Andrew D. Portnoy

Compressive Imaging Sensors

This paper describes a compressive sensing strategy developed under the Compressive Optical MONTAGE Photography Initiative. Multiplex and multi-channel measurements are generally necessary for compressive sensing. In a compressive imaging system described here, static focal plane coding is used with multiple image apertures for non-degenerate multiplexing and multiple channel sampling. According to classical analysis, one might expect the number of pixels in a reconstructed image to equal the total number of pixels across the sampling channels, but we demonstrate that the system can achieve up to 50% compression with conventional benchmarking images. In general, the compression rate depends on the compression potential of an image with respect to the coding and decoding schemes employed in the system.

Compressive Optical MONTAGE Photography

The Compressive Optical MONTAGE Photography Initiative (COMP-I) is an initiative under DARPAs MONTAGE program. The goals of COMP-I are to produce 1 mm thick visible imaging systems and 5 mm thick IR systems without compromising pixel-limited resolution. Innovations of COMP-I include focal-plane coding, block-wise focal plane codes, birefringent, holographic and 3D optical elements for focal plane remapping and embedded algorithms for image formation. In addition to meeting MONTAGE specifications for sensor thickness, focal plane coding enables a reduction in the transverse aperture size, physical layer compression of multispectral and hyperspectral data cubes, joint optical and electronic optimization for 3D sensing, tracking, feature-specific imaging and conformal array deployment.

Design and characterization of thin multiple aperture infrared cameras

We describe a multiple-aperture long-wave infrared camera built on an uncooled microbolometer array with the objective of decreasing camera thickness. The 5 mm thick optical system is an f/1.2 design with a 6.15 mm effective focal length. An integrated image is formed from the subapertures using correlation-based registration and a least gradient reconstruction algorithm. We measure a 131 mK NETD. The systems spatial frequency is analyzed with 4 bar targets. With proper calibration, our multichannel interpolation results recover contrast for targets at frequencies beyond the aliasing limit of the individual subimages.

Multichannel sampling schemes for optical imaging systems

We introduce a framework of focal-plane coding schemes for multichannel sampling in optical systems. A particular objective is to develop an ultrathin imager without compromising image resolution. We present a complete f/2.1 optical system with a thickness of 2.2 mm. The resolution is maintained in the thin optical system by an integrated design of the encoding scheme, the process of making the coding elements, and the decoding algorithms.

Thin Digital Imaging Systems Using Focal Plane Coding

With this work we show the use of focal plane coding to produce nondegenerate data between subapertures of an imaging system. Subaperture data is integrated to form a single high resolution image. Multiple apertures generate multiple copies of a scene on the detector plane. Placed in the image plane, the focal plane mask applies a unique code to each of these sub-images. Within each sub-image, each pixel is masked so that light from only certain optical pixels reaches the detector. Thus, each sub-image measures a different linear combination of optical pixels. Image reconstruction is achieved by inversion of the transformation performed by the imaging system. Registered detector pixels in each sub-image represent the magnitude of the projection of the same optical information onto different sampling vectors. Without a coding element, the imaging system would be limited by the spatial frequency response of the electronic detector pixel. The small mask features allow the imager to broaden this response and reconstruct higher spatial frequencies than a conventional coarsely sampling focal plane.

Pushbroom Hyperspectral Imaging with a Coded Aperture

We describe a hyperspectral camera which operates by translating a scene across the entrance of a coded aperture spectrometer. This applies a sequence of unique codes to the image, allowing full reconstruction of the datacube.

Multi-Aperture Visible High Resolution Thin Imager

We have designed and built a multi-aperture thin imager using a lenslet array and a CCD imager. The thickness of the imager is significantly reduced. We will present experimental results that demonstrate high resolution imaging.

Dual-Disperser Design for Single-Shot Computational Spectral Imaging

We describe a dual-disperser approach to computational spectral imaging. This approach enables flexible code design and avoids problems present in single-disperser systems. We will report on a prototype single-shot spectral imager based on these ideas.