Browsing by Author "Qin, Zong"

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Ambient-light-adaptive image quality enhancement for full-color e-paper displays using a saturation-based tone-mapping method
(2018-03-01)
Qin, Zong
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Chen, Yi-Wen
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Lin, Fang-Cheng
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Hung, Chi-Mao
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Shieh, Han-Ping David
Full-color e-paper displays that have a small color gamut encounter image tone distortions and contour artifacts in high-saturation regions. To solve these issues, in this paper, we comprehensively measure the colorimetric responses of input image signals and demonstrate that the perceptual colorfulness in terms of chroma abnormally declines when the input saturation is beyond a certain value. Accordingly, saturation-based tone-mapping curves are developed to map the abnormal high saturation to the range that the display is able to normally render. By testing several test charts and natural images, the recoveries of the original image tones and the removals of the contour artifacts are experimentally verified. More important, by discussing how to conduct a database of tone-mapping curves for different ambient lights and utilize the database for an unknown ambient light, the proposed method is proven to be completely ambient light adaptive.
Color breakup suppression based on global dimming for field sequential color displays using edge information in images
(2019-02-04)
Lin, Fang-Cheng
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Qin, Zong
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Teng, Kai-Tung
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Huang, Yi-Pai
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光電工程學系
Considering the high complexity of local dimming backlight that is necessary to effectively suppress color breakups for field sequential color liquid crystal displays (FSC-LCDs), a global dimming-based solution is proposed. This solution involves considering that the color breakups mainly occur at object edges of an image. By introducing an algorithm to present the edge information in a single field, evaluating color breakup performances, and experimentally verifying based on a 240-Hz LCD, lighter color breakups are revealed compared with mainstream local dimming-based solutions. Therefore, the proposed solution can achieve FSC-LCDs with better performance and practicality for advanced display applications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Compact and High Resolution Virtual Mouse Using Lens Array and Light Sensor
(2016-01-01)
Qin, Zong
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Chang, Yu-Cheng
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Su, Yu-Jie
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Huang, Yi-Pai
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Shieh, Han-Ping David
Virtual mouse based on IR source, lens array and light sensor was designed and implemented. Optical architecture including lens amount, lens pitch, baseline length, sensor length, lens-sensor gap, focal length etc. was carefully designed to achieve low detective error, high resolution, and simultaneously, compact system volume. System volume is 3.1mm (thickness) x 4.5mm (length) x 2, which is much smaller than that of camera-based device. Relative detective error of 0.41mm and minimum resolution of 26ppi were verified in experiments, so that it can replace conventional touchpad/touchscreen. If system thickness is eased to 20mm, resolution higher than 200ppi can be achieved to replace real mouse.
Contrast-sensitivity-based evaluation method of a surveillance camera's visual resolution: improvement from the conventional slanted-edge spatial frequency response method
(2017-02-10)
Qin, Zong
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Wong, Po-Jung
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Chao, Wei-Chung
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Lin, Fang-Cheng
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Huang, Yi-Pai
Visual resolution is an important specification of a surveillance camera, and it is usually quantified by linewidths per picture height (LW/PH). The conventional evaluation method adopts the slanted-edge spatial frequency response (e-SFR) and uses a fixed decision contrast ratio to determine LW/PH. However, this method brings about a considerable error with respect to subjectively judged results because the perceptibility of the human vision system (HVS) varies with spatial frequency. Therefore, in this paper, a systematic calculation method, which combines the contrast sensitivity function characterizing the HVS and e-SFR, is proposed to solve LW/PH. Eight 720P camera modules in day mode, four 720P modules in night mode, and two 1080P modules in day mode are actually adopted. Corresponding to the three modes, mean absolute error between objective and subjective LW/PH are suppressed to as low as 26 (3.6% of 720P), 27 (3.8% of 720P), and 49 (4.5% of 1080P), while those of the conventional method are 68 (9.4% of 720P), 95 (13.2% of 720P), and 118 (10.9% of 1080P).(C) 2017 Optical Society of America
Digital halftoning method with simultaneously optimized perceptual image quality and drive current for multi-tonal electrophoretic displays
(2020-01-01)
Qin, Zong
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Wang, Hsin-, I
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Chen, Zi-Yu
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Chen, Chun-Ho
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Tien, Pei-Lin
