Fang-Cheng Lin

Dynamic Backlight Gamma on High Dynamic Range LCD TVs

A high dynamic range liquid crystal display (HDR-LCD) can enhance the contrast ratio of images by utilizing locally controlled dynamic backlight. We studied the HDR-LCD as a dual-panel display: a backlight module and a liquid crystal (LC) cell. As the gamma of the LC signal, the backlight module was also endowed with a gamma function to control the contrast ratio of HDR images. The inverse of a mapping function (IMF) method proposed as a dynamic gamma mapping curve for the backlight module, has been demonstrated to further improve in HDR image quality. By implementing the IMF method on a HDR-LCD TV with 88 backlight zones, the image contrast ratio can reach while maintaining high brightness, clear image detail, and an average power reduction of 30%.

A Field Sequential Color LCD Based on Color Fields Arrangement for Color Breakup and Flicker Reduction

The field sequential color (FSC) mechanism can effectively generate multi-primary color fields in temporal sequence to form a full-color image. Color breakup (CBU), however, has appeared intrinsically in conventional FSC displays to degrade visual qualities. A novel CBU suppression method, color fields arrangement (CFA), was proposed to eliminate the artifacts for FSC liquid crystal displays (LCDs). The modified order of consecutive color fields results in superimposed color images on a retina without CBU. Additionally, the 4-CFA method with a field rate of 240 Hz was found to avoid the flicker phenomenon on static images. The proposed method was successfully implemented on a 5.6-in optically compensated bend (OCB) LC panel. Our results confirm that the visibility of CBU artifacts can be reduced as the evaluation of dynamic and static models.

Color-breakup suppression and low-power consumption by using the Stencil-FSC method in field-sequential LCDs

— Field-sequential color (FSC) is a potential technique for low-power liquid-crystal displays (LCDs). However, it still experiences a serious visual artifact, color break-up (CBU), which degrades image quality. Consequently, the “Stencil Field-Sequential-Color (Stencil-FSC)” method, which applies local color-backlight-dimming technology at a 240-Hz field rate to FSC-LCDs, is proposed. Using the Stencil-FSC method not only suppressed CBU efficiently but also enhanced the image contrast ratio by using low average power consumption. After backlight signal optimization, the Stencil-FSC method was demonstrated on a 32-in. FSC-LCD and effectively suppressed the CBU, which resulted in more than a 27,000:1 dynamic contrast ratio and less than 40-W average power consumption.

Eco-Displays: The Color LCD's Without Color Filters and Polarizers

The higher and higher power consumption of LCD-TVs is accompanied by an increase in panel size. By eliminating two of the most power hungry optical components: color filters and polarizers, the stencil-field-sequential-color (Stencil-FSC) with RGBW-LED backlight is applied to LCDs with 120-240 Hz field rates to not only efficiently suppress color breakup but also yield an ultra-low average power consumption. The optical power consumption can be reduced to 13% compared to that of current FSC-LCDs. As a result, a 42-in LCD-TV may only require 9 W optical power consumption.

39.4: Inverse of Mapping Function (IMF) Method for Image Quality Enhancement of High Dynamic Range LCD TVs

A high dynamic range liquid crystal display (HDR-LCD) can much enhance the contrast ratio of the image on a locally controlled dynamic backlight. A novel method, inverse of mapping function (IMF), was demonstrated to further improve the HDR image quality from the information of each frame. By using the IMF method, the image contrast ratio in a 37” HDR-LCD TV was successfully improved to ~20,000:1 while maintaining high brightness and clear image details. Besides, for mass production purpose, the backlight of a 37” HDR-LCD TV was divide into 8×8 zones to reduce hardware computation complexity.

