Christodoulos Chamzas

Democritus University of Thrace | DUTH · Department of Electrical and Computer Engineering

Numerous software solutions implementing the structure-from-motion/multi-view stereo (SFM/MVS) 3D reconstruction approach have been made available over the last two decades. Hence, enabling the production of high quality, in terms of geometry and colour information, 3D objects using solely unordered image sequences depicting a static scene or objec...

Performance evaluation is one of the main research topics in information retrieval. Evaluation metrics in combination with benchmark datasets (groundtruth) are used to quantify various performance aspects of a retrieval algorithm. In this paper, we present the Orion Pottery Repository, a publicly available and domain specific benchmark database. It...

Numerous software solutions that implement the Structure-from-Motion/Multi-View Stereo (SfM/MVS) 3D reconstruction approach have been made available during the last decade. These allow the production of high quality in terms of geometry and colour information 3D models with the use of unordered image collections that depict a static scene or object...

Performance evaluation is one of the main research topics in information retrieval. Evaluation metrics are used to quantify various performance aspects of a retrieval method. These metrics assist in identifying the optimum method for a specific retrieval challenge but also to allow its parameters finetuning in order to achieve a robust operation fo...

The aim of this research is to achieve spatial consistency of the UV map. We present an approach to produce a fully spatially consistent UV mapping based on the planar parameterisation of the mesh. We apply our method on a 3D digital replica of an ancient Greek Lekythos vessel. We parameterise the mesh of a 3D model onto a unit square 2D plane usin...

Performance benchmarking is an absolute necessity when attempting to objectively quantify the performance of content-based retrieval methods. For many years now, a number of plot-based and scalar-based measures in combination with benchmark datasets have already been used in order to provide objective results. In this work, we present the first ver...

The generation of 3D models with the Structure-from-Motion and Multiple View Stereovision (SFM-MVS) techniques is considered popular within the cultural heritage domain. The cost effectiveness in terms of hardware equipment and relatively low background knowledge requirements are two major SFM-MVS properties while the quality of the data produced c...

Web-based dissemination of cultural heritage 3D content has been vividly increased over the last decade. EU-funded research and development projects established affordable pipelines in order to allow efficient 3D documentation and dissemination. Such an example is the 3D-ICONS project that was focused on the 3D digitisation of outstanding cultural...

One of the factors that determine the data quality produced by targetless photogrammetric techniques is the feature richness of the surface being captured. The Structure-From-Motion and Multiple View Stereovision (SFM-MVS) pipeline is no exception to this rule as it relies on the ability to identify corresponding points within a collection of unord...

3D digitisation has been applied in different application domains. Due to the continuous growing interest, commercial and experimental 3D acquisition systems have evolved. Nevertheless, there isn't an all-in-one solution, thus there is a need for combining different technologies in order to exploit the advantages of each approach. In this paper, we...

The paper presents iGuide, a system that aims at enabling a socially enriched mobile tourist guide service, with the aim to address a much wider range of sites and attractions than existing solutions cover, including historic and traditional settlements, sites of natural beauty or unattended sites of cultural heritage where access to information is...

A number of software solutions based on the Structure-From-Motion (SFM) and Dense Multi-View 3D Reconstruction (DMVR) algorithms have been made recently available. They allow the production of high quality 3D models by using unordered image collections that depict a scene or an object from different viewpoints. In this work, we question the quality...

The continuous evolution of 3D computer graphics and the progress of 3D digitization systems resulted in a continuous increase in the available 3D content. The widespread use of 3D objects in diverse domains contributed on forming 3D object retrieval as an active research field. In order to objectively evaluate the performance of retrieval methodol...

It is fascinating to look at any digitization project from the scientific, technical and implementation points of view. However, it is necessary to consider the financial perspective as well. In this work we attempt to evaluate two common practices (photogrammetry and laser scanning) for the creation of 3D reconstructions of Cultural Heritage monum...

The evolution of real time 3D graphics technologies in combination with high bandwidth Internet connections and modern Web browsers enable users to explore complex 3D scenes. As a rule, a virtual visitor has to manually explore the geometrically complex 3D model in order to discover points of interest. This manual exploration is a time consuming pr...

The utilisation of 3D computer graphics technologies in the domain of pottery analysis can enhance archaeological research in terms of data management, indexing and shape matching. In this paper, we attempt to reduce the dimensions of the 3D vessel shape matching problem in order to create Web-enabled compact shape descriptors applicable for conten...

