Thomas J. Naughton

Publications of Thomas J. Naughton

• Multi-heuristic dynamic task allocation using genetic algorithms in a heterogeneous distributed system.

  Authors: Andrew J Page, Thomas M Keane, Thomas J Naughton

  Journal of parallel and distributed computing. 07/2010; 70(7):758-766.

  We present a multi-heuristic evolutionary task allocation algorithm to dynamically map tasks to processors in a heterogeneous distributed system. It utilizes a genetic algorithm, combined with eightWe present a multi-heuristic evolutionary task allocation algorithm to dynamically map tasks to processors in a heterogeneous distributed system. It utilizes a genetic algorithm, combined with eight common heuristics, in an effort to minimize the total execution time. It operates on batches of unmapped tasks and can preemptively remap tasks to processors. The algorithm has been implemented on a Java distributed system and evaluated with a set of six problems from the areas of bioinformatics, biomedical engineering, computer science and cryptography. Experiments using up to 150 heterogeneous processors show that the algorithm achieves better efficiency than other state-of-the-art heuristic algorithms.

• Statistical investigation of the double random phase encoding technique.

  Authors: David S Monaghan, Unnikrishnan Gopinathan, Guohai Situ, Thomas J Naughton, John T Sheridan

  Journal of the Optical Society of America. A, Optics, image science, and vision. 10/2009; 26(9):2033-42.

  The amplitude-encoding case of the double random phase encoding technique is examined by defining a cost function as a metric to compare an attempted decryption against the corresponding originalThe amplitude-encoding case of the double random phase encoding technique is examined by defining a cost function as a metric to compare an attempted decryption against the corresponding original input image. For the case when a cipher-text pair has been obtained and the correct decryption key is unknown, an iterative attack technique can be employed to ascertain the key. During such an attack the noise in the output field for an attempted decryption can be used as a measure of a possible decryption key's correctness. For relatively small systems, i.e., systems involving fewer than 5x5 pixels, the output decryption of every possible key can be examined to evaluate the distribution of the keys in key space in relation to their relative performance when carrying out decryption. However, in order to do this for large systems, checking every single key is currently impractical. One metric used to quantify the correctness of a decryption key is the normalized root mean squared (NRMS) error. The NRMS is a measure of the cumulative intensity difference between the input and decrypted images. We identify a core term in the NRMS, which we refer to as the difference parameter, d. Expressions for the expected value (or mean) and variance of d are derived in terms of the mean and variance of the output field noise, which is shown to be circular Gaussian. These expressions assume a large sample set (number of pixels and keys). We show that as we increase the number of samples used, the decryption error obeys the statistically predicted characteristic values. Finally, we corroborate previously reported simulations in the literature by using the statistically derived expressions.

• Twin-image removal for in-line digital holography

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, Thomas J. Naughton

  Photonics Ireland, Cork, Ireland; 09/2009

• Introducing secure modes of operation for optical encryption.

  Authors: Thomas J Naughton, Bryan M Hennelly, Tom Dowling

  Journal of the Optical Society of America. A, Optics, image science, and vision. 11/2008; 25(10):2608-17.

  We analyze optical encryption systems using the techniques of conventional cryptography. All conventional block encryption algorithms are vulnerable to attack, and often they employ secure modes ofWe analyze optical encryption systems using the techniques of conventional cryptography. All conventional block encryption algorithms are vulnerable to attack, and often they employ secure modes of operation as one way to increase security. We introduce the concept of conventional secure modes to optical encryption and analyze the results in the context of known conventional and optical attacks. We consider only the optical system "double random phase encoding," which forms the basis for a large number of optical encryption, watermarking, and multiplexing systems. We consider all attacks proposed to date in one particular scenario. We analyze only the mathematical algorithms themselves and do not consider the additional security that arises from employing these algorithms in physical optical systems.

• Parallel approaches to reconstruction and noise reduction in digital holography

  Authors: Lukas Ahrenberg, Conor P. Mc Elhinney, Bryan M. Hennelly, Thomas J. Naughton

  ICO Topical Meeting on Optoinformatics / Information Photonics, St. Petersburg, Russia; 09/2008

  We discuss how numerical algorithms for digital holography (DH) may be improved by execution on parallel architecture. In particular we consider implementation on graphics hardware. As an example weWe discuss how numerical algorithms for digital holography (DH) may be improved by execution on parallel architecture. In particular we consider implementation on graphics hardware. As an example we present an algorithm for twin-image removal.

