Yung-Lin Chen

Depth perception with a rotationally symmetric coded camera

A novel design of a phase coded depth-sensing camera is presented. A rotational symmetric phase mask is designed to discriminate the point spread functions (PSF) from different scene distances. The depth information can then be computationally obtained from a single captured photograph through a phase coded lens. The PSF must be carefully optimized at off-axis angles in order to create a restored image which is sharp over the required field of view. In this paper, a phase coded depth camera with a focal length 10.82mm, sensor size 2mm and F-number 5 is designed. Simulation data is exchanged between Matlab and Zemax for co-optimization of optical coding and digital decoding process. The simulation result shows that coarse depth information is investigated for object distance from 513 mm to 1000 mm.

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.

Using liquid lens in wavefront coded imaging system

A novel design of a wavefront coded compact camera system with liquid lens is presented. The point spread function must remain practically constant over a wide range of defocus in order to create an image which is sharp over a large depth of field. Therefore, the trade-off between the effect of extended depth of field and reduction in the signal to noise ratio of the restored image become critical. By combining liquid lens and wavefront coding, the system can deliver much greater depth of field without the restoration problems caused by the similarity of point spread function. This could improve the overall image performance.

Novel approach for merit function optimization in hybrid imaging system through finite impulse response method

Merit function with higher efficiency is helpful for lens design, especially in hybrid imaging system. Although different merit functions have been proposed in recent years, for example, Fisher information, Hilbert space angle, mean square error (MSE) based on optical transfer function, intermediate or restored image, structure similarity, correlation or statistical properties from point spread function (PSF). But it is still an unanswered question that which merit function is best for optimization in hybrid imaging system. So, a novel approach which is based on finite impulse response of hybrid imaging system is proposed. And several merit functions, blur MSE, PSF similarity, modulation transfer function (MTF) area and volume are evaluated by present method. The results show that performance of merit function is not only affected by noise, sampling ratio. But the effect of restoration filter should be also considered. Finally, compare with PSF similarity, blur MTF in area and volume; blur MSE provide much stable results in hybrid imaging system, which means it could be an optimized merit function in hybrid imaging system.

Evaluating distances using a coded lens camera and a blur metric

We propose a method and a system to measure distances to a target and at the same time obtaining an image of the target. The system is based on a wavefront coded lens and an image processing unit. The method requires a calibration phase where a blur metric is related to the distance of the target. The distance to the target for any position is then obtained by computing the blur metric of the target and using the calibration data. The method and system are easy to manufacture and provide an alternative to other distance measuring methods and devices, while also producing an image of the scene. The target is a printed image of pseudo random black and white elements which can be stick or placed nearby objects of which distance is to be evaluated.

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.

Phase coded optics for computational imaging systems

Computational imaging technology can modify the acquisition process to capture extra information at the sensor that can be used for various photographic applications, including imaging with extended depth of field, refocusing photographs after the image is taken or depth extraction for 3D applications. In this paper, we propose a generalized phase coded imaging which involves encoding of the captured light and post-capture decoding for improved features and performance. Phase coded optics utilizes optics to purposely encode specific object information in a more efficient way, which is the most flexible and cost effective solution for correcting optical aberrations or any other optical functions. Practically any shape can be generated on any lens surface for shaping the point spread function of the lens module to achieve desired image results. Phase coded optics is a more general scheme than previous proposed for finding the optimal solutions in digital imaging systems and has proven to be an enabling technology to the imaging problem. Some of the possible applications based on this technique are also investigated in this paper.