Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-11-13
2004-11-09
Tran, Henry N. (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S103000
Reexamination Certificate
active
06816142
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to liquid crystal display devices, and, more particularly, to a liquid crystal display device having a drive means for applying a voltage to each pixel of a liquid crystal display device, and an illumination light source.
The liquid crystal display device (hereinafter referred to as an LCD) produces a highly precise display and has characteristics such as a low consumed power, reduced volume for the display device, or the like. It is expected that liquid crystal display devices will entirely replace a cathode ray tube (hereinafter referred to as a CRT) in various usages, such as a computer monitor, a television display device, or the like. However, since the LCD does not have sufficient image quality in displaying a moving picture as compared with the CRT, improvement in the quality of the moving picture is desired. In particular, it is required that the moving picture can be displayed with a high image quality on the basis of the current television signal at the time of the application of the LCD to a television display device.
It is assumed that problems in the moving picture display of the LCD lie in the following points. In the beginning, in the case where a screen is displayed which shows a white object
50
moving against a black background in a direction of an arrow as shown in FIG.
20
(
a
), an “object blur” is generated in which a contour of an object
50
can be perceived in a blurred manner by an observer as shown in FIG.
20
(
b
). In addition, a “ghost” is also generated in which a residual image
51
of the object
50
before the movement can be perceived as shown in FIG.
20
(
c
).
One problem in such a moving picture display results from a long response time of the liquid crystal with respect to the signal. In the LCD of the twisted nematic type (hereinafter referred to as a TN type) and the super twisted nematic type (hereinafter referred to as a STN type) which are currently generally used, electro-optic response of the liquid crystal is relatively slow so that it takes a long time from the application of an electric field to the attainment of a desired light transmittance with the electrically changed arrangement of the liquid crystal molecule and is several times longer than 16.7 msec, which is a display cycle of one screen (hereinafter referred to as one frame) in a ordinary image signal. Consequently, as shown in
FIG. 21
, even when a voltage for a white display is applied to a liquid crystal which is providing a black display, a relatively long time is required until the liquid crystal attains a completely white state. Thus, an optical response of the liquid crystal at the moving potion is not completed in one frame period. A delay in the optical response of this liquid crystal is visually recognized as a motion blur and a ghost.
Furthermore, it is considered that the fact that displaying in the LCD is of a hold type, in which light emission of same amount continues until the LCD is rewritten by image signal of the next frame, results in a low display image quality with respect to the moving picture. In a thin film transistor type (hereinafter referred to as the TFT type) LCD which is mainstream among LCDs, electric charge for applying electric field to the liquid crystal can be held at a relatively high ratio until the electric field is subsequently applied. Consequently, as shown in FIG.
22
(
a
), each of the pixels of the LCD continuously transmits light until the pixel is rewritten with the application of the electric field on the basis of the image signal of the next frame. On the other hand, in the CRT display device which provides a display by scanning a screen with an electron beam to allow fluorescent material on the screen to emit light, as shown in FIG.
22
(
b
), light emission of each pixel is an impulse-like manner. Consequently, the LCD has a low time frequency characteristic of the image display light as compared with the CRT, so that the spatial frequency characteristic is lowered along with this to provide a blur in a visually observed image.
There is disclosed, for example, in the Japanese Unexamined Patent Publication No. 11-202285 an example in which a backlight is equipped with plurality of lamps and the lamps are sequentially driven in order to improve the image quality in the display of the moving picture of the LCD.
FIG. 23
is a block diagram showing a structure of such liquid crystal display device. A backlight
54
arranged on a rear surface of the liquid crystal panel is divided into a plurality of light emission regions
54
a
through
54
d
, so that a lamp
56
in each of the light emission regions
54
a
through
54
d
is allowed to be subsequently emitted with a lighting control circuit
60
while holding a definite time delay with respect to the operation of writing an image to the liquid crystal in a corresponding region.
FIG. 24
is a timing chart showing a relation between an optical response of the liquid crystal and the backlight emission in such liquid crystal display device. In
FIG. 24
, a signal for each pixel, an optical response of the liquid crystal in each pixel, and turn ON/OFF timing of the lamps in the backlight are shown.
In the beginning, at the previous frame, transmittance
64
of the pixel in the n-th row is rewritten from black, i.e., lower transmittance, to white, i.e., higher transmittance, by applying a voltage corresponding to a white signal. Immediately after rewriting, the transmittance
64
of the pixel increases rapidly and then increases gradually toward a truly white display, taking the time of several frames. In the subsequent frame, transmittance
65
of a pixel in the (n+I)-th row is rewritten from black to white with the same behavior as the pixel in n-th row in a delay of one frame period (about 16 msec).
At the same time, the backlight is lit only in a predetermined period after the lapse of a definite time from the rewriting of the image signal in each frame period as shown in the lower part of FIG.
24
. As a consequence, the halfway transition in the transmittance of the liquid crystal is not apparent to observers so that the image quality in displaying the moving picture is improved. Furthermore, the transmitted light of each pixel comes close to the impulse-like manner, so that the image quality in the moving picture display is improved.
However, in the conventional liquid crystal display which has been explained above, the motion blur is suppressed but the “ghost” cannot be sufficiently erased. As shown in FIG.
20
(
c
), the “ghost” appears as a difference in contrast between the region
52
which is rewritten from the black image to the white image and the region
53
which is rewritten from the white image to the white image. That is, since response of the liquid crystal is relatively slow, the region
52
recently rewritten to white is darker than the region
53
anciently rewritten to white. Although illumination by the backlight is limited to the end of each frame period, transmittance
64
of the liquid crystal in the region
52
which is rewritten from black to white and transmittance
66
of the liquid crystal in the region
53
which is rewritten from white to white are different even in this illuminating period as shown in
FIG. 24
because response time of the general TN-type liquid crystal is several times longer than the frame period. This luminance difference completely disappears several frames after the rewriting of image. Consequently, the “ghost” remains even when the lighting period of the backlight is restricted to the shortest possible level.
Furthermore, as has been already explained in
FIG. 21
, the response of the liquid crystal is relatively slow, so that several frame periods are required until the approximate completion of the response. For all this, in the conventional liquid crystal display device, a voltage is applied to the liquid crystal which produces a desired transmittance in the state in which a sufficient time passes and the response of the liquid crystal is approximately
Kobayashi Kazuhiro
Miyake Shiro
Murayama Keiichi
Oda Kyoichiro
Tahata Shin
LandOfFree
Liquid crystal display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3281645