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Copyright of Journal of Community Service & Empowerment is the property of Journal of Community Service & Empowerment and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Environmental Education is the property of Canadian Journal of Environmental Education and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the heart of the 21st century, we have been surprised witnesses of a coarse pinhole projection among different professionals. This fact shows that in spite of the thorough study made by specialists, the so called Camera Obscura is something that has been talked about but only a few have experimented. Without the help of a lens, the image projected by a camera is dim and not clear. Only in ideal luminous circumstances, a good hole quality and total darkness would it be possible to efficiently trace the outline of the projected image. Once this fact has been confirmed since very old times, it was only a matter of time that curiosity or a stroke of luck led to place a lens in the little opening. While all these was going on, innumerable authors devoted to study the whole process. But, nevertheless, the graphic or written evidence that have reached us, is certainly poor. [ABSTRACT FROM AUTHOR]

Computer generated images are most easily generated as pinhole images whereas images obtained with optical lenses exhibit a Depth-of-Field (DOF) effect. This is due to the fact that optical lenses gather light across finite apertures whereas the simulation of a pinhole lens means that the light is gathered through an infinitesimal small aperture, thus producing sharp images at any depth. Simulating the physical process of gathering light across a finite aperture can be done for example with distributed ray tracing, but it is computationally much more expensive than the simulation through an infinitesimal aperture. The usual way of simulating lens effects is therefore to produce a pinhole image and then post processes the image to approximate the DOF. Post processing algorithms are fast but suffer from incorrect visibilities. In this paper, we propose a novel algorithm that tackles the visibility issue with a sparse set of views rendered through the optical center of the lens and several peripheral viewpoints distributed on the lens. All peripheral images are warped towards the central view to create a Layered-Depth-Image (LDI), so that all observed 3D points located on the same central view-ray are stacked on the same pixel of the LDI. Then, each pixel in the LDI is conceptually scattered into a Point-Spread-Function (PSF) and blended in depth order. While the scatter method is very inefficient on a GPU, we propose a selective-gather method for DOF synthesis, which scans the neighborhood of a pixel and blends the colors from the PSFs covering the pixel. Experiments show that the proposed algorithm can synthesize high-quality DOF effects close to the results of distributed ray tracing but at a much higher speed. [ABSTRACT FROM AUTHOR]

The accurate determination of the local impulse response and the covariance in voxels from penalized maximum likelihood reconstructed images requires performing reconstructions from many noise realizations of the projection data. As this is usually a very time-consuming process, efficient analytical approximations based on the Fisher information matrix (FIM) have been extensively used in PET and SPECT to estimate these quantities. For 3D imaging, however, additional approximations need to be made to the FIM in order to speed up the calculations. The most common approach is to use the local shift-invariant (LSI) approximation of the FIM, but this assumes specific conditions which are not always necessarily valid. In this paper we take a single-pinhole SPECT system and compare the accuracy of the LSI approximation against two other methods that have been more recently put forward: the non-uniform object-space pixelation (NUOP) and the subsampled FIM. These methods do not assume such restrictive conditions while still increasing the speed of the calculations considerably. Our results indicate that in pinhole SPECT the NUOP and subsampled FIM approaches could be more reliable than the LSI approximation, especially when a high accuracy is required. [ABSTRACT FROM AUTHOR]

Multi-pinhole collimators are often used in pre-clinical SPECT systems because they have a better resolution-sensitivity tradeoff than parallel hole collimators when imaging small objects. Most multi-pinhole collimators are designed to allow no or only a limited amount of overlap between the different pinhole projections because the ambiguity introduced by multiplexing pinholes can result in artifacts. The origin of these artifacts is still not fully understood, but previous research has already shown that data incompleteness could be part of the explanation. Therefore, we developed a method to investigate data completeness in multiplexing multi-pinhole systems and showed that a certain activity distribution can be successfully reconstructed when the nonmultiplexed data is complete or when the overlap can be sufficiently de-multiplexed. We validated this method using computer simulated phantom data of different multiplexing systems. We also studied contrast-to-noise and nonprewhitening matched filter signal-to-noise ratio (NPW-SNR) to compare the image quality in a single pinhole system with multiplexing systems. We found that our method can indeed be used to evaluate data completeness in multiplexing systems and found no artifacts in the systems that had complete data. Sensitivity increased significantly with multiplexing but we found only small, nonsignificant differences in contrast-to-noise ratio. However, the NPW-SNR did slightly improve in the multiplexing setups. We conclude that more multiplexing does not necessarily result in more artifacts and that even a high amount of multiplexing can still result in artifact-free images if the nonmultiplexed data is complete or when the overlap can be sufficiently de-multiplexed. [ABSTRACT FROM PUBLISHER]

