We demonstrate a technique for restoring imagery using a computational imaging camera with a phase mask that produces a blurred, space-variant point spread function (PSF). To recover arbitrary images, we first calibrate the computational imaging process utilizing Karheunen-Loeve Decomposition, where the PSFs are sampled across the field of view of the camera system. These PSFs can be transformed into a series of spatially invariant "eigen-PSFs", each with an associated coefficient matrix. Thus the act of performing a spatially varying image deconvolution can be changed into a weighted sum of spatially invariant deconvolutions. After demonstrating this process on simulated data, we also show real-world results from a camera system modified with a diffractive waveplate, and provide a brief discussion on processing time and tradeoffs inherent to the technique.
In this work we present the spatio-temporal characteristics of the surface expressions generated by various species of reef fish in visible and thermal wavebands with the intention of understanding the structures formed during locomotion, station-keeping, and feeding in a large scale aquarium environment. Data collected focused on diurnal events when the majority of the fish were active and overlapped with the feeding cycle of the marine animals. Expressions generated by a sea turtle (1 m) down to smaller fish (0.3 m) were observed and recorded with the resulting surface thermal footprints varying from one meter to several centimeters respectively. Surface thermal wakes and boils were recorded as fish swarmed near the surface, breached the water, and struck at food particles floating on the surface. This collection of surface thermal features serves as a template for expected outcomes in a more complex unconfined environment such as a harbor or blue water.
We experimentally design, construct and test a compact optical system featuring a vortex diffractive waveplate placed in the aperture stop of the lens system. The wavefront coding camera diffracts polarized coherent illumination in the system's focal plane and reduces the peak intensity of the beam by two orders of magnitude while simultaneously recovering an unpolarized incoherent background image.
A Point Spread Function (PSF) engineered imaging system provides functionality at the expense of image distortion. Deconvolution and other post-processing techniques may partially restore the image if the PSF is known. We compare how various phase mask functions (e.g., vortex, axicon, cubic, and circular harmonic) may functionally protect a sensor from a coherent beam, and we discuss the subsequent trade-off between peak irradiance and the integrated modulation transfer function (Strehl ratio). Both experimental and numerical examples demonstrate that the peak irradiance may be suppressed by orders of magnitude without intolerable loss of image fidelity. The design of an optimal phase mask that accomplishes this task is made difficult by the nonlinear relationship between peak irradiance and Strehl. Results from experimental and numerical optimization schemes like simulated annealing, differential evolution, and Nelder-Mead will be compared.
Imaging through scattering media is a highly sought capability for military, industrial, and medical applications. Unfortunately, nearly all recent progress was achieved in microscopic light propagation and/or light propagation through thin or weak scatterers which is mostly pertinent to medical research field. Sensing at long ranges through extended scattering media, for example turbid water or dense fog, still represents significant challenge and the best results are demonstrated using conventional approaches of time- or range-gating. The imaging range of such systems is constrained by their ability to distinguish a few ballistic photons that reach the detector from the background, scattered, and ambient photons, as well as from detector noise. Holography can potentially enhance time-gating by taking advantage of extra signal filtering based on coherence properties of the ballistic photons as well as by employing coherent addition of multiple frames. In a holographic imaging scheme ballistic photons of the imaging pulse are reflected from a target and interfered with the reference pulse at the detector creating a hologram. Related approaches were demonstrated previously in one-way imaging through thin biological samples and other microscopic scale scatterers. In this work, we investigate performance of holographic imaging systems under conditions of extreme scattering (less than one signal photon per pixel signal), demonstrate advantages of coherent addition of images recovered from holograms, and discuss image quality dependence on the ratio of the signal and reference beam power.
One of the desired capabilities for wide-area persistent ISR systems is to reliably locate and subsequently track the movement of targets within the field of view. Current wide-area persistent ISR systems are characterized by large pixel overall counts and very large fields of view. This leads to a large ground sample distance with few pixels-on-target. Locating targets under these constraints is extremely difficult due to the fact that the targets present very little detailed structure. In this paper we will present the application of rich image feature descriptors combined with advanced statistical target detection methodologies to the airborne ISR problem. We will demonstrate that these algorithms can reliably locate targets in the scene without relying on the target's motion to form a detection. This is useful in ISR application where it is desirable to be able to continuously track a target through stops and maneuvers.
Short wave infrared (SWIR) sensors are becoming more common in DoD imaging systems because of their haze penetration capabilities and spectral properties of materials in this waveband. Typical SWIR systems have provided either full motion video (FMV) with framing panchromatic systems or multi-spectral or hyperspectral imagery with line-scanning systems. The system described here bridges these modalities, providing FMV with nine discrete spectral bands. Nine pixel sized SWIR filters are arranged in a repeating 3x3 pattern and mounted on top of a COTS, 2D staring focal plane array (FPA). We characterize the spectral response of the filter and integrated sensor. Spot-scan measurements and data collected with this camera using narrow band sources reveals crosstalk induced nonlinearity in the sensor response. We demonstrate a simple approach to reduce the impact of this nonlinearity on collected imagery.
Short wave infrared (SWIR) spectral imaging systems are vital for Intelligence, Surveillance, and Reconnaissance (ISR)
applications because of their abilities to autonomously detect targets and classify materials. Typically the spectral
imagers are incapable of providing Full Motion Video (FMV) because of their reliance on line scanning. We enable
FMV capability for a SWIR multi-spectral camera by creating a repeating pattern of 3x3 spectral filters on a staring focal
plane array (FPA). In this paper we present the imagery from an FMV SWIR camera with nine discrete bands and
discuss image processing algorithms necessary for its operation. The main task of image processing in this case is
demosaicking of the spectral bands i.e. reconstructing full spectral images with original FPA resolution from spatially
subsampled and incomplete spectral data acquired with the choice of filter array pattern. To the best of author's
knowledge, the demosaicking algorithms for nine or more equally sampled bands have not been reported before.
Moreover all existing algorithms developed for demosaicking visible color filter arrays with less than nine colors assume
either certain relationship between the visible colors, which are not valid for SWIR imaging, or presence of one color
band with higher sampling rate compared to the rest of the bands, which does not conform to our spectral filter pattern.
We will discuss and present results for two novel approaches to demosaicking: interpolation using multi-band edge
information and application of multi-frame super-resolution to a single frame resolution enhancement of multi-spectral
spatially multiplexed images.
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