Appearance-based image splitting for HDR display systems

High dynamic range displays that incorporate two optically-coupled image planes have recently been developed. This dual image plane design requires that a given HDR input image be split into two complementary standard dynamic range components that drive the coupled systems, therefore there existing image splitting issue. In this research, two types of HDR display systems (hardcopy and softcopy HDR display) are constructed to facilitate the study of HDR image splitting algorithm for building HDR displays. A new HDR image splitting algorithm which incorporates iCAM06 image appearance model is proposed, seeking to create displayed HDR images that can provide better image quality. The new algorithm has potential to improve image details perception, colorfulness and better gamut utilization. Finally, the performance of the new iCAM06-based HDR image splitting algorithm is evaluated and compared with widely spread luminance square root algorithm through psychophysical studies

High dynamic range display systems

High contrast ratio (CR) enables a display system to faithfully reproduce the real objects. However, achieving high contrast, especially high ambient contrast (ACR), is a challenging task. In this dissertation, two display systems with high CR are discussed: high ACR augmented reality (AR) display and high dynamic range (HDR) display. For an AR display, we improved its ACR by incorporating a tunable transmittance liquid crystal (LC) film. The film has high tunable transmittance range, fast response time, and is fail-safe. To reduce the weight and size of a display system, we proposed a functional reflective polarizer, which can also help people with color vision deficiency. As for the HDR display, we improved all three aspects of the hardware requirements: contrast ratio, color gamut and bit-depth. By stacking two liquid crystal display (LCD) panels together, we have achieved CR over one million to one, 14-bit depth with 5V operation voltage, and pixel-by-pixel local dimming. To widen color gamut, both photoluminescent and electroluminescent quantum dots (QDs) have been investigated. Our analysis shows that with QD approach, it is possible to achieve over 90% of the Rec. 2020 color gamut for a HDR display. Another goal of an HDR display is to achieve the 12-bit perceptual quantizer (PQ) curve covering from 0 to 10,000 nits. Our experimental results indicate that this is difficult with a single LCD panel because of the sluggish response time. To overcome this challenge, we proposed a method to drive the light emitting diode (LED) backlight and the LCD panel simultaneously. Besides relatively fast response time, this approach can also mitigate the imaging noise. Finally yet importantly, we improved the display pipeline by using a HDR gamut mapping approach to display HDR contents adaptively based on display specifications. A psychophysical experiment was conducted to determine the display requirements

Evaluation of the color image and video processing chain and visual quality management for consumer systems

With the advent of novel digital display technologies, color processing is increasingly becoming a key aspect in consumer video applications. Today’s state-of-the-art displays require sophisticated color and image reproduction techniques in order to achieve larger screen size, higher luminance and higher resolution than ever before. However, from color science perspective, there are clearly opportunities for improvement in the color reproduction capabilities of various emerging and conventional display technologies. This research seeks to identify potential areas for improvement in color processing in a video processing chain. As part of this research, various processes involved in a typical video processing chain in consumer video applications were reviewed. Several published color and contrast enhancement algorithms were evaluated, and a novel algorithm was developed to enhance color and contrast in images and videos in an effective and coordinated manner. Further, a psychophysical technique was developed and implemented for performing visual evaluation of color image and consumer video quality. Based on the performance analysis and visual experiments involving various algorithms, guidelines were proposed for the development of an effective color and contrast enhancement method for images and video applications. It is hoped that the knowledge gained from this research will help build a better understanding of color processing and color quality management methods in consumer video

Gamut extension algorithm development and evaluation for the mapping of standard image content to wide-gamut displays

Wide-gamut display technology has provided an excellent opportunity to produce visually pleasing images, more so than in the past. However, through several studies, including Laird and Heynderick, 2008, it was shown that linearly mapping the standard sRGB content to the gamut boundary of a given wide-gamut display may not result in optimal results. Therefore, several algorithms were developed and evaluated for observer preference, including both linear and sigmoidal expansion algorithms, in an effort to define a single, versatile gamut expansion algorithm (GEA) that can be applied to current display technology and produce the most preferable images for observers. The outcome provided preference results from two displays, both of which resulted in large scene dependencies. However, the sigmoidal GEAs (SGEA) were competitive with the linear GEAs (LGEA), and in many cases, resulted in more pleasing reproductions. The SGEAs provide an excellent baseline, in which, with minor improvements, could be key to producing more impressive images on a wide-gamut display

Vertical Field Switching Blue Phase Liquid Crystals For Field Sequential Color Displays

