Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-02-01
2003-08-05
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S211000, C345S213000, C345S103000, C345S589000, C345S903000, C345S092000, C348S223100, C348S251000, C348S241000, C348S243000, C348S247000, C348S250000, C348S687000, C348S712000
Reexamination Certificate
active
06603452
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color shading correction device and a luminance shading correction device installed in a three-panel type or other multi-panel type LCD projector or a single-panel type LCD projector and, in particular, to a color shading correction device and a luminance shading correction device which can correct the luminance shading caused by uneven thickness of the liquid crystal layer (uneven gap) of the LCD panel and can correct the color shading caused by the luminance shading pattern on the LCD panels.
2. Description of the Related Art
Display devices using LCD screens are diffused recently. For example, pocket-type LCD TV sets, display units for laptop type computers and LCD projectors are in the market.
In particular, in response to the request for a compact and light-weight display unit with a large screen, LCD projectors using LCD panels are developed popularly. Since the LCD projector system can be provided with a large screen easily, it is expected to be used with the high definition TV. It is well known that the LCD projector uses LCD panels as light bulbs and displays the picture by irradiating the light from the light source and changing the transmission rate of the LCD panels in response to the video signal and displays the enlarged image of such picture on the screen using the optical system including the projection lens.
LCD projectors can be classified into the single-panel type using a single LCD panel and the three-panel type using three LCD panels. Single-panel type can be structured easily and at a low cost. However, when a color filter is adopted in a single-panel type for color display, the resolution tends to decline. This is why the three-panel type is often used. A three-panel type LCD projector uses three monochrome LCD panels of active matrix type, etc., having a switching device such as a thin film transistor (TFT) for each pixel.
The three-panel type LCD projector uses three LCD panels and once decomposes the light from the light source into three primary colors R (Red), G (Green) and B (Blue), which are respectively input to each of the LCD panels. Then, it synthesizes the three primary color lights after passing through each of the applicable LCD panels again so as to display the color picture.
Recently, the LCD data projector is drawing attention as a presentation tool used with a PC (Personal Computer). Considering the need of adaptation to various utilization environment, the three-panel structure as described above enabling bright screen and high resolution is suitable for such an LCD data projector.
Usually, the LCD panel used in the above LCD data projector uses an LCD driving circuit which amplifies the voltage of the input video signal to a necessary level and executes AC driving for a longer service life of the LCD.
FIG. 16
is a block diagram to illustrate an example of an LCD driving circuit used in such conventional three-panel type LCD data projector.
As shown in
FIG. 16
, an LCD data projector is, for example, provided with three active matrix type LCD panel sections
10
,
20
and
30
. Each of the LCD panel sections
10
,
20
and
30
comprises an LCD panel, a horizontal driving section (a sample/hold circuit and a horizontal driver circuit) and a vertical driving section (a vertical driver circuit) respectively.
The LCD panel section
10
forms the red (R) image, the LCD panel section
20
forms the green (G) image and the LCD panel section
30
forms the blue (B) image. R video signal (R signal) is supplied via an input terminal
11
, a video processing circuit
12
and an alternation circuit
13
to the LCD panel section
10
, G video signal (G signal) is supplied via an input terminal
21
, a video processing circuit
22
and an alternation circuit
23
to the LCD panel section
20
and B color video signal (B signal) is supplied via an input terminal
31
, a video processing circuit
32
and an alternation circuit
33
to the LCD panel section
30
. The clock pulse and various timing pulses required for displaying the color video signals are supplied from a timing circuit
40
.
The video processing circuits
12
,
22
and
32
are for clamping, amplification, and gamma correction of the input video signals R, G and B. The alternation circuits
13
,
23
and
33
reverse the polarity of the video signals R, G and B for every predetermined period or one line (i.e. one horizontal period), for example, with AC and DC voltages of the signal in order for AC driving of the LCD. This AC driving is executed for a longer service life of the LCD panel. This takes advantage of the theory that the transmission rate of the LCD panel is determined by the voltage difference between the common voltage E
1
, E
2
or E
3
and the video signal voltage of each color regardless of the video signal polarity for the common voltage. In other words, for the video signal of each color, the polarity is reversed around the DC level (Common voltage) E
1
, E
2
or E
3
at the pixel common electrodes (common terminals)
10
a,
20
a
and
30
a
of the LCD panel kept at +7.5 V, for example, with reference to 0V on the substrate. Thus, change in the average DC level caused by each color video signal on each LCD panel is canceled so that the LCD is always driven at a certain DC level and can be used for a longer service life. The timing circuit
40
generates from the horizontal (H) and vertical (V) sync signals input from the input terminal
41
, the alternating pulse fH for the alternation circuits
13
,
23
and
33
and the timing signal to drive the LCD panel sections
10
,
20
and
30
.
The LCD panel has a structure as shown in FIG.
17
and is provided with liquid crystal
100
enclosed between two glass substrates
101
and
102
. In a plan view, it has a structure as shown in FIG.
18
. It comprises pixels constituted by the liquid crystal, a thin film transistor (TFT) such as a field effect transistor (FET) provided for each pixel, a source line to supply the pixel signal sampled and held from the horizontal driving section to the source of the TFT, and a gate line to supply the scanning signal from the vertical driving section to the gate of the TFT.
In the liquid crystal structure as shown in
FIG. 17
, uneven thickness of the liquid crystal layer results in luminance shading. Referring to
FIGS. 19
to
21
, how the luminance shading is generated is described below.
FIG. 19
shows the change in brightness of the liquid crystal layer when the input voltage changes up to the common voltage as the maximum value with the horizontal axis representing the input voltage and the vertical axis representing the brightness (luminance) and with taking the input voltage at the vertical axis as the common voltage. This figure shows the normally black liquid crystal and the closer the input voltage is to the common voltage, the brighter the brightness becomes and the further it becomes from the common voltage, the brightness becomes darker. When the input voltage is close to the common voltage, the brightness becomes saturated (Brightness: 100%). Even with the same input voltage supplied to the source line, the brightness varies depending on the liquid crystal layer thickness. When the liquid crystal layer is thicker, the brightness becomes brighter and when the liquid crystal layer is thinner, the brightness becomes darker. This is called the luminance shading caused by uneven gap.
Further, in case of the three-panel type projector, any difference in pattern or position of the luminance shading generated on each of the LCD panels R, G and B may cause color shading in the synthesized color image. FIG.
20
(
a
) shows an example of the luminance shading on the LCD panel B which has brighter brightness at positions closer to the center of the screen and becomes darker at positions closer to the periphery in both of the horizontal and vertical directions. This is a typical generation pattern of luminance shading. On the other hand, FIG.
20
(
b
) shows an example of the luminance s
Hjerpe Richard
Pillsbury & Winthrop LLP
Zamani Ali
LandOfFree
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