Designing robust network topologies for wireless sensor networks in adversarial environments In this paper, we address the problem of deploying sink nodes in a wireless sensor network such that the resulting network topology be robust. In order to measure network robustness, we propose a new metric, called persistence, which better captures the notion of robustness than the widely known connectivity based metrics. We study two variants of the sink deployment problem: sink selection and sink placement. We prove that both problems are NP-hard, and show how the problem of sink placement can be traced back to the problem of sink selection using an optimal search space reduction technique, which may be of independent interest. To solve the problem of sink selection, we propose efficient heuristic algorithms. Finally, we provide experimental results on the performance of our proposed algorithms. A usual assumption on wireless sensor networks is that they consist of resource constrained and physically unprotected devices that use wireless channels for communications. These limitations make wireless sensor networks vulnerable to denial-of-service type attacks, such as physical destruction of nodes, exhaustion of their batteries, and jamming of the wireless channels. Such attacks may be addressed at different levels in the system architecture; in this work, we focus on mitigating them by controlled node deployment resulting in robust network topologies.. More specifically, we assume that the locations of the sensor nodes are predetermined by the application requirements, which is indeed the case in most civilian applications of sensor networks (see, e.g., [1] for some supporting arguments); however, the network operator has some freedom in choosing the location of the sink nodes (or the gateways to some backbone infrastructure). We aim at determining the location of the sinks in such a way that the resulting network be resistant to node and link removal attacks (abstracting physical node destruction or exhaustion and jamming, respectively).. In order to be able to compare different sink placements in terms of robustness of the resulting network, we need to measure network robustness quantitatively. Measuring and comparing network topologies was recently listed as one of the interesting open research questions in networking [2] . Instead of the usual approach of using connectivity for this purpose, we introduce the notion of persistence. Roughly, the persistence of a network is defined as the minimum ratio between the cost of an attack and the gain of the attacker, where the cost of an attack is related to the difficulty of removing the attacked links or nodes, and the gain of the attacker is determined by the importance of the nodes that, as a result of the attack, get disconnected from the sinks. We explain and give some illustrative examples in Subsection 2.2 and 4.2 why persistence is a better robustness metric for wireless sensor networks than connectivity.. Using persistence as the robustness metric, we formalize and study two variants of the sink deployment problem. In the first variant, we restrict the set of possible sink locations to the set of sensor node locations (in other words, we allow some of the sensors to be extended with sink functionality); we call this variant the sink selection problem. In the second variant, we remove this restriction, and allow sinks to be placed anywhere in the deployment area; we call this the sink placement problem. In both variants, we aim at achieving a given level of persistence while minimizing the deployment cost (or equivalently, maximizing persistence under a given upper bound on the deployment budget). We prove that both sink selection with required persistence and sink placement with required persistence are NP-hard. We propose greedy and genetic heuristic algorithms to solve the sink selection problem efficiently, and we show how the problem of sink placement with required persistence can be traced back to the problem of sink selection with required persistence by an efficient search space reduction technique, which may be of independent interest. We also show how any sink selection algorithm, including our proposed heuristic algorithms, can be used to efficiently obtain solutions to the sink placement problem using our search space reduction technique. Finally, we provide experimental results on the performance of our heuristic algorithms for sink selection and our search space reduction algorithm.. This article is a follow-up work of our previous paper [3] , compared to which here we prove that the problem of sink selection with required persistence is NPhard, propose a new genetic algorithm for sink selection, formalize the problem of sink placement with required persistence and prove that it is NP-hard, propose a new search space reduction technique and show how any sink selection algorithm can be used to find a solution to the placement problem using the reduced search space, and provide experimental results on our algorithms proposed in this article.. The organization of this paper is the following: In Section 2, we give a brief overview of placement problems in wireless sensor networks and previously proposed solutions. We also give an overview of topology robustness metrics and present a motivating example to show why we believe that vertex and edge connectivity as robustness metrics are not practical. In Section 3, we introduce (various versions of) persistence for the purpose of measuring the robustness of networks. In Section 4, we formalize the sink selection problem for a given network topology and prove that it is NP-hard. In Section 5, we present an integer programming model of the sink selection problem, which can be used to find optimal solutions. We also propose efficient greedy and genetic algorithms as heuristics to get solutions that are reasonably close to optimal. In Section 6, we formalize the sink placement problem and prove that it is NP-hard. In Section 7, we propose an algorithm for solving the sink placement problem based on an efficient search space reduction technique. We show that our search space reduction technique guarantees optimal solutions and that it can be applied to a wide range of placement problems. In Section 8, we describe the measurements that we have conducted to analyze the performance of our proposed heuristic algorithm for sink selection and to estimate the effectiveness of our search space reduction technique. Finally, in Section 9, we conclude the paper. In this paper, we have addressed the problem of deploying sink nodes in a wireless sensor network such that the resulting network topology be robust against denial-of-service type attacks such as node destruction, battery exhaustion, and jamming. Instead of the usual approach of using connectivity for measuring the robustness of network topologies, we have introduced the notion of persistence. We explained and gave some illustrative examples why persistence is a better robustness metric for wireless sensor networks than connectivity. Our arguments apply to a wider range of networks, including most types of access networks.. Using persistence as the robustness metric, we have formalized and studied two variants of the sink deployment problem. In the first variant, we restricted the set of possible sink locations to the set of sensor node locations; we called this variant the sink selection problem. In the second variant, we removed this restriction, and allowed sinks to be placed anywhere in the deployment area; we called this the sink placement problem. In both variants, we aimed at achieving a given level of persistence while minimizing the deployment cost, which is equally hard as maximizing persistence under a given upper bound on the deployment budget. We have proved that both sink selection with required persistence and sink placement with required persistence are NP-hard.. We have proposed greedy and genetic heuristic algorithms to solve the sink selection problem efficiently. We have shown how the infinite search space of possible placements can be reduced to a set of candidate locations, which is of polynomial size, such that the resulting set always contains an optimal solution. The proposed search space reduction technique may be of independent interest. We have also shown how any sink selection algorithm, including our proposed heuristic algorithms, can be used to find a solution in the reduced search space.. Finally, we have provided experimental results on the performance of our heuristic algorithms for sink selection and our proposed search space reduction technique. Our results show that the proposed technique could be used to efficiently solve other problems or to enhance the performance of previously proposed algorithms.

