WO2006037987A1 - Directional printed image display apparatus - Google Patents

Directional printed image display apparatus Download PDF

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Publication number
WO2006037987A1
WO2006037987A1 PCT/GB2005/003802 GB2005003802W WO2006037987A1 WO 2006037987 A1 WO2006037987 A1 WO 2006037987A1 GB 2005003802 W GB2005003802 W GB 2005003802W WO 2006037987 A1 WO2006037987 A1 WO 2006037987A1
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WO
WIPO (PCT)
Prior art keywords
lens
printed image
lens array
images
regions
Prior art date
Application number
PCT/GB2005/003802
Other languages
French (fr)
Inventor
Graham John Woodgate
Jonathan Harrold
Original Assignee
Ocuity Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ocuity Limited filed Critical Ocuity Limited
Publication of WO2006037987A1 publication Critical patent/WO2006037987A1/en

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Classifications

    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03BAPPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B35/00Stereoscopic photography
    • G03B35/18Stereoscopic photography by simultaneous viewing
    • G03B35/24Stereoscopic photography by simultaneous viewing using apertured or refractive resolving means on screens or between screen and eye
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B30/00Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
    • G02B30/20Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes
    • G02B30/26Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type
    • G02B30/27Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type involving lenticular arrays
    • G02B30/29Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type involving lenticular arrays characterised by the geometry of the lenticular array, e.g. slanted arrays, irregular arrays or arrays of varying shape or size
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00Simple or compound lenses
    • G02B3/0006Arrays
    • G02B3/0012Arrays characterised by the manufacturing method
    • G02B3/0025Machining, e.g. grinding, polishing, diamond turning, manufacturing of mould parts
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00Simple or compound lenses
    • G02B3/0006Arrays
    • G02B3/0012Arrays characterised by the manufacturing method
    • G02B3/0031Replication or moulding, e.g. hot embossing, UV-casting, injection moulding

