Autostereoscopic video device

The invention relates to a single-camera autostereoscopic picture-taking device implementing an array of cylindrical lenses, characterized in that it comprises in succession: PA1 a single inlet objective (L1, L2); PA1 said lens array (20), which has a focal length such that for an image area equal to the pitch (p) of the lenses making it up, the image of the entrance pupil of the telecentric objective (L1, L2) has a nominal width equal to said pitch; PA1 a transfer optical system (L3, L4) having magnification of less than unity; and PA1 an image sensor (22), the transfer optical system (L3, L4) directing the light rays that emerge from the lens array (20) onto the image sensor (22), the image (21) of the lens array (20) in the transfer optical system (L3, L4) being such that the pitch (p) of the lenses of the lens array (20) corresponds therein to an integer number of image points (pixels) of the image sensor (22).

The present invention relates to a single-camera autostereoscopic video 
device implementing an array of cylindrical lenses. 
United States patent U.S. Pat. No. 3,932,699 discloses an autostereoscopic 
picture-taking device having an array of lenses on which light rays from 
an object are focused, the lens array being placed against a window that 
is sensitive to light and constitutes part of a Vidicon tube, for example. 
Such a picture-taking device suffers from numerous drawbacks, and in 
particular from considerable geometrical distortion and small depth of 
field. 
A much more elaborate stereoscopic picture-taking device was proposed by 
McCormick et al. at the stereoscopic television colloquium that was held 
in London on Oct. 15, 1992. He proposed taking stereoscopic video pictures 
by recording an image that is projected onto a diffusing screen by two 
autocollimated lens arrays. That device suffers from the drawback of 
considerable complexity and in particular the use of three lens arrays 
that must be in perfect alignment otherwise the image is affected by 
extremely troublesome moire phenomena. 
In a first aspect, the present invention provides an autostereoscopic 
picture-taking device that does not suffer from the above-specified 
drawbacks, and more particularly a stereoscopic picture-taking device that 
is simple to implement and that provides high optical quality. 
French patent FR 1 362 617 (Yarmonkine) relates to a picture-taking device 
having a plurality of entrance objectives, specifically two lenses, each 
having its own optical axis, thus providing two entrance objectives with 
two optical axes corresponding to respective viewpoints. To obtain a 
composite image with interlacing, a frosted screen is placed on the plane 
face of the plate 7 and the screen is scanned horizontally by a normal 
camera. The screen gives rise to losses of light intensity and of 
contrast. In addition, given that the microlenses of the array 7 must have 
a field angle enabling them to see both objective lenses, certain light 
rays are very highly inclined relative to the optical axis, thus giving 
rise to problems of vignetting. 
The idea on which the invention is based is to implement a single entrance 
objective, on a single optical axis, while still making it possible 
without a frosted screen to obtain an autostereoscopic image having two or 
more viewpoints. To this end, the invention provides a single-camera 
autostereoscopic picture-taking device implementing an array of 
cylindrical lenses, characterized in that it comprises in succession: 
a) a single inlet objective having a single optical axis; 
b) said lens array is disposed substantially in the image focal plane of 
the entrance objective, said array having a focal length such that for an 
image area equal to the pitch of the lenses making it up, the image of the 
entrance pupil of the entrance objective has a nominal width equal to said 
pitch; 
c) a transfer optical system having magnification of less than unity; and 
d) an image sensor, 
the transfer optical system directing the light rays that emerge from the 
lens array onto the image sensor, the image of the lens array in the 
transfer optical system being such that the pitch of the lenses of the 
lens array corresponds therein to an integer number of image points 
(pixels) of the image sensor, and the image of the pupil of the entrance 
objective, in the absence of the lens array, being situated substantially 
at the pupil of the transfer optical system. 
Because of its orthoscopic transfer optical system, this device makes it 
possible, in particular, to conserve a stereoscopic baseline corresponding 
to the inlet pupil diameter of the entrance objective, in spite of the 
reduction in the format of the image on the sensor. In addition, the 
picture-taking device of the invention uses only one lens array, which is 
particularly favorable for optical quality. 
The image sensor may be a charge-coupled type of sensor, and it is 
preferably constituted by a set of three individual sensors associated 
with a prismatic three-color beam-splitter forming images on the three 
sensors, which images that are nominally in mutual alignment, image point 
by image point. This makes it possible to obtain a high degree of 
separation between viewpoints without having to subdivide the inlet pupil 
into as many sub-pupils. 
Optimum separation between viewpoints is obtained by orienting the lens 
array in the line direction of the image sensor. It may be observed that 
this orientation corresponds to rotation through 90.degree. relative to 
the normal position, given that the orientation of a lens array must be 
such as to provide horizontal separation between the viewpoints. 
The entrance objective may include an inlet lens whose pupil is 
substantially equal to 100 mm. 
The pitch of the lens array may be 0.4 mm. 
The transfer optical system may advantageously have magnification that is 
substantially equal to 0.1. 
The transfer optical system may have a circular diaphragm, in particular of 
the iris type. This diaphragm is equivalent to a diaphragm in the form of 
a horizontal slot disposed in the first objective, but it is much easier 
to position mechanically. 
An autostereoscopic video system may include a picture-taking device as 
defined above. 
In a first aspect, the invention also relates to a method of adjusting a 
device as defined above, characterized in that it comprises the following 
steps: 
making a transcoded image of an autostereoscopic image, such a transcoded 
image comprising a plurality of anamorphosed flat images equal in number 
to the number of stereoscopic viewpoints; and 
adjusting the picture-taking device using said anamorphosed flat images, 
optionally using a diaphragm to black out at least one viewpoint. 
In a second aspect, the invention relates to a method of transmitting 
and/or recording a stereoscopic image, in particular using a single camera 
and implemented by means of an array of cylindrical lenses. The Applicant 
has observed that transmission via a transmission channel (transmitter, 
etc.) or direct recording of such images as obtained at the outlet of the 
CCD sensor 21 does not allow the images to be reproduced with satisfactory 
perception of relief. 
The Applicant has been able to establish that the origin of this problem 
which occurs during image transfer is due to the fact that the relief 
information in the images is at high frequency, i.e. situated in the top 
portion of the video frequency band. Unfortunately, it is well known that 
video recorders, even of professional quality, tend to degrade this type 
of information. In addition, consumer video recorders have a video 
passband that barely exceeds 3 MHz for a nominal video passband of 5 MHz. 
Similarly, transmission channels (terrestrial broadcast networks or 
satellite broadcast networks or indeed cable networks) also present this 
type of degradation. 
U.S. Pat. No. 3,674,921 (Goldsmith) discloses an analog transmission device 
for transmitting a stereoscopic video image that comprises two elementary 
images, namely a left image LE and a right image RE generated by two 
distinct cameras 21 and 23. They are thus not autostereoscopic images. 
Transmission is performed by conserving one of the two images and by 
extracting a high frequency difference signal which is subsequently 
filtered. For recording, use is made of two images that are anamorphosed 
on film. To pass into video mode, it is necessary initially to 
deanamorphose them by means of a deanamorphoser, and then to film them 
with a stereoscopic camera, after which the image is processed in 
conventional manner. 
In a second aspect, the present invention relates to a transfer method, in 
particular for transmitting and/or recording autostereoscopic images, that 
makes it possible to use transmission channels or video recorders of 
standard type, while to a large extent conserving the quality of the 
stereoscopic images. 
To this end, in the second aspect, the invention provides a method of 
transferring single camera autostereoscopic images obtained by means of an 
array of cylindrical lenses, characterized in that it includes a step of 
making a transcoded image of said autostereoscopic image, such a 
transcoded image comprising a plurality of flat images of anamorphosed 
format equal in number to the number of stereoscopic viewpoints, the flat 
images of anamorphosed format being placed side by side, the transcoded 
image being subjected to said transfer, i.e. to transmission and/or 
recording. 
It will be observed that the method of the invention does not make use of 
anamorphosers or of deanamorphosers. On the contrary, the method consists 
in separating out the autostereoscopic image so as to recover flat images 
which normally present an anamorphosed format. 
The image as transmitted or recorded consists merely in a series of flat 
images containing all of the information in the original image and which 
are themselves transmitted or recorded with the losses of quality imparted 
by conventional transmission channels and/or video recorders. However, on 
reception or playback, the autostereoscopic image as reconstituted by 
inverse transcoding turns out, surprisingly, to be very little affected by 
the defects of line transmission and/or of recording. During stereoscopic 
reproduction of the image, the stereoscopic information although situated 
outside the passband of the transmission channel of the recorder, will 
nevertheless have been conserved to a large extent. 