O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Formulation and analysis of in-place MSD radix sort algorithms We present a unified treatment of a number of related inplace MSD radix sort algorithms with varying radices, collectively referred to here as 'Matesort' algorithms. These algorithms use the idea of in-place partitioning which is a considerable improvement over the traditional linked list implementation of radix sort that uses O(n) space. The binary Matesort algorithm is a recast of the classical radixexchange sort, emphasizing the role of in-place partitioning and efficient implementation of bit processing operations. This algorithm is O(k) space and has O(kn) worst-case order of running time, where k is the number of bits needed to encode an element value and n is the number of elements to be sorted. The binary Matesort algorithm is evolved into a number of other algorithms including 'continuous Matesort' for handling floating point numbers, and a number of 'general radix Matesort' algorithms. We present formulation and analysis for three different approaches (sequential, divide-and-conquer and permutation-loop) for partitioning by the general radix Matesort algorithm. The divide-andconquer approach leads to an elegantly coded algorithm with better performance than the permutation-loop-based American Flag Sort algorithm. Sorting is a fundamental problem in computer science, with wide applications [1] . The moment the algorithm run-time and space complexity were formalized, sorting algorithms were at the forefront for analysis and improvement. Early recognition was given to Quicksort [2] and Heapsort [3] algorithms, because they improve on the O(n 2 ) order of running time of other slow sorting algorithms, to O(n log n). Heapsort is O(n log n) in the worst case, while Quicksort is O(n log n) in the average case. In practice, Quicksort runs faster than Heapsort most of the time, although it exhibits O(n 2 ) worst-case order of running time, which happens, for example, when the input data is nearly sorted. In general, sorting algorithms can be divided into two categories: 'comparison-based' and 'distribution-based'. A comparisonbased algorithm, like Heapsort or Quicksort, sorts by comparing two elements at a time. On the other hand, a distribution-based algorithm, like radix sort [4] [5] [6] [7] , works by distributing the elements into different piles based on their values.. Radix sort algorithms fall into two classes: MSD (most significant digit) and LSD (least significant digit). Radix sort algorithms process the elements in stages, one digit at a time. A digit is a group of consecutive bits with the digit size (number of bits) set at the beginning of the algorithm. MSD radix sort starts with the most significant (leftmost) digit and moves toward the least significant digit. LSD radix sort does it the other way. LSD distributes the elements into different groupscommonly known as 'buckets' and treated as queues (first-in-first-out data structure) -according to the value of the least significant (rightmost) digit. Then the elements are re-collected from the buckets and the MSD radix sort algorithms process continues with the next digit. On the other hand, MSD radix sort first distributes the elements according to their leftmost digit and then calls the algorithm recursively on each group. MSD needs only to scan distinguishing prefixes, while all digits are scanned in LSD. For example, for radix-2 MSD (i.e. digit size = 1 bit), two buckets are used and the elements are distributed into either bucket depending on the value of the most significant bit. Then the process continues with the next bit, considering only groups that have more than one element, until all the bits have been scanned. Clearly, such an algorithm uses O(n) space for the combined two buckets and is able to sort n non-negative integers in the range [0,m] in O(n log m) order of running time. In this paper, we have presented and analyzed a number of in-place MSD radix sort algorithms, collectively referred to as Matesort algorithms. These algorithms are evolved from the classical radix exchange sort. Experiments have shown that binary Matesort is of comparable speed to Quicksort for random uniformly distributed integer data. Unlike Quicksort, which becomes slower as data redundancy increases and may degenerate into O(n 2 ) algorithm, binary Matesort algorithm is unaffected and remains bounded by O(kn), where k is the element size in bits.. We have discussed three partitioning methods for use by the general radix Matesort algorithm: sequential, divide-and-conquer and permutation-loop. For English text, experiments have shown that the general radix Matesort using divide-and-conquer partitioning is the fastest. Moreover, the divide-and-conquer method can be optimized further to exploit data redundancy. Finally, the experimental results reported here show that Matesort (and also Quicksort) are much faster (twice as fast in many instances) than the built-in Microsoft .Net Array Sort method, which suggests that Microsoft ought to examine their implementation.

O O O O O O B I O O O O O O O O O O O O O B I O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B I O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O


Oxidative Stress-Induced Depolymerization of Microtubules and Alteration of Mitochondrial Mass in Human Cells ABSTRACT: Mitochondrial biogenesis is a biological process that has been intensively studied over the past few years. However, the detailed molecular mechanism underlying this increase in mitochondria remains unclear. To investigate the mechanism of such a mitochondrial proliferation, we examined alterations in mitochondria of human osteosarcoma 143B cells that had been treated with 100 to 500 M hydrogen peroxide (H 2 O 2 ) for 48 h. The results showed that mitochondrial mass of the cell was increased with the increase of the concentration of H 2 O 2 . On the other hand, by using real-time PCR techniques, we observed the changes of mitochondrial DNA (mtDNA) content in the cells exposed to oxidative stress. The copy number of mtDNA was increased by treatment with a low dose of H 2 O 2 but was drastically decreased after treatment with H 2 O 2 higher than 300 M. Transmission electron microscopic images revealed that mitochondria were abnormally proliferated in cells exposed to oxidative stress. Moreover, we found that the percentage of 143B cells arrested at the G 2 /M phase increased upon treatment with H 2 O 2 . Immunostaining and microtubule fractionation assay revealed that microtubules were depolymerized in the cells that had been treated with H 2 O 2 . To understand the effect of microtubules depolymerization on the mitochondrial mass, we treated the cells with several kinds of microtubule-active drugs, which arrest cultured cells at the G 2 /M phase. The results showed that mitochondrial mass and mtDNA copy number all were increased after such treatments. Taking these findings together, we suggest that oxidative stress-induced microtubule derangement is one of the molecular events involved in the increase of mitochondrial mass upon treatment of human cells with H 2 O 2 . It has been well documented that abnormal proliferation of mitochondria occurs frequently in affected tissues of patients with mitochondrial myopathy and muscle of aged individuals. This is one of the most prominent clinical hallmarks in mito-chondrial diseases such as chronic progressive external ophthalmoplegia (CPEO) and myoclonic epilepsy and ragged-red fiber (MERRF) syndromes. Morphologic features of giant mitochondria were observed in nerve and muscle tissues of elderly subjects and patients with mitochondrial disorders. 