Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to viewing systems, and
in particular to an improved viewing system for
producing a simulation of depth in substantially two-
dimensional visual images such as television images.
The invention also relates to improvements in viewing
systems for improving clarity and color rendition in such
two-dimensional images.
Conventional systems for producing the
appearance of depth in two-dimensional images incorporate
depth information in the image itself, and provide
special viewing means for utilizing the depth
information. For example, in the now obsolete "3-D"
motion pictures, the image displayed on the motion
picture screen was actually two superimposed images
which were separated by means of polarizers or colored
filters. The polarizers or colored filters were
incorporated in special glasses or viewers provided to
the theater patron so that one eye of the patron would
perceive one oE the two images, and the other eye would
perceive the other of the two images.
Various unconventional attempts have been made
in the past to produce the simulation of depth in the
viewing of two-dimensional images containing no special
depth information. For example, the image on a
television screen, or the image of a conventional
motion picture on a motion picture screen, contains no
special depth information, and can be viewed in the
conventional manner without giving the impression of
depth.
One such attempt at depth simulation was
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described in U. S. Patent No. 4,049,339, issued
September 20, 1977 to Antoine Ledan. Ledan described
a pair of eyeglasses for movie viewing which are
designed to produce a simulated three-dimensional effect.
The eyeglasses have flat, triangular-shaped lenses in
an opaque frame. These lenses are arranged so that the
left edge of the image on the movie screen is obscured
from view through the left eye, and so that the right
edge of the image is obscured from view through the
right eye. The eyeglasses described by Ledan produce
the sensation of depth by the so-called "window effect",
i.e. by preventing the observer from determining the
distance between himself and the movie screen. The
effect described in the Ledan patent is somewhat similar
to the effect utilized to simulate depth in wide-screen
and curved-screen movie systems. The purpose of the
wide screen or the curved screen is to fill the
observer's field of view, preventing him from seeing the
edges of the screen and thereby deternlining the distance
between his eyes and the screen.
Another approach to producing illusions of
depth is described by Hugh M. Stevenson in his U. S.
Patent No. 2,922,998, dated January 26, 1960. Stevenson
describes a television having, in front of the picture
area, a sheet of transparent material with opaque or
translucent vertical lines. According to Stevenson,
the illusion of depth is due to the slightly different
picture presentation for each eye combined with the
placement of the substantially vertical parallel lines in
front of and spaced apart from the plane of the picture
presentation.
Another system for depth simulation was
described by H. M. Muncheryan in his U. S. Patent No.
2,986,969, dated June 6, 1961. Muncheryan described a
binocular device having a pair of relatively rotatable
polarizers in each eyepiece. Depth simulation was
achieved by rotating the plane of polarization of one
polarizing lens with respect to the other in one eyepiece
until objects viewed have obtained apparent curvatures
and depths. This effect is said to be more prominent
in the angular range of 30 to 50 degrees between the
polarization axes of the two polarizing elements. After
the polarizers in one eyepiece are adjusted, the
polarizing lens of the other eyepiece is rotated until
the transmitted light intensity through that eyepiece
is comfortable to the eye.
Another optical aid for simulating depth in
two-dimensiona:L images such as screen projections,
drawings and photographs, was described by A. Ames, Jr.
in U. S. Patent No. 1,636,~50, dated July 19, 1927.
Ames used a pair of eyeglasses having a system of prisms
and lenses which eliminated actual perceptive sensations.
The system blurred the image seen by one eye, preferably
by means of a cylindrical lens which blurs only vertical
lines, leaving horizontal lines sharp. The theory of
operation, as explained by Ames, is that the system of
prisms and lenses causes the position of the picture
in space to be indeterminate. The system of prisms and
lenses causes both eyes to be relaxed in convergence and
in their accommodations. The eyes are caused to have
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differently relaxed accommodations, which prevent any
sensory ascertainment of distances by accommodative
stress. The result is to free the observer from any
compulsory suggestion arising from actual perceptive
sensations, and from any compelling belief that the
arrangement of line and light and shade before the viewer
lie in any one plane. The reaction in the observer is
that the picture objects appear in near and far relation
suggested by their sizes, shadows and perspective.
F. Pole, in U. S. Patent No. 2,884,833, dated
May 5, 1959, describes a three-dimensional effect
produced by means of a transparent, curved lenticular
screen, having an array of individual lenses, which
are preferably so small that they cannot be discerned
by the normal eye when viewed from the normal viewing
distance.