The transcoded image may have the same format as the autostereoscopic 
image. 
In a first embodiment, a recording step is performed using a standard 
analog video recorder (VHS, SVHS, etc.). 
In a preferred embodiment, the transfer step is implemented using a digital 
technique, e.g. on a satellite channel and/or a digital video recorder, 
with a bit rate compression algorithm being applied. According to the 
invention, the above considerations are equally applicable to any digital 
processing of the image. Separation of the image into a plurality of flat 
images of anamorphosed format and containing all of the information in the 
original image makes it possible to simplify considerably any bit rate 
compression processing, given that the high frequency components of the 
image comprising the stereoscopic information are ipso facto eliminated to 
a large extent. The compression algorithm may, in particular, be a 
vectorization algorithm as known per se. Numerous types of algorithm are 
known for compressing images and in general they implement the discrete 
cosine transform DCT whether the images are in traditional television 
standards or in so-called "high definition" standards. 
For the transcoding step, the transmission or recording of images according 
to the invention may comprise a first step of digitizing the 
autostereoscopic image, a second step of storing the transcoded image, 
said transcoding being performed by a transcoding memory making it 
possible to perform write addressing in at least one memory, and a third 
step of reading said memory. 
The transformation step may include a fourth step of analog conversion of 
the transcoded image for the purpose of analog transmission or recording 
thereof. 
Said memory may be a pixel transcoding memory, with transcoding being 
performed by permutation of the pixels in each line. The capacity of the 
memory may then be limited to a single line or to certain lines only. 
In a preferred embodiment, the transcoding memory is such that an 
interlace-scan image is transformed into a flat anamorphosed image with 
progressive i.e. non-interlaced! scanning. As a result, relief is 
perceived in greater comfort, in particular when the lines of the 
stereoscopic image are vertical, in which case, because of the vertical 
scanning of the original image, the viewpoints of the stereoscopic image 
blank out in alternation. 
The third step of reading can advantageously be performed at twice the rate 
of the autostereoscopic image. 
In a preferred embodiment, the transformation operations are performed by 
direct transcoding in the image sensor of the camera, which sensor is 
provided with a transcoding matrix, the matrix being preferably disposed 
between the columns of image points (or pixels) and a line shift register. 
In a second aspect, the invention also provides a stereoscopic image 
transfer system characterized in that it comprises: 
a device for generating autostereoscopic images; 
a first transcoding device for making a transcoded image of said 
autostereoscopic image, such a transcoded image comprising a plurality of 
flat images of anamorphosed format in equal number to the number of 
stereoscopic viewpoints, the flat images of anamorphosed format being 
placed side by side; 
an image transfer device; and 
a second transcoding device for implementing a transcoding operation that 
is the inverse of that implemented by the first transcoding device so as 
to reconstitute the autostereoscopic images. 
In a third aspect, the invention relates to a stereoscopic image video 
projector comprising a plurality of video projectors, each of which 
projects an elementary image representing one of the viewpoints of said 
stereoscopic images. 
A stereoscopic video projector is known from the article by Chin Hasegawa 
et al., entitled "Three-dimensional image technology" published on Jul. 
25, 1991 in the proceedings of TEC 1991 (Tokyo, Japan). 
It comprises a first array of cylindrical lenses upstream from a diffusing 
screen, and a second array of cylindrical lenses downstream from the 
diffusing screen. 
Each cylindrical lens of the first lens array corresponds to a number of 
vertical lines equal to the number of viewpoints of the stereoscopic 
image. Such an image as formed in this way on the diffusing (frosted) 
screen is transferred in conventional manner by the second array. 
The arrays have a pitch equal to n times the size of a pixel, where n is 
the number of viewpoints. A drawback is that because of its large pitch, 
the array disposed downstream from the diffusing screen is very visible, 
and in addition it is difficult to avoid the presence of very disagreeable 
moire patterns. 
In a third aspect, the invention provides projection apparatus that avoids 
the above-mentioned drawback. 
According to the third aspect, the invention provides stereoscopic image 
projection apparatus of the above-specified type, characterized in that 
the first and second cylindrical arrays are at a pitch that is less than 
or equal to half the size of an image point or pixel on the screen, and in 
that the pitch of the second cylindrical array is equal or slightly less 
than the pitch of the first cylindrical array. 
As a result, the highest frequency of the image is associated with the 
array and is significantly higher than the initial pixel frequency, and, 
when at the selected nominal observation distance, the spectator sees with 
each eye and through the first lens array, only a single viewpoint 
(without moire fringes). 
The first cylindrical array may be a parallax barrier or a lens array. 
In a preferred embodiment, the arrays may have a focal length and a pitch 
such that a spectator placed at a given nominal distance from the screen 
sees a solid color (i.e. without moire fringes). 
The projection apparatus of the invention may comprise a conversion device 
for transforming a transcoded image comprising a plurality of flat images 
of anamorphosed format equal in number to the number of viewpoints and 
disposed side by side into a plurality of said deanamorphosed elementary 
images, and in that the conversion device has outlets for said elementary 
images, which outlets are coupled to respective inlets of video 
projectors. In a preferred embodiment, the conversion device may include 
an interpolator device such that the flat images are deanamorphosed with 
interposition of intermediate pixels, e.g. calculated by interpolation, so 
as to increase the resolution of the image. 
An autostereoscopic video system may incorporate image projection apparatus 
such as that defined above. It is characterized in that it comprises: 
a device for generating autostereoscopic images; 
an image transcoding device for transcoding the autostereoscopic images 
into a plurality of elementary images and for deanamorphosing them; and 
projection apparatus according to any one of claims 1 to 4.

As shown in the above analysis of the prior art, there are at present two 
main ways of obtaining autostereoscopic images, one of which (U.S. Pat. 
No. 3,932,699) implements a lens array adjacent to a video camera, and the 
other of which is much more elaborate and projects an image filmed by a 
conventional video camera onto a diffusing screen. 
In FIG. 1, a picture-taking device of U.S. Pat. No. 3,932,699 comprises a 
camera 10 which is associated with an objective 9 having a mean plane 9'. 
A point 2 of an object 1 to be displayed emits rays 3 and 4 that are 
received by the full aperture of the lens 9. In the same manner, each 
point 9" receives light from all of the points of the object 1 (extreme 
received and re-emitted rays 5 and 6). The lens 9 is a converging lens 
placed in front of a radiation-sensitive surface 8 of the camera 10. The 
camera may be a Vidicon tube receiver, for example. A dispersing element 
7, in particular a lens array adjacent to the photosensitive element makes 
it possible to achieve a plurality of elementary images of the scene to be 
filmed in a manner that is spatially repetitive, thereby enabling the 
camera 10 to transmit stereoscopic image information. The inlet surface of 
each elementary lens making up the lens array 7 is cylindrical in section 
about a vertical axis, while the outlet surface of each lens element is 
plane. As mentioned above, this picture-taking device presents major 
geometrical aberrations because of the need for the optical system to have 
a very large aperture in order to conserve an adequate stereoscopic 
baseline. In addition, a lens array having the dimensions of a standard 
video sensor is very difficult to make, particularly since its focal 
length must be very short (of the order of 100 microns, which is almost 
incompatible with any practical implementation). 
The stereoscopic television system proposed by McCormick et al. at the 
colloquium on stereoscopic television (London, Oct. 15, 1992) and which is 
summarized in the article "Restricted parallax images for 3D TV" takes 
pictures in the manner shown in FIG. 2. It comprises an autocollimating 
transmission screen 12 having two adjacent arrays of cylindrical lenses 11 
and 13, and a lens L' at whose focus there is placed a screen that is made 
up of a third array of cylindrical lenses 14 and a frosted screen 15. The 
stereoscopic image formed on the frosted screen 15 is transferred by an 
optical system 16 and projected in reduced form onto the sensitive portion 
18 of a detector 19, e.g. a Vidicon tube. The concept of that system is to 
use a video camera (16, 18, 19) to take a picture in conventional manner 
of an image projected on a screen. That picture-taking device is very 
complicated since it uses at least three arrays of cylindrical lenses 
which must be accurately positioned geometrically relative to one another, 
and it also uses projection onto a diffusing screen, thus giving rise to 
losses of light efficiency, of resolution, and of contrast. Such a device 
is also sensitive to mechanical vibration and to temperature variation, 
both of which phenomena are liable to give rise very quickly to moire 
patterns that are most disagreeable in appearance and that considerably 
degrade the stereoscopic information. 