1, 2 Moreover, giant mitochondria also appeared in mtDNA-depleted ρ 0 cells, 3 and mtDNA depletion caused a reduction in the amount of mitochondrial inner membranes. 4 Therefore, structure and distribution of mitochondria are closely related to the oxidative status of mammalian cells.. Mitochondrial biogenesis has been a subject of intensive study in the past few years. Many factors, such as oxidative stress, deficiency in ATP production, cell cycle stage, and even the structure of microtubules, have been shown to affect the mitochondrial mass of mammalian cells. [5] [6] [7] [8] Mitochondria proliferate independently throughout the cell cycle and are inherited by daughter cells upon cell division. They actively move along cytoskeletal tracks and frequently change their shape and size through fission and fusion of the organelles.. Microtubules seem to be the major components of cytoskeletal systems that are involved in the regulation of the distribution of mitochondria in the cells. It has been reported that microtubules in interphase are involved in mitochondrial biogenesis aside from participation in the regulation of mitochondrial distribution in mammalian cells.. In this study, we treated human osteosarcoma 143B cells with sublethal doses of H 2 O 2 to increase reactive oxygen species (ROS) in the cells, and we investigated the role that microtubules may play in oxidative stress-induced alteration of mitochondrial mass. Human cells regulate their energy production by mitochondrial oxidative phosphorylation (OXPHOS) according to their needs. Depending on the challenge, mitochondria respond to the energy demands by subtle change in the activity of respiratory enzymes, by changing the expression of constituent enzyme subunits, or by increasing the number and size of the organelles. It is known that mitochondrial proliferation occurs in skeletal muscles in response to increased contractile activity, in adipose tissues in response to adaptive thermogenesis, and in cardiac myocytes in response to electrical stimulation or hypothermia. In clinical settings, the proliferation of abnormal mitochondria is generally observed in skeletal muscles of patients with a defective respiratory chain of mitochondria caused by mutation or depletion of mtDNA. It is thought that ROS, generated continuously by the respiratory chain, might play a role in mitochondrial biogenesis. However, solid evidence in support of this hypothesis has not yet been available.. The coordination between mitochondrial and cytoplasmic events leading to the growth and division of mammalian cells is largely unknown. It was reported that the mitochondrial mass was closely related to the cell cycle. 8 Our results confirmed the notion that stress-induced mitochondrial mass increase was correlated to the arrest of the cells at G 2 /M phase.. The key elements that regulate cell cycle in mammalian cells are microtubules. Microtubules are the major components of cytoskeletal systems that are responsible for the regulation of the mitochondrial distribution in the cell. Several studies demonstrated that oxidants disassemble the microtubules in human cells. 10 By using immunostaining and microtubule fractionation assay, we showed that microtubules were depolymerized in the cells after H 2 O 2 treatment (FIG. 4) . This finding suggests that H 2 O 2 induces depolymerization of microtubules and results in the alteration of mitochondrial mass in human cells. To substantiate this notion, we treated human osteosarcoma cells and hepatocellular carcinoma cells with microtubule-active drugs, such as Taxol, colchicine, and nocodazole, which stabilize or destabilize microtubules and arrest cultured cells at the G 2 /M phase. The results showed that mitochondrial mass and mtDNA copy number of 143B cells were all increased after treatment with these drugs.. The copy number of mtDNA is an important index of mitochondrial biogenesis. Our results showed that mtDNA copy number was increased by treatment with a low concentration of H 2 O 2 . However, the mtDNA content was drastically decreased after treatment with H 2 O 2 at a concentration higher than 300 µM. This phenomenon may be caused by the low fidelity of the mtDNA template with high oxidative damage or caused by low activity of impaired mitochondrial DNA polymerase γ. 12 This dualphase change of mtDNA copy number is consistent with our previous findings in the cybrids harboring different proportions of mtDNA with a 4,977-bp deletion and in leukocytes from healthy subjects of different ages. 9, 13 It has been reported that Taxol, but not colchicine or nocodazole, promotes the biogenesis of mitochondria in mammalian cells. 5 However, in this study, we demonstrated that the alteration in the stability of microtubules might control the biogenesis of mitochondria and that a H 2 O 2 -induced mitochondrial mass increase might be a result of the depolymerization of microtubules. It is plausible that H 2 O 2 disrupts the organization of microtubules and alters the mitochondrial mass. Further studies are warranted to clarify the mechanism of action of H 2 O 2 on the depolymerization of microtubules and on mitochondrial biogenesis in human cells. Increase of mitochondrial mass and mtDNA content in 143B cells after treatment with microtubule-active drugs. After treatment with 0.1 µg/mL of Taxol, colchicine, and nocodazole, respectively, the 143B cells were arrested at the G 2 /M phase. The results showed that mitochondrial mass (A) and mtDNA content (B) increased after such treatments (n = 4; ‡P < 0.005 vs. control). We first demonstrated that mitochondrial mass was increased in 143B cells that had been treated with 100 to 500 µM of H 2 O 2 for 48 h (FIG. 1A) . After treatment with 100-300 µM H 2 O 2 , the copy number of mtDNA was increased in 143B cells but decreased in the cells that had been treated with 500 µM H 2 O 2 (FIG. 1B) . This dual-phase response to oxidative stress was not caused by the possibility that cells were undergoing apoptosis or necrosis (TABLE 1) . Moreover, we showed that H 2 O 2 treatment may alter the morphology of mitochondria; mitochondria were enlarged and their cristae were disorganized after treatment with varying concentrations of H 2 O 2 for 48 h (FIG. 2) . Moreover, H 2 O 2 treatment cause cell cycle arrest at G 2 /M (FIG. 3) and disruption of microtubules in 143B cells (FIG. 4) . Quantitative immunoblotting demonstrated that polymerized tubulin was decreased by approximately 30% after 400 µM H 2 O 2 treatment; there was no significant decrease in cells treated with 200 µM H 2 O 2 . On the other hand, the monomeric tubulin was increased by approximately 15% and 25% after treatment with 200 and 400 µM H 2 O 2 , respectively. These results suggest that H 2 O 2 induced depolymerization of microtubules and resulted in the alteration of mitochondrial mass in human cells. Furthermore, after treatment of 143B cells with Taxol, colchicine, and nocodazole, we found that mitochondrial mass and mtDNA copy number of the cells were all increased (FIG. 5A and B) . This finding was consistent with our contention that H 2 O 2 may disrupt the organization of microtubules and thus alter the mitochondrial mass in human cells. but decreased in the cells that had been treated with 500 µM H 2 O 2 (n = 4; *P < 0.05 vs. control; **P < 0.01 vs. control).