Nawokich Tanaka in U. S. Patents 2,374,566,
dated April 24, 1945, 2,888,855, dated June 2, 1959 and
3,053,135, dated September 11, 1962, descrlbes several
versions of a system for simulating three-dimensional
viewing in which, by means of a special reflector or
lens system, secondary images are produced which are
said to give rise to a three-dimensional effect.
In French Patent 1,101,550, granted April 20,
1955, Gilbert-Jacques Robin describes the creation of
stereoscopic effects by using a transparent plate having
alternately interpositioned convergent and divergent
cylindrical lenses. The plate has a large number of
lenses, typically one lens for each millimeter of plate
width. The number of lenses is related to the locations
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of the image plane, the plate and the observer so that,
for any given very small area on the image plane, one
eye will see it reduced, and the other eye will see it
enlarged.
In all of the foregoing viewing systems of
the prior art, a simulated three-dimensional effect is
achieved at the expense of i.mage quality. That is, each
system of the prior art either partially obscures the
image or produces a blurring of visual information. In
the former case there is at least a loss of light from
the picture, and the loss of light may be accompanied
by a loss of picture information. In the latter case,
blurring of visual information has a tendency to cause
eyestrain, and to make viewing for extended periods of
time somewhat unpleasant. Nevertheless, apparently
obscuration and/or blurring have been considered
essential heretofore in the production of three-
dimensional e:Efects from conventional two-dimensional
images.
The principal object of this invention is to
provide a simple viewing system for depth simulation in
which obscuration of picture information is avoided, and
in which there is no blurring of visual information. It
is also an object of the invention to produce depth
simulation in the viewing of two-dimensional images
without the need for special eyeglasses or binoculars.
Still another object of the invention is to provide a
viewing system for improving image clarity and color
rendition in addition to providing depth simulation.
In accordance with the invention, the foregoing
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objects are achieved by the use of optical bending means,
located in a path through which the two-dimensional
image is viewed by an observer, for selectively bending
light rays extending from the image plane to the eyes
of the observer so that, for substantially any two
horizontally spaced points in the image plane, the left
and right eyes of the observer perceive a different
horizontal spacing between said points. The optical
bending means maintains substantially the same perceived
overall image size for both eyes of the observer, and is
located sufficiently close to the image plane that any
two rays emanating from a point on the image plane and
passing through the optical bending means are diverging.
The optical shift is carried out by means of
a transparent sheet having an index of refraction higher
than that of air and having undulating horizontal cross-
sections. The undulations may be formed on either or
both surfaces of the sheet. The distance h between the
adjacent peaks and valleys of the undulati.ons is at
least approximately ten times greater than sdl/d2,
where s is the interocular spacing of the observer, dl
is the closest distance between the image plane and the
surface of the optical bending means nearest the image
plane, and d2 is the distance between the image plane
and the observer. The distance h is therefore
sufficiently large that, when the observer is located
at a normal viewing distance from the image plane, any
two rays extending from a single point on the image
plane respectively to the eyes of the observer intersect
the surface nearest the image plane at a spacing of
less than about O.lh, measured in a direction parallel
to the image plane.
The transparent sheet is formed in such a
way that distortion of the image by the undulations is
not readily perceived by the average observer. To this
end the undulations are formed so that, to the extent
they serve as lenses, their effective focal lengths are
greater than approximately 400 mm. That is, any two
rays which approach the sheet in parallel directions
are refracted by the sheet into paths which converge at
a distance of at least approximately 400 mm. from the
sheet. The magnification (or reduction) of any area in
the image plane is only about 5% or less; hence little
if any distortion is evident to the average observer.
The operation of the viewing systern in
accordance with the invention involves the optical
shifting of the horizontal placement of points in the
two-dimensional image so that the eyes of the observer
perceive different spacings between pairs of points.
The horizontal shift of the placement of points in
the two-dimensional image produces a slight but
unobjectionable distortion characterized by a difference
in the spacing between points as observed through the
right and left eyes of the observer. These differences
in spacing produce the sensation of depth, and the
perceived depths of the various objects in the two-
dimensional irnage arise from visual clues such as the
relative sizes of objects, shadows and the obscuration
of farther objects by nearer objects.
The optical bending means neither masks the
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picture nor diminishes the transmission of light from
the picture to the observer. Thus, there is no
obscuration of picture information. The optical bending
means is designed to allow both eyes to perceive the
same overall image size. Consequently there is no
blurring of picture information in either eye by reason
of differential magnification. Blurring by reason of
secondary or "ghost" images is avoided by positioning
the optical bending means in relation to the positions
of the image plane and the observer so that rays from
any point on the image plane diverge in the space between
the optical bending means and the observer. Since the
observer views any given small area through less than
about 10% of the peak-to-valley distance of the
undulating sheet, the invention avoids blurring caused
by magnification of small areas for one eye and
reduction of the same small areas for the other eye.