While using digital halftoning to achieve multi-tones in al bit electrophoretic display (EPD), e.g., a three-pigment chromatic EPD, the drive current is significantly increased because of frequently reversed pixel values. Aimed at this issue, this study first establishes a model that can accurately predict the drive current from image content. Next, based on the direct binary search method, a new halftoning method is proposed by constructing a combined merit function that incorporates both the perceptual image quality and the drive current. As a result, in experiments using a 13.5 in. three-pigment EPD and several test images, compared with the well-developed error-diffusion method, the proposed method produces little image quality degradation, whereas the drive current increase with respect to the minimum current of the EPD is reduced from 71.8 to 33.0 mA, for a significant reduction of 54.0%. (C) 2019 Optical Society of America
Dual-focal-plane augmented reality head-up display using a single picture generation unit and a single freeform mirror
(2019-07-10)
Qin, Zong
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Lin, Shih-Ming
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Lu, Kuang-Tso
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Chen, Cheng-Huan
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Huang, Yi-Pai
Two or more focal planes are required in augmented reality head-up displays (AR HUDs) to respectively present basic and interactive driving information to car drivers; whereas, solutions using two separated picture generation units (PGUs) with two sets of optics incur increased cost, reduced reliability, and expanded volume. To develop an AR HUD using a single PGU and a single curved mirror, we propose to set two logically separated regions on a single PGU and optically relay one of them to a new position to create two focal planes. A single freeform mirror acquired through careful optical and mechanical design optimization produces high image quality in an eyebox of 120 mm by 60 mm, simultaneously for a far image (9 m, 10 degrees by 3 degrees) and a near image (2.5 m, 6 degrees by 2 degrees). Finally, an AR HUD product with a compact volume of 8.5 L is fabricated to experimentally verify the design. (C) 2019 Optical Society of America
Evaluation of a Transparent Display's Pixel Structure Regarding Subjective Quality of Diffracted See-Through Images
(2017-08-01)
Qin, Zong
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Xie, Jing
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Lin, Fang-Cheng
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Huang, Yi-Pai
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Shieh, Han-Ping D.
Transparent displays utilizing transparent windows suffer from blurred see-through images caused by diffraction; however, current studies still rely on experiments with actual display panels and human observers to investigate see-through image quality. Moreover, the influence of pixel structure on subjective see-through image quality has not been clearly demonstrated. To improve the inefficient investigation methodology and quantitatively evaluate pixel structure, we first propose a simulation method for diffracted see-through images. Next, by testing six mainstream full-reference image quality assessment algorithms, multiscale structure similarity (MS-SSIM) is revealed to be the most suitable predictor of subjective image quality for our study. Based on public image databases, the influences of aperture ratio, resolution, and the geometry of the transparent window are evaluated by combining the proposed simulation method and MS-SSIM. As a result, an aperture ratio increase of 0.1 leads to a considerable increase of subjective image quality, as more than eight percentage points. Then, a resolution increase of 100PPI only leads to an approximately three percentage point decrease of image quality. Finally, little influence of the geometry of the transparent window is demonstrated. Additionally, physical reasons why these aspects of pixel structure perform in such a manner are also given.
High Ambient Contrast Ratio OLED Display with Microlens Array and Cruciform Black Matrices
(2015)
Qin, Zong
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Yeh, Yen-Wei
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Huang, Yi-Pai
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Shieh, Han-Ping David
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Lee, Kuo-Ch\'ang
Microlens array and cruciform black matrices were adopted to reduce ambient light reflection by 87.8% in OLED display for a 21mm by 21mm eye box while only 19.8% of reflective layer\'s area was occupied.
High-resolution and compact virtual mouse using lens arrays to capture finger images on light sensors
(2017-11-01)
Qin, Zong
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Chang, Yu-Cheng
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Su, Yu-Jie
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Huang, Yi-Pai
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Shieh, Han-Ping D.
To realize a finger positioning device, as called "virtual mouse," to replace a touchpad, touchscreen, or even real mouse, current positioning technologies cannot achieve a sufficient resolution, a compact volume, and a simple detection algorithm simultaneously. For this problem, using a light-emitting diode source, two lens arrays, and two light sensors, we design and implement a virtual mouse prototype. The optical architecture is carefully determined for a compact volume, a sufficient resolution, and a high detection accuracy. Corresponding to a compact system volume of 3.1 mm (thickness) x 4.5 mm (length) x 2, a theoretical resolution higher than 25 pixels per inch (ppi) can be obtained over a working area of 10 cm x 10 cm. Experiments are also implemented, in which a mean detection error of 0.24 cm that corresponds to approximately two distinguishable points, and a minimal resolution of 26 ppi over the whole working area are verified. If the system thickness is relaxed to 25 mm, a resolution higher than 200 ppi can be achieved. The proposed virtual mouse, which is simple enough and potential to be extended for three-dimensional position detection, can be integrated with a flat panel display to achieve a compact display application that can interact with users.
