A relatively small and low-cost system is provided for projecting a large and bright television image onto a screen. A miniature liquid crystal array is driven by video circuitry to produce a pattern of transparencies in the array corresponding to a television image. Light is directed against the rear surface of the array to illuminate it, while a projection lens lies in front of the array to project the image of the array onto a large screen. Grid lines in the liquid crystal array are eliminated by a spacial filter which comprises a negative of the Fourier transform of the grid

Liu, Hua-Kuang

English

NASA Technical Reports Server

111111 111ll IIIII 11111 11111 Il1 11111 11111 11111 11llil 111111111 
US005 161027A 
United States Patent I191 [i i]  Patent Number: 5,161,027 
Liu [451 Date of Patent: Nov. 3, 1992 
L54] LARGE AREA PROJECTION 
LIQUID-CRYSTAL VIDEO DISPLAY 
SYSTEM WITH INHERENT GRID PA’ITERN 
OPTICALLY REMOVED 
[75] Inventor: Hun-Kuang Liu, South Pasadena, 
Calif. 
[73] Assignee: The United States of America as 
represented by the Administrator, 
National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 632,408 
[22] Filed: Dec. 21, 1990 
Related US. Application Data 
[63] Continuation of Ser. No. 913,433, Sep. 30, 1986, aban- 
doned. 
[51] Int. Cl.5 ......................... H04N 5/74; HMN 9/31 
[52] U.S. C1. ...................................... 358/231; 358/61; 
358/232 
[58] Field of Search ............... 358/231, 230, 232, 236, 
358/241, 56, 59, 60, 63 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,666,881 5/1972 Stein .......... 358/230 
3,723,651 3/1973 G 
3,764,211 10/1973 Morse et ai. ............ 
3,895,866 11/1973 de Quervain 
4,202,010 5/1980 H 
4,299,447 11/1981 Soltan et ai. ........................ 350/334 
4,389,096 6/1983 Hori ... 
4,403,216 9/1983 Yokoi 
4.435,732 3/1984 Hyatt . 
4,461,541 7/1984 Duthie ........ ............ 358/88 
4,533,215 8/1985 Trias et al. ...................... 350/347 E 
4,769,712 9/1988 Polaert ................................ 358/231 
FOREIGN PATENT DOCUMENTS 
3291 VI985 Japan ................................... 358/231 
OTHER PUBLICATIONS 
Electronic Display, copyrighted 1979, Utley Intersci- 
ence. 
Facsimile Printer Utilizing Liquid Crystal Cells, J. 
Rults, The 1970 IDEA Symposium, Society For Infor- 
mation Display, May 1970, pp. 106-107. 
Liquid Crystal Matrix Display, by Bernard J. Lechner 
et al., Proceedings of the IEEE, vol. 59, No. 11, Nov. 
Projection Television, by Angus Robertson, Wireless 
World, Sep. 1976, pp. 47-52. 
Primaly Examiner-Tommy P. Chin 
Attorney, Agent, or Firm-John H. Kusmiss; Thomas H. 
Jones; Guy M. Miller 
A relatively small and low-cost system is provided for 
projecting a large and bright television image onto a 
screen. A minature liquid crystal array is driven by 
video circuitry to produce a pattern of transparencies in 
the array corresponding to a television image. Light is 
directed against the rear surface of the array to illumi- 
nate it, while a projection lens lies in front of the array 
to project the image of the array onto a large screen. 
Grid lines in the liquid crystal array are eliminated by a 
spacial filter which comprises a negative of the Fourier 
transform of the grid. 
1971, pp. 1566-1578. 
1571 ABSTRArn 
4 Claims, 1 Drawing Sheet 
20. 31 30 16 
24 22 26 I & f0  72 II 
https://ntrs.nasa.gov/search.jsp?R=19930004523 2020-03-24T07:23:15+00:00Z
U S .  Patent Nov. 3, 1992 
FIG. I 
5,161,027 
FIG.2 
40 i o  
FIG. 4 
64 
FI G .3 
FIG5 
a 9 
5,16 1,027 
1 
LARGE AREA PROJECI‘ION LIQUID-CRYSTAL 
VIDEO DISPLAY SYSTEM WITH INHERENT 
GRID PATTERN OPTICALLY REMOVED 
This application is a continuation of application Ser. 