Shape matching is one of the main research procedures performed by archaeologists. Real time 3D computer graphics, 3D digitisation and content based retrieval are technologies that can facilitate the automation of the shape matching process. As pottery plays a significant role in understanding ancient societies, we focus on the development of compa...

a b s t r a c t This paper presents a novel compact shape descriptor designed specifically for content-based retrieval of complete or nearly complete 3D vessel replicas. The descriptor consists of two vectors that carry morphological features of the vessel's main body and appendages. The extraction of the descriptor is based on a pose normalisation...

The development of content based retrieval mechanisms is a very active research area. Present studies are mainly focused on automating the information extraction and indexing processes. Usually for the development and evaluation of such mechanisms, there is always a need for a ground-truth database. In this paper, we present a software tool named q...

Virtual reconstruction of urban areas, which are lost due to natural or man-provoked disasters, is nowadays feasible through the usage of contemporary three-dimensional technologies and virtual reality. With the aid of topography, architecture, history and archaeology, the once existed urban areas, or even whole cities, can be reconstructed as clos...

Nowadays commercial 3D range scanning systems have been used for the accurate digitisation of cultural heritage sites by following either terrestrial or aerial scanning approaches. Both approaches require high cost special equipment and software to cope with the vast amount of raw data. These raw data can be characterised as superfluous in cases wh...

The benchmarking of 3D content base retrieval mechanisms is usually performed on test bed datasets composed by 3D models. These usually cover several categories of objects such as ships, airplanes, animals, furniture, etc. In this paper, we attempted the generation of a ground truth database of 3D models that exhibit morphological characteristics s...

Continuity and relation to the past are inherent in human nature. The remains of the past constitute culture and cultural heritage. Preservation and dissemination of cultural heritage appear to be, nowadays, a universal priority. Historic/architectural monuments are among the most significant categories of cultural heritage and their 3D digitizatio...

Complete digital recording of Cultural Heritage is a multidimensional process. It depends highly on the nature of the subject of recording as well as the purpose of its recording. The whole process involves the three-dimensional digitization, digital data processing and storage, archival and management, representation and reproduction. In this pape...

The old city of Xanthi (Thrace-Greece) is one of the biggest traditional settlements in Greece which has the specialty to exhibit mixed traditional Greek, European and Oriental architectural features. This paper presents a 3D reconstruction of a small part of the settlement. It deals with the idea of using open source systems in 3D graphics in orde...

Nowadays, the huge non-indexing quantities of image archives (especially document images) require the development of intelligent tools for their retrieval with convenience comparable of the texts search engines. The proposed technique addresses the document retrieval problem by a word matching procedure. It performs matching directly in the images...

The paper presents definition extensions to MPEG-7 meta-data ones, mainly related to audio descriptors, introduced to e ciently describe traditional Greek music data features in order to further enable e cient music retrieval. A number of advanced content-based retrieval scenarios have been defined such as query by music rhythm, query by example an...

D digitization of monuments is a very specific problem in the digitization domain. Since the size of the digitization subject is one of the most important factors in choosing an appropriate and adequate digitization technology and methodology, this problem cannot be addressed using just one simple digitization technique. Various tech- niques have b...

The proposed technique deals with jigsaw puzzles and takes advantage of both geometrical and color features. It is considered that an image is being divided into pieces. The shape of these pieces is not predefined, yet the background's color is. The whole method concerns a recurrent algorithm, which initially, finds the most important corner points...

In this paper, we present a multi-segment image coding scheme suitable for lossless progressive transmission over noisy or congested networks. The method is a block-wise forward-adaptive context selection technique that employs a low-complexity classification process to separate an image into multiple segments according to local statistics, so that...

To efficiently compress rasterized compound documents, an encoder must be content-adaptive. Content adaptivity may be achieved by employing a layered approach. In such an approach, a compound image is segmented into layers so that appropriate encoders can be used to compress these layers individually. A major factor in using standard encoders effic...

To efficiently compress rasterized compound documents, an encoder must be content-adaptive. Content adaptivity may be achieved by using a layered approach. In such an approach, a compound image is segmented into layers and then the appropriate encoders are employed to compress these layers individually. A major factor in using these standard encode...

Recent developments in three-dimensional technologies and measurement instrumentation combined with multimedia databases offer today new possibilities for the integrated and complete description of Cultural Heritage Objects (CHO). In this work, we present an attempt to develop a database for archaeological ceramic and glass artifacts, where in addi...