While masking or blurring were apparently
previously thought to be essential in the production
of a simulated three-dimensional effect, I have
discovered thatJ with the use of appropriate optical
bending means as hereinafter described in detail, masking
and blurring can be substantially eliminated, and that
sharply defined images having a remarkable appearance
of depth can be produced.
The foregoing objects, as well as various
other objects of the invention will be more apparent
from the following detailed description, when read in
conjunction with the drawings.
Figure 1 is a horizontal section of an
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undulating transparent sheet in accordance with the
invention;
Figure 2 is a perspective view showing the
undulating transparent sheet of Figure 1 used in
conjunction with a television set;
Figure 3 is a schematic diagram illustrating
the operation of the transparent undulating sheet; and
Figure 4 is a top plan view, partly in
section of a television tube incorporating an undulating
transparent sheet as part of its envelope.
In one embodiment of the invention, a
transparent sheet having substantially uniform
undulating horizontal cross-sections is positioned in
the path through which the two-dimensional image is
viewed by the observer. Figure 1 shows a suitable
transparent undulating sheet 10, preferably made from
an acrylic polymer such as poly(methyl methacrylate),
or a similar transparent material having a refractive
index substantially higher than that of air. A series
Z0 of undulations is formed in sheet 10 comprising
alternating ridges and valleys which extend in the
vertical direction. The valleys are indicated at 12
and 14, and the ridges are indicated at 16, 18, and 20.
In the case of polycarbonates, poly(methyl methacrylate),
and other thermoplastic material, the undulations can
be readily formed by the application of heat using
electrically heated strips. A typical undulating sheet
of the type shown in Fig-ure 1 is 13 mm. in thickness.
The depth of the valleys, measured from the peaks in the
direction perpendicular to the sheet is typically
0.8 mm., and the distance between the tops of the
peaks and the bottoms of the adjacent valleys, measured
in the direction parallel to the sheet, is
approximately 30 mm.
Preferably, the undulations are approximately
sinusoidal. However, they may vary from an exact
sinusoidal configuration. For example, they may be in
the form of circular arcs. The undulations should be
smooth so that the surfaces of the sheet do not at any
point exceed the critical angle with respect to the
paths of light rays passing through the sheet, thereby
causing reflections. The smoothness of the undulations
is also important to the avoidance of secondary images.
The faces of the sheet are substantially
straight in the vertical direction. Hence, the
horizontal cross-sections of the sheet are substantially
uniform. While uniformity of the horizontal cross-
sections is desirable from the s-tandpoint of ease of
manufacture, a minor curvature in the vertical
direction can be tolerated, and may even be desirable
in order to avoid the appearance of vertical bands of
light reflected by the sheet from lamps, windows, and
the like. It is likewise unnecessary for the
undulations to be strictly vertical, and in fact some
deviation from a strictly vertical configuration may be
desirable to avoid an artificial appearance in the
image.
Preferably, for convenlent attachment to a
television set, the undulating sheet is mounted in a
four-sided frame 22, the sides of the frame being
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provided with slots receiving the edges of the sheet.
The frame is secured to the television set housing 24
(as seen in Figure 2) by means of screws 26 so that the
sheet is positioned directly in front of the television
screen with its undulations extending in the vertical
direction.
For convenience, the sheet may be placed in
close proximity to the screen, i.e. either touching the
screen or within a distance of about two centimeters
from the screen. If a sheet made for use in close
proximity to the screen is used at a greater distance
than intended, the viewing angle will be reduced
because gaps will appear in the image when it is viewed
obliquely.
The operation of the sheet 10 is illustrated
in Figure 3, in which a portion of the sheet, comprising
peak 18 and valley 14 is shown in close proximity to
image plane 28 of the television set. Points P2 and P3
represent two laterally spaced points in the image
appearing on the television screen. ER is the right eye
of the observer, and EL is the left eye.
Since ER and P2 are directly in line with the
center of peak 18, light path 30, between P2 and ER
passes directly through the sheet without any transverse
displacement. The right eye, therefore, sees point P2
in its correct position. The left eye EL, however,
views point P2 through light paths 32, 34, and 36 as
result of refrclction in the transparent sheet.
Consequently, point P2 is seen by the left eye EL at
the 2osition of point Pl, which (from the observer's
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standpoint) is located to the right of point P2.
The left eye EL views point P3 directly and
without refraction through light path 38. The right
eye ER, however, views point P3 through light paths 40,
42, and 44 as a result of refraction. Consequently,
the right eye ER views point P3 at the point of P4,
which is displaced to the left of position P3.