No. 06/913,433, filed Sep. 30, 1986 now abandoned. 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract, and is sub- 
ject to the provisions of Public Law 96-517 (35 USC 
202) in which the Contractor has elected not to retain 
title. 
BACKGROUND OF THE INVENTION 
In video or television projection, a television image is 
projected on a large screen, to enable a large number of 
people to view the image without the necessity for 
building a large cathode ray tube. Presently available 2o 
projection television systems are expensive. A projec- 
tion system for displaying television or computer- 
generated images, which could be constructed at low 
cost, using available off-the-shelf parts or using avail- 
able technology with only slight modification, would be 
of considerable value: 
SUMMARY OF THE INVENTION 
z low-cost system is provided for projecting television 
images onto a screen. The system includes a liquid crys- 
tal array containing a multiplicity of pixels that can each 
be energized to control its transparency. The array is 
energized by a video signal generating circuit, to ener- 35 
gize the pixels in patterns of transparencies representing 
images. A light source directs light against the rearward 
side of the liquid crystal array, while a projection lens 
lying on the forward side of the array focuses an image 
25 
In accordance with one embodiment of the invention, 3o 
L 
FIG. 4 is a partial elevation view of the array of FIG. 
FIG. 5 is a simplified front elevation view of the 
3. 
spatial filter of FIG. 1. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
FIG. 1 illustrates a system 10 for projecting a large 
television image 12 onto a large screen 14. The system 
includes a liquid crystal array 16 which is driven by a 
video drive circuit 18 to produce transparent areas on 
the array 16 that correspond to a television image. A 
light source 20, which includes a lamp 22, reflector 24, 
and concentrating lens 26, directs light against a rear- 
ward side 30 of the array, to substantially uniformly 
illuminate the array. An infrared filter 31 helps protect 
the array from excessive heating. A projection lens 32, 
which is located forward of the array, focuses an h a g e  
of the array 16 onto the screen 14. 
The array 16 and video circuit 18 are parts of a com- 
mercially available miniature or “pocket TV” television 
set. One example is the Radio Shack LCTV Realistic 
Pocketvision which has a 5.4 cmx4.4 cm screen con- 
taining 146 rows and 120 columns of liquid crystal pix- 
els, each being a square which is 370 um on each side. 
This miniature television set also includes circuitry 
including a receiver for receiving broadcast television 
signals and a video drive circuit for driving the array. 
The set, as originally manufactured, is intended for use 
by a person directly viewing the array while ambient 
light illuminates the rear of the array. Applicant uses 
this small array to create a large video image suitable 
for viewing by many people, by projecting very bright 
light through the array and forming a large projected 
image of the array onto a screen. 
FIG. 2 illustrates a projection system which uses the 
light source 36 and uroiection lens 40 of a Carousel or 
of the array onto the screen. 
A miniature liquid crystal array of a miniature televi- 
sion set, can be used, with the television video signal 
generating circuit of the miniature television set used to 
dnJe the array. It is possible to place the liquid crystal 
array in a slide or transparency projector, to project a 
television image onto a screen. 
The largely opaque grid lines of a liquid crystal array 
can be eliminated by use of a spatial filter. The spatial 
filter is a negative of a Fourier transform of the grid 
lines. The projection lens forms an image of the array at 
an intermediate image location lying between the pro- 
jection lens and the screen, and the spatial filter is lo- 
cated at that intermediate location. 
The novel features of the invention are set forth with 
particularity in the appended claims. The invention will 
be best understood from the following description when 
read in conjunction with the accompanying drawings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a simplified side elevation view of a televi- 
sior. image projecting system constructed in accordance 
with the present invention. 
