STEREOSCOPIC IMAGE The present invention relates to an image-producing apparatus for recording an autostereoscopic image, and a method of incorporating the information of a stereoscopic pair of images in a single frame of sensitive material, or by an electronic imaging device, at the point of exposure. There have been proposed different ways of forming stereoscopic images but, in each case, it is necessary that two photographs notionally the "left eye" and "right eye" images be taken, effectively simultaneously, with the lenses for the two photographs being spaced by a distance equivalent to the distance between the eyes of a human viewer, that, is, of the order of 50mm to 80mm, usually 68mm. In this specification, this will be referred to as the inter—ocular distance.

In one, older, form of stereoscopic picture, there were two completely separate photographic images taken. These were mounted in pairs at the required spacing and then examined through a stereoscopic viewer, in which each eye of the observer effectively saw only the appropriate photograph.

Subsequently it was proposed to provide stereoscopic reproduction by interlacing the two images.

In this arrangement the images were arranged with narrow transparent and broader opaque lines for the panoram effect after Bressiere (late 1890's; and, later, in the 1970's this panoram effect was offered in a large format camera requiring a minimum exposure of one second, clearly limiting useful subject matter to still-life.

More recently it has been proposed tυ make stereoscopic representations by interlacing the two images in a large number of pairs of alternating bars and locating over each

of these pairs of bars an optical grid of corresponding amplitude and suitable cross-section by which arrangement, when the thus combined image was viewed, the eyes of the viewer tended to see that half of the pair of bars from each of these images which was appropriate to the particular eye so that, overall, an impression of three dimensions was achieved.

In the present specification, this will be referred to as an autostereoscopic image. An autostereoscopic image is thus one which may be viewed by a person with normal binocular vision without the assistance of any device save the overlay of a suitably dimensioned effectively transparent optical grid co-directional and in register with the image information lines.

It will be appreciated that the actual image seen by each eye is only half of the total appropriate image area but, as there can be many tens of these image line pairs per centimetre, this does not, overall, detract greatly from the picture quality.

Whilst the final result of such autosteroscopic images was most satisfactory, there have been difficulties in setting up the interlace of these, that is, the intercalation of the alternating lines of information from the images corresponding to each eye.

The present invention overcomes this difficulty.

The first object of the present invention is to provide a photographic system to provide images which can be used to give a stereoscopic effect in a manner which is more satisfactory than those previously used.

A second object of the invention is to provide a moveable mirror means for the sequential exposure of a frame of sensitive material. This mirror means may be in front of or behind the lens or lenses of the imaging apparatus.

A further object of the present invention is to provide a variable masking means to allow the consecutive exposure of selected areas of the said sensitive material. It is a third object of the invention to provide an image-producing system which is readily adaptable to preexisting image processing equipment already in widespread use.

According to the present invention, in its broadest sense, we provide a photographic system having one or more lenses, a lens shutter or focal plane shutter and light sensitive material or an electronic imaging device at the focal plane wherein there is provided a moveable mirror means associated with the lens arrangement which moveable mirror means can selectively adopt at least two conditions and selective masking means at or near the focal plane of said lens arrangement which masking means can selectively adopt at least two conditions so that stereoscopic image information may be received at the focal plane by rapid sequential exposures, with the mirror means and the selective masking means in different conditions, and the image information recorded.

According to one form of the present invention, the imaging apparatus is provided with an arrangement of mirrors which provides a stereoscopic view by means of rapid movement of some members of the mirror-group in such manner as to expose firstly one of the "left eye"-"right eye" pair of views, then the other; there being a brief interruption to exposure whilst the mirrors change their relative positions. This arrangement delivers the two images to the same position on the focal plane.

The two images obtained can impinge on two separate light sensitive receivers which could be replaced during the interruption in the exposure but it is preferred that the apparatus is further provided with a line-screen at or near

the focal plane, which line-screen has alternating opaque and transparent vertical lines and which can be displaced laterally a distance effectively equal to the width of one line of the said screen, such displacement occurring simultaneously with the movement of the mirror means, that is, during the "interruption" to the exposure. Vertical line screens in prior art have not utilised opaque and transparent lines of equal width for the clean-cut interlacing of a stereo-pair into a single frame. As discussed earlier, the image normally occupies a lesser part of the total field than the opaque material. It may ^¬ be preferred that the lines are so formed that there is a certain overlap of the transparent parts of the line screen so as to provide, in the completed exposure, a generally relatively dark line between contiguous image line pairs. Such a line would have little adverse effect on the final image quality but would enhance the appearance of the completed autostereoscopic image.