FIGS. 3a to 3c describe a picture-taking device of the invention. It 
comprises the following elements: 
1) An entrance objective that is preferably telecentric, comprising an 
inlet lens L.sub.1 and an outlet lens L.sub.2 whose focus F.sub.2, in a 
telecentric system, coincides with the optical center O.sub.1 of the lens 
L.sub.1. Such an entrance objective is known per se from European patent 
application EP-A-0 84998 (CNRS). When an optical system is telecentric, 
the image of the central point of the inlet pupil of the lens L.sub.1 is 
sent to infinity by the lens L.sub.2, thereby giving rise to parallelism 
making it possible to engage the lens array in favorable manner. In 
particular, the two lenses L.sub.1 and L.sub.2 may be conjugate, i.e. the 
focus F.sub.1 of the lens L.sub.1 may also coincide with the optical 
center O.sub.2 of the lens L.sub.2. By way of example, the objective 
L.sub.1 may have a focal length of 200 mm and an aperture of f/2, which 
corresponds to a working pupil diameter of 100 mm, which distance 
constitutes the available stereoscopic baseline for taking pictures. This 
value which is significantly greater than the spacing between the eyes of 
an observer (or inter-pupil distance, which is about 65 mm), is 
particularly favorable for achieving realistic stereoscopic perspective 
after projection on a screen. 
2) A lens array having an area of about 70 mm.times.90 mm made up of 
elementary lenses disposed vertically and having a pitch p of 0.4 mm and 
disposed substantially in the focal plane of the entrance objective (in 
practice very slightly downstream therefrom). Each of the elementary 
lenses has a focal length such that, for an image area equal to the pitch 
p of a microlens, i.e. 0.4 mm wide, the image of the pupil of the 
objective F.sub.1 formed through each of the elementary lenses is exactly 
0.4 mm. This makes it possible for all of the pupil images formed by each 
elementary lens (or microlens) to touch one anther exactly. It may be 
observed that since the array 20 is made up of cylindrical type lenses, 
the dimensions of pupil images are naturally to be considered in the 
horizontal plane. 
3) A transfer optical system which is preferably orthoscopic, i.e. which 
does not induce vertical line deformations, and possibly comprising a 
field lens L.sub.3 positioned downstream from the lens array 20 to send 
all of the light rays from the array 20 towards an image transfer 
objective L.sub.4. The objective L.sub.4, e.g. having a focal length of 25 
mm, is mounted on a camera 22 provided with charge-coupled sensors. This 
transfer optical system L.sub.3, L.sub.4 forms a real image 21 of the lens 
array 20 immediately upstream from the sensors of the camera The 
magnification of the transfer optical system L.sub.3, L.sub.4 is selected 
so that rays emerging from the lens array 20 are sent to the camera 22 
under conditions such that the image 21 has a pitch p' corresponding to an 
integer number of image points (pixels) of the image sensor 22. In 
addition, the distance between the image 21 and the image sensor 22 is 
such that focusing takes place on the sensor(s) of the camera 22. 
The elements of the entrance objective and of the transfer optical system 
are disposed in such a manner that in the absence of the lens array, the 
image of the pupil of the entrance objective coincides substantially with 
the pupil of the transfer optical system. This condition ensures, in 
particular, that when the entrance objective is not telecentric, the 
transfer optical system restores parallelism in a manner described below. 
In particular, the sensor 22 integrated in the camera 27 may include three 
charge-coupled sensors 25, and 26 mounted on a prismatic three-color 
beam-splitter 23, which sensors are accurately aligned so that the first 
pixel of the first line coincides for each sensor, and in general, so that 
the images of the three sensors 24, 25, and 26 are thus in alignment pixel 
by pixel. 
The signal from the camera 27 may be applied to a video recorder 40' or to 
a video monitor 40 that has been adapted in known manner for displaying 
autostereoscopic images, or else it may be delivered to a transmitter 41' 
so as to be received by receivers 42'. 
EXAMPLE 
A lens array 20 having a pitch of 0.4 mm and a focal length of 1.66 mm was 
disposed 20 mm from the optical center of L.sub.2 and at 90 mm from the 
optical center of L.sub.3. The lens L.sub.1 was constituted by a doublet 
L'.sub.1, L'.sub.2. Its pupil is written P.sub.1. 
L.sub.1 focal length f.sub.1 =200 mm 
L.sub.2 focal length f.sub.2 =300 mm 
L.sub.3 focal length f.sub.3 =230 mm 
L.sub.4 focal length f.sub.4 =25 mm 
distance O.sub.1 O.sub.2 between the optical centers of the lenses L.sub.1 
and L.sub.2 : O.sub.1 O.sub.2 =180 mm 
distance O.sub.2 O.sub.3 between the optical centers of the lenses L.sub.2 
and L.sub.3 : O.sub.2 O.sub.3 =110 mm 
distance O.sub.3 O.sub.4 between the optical centers of the lenses L.sub.3 
and L.sub.4 : O.sub.3 O.sub.4 =245 mm. 
The system of the invention is particularly advantageous for the following 
reasons. 
To implement a three-dimensional picture taking unit, it is necessary for 
the system to enable a scene to be observed from different viewpoints, 
there being two or more viewpoints, and for each viewpoint to be 
sufficiently far from the preceding viewpoint for there to be a 
considerable difference (or disparity) between the views. When the picture 
is taken using a single objective, and without moving these component 
elements in the plane parallel to the image plane, all of the relative 
displacement of the axes of the viewpoints must be contained within the 
horizontal diameter of the pupil of the objective which thus constitutes 
the total available stereoscopic baseline. In the example described above, 
the total stereoscopic baseline, or working horizontal diameter of the 
pupil is equal to 100 mm, i.e. it is greater than the distance between the 
pupils of an adult human (about 65 mm). In order to obtain a stereoscopic 
baseline of 10 cm with an objective that does not have significant 
defects, and for the perspective of the filmed scene to be no different 
from that perceived by an observer, it has been discovered experimentally 
that a ratio of about 2 between the focal length and the working 
horizontal diameter of the pupil gives the looked-for results. This has 
led, in the above example, to using an objective having a lens L.sub.1 
with a focal length of 200 mm for an aperture f/2. 
The focal length should not be considered as such, since account must be 
taken of the dimensions of the sensitive surface used. For a standard 
tri-CCD camera provided with sensors forming a target of about 8.8 
mm.times.6.6 mm, this focal length defines a very narrow object field, and 
indeed one that is less than one-tenth of the field (about 160 mm) 
provided by the "standard" focal length for such a surface (i.e. about 16 
mm). The solution to this problem of reconciling an appropriate 
stereoscopic baseline with a standard focal length is to separate these 
two incompatible requirements by using an intermediate first image plane 
having an area that is ten times greater, for example. This area is 
physically embodied by a lens array having a working area of 80 
mm.times.60 mm. This image is transferred by a second objective having a 
short focal length, e.g. 25 mm mounted on the camera So as to make the 
image it forms of the array coincide with the CCD charge-coupled sensors. 
Once the stereoscopic baseline has performed its function in forming the 
image on the array of vertical cylindrical lenses, it is possible to 
reduce the image by transferring it in air while conserving the angle of 
the object field. 
More particularly, by using simultaneously both the objective L.sub.1, 
L.sub.2 which is preferably telecentric, and the transfer device L.sub.3, 
L.sub.4, it is possible to reduce the dimensions by a factor of about 10 
in the present example, since the working area of the first image plane is 
about 60 mm.times.80 mm. Since the lens array 20 is disposed substantially 
at the first image plane of the optical system L.sub.1, L.sub.2, this 
makes it possible to conserve the benefit of the 10 cm stereoscopic 
baseline in spite of the reduction of the image format on the sensor 22. 
The use of an initial area of 60 mm.times.80 mm makes it possible to 
combine both the field which is little greater than the standard focal 
length for this format (160 mm) and the large stereoscopic baseline which 
is equal to 10 cm. 
