Motion adaptive CODEC Feedforward Driving for LCD overdrive

Abstract— The authors have been developing a Feedforward Driving scheme as an overdrive technique to improve LCD response time. Focusing on the reduction of frame memory in overdrive in particular, they are now studying a memory‐reduction method by applying an image‐compression technique. An LSI has already been developed that incorporates a Compression Feedforward Driving unit, which successfully reduced image data to 1/3 by means of the image‐compression technique. This paper reports a study of Motion Adaptive CODEC Feedforward Driving in which a motion adaptation process is added to the CODEC section of the Compression Feedforward Driving unit. This motion adaptation process reduces the amount of errors in overdrive that are caused by memory reduction by using a circuit of the same scale as that for Compression Feedforward Driving.     

Reducing the memory of compression Feedforward driving for a new LCD controller

Abstract— The authors have studied a method of reducing the frame memory for signal processing used to improve the response time of liquid crystals. Compared with cases in which quantization is used, the compression Feedforward driving method, which reduces frame memory by applying an image‐compression technique, can effectively reduce the frame‐memory size. The study revealed that errors decrease by 6–10 dB or so if the image data was reduced to 1/3 by means of image compression. Based on the results of the study, the authors have developed a second‐generation LCD controller. With just one SDRAM unit, this LCD controller can produce almost ideal processing effects.     

Motion‐blur‐free LCD for high‐resolution virtual reality displays

A new liquid crystal display device with fast response time, high transmittance, and low voltage for virtual reality is reported. When driven at 90 Hz with 17% duty ratio, the motion picture response time is 1.5 ms, which is comparable with cathode‐ray tube, leading to indistinguishable motion blur. Moreover, this device enables high‐resolution density because only one thin‐film transistor per pixel is needed and it has a built‐in storage capacitor.     

Lapped transform‐based codec for frame‐memory reduction in super‐quality LCD overdrive

Abstract— Overdrive is commonly used to reduce the liquid‐crystal response time and motion blur in liquid‐crystal displays (LCDs). However, overdrive requires a large frame memory in order to store the previous frame for reference. In this paper, a lapped transform‐based codec (LTC) is proposed to reduce the frame memory needed for LCD overdrive. In the latest literature, a directional prediction‐based codec (DPC) employs eight directional predictions, which takes up a large percentage of the computational complexity of the codec and does not consider the de‐correlation of the inter‐blocks. Therefore, the LTC first uses the lapped transform to decompose the correlation of the inter‐blocks in the YUV color space. A hadamard transform is then used for energy compaction. The reordered coefficients are pre‐quantized and encoded using the proposed adaptive bit‐plane coding (ABPC) method for a simple hardware implementation. The simulation results show that the proposed LTC significantly improves the DPC in both subjective and objective performance and outperforms the block truncation coding (BTC) and adaptive multi‐level BTC (AM‐BTC), which have been described in the literature.     

A novel driving method for field sequential color using an OCB TFT‐LCD

We report a new technique for the design of field‐sequential‐color liquid‐crystal displays (FS‐LCDs), which maximizes the liquid‐crystal response,t_LC, by dividing the display area into as few sub‐areas,N, as possible. We obtained the following results: (1) ^tLC increased as N increased, although saturation tended to occur. Increasing N from 1 to 2 gave the largest increase in ^tLC. (2) ^tLC was maximized by dividing the display area unequally.     

A 23‐in. full‐panel‐resolution autostereoscopic LCD with a novel directional backlight system

Abstract— An autostereoscopic display that shows stereoscopic images with full‐panel resolution has been developed,¹ but it has a problem in terms of unit size. To resolve this problem, a new directional backlight system was developed, and it was applied to a prototype autostereoscopic LCD. The backlight system has two light sources — one for the right eye and the another for the left eye — and an elliptically shaped mirror that controls the direction of light from the light sources. The LCD uses a field‐sequential method which re‐writes an image for one eye and one for the other eye at a frame rate of 120 Hz, and the light sources alternately blink in synchronization with each frame so that the LCD shows full‐panel‐resolution stereoscopic images without flicker. In this paper, the new backlight system is described. The backlight system is effective for large screen such as 23 in. on the diagonal. By using this backlight system, the prototype LCD achieved practible unit size, brightness over the entire screen, and cross‐talk.     

