194 research outputs found
Speed up of Fresnel transforms for Digital holography using pre-computation
We show how the common Fresnel reconstruction
of digital holograms can be speeded up on ordinary computers by
precomputing the two chirp factors for a given detector array size
and then calling these values from memory during the
reconstruction. The speedup in time is shown for various
hologram sizes. We also run the same algorithm on a Nvidia GPU
using Matlab
Removing the twin image in digital holography by segmented filtering of in-focus twin image
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 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
A Practical Guide to Digital Holography and Generalized Sampling
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 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
Speed up of Fresnel transforms for Digital holography using pre-computation
We show how the common Fresnel reconstruction
of digital holograms can be speeded up on ordinary computers by
precomputing the two chirp factors for a given detector array size
and then calling these values from memory during the
reconstruction. The speedup in time is shown for various
hologram sizes. We also run the same algorithm on a Nvidia GPU
using Matlab
Reconstruction algorithms applied to in-line Gabor digital holographic microscopy
This paper investigates the application of Fresnel based numerical algorithms for the reconstruction of
Gabor in-line holograms. We focus on the two most widely used Fresnel approximation algorithms,
the direct method and the angular spectrum method. Both algorithms involve calculating a Fresnel integral,
but they accomplish it in fundamentally different ways. The algorithms perform differently for different
physical parameters such as distance, CCD pixel size, and so on. We investigate the constraints for
the algorithms when applied to in-line Gabor digital holographic microscopy. We show why the algorithms
fail in some instances and how to alter them in order to obtain useful images of the microscopic
specimen. We verify the altered algorithms using an optically captured digital hologram
Multispectral lensless digital holographic microscope: imaging MCF-7 and MDA-MB-231 cancer cell cultures
Digital holography is the process where an object’s phase and amplitude information is retrieved from intensity images
obtained using a digital camera (e.g. CCD or CMOS sensor). In-line digital holographic techniques offer full use of the
recording device’s sampling bandwidth, unlike off-axis holography where object information is not modulated onto
carrier fringes. Reconstructed images are obscured by the linear superposition of the unwanted, out of focus, twin
images. In addition to this, speckle noise degrades overall quality of the reconstructed images. The speckle effect is a
phenomenon of laser sources used in digital holographic systems. Minimizing the effects due to speckle noise, removal
of the twin image and using the full sampling bandwidth of the capture device aids overall reconstructed image quality.
Such improvements applied to digital holography can benefit applications such as holographic microscopy where the
reconstructed images are obscured with twin image information. Overcoming such problems allows greater flexibility in
current image processing techniques, which can be applied to segmenting biological cells (e.g. MCF-7 and MDA-MB-
231) to determine their overall cell density and viability. This could potentially be used to distinguish between apoptotic
and necrotic cells in large scale mammalian cell processes, currently the system of choice, within the biopharmaceutical
industry
Resolution limits in practical digital holographic systems
We examine some fundamental theoretical limits on the ability
of practical digital holography DH systems to resolve detail in an
image. Unlike conventional diffraction-limited imaging systems, where a
projected image of the limiting aperture is used to define the system
performance, there are at least three major effects that determine the
performance of a DH system: i The spacing between adjacent pixels on
the CCD, ii an averaging effect introduced by the finite size of these
pixels, and iii the finite extent of the camera face itself. Using a theoretical
model, we define a single expression that accounts for all these
physical effects. With this model, we explore several different DH recording
techniques: off-axis and inline, considering both the dc terms, as well
as the real and twin images that are features of the holographic recording
process. Our analysis shows that the imaging operation is shift variant
and we demonstrate this using a simple example. We examine how
our theoretical model can be used to optimize CCD design for lensless
DH capture. We present a series of experimental results to confirm the
validity of our theoretical model, demonstrating recovery of super-
Nyquist frequencies for the first time
Resolution limits in practical digital holographic systems
We examine some fundamental theoretical limits on the ability
of practical digital holography DH systems to resolve detail in an
image. Unlike conventional diffraction-limited imaging systems, where a
projected image of the limiting aperture is used to define the system
performance, there are at least three major effects that determine the
performance of a DH system: i The spacing between adjacent pixels on
the CCD, ii an averaging effect introduced by the finite size of these
pixels, and iii the finite extent of the camera face itself. Using a theoretical
model, we define a single expression that accounts for all these
physical effects. With this model, we explore several different DH recording
techniques: off-axis and inline, considering both the dc terms, as well
as the real and twin images that are features of the holographic recording
process. Our analysis shows that the imaging operation is shift variant
and we demonstrate this using a simple example. We examine how
our theoretical model can be used to optimize CCD design for lensless
DH capture. We present a series of experimental results to confirm the
validity of our theoretical model, demonstrating recovery of super-
Nyquist frequencies for the first time
Pseudomonas aeruginosa AES-1 exhibits increased virulence gene expression during chronic infection of cystic fibrosis lung
Pseudomonas aeruginosa, the leading cause of morbidity and mortality in people with cystic fibrosis (CF), adapts for survival in the CF lung through both mutation and gene expression changes. Frequent clonal strains such as the Australian Epidemic Strain-1 (AES-1), have increased ability to establish infection in the CF lung and to superimpose and replace infrequent clonal strains. Little is known about the factors underpinning these properties. Analysis has been hampered by lack of expression array templates containing CF-strain specific genes. We sequenced the genome of an acute infection AES-1 isolate from a CF infant (AES-1R) and constructed a non-redundant micro-array (PANarray) comprising AES-1R and seven other sequenced P. aeruginosa genomes. The unclosed AES-1R genome comprised 6.254Mbp and contained 6957 putative genes, including 338 not found in the other seven genomes. The PANarray contained 12,543 gene probe spots; comprising 12,147 P. aeruginosa gene probes, 326 quality-control probes and 70 probes for non-P. aeruginosa genes, including phage and plant genes. We grew AES-1R and its isogenic pair AES-1M, taken from the same patient 10.5 years later and not eradicated in the intervening period, in our validated artificial sputum medium (ASMDM) and used the PANarray to compare gene expression of both in duplicate. 675 genes were differentially expressed between the isogenic pairs, including upregulation of alginate, biofilm, persistence genes and virulence-related genes such as dihydroorotase, uridylate kinase and cardiolipin synthase, in AES-1M. Non-PAO1 genes upregulated in AES-1M included pathogenesis-related (PAGI-5) genes present in strains PACS2 and PA7, and numerous phage genes. Elucidation of these genes' roles could lead to targeted treatment strategies for chronically infected CF patients. © 2011 Naughton et al
Systematic errors of an optical encryption system due to the discrete values of a spatial light modulator
An optical implementation of the amplitude encoded double
random phase encryption/decryption technique is implemented, and
both numerical and experimental results are presented. In particular, we
examine the effect of quantization in the decryption process due to the
discrete values and quantized levels, which a spatial light modulator
(SLM) can physically display. To do this, we characterize a transmissive
SLM using Jones matrices and then map a complex image to the physically
achievable levels of the SLM using the pseudorandom encoding
technique. We present both numerical and experimental results that
quantify the performance of the system
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