Vikrant R. Bhakta

Adaptive flat multiresolution multiplexed computational imaging architecture utilizing micromirror arrays to steer subimager fields of view

A thin, agile multiresolution, computational imaging sensor architecture, termed PANOPTES (processing arrays of Nyguist-limited observations to produce a thin electro-optic sensor), which utilizes arrays of microelectromechanical mirrors to adaptively redirect the fields of view of multiple low-resolution subimagers, is described. An information theory-based algorithm adapts the system and restores the image. The modulation transfer function (MTF) effects of utilizing micromirror arrays to steering imaging systems are analyzed, and computational methods for combining data collected from systems with differing MTFs are presented.

Effects of sampling on the phase transfer function of incoherent imaging systems.

With the advent of modern-day computational imagers, the phase of the optical transfer function may no longer be summarily ignored. This study discusses some important properties of the phase transfer function (PTF) of digital incoherent imaging systems and their implications on the performance and characterization of these systems. The effects of aliasing and sub-pixel image shifts on the phase of the complex frequency response of these sampled systems are described, including an examination of the specific case of moderate aliasing. Key properties of this function in aliased imaging systems are derived and their potential treatment to a range of diverse applications encompassing traditional and computational imaging systems is discussed.

Experimental evidence of the theoretical spatial frequency response of cubic phase mask wavefront coding imaging systems

The optical transfer function of a cubic phase mask wavefront coding imaging system is experimentally measured across the entire range of defocus values encompassing the systems functional limits. The results are compared against mathematical expressions describing the spatial frequency response of these computational imagers. Experimental data shows that the observed modulation and phase transfer functions, available spatial frequency bandwidth and design range of this imaging system strongly agree with previously published mathematical analyses. An imaging system characterization application is also presented wherein it is shown that the phase transfer function is more robust than the modulation transfer function in estimating the strength of the cubic phase mask.

Super Resolution results in PANOPTES, an adaptive multi-aperture folded architecture

We present experimental results of digital super resolution (DSR) techniques on low resolution data collected using PANOPTES, a multi-aperture miniature folded imaging architecture. The flat form factor of PANOPTES architecture results in an optical system that is heavily blurred with space variant PSF which makes super resolution challenging. We also introduce a new DSR method called SRUM (Super-Resolution with Unsharpenning Mask) which can efficiently highlight edges by embedding an unsharpenning mask to the cost function. This has much better effect than just applying the mask after all iterations as a post-processing step.

Image-based Measurement of Phase Transfer Function

A method for measuring the Phase Transfer Function (PTF) from a high-contrast edge image is proposed and the advantages of utilizing the knowledge of PTF in computational, sparse aperture and multiplexed imaging are discussed.

Experimentally validated computational imaging with adaptive multiaperture folded architecture

We present experimental results of imaging and digital superresolution in a multiaperture miniature folded imaging architecture called PANOPTES. We prove the feasibility of integrating a low f-number folded imagers within a steerable multiaperture framework while maintaining a thin profile. Stringent requirements including low f-number and compact form factor, combined with the need for an ability to steer individual fields of view necessitate an off-axis design, resulting in a plane symmetric optical system. We present a detailed description of the ensuing optical design and its performance. The feasibility of this architecture is demonstrated through experiments and preliminary reconstruction results.

Performance Metric for Multi-Aperture Computational Imaging Sensor

Determining the effective MTF, SNR and Sensor geometries of multi-aperture computational imaging architectures will allow the National Image Interpretability Rating Scale to be applied to computational imagers. An approach for determining these values is presented.

Applications of the phase transfer function of digital incoherent imaging systems

The phase of the optical transfer function is advocated as an important tool in the characterization of modern incoherent imaging systems. It is shown that knowledge of the phase transfer function (PTF) can benefit a diverse array of applications involving both traditional and computational imaging systems. Areas of potential benefits are discussed, and three applications are presented, demonstrating the utility of the phase of the complex frequency response in practical scenarios. In traditional imaging systems, the PTF is shown via simulation results to be strongly coupled with odd-order aberrations and hence useful in misalignment detection and correction. In computational imaging systems, experimental results confirm that the PTF can be successfully applied to subpixel shift estimation and wavefront coding characterization tasks.

Space-Variant Optical Super-Resolution using Sinusoidal Illumination

The present work extends the scope of Optical Super-Resolution to imaging systems with spatially-varying blur, by using sinusoidal illumination. It also establishes that knowledge of the space-variant blur is not a pre-requisite for super-resolution.

Experimentally Validated High-Resolution Imaging with Adaptive Multi-Aperture Folded Architecture

We present experimental results of imaging and digital super-resolution in a multi-aperture miniature folded imaging architecture called PANOPTES. We prove the feasibility of integrating folded imagers within a steerable multi-aperture framework while maintaining thin profiles.