Young-Tae Lim

With the development of the holographic printer, printing synthetic hologram requires smaller holographic element (hogel) size to improve spatial resolution of the reconstruction. On the contrary, a larger hogel size affords higher angular resolution, but it leads to a lower lateral resolution and there exists a trade-off problem. In this paper, a hologram synthesis method based on three-dimensional (3D) rendering of computer-generated holographic stereogram (HS) is proposed to limit the spatial-angular trade-off problem. The perspectives of the 3D scene are captured by re-centering the camera method and transformed into parallax-related images by a proposed pixel re-arrangement algorithm for holographic printing. Unlike the conventional approaches, the proposed algorithm not only improves the angular resolution of the reconstruction while maintaining the hogel size fixed, but also keeps the spatial resolution without degradation. The effectiveness of the proposed method is verified by numerical simulation and an optical experiment.

In this paper, we propose an advanced three-dimensional visualization method for an integral imaging microscope system to simultaneously improve the resolution and quality of the reconstructed image. The main advance of the proposed method is that it generates a high-quality three-dimensional model without limitation of resolution by combining the high-resolution two-dimensional color image with depth data obtained through a fully convolutional neural network. First, the high-resolution two-dimensional image and an elemental image array for a specimen are captured, and the orthographic-view image is reconstructed from the elemental image array. Then, via a convolutional neural network-based depth estimation after the brightness of input images are uniformed, a more accurate and improved depth image is generated; and the noise of result depth image is filtered. Subsequently, the estimated depth data is combined with the high-resolution two-dimensional image and transformed into a high-quality three-dimensional model. In the experiment, it was confirmed that the displayed high-quality three-dimensional model could be visualized very similarly to the original image.

We propose a time-sequential switching light-field (LF) camera for alternative image capture of high-resolution two-dimensional (2D) images and three-dimensional (3D) LF elemental images as additional functionalities. For image data acquisitions of both the 2D and 3D LF imaging of moving objects at a video-frame rate (or even higher frame rate up to approximately 1000 fps), a polarization-dependent-switching micro-lens array (PMLA) is implemented in the LF camera system instead of a conventional passive-type MLA. By controlling the incident polarization conditions using an electrically fast-switching liquid crystal layer, the imaging mode can be time-sequentially switched quite rapidly (switching times of approximately 220 μs and 290 μs for the mode conversions from the 3D LF to the 2D mode, and the reversal mode change, respectively). Using the elemental image sets sampled from the alternating time-sequential imaging results, either directional-view images or depth-refocused images can be reconstructed and provided at a moving picture frame-rate. The depth-refocused images are possible for a wide depth range from 25 cm to 350 cm. Directional views of 22 x 22 and 9 x 9 in portions can be reconstructed for the single shot image capture and the time-sequential video-rate image capture, respectively.

A design and implementation of full-parallax holographic stereogram printer is presented. The holographic stereogram is synthesized using 2D perspective images of the 3D object that are rendered from multiple directions. The perspective images of the 3D scene are firstly captured by a virtual camera and transformed to two-dimensional holographic elements called hogels. The hogels are exposed using the perspective images to form the whole holographic stereogram. After all the hogels are exposed successively, a holographic stereogram can be achieved. Numerical simulation and optical reconstructions are implemented.