118 research outputs found
Demonstration of 136 dB dynamic range capability for a simultaneous dual optical band CAOS camera
For the first time, proposed and demonstrated is a simultaneous dual optical band coded access optical sensor (CAOS) camera design suited for extreme contrast multispectral bright target scenarios. Deploying a digital micromirror devices (DMDs)-based time-frequency agile pixels CAOS-mode within a two point detector spatially and spectrally isolating framework, this imager simultaneously and independently detects pixel selective image information for two different broad spectral bands that further undergo independent spectral image data extraction via finer-tuned wavelength filtering using all-optical or CAOS-mode electronic filters. A proof-of-concept visible-near infrared band CAOS imager is successfully demonstrated using a target scene containing LEDs and engaging narrowband optical filters. In addition, using the CAOS-mode, demonstrated is the RF domain simultaneous color content monitoring of a white light LED image pixel. Also proposed is the use of a higher bit count analog-to-digital converter (ADC) with both range and sampling duration parameter control along with a larger data set electronic DSP to extract higher DSP gain and realize additional noise suppression. Using a 16-bit ADC and 2,097,152 point fast Fourier transform (FFT) digital signal processing (DSP) for a 633 nm laser engaged test target scene that is subject to nearly 7 decades (107) of gradual optical attenuation, the experimental camera demonstrates an agile pixel extreme dynamic range of 136 dB, which is a 56 dB improvement over the previous CAOS-imaging demonstrations
Enhancement of CASSI by a zero-order image employing a single detector
Coded aperture snapshot spectral imaging (CASSI) makes it possible to recover
3D hyperspectral data from a single 2D image. However, the reconstruction
problem is severely underdetermined and efforts to improve the compression
ratio typically make the imaging system more complex and cause a significant
loss of incoming light intensity. In this paper, we propose a novel approach to
CASSI which enables capturing both spectrally sheared and integrated image of a
scene with a single camera. We performed hyperspectral imaging of three
different testing scenes in the spectral range of 500-900 nm. We demonstrate
the prominent effect of using the non-diffracted image on the reconstruction of
data from our camera. The use of the spectrally integrated image improves the
reconstruction quality and we observed an approx. fivefold reduction in
reconstruction time
Source Modulated Multiplexed Hyperspectral Imaging: Theory, Hardware and Application
The design, analysis and application of a multiplexing hyperspectral imager is presented.
The hyperspectral imager consists of a broadband digital light projector that uses a digital
micromirror array as the optical engine to project light patterns onto a sample object. A
single point spectrometer measures light that is reflected from the sample. Multiplexing
patterns encode the spectral response from the sample, where each spectrum taken is the
sum of a set of spectral responses from a number of pixels. Decoding in software recovers
the spectral response of each pixel. A technique, which we call complement encoding, is
introduced for the removal of background light effects. Complement encoding requires
the use of multiplexing matrices with positive and negative entries.
The theory of multiplexing using the Hadamard matrices is developed. Results from
prior art are incorporated into a singular notational system under which the different
Hadamard matrices are compared with each other and with acquisition of data without
multiplexing (pointwise acquisition). The link between Hadamard matrices with strongly
regular graphs is extended to incorporate all three types of Hadamard matrices. The effect
of the number of measurements used in compressed sensing on measurement precision is
derived by inference using results concerning the eigenvalues of large random matrices.
The literature shows that more measurements increases accuracy of reconstruction. In
contrast we find that more measurement reduces precision, so there is a tradeoff between
precision and accuracy. The effect of error in the reference on the Wilcoxon statistic is
derived. Reference error reduces the estimate of the Wilcoxon, however given an estimate
of theWilcoxon and the proportion of error in the reference, we show thatWilcoxon
without error can be estimated.
Imaging of simple objects and signal to noise ratio (SNR) experiments are used to
test the hyperspectral imager. The simple objects allow us to see that the imager produces
sensible spectra. The experiments involve looking at the SNR itself and the SNR boost,
that is ratio of the SNR from multiplexing to the SNR from pointwise acquisition. The
SNR boost varies dramatically across the spectral domain from 3 to the theoretical maximum
of 16. The range of boost values is due to the relative Poisson to additive noise
variance changing over the spectral domain, an effect that is due to the light bulb output
and detector sensitivity not being flat over the spectral domain. It is shown that the SNR boost is least where the SNR is high and is greatest where the SNR is least, so the boost
is provided where it is needed most. The varying SNR boost is interpreted as a preferential
boost, that is useful when the dominant noise source is indeterminate or varying.
Compressed sensing precision is compared with the accuracy in reconstruction and with
the precision in Hadamard multiplexing. A tradeoff is observed between accuracy and
precision as the number of measurements increases. Generally Hadamard multiplexing is
found to be superior to compressed sensing, but compressed sensing is considered suitable
when shortened data acquisition time is important and poorer data quality is acceptable.
