Guillem Carles

Super-resolution imaging using a camera array

The angular resolution of many commercial imaging systems is limited, not by diffraction or optical aberrations, but by pixilation effects. Multiaperture imaging has previously demonstrated the potential for super-resolution (SR) imaging using a lenslet array and single detector array. We describe the practical demonstration of SR imaging using an array of 25 independent commercial-off-the-shelf cameras. This technique demonstrates the potential for increasing the angular resolution toward the diffraction limit, but without the limit on angular resolution imposed by the use of a single detector array.

Extended depth-of-field imaging and ranging in a snapshot

Traditional approaches to imaging require that an increase in depth of field is associated with a reduction in numerical aperture, and hence with a reduction in resolution and optical throughput. In their seminal work, Dowski and Cathey reported how the asymmetric point-spread function generated by a cubic-phase aberration encodes the detected image such that digital recovery can yield images with an extended depth of field without sacrificing resolution [Appl. Opt.34, 1859 (1995)10.1364/AO.34.001859APOPAI1559-128X]. Unfortunately recovered images are generally visibly degraded by artifacts arising from subtle variations in point-spread functions with defocus. We report a technique that involves determination of the spatially variant translation of image components that accompanies defocus to enable determination of spatially variant defocus. This in turn enables recovery of artifact-free, extended depth-of-field images together with a two-dimensional defocus and range map of the imaged scene. We demonstrate the technique for high-quality macroscopic and microscopic imaging of scenes presenting an extended defocus of up to two waves, and for generation of defocus maps with an uncertainty of 0.036 waves.

Multi-aperture foveated imaging

Foveated imaging, such as that evolved by biological systems to provide high angular resolution with a reduced space-bandwidth product, also offers advantages for man-made task-specific imaging. Foveated imaging systems using exclusively optical distortion are complex, bulky, and high cost, however. We demonstrate foveated imaging using a planar array of identical cameras combined with a prism array and superresolution reconstruction of a mosaicked image with a foveal variation in angular resolution of 5.9:1 and a quadrupling of the field of view. The combination of low-cost, mass-produced cameras and optics with computational image recovery offers enhanced capability of achieving large foveal ratios from compact, low-cost imaging systems.

Compact multi-aperture imaging with high angular resolution

Previous reports have demonstrated that it is possible to emulate the imaging function of a single conventional lens with an N×N array of identical lenslets to provide an N-fold reduction in imaging-system track length. This approach limits the application to low-resolution imaging. We highlight how using an array of dissimilar lenslets, with an array width that can be much wider than the detector array, high-resolution super-resolved imaging is possible. We illustrate this approach with a ray-traced design and optimization of a long-wave infrared system employing a 3×3 array of freeform lenslets to provide a fourfold reduction in track length compared to a baseline system. Simulations of image recovery show that recovered image quality is comparable to that of the baseline system.

Combined high contrast and wide field of view in the scanning laser ophthalmoscope through dual detection of light paths

Abstract. We demonstrate a multimode detection system in a scanning laser ophthalmoscope (SLO) that enables simultaneous operation in confocal, indirect, and direct modes to permit an agile trade between image contrast and optical sensitivity across the retinal field of view to optimize the overall imaging performance, enabling increased contrast in very wide-field operation. We demonstrate the method on a wide-field SLO employing a hybrid pinhole at its image plane, to yield a twofold increase in vasculature contrast in the central retina compared to its conventional direct mode while retaining high-quality imaging across a wide field of the retina, of up to 200 deg and 20  μm on-axis resolution.

Computational localization microscopy with extended axial range

A new single-aperture 3D particle-localization and tracking technique is presented that demonstrates an increase in depth range by more than an order of magnitude without compromising optical resolution and throughput. We exploit the extended depth range and depth-dependent translation of an Airy-beam PSF for 3D localization over an extended volume in a single snapshot. The technique is applicable to all bright-field and fluorescence modalities for particle localization and tracking, ranging from super-resolution microscopy through to the tracking of fluorescent beads and endogenous particles within cells. We demonstrate and validate its application to real-time 3D velocity imaging of fluid flow in capillaries using fluorescent tracer beads. An axial localization precision of 50 nm was obtained over a depth range of 120μm using a 0.4NA, 20× microscope objective. We believe this to be the highest ratio of axial range-to-precision reported to date.

Superimposed multi-resolution imaging

We present a novel approach to foveated imaging based on dual-aperture optics that superimpose two images on a single sensor, thus attaining a pronounced foveal function with reduced optical complexity. Each image captures the scene at a different magnification and therefore the system simultaneously captures a wide field of view and a high acuity at a central region. This approach enables arbitrary magnification ratios using a relatively simple system, which would be impossible using conventional optical design, and is of importance in applications where the cost per pixel is high. The acquired superimposed image can be processed to perform enhanced object tracking and recognition over a wider field of view and at an increased angular resolution for a given limited pixel count. Alternatively, image reconstruction can be used to separate the image components enabling the reconstruction of a foveated image for display. We demonstrate these concepts through ray-tracing simulation of practical optical systems with computational recovery.

Monte-Carlo Simulation of Imaging Systems with Turbid Media through Optical Ray-Trace

Recognising optical raytrace as a form of Monte-Carlo simulation, we report using Zemax-OpticStudio to holistically model optical-imaging instrument and sample as a single system. We illustrate the potential of the approach for imaging-through-turbid-media and fluorescence.

3D imaging and ranging in a snapshot

Imaging samples with a depth in excess of the depth of field of the objective poses a serious challenge in microscopy. The available techniques such as focus-stacking accomplish the task; however, besides necessitating complicated optical and mechanical arrangements, these techniques often exhibit very long acquisition times. As a result, their applicability is limited to static samples. We describe a simple and practical hybrid 3D imaging technique which permits the acquisition of 3D images in a single snapshot. Additionally, the proposed method solves the post-recovery artefact formation problem which plagues hybrid imaging systems; thus, enabling high-quality, artefact-free images to be obtained. Experimental results indicate that this method can yield an image quality comparable to that given by a focus-stack (which can require up to a few hundred snapshots) from a single snapshot.

Multi-Aperture Imaging in the Visible and Thermal Infrared

Multi-aperture imaging brings super-resolution as an additional tool for computational imaging. Optical design and simulation results for a 3x3-multi-aperture system and experimental results using a 5x5-multi-camera device are reported.