Low power consumption is a critical requirement for all liquid crystal display (LCD) devices. A field sequential color (FSC) LCD was proposed by using red (R), green (G) and blue (B) LEDs and removing the lossy component of color filters which only transmits ~30% of the incoming white light. Without color filters, FSC LCDs exhibit a ~3X higher optical efficiency and 3X higher resolution density as compared to the conventional color filters-based LCDs. However, color breakup (CBU) is a most disturbing defect that degrades the image quality in FSC displays. CBU can be observed in stationary or moving images. It manifests in FSC LCDs when there is a relative speed between the images and observers’ eyes, and the observer will see the color splitting patterns or rainbow effect at the boundary between two different colors. In Chapter 2, we introduce a five-primary display by adding additional yellow(Y) and cyan(C) colors. From the analysis and simulations, five primaries can provide wide color gamut and meanwhile the white brightness is increased, as compared to the three-primary. Based on the five-primary theorem, we propose a method to reduce CBU of FSC LCDs by using RGBYC LEDs instead of RGB LEDs in the second section. Without increasing the sub-frame rate as three-primary LCDs, we can reduce the CBU by utilizing proper color sequence and weighting ratios. In addition, the color gamut achieves 140% NTSC and the white brightness increases by more than 13%, as compared to the three-primary FSC LCDs. Another strategy to suppress CBU is using higher field frequency, such as 540 Hz or even up to 1000 Hz. However, this approach needs liquid crystals with a very fast response time

차세대 액정 디스플레이용 광시야각 및 칼라구현 기술에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 이신두.In the past decades, liquid crystal display (LCDs) have been extensively studied for use in flat panel displays (FPDs) because of light weight panel, thin thickness and low power consumption. Due to their high contrast, uniform brightness, and rapid switching times compared to conventional cathode ray tubes, LCDs have achieved a significant position in the FPD industry. However, according to the development of other FPD technologies including organic light-emitting didoes, the enhancement of LCD performances such as wide-viewing angle and vivid coloration has been demanded. In this thesis, novel image generation technologies for high performance LCD are proposed. At first, for the reduction of the gamma distortion, wide-viewing technology was demonstrated by sophisticated multi-domain configuration in which liquid crystal (LC) molecules are aligned along different polar directions at middle gray scale. In order to realize the multi-domain LC cell, a new alignment layer which can control polar LC alignment properties including the pretilt angle and the anchoring energy was developed. Uncured hydrophobic oligomers in a cross-linked polymer mold were transferred onto a substrate to change the surface wettability of the substrate. The thermal-transfer printing, which is a contact-transfer printing method including an additional heat treatment process, accelerated the molecular diffusion of oligomers from the polymer mold onto the substrate, resulting in the increase of the amount of transferred oligomer. Consequently, the surface energy of the substrate was manipulated according to the heat treatment temperature during the thermal-transfer printing. Then, the LC alignment properties in both azimuthal and polar directions were measured through LC cell fabrication and electro-optical characterization. It was found that the polar pretilt angle and polar anchoring energy were changed in a wide-range, resulting from the adjustment of the substrate surface energy. Based on the results described above, the reduction of the gamma distortion through the multi-domain configuration in the vertical alignment (VA) mode was demonstrated. The oligomer layer was formed onto a conventional VA alignment layer to control the polar alignment properties. The ultra-violet ozone (UVO) treatment for the enhancement of the oligomer transfer onto hydrophobic substrates was added in the fabrication process. The surface energy and anchoring energy of the stacked alignment layers depending on the UVO treatment was examined. The anchoring disparity, which is the anchoring energy difference between sub-domains as a result of the oligomer layer patterning, induced the threshold voltage difference in the sub-domains and constructed the multi-domain at applied voltages. The experimental measurements for the assessment of the gamma distortion were performed in a conventional patterned VA mode cell and proposed multi-domain cell. Next, for the expansion of the color space, a new type of coloration technique based on the photo-luminescent emission of the quantum dots (QDs) in an organic polymer matrix was described. Recently, QD patterning technologies based on the polymer matrix have been extensively studied to accurately express the primary color in pixel units, but suffered from the non-uniform light emission owing to uneven distribution of the QDs in the polymer matrix. Reactive mesogen (RM), which is photo-curable, transparent, and soluble in organic solvents, was used for the fabrication of uniformly distributed QDs in the RM matrix. The emission characteristics of QD-RM composites depending on the concentration ratios of QD and RM were examined. In addition, color-separated patterns of QD-RM composites on a single substrate through conventional photo-lithography processes were demonstrated. Finally, a novel QD emissive LCD based on the color-separated pattern for high color purity was proposed. The proposed LCD consists of modulation part and emission part. LC cells acts as a role of electrically tunable lightwave retarder depending on the applied voltage. The transmitted light through the modulation part emits the photo-luminescent light from the color-separated QD pattern. The color purity and color gamut of the QD emissive LCD was measured in comparison with previous LCDs such as the color filter LCD and QD compensated LCD. In conclusion, the applicability of proposed image generation technologies to the FPD industry was explored. The new concepts and experimental results will lead to the development of the advanced LCD performance.Chapter 1 Introduction 1 1.1 Overview of Flat Panel Displays 1 1.2 Outline of Thesis 9 Chapter 2 Emerging Technologies of Liquid Crystal Display 13 2.1 Operating Principles of LCD 13 2.1.1 Properties of LCs 14 2.1.2 Main LCD modes 21 2.2 Wide-Viewing Angle Technologies 28 2.2.1 General description of viewing properties 28 2.2.2 Recent technologies for wide-viewing 35 2.3 Coloration Technologies 43 2.3.1 Coloration in flat panel displays 43 2.3.2 Recent technologies for wide color gamut 52 Chapter 3 Enhancement of Viewing Angle of LCD by Multi-Domain 65 3.1 Control of Molecular Alignment by Thermo-Transfer Printing 65 3.1.1 Introduction 66 3.1.2 Thermo-transfer printing for surface modification 67 3.1.3 Fabrication process 69 3.1.4 Experimental results and discussions 72 3.1.5 Summary 83 3.2 Wide-Viewing by Anchoring Disparity 85 3.2.1 Introduction 85 3.2.2 Anchoring disparity by thermo-transfer printing 86 3.2.3 Fabrication of 8-domains 95 3.2.4 Experimental results and discussions 98 3.2.5 Summary 100 Chapter 4 Novel Quantum Dot-Based LCD for High Color Purity 101 4.1 Color-Separated Pattern of QDs 101 4.1.1 Introduction 101 4.1.2 Fabrication of color-separated QD patterns 103 4.1.3 Experimental results and discussions 105 4.2 QD Emissive LCD 109 4.2.1 Device concept 109 4.2.2 Fabrication of QD-based LCD 110 4.2.3 Experimental result and discussions 111 4.2.4 Summary 118 Chapter 5 Concluding Remarks 119 Bibliography 123 Publication 135 국문 초록 141Docto