FIG. 2 is a perspective view of a slide projector, 
modified to project a television image. 
FIG. 3 is an enlarged sectional view of a portion of he 65 tion Green. 
liquid crystal array of the system of FIG. 1, this view 
being of a portion of the system which is known in the 
prior art. 
The images projected in a manner described above 
have not been satisfactory, because they have suffered 
from the presence of a dark grid which is superimposed 
other type slide projector 42 to project an image of the 
liquid crystal array 16 onto a screen. Where the array 16 
40 is of about the same size as that of a slide which can be 
projected, the array is placed at a projection location or 
film gate 44 of the slide projector, where slides are 
normally placed. Apparatus at the location 44 may have 
to be altered to accept a particular liquid crystal array 
45 that may be thicker and have a greater width or height 
than a slide which includes a cardboard holder and a 
positive photograph. The video circuitry 18 lies outside 
the slide projector but is connected to the array by a 
flexible ribbon-type cable. In this way, an available slide 
50 projector can be used, with small modifications, to 
project a large and bright television image onto a 
screen. Applicant has used an overhead slide projector, 
sometimes referred to as an overhead projector, of the 
type which has a horizontal surface on which slides or 
55 transparencies are laid, to project a large and bright 
television image onto the screen where the images of 
transparencies are otherwise projected. 
Those pixels of the above TV set which are energized 
to become relatively opaque, have been found to trans- 
60 mit a small but appreciable amount of light, 80 the 
brightness of light should be limited to avoid “wash 
out.” Contrast ratios of 10:l to 201 are achieved with 
brightness levels about equal to that achieved using 
CRT projection systems that project onto a rear projec- 
3 
5,16 1.027 
on the projected image. FIG. 3 illustrates some details 
of one liquid crystal array, which includes such a grid. 
The array includes a layer 50 of liquid crystal material 
smdwiched between a pair of glass plates 52, 54 which 
are, in turn, sandwiched between a pair of polarizer 
sheets 56, 58. The glass plates bear conductors 60, 62 
that extend in perpendicular directions. When no volt- 
age is applied between wires 61, 63 connected to the 
conductors, the pixel is energized at zero voltage, and 
the area of the array at the crossing becomes transpar- 
ent. The crossing of a pair of conductors 60,62 forms a 
pixel such as indicated at 64 in FIG. 4. While all of the 
layers are largely transparent (in that about one-half of 
incident light passes through for a black and white TV), 
the conductors 60, 62 are substantially opaque. These 
opaque grid lines, which are about 1/1,OOOth inch wide 
in the above TV set, become noticeable when a large 
bright image of the array is projected onto a screen. 
Applicant eliminates the grid pattern by using a spa- 
tial filter such as shown at 70 in FIG. 1. The spatial filter 
70 forms a pattern of light and dark areas substantially 
representing the Fourier transform of the grid pattern 
66 of the array. The filter 70 is placed at an intermediate 
image location 72 where the projection lens forms a 
Fourier transform of the array, the intermediate image 
location 72 being located between the projection lens 
and the screen. If the light passing through the array is 
ccllimated, the location 72 is a distance from lens 32 
equal to its focal length. FIG. 5 indicates the overall 
view of the spatial filter 70, showing that it contains 
numerous opaque areas 74 representing the negative of 
substantially a Fourier transform of the grid. The filter 
70 can be constructed using the system of FIG. 1 by 
placing an unexposed film 90, which may include a 
plastic or glass plate with a photosensitive emulsion 
thereon, at the location 72 (but with no filter 70 thereat). 
The array is operated so all pixels are transparent (as by 
nc! applying any image in formation, and light from the 
Source 20 is allowed to expose the film. If the emulsion 
crl the film 90 is a negative type so that after developing 
it, bright spots appear dark and vice versa, then the 
developed film 90 (and copies of it) can be used as a 
spatial filter. If the emulsion on film 90 is a positive, then 
a negative of it is used. It may be noted that if the light 
8@ which passes through the array 16 is collimated, then 
the spatial filter 70 will be a Fourier transform of the 
grid. 
