Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-03-29
2004-09-14
Tran, Henry N. (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S088000, C345S089000, C345S690000, C348S268000, C348S687000
Reexamination Certificate
active
06791527
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a liquid crystal display apparatus using a liquid crystal device as a light value for use in flat-panel displays, projection displays, etc., and a driving method for the liquid crystal display apparatus.
A twisted nematic (TN) liquid crystal has widely been used conventionally as a material for flat-panel displays as described by M. Schadt and W. Helfrich, “Applied Physics Letters”, Vol. 18, No. 4 (Feb. 15, 1971), pp. 127-128. The TN liquid crystal is used in an active matrix-type liquid crystal device (panel) in combination with switching elements such as thin film transistors (TFTs). The active matrix-type liquid crystal device is free from a problem of cross-talk since each pixel is provided with a switching element and is produced with high productivity with respect to that having a size (diagonal length) of 10-17 in. with quick a progress of production technique in recent years.
However, the above-mentioned liquid crystal device using the TN liquid crystal has been accompanied with problems such as a slower response speed and a narrower viewing angle in order to well display clear motion (picture) images.
In order to solve the problems, various alignment modes including an optically compensated bend or birefringence (OCB) mode for improving a response speed, and In-Plain Switching mode and MVA (Multi-domain Vertical Alignment) mode for improving a viewing angle have been developed and proposed.
Further, in order to solve the problems of the conventional TN liquid crystal devices, a liquid crystal device using a chiral smectic liquid crystal exhibiting bistability has been proposed by Clark and Lagerwall (Japanese Laid-Open Application (JP-A) 56-107216, U.S. Pat. No. 4,367,924). As the liquid crystal exhibiting bistability, a ferroelectric liquid crystal having chiral smectic C phase (SmC*) or H phase (SmH*) is generally used. Such a ferroelectric liquid crystal provides a very quick response speed because it causes inversion switching of liquid crystal molecules based on their spontaneous polarizations. In addition, the ferroelectric liquid crystal assumes bistable state showing a memory characteristic.
In recent years, an anti-ferroelectric liquid crystal exhibiting tristable state has been proposed by (chandani, Takezoe et al. (“Japanese Journal of Applied Physics”, vol. 27 (1988), pp. L729-). The anti-ferroelectric liquid crystal also provides a very quick response speed similarly as in the ferroelectric liquid crystal.
As another type of the anti-ferroelectric liquid crystal, there has been recently proposed a chiral smectic liquid crystal providing a V-character shaped response characteristic (voltage-transmittance characteristic) which is advantageous for gradational image display and is free from hysteresis (e.g., “Japanese Journal of Applied Physics”, Vol. 36 (1997), pp. 3586-). Further, an active matrix-type liquid crystal device using such a chiral smectic liquid crystal providing the V-shaped voltage-transmittance characteristic has also been proposed (JP-A 9-50049).
As described above in order to provide a liquid crystal display apparatus with a high-speed responsiveness and a good gradational display characteristic, liquid crystal displays of the above-mentioned OCB-mode and anti-ferroelectric liquid crystal materials have been extensively researched and developed more popularly than ever.
Further, with the development of high-speed liquid crystal device, another color liquid crystal device (scheme) has been proposed.
Generally, a conventional color liquid crystal display apparatus (device) comprises a pair of substrates between which color filters of red (R), green (G) and blue (B) and a liquid crystal are disposed and includes a plurality of pixels each comprising a set of color pixels (sub-pixels) of R, G and B which transmittances are independently controllable. Specifically, the transmittances of the color pixels (R, G, B) are controlled for each color pixel at each corresponding portion of the liquid crystal or in combination with a pair of polarizers, thus ordinarily displaying color images according to the additive process of R, G and B. In that case, as a light source, a transmission-type backlight (unit) emitting white light or a reflection-type light source utilizing an external light may be applicable but their display principals of color space are identical to each other.
Such a color liquid crystal display apparatus is, however, accompanied with a lower efficiency of utilizing light. For example, a white color image is displayed based on the additive process of R, G and B by color-mixing ⅓ (as a wavelength region) of Red (red)-light flux, ⅓ of G (green)-light flux, and ⅓ of B (blue)-light flux, on the basis of light fluxes entering the R-color filters spatially occupying ⅓ of all the incident light. Accordingly, an efficiency of light utilization is merely ⅓ before the incident light enters the liquid crystal layer. This means that a larger power consumption is required of the backlight occupying a major part of all the power consumption of the liquid crystal display apparatus.
Further, for each pixel, three color pixels have to be driven independently. As a result, it becomes difficult to effect a pixel design with an increasing definition, thus lowering an opening rate leading to light utilization efficiency. In addition, from the viewpoint of production costs, the above-mentioned color liquid crystal display apparatus is required to use driver ICs and color filters each with larger bits which are constraint factors to the cost of the liquid crystal display apparatus, thus being disadvantageous.
In view of these circumstances, another type of a color liquid crystal display apparatus has been developed extensively. Particularly, a color liquid crystal display apparatus using a backlight-color switching system as described in JP-A 56-27198 has been actively studied. According to the backlight-color switching system, the color of illumination light (backlight) is switched within a time period of at most the flicker frequency and in synchronism therewith, a (light-)transmission state of the liquid crystal panel is controlled to realize color reproduction by using the spatial additive process. The switching system is also called a RGB field sequential display scheme or field sequential color scheme.
FIG. 6A
shows an embodiment of a light emission state at a pixel of a hold-type liquid crystal display apparatus and
FIG. 6B
shows an embodiment of a light emission state at a pixel of an impulse-type display apparatus.
Referring to
FIG. 6A
, most of the liquid crystal display apparatus, when a certain pixel is placed in a light emission (open) state, the pixel holds a relatively constant luminance until a subsequent field period (frame period), thus continuing display. On the other hand, in a CRT display of an impulse-type as shown in
FIG. 6B
, a change in light emission with time is caused instantaneously to provide a high luminance. As a result, at a certain pixel, an instantaneous light emission state is observed one time within one field. At that time, the light emission period varies depending on a characteristic and a resolution of the CRT used.
In the impulse-type liquid crystal display apparatus, when a display image in n-th frame period is changed to that in n+1-th frame period, a sufficient non-display period is ensured before and after the light emission for each frame, thus obtaining displayed data smoothly on the retina.
On the other hand, in the case of the hold type liquid crystal display apparatus, however, even when the liquid crystal device used has a quick response speed, a display image in n-th frame is continuously displayed immediately before the n-th frame period is changed to n+1-th frame, thus leading to blur at an image contour portion or a judder disturbance (such a phenomenon that movement of the image becomes jerky and is observed unnaturally).
Accordingly, although the image deterioration due to double
Mori Hideo
Yoshinaga Hideki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Henry N.
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