AutoGraff: towards a computational understanding of graffiti writing and related art forms.

The aim of this thesis is to develop a system that generates letters and pictures with a style that is immediately recognizable as graffiti art or calligraphy. The proposed system can be used similarly to, and in tight integration with, conventional computer-aided geometric design tools and can be used to generate synthetic graffiti content for urban environments in games and in movies, and to guide robotic or fabrication systems that can materialise the output of the system with physical drawing media. The thesis is divided into two main parts. The first part describes a set of stroke primitives, building blocks that can be combined to generate different designs that resemble graffiti or calligraphy. These primitives mimic the process typically used to design graffiti letters and exploit well known principles of motor control to model the way in which an artist moves when incrementally tracing stylised letter forms. The second part demonstrates how these stroke primitives can be automatically recovered from input geometry defined in vector form, such as the digitised traces of writing made by a user, or the glyph outlines in a font. This procedure converts the input geometry into a seed that can be transformed into a variety of calligraphic and graffiti stylisations, which depend on parametric variations of the strokes

CopyRNeRF: Protecting the CopyRight of Neural Radiance Fields

Neural Radiance Fields (NeRF) have the potential to be a major representation of media. Since training a NeRF has never been an easy task, the protection of its model copyright should be a priority. In this paper, by analyzing the pros and cons of possible copyright protection solutions, we propose to protect the copyright of NeRF models by replacing the original color representation in NeRF with a watermarked color representation. Then, a distortion-resistant rendering scheme is designed to guarantee robust message extraction in 2D renderings of NeRF. Our proposed method can directly protect the copyright of NeRF models while maintaining high rendering quality and bit accuracy when compared among optional solutions.Comment: 11 pages, 6 figures, accepted by iccv 2023 non-camera-ready versio

StrokeStyles: Stroke-based Segmentation and Stylization of Fonts

We develop a method to automatically segment a font’s glyphs into a set of overlapping and intersecting strokes with the aim of generating artistic stylizations. The segmentation method relies on a geometric analysis of the glyph’s outline, its interior, and the surrounding areas and is grounded in perceptually informed principles and measures. Our method does not require training data or templates and applies to glyphs in a large variety of input languages, writing systems, and styles. It uses the medial axis, curvilinear shape features that specify convex and concave outline parts, links that connect concavities, and seven junction types. We show that the resulting decomposition in strokes can be used to create variations, stylizations, and animations in different artistic or design-oriented styles while remaining recognizably similar to the input font

