Personal video viewing apparatus

A video display apparatus has a pair of displaying devices for displaying, by using television signals, images to be respectively viewed with left and right eyes; a pair of magnifying lenses for the left and right eyes; and a frame for supporting the displays and the magnifying lenses so that left and right virtual images formed by the magnifying lens, when images on the screens of the displays are viewed with the left and right eyes, coincide with each other. This video display apparatus enables stereoscopic vision by displaying video images on the displays on the basis of the principle of binocular parallax. half mirrors may be disposed between the magnifying lens and the eyes to enable images on the displays or the outside scenery to be selectively viewed. A shutter may also be provided between the half mirrors and the outside scenery to facilitate viewing of the displayed image.

BACKGROUND OF THE INVENTION 
This invention relates to a video display apparatus which is capable of 
magnifying the display on a video display terminal (VDT) operating with 
video signals and which enables stereoscopic vision of the displayed 
image. 
Ordinarily, video display apparatus represented by home TV receivers are 
used in such a manner that a VDT having a single screen is placed on the 
floor or a table and the image on the screen is viewed at a distance. 
Recently, lighter-weight and portable display apparatus such as a TV 
receiver having a liquid crystal display are becoming widely used. 
However, they are still based on the system of viewing one screen with two 
eyes. 
This type of conventional video disk play apparatus has some drawbacks, 
which are described below. 
1 The viewer will experience fatigue if he watches images on a stationary 
video display apparatus for a long time because he must fix his eyes on 
the apparatus and must generally maintain the same posture during viewing. 
The limited number of variations of posture which the viewer can maintain 
while keeping his eyes fixed on the stationary video display apparatus are 
usually unnatural and not easy to hold. 
2 In the case of a portable video display apparatus, it is possible to 
reduce this type of burden by changing the position of the apparatus. 
However, the number of positions where the video display apparatus can be 
placed is limited. If the viewer wishes to watch the screen while lying on 
his back, he must support the apparatus with his arm, resulting in fatigue 
of the arm. 
3 In general, portable video display apparatus have smaller screens because 
they need to be reduced in weight. It is therefore difficult to enjoy 
watching large and impressive images when using portable video display 
apparatus. 
4 Ordinarily, the space between the video display apparatus and the viewer 
is shared by him or her and other persons in the room. There is therefore 
a possibility of disturbing these other persons. It is also difficult to 
maintain secrecy of displayed images. 
SUMMARY OF THE INVENTION 
In view of these problems, an object of the present invention is to provide 
a video display apparatus based on a totally new system which enables 
stereoscopic image display by virtue of its specific structural features. 
To achieve this object, in accordance with the present invention, there is 
provided a video display apparatus having: left and right display devices 
for displaying images to be respectively seen with left and right eyes by 
using television signals; magnifying lenses for the left and right eyes; 
and a frame for supporting the display devices and the magnifying lenses 
so that left and right virtual images formed by the magnifying lens when 
images on the screens of the left and right display devices are viewed 
with the left and right eyes coincide with each other. 
The viewer can watch images on the large screen by wearing the 
above-described apparatus put on in association with his two eyes. During 
this viewing, variations of the posture of the viewer are not restricted 
and the secrecy of the images can be effectively maintained. 
The video display apparatus enables stereoscopic vision by displaying 
images on the left and right display devices by using left and right video 
signals formed on the basis of the principle of three-dimensional display 
relating to binocular parallax. The video display apparatus may be 
provided with at least one half mirror disposed between the magnifying 
lens and the eyes while the magnifying lenses and the display devices are 
disposed on the reflection side of the half mirror. The amounts of light 
transmitted through the display devices are changed or controlled in such 
a manner that images displayed on the display devices and the outside 
scenery seen through the half mirror can be viewed by being selected or by 
being simultaneously superposed on each other. A shutter may also be 
provided between the half mirror and the outside scenery in the direction 
of transmission through the half mirror. Even if the brightness on the 
outside is high as compared with the amount of light emitted from the 
display devices, it is possible to view the images displayed on the 
screens of the display devices alone by closing the shutter so as to shut 
off light transmitted through the half mirror.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described below in detail with reference to 
the accompanying drawings. 
FIG. 1 schematically shows the principle of a video display apparatus in 
accordance with the present invention. 
