Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTIO_
Field of the Invention
The present invention relates to stereoscopic image
viewing devices, and, in particular, is directed to stereo-
scopic image viewlng devices which utilize the Pulfric~ effect.
Des ription of the Prior Art
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A variety of stereoscopic imag,e viewing devices have
b~en proposed. In one such devi.ce, ~ime-division multiplexing
: is utilized to produce the illusion of dep-th in an image
presented on a video screen. In such device, video si~nals
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are time-division multiplexed on a field basis by a synchro-
nized mul~iplexer. The video display device presents on the
video screen images, corresponding ~o a sequence of odd-field
signals, which are to be viewed with the left eye, alternating
with images, corresponding to a sequence of even-field signals,
which are to be viewed with the right eye. The images presented
on the video screen correspond to a sequence of alternating
left-eye and right-eye stereoscopic viewsj for example, as
obtained by alternately operative left-and right-hand ca.meras.
The viewer must be provided with special g,oF,gles or spectacles
which alternately, at the fieId frequency, block the viewing
of the displayed image by the right eye. and the leEt eye in
synchronism with the displayed video~ As is apparent, the
time-division stereoscopic viewing apparatus requires complex
goggles which must be electrically connected to the television
receiver, and further requires substantial and complex multiplexing
equipment. Further, left-and right-hand cameras, or a complex
camera providing images from spaced points of view are required
to produce the lmages displayed ~or the odd and even fields, :
respectively,
: There has also been proposed a so called "stexeochrome"
viewing apparatus, in which a selectively colored image is
viewed through prismatic spectacl.es. Because of the dispersion
property of the prism material. in the spectacles, red light
emanating from the displayed image is bent more by the prism
than blue light.~Therefore, the red images can be made to
appear to be nearer to the viewer than the blue images. Such
a "skereoch~ome" s~stem has been used only in presenting animated .:
cartoons The "stereochrome'l system is extremely color sensitive,
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and therefore limited in subject matter. Because the color of
the images must be carefully controlled, the cost of a "stereo-
chrome" program is approximately double the production cost of
a standard or two-dimensional program.
There has àlso been proposed to provide a stereoscopic
viewing apparatus utilizing the Pulfric.~ effect to simulate a
three-dimensional effect, particularly in respect to an image
moving laterally across the viewing screen. In the previously
proposed apparatus, a dark-filter lens is provided for use with
one eye only which becomes dark-adapted with respect to the
image presented on the viewing screen while the other eye remains
adapted to the ambient brightness of the viewing screen and o~
the surrounding room. Wi~h such apparatus, a laterally moving
image or portion thereof will appear to be displaced from the
plane of the~viewing screen and thus will simulate a stereoscopic
effect. .~.
However, in the above described prior art apparatus
utiIizing the Pulfric~ effect, a dark filter lens is used with
one eye onl.y to limit the light reaching such eye from the
viewing screen and also from ambient sources so that there is a
substaDtial dlfference between the amounts of light reaching the .:
right and left eyes, respectively. Thus, the pupils of the two
eyes are dilated differently, which can result in eye`strain`or
fat~ique~ especially to a viewer using the apparatus for an
extended period of time. ~ ~;
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OBJECTS AND SUMMARY OF' THE IMVENTION
According].y, it is an obj ect of the present invention
to provide a stereoscopic image vi-ewing apparatus which is free
of the above described disadvantages and drawbacks of the prior
art.
More partlcularly, it is an object o~ the present
invention to provide an improved apparatus utilizing the Pulfrich
effect to afford an illusion of depth when viewing a two-dimen-
sional image, for example, on a television screen.
A further object is to provide a stereoscopic image
viewing apparatus which permits viewing for ex~ended periods of
time withou~ inducing eye-st~rain or :Eatigue.
In accordance with an aspect of this invention, a
stereoscopic image viewing apparatus for viewing a monocular
image presented on an image display screen comprises a polarizing
plate for polarizing substantially in one plane the light emanating
from the displayed image and polarizing spec~acles through which
the polarized image is viewed. The polarizing spectacles have
one of the lenses thereof with a plane of polarization different
from the plane~of polarization o~ the polarizing plate, and the
other lens with a plane of polarization substantially the same
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~ ~ ; as the plane of polarization of the polarizing plate.