In this presentation we establish new bounds on functions, which have their n-th order Hankel Transform bandlimited. This class of functions is proved to be also Fourier Transform bandlimited. N-th order Hankel Transforms and the consequent bounds are important for the reconstruction in CAT, MRI (Magnetic Resonance Imaging) etc. Indeed many algorit...

By applying the latest technologies in image compression for managing the storage of massive image data within cultural heritage databases and by exploiting the universality of the Internet we are now able not only to effectively digitize, record and preserve, but also to promote the dissemination of cultural heritage. In this work we present an ap...

By applying the latest technologies in image compression for managing the storage of massive image data within cultural heritage databases and by exploiting the universality of the Internet we are now able not only to effectively digitize, record and preserve, but also to promote the dissemination of cultural heritage. In this work we present an ap...

In complex color documents, text, drawings and graphics are appeared with millions of different colors. In many cases, text regions are overlaid onto drawings or graphics. In this paper, a new method is proposed to automatically detect and extract text in mixed type color documents. The proposed method is based on a combination of an adaptive color...

This paper presents the theoretical analysis of a downlink MAC protocol, which features power-saving characteristics and has been previously proposed [3], [7] for implementation in mobile data networks. The main objective of the protocol is to conserve valuable battery energy at the portable terminals of a wireless network. To accomplish this, the...

In this paper a new protocol is proposed for reducing the power consumption of the battery-powered terminals in a mobile computing environment. We exploit the fact that, in a mobile data network mobile terminals do not continuously receive data and therefore they need not continuously operate their receivers. Nevertheless, they need to periodically...

A new alternative is proposed for reducing the power consumption of the portable (battery-powered) units operating in a mobile packet-data network. First, a short review of the current power-saving protocols is taking place. It is shown that the most common means for conserving power is the intermittent operation of the receivers (at the portable u...

In complex color documents, text, drawings and graphics are appeared with millions of different colors. In many cases, text regions are overlaid onto drawings or graphics. In this paper, a new method is proposed to automatically detect and extract text in mixed type color documents. The proposed method is based on a combination of an Adaptive Color...

Vector quantization (VQ) has been used extensively in the past for image compression. The quantized image can be further compressed via a standard entropy coder (such as the arithmetic coder). In this paper, we present a simple equivalent to VQ, where unsupervised neural nets (NN) are used to find the appropriate codevectors. Furthermore, by imposi...

In this paper, we examine the behavior of the JPEG2000 coding scheme over noisy or congested communication channels and highlight a cost policy aspect. Two error schemes are considered, involving bit errors (noisy channel) and packet-dropping (congested channel) effects. Two bit error methods are used, consisting of flipping or eliminating the bits...

Recent developments in 2D and 3D digitization and visualization technologies, as well as in measurement instrumentation, combined with the emerging multimedia databases and network technologies offer today new possibilities for the integrated and complete description of cultural objects. Our Institute, with main interest in the preservation of Cult...

A new protocol is proposed for reducing the power consumption of battery-powered terminals in a mobile computing environment. We exploit the fact that, in a mobile data network, mobile terminals do not continuously receive data and therefore they need not continuously operate their receivers. Nevertheless, they need to check their traffic condition...

We present the behavior of the JPEG2000 coding scheme over noisy or congested communication channels and highlight the cost analysis aspect. Two error schemes are considered including bit errors and packet dropping effects. Two bit error methods are used, consisting of flipping or dropping the bits, and various packet sizes are put to the test of p...

In this paper, we present a multi-segment coding scheme applicable to the compression of residual images for lossless progressive transmission over noisy or congested telecommunication networks. The technique assumes that at a previous stage an encoder and a decoder produced the residual image from a gray-level original and its encoded lossy counte...

Recent developments in 3D technologies and measurement instrumentation combined with multimedia databases offer today new possibilities for the integrated and complete description of cultural heritage objects. A first attempt is made to develop a database for archaeological ceramic and glass artifacts where in addition to the digitized 2D and 3D im...

Developments in 2D and 3D digitization and visualization technologies, as well as in measurement instrumentation, combined with the emerging multimedia databases and network technologies offer new possibilities for the integrated and complete description of cultural objects. Our Institute, with main interest in the preservation of cultural heritage...

In recent years, research and presentation of cultural heritage have an important ally: technology. The "Ark of Refugee Heirloom" is a project of high cultural importance, since it aims at the recording and documentation of unknown heirlooms, kept mainly in private collections. The objective is the classification and publication of primary data, in...