In multi-pinhole SPECT, overlapping the projections from different pinholes has been used to increase sensitivity. However, the prevailing view is that the overall quality of the reconstructed image is not improved by the overlaps in the projections. It is often stated in literatures that overlaps introduce ambiguous information, which can lead to nonuniqueness of solution for the inverse problem, and thus artifacts are introduced in the reconstructed image. On the other hand, contrary to the prevailing view, a recent study on slit-slat collimators shows that artifacts can be removed with the “help” of an extra complete nonoverlapped projection data set. In this paper, two types of artifact-free projection overlaps are defined in general, and the criteria for designing artifact-free multi-pinhole systems with overlaps are proposed. It is shown that once the criteria are satisfied, the solution of the inverse problem is unique, and thus no artifact is expected in the reconstructed image. Via extensive simulation study, various artifact-free overlapping multi-pinhole systems are designed and validated. It is shown that overlaps in the artifact-free systems can improve contrast-to-noise ratio (CNR). With a proper design, the CNR for an artifact-free overlapping system can be significantly higher than that for the corresponding nonoverlapping system. The improved image quality is also confirmed with noisy reconstructions. [ABSTRACT FROM AUTHOR]

In the past decade Kirkpatrick-Baez (KB) mirrors have been established as powerful focusing systems in hard X-ray microscopy applications. Here a ptychographic characterization of the KB focus in the dedicated nano-imaging setup GINIX (Göttingen Instrument for Nano-Imaging with X-rays) at the P10 coherence beamline of the PETRA III synchrotron at HASLYLAB/DESY, Germany, is reported. More specifically, it is shown how aberrations in the KB beam, caused by imperfections in the height profile of the focusing mirrors, can be eliminated using a pinhole as a spatial filter near the focal plane. A combination of different pinhole sizes and illumination conditions of the KB setup makes the prepared optical setup well suited not only for high-resolution ptychographic coherent X-ray diffractive imaging but also for moderate-resolution/large-field-of-view propagation imaging in the divergent KB beam. [ABSTRACT FROM AUTHOR]

Concentration solar arrays require greater solar tracking precision than conventional photovoltaic arrays. This paper presents a high precision lowcost dual axis sun tracking systembased on image processing for concentration photovoltaic applications. An imaging device is designed according to the principle of pinhole imaging, making sun rays to be received on a screen through pinhole and to be a sun spot. The location of the spot is used to adjust the orientation of the solar panel. A fuzzy logic controller is developed to achieve this goal. A prototype was built, and experimental results have proven the good performance of the proposed system and low error of tracking. The operation of this system is independent of geographical location, initial calibration, and periodical regulations. [ABSTRACT FROM AUTHOR]

Photography can be applied to life stories, making photographs a way to trace self in the world. In this case study, we explore Jade's autobiographical inquiry and investigate the visual expressions she created in an introductory photography course. Jade's story brings us into conversation about issues of childhood sexual abuse, and while her photographs do not recreate events, her compositions represent her ongoing self-reflection. Jade demonstrates through pinhole photography the transformative shifts possible in the postsecondary classroom: How students can move from storying to becoming; and how students find ways into experiences that move from silence and the deeply private to voicing in public forums through visual expressions. The complexity of her art and life writing remind us as educators that inquiry into the everyday lived experiences of students can help reform understandings of teaching and learning. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop fully 3D image reconstruction techniques for pinhole SPECT imaging with our Micro-SPECT system. Our studies involve in the derivation of projection operators, analysis of the sampling characteristics of pin-hole SPECT imaging in Radon space, development of effective geometric calibration method for system misalignment, and 3D image reconstruction development and implementation with quantitative degrading compensation for pinhole SPECT with both circular and helical scan. The performances of pinhole SPECT imaging were evaluated using computer simulations and experiments with the Ultra-Micro Hot-Spot phantom, Ultra-Micro Defrise phantom and small-animal imaging. The results from the computer simulations and phantom imaging experiments indicate that the statistically-based iterative algorithms with quantitative compensation provide overall image quality improvement, and the system resolution is significantly recovered for quantitative imaging. The helical pinhole SPECT improves the axial field-of-view (FOV) as compared with the standard pinhole SPECT with circular-orbit scan. The mouse bone imaging experiment shows that the helical pinhole SPECT imaging also provides decent high-resolution whole-body small animal imaging. In conclusion, we have successfully developed a set of valid fully 3D image reconstruction techniques for single-pinhole SPECT imaging. These techniques can be easily extended to multi-pinhole SPECT imaging. [ABSTRACT FROM AUTHOR]