,~ In a preferred embodiment of the invention, the planes
of polarization of the irst and second polariz;ing lenses are
inclined oppositely at substantially equal angles from the
vertically polarized bac~ground or amblent light will be attenuated
equally by~both~lenses.~
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The above, and other objects, features and advantages
of the invention, will be apparent from the following detailed
description to be read in conjunction with the accompanying
drawings.
BRIEF DESC~IPTION OF THE DRAWINGS
Fig. 1 is a schematic, exploded perspective view
of an embodiment of a stereoscopic i~age viewing apparatus
according to the present inve~tion; and
- Fig 2 is a view similar to that of Fig. 1, but showing
a portion of a stereoscopic image viewing apparatus according to
another embodiment of the present invention.
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As is known, time, delay in the transmission of an
image from a dark-adapted eye to the visual cortex of the brain,
t~at is, the Pulfrich e:Eect, can cause the brain to perceive
a two-dimentsion~displày or monocular image as a three-dimensional
i.mage. The Pulfrich effect is described in R.L. Gregory, Ey~
and Braln--~The~:Psychology of Seeing, World University Library,
London, 2d~Ed. 1972, Chap, 6, and particularly pages 78 - 80,
thereof.
i An embodiment o~ the present invention for use with
an image display device 20 such as a conventional television
receiver, a projector using a rear-view screen, or the like, is
shown~m Flg~ The image display device 20 has a viewing
screen 21 on which a two-dimensional display or monocular image
is psesented for~viewing. ~In this specification, the term
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"monocular image" is intended to mean an image developed from
a single point of view, as distinguished from a stereoscopic
display which includes images from two spaced points of view.
A polarizing plate 22 is positioned and dimensioned to extend
the entire surface of screen 21. The plane of polarization of
the polarizing plate 22 is represented of Fig. 1 by the i.nclined
shading or cross-batch~ngs and is shown to be at an angle ~
relative to the vertical which is preferably approximately 45.
The apparatus is also shown to include polarizing
spectacles 23 to be worn by a viewer while viewing the screen
21 so that the left eye 24L of the viewer sees screen 21 through
a le~t lens 23L and the viewer's right eye 24~ sees the screen
through a right lens 23R of the spectacles 23 The right lens
23R is made of polarizing matérial whose plane of polarization
is inclined at an angel ~, to the right of the vertical so as to
substantially coincide with the plane of polarization of polarizing
plate 22. The left lens 23L is made of similar polarizing material
whose plane of polarization is inclined to the left of the vertical
b~ the angle ~2which is equal, but opposed to t~e angle ~.
Because of the relative alignment of the planes of polarization of
plate 22 and right lens 23R, that lens 23R acts to transmit, with
only relatlvely~smal~l alternation, light emanating from the viewing
screen 21 and passing through the plate 22 to the right eye 24R,
However, because the pl~-mes of polarization of plate 22 and left
lens 23L are crossed or at substanti.al angles to each other, lens
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23L acts as a dark filter m respect to light passing through
plate~22, and the image~seen by the viewer's left eye 24L will
appear to be substantially~ darkened. ~n this example, the
polarlzing spectacles 23 act as a darkening filter for the left
eye 24L only, so that~a three-dimensional effect is given to
~ ; the two-dim~nsional imagè displayed on screen 21 by reason of the
i ~ ~ Pulfrich effect.
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However, it will be seen that both lenses 23L, 23R
of polarizing spectacles 23 are substantially equally transparent
in respect to ambient non-polarized and also in respect to
polarized background light re~lected from the walls, floors, and
furniture in the room in which the viewing takes place. Because
the planes of polarization of 'left lens 23L and right lens 23R
of the spectacl.es 23 are inclined substantially at equal angles
from the vertical, the background light reflected from floors,
walls and furniture will be received by the viewer's lzft and
right eyes 24L and 24R with substantially equal ln~ensity. The
light ref'lected from floors tends to be polarized in the horizontal
' direction, while light reflected from walls tends to be polarized
in the vertical direction. Therefore it is preerrecl that the
planes of polarization of the left and right lenses 23L, 23R be
inclined at approximately 45 from the vertical, so that approxi-
mately the same amount of polarized background light reflected
from the walls of floors will be transmitted to both the left
and right eyes 24L, 24R. Because this polarized or reflected
background light and also the non-polarized ambi.ent light is
transmitted equally'to both the left and right eyes 24L, 24R,
the pupils of the left and right eyes are equally dilated, and
eye fatigue is substantially prevented.