To further show the use of the hyperspectral imager, volumetric mapping and analysis
of beef m. longissimus dorsi are performed. Hyperspectral images are taken of successive
slices down the length of the muscle. Classification of the spectra according to visible
content as lean or nonlean is trialled, resulting in a Wilcoxon value greater than 0.95,
indicating very strong classification power. Analysis of the variation in the spectra down
the length of the muscles is performed using variography. The variation in spectra of a
muscle is small but increases with distance, and there is a periodic effect possibly due to
water seepage from where connective tissue is removed from the meat while cutting from
the carcass. The spectra are compared to parameters concerning the rate and value of
meat bloom (change of colour post slicing), pH and tenderometry reading (shear force).
Mixed results for prediction of blooming parameters are obtained, pH shows strong correlation (R² = 0.797) with the spectral band 598-949 nm despite the narrow range of
pH readings obtained. A likewise narrow range of tenderometry readings resulted in no
useful correlation with the spectra.
Overall the spatial multiplexed imaging with a DMA based light modulation is successful.
The theoretical analysis of multiplexing gives a general description of the system
performance, particularly for multiplexing with the Hadamard matrices. Experiments
show that the Hadamard multiplexing technique improves the SNR of spectra taken over
pointwise imaging. Aspects of the theoretical analysis are demonstrated. Hyperspectral
images are acquired and analysed that demonstrate that the spectra acquired are sensible
and useful
Smart optical imaging systems with automated electronics
In this dissertation, proposed and demonstrated are several novel smart electronically automated optical designs to efficiently solve existing real-world problems in the field of shape sensing and imaging. First half of the thesis proposes shape sensing techniques that use an Electronically Controlled Variable Focus Lens (ECVFL) within a smart optical design suitable for a wide range of applications including shape sensing and projection displays. The second part of this dissertation involves the use of the Digital Micromirror Device (DMD) deployed within several smart optical designs including an embedded laser beam profiler and a new camera idea which is inspired by the Telecommunication science field. Specifically, proposed and demonstrated is the design and implementation of the novel imaging device called Coded Access Optical Sensor (CAOS) where CAOS is able of operating with different application dependent working modes. Experimentally and successfully demonstrated for the first time are its use for coherent light laser imaging as well as for incoherent imaging of a high dynamic range white light scenario. It is also shown how its design can be further extended for multispectral and hyperspectral imaging applications
Optical imaging for breast cancer prescreening
Breast cancer prescreening is carried out prior to the gold standard screening using X-ray mammography and/or ultrasound. Prescreening is typically carried out using clinical breast examination (CBE) or self-breast examinations (SBEs). Since CBE and SBE have high false-positive rates, there is a need for a low-cost, noninvasive, non-radiative, and portable imaging modality that can be used as a prescreening tool to complement CBE/SBE. This review focuses on the various hand-held optical imaging devices that have been developed and applied toward early-stage breast cancer detection or as a prescreening tool via phantom, in vivo, and breast cancer imaging studies. Apart from the various optical devices developed by different research groups, a wide-field fiber-free near-infrared optical scanner has been developed for transillumination-based breast imaging in our Optical Imaging Laboratory. Preliminary in vivo studies on normal breast tissues, with absorption-contrasted targets placed in the intramammary fold, detected targets as deep as 8.8 cm. Future work involves in vivo imaging studies on breast cancer subjects and comparison with the gold standard X-ray mammography approach
Design and simulation of compressive snapshot multispectral imaging system
Compressive Snapshot Spectral Imaging combines compressive sensing and snapshot spectral imaging (SSI) for restoring the image of the scene in both spatial and spectral contexts by using only a fewer number of sampling measurements of the captured image under the sparsity assumption. SSI is often realised through a coded aperture mask together with a single dispersive element as the main spatial modulator to implement compressive sampling. As one of the representative frameworks in this field, Coded Aperture Snapshot Spectral Imagers (CASSI) has prototyped a low-cost, compact platform to achieve compressive snapshot spectral imaging in the recent decade. Active research in the field includes advanced de-compressive recovery algorithms and also the employment of more sophisticated optical hardware for the design of more robust SSI system. This research addresses more of the latter direction and it focuses on how the CASSI framework can be further developed for various applications such as magnetic resonance imaging for medical diagnosis, enhancement of radar imaging system, facial expression detection and recognition, digital signal processing with sparse structure in terms of image denoising, image super-resolution and image classification. This thesis presents a summary of the research conducted over the past 4 years about the basic property of the CASSI system, which leads to the development of the spectral tuneable SSI design proposed during the course of the PhD study. This new design utilises a Dual-Prism assembly to embed the capability of