A correct alignment of the tibial and femoral component is one of the most important factors determining favourable long-term results of a total knee arthroplasty (TKA). The accuracy provided by the use of the computer navigation systems has been widely described in the literature so that their use has become increasingly popular in recent years; however, unpredictable complications, such as displaced or stress femoral or tibial fractures, have been reported to occur a few weeks after the operation. We present a case of a stress tibial fracture that occurred after a TKA performed with the use of a computer navigation system. The stress fracture, which eventually healed without further complications, occurred at one of the pinhole sites used for the placement of the tibial trackers. [ABSTRACT FROM AUTHOR]

Chapter 3 of the book "Foundations and Trends in Computer Graphics and Vision," by P. Sturm and colleagues is presented. It explores the various computational camera models. It says that pinhole camera model assumes camera rays' passage to a single point called the optical center and that the relationship between image point position and camera ray direction is linear and can be expressed in a calibration matrix. It tackles other models including global and local, two-plane, and discrete models.

A technique is described for measuring the far-field radiation pattern, gain, and the transmissivity of each portion of an aperture of lightwave (optical) antennas. First, the compatibility of lightwave antennas to a system is mentioned. Then, the principles and setup for each measurement term are presented. A comparison with radio-wave antennas is also given. [ABSTRACT FROM AUTHOR]

This paper presents a modified Uniform Cramer-Rao bound (UCRB) for studying estimator spatial resolution and variance tradeoffs. We proposed to use a resolution constraint that is imposed on mean gradient vectors of achieved estimators and derived the minimum achievable variance for any estimator satisfies this resolution constraint. This approach partially overcomes the limitations of the former UCRB approach based on a bias gradient norm constraint. We applied this method in a feasibility study of using multiple pinhole apertures for small animal SPECT imaging applications. The SPECT system studied was based on an existing gamma camera. The achievable spatial resolution and variance tradeoffs for systems with different design parameters, such as number of pinholes and pinhole size, were studied. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of calibrating a pinhole camera from images of a surface of revolution. Camera calibration is the process of determining the intrinsic or internal parameters (i.e., aspect ratio, focal length, and principal point) of a camera, and it is important for both motion estimation and metric reconstruction of 3D models. In this paper, a novel and simple calibration technique is introduced, which is based on exploiting the symmetry of images of surfaces of revolution. Traditional techniques for camera calibration involve taking images of some precisely machined calibration pattern (such as a calibration grid). The use of surfaces of revolution, which are commonly found in daily life (e.g., bowls and vases), makes the process easier as a result of the reduced cost and increased accessibility of the calibration objects. In this paper, it is shown that two images of a surface of revolution will provide enough information for determining the aspect ratio, focal length, and principal point of a camera with fixed intrinsic parameters. The algorithms presented in this paper have been implemented and tested with both synthetic and real data. Experimental results show that the camera calibration method presented here is both practical and accurate. [ABSTRACT FROM AUTHOR]

Presents information on the use of pinhole cameras, while highlighting its application in Renaissance art. Reference to the development of pinhole cameras; Details on theorems of projective geometry; Hypotheses made regarding pinhole cameras.

At the turn of the sixteenth century Tycho Brahe and Johannes Kepler made single pinhole measurements of the solar diameter. Their accuracy was limited by diffraction (unknown to them) and the motion of the image on the screen. We discuss how two pinholes built on the same mask can be used to bypass all the problems inherent in the single pinhole approach. The distance at which the two images of the Sun are in contact is the only measurement needed, and the experimental accuracy is much better than measuring the diameter of a single moving image. We obtained 0.5% accuracy, sufficient to follow the angular variations of the solar diameter due to the motion of the Earth in its orbit. [ABSTRACT FROM AUTHOR]

Experiments in the context of fast ignition were carried out by focusing a 6-TW laser beam into a preformed plasma. An electron population with a quasi-temperature of 2 MeV was generated. The 2ω self-emission image reveals a self-focused plasma channel formation, whereas X-ray pinhole photography shows a postheating of the preformed plasma. [ABSTRACT FROM AUTHOR]

Details the construction of a pinhole camera or camera obscura. Designing of pinhole lens; Construction of pinholes; Experimental set-up.

A letter to the editor is presented in response to an article about eclipse pinhole images of a partially eclipsed sun, published in the November 2013 issue.

A correction to the article "Improving spinning disk confocal microscopy by preventing pinhole cross-talk for intravital imaging," by Togo Shimozawa and colleagues that was published in the February 26, 2013 issue is presented.