• Extended focused imaging for digital holograms of macroscopic three-dimensional objects.

  Authors: Conor P McElhinney, Bryan M Hennelly, Thomas J Naughton

  Applied optics. 08/2008; 47(19):D71-9.

  When a digital hologram is reconstructed, only points located at the reconstruction distance are in focus. We have developed a novel technique for creating an in-focus image of the macroscopicWhen a digital hologram is reconstructed, only points located at the reconstruction distance are in focus. We have developed a novel technique for creating an in-focus image of the macroscopic objects encoded in a digital hologram. This extended focused image is created by combining numerical reconstructions with depth information extracted by using our depth-from-focus algorithm. To our knowledge, this is the first technique that creates extended focused images of digital holograms encoding macroscopic objects. We present results for digital holograms containing low- and high-contrast macroscopic objects.

• Removing the twin image in digital holography by segmented filtering of in-focus twin image

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, Lukas Ahrenberg, Thomas J. Naughton

  Proceedings of SPIE, San Diego, CA, USA; 08/2008

  We propose and investigate a new digital method for the reduction of twin-image noise from digital Fresnel holograms. For the case of in-line Fresnel holography the unwanted twin is present as aWe propose and investigate a new digital method for the reduction of twin-image noise from digital Fresnel holograms. For the case of in-line Fresnel holography the unwanted twin is present as a highly corruptive noise when the object image is numerically reconstructed. We propose to firstly reconstruct the unwanted twin-image when it is in-focus and in this plane we calculate a segmentation mask that borders this in focus image. The twin-image is then segmented and removed by simple spatial filtering. The resulting digital wavefield is the inverse propagated to the desired object image plane. The image is free of the twin-image resulting in improved quality reconstructions. We demonstrate the segmentation and removal of the unwanted twin-image from in-line digital holograms containing real-world macroscopic objects. We offer suggestions for its rapid computational implementation.

• Segmentation of three-dimensional scenes encoded in digital holograms

  Authors: Karen M. Molony, Conor P. Mc Elhinney, Bryan M. Hennelly, Thomas J. Naughton

  Proceedings of SPIE, San Diego, CA, USA; 08/2008

  This study investigates segmentation algorithms applicable to digital holography. An assessment of image seg- mentation tecnhniques applied to intensity images of reconstructions of digital hologramsThis study investigates segmentation algorithms applicable to digital holography. An assessment of image seg- mentation tecnhniques applied to intensity images of reconstructions of digital holograms is provided. Digital holography differs from conventional imaging as 3D information is encoded. This allows depth information to be exploited so that focusing of 3D objects, or part there of, at different depths can be achieved. In this paper, segmentation of features is attained in microscopic and macroscopic scenes. We investigate a number of recently proposed segmentation techniques including (i) depth from focus, (ii) active contours and (iii) hierarchical thresholding. The influence of noise reduction on the segmentation capabilities of each of the techniques on these scenes is demonstrated. For the macrocsopic scenes, each technique is applied before and after speckle noise reduction is performed using a wavelet based approach. The performance of the segmen- tation techniques on the intensity information obtained from reconstructed holograms of microscopic scenes is also investigated before and after twin-image reduction has been applied. A comparison of the techniques and their performances in these circumstances is provided.

• A practical guide to digital holography and generalized sampling

  Authors: Damien P. Kelly, Bryan M. Hennelly, Conor P. Mc Elhinney, Thomas J. Naughton

  Proceedings of SPIE, San Diego, CA, USA; 08/2008

  The theorems of Nyquist, Shannon and Whittaker have long held true for sampling optical signals. They showed that a signal (with finite bandwidth) should be sampled at a rate at least as fast asThe theorems of Nyquist, Shannon and Whittaker have long held true for sampling optical signals. They showed that a signal (with finite bandwidth) should be sampled at a rate at least as fast as twice the maximum spatial frequency of the signal. They proceeded to show how the continuous signal could be reconstructed perfectly from its well sampled counterpart by convolving a Sinc function with the sampled signal. Recent years have seen the emergence of a new generalized sampling theorem of which Nyquist Shannon is a special case. This new theorem suggests that it is possible to sample and reconstruct certain signals at rates much slower than those predicted by Nyquist-Shannon. One application in which this new theorem is of considerable interest is Fresnel Holography. A number of papers have recently suggested that the sampling rate for the digital recording of Fresnel holograms can be relaxed considerably. This may allow the positioning of the object closer to the camera allowing for a greater numerical aperture and thus an improved range of 3D perspective. In this paper we: (i) Review generalized sampling for Fresnel propagated signals, (ii) Investigate the effect of the twin image, always present in recording, on the generalized sampling theorem and (iii) Discuss the effect of finite pixel size for the first time.