HD motion‐picture evaluation method for overdrive technology in the frequency domain

Abstract— In this paper, the development of an advanced level‐adaptive overdrive (A‐LAO) method applicable to a full‐HD LC projector with 1.84 Mpixels, which reduced the gray‐level response time to less than 16 msec, is introduced. In addition, it is shown that a response of less than 8 msec can be achieved by combining the A‐LAO method with a frame interpolation method (120‐Hz refresh). A new motion‐picture evaluation method using frequency‐domain analysis, in other words, perceived bandwidth instead of the conventional time‐domain‐analysis response time evaluation, is reported.     

Guiding principles for high‐quality moving picture in LCD TVs

Abstract— The moving‐picture quality of several LCD modules was evaluated by using the quantitative parameter, normalized blurred edge width (N‐BEW), or the N‐BEW value normalized by time (N‐BET), measured and calculated by the developed time‐sequence‐image integration system which has taken LCD‐response characteristics and human‐vision characteristics into consideration. The quality of several LCD TVs is also discussed by using subjective evaluation and the unified quantitative parameter moving‐picture response time (MPRT), which is based on N‐BEW. According to the experimental and calculated results, it is clear that the value of N‐BET can express moving‐picture quality, which depends on the liquid‐crystal response time and the hold‐type character of LCDs. Also, it is confirmed that the value of MPRT can express the moving‐picture quality by comparison with subjective evaluation. The target values of MPRT and N‐BET for the motion‐blur‐less picture are deduced by extrapolating the subjective evaluation results. Then, guidelines to improve the moving picture quality are demonstrated.     

LCD motion‐blur estimation using different measurement methods

Abstract— The primary goal of this study was to find a measurement method for motion blur which is easy to carry out and gives results that can be reproduced from one lab to another. This method should be able to also take into account methods for reduction of motion blur such as backlight flashing. Two methods have been compared. The first method uses a high‐speed camera that permits us to directly picture the blurred‐edge profile. The second one exploits the mathematical analysis of the motion‐blur formation to construct the blurred‐edge profile from the temporal step response. Measurement results and method proposals are given and discussed.     

Advanced level‐adaptive overdrive (ALAO) method applicable to full‐HD LC TVs

Abstract— In this paper, we report on the development of an advanced level‐adaptive overdrive (ALAO) method applicable to full‐HD LC TVs, which makes it possible not only to reduce the gray‐level response time to less than one fourth, but also to improve the S/N ratio for still images by 10 dB; and further to reduce the circuit cost for the LAO method to almost half that of the prior LAO circuit. We have applied the ALAO method to a full‐HD LC front projector with 1.84 Mpixels and a screen size larger than 100 in., and we obtained high‐quality full‐HD moving images.     

A dual‐cell‐gap transflective liquid‐crystal display with identical response time in transmissive and reflective regions

Abstract— A dual‐cell‐gap transflective liquid‐crystal display (TR‐LCD) with identical response time in both the transmissive and reflective regions is demonstrated. In the transmissive region, strong anchoring energy is used to decrease the response time, while in the reflective region, weak anchoring energy is used to increase the response time. And overdrive voltage technology is adopted to make the response time identical in both the transmissive and reflective regions. The device structure and operating principle of the TR‐LCD was analyzed, the anchoring energy in the transmissive and reflective regions was designed, and the response time and electro‐optic characteristics of the TR‐LCD was calculated. The simulated dual‐cell‐gap TR‐LCD demonstrated good performances.     

Design and implementation of a wavelet‐based addressing technique (WAT)

Abstract— The design and implementation of a wavelet‐based addressing technique capable of displaying gray shades is presented. The hardware complexity of the display drivers has been reduced by adding a few analog multiplexers that are common to the drivers. The controller was implemented by using a low‐cost complex programmable logic device (CPLD) and it was demonstrated by displaying 16 gray shades in a liquid‐crystal display.     

Moving‐picture response time (MPRT) of LCDs for the oblique viewing direction

Abstract— The dynamic performance of displays is an important characteristic for multimedia applications. Motion‐picture response time (MPRT) has been used as an indicator of the dynamic performance of LCDs. This paper describes a comprehensive method of MPRT evaluation for the oblique viewing direction. By using a tilted camera configuration, the angular dependency of MPRT is investigated for the condition that the horizontally scrolling patterns are observed from the vertical direction. For each gray‐to‐gray transition, distinct changes in MPRT and the luminance profile of blur are observed.     