The distance between Pl and P3 is slightly less
than the distance from P2 to P4. Therefore, the right
eye perceives a greater distance between the two points
than does the left eye.
The undulations in sheet 10 cause the eyes of
the observer to observe different distances between
laterally spaced points except in the relatively few
instances where symmetry causes pairs of points to be
perceived at the same lateral spacing by both eyes.
Consequently, for substantially any two horizontally
spaced points in the image on television screen 28,
the left and right eyes of the observer perceive a
different horizontal spacing between the points. The
resultant slight distortion caused by the interposition
of undulating sheet 10 between the image and the observer
is unobjectionable, and i.s apparently compensated for
in the brain of the observer with the result that the
observer receives the impression of depth in the image.
The relative depths of the various components of the
image are apparently determined by the observer
automatically by taking into account his experiences
in the real three-dimensional world. The observer
automatically takes into account visual clues such as,
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for example, the fact that two objects, known to be
the same size in actuality, are seen to be of different
sizes. The differences in sizes is interpreted in such
a way that the smaller-appearing object appears to be
farther away than the larger-appearing object. The
observer also apparently takes into account other clues
such as shadows, and relative velocities in the case of
a moving image.
The undulating sheet, while causing minor
distortions in the horizontal distances between points
as observed through the sheet, does not materially
change the overall image size. Consequently, each eye
of the observer perceives substantially the same
overall image size.
The sheet can, of course, be modified so
that it produces an overall magnification or reduction.
This can be accomplished, for example, by adding a
large magnifying lens, or by making the front face
entirely convex, and forming undulations only on the
back face. Various other means for overall
magnification or reduction, of course, can be used.
The various parameters of the viewing system
such as the depth of the undulations, the index of
refraction of the transparent sheet, the thickness of
the sheet, and the distance between the sheet and the
image on the television screen are interdependent in
certain respects. For example, a given differential
displacement (the distance P2, P4 - P3, Pl) can be
achieved by reducing the depth of the undulations of
the transparent sheet, and at the same time increasing
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the thickness of the sheet, the index of refraction,
or the distance between the sheet and the screen.
Combinations of the parameters may also be taken into
account so that, for example, the depth of the
undulations can be decreased, and the thickness and
distance from the screen can both be altered to
produce the same results.
The depth of the undulations, the index of
refraction, and the distance between the undulating
sheet and the television screen also determine the
maximum viewing angle. The maximum viewing angle is the
horizontal angle through which the image may be viewed
without the appearance of gaps resulting from interior
reflections of light in the undulating sheet. These
gaps would appear where the observer attempts to view
a point on the image through a path such that the light
ray from the point strikes the front surface of the
undulating sheet at an angle of incidence exceeding the
critical angle, i.e. that angle at which total reflection
occurs. For a given sheet the viewing angle decreases
as the depth of the undulations increases; it decreases
with distance between the undulating sheet and the
television screen; and it decreases with increases in the
index of refraction of the undulating sheet material.
Preferably, the viewing angle is at least 120,
measured from one extreme position of the viewer to the
other extreme position. For a given undulating sheet,
the range of the viewing angle can be readily adjusted
by adjusting the distance between the sheet and the
television screen.
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The dimensions of sheet 10 and its proximity
to the image plane at screen 28 are also important from
the standpoint of eliminating secondary or ghost images.
While the sheet has a uniform thickness, portions of the
sheet act as lenses, causing magnification or reduction
depending upon the curvature. In the overall image,
magnification and reduction caused by the peaks and
valleys cancel each other out so that the apparent image
size is not materially affected. However, depending
on the curvature of the undulations, the peaks of the
undulations can act as magnifying lenses.
As is well known, a pair of rays diverging
from a point and passing through a conventional
magnifying lens may become parallel, or they may diverge
or converge depending upon the distance between the lens
and the point. In the event that the rays tend to
converge, the point of convergence is affected by the
distance between the lens and the point in the image.
In the case of a powerful magnifying lens, convergence
of the rays may occur at a location quite near the lens.
If the observer is positioned at a point behind the
point of convergence he will see an inverted image. If
the observer is positioned between the lens and the
point of convergence, he will see a blurred image
(i.e. ghost images). In the case of an object at the
focal point of a spherical lens, the observer will not
see any image at all. In the case of an object at the
focal point of a cylindrical lens, the image will be
severely blurred.