The role of stimulus change in interval duration judgments

Κατά τη συγκρότηση της αίσθησης του περάσματος του χρόνου, απαρτιώνουμε χρονικές ενδείξεις από αλλαγές του εσωτερικού και εξωτερικού κόσμου. Γι αυτό η επίδραση δυναμικών ερεθισμάτων στο χρονική εκτίμηση έχει εξεταστεί σε μεγάλο βαθμό. Ωστόσο, δεν είναι ξεκάθαρο ακόμη πως επηρεάζει η αντίληψη της αλλαγής την αίσθηση του χρόνου. Έτσι εξετάσαμε τρεις θεωρίες για το πως οι μετασχηματισμοί ενός ερεθίσματος σχετίζονται με την αντίληψης της χρονικής διάρκειας. Η πρώτη δίνει έμφαση στον αριθμό των εμφανιζόμενων αλλαγών, η δεύτερη στη φαινόμενη έντασή τους, και η τρίτη στη ένταση της σχετιζόμενης νευρωνικής δραστηριότητας. Επιπλέον εξετάσαμε τη σημασία της επίγνωσης της αλλαγής και του ρόλου της προσοχής στην εκτίμηση διάρκειας διαστημάτων 1.6 – 3.8 δευτερολέπτων. Η πειραματική μας μέθοδος περιελάμβανε ένα έργο εντοπισμού αλλαγής και ένα έργο χρονικής αναπαραγωγής. Χρησιμοποιήθηκαν απλά οπτικά ερεθίσματα, όπου ένα από αυτά άλλαζε θέση, η οποία όμως δεν ήταν αντιληπτή λόγω της επαναλαμβανόμενα διακοπτόμενης, από μία μάσκα, παρουσίασής τους. Για την ανεξάρτητη μεταβολή μεταξύ νευρωνικής διέγερσης και έντασης αλλαγής χειριστήκαμε τον αριθμό των αντικειμένων (Πείραμα 1), το χρόνο εμφάνισής τους (Πείραμα 2), και χρώμα του αντικειμένου με αλλαγή (Πείραμα 3). Τα αποτελέσματά μας δεν συμφωνούν πλήρως με καμία από τις βασικές μας υποθέσεις, παρότι η χρονική εκτίμηση φάνηκε κυρίως να επηρεάζεται από το αριθμό των συνειδητά αντιληπτών αλλαγών. Ο διαμοιρασμός της προσοχής είχε μικρή επίπτωση στη εκτίμηση της χρονικής διάρκειας, σύμφωνη με το Attentional Gate Model. Συνολικά, τα ευρήματά μας υποδεικνύουν πως η παρουσία ερεθίσματος με έντονη και προβλεπόμενα επαναλαμβανόμενη εμφάνιση, παρέχει μία συνεκτική χρονική δομή και επάγει τον διακυμαινόμενο συντονισμό της προσοχής, ώστε γεγονότα εκτός της συγκεκριμένης χρονικότητας όπως και άλλοι μη-χρονική παράγοντες να μην μπορούν να υπερισχύσουν της επίδρασης της επαναληπτικότητας του ερεθίσματος.To inform our sense of the elapsed time, we intergrade temporal cues based on changes of our internal and external world over time. Therefore, dynamic stimuli have long been studied on their effects on duration estimates. However, it is not yet clear which aspect of change is the critical factor that affects perceived time. In our study, we tested three theories that account for how the transformations of a stimulus in a time interval relate to its perceived duration, where the first one emphasizes the role of the absolute number of presented changes, the second one the saliency of the changes, and the third one the neural energy expended to processing its content. We examined, additionally, the significance change’s awareness and the modulatory role of attention on perceived duration of suprasecond intervals. Our experimental method included a dual task in a flickering paradigm with a change detection task and a temporal reproduction task. We used simple visual geometrical stimuli one of which had a positional change, throughout a trial’s duration, which was masked due to the flickering presentation. The timing of perceived change was recorded to examine how attentional distribution affects duration estimates and change’s awareness was assessed in a 4 alternative forced choice task. To independently modulate the neural energy for stimulus processing and the change’s saliency, we manipulated: the number of presented objects (Experiment 1), their presented duration, without changing the interval’s duration (Experiment 2), and the color of the stimuli with a positional change (Experiment 3). Our results did not consistently follow the predictions of any change-related account, although judged duration was affected from the number of perceived changes in about half of our experimental conditions (in Exps. 1 and 2). Change’s detection influenced perceived time only when reached awareness. Attention elicited a minor direct impact on duration judgments and had a weak effect in cases where increased allocation to temporal processing lengthened subjective time according to the Attentional Gate Model. Overall, our findings indicate that in the presence of a salient and predictable flickering stimulus that provides a coherent temporal structure and entrains attention to oscillate, events presented out of this temporality and other, non-temporal, parameters, cannot override the influence of flicker’s frequency on duration estimates

Improving visual search performance in augmented reality environments using a subtle cueing approach: Experimental methods, apparatus development and evaluation.

Ph.DDOCTOR OF PHILOSOPH

Guiding the Eye: A Non-photorealistic Solution for Controlling Viewer Interest

In film and still photography, depth of field control is often employed to control viewer interest in an image. This technique is also used in computer animation, but, in a medium where artists have near infinite control, must we rely on replicating photorealism? This research is a viable, non-photorealistic solution to the problem of directing viewer interest. Vision is directed by reducing superfluous visual information from parts of the image, which do not directly affect the depictive meaning of that image. This concept is applied to images and animations rendered from three-dimensional, computergenerated scenes, where detail is defined as visual information pertaining to the surface properties of a given object. A system is developed to demonstrate this concept. The system uses distance from a user-defined origin as the main mechanism to modulate detail. This solution is implemented within a modeling and shading environment to serve as a non-photorealistic, functional alternative for depth of field. This approach is conceptually based on a model of human vision, specifically, the relationship between foveal and peripheral vision, and is artistically driven by various works in the disciplines of painting and illustration, that through the careful manipulation of detail, control interest and understanding within the image. The resulting images and animations produced by this system provide viable evidence that detail modulation can be used to control effectively viewer interest in an image eliminating the need to use photographic techniques like depth of field