Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-01-09
2004-09-21
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S089000
Reexamination Certificate
active
06795053
ABSTRACT:
TECHNICAL FIELD
The present invention relates to image display apparatuses and image display methods and, more particularly, to an image display apparatus and method using a passive light modulation device and dynamically adjusting contrast and light source brightness according to an input video signal. Further, the image display apparatus and method of the present invention improve light-emitting efficiency of the light source at the time of dynamically adjusting intensity (light amounts) thereof according to the input signal.
BACKGROUND ART
As well known, a large number of image display apparatuses are used as screen display apparatuses for a television receiver, computer, and the like. Among those, a passive light modulation type apparatus typified by a liquid crystal display apparatus, displays images on a passive light modulation part, which does not emit light by itself (liquid crystal panel, for example). Therefore, the screen of such apparatus look dim compared with display apparatuses of a light-emitting type such as CRTs. To cope with this, passive light modulation type image display apparatuses are generally provided with a light source (backlight, for example) which emits light from the rear side of a passive light modulation part therein to increase visual brightness of display screen. Accordingly, brightness of the light source can be adjusted in addition to general contrast adjustment, thereby improving visibility of displayed images.
The levels of contrast and light source are basically adjusted manually by a user and fixedly set. In the recent years, however, to make the images more visible, various methods have been suggested to achieve dynamic adjustment of contrast and intensity of a light source (hereinafter, referred to as light adjustment) according to an input video signal that varies with time.
Such conventional methods for dynamically adjusting contrast and light source are exemplarily disclosed in Japanese Patent Laid-Open Publication Nos. 5-127608 and 8-201812 titled “liquid crystal display apparatus”. In the conventional adjustment methods disclosed in these publications, a maximum brightness level (MAX) and a minimum brightness level (MIN) of an input video signal are detected. When a difference between the maximum brightness level and the minimum brightness level is large, contrast is reduced, and is increased when the difference is small. Further, in the conventional adjustment methods, an average brightness level (APL) of the input video signal is detected. When the average brightness level is higher than a predetermined reference brightness level, brightness of the light source is reduced, and is increased when lower. As such, the conventional adjustment methods aim to always achieve constant display brightness.
In the conventional adjustment methods disclosed in the above publications, however, contrast adjustment (i.e., signal amplitude control) and light source brightness adjustment are separately performed (that means there is no correlation between both adjustments). Accordingly, the above described conventional adjustment methods cannot provide sufficient effect in improvement of a sense of contrast.
The light source is mainly implemented by a fluorescence lamp in view of light-emitting efficiency. General characteristics of the fluorescence lamp is now described by referring to
FIG. 27
to FIG.
29
.
FIG. 27
is a diagram exemplarily showing a characteristic of a general fluorescence lamp, that is, a characteristic of lamp temperature to light emitting-efficiency.
FIG. 28
is a diagram exemplarily showing a characteristic of lamp tube current to lamp temperature. Note that
FIG. 28
shows a case where the fluorescence lamp is used as a back lamp, and shows a characteristic that the lamp temperature becomes 65° C. at current i
0
.
FIG. 29
is a diagram exemplarily showing a characteristic of lamp tube current to brightness.
First, as shown in
FIG. 27
, for the general fluorescence lamp in use, there exists a temperature at which its light-emitting efficiency reaches maximum due to vapor pressure of mercury inside the lamp tube (in the drawing, 65° C.). Next, as shown in
FIG. 28
, the general fluorescence lamp, due to heat produced by itself, shows such a relation that the lamp temperature is in proportion to the lamp tube current. According to the characteristics shown in FIG.
27
and
FIG. 28
, the efficiency of brightness adjustment (light-emitting efficiency) of the fluorescence lamp is resultantly declined in either case of the lamp tube current being larger or smaller than the current i
0
, as shown in FIG.
29
.
If taking this into consideration, the conventional adjustment methods as disclosed in the above publications are inevitably required to utilize a linear part of the characteristic shown in FIG.
29
. This is because the methods aim to achieve constant visual brightness (display brightness) by adjusting the intensity of the light source based on the detected average brightness level. Accordingly, in the conventional adjustment methods, the light source cannot be efficiently used (that is, the maximum brightness cannot be obtained).
Further, the life of the lamp used as the light source varies with lamp tube current and temperature. Therefore, in the conventional image display apparatuses that adjust the intensity of the light source brightness according to a video signal, such a problem has been existed that, if the video signal is uneven in its characteristic, a lamp tube current (drive current) of a large value flows in the tube for a long time, thereby shortening the lamp life.
Therefore, a first object of the present invention is to provide an image display apparatus and an image display method capable of visually improving a sense of contrast without increasing power consumption of a light source by carrying out contrast adjustment (signal amplitude control) and brightness adjustment of the light source such that they correlate.
A second object of the present invention is to provide an image display apparatus and an image display method capable of dynamically and optimally adjusting the intensity of the light source according to an input video signal by utilizing a range in the vicinity of a characteristic to maximize the light-emitting efficiency of the light source.
Further, a third object of the present invention is to provide an image display apparatus and an image display method capable of dynamically and optically adjusting the intensity of the light source according to an input video signal while securing the life of the light source required as a product.
DISCLOSURE OF THE INVENTION
To achieve the objects above, the present invention has the following aspects.
A first aspect of the present invention is directed to an image display apparatus and method for displaying a video signal to be inputted on a passive light modulation part including a light source as an image. In the present image display apparatus and method, an amplitude of the video signal is dynamically adjusted to become a predetermined amplitude value. Then, brightness of the light source is adjusted according to amplitude adjustment so that the image displayed on the passive light modulation part based on the video signal after amplitude adjustment does not vary visually from a predetermined level. As such, according to the present image display apparatus and method, brightness adjustment of the light source is carried out to have correlation between amplitude adjustment, thereby not varying the visual average brightness level. Thereby, a sense of contrast can be visually improved without increasing average power consumption of the light source.
In the present invention, an average brightness level of each frame in the input video signal is preferably used as the predetermined level. In the following second and third aspects, disclosed are image display apparatuses and methods adjusting amplitude and brightness of the light source by using the average brightness level as the predetermined level.
The second aspect of the present invention i
Arimoto Katsuyuki
Funamoto Taro
Kobayashi Takahiro
Machidori Wataru
Ota Yoshihito
Chang Kent
Sheng Tom
Wenderoth , Lind & Ponack, L.L.P.
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