This present invention includes an arrangement of moveable mirrors and a line screen which used with modern sensitive material makes satisfactory rapidly-successive exposures of "left-" and "right-eye" images in a total time as short as 10 milliseconds thus bringing most subjects within the scope of the apparatus.

In a first form of imaging device, the moveable mirror system is located in front of a single lens and may have two rest positions wherein the effective central axes of the outward-facing mirrors are spaced at, say, 50-80mm, the arrangement being such that the exposures occur when the mirror system is in each of these rest positions. Alternatively, there can be two lenses having their effective central optical axes at a spacing of, say 50-80mm and the mirror system is behind the lenses and selectively passes the image from each lens to the focal plane.

In the first form of device mentioned above we provide a mirror system which has a section associated with each of two positions, one of which can be considered the "left eye position" and the other the "right eye position" as is well known in the stereoscopic art, wherein the required images are developed from the images that would be seen by each of a viewer's eyes.

The arrangement, could comprise a pair of mirrors for each side, the mirrors of each pair being parallel to each other and one located on the axis of the eye position and the other on the central axis perpendicular to the light-sensitive material plane and angled so that the image striking the first mirror is transfered to the second mirror and from thence to the light-sensitive material plane, as in a periscope.

In order to ensure that the required image is received on the light-sensitive material plane a lens is located between the second mirror and the plane. This lens is mounted with its axis central to the film or other medium which is to receive the image.

In the imaging device of the invention, the mirror assembly is moveable from the position described to a second position wherein a second mirror system, which is the mirror image of the first, is brought into position in front of the lens so the image from the "other eye" passes through the lens.

That, is to say the moveable mirror means comprises two pairs of parallel mirrors, each pair of said mirrors equally and oppositely inclined to an axis perpendicular to the focal plane so that the one of each pair of mirrors furthest from the said axis can be described as generally facing away from the focal plane, and the one of each pair of mirrors closest to said axis can be described as generally facing toward the focal plane wherein the two

SUBSTITUTE SHEET

mirrors furthest from the axis perpendicular to the focal plane have their central axes effectively separated by a distance of 50mm - 80mm.

The mirror means is moved horizontally between a first exposure position in which the effective central axis of that, one of the first pair of mirrors which is closest to the axis perpendicular to the focal plane is optically central to the said focal plane and a second exposure position in which the effective central axis of that one of the other pair of mirrors closest to the axis perpendicular to the focal plane is optically central to the said focal plane.

In order that the invention can more readily be understood, certain forms of mirror means shall now be described with reference to the drawings. In these drawings:

Fig 1 shows, in a plan view, the mirrors positioned for the left exposure; Fig 2 is a view similar to that, of Fig 1 showing the mirrors positioned for the right exposure; Fig 3 is a view of a second form of mirror system arranged for the left exposure; Fig 4 is a view similar to that of Fig 3 showing the mirrors arranged for the right exposure; Fig 5 is an arrangement showing the vertical movement of the mirror system and the lenticular screen positioned for the left exposure; Fig 6 is an arrangement similar to that of Fig 5 showing the arrangement for the right exposure; and Fig 7 shows a modified form of masking screen.

In each of the embodiments, the spacing between the optical axes of the left and right exposure will be the inter- ocular distance as this is the distance at which the required stereoscopic effect is maximised.

Also, in the illustrated embodiments, the lens systems necessary for the correct operation of the camera are not fully illustrated but the required systems will be well understood by persons skilled in the art.

In the embodiment illustrated in Figs 1 and 2, the moving mirror system 10 travels horizontally with respect to the masking screen 11 at the focal plane on which there is a sensitive material 12.

The mirrors 10 can be considered to be in a carriage which is constrained for movement between the two required positions and at each extreme position of movement, the mirrors are correctly located relative to the lens or lens system 15 and the focal plane.