• Role of phase key in the double random phase encoding technique: an error analysis.

  Authors: David S Monaghan, Guohai Situ, Unnikrishnan Gopinathan, Thomas J Naughton, John T Sheridan

  Applied optics. 07/2008; 47(21):3808-16.

  We perform a numerical analysis of the double random phase encryption-decryption technique to determine how, in the case of both amplitude and phase encoding, the two decryption keys (the image- andWe perform a numerical analysis of the double random phase encryption-decryption technique to determine how, in the case of both amplitude and phase encoding, the two decryption keys (the image- and Fourier-plane keys) affect the output gray-scale image when they are in error. We perform perfect encryption and imperfect decryption. We introduce errors into the decrypting keys that correspond to the use of random distributions of incorrect pixel values. We quantify the effects that increasing amounts of error in the image-plane key, the Fourier-plane key, and both keys simultaneously have on the decrypted image. Quantization effects are also examined.

• Twin-image reduction in inline digital holography using an object segmentation heuristic (Invited paper)

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, Thomas J. Naughton

  Euro-American Workshop in Information Optics, Annecy, France; 06/2008

  We present a digital image processing heuristic for the removal of the twin-image in inline digital holograms. Typically, the unwanted twin manifests itself as visible corruptive noise in theWe present a digital image processing heuristic for the removal of the twin-image in inline digital holograms. Typically, the unwanted twin manifests itself as visible corruptive noise in the reconstruction plane. We reconstruct the unwanted twin-image at its in-focus plane and suppress it by first finding the boundary of the object, and then removing the optical energy within this boundary. In this plane, the wanted twin-image optical energy is largely dispersed outside this boundary and so it is retained. The heuristic's effectiveness is demonstrated using a digital hologram of a real-world object.

• Segmentation of macroscopic object digital holographic reconstructions using extracted depth information

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, John B. McDonald, Thomas J. Naughton

  Proceedings of SPIE, Strasbourg, France; 04/2008

  The nature of digital hologram’s allows for the implementation of segmentation process’ using volumes of recon- structions as their input, where each reconstruction in the volume is a reconstructionThe nature of digital hologram’s allows for the implementation of segmentation process’ using volumes of recon- structions as their input, where each reconstruction in the volume is a reconstruction at a different focal plane. Our segmentation technique utilizes extracted focus and shape information. In the case of digital hologram’s encoding macroscopic objects, this information is generally obtained using data extraction algorithms applied to a volume of reconstructions. We have developed a three stage segmentation algorithm for macroscopic objects encoded in digital hologram’s. This algorithm uses a depth-from-focus technique applied to a set of numerical reconstructions from a single perspective of the digital hologram to extract focus and shape information in the form of a depth map and a maximum focus map. First we estimate the degree of focus at each coordinate. We then calculate a depth map of the scene and segment all object coordinates from background coordinates in the second stage. Finally in the third stage, we perform the segmentation of a digital hologram’s reconstruction into independent objects or object regions. A segmentation image is created through applying histogram and image processing algorithms to the depth map. We present results of applying our technique to digital hologram’s containing single and multiple macroscopic objects.

• Focused image creation approaches for macroscopic objects encoded in digital holograms

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, Thomas J. Naughton

  Proceedings of SPIE, Strasbourg, France; 04/2008

  When a digital hologram is reconstructed only points on objects within the depth of focus at the reconstruction distance are in focus. For complex scenes, scenes containingmultiple objects ormultipleWhen a digital hologram is reconstructed only points on objects within the depth of focus at the reconstruction distance are in focus. For complex scenes, scenes containingmultiple objects ormultiple object features located at different depths, this can lead to a reconstruction with large blurred regions. Using a depth-from-focus algorithm we have developed an approach to extract an objects depth information in the form of a depth map from volumes of reconstructions, where each reconstruction in the volume is a reconstruction at a different focal plane. By combining the depth map with the volume of reconstructions used to calculate the depth map we can create an image, an extended focus image, where the full scene is in focus. To our knowledge, this is the first technique which creates extended focused images of digital holograms encoding macroscopic objects. We present results for digital holograms containing low and high contrast macroscopic objects.