Another advantage of the invention consists in greater ease of manufacture 
and of positioning of the lens array 20. It is much easier to manufacture 
one array, particularly when its pitch is 0.4 mm, than it is to 
manufacture three arrays at a pitch of 0.04 mm. It would also be extremely 
difficult to position three microarrays in the three CCD sensors while 
ensuring exact superposition of the three color images (red, green, blue) 
obtained in this way taking account simultaneously of the parallelism of 
the microlenses and of the image planes, and of the pitch and the phase of 
the lenses, while nevertheless conserving the functionality and the 
cleanness of the sensors. That could only be done by a manufacturer of 
camera sensors. By transferring the image in air in accordance with the 
invention it becomes possible to use a single array that is easily 
adjustable and removable, should total compatibility of equipment be 
desired (between taking pictures in relief and equipment as used today). 
The picture-taking device of the invention makes it possible firstly to use 
a single array 20 for all three colors, and secondly for this array to be 
of large dimensions, thereby making it easier to manufacture and to 
position with the desired accuracy. This avoids the drawbacks both of FIG. 
1 (small sized array difficult to position in the sensor, and in any event 
not avoiding the geometrical distortions inherent to that geometry), and 
of FIG. 2 (large number of lens arrays which are practically impossible to 
keep in alignment except under very severe experimental conditions). 
In a preferred embodiment, the second objective L.sub.4 for transferring 
the image has an iris diaphragm. Such a diaphragm is equivalent to a 
diaphragm in the form of a horizontal slot in the first objective L.sub.1, 
L.sub.2, but it is easier to position since the only parameter is the 
centering thereof. The centered iris diaphragm of the second objective is 
equivalent to a diaphragm in the form of a horizontal slot in the first 
objective. Since the array used is of the vertical cylinder type, the 
light rays emerging from the first pupil are not disturbed in the 
direction parallel to the axis of the microlenses, whereas in the 
horizontal direction, these rays are definitively tied to the images of 
the pupil as obtained by each microlens. The images of the pupil cannot be 
affected by reducing the size of the pupil in the second objective. 
Because the sensors 24, 25, and 26 of the camera operate in discrete 
manner, it is possible to avoid dividing the pupil into as many sub-pupils 
as there are selected viewpoints. While the image is being transferred, 
the image of the array 20 is positioned in such a manner that each image 
of each lens (or microimage of the pupil) is formed on an integer number 
of image points (or pixels) equal to the number of viewpoints. The 
discrete nature of the sensitive surface of CCD sensors gives rise to the 
first pupil of the system being rendered discrete by the reversibility of 
light paths. Because the microimages of pupil No. 1 that are formed at the 
location of the lens array (in the manner of a continuum) are projected 
onto a structure that is discrete not only in space but also with respect 
to energy, it is possible to subdivide the pupil into distinct 
geographical zones that are equal in number and in relative disposition to 
the pixels put into exact correspondence with the lenses of the array. In 
the above example, each microlens image is formed horizontally on four 
pixels, thereby subdividing the main pupil into four equal zones separated 
by portions that are made blind because they correspond to the inter-pixel 
gaps of CCD sensors. The horizontal structure of the selected sensitive 
surface determines the resulting structure of the pupil available for 
taking pictures in relief and consequently determines the means for 
processing the image obtained in this way. The fact of using four pixels 
per microlens leads to four viewpoints being filmed simultaneously (one 
viewpoint per sub-pupil). Electronic processing of the image becomes 
possible because the processing is performed on the smallest entity of the 
resulting composite image: the pixel, thus giving rise to excellent 
separation between the viewpoints. Permutation of pixels in columns 
defined by the edges of the images of the microlenses corresponds to 
permutation of the positions of the above-described sub-pupils. 
Even better stereoscopic separation can be obtained by having the direction 
of the lines of the sensor 22 parallel to the axes of the lenses in the 
lens array 20. The separation between adjacent image points belonging to 
different lines is greater than that between adjacent image points 
belonging to the same line. This corresponds to positioning that is at 
90.degree. compared with ordinary conditions (vertical line scanning), but 
if so desired, that can be reestablished by appropriate electronic 
processing. 
When the image from the tri-CCD camera is processed at pixel frequency or 
at line frequency (depending on the direction in which it is desired to 
film a scene in three dimensions) in the mode referred to as "N image 
mode" (in columns or lines), the image is recomposed in real time in such 
a manner that on the receiver there appears an image that is cut up into 
four vertical portions (when processing with a pitch of four) each 
containing one viewpoint. Pixel No. 1 remains in place, No. 2 becomes No. 
1 for the second viewpoint, No. 3 becomes No. 1 for the third viewpoint, 
and No. 4 becomes No. 1 for the fourth viewpoint. No. 5 becomes pixel No. 
2 of the first viewpoint and so on modulo 4. This implies that when the 
viewpoint No. 1 is being observed, only one pixel in four of the initial 
image is being observed. For viewpoint No. 1, the numbers of consecutive 
pixels in the first line correspond to 1, 5, 9, 13, 17, 21, 25, 29, 33, 
37, 41, etc. . . . up to the end of the working line. For the second line, 
the sequence beings again identically and so on for the entire image. The 
total width of a viewpoint is equal to one-fourth of the screen, and the 
viewpoint is represented by a flat image of the filmed scene which is 
compressed in the horizontal direction, i.e. a flat image of anamorphosed 
format for each of the four viewpoints. The connection between the pixels 
of CCD sensors, the microlenses situated in the first image plane, and the 
sub-pupils of the main objective has been shown above. It can be seen that 
the viewpoint as reconstructed in this way corresponds exactly to one of 
the four sub-pupils (assuming a setting of four pixels per microlens). 
When, by means of a diaphragm positioned in the main objective, the optical 
path corresponding to one of the sub-pupils is interrupted, the 
corresponding viewpoint on the display screen disappears. If the lens 
array of the camera system is observed, it can be seen that light then 
illuminates no more than three-fourths of each microlens, and if the CCD 
sensor could be observed directly, it would be seen that one pixel in four 
was receiving no light. 
Thus, the slightest error in positioning the camera relative to the array 
gives rise to defects that are perfectly identifiable and reproducible in 
the correspondence between the array and the sensors of the camera. Such 
projection errors give rise to darkening defects of viewpoints in the N 
image mode associated with a partial diaphragm at the location of the 
sub-pupils. Without this mode of processing, it would be necessary to 
identify darkening defects on one pixel out of four and to be capable of 
identifying the portions of the screen where the dark pixel no longer 
belongs to the same series. Adjustment defects give rise to 
non-orthoscopic projection of the array and the resulting moire shapes are 
highly changeable, giving rise to moire patterns of increasing size as the 
lens frequency comes close to the pixel frequency divided by four assuming 
only the magnification of the projection is not perfect), to trapezium 
shapes or to moire patterns that are curved at progressive frequencies. N 
image mode makes it possible to magnify the phenomenon about 200 times, so 
defects are observable on the scale of one-fourth of the screen rather 
than on pixel scale. Adjustment accuracy and repeatability becomes 
accessible without inspection apparatus of the kind to be found in optical 
laboratories. Once experience has been gained, it is easy to associate a 
correction in the positioning of the camera in three dimension by means of 
micrometer screws with defects observed macroscopically in each viewpoint 
by this method, so as to obtain a good spatial distribution of viewpoints 
on display and/or on recording. Errors of this kind cannot be put right 
subsequently. 
In FIG. 4, a transcoding module comprises: an input module ME having an 
analog-to-digital converter ADC, and a synchronization and phase-locked 
loop circuit BVP/SYN; a control module MC including an interface operator 
INT, a microprocessor MP, and a databank DB; a digital module MD having a 
circuit GSE for generating write address signals, a circuit GSL for 
generating read address signals, a transcoding line memory MLT, a 
transcoding pixel memory MPT, a first image memory MI.sub.1, and a second 
image memory MI.sub.2 ; and an output module comprising a circuit GSS for 
generating output synchronization signals, a digital-to-analog converter 
DAC, and/or a module DT for generating video digital images on an input 
bus DV. The digital output of the circuit DT or the analog outputs of the 
converter DAC make it possible to obtain a transcoded image 30 comprising 
a plurality (in this case four) flat images 31 to 34 of anamorphosed 
format that are disposed side by side. Each flat image contains all of the 
information for a single stereoscopic viewpoint. Its height is equal to a 
normal image, and its width is equal to one-fourth the width of a normal 
image. 
For color images, the converter circuits ADC and DAC operate in three times 
8-bit mode, i.e. with a definition of 8 bits for each of the three colors. 