Hybrid light field head-mounted display using time-multiplexed liquid crystal lens array for resolution enhancement
(2019-01-21)
Chou, Ping-Yen
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Wu, Dui-Yi
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Huang, Shang-Hao
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Wang, Chun-Ping
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Qin, Zong
In recent years, head-mounted display technologies have greatly advanced. In order to overcome the accommodation-convergence conflict, light field displays reconstruct three-dimensional (3D) images with a focusing cue but sacrifice resolution. In this paper, a hybrid head-mounted display system that is based on a liquid crystal microlens array is proposed. By using a time-multiplexed method, the display signals can be divided into light field and two-dimensional (2D) modes to show comfortable 3D images with high resolution compensated by the 2D image. According to the experimental results, the prototype supports a 12.28 ppd resolution in the diagonal direction, which reaches 82% of the traditional virtual reality (VR) head-mounted display (HMD). (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Image content adaptive color breakup index for field sequential color displays using a dominant visual saliency method
(2018-02-01)
Qin, Zong
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Lin, Ying-Ju
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Lin, Fang-Cheng
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Kuo, Chia-Wei
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Lin, Ching-Huan
An index that can predict the perceptual visibility of color breakup for varying image content is valuable in field sequential color displays, whereas the current indices are usually for fixed patterns. To solve this problem, an image database containing 25 diverse reference images and 125 test cases with various color breakup visibility was first established. Next, visual experiments using a 240-Hz liquid crystal display were performed to acquire the subjective color breakup scores of the test cases. A theorem based on visual saliency theory was proposed that the color breakup perception is mainly determined by the image regions with visual saliency values higher than a certain threshold, called the dominant visual saliency regions. A computational model based on this theorem was developed to obtain objective color breakup scores of the test cases from retinal images with and without color breakup. An analysis of the objective and subjective results revealed a Pearson linear correlation coefficient as high as 0.82, which matches the top-level image quality assessment algorithms. Finally, the proposed color breakup index was used to benchmark against several mainstream field sequential color algorithms to determine their performances in color breakup suppression.
Image formation modeling and analysis of near-eye light field displays
(2019-04-01)
Qin, Zong
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Chou, Ping-Yen
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Wu, Jui-Yi
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Chen, Yu-Ting
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Huang, Cheng-Ting
Near-eye light field displays based on integral imaging through a microlens array provide attractive features like ultra-compact volume and freedom of the vergence-accommodation conflict to head-mounted displays with virtual or augmented reality functions. To enable optimal design and analysis of such systems, it is desirable to have a physical model that incorporates all factors that affect the image formation, including diffraction, aberration, defocusing, and pixel size. Therefore, in this study, using the fundamental Huygens-Fresnel principle and the Arizona eye model with adjustable accommodation, we develop an image formation model that can numerically calculate the retinal light field image with near-perfect accuracy, and experimentally verify it with a prototype system. Next, based on this model, the visual resolution is analyzed for different field of views (FOVs). As a result, a rapid resolution decay with respect to FOV caused by off-axis aberration is demonstrated. Finally, resolution variations as a function of image depth are analyzed based on systems with different central depth planes. Significantly, the resolution decay is revealed to plateau when the image depth is large enough, which is different from real-image type light field displays.
Long working range light field microscope with fast scanning multifocal liquid crystal microlens array
(2018-04-16)
Hsieh, Po-Yuan
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Chou, Ping-Yen
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Lin, Hsiu-An
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Chu, Chao-Yu
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Huang, Cheng-Ting
The light field microscope has the potential of recording the all information of biological specimens in real time with a conventional light source. To further extend the depth of field to broaden its applications, in this paper, we proposed a multifocal high-resistance liquid crystal microlens array instead of the fixed microlens array. The developed multifocal liquid crystal microlens array can provide high quality point spread function in multiple focal lengths. By adjusting the focal length of the liquid crystal microlens array sequentially, the total working range of the light field microscope can be much extended. Furthermore, in our proposed system, the intermediate image was placed in the virtual image space of the microlens array, where the condition of the lenslets numerical aperture was considerably smaller. Consequently, a thin-cell-gap liquid crystal microlens array, with fast response time can be implemented for time-multiplexed scanning. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Luminance enhancement without sacrificing the viewing angle in a direct-lit backlight by addressing the angle-dependent characteristic of the prism film
(2017-12-01)
Qin, Zong
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光電工程學系
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顯示科技研究所
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Department of Photonics
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Institute of Display
In a conventional backlight, suppression of light loss caused by the prism film(s) is desired to enhance the luminance without sacrificing the viewing angle. In this paper, in a direct-lit light-emitting diode (LED) backlight, where an LED array is placed under the display panel, the transmission efficiency against the prism film(s) is investigated for incident light with different zenith and azimuth incident angles. A strong angle-dependent characteristic is found, even when the reflective recycling effect is available. To address this angle-dependent characteristic in a direct-lit LED backlight, a freeform lens is designed to deflect the light emitted from an LED into the incident angle range with high transmission efficiency. Two design examples are implemented by adopting dual- and single-layer prism film(s). The simulation results show that the freeform lens can enhance the on-axis luminance by 26% and 35%, respectively, while the viewing angle remains nearly unchanged. Furthermore, using a single layer of prism film, a 19-in. direct-lit LED backlight module is constructed for experimental verification. By fabricating the freeform lenses and adding them to the backlight module, the on axis luminance is enhanced by 24%, and the viewing angle is decreased by no more than 2 degrees. Finally, the influence of the diffusers, which causes the experimental results to degrade slightly compared with the simulation results, is analyzed.