• Low memory distributed reconstruction of large digital holograms.

  Authors: Andrew J Page, Lukas Ahrenberg, Thomas J Naughton

  Optics express. 03/2008; 16(3):1990-5.

  We present a parallel implementation of the Fresnel transform suitable for reconstructing large digital holograms. Our method has a small memory footprint and utilizes the spare resources of aWe present a parallel implementation of the Fresnel transform suitable for reconstructing large digital holograms. Our method has a small memory footprint and utilizes the spare resources of a distributed set of desktop PCs connected by a network. We show how we parallelize the Fresnel transform and discuss how it is constrained by computer and communication resources. Finally, we demonstrate how a 4.3 gigapixel digital hologram can be reconstructed and how the efficiency of the method changes for different memory and processor configurations.

• Focused image creation algorithms for digital holograms of macroscopic three-dimensional objects

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, Thomas J. Naughton

  Digital Holography and Three-Dimensional Imaging, St. Petersburg, Florida, USA; 03/2008

  When a digital hologram is reconstructed only points located at the reconstruction distance are in-focus. We have developed a novel technique for creating an in-focus image of the macroscopic objectsWhen a digital hologram is reconstructed only points located at the reconstruction distance are in-focus. We have developed a novel technique for creating an in-focus image of the macroscopic objects encoded in a digital hologram.

• Noninterferometric phase retrieval using a fractional Fourier system.

  Authors: Unnikrishnan Gopinathan, Guohai Situ, Thomas J Naughton, John T Sheridan

  Journal of the Optical Society of America. A, Optics, image science, and vision. 02/2008; 25(1):108-15.

  The signal extraction method based on intensity measurements in two close fractional Fourier domains is examined by using the phase space formalism. The fractional order separation has a lower boundThe signal extraction method based on intensity measurements in two close fractional Fourier domains is examined by using the phase space formalism. The fractional order separation has a lower bound and an upper bound that depend on the signal at hand and the noise in the optical system used for measurement. On the basis of a theoretical analysis, it is shown that for a given optical system a judicious choice of fractional order separation requires some a priori knowledge of the signal bandwidth. We also present some experimental results in support of the analysis.

• A projection system for real world three-dimensional objects using spatial light modulators

  Authors: Unnikrishnan Gopinathan, David S. Monaghan, Bryan M. Hennelly, Conor P. Mc Elhinney, Damien P. Kelly, John B. McDonald, Thomas J. Naughton, John T. Sheridan

  Journal of Display Technology. 01/2008; 4(2):254-261.

• Extraction of three-dimensional information from reconstructions of in-line digital holograms

  Authors: Conor P. Mc Elhinney, Bryan M. Hennelly, Bahram Javidi, Thomas J. Naughton

  01/2008;

  ISBN: 0387793348

• Key-space analysis of double random phase encryption technique.

  Authors: David S Monaghan, Unnikrishnan Gopinathan, Thomas J Naughton, John T Sheridan

  Applied optics. 10/2007; 46(26):6641-7.

  We perform a numerical analysis on the double random phase encryption/decryption technique. The key-space of an encryption technique is the set of possible keys that can be used to encode data usingWe perform a numerical analysis on the double random phase encryption/decryption technique. The key-space of an encryption technique is the set of possible keys that can be used to encode data using that technique. In the case of a strong encryption scheme, many keys must be tried in any brute-force attack on that technique. Traditionally, designers of optical image encryption systems demonstrate only how a small number of arbitrary keys cannot decrypt a chosen encrypted image in their system. However, this type of demonstration does not discuss the properties of the key-space nor refute the feasibility of an efficient brute-force attack. To clarify these issues we present a key-space analysis of the technique. For a range of problem instances we plot the distribution of decryption errors in the key-space indicating the lack of feasibility of a simple brute-force attack.

• Resistance of the double random phase encryption against various attacks.

  Authors: Yann Frauel, Albertina Castro, Thomas J Naughton, Bahram Javidi

  Optics express. 09/2007; 15(16):10253-65.

  Several attacks are proposed against the double random phase encryption scheme. These attacks are demonstrated on computer-generated ciphered images. The scheme is shown to be resistant against bruteSeveral attacks are proposed against the double random phase encryption scheme. These attacks are demonstrated on computer-generated ciphered images. The scheme is shown to be resistant against brute force attacks but susceptible to chosen and known plaintext attacks. In particular, we describe a technique to recover the exact keys with only two known plain images. We compare this technique to other attacks proposed in the literature.