Fast‐response liquid‐crystal displays using crossed fringe fields

Abstract— A fast‐response and wide‐view liquid‐crystal display (LCD) using the crossed fringe‐field‐switching (CFFS) mode is proposed, where the fringe‐field electrodes exist on both the top and bottom substrates. The bottom fringe field is used to turn on the LC directors and the top fringe field is used to assist in the LC decay process. The decay time is reduced by ～2× compared to that of the conventional FFS mode between the full bright and dark states, and more than a 2× improvement is obtained for other gray‐scale transitions. This CFFS mode also preserves the wide‐view characteristics as the conventional FFS mode. Its applications to LCD TVs and monitors for reducing image blur are addressed.     

Moving‐image‐sticking phenomenon induced by an outside force in liquid‐crystal displays

Abstract— Image deformation caused by an outside force is observed to remain for hours at high gray levels for liquid‐crystal displays (LCDs) in the multi‐domain (MD) vertical‐alignment (VA) mode. This so‐called moving‐image‐sticking phenomenon demonstrated a non‐symmetric luminance profile for the left and right viewing direction for MDVA‐mode LCDs which have original symmetric viewing‐angle characteristics. The generation of a stable reverse‐tilt domain by an outside force was assumed to be the cause of this phenomenon, and the stability of a reverse‐tilt domain under an electric fringe field was calculated by changing the electric‐fringe‐field distribution which determines the LC tilt direction. The domain of a given tilt direction is calculated to change to other tilt direction induced by a fringe field at a low gray condition, but to remain unchanged at a high gray condition. This agrees with the observed trends of duration time of the moving‐image‐sticking phenomenon.     

Precise evaluation of LCD gray‐to‐gray response time based on a reference pattern synchronous measurement using high speed charge‐coupled device camera

A reference pattern method based on synchronous measurement for evaluating the response time of liquid crystal display was proposed to overcome the shortcomings of the unsmooth response curve induced by the backlight modulation. The feasibility of the method is verified by measurement using a high speed charge‐coupled device camera. The measured gray‐to‐gray response time results are compared with those obtained from standard measurement approach. The results indicate that the proposed method improves the accuracy and repeatability of the response time measurement.     

Analysis of the dependence of optical response time of liquid‐crystal displays on the viewing direction

Abstract— The optical response time of liquid‐crystal displays (LCDs) has recently been observed to be dependent on the viewing direction. For the vertically aligned LC mode, response time increased as the viewing angle increased when the final state is the zero gray level of the minimum luminance. This change in response time is analyzed to relate to the deformation of the normalized luminance curve of LCDs for different viewing directions. The dependency trends of the optical response time for the oblique direction can be estimated from the temporal luminance measurement data along the normal direction and the normalized luminance curve for oblique viewing directions.     

A 15‐in. XGA thresholdless antiferroelectric LCD addressed by TFTs and using the quasi‐dc driving method

Abstract— A 15‐in. TFT‐LCD with XGA resolution using thresholdless antiferroelectric liquid crystal (TLAF) has been developed. TLAF materials show V‐shaped switching and enable display of analog gray scale, wide viewing angle, and fast response. However, in the case that high‐resolution TFT‐LCDs using materials with large spontaneous polarization such as TLAF were driven by the conventional method, alternating current (ac) driving, the obtained contrast ratio was limited because of a sharp decline of holding voltage due to the growth of a depolarization field. In order to enhance the contrast ratio, a novel driving method referred to as quasi‐dc driving was proposed. In the quasi‐dc driving, the polarity of the applied voltage to liquid crystals inverts at certain intervals of several seconds. Moreover, the applied voltage and the charging time at the time of polarity inversion are increased more than the intended signals. By this method, the 15‐in. TFT‐LCD using TLAF with high contrast ratio (more than 100:1) and wide viewing angle was realized.     

Advanced monochrome gray‐scale TFT‐LCD using diamond‐like‐carbon/ion‐beam alignment technology

Abstract— A novel liquid‐crystal alignment method, diamond‐like carbon and ion beam alignment (DLC/IB) technology, was announced at the 2001 SID Symposium. And since December 2001, a new‐generation ion‐beam machine has been placed into the manufacturing line of IDTech. DLC/IB technology is mainly used for medical displays, which require a monochrome high‐density and super‐uniform display. We report on the latest developments of these advanced monochrome displays.     

Forward‐adaptive method for context‐based compression of large binary images

A method for compressing large binary images is proposed for applications where spatial access to the image is required. The proposed method is a two‐stage combination of forward‐adaptive modeling and backward‐adaptive context based compression with re‐initialization of statistics. The method improves compression performance significantly in comparison to a straightforward combination of JBIG and tiling. Only minor modifications to the QM‐coder are required, and therefore existing software implementations can be easily utilized. Technical details of the modifications are provided. Copyright © 1999 John Wiley & Sons, Ltd.