In this embodiment there are four mirrors, the outer two of which 21 22 are at the required left and right positions so that the effective spacing of these when in their respective exposure positions is the inter-ocular distance. The other two mirrors 23 24 are each parallel to their associated mirror and are centrally located about the optical axis of the image receiving area when in their respective exposure positions.

The two optical paths are illustrated in the drawings. The masking screen 11, as will be described more fully hereinafter, comprises alternating opaque and transparent lines which permit the transmission of an image to the sensitive material 12 only through the transparent portions and this screen is moveable between two positions, spaced by the effective width of the lines, and which enable the making of two exposures on the same sensitive material, each being effectively the image from one of the positions.

SUBSTITUTE SHEET

The movement of the screen is effected together with the movement of the mirror system 10 and this movement will be described hereinafter.

A shutter arrangement, not shown, permits the two exposures to be sequentially made with the shutter being closed during the movement of the mirror system 10 and the masking screen 11.

In the embodiment of Figs 3 and 4 there is a single moving mirror 30 which operates in cooperation with a pair of fixed mirrors 31 32. The mirror 30 is pivoted and transposable by rotation on its pivot from a first exposure position, illustrated in Fig 3, parallel to the fixed mirror 32 to a second exposure position, illustrated in Fig

4, parallel to the other fixed mirror 31. The mirror pivot is vertical and positioned on the notional extension of the optical axis of the lens.

Each of the said pair of fixed mirrors 31 32 is equally and oppositely inclined to the axis perpendicular to the centre of the focal plane and laterally spaced an equal distance from the said axis and on opposite sides of it, the total spacing between the mirrors being the intei— ocular distance. The fixed mirrors are generally facing away from the focal plane.

The pivoted mirror 30 could be surface-silvered on one or both sides.

This embodiment is particularly suitable for a two-lens imaging device where the two lenses are spaced at the intei—ocular distance and the mirror system is situated between the lenses and the focal plane as illustrated. In this case, as illustrated, the pivot is vertical and situated on the axis perpendicular to the centre of the focal plane.

A further embodiment illustrated in Fig's 5 and 6 employs a vertical movement of the central mirrors 40. In this

embodiment there are two fixed mirrors 43 44 and the central mirrors 40 comprise two mirrors 42 41 each of which can selectively be brought into the optical path on vertical movement.

This embodiment can, in use, be considered equivalent to that of Figs 3 and 4 in that the mirrors 43 44 are fixed and are spaced at the inter-ocular distance and the mirrors 41 42 are parallel to the mirrors 43 44 respectively. The moveable mirrors 40 are displaced vertically from a first exposure position, illustrated in Fig 5, where the mirror 42 has its effective central axis on the optically central axis perpendicular to the focal plane, to a second exposure position, illustrated in Fig 6, where the other moveable mirror 41 has its effective central axis on the optically central axis perpendicular to the focal plane. Figs 5 and 6 also show the general form of the masking screen having alternate opaque and transparent bars. It is envisaged that combinations of the above embodiments may be used for, say, miniaturisation of the camera, for example a fixed double-periscope system as in embodiment one combined with two lenses and the moveable mirror means of the second embodiment, but these combinations lie within the scope of the present invention.

It is envisaged that in the several embodiments described above and others within the scope of the invention various motive means for the transport of the non-fixed mirrors between the successive exposures may be employed, including spring loading, solenoid or other electrically motivated, magnetic, hydraulic or pneumatic, electronic, mechanical, or any combination of the aforementioned means, for example magnetic restraint and spring loaded movement or vice versa, and are all comprehended within the scope of the present invention.

During the "interruption" between successive exposures which may be achieved by means of closure of a lens shutter, or focal plane shutter, and simultaneous with the mirror transport operation, the masking displacement function must also be carried out.

In its simplest form the masking means 11 is a plate of thin glass bearing the alternating opaque and transparent lines which are made by techniques widely used in photoengraving. The side of the screen bearing the lines is in as close proximity as possible, to the light-sensitive surface 12 during the exposures. The said masking means can be displaced laterally by the width of one line of the screen, or a convenient multiple thereof to effectively give a single line displacement, and this displacement may be achieved by similar motive means to those already described with respect to the mirror motive means of the present invention.