High-dynamic-range Foveated Near-eye Display System

Wearable near-eye display has found widespread applications in education, gaming, entertainment, engineering, military training, and healthcare, just to name a few. However, the visual experience provided by current near-eye displays still falls short to what we can perceive in the real world. Three major challenges remain to be overcome: 1) limited dynamic range in display brightness and contrast, 2) inadequate angular resolution, and 3) vergence-accommodation conflict (VAC) issue. This dissertation is devoted to addressing these three critical issues from both display panel development and optical system design viewpoints. A high-dynamic-range (HDR) display requires both high peak brightness and excellent dark state. In the second and third chapters, two mainstream display technologies, namely liquid crystal display (LCD) and organic light emitting diode (OLED), are investigated to extend their dynamic range. On one hand, LCD can easily boost its peak brightness to over 1000 nits, but it is challenging to lower the dark state to \u3c 0.01 nits. To achieve HDR, we propose to use a mini-LED local dimming backlight. Based on our simulations and subjective experiments, we establish practical guidelines to correlate the device contrast ratio, viewing distance, and required local dimming zone number. On the other hand, self-emissive OLED display exhibits a true dark state, but boosting its peak brightness would unavoidably cause compromised lifetime. We propose a systematic approach to enhance OLED\u27s optical efficiency while keeping indistinguishable angular color shift. These findings will shed new light to guide future HDR display designs. In Chapter four, in order to improve angular resolution, we demonstrate a multi-resolution foveated display system with two display panels and an optical combiner. The first display panel provides wide field of view for peripheral vision, while the second panel offers ultra-high resolution for the central fovea. By an optical minifying system, both 4x and 5x enhanced resolutions are demonstrated. In addition, a Pancharatnam-Berry phase deflector is applied to actively shift the high-resolution region, in order to enable eye-tracking function. The proposed design effectively reduces the pixelation and screen-door effect in near-eye displays. The VAC issue in stereoscopic displays is believed to be the main cause of visual discomfort and fatigue when wearing VR headsets. In Chapter five, we propose a novel polarization-multiplexing approach to achieve multiplane display. A polarization-sensitive Pancharatnam-Berry phase lens and a spatial polarization modulator are employed to simultaneously create two independent focal planes. This method enables generation of two image planes without the need of temporal multiplexing. Therefore, it can effectively reduce the frame rate by one-half. In Chapter six, we briefly summarize our major accomplishments