Optics: image projectors – Distortion compensation
Reexamination Certificate
2000-06-08
2002-03-12
Dowling, William (Department: 2851)
Optics: image projectors
Distortion compensation
Reexamination Certificate
active
06354707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) projection system and, more particularly, to an LCD projection system in which an image formed on a screen with curvilinear distortion and/or field curvature due to distortion aberration and curvature aberration generated in an optical system of a projection lens unit is corrected.
2. Description of the Related Art
An LCD projection system, which is one type of image projection system for displaying an image, generates an image using an LCD as an image generating means, and magnifies and projects the generated image onto a screen via a projection lens unit. The LCD projection system makes it easy to adjust the size of a screen and exhibits superior color reproducibility so that it is widely used as a large (over 40 inches) multimedia display device for HDTVs or video conferences.
LCDs are divided into a dispersion type such as a polymer dispersed liquid crystal (PDLC), and a polarization type such as twisted nematic (TN), according to a liquid crystal mode, and into a transmission type and a reflection type according to a transmission mode or a reflection mode of a light beam forming an image. Also, an LCD projection system is divided into a one panel type and a three panel type according to the number of LCD panels.
Referring to
FIG. 1
, a conventional one panel reflection type LCD projection system includes a light source
110
for generating and emitting light, a glass rod
130
for mixing incident light emitted from the light source
110
to emit light having a uniform intensity profile, a focusing lens
131
, a collimating lens
132
, a polarization beam splitter
140
for altering the optical path of incident light by transmitting or reflecting the incident light according to its polarization component, an LCD device
150
for generating an image by selectively reflecting incident light, and a projection lens unit
160
for magnifying and projecting incident light onto a screen S.
The light source
110
consists of a lamp
111
for generating light and a reflection mirror
112
such as a parabolic mirror or an elliptical mirror for reflecting the light emitted from the lamp
111
and guiding the reflected light along a predetermined proceeding path.
Reference numeral
120
denotes a color wheel which is rotatably installed on the proceeding path of light emitted from the light source
110
. The color wheel
120
has red (R), green (G) and blue (B) color filters equally arranged on the surface thereof so that light of a particular color of the light emitted from the light source
110
is selectively transmitted.
The glass rod
130
mixes incident light by irregularly reflecting the light to emit light having a uniform intensity profile. The focusing lens
131
focuses and diverges the light passing through the glass rod
130
to enlarge the transmission width of the light. The collimating lens
132
collimates the diverging incident light to make a parallel beam.
The polarization beam splitter
140
is arranged on the optical path between the collimating lens
132
and the LCD device
150
. The polarization beam splitter
140
alters the proceeding path of incident light by transmitting or reflecting the incident light by a mirror surface
141
according to its polarization component (P polarization or S polarization). The light passing through the polarization beam splitter
140
is incident upon the LCD device
150
and reflected by the LCD device
150
with the polarization direction being rotated by 90°. The light reflected by the LCD device
150
is incident upon the polarization beam splitter
140
again and totally reflected by the mirror surface
141
. The totally reflected light passes through the projection lens unit
160
and is magnified and projected onto the screen S.
FIG. 2
shows an optical structure of a conventional one panel transmission type LCD projection system. Referring to the drawing, a transmission type LCD device
250
is arranged on the proceeding path of light. The LCD device
250
generates an image by selectively driving individual pixels to determine transmission of the light emitted from a light source
210
. Reference numerals L
1
, L
2
and L
3
denote optical lenses for forming a parallel light beam. Reference numeral M denotes a reflection mirror for altering the proceeding path of light so that the light proceeds toward a projection lens unit
260
and a screen S.
In the above LCD projection systems, optical aberration is usually generated when an image is formed on the screen S via the projection lens unit (
160
or
260
). That is, optical aberration such as curvilinear distortion or field curvature is generated.
As is well known, the distortion is generated by lens aberration, which refers to the focal distance at points near the optical axis and far from the optical axis being different. That is, with respect to an ideal state where no distortion is generated, such as an image surface
31
as shown in
FIG. 3A
, a positive (+) distortion image
32
(pin-cushion distortion), having concave sides as shown in
FIG. 3B
, or a negative (−) distortion image
33
(barrel distortion), having convex sides as shown in
FIG. 3C
are generated.
The positive (+) distortion image
32
, as shown in
FIG. 3D
, means that a square image generated by the flat type LCD device
150
(
250
) is distorted to positive (+) due to aberration of a lens
160
a
(
260
a
) and formed on the screen S by being distorted in a pin-cushion shape. The negative (−) distortion image
33
, as shown in
FIG. 3E
, means that a square image generated by the flat type LCD device
150
(
250
) is distorted to negative (−) due to aberration of a lens
160
b
(
260
b
) and formed on the screen S by being distorted in a barrel shape.
The above-mentioned curvature distortion is caused by lens aberration which forms an image to focus on a curved (concave or convex) surface with respect to a flat screen S, as shown in FIG.
4
. Due to the curvature distortion, a flat image generated by the flat type LCD device
150
(
250
) is formed as an image
34
in a state of field curvature.
FIG. 4
shows a case in which the surface of the image formed on the screen S is concave due to lens aberration. Although not shown in the drawing, the surface of the image may be formed on the screen S to be convex due to lens aberration. The curvature mentioned below includes both the concave and convex states.
In the conventional LCD projection system, the distortion and curvature are generated in combination in an actual projection lens unit optical system to make an image light having a plane shape generated by the flat type LCD device
150
(
250
) to be an image having the sides curved and simultaneously the surface curved (concave or convex). Finally, the image becomes a complexly distorted image.
Also, the projection lens unit
160
(
260
) generates chromatism according to the wavelength of incident light. Due to chromatism, a red ray, of which the wavelength is relatively longer than other rays incident in parallel on an optical lens (convex lens) of the projection lens unit
160
(
260
) is focused at a point beyond the focal distance of the optical lens (convex lens). A blue ray, of which the wavelength is relatively shorter than other rays incident in parallel on an optical lens (convex lens) of the projection lens unit
160
(
260
), is focused at a point located closer than the focal distance of the optical lens (convex lens). Thus, the red, green and blue color images formed by the LCD device are not formed to be the same size on the screen. In this case, differences in the magnification power of red, green and blue color images are generated so that mismatch among the red, green and blue color images gradually increases from the center to the periphery of the screen, lowering the quality of the image.
Thus, in the LCD projection system, the projection lens unit
160
(
260
) needs an optical configuration designed to perform an optima
Chin Dae-je
Jeon Kee-uk
Dowling William
Samsung Electronics Co,. Ltd.
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