O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Backward compatible HDR stereo matching: a hybrid tone-mapping-based framework Stereo matching under complex circumstances, such as low-textured areas and high dynamic range (HDR) scenes, is an ill-posed problem. In this paper, we introduce a stereo matching approach for real-world HDR scenes which is backward compatible to conventional stereo matchers. For this purpose, (1) we compare and evaluate the tone-mapped disparity maps to find the most suitable tone-mapping approach for the stereo matching purpose. Thereof, (2) we introduce a combining graph-cut based framework for effectively fusing the tone-mapped disparity maps obtained from different tone-mapped input image pairs. And finally, (3) we generate reference ground truth disparity maps for our evaluation using the original HDR images and a customized stereo matching method for HDR inputs. Our experiments show that, combining the most effective features of tone-mapped disparity maps, an improved version of the disparity is achieved. Not only our results reduce the low dynamic range (LDR), conventional disparity errors by the factor of 3, but also outperform the other well-known tone-mapped disparities by providing the closest results to the original HDR disparity maps. High dynamic range (HDR) images provide greater detail and larger brightness levels than conventional low dynamic range (LDR) ones. Even though capturing and displaying HDR images has been widely explored during the last two decades [1] [2] [3] [4] [5] , they are not broadly used in image processing and computer vision applications such as stereo matching and 3D reconstruction, segmentation, alpha matting, and face recognition. Working in HDR space can lead to better results by using more detailed brightness information. The pixel values in HDR space are calculated using an estimated camera response function to fuse the multiple photographs into a single, high dynamic range radiance map whose pixel values are proportional to the true radiance values in the scene. Differently exposed images are used to estimate the camera response function [1] . It is not hard to predict that working in HDR space provides more informative disparities. This is especially true in challenging lighting conditions *Correspondence: takhavan@ims.tuwien.ac.at Institute of Software Technology and Interactive Systems, Vienna University of Technology, Favoritenstrasse 9-11, Vienna, Austria and low-textured areas. However, two important challenges when switching calculations from LDR to HDR domain are lack of data and backward compatibility.. To generate a backward compatible solution to conventional stereo matchers, we use tone mapping operations (TMO) to compress the dynamic range into conventional range while preserving details of an HDR image. After comparing disparity maps achieved from different TMOs, we propose a fusion framework for achieving more informative disparity maps from tone-mapped HDR image pairs. In order to estimate the corresponding ground truth disparity maps, we make use of recently introduced HDR stereo images and an implementation of a customized stereo matching approach [6] . Based on these estimated disparities, we perform an objective evaluation of stereo matching approaches.. Why do we need a backward compatible HDR stereo matcher? Most of the available stereo matching software approaches are hard-coded to work with 8-bit input images, including the top-ranked methods in Middlebury [7] , although a few methods including some hardware solutions implemented on microprocessors have the advantage of running on floating point data [8] . Furthermore, most of the available stereo matching codes assume a fixed range of intensities for both left and right images while an HDR image pair most probably have different maximum luminance values for each image due to angular differences. See Section 5.1 for information regarding the maximum luminance values in the left and right images of our data set.. The described modifications are not hard to make in code level but will cause reviewing and re-factoring available stereo matching implementations (see Section 5.3 for an example). Stereo matching is an old research and industrial field, it is important for new stereo data sets to be runnable on conventional approaches. Therefore, we use tone-mapped image pairs with the standard interface to legacy stereo matchers and propose an algorithm to optimize the disparity maps to achieve the closest results to HDR stereo matching.. Even though we captured the HDR stereo data, we only used them for our ground truth disparity calculation and used HDR tone-mapped data in our proposed framework. The first reason for using tone-mapped images (not the original HDR image pairs) is described in the previous paragraph regarding backward compatibility. The second reason is, although our HDR stereo matching approach outperforms the tone-mapped and LDR approaches, it is not fully automatic. We used a manual in-painting post processing to fill-in some of the holes in the disparity maps as shown in Fig. 2 . Manual post processing and in-painting of disparity maps for the purpose of ground truth generation (evaluation) is a common approach [9, 10] but usually not a scalable or real-time method. We used the original HDR disparity maps just as a reference for our evaluation method for the same mentioned reasons. The manual post processing method will be discussed in more detail in Section 5.3.. In this paper, we present a graph-cut based disparity map fusion framework using different tone-mapped stereo matching results in order to take into account the best features for stereo matching from several different TMOs. Stereo matching in HDR scenes introduces new challenges to the state-of-the-art matching. Computing the disparity on the tone-mapped image pairs is an approach to solve these challenges, but not so many tonemapping operators are suitable to be applied on more than one frame or image while keeping the consistency of the images or frames. This problem has recently been addressed in video tone-mapping [11] .. The remainder of the paper is structured as follows. The related work and background are discussed in the next section. We compare the disparity results obtained from different tone-mapped image pairs with a focus on edgeaware filtering based TMOs in Section 3. Our proposed framework to combine several computed disparity maps is introduced in Section 4. Finally, Section 5 debates our experimental results, evaluation, and discussions. This Section discusses the HDR stereo image pairs as well as our reference disparity map generation approach used for the quantitative evaluation. We proposed a novel framework for combining several tone-mapped disparity maps in order to reduce the number of incorrect matching points and improve the performance of image matching in the HDR scenes. We used TMOs to compress HDR stereo images in order to keep backward compatibility to conventional stereo matchers. Our obtained disparities from different tonemapped stereo images are used along with our graph-cut implementation using α-expansion moves to select the minimum cost disparity value per pixel. To evaluate our results, we created the ground truth disparity map using original HDR stereo images and customized matching calculations to radiance space. Our qualitative and quantitative evaluations of seven different tone-mapped disparity maps, LDR, HDR, and proposed combined disparities show that there is a lot of room for disparity improvement in challenging lighting environments. Our novel fusion approach reduced the average RMSE of the conventional LDR stereo matching by the factor of 3. Using more disparity maps in the combining framework might improve our results but for sure will slow the combination process down. Finding the maximum number of the disparities which can effectively improve the results is a challenge that can be investigated in the future. In this work, one specific stereo matching algorithm is used for all the disparity map calculations. An interesting future research project can be dedicated to investigate how the proposed framework affects other stereo matching methods. Even though there is a considerable amount of literature on the state-of-the-art in each of the HDR and stereo matching fields, not much work has been done on joining the two. Several approaches have been presented for constructing an HDR image from two differently exposed LDR stereo images by calculating the depth information of the scene [12] [13] [14] [15] [16] [17] . More recently, Batz et al. [18] and Orozco et al. [19] proposed interesting approaches for HDR video reconstruction using depth information. Orozco et al. introduced a patch match-based method to generate 3D HDR video sequences using available hardware. The main goal in the mentioned articles is to generate better quality HDR image/video while our main focus is to use the available HDR content to achieve more informative disparity maps. Few approaches have been introduced for subjectively comparing tone-mapped stereo images with the focus on stereoscopic data generation [20] or disparity map calculation [6] . Recently, Aydin et al. [21] evaluated some of the TMOs based on edgeaware filters for HDR video tone-mapping taking into account the visual artifacts and temporal coherency in the tone-mapped video. The authors also introduced a faster and more efficient filter for high motion scenes. The key contribution of this filter is for achieving temporal stability without ghosting on high motion videos. Our work focuses on still stereo image pairs and does not contain motion.. Combining multiple TMOs. Combining results achieved from different methods is a common approach in image processing and computer vision research [22, 23] . More specifically, fusing several TMOs to achieve better quality images is addressed in [24] . The idea behind this fusion is that each TMO works better in a special image region and under some specific conditions and the best output can be calculated taking into account the suitable TMO for each image region. Mai et al. [20] explored that HDR tonemapping can significantly enhance perceptual quality of 3D images. We go one step further and use tone-mapped stereo pairs to obtain better disparity information.. Although, our first objective was to report the best TMO regarding stereo matching, the outcome of our experiments is consistent to the result of many evaluations that have been done on TMOs [25] [26] [27] ; there is no single TMO which performs the best in all conditions. Therefore, we combined the disparity maps from the tone-mapped images to maximize the quality of the disparity map taking into account the strong points of each TMO.. Combining multiple depth maps. Combining several depth maps achieved from different view points is studied by Schuon et al. [28] . Combining range information to generate a more accurate result is a well-known approach in the 3D society [29] . Another successful example was introduced by Izadi et al. [30] to fuse a sequence of depth maps generated by a kinect camera. We use information from several tone-mapped disparity maps and combine them to provide backward-compatible stereo matching results for HDR scenes.. Many different methods can be used for combining results. Some of the simple ways are to calculate the average, weighted average, or median of the candidate results. In most applications, using simple combination methods without taking into account any prior or statistical knowledge of candidate results does not achieve the best outcome. Akhavan et al. used a machine learningbased approach to combine results of color constancy in [31] . Markov random field (MRF)-based method was described and used is [29] to combine range information in 2005. In [23] , a fuzzy integral method was introduced as a combination method which considers the dependencies between the candidate results. In this paper, we use Markov random field and more specifically graph-cuts to combine the disparity maps. Using MRF is proved to be effective in labeling problems such as stereo matching [32] , since the output values of the matching algorithms are cost values that are suitable targets for energy minimization algorithms. In Section 5.5, the combination outcomes using average, median, and our method are compared.