The line memories or transcoding pixel memories (MLT, MPT) serve to 
perform write addressing, and the read and write signal generators GSL and 
GSE communicate via 10-bit buses. 
The digital module MD performs all of the processing required for 
implementing the algorithm specific to the selected mode (N anamorphosed 
images, relief mode) with output that is interlaced or progressive. 
By way of example, the ADC converter circuit may be a triple BT 253 
converter (Brooktree), the DAC converter circuit may be a triple BT 473 
converter (Brooktree). The synchronization extractor SYN may be an LM 1881 
circuit (National Semiconductor) operating directly on video signals by 
extracting composite synchronization therefrom. The phase-locked loop BVP 
may be a 74HC4046 circuit (Motorola). 
Write address signal generation GSE may be integrated in a programmable 
logic circuit. The same applies to read address signal generation in the 
circuit GSL. The microprocessor MP is also programmable to perform other 
functions such as freezing an image, or freezing an image color by color. 
The image memories MI.sub.1 and MI.sub.2 constitute image planes that 
alternate in writing and reading at the end of each image coming from the 
CCD camera. For each color, each image memory MI.sub.1, MI.sub.2 can 
accept 1024 lines of 1024 pixels, for example, and given that there are 
three colors, that corresponds to 3 megabytes for each memory. 
Under such circumstances, 20 address bits are used to access all of the 
pixels in a plane. 
Whether for reading or writing, the address generators or counters are made 
up as follows: 
the 10 least significant bits represent the position of an image point or 
pixel along a line, and 
the 10 most significant bits represent the position of the line in the 
image (line number). 
The counters provide a linear value starting at zero and incrementing 
regularly up to the programmed maximum value corresponding to the selected 
video standard. 
All of the image processing performed in the context of the invention 
relies on permutations of pixels and/or lines in application of an 
algorithm that is specific to the selected mode. 
Given that such algorithms are practically impossible to compute in real 
time (less than 70 ns), the switchovers or permutations are precalculated 
and are held in the data bank DB of the control module MC. This data bank 
DB serves to load one or other of the memories MLT and MPT which are 
placed as buffers between the image memories (MI.sub.1, MI.sub.2) and the 
outputs from the address generators. 
Thus, for each address coming from the write counter, a new address is 
issued enabling the pixel or the line coming from the camera to be written 
into any location in image plane MI.sub.1 or MI.sub.2. This is implemented 
by using a transcoding memory MLT or MPT. 
Each address block of said bit leaving the counters is associated with a 
transcoding memory MLT or MPT to a depth of 1024 times 10 bits. The 
outputs from these memories constitute new 20-bit addresses which are 
connected directly to the memories MI.sub.1 and MI.sub.2 while writing. A 
special feature of these memories is that they are very fast (response 
time less than 20 nanoseconds). 
The 10 bits of the pixel address CP (see FIGS. 5 and 6) are incremented by 
the clock at the frequency of 14.1875 MHz of the synchronizing and phase 
locking circuit BVP/SYN. This frequency is tuned to the internal clock of 
the CCD camera. 
The 10 line address bits CL are incremented by line synchronization coming 
from the circuit BVP/SYN. 
The pixel transcoding memory MPT is always addressed with a 10-bit counter 
and is therefore seen as a single block running from 0 to 1023 whatever 
the mode, whether: in relief; N image; interlaced outputs; or progressive 
outputs. 
The line transcoding memory MLT is split into two portions, i.e. addresses 
0 to 511 for the first field including the odd lines of the image in 
interlaced mode coming from the CCD camera, and addresses 512 to 1023 for 
the second field that comprises the even lines of the image. The address 
is obtained by a 10-bit counter CL whose tenth bit is constituted by the 
field parity signal PTR (see FIGS. 5 and 6). 
For an output in interlaced mode (FIG. 5), the image memories MI.sub.1 and 
MI.sub.2 are also subdivided into two blocks each, with the transcoding 
algorithm being such as to make it possible during reading to find odd 
lines corresponding to the first field (field 1 to be displayed) in the 
first block, and even lines corresponding to the second field (field 2 to 
be displayed) in the second block. Under such circumstances, the 
organization is as follows. The first field has addresses 0 to 511 Kbytes 
and the second field has addresses between 512 Kbytes and 1023 Kbytes (1 
Kbyte=1024 bytes). 
For all modes with progressive outputs (50 images/s), (FIG. 6), the image 
memories MI.sub.1 and MI.sub.2 are each constituted as a single block, 
reading finding the lines to be displayed in the first 576 Kbytes of the 
image plane. 
This organization has the advantage that, since the transcoding memory is 
split into two by the tenth bit (or parity bit) that does not belong to a 
counter, image memory MI.sub.1 or MI.sub.2 is split into two for 
interlaced output merely by the contents of information in the line 
transcoding memory MLT. This organization facilitates the programming of 
algorithms. 
In addition, transcoding is performed at write time for reasons of speed, 
it being understood that reading may take place at twice the frequency 
when providing progressive output. This architecture therefore makes it 
possible to take best account of all possible cases. 
It will be understood that if it is not desired to provide an output in 
progressive mode, then transcoding could be performed while reading, or 
part of it could be performed while writing and another part while 
reading. 
The input module M3 serves to digitize the levels of the analog signals 
that represent the colors of each image point or pixel. The digitizing 
frequency is close to 14 MHz and the resolution for each color is 8 bits. 
The analog-to-digital converter ADC programmed by the control module MC 
enables gain and black level for each color to be adjusted, with the 
clamping circuits for each color being incorporated in known manner in the 
converter (it is recalled that with standardized television transmission, 
e.g. SECAM, , or NTSC, this is done by using levels given at the 
beginning of each line). 
The synchronization extractor SYN and the phase-locked loop BVP may be 
integrated in a single component. It may be observed that the component 
may be selected from those that present jitter remaining within very small 
limits (less than 5 nanoseconds). 
This quality makes it possible to obtain an image point or pixel of the 
same size at the beginning and at the end of a line. 
In addition, the frequency of the phase-locked loop BVP is selected to be 
identical to the sampling frequency of the camera. This makes it possible 
to ensure that no original pixel is repeated twice or is lost. Accurate 
latching onto image points or pixels is very important when providing 
images in relief, since any offset can give rise to complete or partial 
loss of the perception of relief. 
To make implementation simple, the frequency of the phase-locked loop BVP 
is doubled so as to make it possible to double the speed of image reading 
for all operating modes when using progressive output. A divide-by-two 
bistable thus provides a pixel clock for writing. This bistable is reset 
to zero on each line to eliminate a 1-pixel shift on display that would 
arise each time the apparatus is switched on. 
The output module MS serves to play back the color image that has been 
processed, either in analog form (converter DAC) or in digital form 
(module DT and output bus DV). The playback frequency is either the 
digitizing frequency or twice that frequency, giving a maximum of 30 MHz 
with 8-bit resolution per color. 
The digital-to-analog converter DAC combines several functions, in 
particular the function of synchronization mixing, and the function of 
color adjustment, in a manner that is known per se. 
The logic circuit GSS for generating output synchronization is practically 
transparent in all interlaced output modes. The original synchronization 
signals coming from the phase-locked loop BVP are put through directly to 
the output. 
In progressive output modes, the logic circuit uses the original 
synchronization to recreate synthetic synchronization signals for 
televisions and monitors that accept scanning speeds that are twice those 
provided by the input camera (50 images per second or 60 images per 
second). The main advantage of scanning at twice the speed is to eliminate 
the flicker which can sometimes be seen on present-day standards, with the 
flicker phenomenon being made worse by the process of providing television 
in relief. This logic circuit is integrated in programmable logic 
circuits. 
The control module MC makes it possible to program the adjustment of black 
level clamping for the input signals, to configure the programmable logic 
circuits of the digital module as a function of the selected mode, to 
configure the programmable logic circuit of the synchronization 
synthesizer GSS depending on the selected mode, to correct output colors 
by means of tables integrated in the digital-to-analog converter DAC, and 
in general to perform auxiliary functions via an interface INT. 
The data bank DB contains all of the information to be copied into the line 
and pixel transcoding memories MLT and MPT for pitches 1 to 8 (i.e. for 
numbers of viewpoints lying in the range 1 to 8), and for all the modes 
that are described below. 
