Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-04-13
2004-02-10
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S099000, C345S100000, C345S104000, C348S766000, C348S767000, C359S303000, C359S490020, C359S490020
Reexamination Certificate
active
06690346
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image display for displaying images with image shift by wobbling.
Japanese Patent Disclosure No. 6-324320 discloses an image display, which comprises a shifting means disposed on an optical path between a display element having a discrete pixel array and an observing position for shifting the optical axis of light emitted from the display element in predetermined directions. In this display, odd and even field images are successively written in the same pixel of the display element for display, and in synchronism to the fields the shifting means shifts the optical axis of light emitted from the display element in predetermined directions, that is, shifts the position of the projected pixel on the display surface of the display element, thus spatially separating the odd and even field images from one another. In this way, equivalent pixels are displayed on a pixel-free black matrix portion of the display surface, thus improving resolution.
FIG. 8
shows the construction of this prior art image display. The illustrated image display comprises a color liquid crystal panel (hereinafter referred to as LCD)
1
as a display element), having a backlight
1
a
and a color liquid crystal display element
1
b,
and a means including a polarization converting element
2
and a double refractor
3
disposed one in front of the other on the front surface side of the LCD
1
. The LCD
1
has, for instance, one half the scanning lines of the NTSC, and as shown in a fragmentary plan view in
FIG. 9
, has delta arrays of R, G and B pixels. In
FIG. 8
, a reduced number of, i.e., several, scan lines are shown for the sake of the clarity of the drawing.
As the polarization converting element
2
, a twist nematic liquid crystal shutter (hereinafter referred to as TN shutter) is usually used, which is relative inexpensive and is manufactured on the basis of an established technique. As shown in FIGS.
10
(
a
) and
10
(
b
), the TN shutter
2
includes a pair of polarizing members
6
having transparent electrodes
5
and a TN liquid crystal layer
7
sandwiched between the transparent electrodes
5
. An AC power source
9
is connected between the pair transparent electrodes
5
via a switch
8
. As shown in FIG.
10
(
a
), with an AC voltage applied across the TN liquid crystal layer
7
by turning on the switch
8
, the polarization of light incident on the polarization converting element
2
is transmitted without being rotated. As shown in FIG.
10
(
b
), with no AC voltage applied across the TN liquid crystal layer
7
by switching off the switch
8
, the polarization of the incident light is transmitted while it is rotated by 90 degrees.
The double reflector
3
is formed from an anisotropic crystal, such as rock crystal (&agr;-SiO
2
), lithium niobate (LiNbO
3
), rutile (TiO
2
), calcite (CaCo
3
), Chile nitre (NaNo
3
) and YVO
4
. As shown in
FIG. 11
, it transmits incident light of a first polarization as normal light, and transmits incident light of a second polarization at right angles to the first polarization as abnormal (shifted) light. Denoting the thickness of the double refractor
3
in z-axis direction perpendicular to xy coordinates of the display surface of the color LCD
1
, i.e., the direction of incidence of light beam by d and the angle of separation between the normal light and abnormal light by &thgr;, the normal and abnormal light beams emitted from the double reflector
3
are spatially separated by d×tan&thgr;.
Thus, with the crystallization axis
3
a
of the double refractor
3
set in a suitable direction, as shown in
FIG. 12
, by turning off the TN shutter
2
the polarized light is rotated in the TN shutter
2
by 90 degrees and transmitted therethrough as a second polarized light, and is then transmitted through the double refractor
3
as, for instance, abnormal light. In this way, as shown in
FIG. 13
, the pixels of the display surface of the color LCD
1
can be observed in black matrix positions which are obliquely upwardly and rightward from their original (non-shifted) position by substantially one half pixel pitch from the original pixel positions. As shown in
FIG. 14
, by turning on the TN shutter
2
the polarized light from the color LCD
1
is transmitted through the TN shutter
2
without being rotated but as the input first polarized light itself, and is transmitted through the double refractor
3
as normal light. In this case, the pixels of the display surface of the color LCD
1
can be observed in their original positions as shown in FIG.
9
.
In the prior art image display as shown in
FIG. 8
, the properties of the TN shutter
2
and the double refractor
3
are utilized such that, while odd and even field images of the input image signal are successively displayed on the same pixel of the color LCD
1
under control of an image display control circuit
11
, the voltage applied to the TN shutter
2
is on-off controlled fixedly by an TN shutter drive circuit
12
which constitutes a vibrating means. Thus, pixel shifting, i.e., changing of the pixel position observed through the double refractor
3
according to the direction of polarization of light transmitted through the TN shutter
2
, is obtained to improve the resolution. More specifically, in the odd field the TN shutter
2
is held “off”, and, as shown in
FIG. 15
, the observed pixel positions are shifted obliquely upwardly and rightward by substantially one half pixel pitch from the original pixel positions (the shifted pixel positions in this case being shown as Ro, Go and Bo). In the even field the TN shutter
2
is held “on”, and, as shown in
FIG. 16
, the original pixel positions are restored as the observed pixel positions (the pixel positions in this case being shown as Re, Ge and Be). It is thus possible to permit observation of images with double the pixel number of the color LCD
1
.
For the odd and even field images displayed on the color LCD
1
, the image signal is sampled at timings which are different from each other by a time corresponding to the extent of image shift. More specifically, when displaying the odd field images, the timing of sampling of the image signal is delayed to be behind the timing of when displaying the even field images by a time corresponding to substantially one half pixel pitch. Also, since the color LCD
1
holds the entire image on the display until it is re-written by the next field image, one of the pair electrodes of the TN shutter
2
is divided into a plurality of lines, for instance about
5
lines, while the other electrode is used as a common electrode. The voltage application is thus controlled by selecting the divided electrodes according to the timing of the line scanning of the color LCD
1
.
However, various experiments conducted by the inventor with the prior art image display adopting the pixel shifting technique described above, reveal that when the TN shutter
2
is on-off controlled fixedly at the same timings as those of switching of the odd and even field images displayed on the color LCD
1
, i.e., at an interval of {fraction (1/60)} second, sufficient resolution improvement can not be obtained due to influence of the response characteristic in the rotation of the polarized light from the TN shutter
2
.
FIGS.
17
(
a
) and
17
(
b
) are views for describing the response characteristics in the rotation of the polarized light in the TN shutter
2
. Specifically, FIG.
17
(
a
) shows the first polarized light transmittance, and FIG.
17
(
b
) shows the drive voltage. It is assumed that a high frequency voltage is applied as the drive voltage. The TN shutter
2
has a rise response time &tgr;
ON
when the drive voltage is turned on and a fall response time &tgr;
OFF
when the drive voltage is turned off. Denoting the maximum and minimum first polarized light transmittances of the TN shutter
2
by Tm and To, respectively, the rise response time &tgr;
ON
is represented by the sum of a rise delay time td
ON
from the instant when the drive voltage is tu
Abdulselam Abbas
Hjerpe Richard
Olympus Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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