We have developed a high performance OCB-III LCDs with dynamic backlight control technology having a high contrast ratio of 1,000,000:1 and a MPRT of 2.0ms with the 32 inch panel. With OCB-III driving, which is suitable for dynamic backlight control, we have realized a high contrast ratio without sacrificing its fast response time. IntroductionRecently, the needs for TFT-LCDs have been dramatically increasing, especially for TV applications. LCDs have numerous advantages including high resolution, low power consumption, light weight, and slim size. However, conventional LCDs such as TN have mainly three big subjects: narrow viewing angle, slow response time and low contrast ratio.At present, the subject of narrow viewing angle has mostly improved by adopting new LCD modes such as IPS, VA and OCB [1]. But the subjects of slow response and low contrast ratio are unsolved. Many companies have proposed these improvement means to address these subjects. For example, high frame ratio, Over-drive, OCB-mode are used to improve slow response time. Among these techniques, dynamic backlight control technology dramatically improves contrast ratio [2]. In this paper, we propose a new dynamic backlight control technology for high speed OCB mode. Conventional LCDThe contrast ratio of conventional LCDs has been improved by dynamic backlight control technology. However, this technology needs a very complex algorithm to prevent a flashing problem caused by a sudden image change. Figure.1 shows a concept of the flashing problem on a conventional LCD. The first frame is dark image with a gray ball, the second and third frame suddenly appear a bright big ball. As the conventional LCD's driving takes one frame for data addressing, the image of the first frame remains at the beginning of the second frame and mixes with the second image in the middle of the second frame. If the backlight brightness is changed at the beginning of the second frame, the flashed small ball appears for a moment, which results in a flashing problem. To avoid this problem, the dynamic backlight control of usual conventional LCD delays the changing point of backlight brightness.Figure2 shows a concept of a conventional LCD adopting dynamic backlight control technology. This backlight control system solves the flashing problem because backlight brightness changes after completing the second frame image. However, the brightness of a big ball image changes stepwise. This means that the response speed become slow in this system. Furthermore, this system needs the complex algorithm for adjusting the backlight brightness to variations of each image.

This paper proposes a wide gamut LCD using locally dimmable four‐primary‐color (4PC) LED backlight. Although the color gamut of LCDs has been improved in recent years, it is insufficient to reproduce all the colors in the real world. The objective of this paper is to propose a wide gamut LCD that reproduces all the colors in the real world while keeping the cost increases to a minimum. We evaluated the color gamut reproduced by LEDs of multiple primary colors and selected cyan as the optimal color to be added to the three primary colors to reproduce all the colors in the real world. Therefore, we designed an LED backlight consisting of an additional only‐cyan LED with three‐primary‐color LEDs and developed a prototype LCD with 4PC LED backlight. Furthermore, we developed a local dimming algorithm for the 4PC LED backlight. As a result, we confirmed that the prototype LCD with the 4PC LED backlight is able to cover almost all the colors in the real world and also able to display natural images with highly saturated colors by local dimming.

In regard to local dimming LCD, we defined a new objective function to evaluate reproducibility both at higher and lower luminance based on human vision characteristics and optical characteristics of backlight and LCP. And we developed a local dimming algorithm that can combine higher luminance reproducibility and low power consumption. P-57 / R. Nonaka 1314 • SID 11 DIGEST

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