Of course, the transparent substrate of the screen is not restricted to a thin sheet of glass and may be any sufficiently transparent appropriate substrate. A further embodiment which provides a precise method of achieving the shielding of the first exposed lines whilst the second exposure takes place is to use a screen as illustrated, in gross scale, in Fig 7.

The areas of the screen above and below the axis X-Y are large enough to each entirely cover the sensitive material.

In a first position the first (say "left") exposure takes place. Immediatels' this exposure has been effected the screen is moved vertically to a second position without any lateral movement occurring thus opaque lines cover the recently exposed sections of the sensitive material whilst leaving ready for exposure through the transparent lines of the screen those areas as yet unexposed due to these having

been shielded by the opaque lines when the screen was positioned for the first exposure. This movement of the screen takes place simultaneously with the transport of the mirror means, and the operation of the abovementioned shutter.

A further and preferred embodiment of the masking means comprises a back plane plate having a transparent substrate with a Liquid Crystal Display (L.C.D.) array on one surface thereof and means whereby this L.C.D. array can be selectively changed from a normally opaque display to a selectively or totally transparent display. For the purposes of the masking means of the present invention it is envisaged that the whole of the back plane plate can be opaque, or that either of two sets of alternate bars can be selectively transparent, which bars are vertical and extend across the width and height of the area to be exposed. The spacing of the bars depends of the quality of the final product but can be up to, say, 200 bars per centimetre.

In this arrangement, the L.C.D. bars are interconnected in alternating pairs. That is, every second bar is interconnected, as are the alternate second bars. It is also envisaged that the L.C.D. array can be made totally transparent and with a single exposure provide a normal two dimensional image.

In the present speci ication, when referring to normally opaque, an opacity of the order of 95% is envisaged and, when referring to transparent, a transmission loss of the order of 5% or less is envisaged. These values are appropriate for L.C.D. 's which are available today, but there is reason to expect that, in the future, opacity will be higher and the transmission loss lower.

Preferably, rather than use a single display array a pair of L.C.D. arrays may be used, one on each side of the back

plane plate, and, in this case, it will be appreciated that the total opacity will be very substantially increased over a single array of L.C.D. 'S although there will be a higher transmission loss. This is not of great importance where relatively high speed photosensitive materials are employed.

The arrangement is such that, under normal conditions, the back plane plate is opaque; under a first exposure condition, one set of bars is forced to become transparent so that the light sensitive surface behind these can be exposed and, under the second exposure condition, the alternate bars are caused to become transparent, whilst the ^• first set is opaque, so that the remaining area of light sensitive surface is exposed. The said first and second exposure conditions occur when the mirror means is in its corresponding first and second exposure conditions. A double-sided L.C.D. array as described may, in the opaque condition, be used instead of, or may assist the operation of a mechanical shutter system.

The present specification describes an arrangement wherein the image is formed on a light-sensitive surface. It is to be appreciated that the imaging device of the invention can be used for many applications. For example it could be used to provide a stereoscopic photograph, X-ray or infra¬ red image or it could be used to provide the necessary information onto other media, such as a magnetic medium, or a television screen or monitor having an optically suitably cross-sectioned grid on its surface and means of registering the cathode ray image with this grid. Where the display is to be on a television screen or monitor, it is possible to form the images digitally and to have the bars of the images, and a separation bar, incorporated in the trace.

That is, the masking means can be digitally generated, and the visual information lines of each image can be transmitted either as a combined signal or sequentially. A conventional photographic film prepared by the method of the invention can be processed and printed in any normal way and then a sheet of transparent optical linegrid in which each optically suitable linegrid profile effectively overlies one pair of "left-right" image lines is placed in register directly over the print thus providing a satisfactory autostereoscopic picture.

It will be seen that the arrangement of the invention provides, very much more simply than has been possible in the past, a method of producing an image containing the visual information of a stereoscopic pair directly into the final required form and this avoids the difficulties in registration and combination if two negatives are interlaced to provide such an arrangement.

It will be appreciated that variations and modifications for example, adaptation to a photographic enlarger can be made in the described invention without departing from the spirit and scope thereof.