Further, as t'he lenses 23L, 23R, have approximately
the same transparency, and have their planes of po'l.arization
inclined at the same angle from the vertical, a viewer can use
the polarizing spectacles 23 as sunglasses.
However, it is not nece~ssary that the planes of polar-
izatioD a polarizing lenses 23L, 23R be inclined at 45 for
the apparatus to produce a three dimensional effect. It i.s
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sufficient -that the angle between the p'Lanes of polarization
of the left and right lenses 23L, 23R be in the vicinity of 90.
It should be noted that, if the angle between the planes of
polarization of the plate 22 and the left lens 23L is precisely
equal to 90, the l.ens 23L would act as a substantially opaque
filter. l'herefore, it is prefer'able to select an orientation
between the polarization planes of the left lens 23L and the
plate 22 at an angle somewhat different from 90, so that lens
23L a-ttenuates light`passing through plate 22 but does not block
the light completely.
Fig. 2 illustrates another embodiment of the presen-t
invention in which elements corresponding to these described
above with reference to Fig. 1 are iden-tified by the same
reference characters, and the detailed description thereof is
omitted. The apparatus of Fig. 2 differs subs-tantially from
that sho~n on Fig. l onl~ in that the simple plate 22, having
a fixed plane of polarization, is replaced by a polarizing
d0vi.ce 122 whieh is operable to rotate its plane of polarization
for selective alignment thereof with either the plane o polari-
zation of the left elns 23L or t'he plane of polarization of the
right lens 23R, This feature permits the le:Et and right lenses
23L, 23R to exchange'roles so t'hat, in one condition of device
122, lens 23L acts to transmit light passing through the polari-
zlng device 122 while the right lens 23R acts as a dark filter
and, in another condition of device 122, lenses 23L and 23R
respectively block and transmit the light passing through the
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polarizing device. Preferably, ro~ation of the planes of
polarlzation in device 122 is accomplished by a Kerr-effect cell
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25 is made of an optically active material which rotates the
plane of polarization of polarized light passing through it in :'
response to a potential applied across opposed electrodes 25a,
25b of cell 25 from a control voltage source 26. The source 26
can supply the mentioned potential in response to a cue signal
transmitted toge~her with a video signal in the case of a tele-
vision display,or in response to a signal recorded on film in
the case of a filmed presentation. The Kerr-effect cell 25
can be made of PL~T (polycrystalline lanthanum-modified lead ~.
zirconate titanate) or other known ferroelectric cer'amic
materials.
With the embodiment of Fig. 2, the apparatus is not
limited to presenting an image which, due to -the Pulfrich eE~ect,
appears to be closer to the viewer only when the'image moves
laterally in one direction and appears to be more distant. only
when the image moves latera1ly in the opposite direction. With
the embod1ment of Fig. 2, either the left lens 231 or the'right
lens 23R can be s:elected to act as a dark filter, thereby maki.ng
it possible to make the image appear to be closer to, or farther
~rom the viewer:as desired.
It should be noted that in the embodiment of Fig. l, it
is possible to achieve~approx.imately the'same results as pre- ~
viously described if the spectacles 23 have only the'polarizing `
lens 23L for the le:Et eye 24L, and the lens 23R is either omitted
or replaced by non-polari~ing glass or other transparent material.
In that case, the~oIar1zing plate 22 and the lens 23L act as a
dark filter to achieve the three-dimensional simulatio~ by the
Pulfrich effec't,~and yet the amount'of Iight reaching the left
eye 24L is substaneia11y the''same'as the amount of light reaching
the right eye 24R so that eye~fatigue is prevented.
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Although illustrative embodiments of the invention
have been described in detail herein with reference to the
accompanying drawings, it is to be unders-tood tha~ the
invention is not limited to those precise e~bodiments, and
that various changes and modifications can be effected therein
by one skilled in the art without departing from the scope or
spirit of ~he invention as defined in the appended claims.
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