It is assumed here that two liquid crystal displays 1 and 2 display images 
on the basis of the same video signals. 
First, a right magnifying lens 4 is positioned between a right eye 6 and 
the liquid crystal display 2 for the right eye so that the distance 
between the liquid crystal display and the magnifying lens is u while the 
distance between the magnifying lens and the right eye is t. A virtual 
image 8 enlarged by the magnifying lens is formed on the screen of the 
liquid crystal display at distance D from the right eye. 
Similarly, a left magnifying lens 3 is positioned between a left eye 5 and 
the liquid crystal display 1 for the left eye so that the distance between 
the liquid crystal display and the magnifying lens is u while the distance 
between the magnifying lens and the left eye is t. A virtual image 7 
expanded by the magnifying lens is formed on the screen of the liquid 
crystal display at a distance D from the left eye. 
If the focal lengths of the left and right magnifying lenses is f, the 
following relationship is established between D, u, t and f from a lens 
formula: 
EQU 1/f=-1/(D-t)+1/u (1) 
If the multiplication factor of the magnifying lens is m, 
EQU m=(D-t)/u (2) 
The left and right eyes are distanced from each other by a distance de 
(ordinarily, 58 to 72 mm, 65 mm on average, or 62 mm on average in the 
case of Japanese). It is known that the distance between the two eyes is 
an important factor of a process of obtaining information on the object. 
If a person views an object located at the distance D from the eyes, he 
focuses the eyes to the distance D while effecting convergence by 
directing the optical axes of the eyes to the object. As focusing and 
convergence are effected in a linked relationship, a process of fusing 
images obtained through the two eyes is performed by the cerebrum without 
imposing any burden on the eyes. 
In a case where the centers of the frames on the liquid crystal displays 
are adjusted to the optical axes of the lenses as shown in FIG. 2(a), the 
convergence angle is 0.degree., that is, the eyes are converged to an 
infinite distance while the eyes are focused to the distance D, and there 
is an extremely high degree of nonconformity therebetween, resulting in 
unnatural perception. 
In a case where the optical axes of the lenses are converged as shown in 
FIG. 2(b), both focusing and adjustment of the convergence angle match the 
distance D, but the left and right images do not coincide with each other. 
If the frame size is large or if D is small, image fusion in the cerebrum 
is difficult, resulting in perception of a doubled image or visual field 
struggle. Even if image is effected suitably, certain burdens are imposed 
on the eyes. 
Then, a case where, as shown in FIG. 1, an imaging surface on which the 
enlarged left and right virtual images coincide with each other will be 
examined below. In this case, the optical axes of the left and right 
lenses are spaced apart from each other by de at the imaging surface also. 
Conversely, to establish this state, it is sufficient to adjust the axes 
of the lenses to points distanced from the centers of the frames on the 
liquid crystal displays outward in the horizontal direction by 
EQU de/2m=de u/2(D-t) 
The left and right liquid crystal displays and the left and right 
magnifying lenses are disposed so as to satisfy this condition, thereby 
enabling the viewer to see as if a large screen is placed at the position 
D from the eyes. For instance, when the centers of the frames on the 
liquid crystal displays are viewed, the left and right eyes are focused to 
the centers of the enlarged virtual images formed at the distance D from 
the eyes and are converged with an convergence angle of .theta.. In this 
state, focusing and convergence of the two eyes are smoothly effected in a 
linked relationship, and image fusion is effected in the cerebrum without 
imposing any burden on the eyes. 
Then, a case where two video signals obtained by imaging in the manners 
shown in FIGS. 3(a) and 3(b) are used to display on the left and right 
liquid crystal displays of the video display apparatus based on the system 
illustrated in FIG. 1. 
Objects Pa and Pb are provided, as shown in FIGS. 3(a) and 3(b). It is 
assumed here that there is a plane located at a distance D from the eyes 
as shown in FIG. 3(a), and that an image 7 is projected on this plane with 
respect to a reference point corresponding to the left eye. Similarly, an 
image 8 is formed on the plane with respect to a reference point 
corresponding to the right eye. Two convex lenses are provided in place of 
the eyes, and the images 7 and 8 are converted into video signals as a 
result of imaging on image pickup devices 9 and 10. 
