Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2002-03-18
2004-09-14
Bella, Matthew C. (Department: 2676)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S204000, C345S044000, C345S690000, C348S678000
Reexamination Certificate
active
06791566
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image display device.
BACKGROUND ART
Image display devices are generally categorized into two types—non-emissive type and emissive type. Non-emissive type devices have an external light source means and employ a display element which modulates the light from the light source means in order to display images. Examples include liquid crystal monitors, liquid crystal projectors, and the like. Emissive type devices do not have an external light source means but the display element itself emits light to display images. For example, CRTs, PDPs, FEDs, organic ELs, and the like fall under this type.
For these conventional image display devices, high luminance, high contrast, high resolution, and lower power consumption have been desired to improve the picture quality. Of these, luminance has the greatest influence on the viewer's perception of images and therefore is the most important parameter.
In view of this, various attempts have been made in the past to make luminance uniform over the display screen. Such attempts include, for example, in the case of non-emissive type devices, using the characteristics of the light source means, and in the case of the emissive type devices, varying video signal in an appropriate manner, in order to achieve more uniform display screen luminance.
Taking a liquid crystal display device as an example, a conventional technique for making the luminance uniform within the screen is discussed below. The liquid crystal display device comprises, as shown in
FIG. 32
, a liquid crystal display element
1901
, a backlight
1902
, and a driving means
1903
for the liquid crystal display element
1901
. The backlight
1902
comprises at least a light source
1904
, a transparent light guiding plate
1905
for supplying light from the light source to the liquid crystal display element
1901
, and a reflective cover
1906
for covering the light source. ON the back surface of the light guiding plate, a plurality of scattering microdots
1907
are formed numerously so that the luminance within the plane is controlled by the shapes and positions of the formed scattering microdots
1907
.
The light discharged from the light source
1904
enters from an end face of the light guiding plate
1905
and is transmitted inside the light guiding plate, repeating the total reflection. All or part of the light which has entered the scattering microdots
1907
changes traveling direction, and the light which is incident on the upper surface of the light guiding plate at an angel smaller than a critical angle is discharged as output light, entering the liquid crystal display element
1901
.
Accordingly, the distribution of scattering microdots on the back surface determines the luminance distribution in the screen; the conventional backlight
1902
has such a configuration that the areas of the dots are made greater from the peripheral portion of the screen towards the center portion and thereby the distribution of screen luminance is made 80% or greater such that uniform brightness is achieved.
For example, let us assume a case where light sources are horizontally disposed at end faces of the light guiding plate, the end faces being at the top and bottom of the screen. It has been known that, supposing the areas of the scattering microdots on the back surface are uniform over the entire screen, the luminance distribution is mostly formed in a vertical direction (along the y axis), resulting in a distribution in which a region including the center is dark, as shown in FIG.
33
. This is due to the fact that a large portion of the light is scattered in portions of the light guiding plate which are near the light source and is discharged therefrom.
In order to compensate such a luminance distribution, it has been suggested that the areas of the scattering microdots be varied such as to be proportional to the reciprocal of the luminance distribution obtained in the case when the areas of the scattering microdots are uniform over the entire area of the display screen. That is, the areas of the scattering microdots are varied in the vertical direction in the screen so that the scattering microdots nearer to the center have larger areas. Thereby, uniformity of the luminance within the screen can be increased to as high as 80% or higher.
Next, a case of an emissive type display is described as an example. In a emissive type, it has been suggested that non-uniformity in the display element itself be corrected. Specifically, in order to compensate the luminance variation between the pixels, luminance variation is compensated in each pixel by only the varied value.
Generally, a driving means of a display device comprises a video signal decoding means
2101
, a signal correcting means
2102
, and a display element interface means
2103
. The video signal decoding means
2102
serves the purpose of producing RGB color signals and horizontal and vertical synchronizing signals from ordinary NTSC signals.
The signal correcting means
2102
corrects each signal of R, G, and B and, essentially, corrects gray level characteristics in consideration of input-output characteristics of a display element
2104
. The display element interface means
2103
serves the purpose of adjusting the corrected signal to match a signal level of the display element.
The signal correcting means
2102
is provided primarily for the purpose of achieving good gray level characteristics; however, when the image display means
2104
has some factors leading to luminance variation, it additionally comprises a means for correcting luminance variation. For example, there are cases where luminance variation between pixels, for example, is caused by inaccuracy in the production of display elements. In such cases, to make luminance in the screen uniform, gray level characteristics is varied for each pixel so that the luminance is made uniform at a certain level. More specifically, the signal correcting means comprises, in the form of an integrated memory, a lookup table which defines a gray level characteristic for each of the pixels, and a table lookup is performed synchronized with the synchronizing signals, so that luminance is appropriately modulated.
As described above, in prior art display devices, various attempts have been made to make brightness uniform in the display screen.
In recent years, display screen sizes have been increased, and even for home use TVs, 20-inch or larger screens have been desired. However, conventional display devices have drawbacks in that power consumption considerably increases as screen sizes increase. When a given luminance is required, the amount of power consumed increases in proportion to the area. Moreover, when a higher resolution is required as display size increases, the area per each pixel becomes smaller and therefore efficiency generally reduces. For this reason, when larger screen sizes and higher resolutions are desired without changing the luminance, the amount of power consumed increases even further.
Thus, if the luminance in the display screen is kept uniform, an increase in power consumption is inevitable. In addition, simply reducing luminance may make it possible to suppress an increase in power consumption, but the image will appear dark to the viewer of the image.
DISCLOSURE OF THE INVENTION
It is therefore an object of a first aspect of the present invention to provide a display device which is capable of reducing power consumption while displaying images that can create the viewer impression of bright images. More specifically, in order to solve the foregoing and other problems, there is provided in accordance with the first aspect of the present invention a display device in which the luminance is gradually decreased from the center of the display screen towards the peripheral portion, and by making the luminance gradient less perceivable utilizing a certain type of optical illusion, a reduction in power consumption is achieved without impairing viewer perception of a bright image.
It is an object of a s
Asayama Junko
Komori Kazunori
Kuratomi Yasunori
Ogiwara Akifumi
Uemura Tsuyoshi
Bella Matthew C.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Sajous Wesner
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