It also contains data enabling the programmable logic circuits of the 
synchronization synthesizer GSS, of the write signal generator GSE, and of 
the read signal generator GSL to be reinitialized as a function of the 
algorithms and the output modes selected by the operator. 
The operator interface INT includes a liquid crystal display screen and a 
keyboard, and it is connected to the system, e.g. via a synchronous serial 
link of the "I2C BUS" type from Philips. 
It is also possible to replace the operator interface INT by an external 
computer which optionally makes it possible to load the read/write 
transcoding memories with algorithms that were not initially provided in 
the apparatus. 
In the description below, each of its modes is analyzed on the basis of 
three graphical representations, as follows: 
a representation of the screen after processing; 
a table showing the action of the transcoding memory; and 
a summary of the hardware elements and of the signals involved. 
For the tables representing the action of the transcoding memory, MLT or 
MPT, the following are identified on the basis of the input standard 
(normal stereoscopic image or in "N image" mode, i.e. corresponding to a 
plurality of flat images of anamorphosed format disposed side by side): 
transcoding mode (relief mode or N image mode, e.g. for output to the video 
recorder 46); and 
output standard (interlaced mode and/or progressive mode). 
It should be observed that the Applicant's U.S. Pat. No. 5,099,320 issued 
on Mar. 24, 1992 describes how to obtain an image in relief mode from 
cylindrical lenses that provide an image in inverted relief. That patent 
describes in particular the address permutations which make it possible to 
obtain an image in true relief. 
FIG. 7 shows a transcoding module corresponding to FIG. 4, but which shows 
only the elements required for transcoding between an input image made up 
of interlaced images at 25 images per second, and an output image made up 
of interlaced images at 25 images per second, and on which "pixel mode" 
processing is performed. Pixel mode is defined as a mode having horizontal 
line scanning and in which information in relief is processed by 
permutation of pixels within a line, without permutation between the 
lines. 
As described above, the circuit BVP/SYN receives in known manner a 
composite synchronization signal SYNC at low level from the 
analog-to-digital converter ADC, and at its output it delivers a line 
synchronization signal SYNL, a field parity signal PTR, and a pixel clock 
signal at twice the frequency of the frequency corresponding to 25 images 
per second, said signal having its frequency divided by two by the 
frequency divider D.sub.1 which is reset to zero at the beginning of each 
line by the signal SYNL. The pixel clock signal HLP provided at the output 
from the divide-by-two circuit D.sub.1 is applied firstly to the clock 
input of the digital-to-analog converter DAC, and secondly to the count 
input H of a pixel precounter PCP which is reset to zero at the beginning 
of each line by the signal SYNL, and finally to one of the inputs of an 
AND gate E.sub.1 whose other input receives the output from the pixel 
precounter PCP, the output of the AND gate being applied to the count 
input H of a working pixel counter CPI which is likewise reset to zero at 
the beginning of each line by the signal SYNL. 
The field parity signal PTR is divided by two by a divider D.sub.2 so as to 
interchange the write and read operations between the image memories 
MI.sub.1 and MI.sub.2 for each image. In other words, the images provided 
by the camera are recorded first one in the memory MI.sub.1, then the next 
in the memory MI.sub.2, then the next again in the memory MI.sub.1, and so 
on. This facilitates reading since the memory MI.sub.1 is read during the 
time while the memory MI.sub.2 is being written, and vice versa. 
The field parity signal is also supplied to the 10-bit control bus for the 
plane addresses of the image memories MI.sub.1 and MI.sub.2 so as to 
identify the sector within said memories that corresponds to one or other 
of the fields of an image. 
For line counting, the synchronization signal SYNL is supplied to a line 
precounter PCL which is reset to zero by a field synchronization signal 
SYNT supplied by the synchronization circuit SYN that is integrated with 
the phase-locked lock BVP. The signal SYNL and the output signal from the 
line precounter are applied to the inputs of an AND gate E2 whose output 
is applied to the count input H of a working line counter CLU which is 
reset to zero by the field synchronization signal SYNT. The output from 
the working line counter CLU serves to address the image memories MI.sub.1 
and MI.sub.2 from a 10-bit address bus. The writing and reading of data in 
the image memories MI.sub.1 and MI.sub.2 are performed under the control 
of a bus comprising three times 8 bits, with this being done in writing 
from the analog-to-digital converter ADC, and in reading to the data 
inputs D of the digital-to-analog converter DAC which also receives a 
composite synchronization signal SYNC-TTL supplied by the circuit BVP/SYN. 
In the configuration of FIG. 7, the line address ADRL is supplied directly 
in conventional manner to the image memories MI.sub.1 and MI.sub.2, 
whereas the pixel addresses ADRP are supplied by taking account of the 
correspondence table that is stored in the pixel transcoding memory MPT. 
It should be observed that in all cases of processing applied to pixels at 
25 images per second, the size of the memory can be very small since the 
processing can be performed line by line instead of image by image (or 
field by field). 
FIG. 8 shows a transcoding module in which the input is at 25 interlaced 
images per second while the output is at 50 progressive images per second, 
with processing being by pixel. For write operations, the organization of 
the architecture is the same as in FIG. 7 (circuits D1, PCP, CPI, MPT, 
PCL, CLU, D2, E1 and E2). The difference in architecture relates to 
reading because of the need to generate synthetic synchronization signals 
at 50 images per second (or at 60 images per second for the NTSC 
standard). 
To synthesize these synchronization signals, the transcoding module has a 
second working pixel counter CPI2 whose count input H is connected to the 
output of an AND gate E3 having one input that receives the 2.times.HLP 
signal provided by the synchronization circuit SYN and whose other input 
is connected to the output of a second pixel precounter PCP2 whose count 
input H receives the 2.times.HLP signal. A synthetic synchronization 
generator GSS receives from the circuit BVP/SYN both the field 
synchronization signals SYNT and the line synchronization signals SYNL 
together with the signal 2.times.HLP. By way of example, the circuit GSS 
may be an LM 1882 integrated circuit (National Semiconductor). On the 
basis of these signals, it provides at its output a synthetic field 
synchronization signal SYNTS and a line synchronization signal SYNLS 
corresponding to a video image in 50 progressive images per second mode in 
the present example. The circuits CPI2 and PCP2 are reset to zero at the 
beginning of each line by the signal SYNLS. The signal SYNLS is applied to 
the count input H of a line precounter PCL2 which is reset to zero by the 
signal SYNTS. The output of the line precounter PCL2 is applied to an AND 
gate E4 whose other input receives the synthetic line synchronization 
signal SYNLS. The output from the AND gate E4 is applied to the count 
input H of a working line counter circuit CLU2 which is reset to zero by 
the signal SYNTS. The circuit CLU2 provides line addresses for reading 
alternately from the memories MI.sub.1 and MI.sub.2. Clock sequencing is 
as follows: a first image in 25 interlaced images per second mode is 
recorded in memory MI.sub.1, the following image is recorded in memory 
MI.sub.2. While writing is taking place in the memory MI.sub.2, the memory 
MI.sub.1 is read twice over in such a manner as to produce two images at 
twice the rate, each of the images being in progressive mode, by reading 
the first line of the first field, then the first line of the second 
field, then the second line of the first field, then the second line of 
the second field, and so on. 
FIG. 9 corresponds to a transcoding module having an input at 25 interlaced 
images per second and an output at 25 interlaced images per second with 
line processing, i.e. the scanning of the image lines is vertical. This 
module is similar to that of FIG. 7 except insofar as the pixel 
transcoding memory MPT is replaced by a line transcoding memory MLT which 
is fed by a 10-bit bus from the working line counter CLU and also by the 
field parity signal PTR. 
FIG. 10 relates to the case of a 25 interlaced images per second input and 
a 25 progressive images per second output with line processing, and it 
differs from FIG. 8 in the same way as FIG. 9 differs from FIG. 7. 
FIG. 11 shows an interversion table for pixels in N image mode, e.g. four 
flat anamorphosed images 31 to 34, starting from an image in fields whose 
line addresses are successively 0, 1, 2, 3, 4 up to 511 for the first 
field and 512, 513, 514, etc. up to 1023 for the second field (making 1024 
lines in all). 