We develop the nth order Fourier-Bessel series expansion of 1-D functions in the interval (0,#). Hence we establish the sampling theorem for a function with #-bandlimited nth order Hankel Transform. The latter statement implies that the function is also Fourier Transform #-bandlimited. The samples' locations are given by the roots of nth order Bess...

Recent developments in 3D technologies and measurement instrumentation combined with multimedia databases offer today new possibilities for the integrated and complete description of Cultural Heritage objects. A first attempt is made to develop a database for archaeological ceramic artifacts where in addition to the digitized 2D and 3D image, descr...

N-th order Hankel Transforms are important for the reconstruction in Magnetic Resonance Imaging (MRI), CAT etc. In this contribution we derive new bounds on functions, which have bandlimited their n-th order Hankel Transform.

This paper presents the theoretical analysis of a downlink MAC protocol, which features power-saving characteristics and has been previously proposed for implementation in mobile data networks. The main objective of the protocol is to conserve valuable battery energy at the portable terminals of a wireless network. To accomplish this, the terminals...

This paper describes a new method for document page layout analysis. The proposed approach is based on the use of the run-length smoothing algorithm (RLSA) and a neural network block classi®ed (NNBC). The RLSA is used locally and globally for the block segmentation by using optimal pre-estimated smoothing values. The NNBC is used in the classi®cati...

Software for estimation and processing simulation of microphone line arrays was developed, based on the fundamentals of sensor array theory and the basic concepts governing the array beamforming. Periodical, nonperiodical, and logarithmic microphone line arrays can be designed in a convenient way. Spatial structures, directivity patterns, and other...

A new alternative is proposed for reducing the power consumption of the portable (battery-powered) units operating in a mobile packet-data network. First, a review of the current power-saving protocols is given. It is shown that the most common means for conserving power is the intermittent operation of the receivers (at the portable units) and a c...

Two forms of a sampling theorem for concentric circles are established for a bandlimited two-dimensional (2-D) function. The location of the samples is prescribed either on equidistant circles or on the roots of the Bessel function J₀(). Both methods give comparable results, however, the number of samples required for their numerical ev...

Two forms of a sampling theorem for concentric circles are established for a bandlimited two-dimensional (2-D) function. The location of the samples is prescribed either on equidistant circles or on the roots of the Bessel function Both methods give comparable results, however, the number of samples required for their numerical evaluation is signif...

This paper addresses the design and implementation of a wireless network, proposed as a cost-effective support platform for remote control and/or monitoring applications. With this network, one or more supervising stations may access remote equipment like PLCs, data acquisition systems, weather stations, etc., in a reliable, transparent fashion. A...

This paper proposes a computationally efficient procedure for skew detection and text line position determination in digitized documents, which is based on the cross-correlation between the pixels of vertical lines in a document. The determination of the skew angle in documents is essential in optical character recognition systems. Due to the text...

2-D sampling on polar coordinates is important for many applications. Two forms of a sampling theorem for concentric circles are established for a bandlimited 2-D function. The location of the samples is prescribed either on equidistant circles or on the roots of the Bessel function J₀(). Both methods give comparable results, however the...

The identification of text areas in a document is crucial for optical character recognition (OCR), imagecompression and image-storage systems. This paper presents a new method for text identification in mixed-type documents. This type of document contains text, drawings and halftones. The proposed method separates the document into text and non-tex...

This paper describes the structure of an optical character recognition (OCR) system for printed documents. This system is trained for Latin and Greek typewritten text, but it can be easily adapted to any typewritten character set. The proposed method is divided into two main stages. In the first stage suitable binary features are extracted, most of...

This paper proposes a new method for character recognition which is based on a novel sequential multiclassifier scheme that uses curvature features in conjunction with other outstanding features. The curvature features are obtained according to the slopes of the character edge pixels. These slopes are observed from certain outer and inner character...

Mobile data networks offer a cost-effective and efficient alternative for data communication. In order to present some aspects of mobile data technology, this article offers some insight into the basic networking layers of a popular and widely deployed network, MOBITEX. MOBITEX technology offers a versatile architecture to support wireless packet d...

Adaptive filters find applications in many areas of signal processing and echo cancellation is one of them. It has been observed that, due to non-linearities inherent in the implementation, echo cancelers can diverge when their input is periodic. In this paper we examine the behaviour of adaptive filters in the presence of periodic inputs and provi...

A post-processing method suitable for low bit rate spatial domain block-coded images is described. An adaptive filtering process is employed to reduce the visually annoying artefacts introduced from compression. The decision-based filtering uses an estimation of the local characteristics of the coded image. For the areas of low image detail a smoot...