Hsin-Yueh Sung

Image restoration based on multiple PSF information with applications to phase-coded imaging system

Conventional image restoration technique generally uses one point-spread function (PSF) corresponding to an object distance (OD) and a viewing angle (VA) in filter design. However, for those imaging systems, which concern a better balance or a new tradeoff of image restoration within a range of ODs or VAs, the conventional design might be insufficient to give satisfactory results. In this paper, an extension of the minimum mean square error (MMSE) method is proposed. The proposed method defines a cost function as a linear combination of multiple mean square errors (MSEs). Each MSE is for measuring the restoration performance at a specific OD and VA and can be computed from the restored image and its correspondent target image. Since the MSEs for different ODs are lumped into one cost function, the filter solved can provide a better balance in restoration compared with the conventional design. The method is applied to an extended depth-of-field (EDoF) imaging system and computer simulations are performed to verify its effectiveness.

Manufacturing process optimization of phase plates for depth extension microscopy systems

Extended depth of field (EDoF) technology can be applied to imaging systems by merging phase-coding design and digital signal processing. This paper presents an application of EDoF to the microscope platform and shows the capability to capture EDoF images in a single shot. Ultra-precision machining conditions for a phase-coding component were compared the peak-to-valley (P-V) error of the cubic surface with the performance of the EDoF. For the phase variation is very small for this phase plate, determining the optimal cutting condition at which the quality of phase plate is stabilized is very important. Therefore, the single point diamond turning (SPDT) was used to manufacture the optical components for its high precision. And the results are as following, the accuracy of non-symmetric phase plate found between 0.4 μm and 1μm had better performance of the EDoF image. Overall, the depth of field of the new objective could be increased more than five times compared to an objective having no such phase plate. The purpose of this study is to compare the relationship between PV error of phase plate surface and imaging restoration quality, which maybe a good benchmark in this field.

Miniaturized 3D microscope imaging system

We designed and assembled a portable 3-D miniature microscopic image system with the size of 35x35x105 mm3 . By integrating a microlens array (MLA) into the optical train of a handheld microscope, the biological specimen’s image will be captured for ease of use in a single shot. With the light field raw data and program, the focal plane can be changed digitally and the 3-D image can be reconstructed after the image was taken. To localize an object in a 3-D volume, an automated data analysis algorithm to precisely distinguish profundity position is needed. The ability to create focal stacks from a single image allows moving or specimens to be recorded. Applying light field microscope algorithm to these focal stacks, a set of cross sections will be produced, which can be visualized using 3-D rendering. Furthermore, we have developed a series of design rules in order to enhance the pixel using efficiency and reduce the crosstalk between each microlens for obtain good image quality. In this paper, we demonstrate a handheld light field microscope (HLFM) to distinguish two different color fluorescence particles separated by a cover glass in a 600um range, show its focal stacks, and 3-D position.

Fidelity tolerance analysis for computational imaging system

Computational imaging has been using for depth of field extension, distance estimation and depth map for stereo imaging and displaying with great successfully, which are realized by using special designed imaging lens and optimized image post-processing algorithm. Several special coding structures have been presented, like cubic, generalized cubic, logarithmic, exponential, polynomial, spherical and others. And different image post-processing algorithms like Wiener filter, SVD method, wavelet transform, minimum mean square error method and others are applied to achieve jointly-optimization. Although most of studies have shown excellent invariant of optical transfer function for imaging lens, but such invariance will be unsatisfied when manufacturing errors are considered. In this paper, we present a method to consider behavior of tolerance in computational imaging system from pure optical to optical - digital, which means lens and image post-processing are both included. An axial irradiance equalization phase coded imaging system is illustrated for tolerance sensitivity by using similarity of point spread function (PSF), Strehl ratio (SR), and root mean square error (RMSE) of restored images. Finally, we compare differences between presented method and Zemax.