The pixels of the liquid crystal array 16 are address- 
able to control the transparency of individual pixels or 
lines of pixels. While the means for generating video 
signals representing images that energize the pixels, can 
include a television broadcast receiver or video camera, 
it is also possible to use a computer to generate images 
thar are locally produced (not broadcast) and that do 
not represent only an actual scene. While applicant has 
projected monochrome or black-and-white images, 
color images can be displayed by the use of a color- 
transmitting liquid crystal array where each pixel may 
transmit only one color (e.g., blue, red, or green) and 
the array is illuminated with white light. 
Thus, the system provides an economical system for 
producing a large bright projection television image 
4 
tially opaque lines, these are eliminated by using a spa- 
tial filter representing a negative of largely the Fourier 
transform of the grid. 
Although particular embodiments of the invention 
5 have been described and illustrated herein, it is recog- 
nized that modifications and variations may readily 
occur to those skilled in the art, and consequently, it is 
intended that the claims be interpreted to cover such 
modifications and equivalents. 
What is claimed is: 
1. A system for projecting video images on a screen, 
comDrisina: 
I5 
20 
25 
30 
35 
a iiquigcrystal array containing a multiplicity of 
pixels arranged in a multiplicity of rows and col- 
umns, and including a multiplicity of largely 
opaque row and column conductors extending 
along said rows and columns and forming a grid, 
each pixel being energizable to control its transpar- 
ency, said array having rearward and forward 
sides; 
means for generating video signals representing said 
video images, said generating means connected to 
said array to energize said pixels in patterns of 
opacities and transparencies representing said 
video images; 
a light source which directs light against said rear- 
ward side of said array to pass in a forward direc- 
. tion to said screen through transparent pixels 
thereof; 
a projecting lens lying forward of said array, said lens 
constructed to focus said video images of said pat- 
terns of opacities and transparencies onto said 
screen, and to focus an image of light passing 
through said array at an intermediate plane be- 
tween said lens and said screen; and 
a spatial filter lying at said intermediate plane, said 
spatial filter forming a pattern of light and dark 
areas representing largely a Fourier transform of 
said grid in said liquid crystal array. 
2. The system described in claim 1 wherein said spa- 
40 tial filter comprises a plurality of opaque dots arranged 
3. A method for projecting television scenes onto a 
passing light through a liquid crystal array to said 
screen, said liquid crystal array having a multiplic- 
ity of pixels that are each energizable to control its 
transparency by selective energization of a control 
grid comprised of a multiplicity of largely opaque 
conductors lying in said array and forming an 
opaque grid pattern in said light passed through 
said liquid crystal onto said screen; 
energizing said array with video signals representing 
said television Scenes to produce patterns of 
. opaque and transparent pixels representing said 
television scenes; 
forming a projected image of light passing through 
said array on said screen using a projecting lens at 
an intermediate location between said array and 
said screen. and 
in rows and columns. 
screen comprising: 
45 
50 
55 
I placing a spatial fdter forming a pattern of light and 
onto a screen, and a lowcost method for producing a dark areas r e p r m n k g  largely a Fourier transform 
large bright image from a small LCD (liquid crystal of said opaque grid pattern at said intermediate 
display) television. The rear of the liquid crystal array is location. 
illuminated by a bright light, and a projection lens in 4. The method described in claim 1 wherein said step 
front of the array focuses an image of the array onto a of placing said spatial filter includes forming said spatial 
screen. The area of the image on the screen is preferably 65 filter so it represents light and dark areas that are a 
at least one order of magnitude larger than that of the negative of.said video image at said intermediate loca- 
display, and preferably two orders magnitude (100 tion when said pixels are transparent. 
times as great). Where the array has a grid of substan- * * * * *  


Large area projection liquid-crystal video display system with inherent grid pattern optically removed

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server