These video signals are used to display left and right images in 
corresponding positions on the video display apparatus based on the system 
illustrated in FIG. 1. As a result, the objects Pa and Pb are displayed 
three-dimensionally as if they are actually located at the viewed 
positions. 
This is based on the principle of binocular parallax. The images of the 
objects are seen three-dimensionally due to the difference between the 
convergence angles at which the objects Pa and Pb are viewed. 
In a case where two left and right images projected on a plane located at a 
distance 2D from the eyes are viewed through the video display apparatus, 
the overall positional relationship is seen on a 1/2 scale. Thus, zooming 
of three-dimensional images can be effected. 
Thus, the video display apparatus in accordance with the present invention 
enables the viewer to see images on a large scale through the liquid 
crystal displays having small screens without experiencing fatigue of his 
eyes. Also, the apparatus enables stereoscopic vision. 
FIGS. 4(a) to 4(c) are a front view, a side view and a plan view, 
respectively, of a first embodiment of a video display apparatus of the 
present invention. 
A pair of liquid crystal displays 21 and a pair of magnifying lenses 22 are 
disposed in optical positions as indicated in FIG. 1 and are mounted on a 
main frame 23. A pair of white acrylic plates 24 are provided at the rear 
of the liquid crystal displays in order to enable the viewer to see the 
liquid crystal display with natural light. External light is introduced 
into the apparatus through these acrylic plates. 
Driving circuit boards 25 for driving the liquid crystals are mounted on 
upper and lower side portions of the main frame 23, and signal processing 
circuit boards 26 are mounted on left and right side portions of the main 
frame 23. 
Connection cables 27 are provided. In this embodiment, two video signal 
lines, a power supply line and a ground line are connected as the 
connection cables 27 to an external power adaptor (not shown) and to an 
external video apparatus (not shown). FIG. 5 shows a state in which the 
viewer has the video display apparatus on. 
The above-described embodiment apparatus can serve to achieve the object of 
the present invention. However, there is still room for improvements, as 
described below. 
1 Since the liquid crystal display uses external light, images on the 
display cannot be seen in the nighttime or in a dark place. 
2 The total weight of the liquid displays, the magnifying lenses and the 
circuit boards is received by the nose, and the degree of burden on the 
nose is therefore high. 
3 The viewer cannot see outside the display while wearing the display 
apparatus; he must take it off if he wishes to see the outside. 
The first problem can be solved by attaching a backlight to the 
above-described apparatus. However, the second problem may become more 
serious by the addition of the weight of this backlight. 
To cope with this problem, the apparatus may have the form of ski goggles 
instead of the illustrated form similar to spectacles. FIG. 6(a) shows a 
front view of an example of the apparatus in accordance with the present 
invention, and FIG. 6(b) shows a side view of the same when in use. This 
apparatus is worn so that its weight is distributed to the forehead, 
portions in the vicinity of the forehead, cheeks and so on, thereby 
solving the first and second problems. 
This goggle-like form is disadvantageous in terms of the third problem 
because it makes it more difficult to take off the display apparatus. 
Moreover, the backlight is disposed on a prolongation of each optical 
axis, and the dimension between the eyes and the front end of the main 
frame is thereby increased, which result is considerable in terms of 
safety. 
The above-described apparatus entails a problem relating to this in that 
the size of each liquid display is restricted because the optical axes of 
the lenses are located on parallel straight lines. 
It is possible to solve these problems by adopting a half mirror, as 
described below. 
FIGS. 7(a) and 7(b) are schematic diagrams of basic optical systems. In the 
example illustrated in FIG. 7(a), a half mirror 45 is disposed between an 
eye 43 and a magnifying lens 42 with a liquid display 41 and the 
magnifying lens 42 being disposed on the reflection side of the half 
mirror 45, while these components are maintained in the same optical 
positions as those shown in FIG. 1. The structure including the space 
between the liquid display 41 and the half mirror 45 is designed to 
prevent any external light from entering this space. The outside scenery 
can be viewed from the eye 43 during the time when reflection on the half 
mirror 45 is eliminated by turning off a backlight 44. 
During the time when the backlight 44 is turned on, the amount of 
reflection light from the half mirror is larger than the amount of 
external light transmitted from the outside through the half mirror 45, 
thereby enabling the screen of the display 41 to be seen from the eye 43. 