Line address 0 corresponds to line 1 of the first field, address 512 to the 
first line of the second field which is the second line of the image, and 
so on. For "N-image" mode, with a pitch of 4, the first flat image of 
anamorphosed format contains pixels of ranks 1, 5, 9, 13 in each line, so 
that one line of a flat image in anamorphosed format has 185 pixels. The 
second flat image comprises pixels of ranks 2, 6, 10, 14, and so on, with 
the pixel of rank 2 in each original line appearing, after transcoding, on 
the 186th column of the image, i.e. at pixel address 185. The same applies 
to the third and fourth flat images in anamorphosed format with pixels 3, 
7, 11, 15, etc. appearing from pixel address 370 and pixels 4, 8, 12, 16, 
etc. appearing from address 555 (respectively the 371th column and the 
556th column). 
The table stored in the pixel transcoding memory MPT and corresponding to 
this conversion is shown in the lefthand portion of FIG. 12 in which the 
first pixel of a line is applied on output at pixel address 0, the 
following pixel at address 1 is applied on output pixel address 185, and 
so on. The righthand portion shows the permutation effect obtained by the 
memory MPT as written to the memories MI.sub.1 and MI.sub.2. The first 
pixel from the camera is sent to address 0, the fifth pixel to address 1, 
the ninth pixel to address 2, the thirteenth pixel to address 3, the 
second pixel to address 185, the sixth pixel to address 186, and so on, 
thereby reproducing N image mode in which all of the information in the 
autostereoscopic image is conserved in the form of four flat images of 
anamorphosed format and without loss of information. 
The diagram of FIG. 12 makes it possible, on reading, either to provide 
interlaced mode or progressive mode as described above. Going from 
interlaced mode to progressive mode merely requires special addressing of 
the lines being read and therefore has no influence on the pixel 
permutation which is the same for all the lines. 
FIG. 13 shows an implementation in N image mode with a pitch of 4 and with 
line permutation, i.e. for an image having vertical scan lines. The first 
line corresponding to line address 0 remains unchanged. The second line of 
a flat image in anamorphosed format must be line 5 of the original image 
having fields, the third line must be line 9, and so on. The second flat 
image is made up of lines 2, 6, 10, 14, etc., of the original image having 
fields. The third image is made up of lines 3, 7, 11, 15, 19, etc. of the 
original image having fields, and the fourth flat image of anamorphosed 
format is made up of lines 4, 8, 12, 16, 20, etc. of the original image 
having fields. Each flat image comprises 144 vertical lines, i.e. a total 
number of lines equal to 576 in the above example. 
The line transcoding memory MLT shown in the lefthand portion of FIG. 14 
corresponds to the table of FIG. 13 (but at a pitch of N=8). The 
organization of an image memory MI.sub.1 or MI.sub.2 as mentioned in FIGS. 
5 and 6 is recalled. The first line of address 0 of the first field 
becomes, on output, the first line of address 0, the second line of 
address 1 of the first field becomes, on output, the 145th line of address 
144, and so on. For the second field, the first line of address 512 
becomes, on output the line of address 72. Given that the image comprises 
576 lines in the present example, each flat image has a width of 72 lines. 
Further, the conversion table takes account of the fact that the image 
output is provided in interlaced mode. The righthand portion of FIG. 14 is 
similar to FIG. 12 and shows the result of address permutation performed 
when writing into the memories MI.sub.1 and MI.sub.2, with the first flat 
image being made up of lines 1, 9, 17, 25, etc., and so on. 
FIG. 15 corresponds to the case shown in FIG. 13 but for output in 
progressive mode, with the resulting correspondence in the line 
transcoding memory MLT and in the write plane being shown in FIG. 16. For 
N=4, each flat image has a width of 144 lines. The first line of the first 
field retains its address (=0). The first line of the second field which 
is the second line of the original image is positioned at address 144, and 
so on. 
A CCD camera records a full image in two stages (field 1, then field 2). 
Between the two fields, a moving scene will have shifted. During playback, 
it is necessary to keep account of the ages of fields, otherwise a 
front/back effect occurs that is increasingly pronounced as movement in 
the scene becomes increasingly ample and rapid. By displaying the image 
all on a single occasion (progressive mode), the time shift of the fields 
gives rise to slight fuzziness only. 
The following figures show how it is possible to go from an image 
transcoded in N anamorphosed image mode to an output in relief mode, while 
taking account of the fact that the original image was in inverse relief. 
For a horizontally scanned image, i.e. in "pixel mode", the conversion is 
shown in FIG. 17 in which the first four pixels 1, 2, 3, 4 of a line are 
inverted. The first of the pixels is pixel No. 4, the second is No. 3, the 
third is No. 2, and the fourth is No. 1, and so on. It may be observed 
that this inversion has already been described as such in above-mentioned 
U.S. Pat. No. 5,099,320. FIG. 18 shows a conversion table in the pixel 
transcoding memory MPT for an input in N image mode (cf. FIG. 12) and an 
output in true relief mode, regardless of whether the image is in 
interlaced mode or in progressive mode. The righthand portion of the 
figure shows the result of the transcoding performed by writing into the 
memories MI.sub.1 and MI.sub.2. The first pixel of the relief image is 
constituted by the first pixel of flat image IP4. Its address (555) 
becomes (0), the second, third and fourth pixels of the relief image are 
respectively constituted by the first pixel of flat image IP3 (address 
370), of IP2 (address 185), and of IP1 (address 0), and so on. 
FIG. 19 shows the case of an input in N image mode by lines with an 
interlaced output in relief mode with a pitch of N=4. FIG. 20 is the table 
corresponding to the transcoding line memory MLT and the consequence that 
results from writing thereto. 
FIG. 21 corresponds to the case shown in FIG. 20 except that the image is 
output in progressive mode, in application of the table of FIG. 22. 
The invention can be implemented in ways other than transcoding the image 
on the basis of digital conversion. In particular, the transcoding may be 
performed directly in the charge-coupled sensor CCD. FIG. 23 shows 
transcoding that may be performed in line mode by interposing identical 
transcoding matrices 102, 112, 122, 132, etc., which matrices are 
hard-wired and interposed between the photosensitive elements that are 
organized in columns 101, 111, 121, 131, etc., and the pixel column shift 
registers respectively 100, 110, 120, 130, etc. The transcoded image is 
recovered by the output shift register 200. 
In FIG. 24, the outputs of the shift registers 100, 110, 120, 130, etc. are 
fed into a pixel transposition matrix TP which has interconnections that 
ensure that the pixels in the output register 200 are properly reorganized 
in application of the desired transcoding mode. 
FIG. 25a shows a projection device (or back projection device) having four 
projectors 41, 42, 43, and 44 fed by an electronic system 50, each sending 
a flat image onto a display device, the various flat images being 
superposed. It will be understood that in the meaning of the present 
application, the term "projector" should be understood generically and in 
particular that it includes back projectors, i.e. projectors fitted with 
one or more mirrors. 
The embodiment of FIG. 25a uses four liquid crystal video projectors 41 to 
44 of the SHARP XV100 type, each of which has a resolution of 280 lines 
with 370 points per line in true superposed red, green, and blue colors. 
The image points or pixels are square in shape. 
The images are projected on a frosted screen 52 through a first optical 
array of the type comprising vertical cylindrical lenses or of the 
parallax barrier type. Downstream from the screen 52, there is a second 
optical array of the vertical cylindrical lens type. The image is observed 
by the eyes of an observer 55. A description of parallax barriers can be 
found, in particular in the article by Ian Sexton entitled "Parallax 
barrier display systems", published under the reference 99/2173, in the 
proceedings of the colloquium on stereoscopic television held on Oct. 15, 
1992 by the Institution of Electrical Engineers, London 1992. 
To obtain a stereoscopic display for four viewpoints, each projector 41 to 
44 projects a flat image, the four flat images being superposed on the 
frosted screen in conventional manner. As explained below, in an 
advantageous embodiment, in this mode of projection it is possible to use 
flat images in transcoded anamorphosed format as described above, and 
optionally recorded on a medium. In this case, the camera system is 
preferably used in its "pixel mode" version. Since the projectors use 
liquid crystal screens that have better remanence than cathode ray tubes, 
there is no need to operate in progressive 50 Hz mode. In other words, 
each fourth of the image contains the same pixels as in N image pixel 
mode, but they are reproduced differently on the screen, each fourth of 
the image being deanamorphosed and occupying the entire screen, with the 
various images being superposed. The stereoscopic effect is reconstituted 
by the directional effect obtained by the array 53. 