O O O B I O O O O B I O O O O O O O O B I I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Generating a pronunciation dictionary for European Portuguese using a joint-sequence model with embedded stress assignment This paper addresses the problem of grapheme to phoneme conversion to create a pronunciation dictionary from a vocabulary of the most frequent words in European Portuguese. A system based on a mixed approach funded on a stochastic model with embedded rules for stressed vowel assignment is described. The implemented model can generate pronunciations from unrestricted words; however, a dictionary with the 40k most frequent words was constructed and corrected interactively. The dictionary includes homographs with multiplepronunciations. The vocabulary was defined using the CETEMPúblico corpus. The model and dictionary are publicly available. This is a revised and extended version of a previous paper that appeared at STIL 2011, the 8th Brazilian Symposium in Information and Human Language Technology The grapheme to phone(me) 1 conversion (G2P), also called letter-to-sound conversion, maps a written text into a string of symbols which represent the speech sounds exactly and unequivocally. Several frameworks have been proposed to tackle the G2P conversion, among which linguistically rulebased modules [18] and statistical approaches [10] can be mentioned. Mainly in the languages in which orthography is roughly phonologically based, such as the Portuguese and other Romanic Languages, linguistic rule-based systems should provide a good coverage of the association between letters and sounds [6, 25, 29] . However, probably no natural human-language satisfies this assumption exactly, because exceptions from the G2P conversion can be found perhaps in every language. The most common irregularity covers situations when the association between grapheme and phoneme is not quite one-to-one but can be, to some extent, ambiguous and greatly dependent on the neighbor-contexts.To deal with this problem, rule-based systems have been adopted along with a list of exceptions to cover the unruled situations. But this solution turns the development and the maintenance of the system very complex, hard and tiresome. Moreover, the rule-based G2P is more likely to make mistakes for new words. In contrast to the rule-based systems outlined above, a number of authors have addressed the G2P conversion from a stochastic perspective. This approach to G2P conversion is based on the idea that using pronunciation examples it could be possible to predict the pronunciation of unseen words by analogy. This method was already implemented by [8] and [2] , among others, for Portuguese. In this paper, we use a new statistical approach for which outstanding results have been reported, named the joint-sequence model, [5] . In this model, graphemes and phonemes are combined into a single state, giving rise to "graphonemes".. Although the joint-sequence model has shown to be a powerful tool, we also shown in this paper that for the case of the Portuguese language the determination of the stressed vowel leads to a substantial improvement in the system performance, as was also reported in [8] . Thus, we included a linguistically rule-based pre-processing stage, for stress assignment,which marks and disambiguates most of the pronunciations.. Common errors in the conversion procedure occur with the heterophonic homographs. Some theoretical frameworks with experimental results were recently proposed, e.g. [32, 33] and [34] for European Portuguese (EP); and [35] [36] [37] [38] and [39] for Brazilian Portuguese (BP). The study by Braga and Marques [34] proposed algorithms to deal with this problem of the homograph ambiguity in EP, using a linguistic rule-based methodology. Working with a part-of-speech (PoS) parser to disambiguate homographs which belong to different PoS, and a semantic analyser to disambiguate homographs that belong to the same PoS, the authors extended the approach proposed in [35, 36] . In fact, PoS categorization is insufficient to disambiguate entries in a pronunciation dictionary. Our solution consists in including PoS as well as pronunciation information for each dictionary entry.. The vocabulary used to generatethe pronunciation dictionary is in its previous form of the current "Acordo Ortográfico" (AO). 2 However, we think that this mixed-based G2P can also achieve good performance for EP with the AO. The inherent flexibility in dealing with the EP could be extended to other Romanic languages, which make this an advantageous approach.. The remainder of the paper is organized as follows. In Sect. 2, the joint-sequence model is briefly discussed. Section 3 presents how the vocabulary and dictionary were generated while Sect. 4 describes the linguistic model. In Sect. 5, experimental results are presented and the methodology used to deal with the heterophonic homographs is explained in Sect. 6. Then, the main conclusions are summarized and future work directions are foreseen.. 2 Joint-sequence model Given a sequence of N graphemes defined by G = G N 1 = {g 1 , g 2 , ..., g N }, the goal is to find a sequence of M phonemes,. .., f M }, that best describes the phonetic transcriptionof the original sentence. The statistical approach to this problem corresponds to the determination of the optimal sequence of phonemes, F * , that maximizes the conditional probability of phonemes, F, given a sequence of graphemes, G:. It is difficult to determine F * directly by calculating P(F|G) for all possible sequences F. However, using the Bayes theorem, we can rewrite the problem as:. Since P(G) is common to all sequences F, the problem can be simplified in the following way:. Using a phonological dictionary, previously created, it is possible to estimate P(G|F) and the a priori probability, P(F), for all sequences F and G found in this dictionary. The Markov-based approaches estimate a model for each phoneme and use n-gram models to computeP(F). These approaches model the dependency between graphemes and phonemes and the dependency between phonemes, but do not model dependencies between graphemes [12, 17, 28] . Due to these constraints, other statistical approaches emerged proposing joint probability models P(F, G) to determine the optimal sequence of phonemes [4, 14] , directly using the expression of the joint probability in (1) in place of the conditional probability. In this approach, all the dependencies present in the dictionary were modeled, resulting in improved performances than those obtained by the other models. The generation of a pronunciation dictionary for European Portuguese is described in this work. The technique used for the grapheme to phoneme conversion is based on a stochastic model, the joint-sequence model, which uses the concept of graphonemes and in which rules for stressed vowel assignment were embedded. The vocabulary includes the most frequent words that occur in Portuguese, as found in the CETEMPúblico corpus. A list of about 600 homographic words was also included, to disambiguate the cases of multiple pronunciations occurring on Portuguese. The results presented here are the best reported in similar works, although not directly comparable due to the use of different databases.. The G2P system is freely available on the website http:// lsi.co.it.pt/spl/ in the "resource" section, which contains the models, dictionaries and the G2P module.. There is an ongoing study on the analysis of the phonological behavior of the foreign words. Morphological information in terms of masculine/feminine, singular/plural and the inflection of the verbs can also be included in future developments. We also intend to enlarge the dictionary to other varieties of Portuguese.

