1,721,037 research outputs found
How many planar viewing surfaces are there in catadioptric cameras? Towards single-image localization of 3D lines
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POSTER: Fast, Automatic iPhone Shoulder Surfing
No full textTouchscreen devices increase the risk of shoulder surfing to such an extent that attackers could steal
sensitive information by simply following the victim
and observe his or her portable device. We underline
this concern by proposing an automatic shoulder
surfing attack against modern touchscreen keyboards
that display magnified keys in predictable
positions. We demonstrate this attack against the
Apple iPhone—although it can work with other
layouts and different devices—and show that it
recognizes up to 97.07% (91.03% on average) of the
keystrokes, with only 1.15% of errors, at 37 to 51
keystrokes per minute: About eight times faster than
a human analyzing a recorded video. Our attack
accurately recovers the sequence of keystrokes input
by the user. A previous attack, which targeted
desktop scenarios and thus worked with very
restrictive settings, is similar in spirit to
ours. However, as it assumes that camera and target
keyboard are both in fixed, perpendicular position,
it cannot suite mobile settings, characterized by
moving target and skewed, rotated viewpoints. Our
attack, instead, requires no particular settings and
even allows for natural movements of both target
device and shoulder surfer's camera. In addition,
our attack yields accurate output without any
grammar or syntax checks, so that it can detect
large context-free text or non-dictionary words
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Position and Radius of Spheres from Single Off-Axis Catadioptric Images
No full textInternational audienceIn this paper we address the problem of sphere localization from a single image taken with a noncentral catadioptric camera. We propose a method for determining both the radius and the position of an unknown sphere from a single, catadioptric image. The method can find its application in the field of robotic vision, especially in mobile robots playing soccer in RoboCup contests, in order to improve robot capabilities related to playing with a flying ball. Recently, a method for sphere reconstruction from single image taken with a noncentral, axial-symmetric, catadioptric camera has been proposed. In an axial symmetric catadioptric cameras, the pinhole of the camera is placed on the mirror axis. Though axial symmetric cameras help to simplify the geometrical treatment of the problem, they are difficult to set up since they require a precise alignment, usually hard to check. In this paper we deal with the general case of off-axis catadioptric cameras, with the camera pinhole placed in a general position w.r.t. the mirror. We devise a simple geometrical method by which we determine both the position of a sphere and its radius from its apparent image contour. Since our approach is based on coplanar viewing rays, it has a wider applicability w.r.t. the previous method, as it relaxes the constraint on camera position, i.e. it does not require a precise alignment, and the constraint on mirror axial symmetry, i.e. it can be applied to a wider class of mirrors. Some preliminary experiments both on simulated and real image are also presented
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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