Yangyang Sun

High-speed compressive range imaging based on active illumination.

We report a compressive imaging method based on active illumination, which reconstructs a 3D scene at a frame rate beyond the acquisition speed limit of the camera. We have built an imaging prototype that projects temporally varying illumination pattern and demonstrated a joint reconstruction algorithm that iteratively retrieves both the range and high-temporal-frequency information from the 2D low-frame rate measurement. The reflectance and depth-map videos have been reconstructed at 1000 frames per second (fps) from the measurement captured at 200 fps. The range resolution is in agreement with the resolution calculated from the triangulation methods based on the same system geometry. We expect such an imaging method could become a simple solution to a wide range of applications, including industrial metrology, 3D printing, and vehicle navigations.

Compressive high-speed stereo imaging

A compressive high-speed stereo imaging system is reported. The system is capable of reconstructing 3D videos at a frame rate 10 times higher than the sampling rate of the imaging sensors. An asymmetric configuration of stereo imaging system has been implemented by including a high-speed spatial modulator in one of the binocular views, and leaving the other view unchanged. We have developed a two-step reconstruction algorithm to recover the irradiance and depth information of the high-speed scene. The experimental results have demonstrated high-speed video reconstruction at 800fps from 80fps measurements. The reported compressive stereo imaging method does not require active illumination, offering a robust yet inexpensive solution to high-speed 3D imaging.

Talbot interferometry with curved quasi-periodic gratings: towards large field of view X-ray phase-contrast imaging.

X-ray phase-contrast imaging based on grating interferometry has become a common method due to its superior contrast in biological soft tissue imaging. The high sensitivity relies on the high-aspect ratio structures of the planar gratings, which prohibit the large field of view applications with a diverging X-ray source. Curved gratings allow a high X-ray flux for a wider angular range, but the interference fringes are only visible within ~10° range due to the geometrical mismatch with the commonly used flat array detectors. In this paper, we propose a design using a curved quasi-periodic grating for large field of view imaging with a flat detector array. Our scheme is numerically verified in the X-ray regime and experimentally verified in the visible optical regime. The interference fringe pattern is observed over 25°, with less than 10% of decrease in visibility in our experiments.

Compressive video sensing with side information

Our temporally compressive imaging system reconstructs a high-speed image sequence from a single, coded snapshot. The reconstruction quality, similar to that of other compressive sensing systems, often depends on the structure of the measurement, as well as the choice of regularization. In this paper, we report a compressive video system that also captures the side information to aid in the reconstruction of high-speed scenes. The integration of the side information not only improves the quality of reconstruction, but also reduces the dependence of the reconstruction on regularization. We have implemented a system prototype that splits the field of view of a single camera into two channels: one channel captures the coded, low-frame-rate measurement for high-speed video reconstruction, and the other channel captures a direct measurement without coding as the side information. A joint reconstruction model is developed to recover the high-speed videos from the two channels. By analyzing both the experimental and the simulation results, the reconstructions with side information have demonstrated superior performances in terms of both the peak signal-to-noise ratio and structural similarity.

Multi-perspective scanning microscope based on Talbot effect

We report a multi-perspective scanning microscope based on the Talbot effect of a periodic focal spot array. Talbot illumination decouples the lateral scanning and the focal spots tuning. Large field of view fluorescence Talbot Microscope has been demonstrated by globally changing the incident wavefront gradient. Here, we explore the design freedom of adjusting the wavefront locally within each period and thus engineer the point spread function of the focal spots. We demonstrate an imaging system capable of reconstructing multi-perspective microscopic images in both bright field and fluorescence mode. With the multi-perspective imaging capability, we envision a more robust microscopic imaging system for large field of view fluorescence microscopy applications. This method is also suitable for compact imaging systems for multi-layer microfluidic systems.

Spatially encoded fast single-molecule fluorescence spectroscopy with full field-of-view

We report a simple single-molecule fluorescence imaging method that increases the temporal resolution of any type of array detector by >5-fold with full field-of-view. We spread single-molecule spots to adjacent pixels by rotating a mirror in the detection path during the exposure time of a single frame, which encodes temporal information into the spatial domain. Our approach allowed us to monitor fast blinking of an organic dye, the dissociation kinetics of very short DNA and conformational changes of biomolecules with much improved temporal resolution than the conventional method. Our technique is useful when a large field-of-view is required, for example, in the case of weakly interacting biomolecules or cellular imaging.

Video compressed imaging using side information (Rising Researcher Presentation) (Conference Presentation)

Video compressive imaging system reconstructs high-speed image sequence from a single, coded snapshot. In this paper, we report a compressive video sensing system that captures the side information in addition to the main measurement to aid the reconstruction of high-speed scenes. The integration of the side information not only improves the quality of reconstruction, but also reduces the dependence of the reconstruction on regularization. We have implemented a system prototype, which splits the field of view of a single camera into two channels: one channel captures the coded, low-frame-rate measurement for high speed video reconstruction; the other channel captures a direct measurement without coding as the side information. A joint reconstruction model is developed to recover the high-speed videos from the two channels.

Compressive temporal stereo-vision imaging

We report a binocular stereo-vision imaging system acquiring videos exceeding the cameras’ frame rate. An iterative reconstruction algorithm with the knowledge of the correspondence between the cameras demonstrated a 4x faster frame rate in simulation.

Compressive Temporal RGB-D Imaging

We report a compressive imaging system for high-speed color (RGB) video and range sensing based on the structured illumination. Random patterns are projected on the scene at a higher frame rate than that of the color camera. High-speed RGB-D scenes are reconstructed from a single 2D measurement via efficient algorithms.

Large-field-of-view, multi-perspective Talbot microscopy

Common microscope objectives have fields of view (FOVs) of less than a few millimeters because of limits imposed by optical aberrations. To scale up the FOVs, additional lens elements and heroic design efforts are required to compensate for the aberrations, leading to reduced transmissions and higher system costs. Such FOV limitations have thus become a major bottleneck in microscopy for large-scale imaging applications (e.g., phenotype screening and semiconductor wafer inspection). In stateof-the-art commercialized systems, for instance, the samples are transported under a conventional microscope to increase the effective FOV, but this involves extended imaging times. For our previous development of a compact microscopic imaging system,1 we did not follow a single-aperture optical design approach. Instead, we used the self-imaging effect to project a grid of excitation light spots onto a sample. This self-imaging effect—also known as the Talbot effect—was first explained by Lord Rayleigh using diffraction theory. In conventional high-throughput scanning microscope setups, the sample is directly scanned by the focal spots of a microlens array. Our Talbot microscope, which uses Talbot images of the focal spots, however, has a longer working distance and a higher phase sensitivity. A slight gradient of the global incident wavefront on the microlens array can therefore shift the Talbot focal spots by a significant distance, without introducing much off-axis aberration. In addition, the self-imaging has a self-healing effect, which generates an improved uniformity among the focal spots. By scanning the grid of focal spots across the sample in our Talbot microscope setup, we can collect a sequence of local images and thus reconstruct a high-resolution image with a large FOV.1 In contrast to conventional microscopes, the resolution and the FOV of our system are not coupled to each other. Using a Figure 1. Large-field-of-view, multi-perspective microscope that is based on the Talbot effect. A microlens array (white) generates a grid of Talbot focal spots for parallel scanning. Local wavefront (red) engineering enables multi-perspective imaging.