wavelength-tuning without physically changing its optical elements. This Dual-Prism CASSI (DP-CASSI) adapts to dynamic environments far better than all the CASSI types of imagers published in the open domain which only function for a fixed set of wavelengths. This piece of work has been vii accepted by journal papers for publication. Other contributions of this research has been the enhancement of the Single-Prism (SP-CASSI) architecture and to produce a snapshot system with less aberration and better image quality than that published in the open domain. Moreover, the thesis also provides information about optical design of four different types of CASSI with slightly in-depth analysis about their optical system constructions, optical evaluations of system structure and their dispersive capabilities as the background of this research. Then a more detailed description of the proposed DP-CASSI with respected to its design and performance evaluation particularly its dispersion characteristics and the effects of system resolutions, are given. System verifications were conducted through ray-tracing simulation in three-dimension visualisation environments and the spectral characteristics of the targets are compared with that of the ground truth. The spectral tuning of the proposed DP-CASSI is achieved by adjusting the air gap displacement of dual-prism assembly. Typical spectral shifts of about 5 nm at 450 mm and 10 nm at 650 nm wavelength have been achieved in the present design when the air gap of the dual-prism is changed from 3.44 mm to 5.04 mm. The thesis summaries the optical designs, the performance and the pros and cons of the DP-CASSI syste
Bio-Inspired Multi-Spectral and Polarization Imaging Sensors for Image-Guided Surgery
Image-guided surgery (IGS) can enhance cancer treatment by decreasing, and ideally eliminating, positive tumor margins and iatrogenic damage to healthy tissue. Current state-of-the-art near-infrared fluorescence imaging systems are bulky, costly, lack sensitivity under surgical illumination, and lack co-registration accuracy between multimodal images. As a result, an overwhelming majority of physicians still rely on their unaided eyes and palpation as the primary sensing modalities to distinguish cancerous from healthy tissue. In my thesis, I have addressed these challenges in IGC by mimicking the visual systems of several animals to construct low power, compact and highly sensitive multi-spectral and color-polarization sensors. I have realized single-chip multi-spectral imagers with 1000-fold higher sensitivity and 7-fold better spatial co-registration accuracy compared to clinical imaging systems in current use by monolithically integrating spectral tapetal and polarization filters with an array of vertically stacked photodetectors. These imaging sensors yield the unique capabilities of imaging simultaneously color, polarization, and multiple fluorophores for near-infrared fluorescence imaging. Preclinical and clinical data demonstrate seamless integration of this technologies in the surgical work flow while providing surgeons with real-time information on the location of cancerous tissue and sentinel lymph nodes, respectively. Due to its low cost, the bio-inspired sensors will provide resource-limited hospitals with much-needed technology to enable more accurate value-based health care
Snapshot hyperspectral imaging : near-infrared image replicating imaging spectrometer and achromatisation of Wollaston prisms
Conventional hyperspectral imaging (HSI) techniques are time-sequential and rely on
temporal scanning to capture hyperspectral images. This temporal constraint can limit
the application of HSI to static scenes and platforms, where transient and dynamic
events are not expected during data capture.
The Near-Infrared Image Replicating Imaging Spectrometer (N-IRIS) sensor described
in this thesis enables snapshot HSI in the short-wave infrared (SWIR), without the
requirement for scanning and operates without rejection in polarised light. It operates in
eight wavebands from 1.1μm to 1.7μm with a 2.0° diagonal field-of-view. N-IRIS
produces spectral images directly, without the need for prior topographic or image
reconstruction. Additional benefits include compactness, robustness, static operation,
lower processing overheads, higher signal-to-noise ratio and higher optical throughput
with respect to other HSI snapshot sensors generally.
This thesis covers the IRIS design process from theoretical concepts to quantitative
modelling, culminating in the N-IRIS prototype designed for SWIR imaging. This effort
formed the logical step in advancing from peer efforts, which focussed upon the visible
wavelengths. After acceptance testing to verify optical parameters, empirical laboratory
trials were carried out. This testing focussed on discriminating between common
materials within a controlled environment as proof-of-concept. Significance tests were
used to provide an initial test of N-IRIS capability in distinguishing materials with
respect to using a conventional SWIR broadband sensor.
Motivated by the design and assembly of a cost-effective visible IRIS, an innovative
solution was developed for the problem of chromatic variation in the splitting angle
(CVSA) of Wollaston prisms. CVSA introduces spectral blurring of images. Analytical
theory is presented and is illustrated with an example N-IRIS application where a sixfold
reduction in dispersion is achieved for wavelengths in the region 400nm to 1.7μm,
although the principle is applicable from ultraviolet to thermal-IR wavelengths.
Experimental proof of concept is demonstrated and the spectral smearing of an
achromatised N-IRIS is shown to be reduced by an order of magnitude. These
achromatised prisms can provide benefits to areas beyond hyperspectral imaging, such
as microscopy, laser pulse control and spectrometry
- …