Simple method of acquiring high-quality light fields based on the chromatic aberration of only one defocused image pair.

Direct light field acquisition method using a lens array requires a complex system and has a low resolution. On the other hand, the light fields can be also acquired indirectly by back-projection of the focal stack images without lens array, providing a resolution as high as the sensor resolution. However, it also requires the bulky optical system design to fix field-of-view (FOV) between the focal stacks, and an additional device for sensor shifting. Also, the reconstructed light field is texture-dependent and low-quality because it uses either a high-pass filter or a guided filter for back-projection. This paper presents a simple light field acquisition method based on chromatic aberration of only one defocused image pair. An image with chromatic aberration has a different defocus distribution for each R, G, and B channel. Thus, the focal stack can be synthesized with structural similarity (SSIM) 0.96 from only one defocused image pair. Then this image pair is also used to estimate the depth map by depth-from-defocus (DFD) using chromatic aberration (chromatic DFD). The depth map obtained by chromatic DFD is used for high-quality light field reconstruction. Compared to existing light field indirect acquisition, the proposed method requires only one pair of defocused images and can clearly reconstruct light field images with Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) scores lowered by 17%-38% and with Perception-Based Image Quality Evaluator (PIQE) scores lowered by 19%-45%. A defocused image pair is acquired by our customized compact optical system consisting of only three lenses, including a varifocal lens. Image processing and image quality evaluation are all performed using MATLAB.

Compact and fast depth sensor based on a liquid lens using chromatic aberration to improve accuracy.

Depth from defocus (DFD) obtains depth information using two defocused images, making it possible to obtain a depth map with high resolution equal to that of the RGB image. However, it is difficult to change the focus mechanically in real-time applications, and the depth range is narrow because it is inversely proportional to the depth accuracy. This paper presents a compact DFD system based on a liquid lens that uses chromatic aberration for real-time application and depth accuracy improvement. The electrical focus changing of a liquid lens greatly shortens the image-capturing time, making it suitable for real-time applications as well as helping with compact lens design. Depth accuracy can be improved by dividing the depth range into three channels using chromatic aberration. This work demonstrated the improvement of depth accuracy through theory and simulation and verified it through DFD system design and depth measurement experiments of real 3D objects. Our depth measurement system showed a root mean square error (RMSE) of 0.7 mm to 4.98 mm compared to 2.275 mm to 12.3 mm in the conventional method, for the depth measurement range of 30 cm to 70 cm. Only three lenses are required in the total optical system. The response time of changing focus by the liquid lens is 10 ms, so two defocused images for DFD can be acquired within a single frame period of real-time operations. Lens design and image processing were conducted using Zemax and MATLAB, respectively.

Novel biconvex structure electrowetting liquid lenticular lens for 2D/3D convertible display.

Recently, a planoconvex structure electrowetting lenticular lens capable of 2D/3D conversion through a varifocal property by an electrowetting phenomenon has been developed. However, even though it has a similar planoconvex structure to that of a commercial solid lenticular lens, comparable 3D performance could not be realized because the refractive index difference between nonconductive liquid and conductive liquid was not large. Therefore, the goal of the present study is to obtain better 3D performance compared to the conventional planoconvex structure by introducing a novel biconvex structure using ETPTA. The newly developed biconvex structure electrowetting lenticular lens showed greatly improved characteristics compared to the planoconvex structure: dioptric power (171.69D → 1,982.56D), viewing angle (26degrees → 46degrees), and crosstalk ratio (27.27% → 16.18%). Thanks to these improvements, a fine 3D image and a natural motion parallax could be observed with the biconvex structure electrowetting lenticular lens. In addition, the novel biconvex structure electrowetting lenticular lens was designed to achieve a plane lens state with a no voltage applied condition, and as such it could show a clean 2D image at 0 V. In conclusion, a novel biconvex structure electrowetting lenticular lens showed 2D/3D switchable operation as well as excellent 3D performance compared to a solid lenticular lens.