However, when the outside is extremely bright, images from the outside and 
the image on the screen are seen in a superposed state. To cope with this 
problem, a shutter may be disposed on a prolongation of the line of 
transmission through the half mirror, that is, between the half mirror 45 
and the outside. This shutter is closed to shut off any external light 
during viewing on the screen of the display 41. 
In the example illustrated in FIG. 7(a), the light from the screen is 
reflected on the half mirror 45 only one time, and the image perceived 
with the eye corresponds to an image obtained by inverting the image 
displayed on the screen of the liquid crystal display 41. For this reason, 
it is necessary to adopt special means in order to enable normal viewing, 
e.g., reversing the direction of the liquid crystal plate of the liquid 
crystal display or inverting the left and right by specific signal 
processing. 
FIG. 7(b) shows another example of the optical system in accordance with a 
further different embodiment of the present invention which is designed to 
use another mirror 46 in order to eliminate the above-described problems. 
A video display apparatus in accordance with this embodiment of FIG. 7(b) 
will be described below. FIGS. 8(a) and 8(b) are a plan view and a front 
view of this embodiment, respectively; FIG. 9 is a schematic diagram of a 
state in which the embodiment apparatus is put on; and FIG. 10 is a 
perspective view of main component parts of this embodiment. 
As illustrated in FIG. 10, the optical positions of the components are 
essentially the same as those shown in FIG. 1 and in FIG. 7(b). 
In this embodiment, however, half mirrors 54 or 56 are turned outwardly 
while maintaining the parallelism with the other half mirrors 56 or 54 so 
that the distance between the optical axes at the liquid crystal displays 
51 becomes larger than the distance between the eyes. 
In this embodiment, a liquid crystal shutter 55 is used as the shutter. A 
lock type switch 61 which is turned on or off each time it is depressed is 
provided to control a backlight 53 and the liquid crystal shutter 55. 
During the off state of the power supply, the liquid crystal shutter 55 is 
transparent and therefore allows the outside scenery to be seen from the 
eyes. 
During the on state of the power source, the liquid crystal shutter 55 is 
closed, and the backlight of each liquid crystal display 51 is lighted up, 
thereby enabling the screens of the liquid crystal displays 51 to be seen 
from the eyes. 
If the switch 61 is depressed, the backlight is extinguished and the liquid 
crystal shutter 55 becomes transparent, thereby enabling viewing of the 
outside. If the switch 61 is depressed again, the power on state is 
restored and the screens of the liquid crystal displays 51 become visible. 
This embodiment enables the total weight of the display apparatus to be 
supported mainly on the whole of the forehead, as shown in FIG. 9, thereby 
avoiding localization of the load. In addition, the front extreme end is 
not located on the prolongation of the eye optical path, thereby enabling 
the viewer to see the outside immediately when he wishes to do so. This 
function is preferable in terms of safety. 
In the above-described embodiments, the liquid crystals are employed. 
However, in accordance with the present invention, it is possible to use 
CRTs, plasma displays or other types of flat displays in place of the 
liquid displays. 
It is also possible to use three layers of liquid displays for each of the 
left and right display for the purpose of overcoming the problem of 
difficulty in increasing the number of picture elements of the liquid 
crystal display. 
FIG. 11 shows in section a still further embodiment of the present 
invention having three layers of liquid crystal displays. 
Electroluminescent elements 77 are used as backlights. Images 
corresponding to red (R), green (G) and blue (B) signals are displayed on 
three liquid crystal displays 71 to 73. Color filters 74 to 76 
corresponding to red, green and blue are provided. 
Unnecessary components of light emitted from the backlights are cut off by 
the color filters 74 to 76. The lights transmitted through the color 
filters, i.e., R, G and B lights are introduced into the corresponding 
liquid crystal plates. 
Images thereby displayed independently are superposed by a dichroic prism 
78 and are viewed through a magnifying lens 79 as a displayed color image. 
This arrangement enables an improvement in resolution because, if liquid 
crystal displays each having a hundred thousand picture elements are used, 
the resulting image can be displayed with three hundred thousand picture 
elements. 
FIG. 12 shows a schematic illustration of a used state of an example of 
application of this principle. In this example, a headset 85 is also 
provided integrally with the video display apparatus.