O O B I O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Digital transformations and the archival nature of surrogates Abstract Large-scale digitization is generating extraordinary collections of visual and textual surrogates, potentially endowed with transcendent long-term cultural and research values. Understanding the nature of digital surrogacy is a substantial intellectual opportunity for archival science and the digital humanities, because of the increasing independence of surrogate collections from their archival sources. The paper presents an argument that one of the most significant requirements for the long-term access to collections of digital surrogates is to treat digital surrogates as archival records that embody traces of their fluid lifecycles and therefore are worthy of management and preservation as archives. It advances a theory of the archival nature of surrogacy founded on longstanding notions of archival quality, the traces of their source and the conditions of their creation, and the functional ''work of the archive.'' The paper presents evidence supporting a ''secondary provenance'' derived from re-digitization, re-ingestion of multiple versions, and de facto replacement of the original sources. The design of the underlying research that motivates the paper and summary findings are reported separately. The research has been supported generously by the US Institute of Museum and Library Services.

O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Cycle structure of random permutations with cycle weights Abstract. We investigate the typical cycle lengths, the total number of cycles, and the number of finite cycles in random permutations whose probability involves cycle weights. Typical cycle lengths and total number of cycles depend strongly on the parameters, while the distributions of finite cycles are usually independent Poisson random variables. Weighted random partitions and random permutations appear in mathematical biology and in theoretical physics. They are appealing because of their natural probabilistic structure and their combinatorial flavor. The sample space for random permutations is the set S n of permutations of n elements. Given σ ∈ S n , we let R j (σ) denote the number of cycles of length j in σ. The probability of a permutation σ is then defined as P n (σ) = 1 n!h n j 1 θ. Here, θ 1 , θ 2 , . . . are nonnegative parameters and h n is the normalization that makes P n a probability distribution, i.e.,. Notice that R 1 , R 2 , . . . satisfy the following identity for all σ ∈ S n : n j=1 jR j (σ) = n.. (1.. 3). The case θ j ≡ 1 corresponds to random permutations with uniform distribution and it has been studied e.g. in [11, 3, 10] . The case θ j ≡ θ is known as the Ewens distribution and it was introduced for the study of population dynamics in mathematical biology [12] . See [2, 15, 13] and references therein. Random permutations with restriction on the cycle lengths can be described with parameters θ j ∈ {0, 1}. Results have been obtained for random permutations restricted to finite cycles [18, 5] or to cycle lengths of given parity [16] . Another situation of interest is when we fix the asymptotic behavior of θ j for large j. Such a setting was considered in [4] , and it also appears in the study of the quantum Bose gas in statistical mechanics [7, 8] . The case where θ j converges to a constant (i.e., the Ewens case, asymptotically) was considered in [16, 9] . Vanishing parameters θ j → 0 were studied in [4, 9] where logarithmic cycle lengths were observed.. The random variables to be discussed in this article are the following:. • L 1 (σ) gives the length of the cycle that contains the index 1. Since our probability distribution is invariant under relabeling, we can interpret L 1 as giving the length of a "typical cycle", i.e. the length of the cycle that contains a random index.. • K(σ) = n j=1 R j (σ) gives the total number of cycles in the permutation σ.. • We also consider the distributions of R 1 , R 2 , . . . as n → ∞, i.e., the number of finite cycles. In most cases, they will be seen to converge to independent Poisson random variables.. The probability distribution P n depends only on the cycle structure (R 1 (σ), . . . , R n (σ)) of σ ∈ S n . It can therefore be understood as a distribution on nonnegative integers (r 1 , . . . , r n ) that satisfy jr j = n. As is well-known, these numbers are in one-to-one correspondence with integer partitions (λ 1 , λ 2 , . . . ) with λ 1 λ 2 . . . and λ i = n, by defining r j = #{i : λ i = j}. Taking into account the number of partitions that correspond to a given set (r 1 , . . . , r n ), the probability of a weighted random partition is then. (

B I O B I O B I O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A mixed digital / physical snapshot of early internet / web usage in New Zealand We are in the early stages of developing a unique physical and digital record of New Zealand's early experience of the Internet. Internet archives have been created as permanent records of the Web and other Internet documents. The Internet Archive (www.archive.org)-a collection of general Web pages-is the best known, but national collections (eg, Australia, pandora.nla.gov.au; Sweden, kulturarw3.kb.se) also exist. These archives capture the raw material of the Web, but cannot record usage [1] : which resources the Internet denizens of that moment found most useful or compelling, how the resources were accessed, how they were shared within a community, etc.. For New Zealand, a partial record of Internet / WWW usage from the early 1990s still exists; though the Web logs and Internet traffic records from that time are long gone, paper records remain from those early heady days. For years the entire country was dependent on a single Internet feed through Waikato University (Hamilton) [2] . In the early 1990s, Waikato University staff were also looked to as experts in accessing and using these new resources. Connection speeds were painfully slow and terminals were scarce, so University Library reference staff created paper records of useful internet documents (Figure 1 ). This dusty filing cabinet contains the only records of Internet usage in New Zealand when the Internet and WWW were introduced. These documents will be the core of a physical and digital archive of New Zealand's early Internet experiences.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


An explorational exhibit of a pig's heart Coronary heart diseases (CHD) are one of the main causes of deaths in the United States. Although it is well known that CHD mainly occurs due to blocked arteries, many of the specifics of this disease are still subject to current research. It is commonly accepted that certain factors, such as a cholesterol high diet, increase the risk of coronary heart disease. As a consequence, people should be educated to adhere a diet low in low-density lipoprotein (LDL or bad cholesterol). In order for children to become familiar with these facts, educational, explorative computer systems can be employed to raise some awareness. This poster describes an educational computer system for children that serves this purpose. While practicing their navigation skills, the children can learn about the various types of blood cells and particles within the blood stream. A geometric model of the arterial vascular system of the heart has been developed, which considers vessels of different sizes. An interactive flythrough using a standard game controller facilitates the exploration of the interior structure of the vasculature. A blood flow simulation including several different particles within the blood stream allows the young explorer to understand their functionality. This system has been deployed as an interactive museum exhibit for children. The primary age group addressed by the science museum where it is currently being displayed is 4-9 years. With proper guidance by the museum personnel and the instructional material provided at the exhibit the game is also suitable for slightly younger and much older children. The implemented system simulates a submarine-style navigation through the blood stream inside an arterial vascular tree of a heart. The vasculature is based on a computed tomography (CT) scan of a pig's heart. The user has full control over the navigation by using a Logitech c WingMan R Cordless Rumblepad TM as input device. This controller provides two analog joysticks that can be used to achieve six-degrees-of-freedom input. In this application, the user controls forward and backward movement (acceleration and deceleration) with the left joystick while changing the orientation (left, right, up and down) by using the right joystick. Collision detection with the vessel walls ensures that the vasculature cannot be left. On collision with the vessel wall as well as with any of the particles within the blood stream force feedback is provided by using the rumble feature of the input device. In addition, audio feedback with different types *