Color Filter-Less LCDs in Achieving High Contrast and Low Power Consumption by Stencil Field-Sequential-Color Method

The field-sequential-color liquid crystal display (FSC-LCD) without a color filter enables high light efficiency, wide color gamut, and low material cost. However, the visual defect of color breakup (CBU) is perceived when relative velocities exist between the screen image and the human eye. We proposed the Stencil-FSC method with a 240-Hz field rate to make CBU imperceptible. Given the Stencil-FSC method, the hardware parameters were optimized to reduce hardware complexity while maintaining sufficient suppression of CBU. After implementing Stencil-FSC on a 32-in FSC-LCD, the image contrast ratio was shown to be ten times more than that of a conventional CCFL LCD, and the average power consumption was reduced to less than 35 W-a 67% savings in power consumption.

Adaptive LC/BL Feedback Control in Field Sequential Color LCD Technique for Color Breakup Minimization

A full-color image on field sequential color (FSC) displays is composed of color fields in temporal sequence. With the FSC mechanism, color filters of liquid crystal displays (LCDs) can be removed to heighten the light efficiency and lower the material cost. Color breakup (CBU), however, has appeared intrinsically to degrade visual qualities. A novel gray level determination of liquid crystal and backlight (LC/BL) was proposed to suppress the CBU artifact on FSC-LCDs. Based on the image content in each frame, a dominated color-mixed field was found to minimize the color difference between the CBU and original image. Additionally, the feedback algorithm for the adaptive LC/BL signals was developed and implemented on a 32-inch optically compensated bend (OCB) mode LC panel. According to the evaluation of experiments and observations, the proposed method has been demonstrated to greatly suppress CBU in LCD applications.

Polychromatic SSVEP stimuli with subtle flickering adapted to brain-display interactions

OBJECTIVE Interactive displays armed with natural user interfaces (NUIs) will likely lead the next breakthrough in consumer electronics, and brain-computer interfaces (BCIs) are often regarded as the ultimate NUI-enabling machines to respond to human emotions and mental states. Steady-state visual evoked potentials (SSVEPs) are a commonly used BCI modality due to the ease of detection and high information transfer rates. However, the presence of flickering stimuli may cause user discomfort and can even induce migraines and seizures. With the aim of designing visual stimuli that can be embedded into video images, this study developed a novel approach to induce detectable SSVEPs using a composition of red/green/blue flickering lights. APPROACH Based on the opponent theory of colour vision, this study used 32 Hz/40 Hz rectangular red-green or red-blue LED light pulses with a 50% duty cycle, balanced/equal luminance and 0°/180° phase shifts as the stimulating light sources and tested their efficacy in producing SSVEP responses with high signal-to-noise ratios (SNRs) while reducing the perceived flickering sensation. MAIN RESULTS The empirical results from ten healthy subjects showed that dual-colour lights flickering at 32 Hz/40 Hz with a 50% duty cycle and 180° phase shift achieved a greater than 90% detection accuracy with little or no flickering sensation. SIGNIFICANCE As a first step in developing an embedded SSVEP stimulus in commercial displays, this study provides a foundation for developing a combination of three primary colour flickering backlights with adjustable luminance proportions to create a subtle flickering polychromatic light that can elicit SSVEPs at the basic flickering frequency.

Mechanism and Improvement of Charged-Particles Transition in Microcup Electrophoretic Displays

Electrophoretic display (EPD) is one of the most prominent technologies used in electronic paper. EPDs have good paper-like readability in ambient sunlight, and their bistability characteristics allow them to use very little power. To understand the physical mechanism at work in EPDs in terms of optical phenomena and current responses, we investigated EPD charging behavior using a transient current, an intermediate-state current, a discharge current, and a current bump. After establishing the microcup EPD model, we developed recommendations for a shortened transition time. As our experiments show, the method can reduce the transition time by 20%.

P‐40: A Visual Model of Color Break‐Up for Design Field‐Sequential LCDs

A model to evaluate the color break-up (CBU) of field-sequential color liquid crystal display (FSC-LCD) had been successfully established. In order to quantify the CBU, “Color Break-Up Angle (CBUA)” was proposed as the evaluation index. From the psychophysical experiments, the CBUA=0.22° was reported as the averaged threshold value for indistinguished color break-up. Consequently, the minimum frame rate could be derived from the model to suppress CBU in the various FSC-LCDs.