactive learning application in the form of a virtual reality game, that aims to help users to improve their salsa dancing skills. The application consists of three components, a virtual partner with interactive control to dance with, visual and haptic feedback, and a game mechanic with dance tasks. Learning is evaluated and analyzed using Musical Motion Features and the Laban Motion Analysis system, prior and after training, showing convergence of the profile of non-dancer toward the profile of regular dancers, which validates the learning process.
Digital Dance Ethnography: Organizing Large Dance Collections
Andreas Aristidou, Ariel Shamir, Yiorgos Chrysanthou
ACM Journal on Computing and Cultural Heritage, 12(4), Article 29, Nov 2019
This paper presents a method for contextually motion analysis that organizes dance data semantically, to form the first digital dance ethnography. The method is capable of exploiting the contextual correlation between dances, and distinguishing fine-grained difference between semantically similar motions. It illustrates a number of different organization trees, and portray the chronological and geographical evolution of dances.
Why did the human cross the Road?
Panayiotis Charalambous, Yiorgos Chrysanthou
Presented at: ACM SIGGRAPH Conference on Motion, Interaction and Games (MIG ’19), Article 47, 1–2. Best Poster Award, Oct 2019
Humans at rest tend to stay at rest. Humans in motion tend to cross the road – Isaac Newton.” Even though this response is meant to be a joke to indicate the answer is quite obvious, this important feature of real world crowds is rarely considered in simulations. Answering this question involves several things such as how agents balance between reaching goals, avoid collisions with heterogeneous entities and how the environment is being modeled. As part of a preliminary study, we introduce a reinforcement learning framework to train pedestrians to cross streets with bidirectional traffic. Our initial results indicate that by using a very simple goal centric representation of agent state and a simple reward function, we can simulate interesting behaviors such as pedestrians crossing the road through crossings or waiting for cars to pass.
Real-time 3D Human Pose and Motion Reconstruction from Monocular RGB Videos
Anastasios Yiannakides, Andreas Aristidou, Yiorgos Chrysanthou
Comp. Animation & Virtual Worlds, 30(3-4), May 2019
Presented at: Computer Animation and Social Agents - CASA'19
In this paper, we present a method that reconstructs articulated human motion, taken from a monocular RGB camera. Our method fits 2D deep estimated poses of multiple characters, with the 2D multi-view joint projections of 3D motion data, to retrieve the 3D body pose of the tracked character. By taking into consideration the temporal consistency of motion, it generates natural and smooth animations, in real-time, without bone length violations.
Deep Motifs and Motion Signatures
Andreas Aristidou, Daniel Cohen-Or, Jessica K. Hodgins, Yiorgos Chrysanthou, Ariel Shamir
ACM Transaction on Graphics, 37(6), Article 187, 2018, Dec 2018
Presented at: SIGGRAPH Asia 2018
We introduce deep motion signatures, which are time-scale and temporal-order invariant, offering a succinct and descriptive representation of motion sequences. We divide motion sequences to short-term movements, and then characterize them based on the distribution of those movements. Motion signatures allow segmenting, retrieving, and synthesizing contextually similar motions.
Style-based Motion Analysis for Dance Composition
Andreas Aristidou, Efstathios Stavrakis, Margarita Papaefthimiou, George Papagiannakis, Yiorgos Chrysanthou
The Visual Computer, 34(12), 1725-1737, Dec 2018
This work presents a motion analysis and synthesis framework, based on Laban Movement Analysis, that respects stylistic variations and thus is suitable for dance motion synthesis. Implemented in the context of Motion Graphs, it is used to eliminate potentially problematic transitions and synthesize style-coherent animation, without requiring prior labeling of the data.
How Responsiveness, Group Membership and Gender Affect the Feeling of Presence in Immersive Virtual Environments Populated With Virtual Crowds
Marios Kyriakou and Yiorgos Chrysanthou
Presented at: ACM SIGGRAPH Conference on Motion, Interaction, and Games, MIG'18, Limassol, Cyprus, Nov 2018
Inverse Kinematics Techniques in Computer Graphics: A Survey
Andreas Aristidou, Joan Lasenby, Yiorgos Chrysanthou, Ariel Shamir
Computer Graphics Forum, 37(6): 35-58, Sep 2018
Presented at: Eurographics 2018 (STAR paper).
In this survey, we present a comprehensive review of the IK problem and the solutions developed over the years from the computer graphics point of view. The most popular IK methods are discussed with regard to their performance, computational cost and the smoothness of their resulting postures, while we suggest which IK family of solvers is best suited for particular problems. Finally, we indicate the limitations of the current IK methodologies and propose future research directions.
Self-similarity Analysis for Motion Capture Cleaning
Andreas Aristidou, Daniel Cohen-Or, Jessica K. Hodgins, Ariel Shamir
Computer Graphics Forum, 37(2): 297-309, May 2018
Presented at: Eurographics 2018
Our method automatically analyzes mocap sequences of closely interacting performers based on self-similarity. We define motion-words consisting of short-sequences of joints transformations, and use a time-scale invariant similarity measure that is outlier-tolerant to find the KNN. This allows detecting abnormalities and suggesting corrections.