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


An extension of min/max flow framework a b s t r a c tIn this paper, the min/max flow scheme for image restoration is revised. The novelty consists of the fol-

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An identity-based key infrastructure suitable for messaging and its application to e-mail Identity-based encryption (IBE) systems are relatively recently proposed; yet they are highly popular for messaging applications since they offer new features such as certificateless infrastructure and anonymous communication. However, recent studies also reveal that the infrastructure needed for IBE systems may be as complicated as the conventional public key cryptosytems and not sufficient research has been conducted in relevant issues concerning the infrastructure. In this paper, we intended to propose an IBE infrastructure for messaging applications. The proposed infrastructure requires one registration authority and at least one public key generator and they secret share the master secret key. In addition, the PKG also shares the same master secret with each user in the system in a different way. Therefore, the PKG will never be able to learn the private keys of users under non-collusion assumption. Users can also select meaningful pseudonyms and communicate anonymously using them with other users in the system. We discuss different aspects of the proposed infrastructure such as security, key revocation, uniqueness of the identities, and non-repudiation that constitute the main drawbacks of other IBE schemes. We demonstrate that our infrastructure solves many of these drawbacks under certain assumptions. We also provide some implementation results to show the feasibility of the proposed infrastructure. Identity-based encryption (IBE) scheme is a public key cryptosystem where the public keys are unique identities in arbitrary string forms. For instance; e-mail addresses, names, pseudonyms or IP addresses can serve as a public key in IBE systems. The original concept was initially introduced by Shamir in 1984 [19] while the first practical realization of IBE system becomes feasible via pairing-based cryptography proposed by Boneh and Franklin [2] . With the advent of pairing-based cryptography; new applications of IBE cryptosystem as well as new techniques, to realize it more efficiently, become the major focus of the contemporary research. Generally speaking, in IBE cryptosystems, there exists a trusted third party, so-called Private Key Generator (PKG), which is responsible for generating global parameters to be employed in the system as well as the private keys for the registered users. Users obtain their private keys from the PKG, in order to decrypt their messages intended for them. The secure delivery of private keys should be performed over secure channels, where confidentiality and authentication are provided.. In principal; IBE is a public key cryptosystem, where each user has a public and private key pair. To illustrate, suppose that a user, Alice, wants to send a message to Bob. She encrypts the message with Bob's unique public key, e.g. his e-mail address 'bob@openuniv.edu'. Bob requests the corresponding private key from the PKG, to decrypt the message. The PKG calculates the private key, sends it to Bob, and Bob consequently decrypts the message.. Since the bound between the user and the user's public key is based on an inherent or real-word relationship (e.g. user/name, user/e-mail address, user/assumed role etc.), the need for an infrastructure is seen by some not as comprehensive as the conventional public key infrastructure (PKI). Whereas, as elaborately pointed out in [6] , a fully-functional IBE system would also require a complex infrastructure in which some aspects have not been fully investigated. Firstly, there is the issue of uniqueness of public keys in IBE since real world names or identities tend to be not unique. Therefore, there should be a registration authority to keep track of used names, i.e. public keys. Secondly, the key revocation could lead to some inconvenience since one may find it difficult to obtain a new descriptive name for oneself such as finding a new name. One way to revoke a key without actually changing the public key requires that system parameters be changed resulting in changing of private key of every user in the system. And finally, all IBE schemes have the key escrowing property, which is considered as a weakness since the PKG knows the private key of every user. Thus, the PKG not only is able to decrypt any message but also can fabricate a signature on behalf of any user. The former results in the loss of privacy and anonymity of users in their communications while the latter leads to loss of nonrepudiation property. There have also been previous works in literature, e.g. [16] , [1] , [3] on the IBE infrastructure, that essentially proposed similar techniques to overcome the mentioned drawbacks and provide the user privacy.. In this paper, our contribution is proposing solutions to some of the shortcomings of IBE systems. Limiting our attention to messaging systems such as instant messaging and e-mail applications we outline an infrastructure for IBE system. Our basic construction follows the idea of secret sharing of the master secret key between two semi-honest parties, namely the private key generator (PKG) and the registration authority (RA). In addition, the PKG shares the same master secret key with each user in a different way, having one share for each user registered in the system. Thus, a user and the PKG have to participate in a protocol to generate the private key for the user. A user's only interaction with the RA is during the registration phase, in which the RA not only checks the uniqueness of the identity but also assists in the protocol that generates two new shares of the master secret key; one for the user and the other for the PKG. One benefit of our model is that there is no need to employ a secure channel between the PKG and users to deliver private keys since the PKG sends only its share of the private key to users, which carries no information about the private key itself.. We also propose to use ever-changing public keys by attaching date information to the natural identities of users whose frequency is determined by the underlying communication model. While public keys changing on daily basis are convenient for instant messaging applications, weekly or monthly public keys in case of asynchronous persistent communication models such as e-mail systems seem feasible. The PKG's shares of the private keys are sent to users automatically. The PKG does not need to be a global party in the system; there can be many local PKGs serving intranets or subdomains. For instance, the message exchange server is a candidate for a local PKG.. In our infrastructure, the users can freely adopt pseudonyms or nicknames for anonymous communication. The hardness of elliptic curve discrete logarithm problem protects the anonymity of users from the scrutiny of the PKG or any other party.. Our most basic assumption is that the RA and PKG never collude since they are semi-honest and follow the protocol steps exactly. Similarly, we also assume that a user and the PKG do not collude since we believe that there are many incentives for users not to collude with the PKG such as losing their privacy and/or anonymity if they do so. Furthermore, we can prevent users from colluding with the PKG or revealing their secrets using tamper-proof crypto modules.. This work basically extends our previous work in [11] by fixing certain security problems in the registration phase, providing extensive security analysis illustrating possible attacks, and presenting the integration of our protocol to an e-mail client Mozilla Thunderbird.. We give a brief information about identity-based encryption systems and their mathematical background in the second section. The third section includes a detailed explanation of our infrastructure. An additional property, namely the anonymity of our system is discussed in section 4. The analysis of our proposed scheme is given in section 5. In the sixth section, implementation details are given. The paper ends up with conclusion and future works.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