The peaks in an undulating sheet act as
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relatively weak lenses and are generally subject to the
same effect unless the undulating sheet is of uniform
thickness. Thus, if an undulating transparent sheet of
non-uniform thickness, and having a given set of
parameters, is positioned too far from the image plane,
at least some rays emanating from a point on the image
plane will tend to reconverge on the opposite side of
the undulating sheet. If the observer is located behind
the point of reconvergence, he will see a series of
alternating erect and inverted images. If the observer
is located in front of the point of reconvergence, or
if the object is at the focal point, the image will be
partially blurred.
With the viewing system in accordance with
the invention, a three-dimensional effect can be
produced, while retaining a sharp picture image by
positioning the undulating sheet sufficiently close to
the image plane that substantially any two rays
emanating from any point on the image plane and passing
through the undulating sheet are diverging. In this
way, the image can be seen clearly without the need for
the observer to wear special corrective glasses.
Preferably, the undulating sheet is smooth
(i.e. free of sharp bends~ in which event it can be
spaced some distance away from the image plane without
causing blurring. If sharper bends are present in the
sheet, it is necessary to position the sheet veryclose
to the image plane. In the case of an undulating
sheet having extremely sharp bends, it may be impossible
in practice to bring it sufficiently close to the image
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plane to achieve divergence of substantially all
points in the image plane.
Another important parameter of the undulating
sheets is the horiæontal distance between the high
points of the peaks and the low points of the adjacent
valleys. For the maximum differential displacement of
horizontally spaced points in the image plane, the
undulating sheet would be placed a considerable distance
from the image plane and the horizontal distance h
between adjacent peaks and valleys of the undulations
would be related to the interocular spacing s of the
observer in accordance with the following proportionality:
h = dl where: dl is the distance between the image
S d2
plane and the side of the undulating sheet nearest the
image plane; and d2 is the distance between the image
plane and the observer. Where this relationship exists
or is approximated, a point in the image plane is
displaced in opposite directions for the two eyes of
the observer. The above relationship gives rise to
various practical problems. If the peaks and valleys
are wide, the relationship h = dl requires the sheet
s d2
to be spaced a considerable distance from the image
plane, in which case, it severely limits the viewing
angle. On the other hand, if the undulating sheet is
placed very close to the image plane, the above
proportionality could only be achieved by placing the
peaks and valleys very close together, in which case,
the effect would not approximate what occurs in a
natural three-dimensional scene. In either case, the
sheet would magnify small areas for one eye and reduce
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the same small areas for the other eye. This would
interfere wi~h image quality, and the interference would
be more severe with greater degrees of magnification
and reduction. The system in accordance with the
invention uses a relatively wide spacing between the
high points of peaks and the low points of adjacent
valleys such that h is at least approximately ten
times 1 . The invention relies upon the fact that,
even though most points are shifted in the same direction,
they are shifted by different amounts for the two eyes
of the observer.
In a typical system using a small screen
television dl is 13 mm., d2 is 750 mm., and h is 30 mm.
S is assumed to be 65 mTn. Thus h is approximately
twenty six times ~ .
For a large screen television, dl might be
63 mm. and d2 might be 1500 mm. A typical value for h
would be 63 mm. Here h would be approximately twenty
three times ~dl
d2
Finally, focal length is an important
parameter, since it is necessary to avoid localized
distortion of small areas due to excessive magnification
or reduction by lens effect of the undulations. In
accordance with the invention the minimum focal length
of the undulating screen is preferably at least
approximately 400 mm., as shorter focal lengths would
tend to produce readily perceptible distortion of the
image.
The optical bending means can be built into
a television tube, as illustrated in Figure 4, in which a
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series of vertically extending undulations 46 is formed
in screen 48, which is part of the envelope of
television tube 50. The interior side of screen 48 is
provided with a phosphor coating 52, and is curved in
the conventional manner so that it forms what is
essentially an image "plane". The glass of screen 48
varies in thickness by reason of the undulations 46 on
its outer surface. Here again, the undulations are
smooth, and free of sharp bends, and screen 48 is
sufficiently close to the image plane at phosphor
coating 52 that rays diverging from any point in the
image plane continue to diverge in the space between
screen 48 and the observer. Since the undulations 46
are very close to the image plane, the high points of
the peaks can be fairly close to the low points of the
valleys while still satisfying the requirements that h
be at least about ten times 1 at a normal viewing
distance. For example, if dl is 10 mm. and h is 26 mm.,
the observer will satisfy the relationship h ' lOsdl
~.~ ...
at any viewing distance up to as close as 25 cm., which
is as close as most observers can get while still
focusing their eyes on the image.
In the case of an undulating television tube
envelope, the depths of the undulations will normally be
relatively shallow compared to those of the undulating
sheet of Figure 1 in order to satisfy the requirement that
the minimum focal length be at least approximately 400 mm.
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