The maximum number of pixels available in a line is 740 in the application 
given by way of example, giving a maximum of 185 pixels per source. The 
SHARP XV100 back projector has a definition of about 380 pixels per line, 
i.e. half that of a television but twice that of the information available 
from each source. 
Each SHARP XV100 projector includes a source of white light, three liquid 
crystal panels, mirrors with coatings for filtering red, blue, or green 
rays depending on the panel, and a single optical system having a focal 
length of 90 mm. 
The four images are superposed on the projection plane by the optical 
systems being off-center, the planes of the panels remaining parallel to 
the planes of the images and the edges of each image being exactly 
superposed and rectangular. 
As shown in FIG. 25a, a few millimeters from the image plane (frosted 
screen 52), the four elementary images are cut up into slices by the 
optical array 51 so that for each of the four viewpoints there are formed 
small vertical lines that are interleaved and equal in number to the 
number of microlenses in the array used, without there being any 
superposition of the light information or absence thereof on the fine 
frosted screen used as the image plane. 
According to the invention, the pitch of the array 51 is chosen so as to 
avoid any moire effect with the smallest periodic structure in the 
displayed image, i.e. the pitch of the array is smaller than half a pixel. 
By way of example, for an image that is 0.9 meters wide, the array 51 has 
a pitch of about 0.8 mm, giving 0.2 mm wide elementary lines per viewpoint 
(modulo 0.8 mm) for an image having four viewpoints. 
For the projectors 41 to 44 disposed at a distance d.sub.1 from the array 
51 of pitch p.sub.1 and of focal length f.sub.1 (see FIG. 25b), and for a 
spectator placed at a distance d.sub.2 from the array 53 of pitch P.sub.2 
and of focal length f.sub.2, the condition for obtaining a solid color is: 
##EQU1## 
When observing the resultant image on the frosted screen 52, it is possible 
to see that the entire surface of the screen is illuminated and that every 
0.2 mm there is a change in viewpoint. It is necessary to travel 
horizontally through a distance equal to the total width of the image 
divided by the number of pixels for each viewpoint in order for the 
information of each viewpoint to be modified. As a result, the high 
frequency of the image is associated with the pitch of the array 51 and 
that is significantly higher than the initial pixel frequency. This avoids 
moire phenomena without degrading image definition. 
The second optical lens array 53 located between the spectator 55 and the 
frosted screen 52 is selected so as to enable binocular observation of the 
multiplexed image, the pitch and the focal length of the array 53 being 
selected in such a manner that, at the selected observation distance the 
spectator perceives in each eye only one viewpoint (a solid color, i.e. 
without moire fringes), and that both eyes see two complementary 
viewpoints (a stereoscopic pair). The solid color obtained by this system 
depends on the ratio between the distance of the first projectors 41 to 44 
from the first array 51 used for splitting up the image, and the choice of 
pitch and focal length for said array, relative to the distance between 
the spectator 55 and the observation array 53, and also the choice of 
pitch and focal length for that array. Adjustment can be performed by 
superposing lines of light coming from one of the projectors with lines 
coming from a lamp simulating one of the eyes of the observer for a given 
viewpoint. 
The pitch of the lens arrays may be selected to be as small as possible 
given the graining of the frosted screen. If the pitch of the arrays is 
too small, then the graining of the screen gives rise to a loss of 
definition. 
EXAMPLE 
The projectors 41 to 44 were 100 mm apart from one another and were placed 
at a distance (or optical path length) of 1600 mm from the frosted screen 
52. For projectors of housing width greater than 100 mm, two projectors 
were disposed horizontally, interposed with two projectors disposed 
vertically and each provided with a mirror. The first array was of the 
parallax barrier type having a pitch of 0.803 mm and a focal length of 
3.245 mm, the frosted screen 52 being placed at the focus of the parallax 
array. The second array was a vertical cylindrical optical array having a 
pitch of 0.8 mm (i.e. slightly smaller than the pitch of the first array) 
and a focal length of 17.56 mm, thus making it possible to obtain a solid 
color for an observer placed at 3000 mm. An observer having eyes spaced 
apart by an inter-pupil distance of 65 mm could see viewpoints 1 and 3 or 
2 and 4, and each eye could see an image for a single viewpoint without a 
moire pattern. 
FIG. 26 shows an output module for feeding the projectors 41 to 44. It 
comprises an interpolation delay compensator circuit RET whose output 
feeds a first shift register SR1. The circuit RET is fed with the original 
composite synchronization SYNC and also with the pixel clock 2.times.HLP 
at double rate (30 MHz). The double rate pixel clock signal 2.times.HLP 
feeds the data input of a shift register SR2 via a divide-by-four circuit 
D4 and it feeds the clocking inputs of the shift registers SR1 and SR2. 
The shift register SR1 produces shifted synchronization signals SY1, SY2, 
SY3, and SY4 which are fed to the synchronization inputs of 
digital-to-analog converters DAC1, DAC2, DAC3, and DAC4 each corresponding 
to one of the projectors 41 to 44. The shift register SR2 provides the 
line clock signals HL1, HL2, HL3, and HL4 at its outputs, which signals 
are applied to the clock inputs H of the converters DAC1, DAC2, DAC3, and 
DAC4, and also to the clock inputs H of interpolators INT1, INT2, INT3, 
and INT4. Memories MEM1, MEM2, MEM3, and MEM4 for performing amplitude 
corrections are disposed as buffers between the outputs of the memories 
MI.sub.1 and MI.sub.2 of the above-described transcoding modules and the 
data inputs of respective interpolation circuits INT1, INT2, INT3, and 
INT4. The converters DAC1, DAC2, DAC3, and DAC4 produce red, green and 
blue signals R1, G1, B1; R2, G2, B2; R3, G3, B3; and R4, G4, B4 which are 
suitable for feeding the projectors 41 to 44 via video encoders operating 
in the standard or in the S-VHS standard, which encoders are 
referenced as ENC1, ENC2, ENC3, and ENC4. 
FIG. 27 shows a transcoding operation suitable for passing from a pitch 4 
relief image to a set of non-anamorphosed flat images each suitable for 
being applied to a respective one of the projectors 41 to 44. The 
projector 41 thus receives pixels 1, 5, 9, etc., the projector 42 receives 
pixels 2, 6, 10, etc., the projector 43 receives pixels 3, 7, 11, etc., 
and the projector 44 receives pixels 4, 8, 12, and so on. Between each of 
the pixels 1, 5 and 9 there are interposed intermediate pixels represented 
by the letter I, and the same applies to each of the projectors 41 to 44. 
FIG. 28 shows a transcoding operation starting from N images in 
anamorphosed format, with this transcoding on the pixels (pixel 
transcoding memory MPT) making it possible to deanamorphose and to 
interpolate the images so as to provide the pixels in the proper order to 
the projectors 41 to 44. 
The invention is not limited to the embodiments described and shown. In 
particular, it may be observed that the lens array 20 acts in one 
direction only (horizontally). A linear object having a horizontal axis 
and placed at infinity gives rise to a real image in the downstream focal 
plane P of the array 20 (downstream in the propagation direction of the 
light rays). A linear object having a vertical axis placed at infinity 
gives a real image substantially at the focus F of the entrance objective 
(L.sub.1, L.sub.2) which focus F must be situated upstream from the 
diverging lens array 20. This gives rise to astigmatism which, in the 
present case, can disturb focusing, particularly on distant objects. 
To compensate it, it is possible to place a diverging cylindrical lens 40 
of long focal length e.g. downstream from the pupil P.sub.2 of the 
entrance objective, and preferably between L.sub.1 and L.sub.2, the 
generator lines of the diverging lens 40 being horizontal (i.e. it is 
crossed relative to the lens array 20 which is disposed vertically). Its 
focal length is calculated to move together and preferably cause to 
coincide the convergence point for vertical objects and the focal plane F 
of the diverging array. 
For horizontal objects, the light rays converge on the focus F and a 
virtual image is formed on the plane P. For vertical objects, the 
cylindrical lens 51 crossed with the lens array 20 has the effect of 
causing real images thereof to be formed in the plane P. 
Another solution is to place a second converging lens array practically in 
the same plane as the first, having the same focal length as the first, or 
a focal length calculated so that the two focal planes coincide, and whose 
pitch corresponds to a pixel (on one-fourth the pitch of the first array 
for square pixels and four viewpoints). The pupil parameters are then 
fixed. 
The transfer method of the invention is appropriate for any type of 
autostereoscopic image, and in particular for synthesized images.