SOME COMBINATORIAL ASPECTS OF CONGRUENCE LATTICE REPRESENTATIONS Abstract. A finite distributive lattice D can be represented as the congruence lattice, Con L, of a finite lattice L. We shall discuss the combinatorial aspects of such-and related-representations, specifically, optimal size, breadth, and degree of symmetry. The congruence lattice, Con L, of a finite lattice L is a finite distributive lattice according to a result of N. Funayama and T. Nakayama [5] . The converse is a result of R. P. Dilworth from 1944: Every finite distributive lattice D can be represented as the congruence lattice, Con L, of a finite lattice L.. This result was first published in 1962 in the paper [13] of the present authors, where-and, one assumes, in the original proof by Dilworth-the lattice L constructed was very large.. Since a finite distributive lattice D is determined by the poset J(D) of its joinirreducible elements, it is logical to measure the size of the lattice L representing D as a function of n = |J(D)|. The original constructions produced lattices of size O (2 2n ). This was improved to O(n 3 ) in G. Grätzer and H. Lakser [8] ; it was conjectured that O(n 3 ) can be improved to O(n 2 ) and that O(n 2 ) is best possible. In Section 2, we sketch the O(n 2 ) construction as given in G. Grätzer, H. Lakser, and E. T. Schmidt [9] . The real combinatorics is in G. Grätzer, I. Rival, and N. Zaguia [12] , proving that O(n 2 ) is, indeed, best possible; this is also outlined in Section 2.. The original construction produced a lattice L of breadth O(2n). This was reduced to 2 in G. Grätzer and H. Lakser [8] , and retained in G. Grätzer, H. Lakser, and E. T. Schmidt [9] . So the final result constructs a planar lattice L of size O(n 2 ). What is more combinatorial than symmetry? We can measure the symmetry of a lattice L with its automorphism group, Aut L. It is a result of G. Birkhoff [4] that every finite group is isomorphic to the automorphism group of a finite lattice.. In [6] , the first author raised the question whether every finite distributive lattice D can be represented as the congruence lattice of a finite lattice L with a prescribed automorphism group. This problem was solved for finite lattices by V. A. Baranskiȋ [3] and A. Urquhart [22] , independently.. In [14] , the present authors have developed a new approach to this problem; we shall discuss this in Section 3. For a general lattice L, it is well known that Con L is a distributive algebraic lattice. A long standing conjecture is that the converse also holds. One can attempt to solve this conjecture-at least for some classes of distributive algebraic lattices-by considering a finite lattice K, a sublattice of the finite lattice L, and ask how Con K is related to Con L? One can then hope to represent an infinite distributive algebraic lattice as a congruence lattice by a direct limit. (In a recent manuscript [23] , F. Wehrung exhibits a distributive algebraic lattice for which this method cannot be successful.). It turns out that if K is a sublattice of L, then there is a natural 0-preserving joinhomomorphism from Con K to Con L. Let K and L be lattices and let ϕ : K → L be a lattice homomorphism (not necessarily an embedding). We define the map. as follows: for each Θ ∈ Con K, define the set Θϕ of pairs of elements of L that are ϕ-images of Θ-congruent pairs of elements of K, that is,. then the image of Θ under ϕ is the congruence of L generated by Θϕ. Now the representation theorem takes the following form: for finite lattices K and L, the map ϕ can be characterized as a 0-preserving join-homomorphism. This major result is due to A. P. Huhn [17] .. In Section 4 we discuss some combinatorial questions related to Huhn's theorem: how large the lattices must be and what can be said about the breadth? Recent results of G. Grätzer, H. Lakser, and E. T. Schmidt prove that if ψ is a 0-preserving join-homomorphism of D into E (D and E are finite distributive lattices) and n = max(|J(D), |J(E)|), then there are finite lattices K and L and there is a lattice homomorphism ϕ : K → L that represent ψ so that the size of K and L is O(n 5 ) and K and L are of breadth 3. We conjecture that this result is the best. For the basic concepts and notations, we refer the reader to G. Grätzer [6] , as reviewed in the lecture "Congruences lattices 101".

O O O O B I O O O B B O O O O O O O B I O O O O B O O O O O O O O O O O O O O B O O O O O B I O O O O B O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O B I O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B O O O O O B I O O B O O O O O O O O O O O O B B O O O O O O O B I O O B O O O O O B I O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O B I O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O B B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Structure from silhouettes: a new paradigm for fast sketch-based design of trees Modeling natural elements such as trees in a plausible way, while offering simple and rapid user control, is a challenge. This paper presents a method based on a new structure from silhouettes paradigm. We claim that sketching the silhouettes of foliage at multiple scales is quicker and more intuitive for a user than having to sketch each branch of a tree. This choice allows us to incorporate botanical knowledge, enabling us to infer branches that connect in a plausible way to their parent branch and have a correct distribution in 3D. We illustrate these ideas by presenting a seamless sketch-based interface, used for sketching foliage silhouettes from the scale of an entire tree to the scale of a leaf. Each sketch serves for inferring both the branches at that level and construction lines to serve as support for sub-silhouette refinement. When the user finally zooms out, the style inferred for the branching systems he has refined (in terms of branch density, angle, length distribution and shape) is duplicated to the unspecified branching systems at the same level. Meanwhile, knowledge from botany is again used for extending the branch distribution to 3D, resulting in a full, plausible 3D tree that fits the user-sketched contours. As our results show, this system can be of interest to both experts and novice users. While experts can fully specify all parts of a tree and over-sketch specific branches if required, any user can design a basic 3D tree in one or two minutes, as easily as sketching it with paper and pen. This paper presented the first sketch-based method for trees based on a structure from silhouettes paradigm. Our results have shown that it saves user time and improves shape control when compared to only sketching structure directly. Automatic inference of the branch shapes, their 2D distribution and their 3D arrangement around a parent rely on strong a priori knowledge from the field of botany. This enables the creation of plausible trees while reducing the need for user expertise. Our approach thus bridges the gap between the direct sketch-based methods such as [OOI05] and procedural systems with little shape control.. An extension would be to extract automatically silhouette parameters from photograph such as [TFX * 08]. For the future, one could imagine using our approach of seamless, coarse to fine sketching from any viewpoint at the scale of a full landscape. For quickly shaping a coarse forest on a hill in the background, the user could just sketch one silhouette per tree, which could be recursively duplicated at a smaller scale in a fractal style, as a first guess for finer details. Then, the user could add detail to the important trees in the foreground to ensure that the design would meet the art director's requirements for the different scenes. We believe that such a system, providing a quick first guess but still enabling simple manual editing where needed, would be of a great help in production pipelines.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O