Maximal Acceptable Ghost Images for Designing a Legible Windshield-Type Vehicle Head-Up Display
(2017-12-01)
Qin, Zong
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Lin, Fang-Cheng
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Huang, Yi-Pai
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Shieh, Han-Ping D.
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光電工程學系
Windshield-type vehicle head-up displays (HUDs) are increasingly popular and stepping forward augmented reality; however, the windshield causes an annoying problem- ghost images. By now, the maximal extent of ghost images has not been determined for an HUD with an acceptable legibility. In this paper, to find the quantitative criterion of ghost images regarding subjective perceptions, we first design an HUD using a rotatable aspheric reflector and a wedge-glass windshield. Optical design of the HUD and experimental results of high-quality images are discussed. Next, eight different disparity angles between the primary and ghost images are controllably generated by rotating the aspheric reflector. Based on this HUD platform, human factor experiments utilizing a simulative automotive driving environment are conducted, in which the eight disparity angles are provided to 12 subjects under three ambient contrast ratios (ACRs). The human factor experiments demonstrate that the maximal disparity angles for an acceptable legibility under the ACRs of 3.90, 2.49, and 1.80 are 0.006 degrees , 0.017 degrees, and 0.024 degrees, respectively. These maximal acceptable disparity angles are important references for quantitatively and efficiently evaluating the optomechanical system of an HUD. In addition, they can help to make vehicle laws and regulations for HUDs.
Resolution-enhanced light field displays by recombining subpixels across elemental images
(2019-05-15)
Qin, Zong
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Chou, Ping-Yen
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Wu, Jui-Yi
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Huang, Cheng-Ting
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Huang, Yi-Pai
Light field displays based on integral imaging feature ultra-compact volume and freedom of the vergence-accommodation conflict for advanced virtual reality and augmented reality devices; however, they currently suffer from low visual resolution. Considering that subpixels have an intrinsically tripled resolution compared with triad pixels, this Letter develops a subpixel-level algorithm by recombining subpixels with relatively small raytracing errors from different elemental images. As a result, based on a highly accurate image formation model, the resolution of a typical system (pixel size, 7.8 mu m; system thickness, 4.07 mm) is remarkably enhanced from 8.3 to 20.0 pixels per degree, for a gain of 2.41. In addition, the color breakup introduced by the chromatic subpixels is largely suppressed. (C) 2019 Optical Society of America
Revelation and addressing of accommodation shifts in microlens array-based 3D near-eye light field displays
(2020-01-01)
Qin, Zong
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Wu, Jui-Yi
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Chou, Ping-Yen
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Chen, Yu-Ting
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Huang, Cheng-Ting
In a 3D near-eye light field display using microlens arraybased integral imaging, the accommodation response is presumed to exactly coincide with the reconstructed depth plane (RDP) which, however, has been little examined. By employing a highly accurate image formation model to analyze retinal images, the accommodation response is revealed to significantly shift towards the central depth plane (CDP) because of defocusing. The shift is quantitatively characterized for various CDPs and RDPs with a preliminary verifying experiment to provide content producers an approach to address the accommodation shift to fully mitigate the vergence-accommodation conflict. (C) 2019 Optical Society of America
See-Through Image Blurring of Transparent Organic Light-Emitting Diodes Display: Calculation Method Based on Diffraction and Analysis of Pixel Structures
(2016-11)
Qin, Zong
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Tsai, Yu-Hsiang
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Yeh, Yen-Wei
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Huang, Yi-Pai
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Shieh, Han-Ping David
In this paper, the issue of see-through image blurring of transparent organic light-emitting diodes display is demonstrated, and a systematic method is proposed to calculate blurred see-through image based on diffraction theory. In the calculation, distances of background object and the viewer are considered to correct Fresnel diffraction and chromatic image can be finally synthesized. Calculated and actually captured see-through images match well by using different background distances and pixel structures to verify, as error ratio of only 2.3% and 4.3%, respectively, in the term of blurred image\'s fringe length. Based on the calculation results, see-through image qualities corresponding to four pixel structures are evaluated and two structures are verified to have better image quality. Finally, higher resolutions that lead to much more significant see-through image blurring are discussed.