Definitions

  • the present invention relates to a directional print apparatus.
  • Such an apparatus may be used in a three dimensional (3D) autostereoscopic print apparatus.
  • 3D three dimensional
  • Such systems may be used for printed output from computer systems.
  • Normal human vision is stereoscopic, that is each eye sees a slightly different image of the world.
  • the brain fuses the two images (referred to as the stereo pair) to give the sensation of depth.
  • Three dimensional stereoscopic prints replay a separate, generally planar, image to each of the eyes corresponding to that which would be seen if viewing a real world scene.
  • the brain again fuses the stereo pair to give the appearance of depth in the image.
  • Fig. Ia shows in plan view a print surface in a print plane 1.
  • a right eye 2 views a right eye homologous image point 3 on the print plane and a left eye 4 views a left eye homologous point 5 on the print plane to produce an apparent image point 6 perceived by the user behind the print plane.
  • Fig. Ib shows in plan view a print surface in a print plane 1.
  • a right eye 2 views a right eye homologous image point 7 on the print plane and a left eye 4 views a left eye homologous point 8 on the print plane to produce an apparent image point 9 in front of the print plane.
  • Fig. Ic shows the appearance of the left eye image 10 and right eye image 11.
  • the homologous point 5 in the left eye image 10 is positioned on a reference line 12.
  • the corresponding homologous point 3 in the right eye image 11 is at a different relative position 3 with respect to the reference line 12.
  • the separation 13 of the point 3 from the reference line 12 is called the disparity and in this case is a positive disparity for points which will lie behind the print plane.
  • Fig. Ia For a generalised point in the scene there is a corresponding point in each image of the stereo pair as shown in Fig. Ia. These points are termed the homologous points.
  • the relative separation of the homologous points between the two images is termed the disparity; points with zero disparity correspond to points at the depth plane of the print.
  • Fig. Ib shows that points with uncrossed disparity appear behind the print and
  • Figl c shows that points with crossed disparity appear in front of the print.
  • Stereoscopic type prints are well known in the prior axt and refer to prints in which some kind of viewing aid is worn by the user to substantially separate the views sent to the left and right eyes.
  • the viewing aid may be colour filters in which the images are colour coded (e.g. red and green); or polarising glasses in which the images are encoded in orthogonal polarisation states.
  • Autostereoscopic prints operate without viewing aids worn by the observer. In autostereoscopic prints, each of the views can be seen from a. limited region in space as illustrated in Fig. 2.
  • Fig. 2a shows a print device 16 with an attached parallax optical element 17.
  • the print device produces a right eye image 18 for the right eye channel.
  • the parallax optical element 17 directs light in a direction shown by the arrow 19 to produce a right eye viewing window 20 in the region in front of the print.
  • An observer places their right eye 22 at the position of the window 20.
  • the position of the left eye viewing window 24 is shown for reference.
  • the viewing window 20 may also be referred to as a vertically extended optical pupil.
  • Fig. 2b shows the left eye optical system.
  • the print device 16 produces a left eye image 26 for the left eye channel.
  • the parallax optical element 17 directs light in a direction shown by the arrow 28 to produce a left eye viewing window 30 in the region in front of the print.
  • An observer places their left eye 32 at the position of the window 30.
  • the position of the right eye viewing window 20 is shown for reference.
  • the system comprises a print and an optical steering mechanism.
  • the light from the left image 26 is sent to a limited region in front of the print, referred to as the viewing window 30. If an eye 32 is placed at the position of the viewing window 30 then the observer sees the appropriate image 26 across the whole of the print 16.
  • the optical system sends the light intended for the right image 18 to a separate window 20. If the observer places their right eye 22 in that window then the right eye image will be seen across the whole of the print.
  • the light from either image may be considered to have been optically steered (i.e. directed) into a respective directional distribution.
  • Fig. 3 shows in plan view a print device 16,17 in a print plane 34 producing the left eye viewing windows 36,37,38 and right eye viewing windows 39,40,41 in the window plane 42.
  • the separation of the window plane from the print is te ⁇ rxed the nominal viewing distance 43.
  • the windows 37,40 in the central position with respect to the print are in the zeroth lobe 44.
  • Windows 36,39 to the right of the zeroth lobe 44 are in the +1 lobe 46, while windows 38,41 to the left of the zeroth lobe are in the -1 lobe 48.
  • the viewing window plane 42 of the print represents the distance from the print at which the lateral viewing freedom is greatest.
  • a diamond shaped autostereoscopic viewing zone as illustrated in plan view in Fig. 3.
  • the light from each of the points across the print is beamed in a cone of finite width to the viewing windows.
  • the width of the cone may be defined as the angular width.
  • the longitudinal viewing freedom of the print is determined by the length of these viewing zones.
  • the variation in intensity 50 across the window plane of a print (constituting one tangible form of a directional distribution of the light) is shown with respect to position 51 for idealised windows in Fig. 4.
  • the right eye window position intensity distribution 52 corresponds to the window 41 in Fig. 3
  • intensity distribution 53 corresponds to the window 37
  • intensity distribution 54 corresponds to the window 40
  • intensity distribution 55 corresponds to the window 36.
  • Fig. 5 shows the intensity distribution with position schematically for more realistic windows.
  • the right eye window position intensity distribution 56 corresponds to the window 41 in Fig. 3
  • intensity distribution 57 corresponds to the window 37
  • intensity distribution 58 corresponds to the window 40
  • intensity distribution 59 corresponds to the window 36.
  • Fig. 4 shows the ideal viewing windows while Fig. 5 is a schematic of the actual viewing windows that may be outputted from the print.
  • Several artefacts can occur due to inadequate window performance. Cross talk occurs when light from the right eye image is seen by the left eye and vice versa. This is a significant 3D image degradation mechanism which can lead to visual strain for the user. Additionally, poor window quality will lead to a reduction in the viewing freedom of the observer.
  • the optical system is designed to optimised the performance of the viewing windows.
  • a printed image is typically composed of an array of dots printed on to a surface of an image bearing substrate.
  • a type of parallax optic well known in the art for use in stereoscopic prints is called the lenticular screen, which is an array of vertically extended cylindrical microlenses.
  • the image bearing substrate is positioned substantially at the focus of the lenses of the lenticular screen so that the curvature of the lenses is set substantially so as to produce an image of the printed dots at the window plane.
  • the image bearing substrate may comprise one surface of the lenticular screen or may be a separate substrate attached to the lenticular screen.
  • lenticular prints have the full brightness of the base print.
  • the pitch of the lenticular screen is slightly smaller than an integer multiple of the pitch of the dot array where the integer multiple generally represents the number of views in each viewing lobe. This condition is known as "viewpoint correction".
  • viewpoint correction In a two view print, the resolution of each of the stereo pair images is half of the horizontal resolution of the base print.
  • a lenticular screen type print the columns directly under the lenses are imaged to a first set of windows in the zeroeth lobe of the print.
  • the adjacent dot columns are also imaged to viewing windows, in +1 and -1 lobes of the print.
  • Fig. 3 if the user moves laterally outside the orthoscopic zone then light from the incorrect image will be sent to each eye.
  • a two view print when the right eye sees the left eye view and yice versa, the image is termed 'pseudoscopic', compared to the correct orthoscopic condition.
  • more than two dot columns can be placed under each lens.
  • four columns will create four windows in which the view is changed for each window.
  • windows 38,41,37,40,36,39 may represent views 1,2,3,4,5,6 respectively.
  • Such a print will give a 'look-around' appearance as the observer moves.
  • the longitudinal freedom is also increased by such a method.
  • the resolution of the print is limited to one quarter of the resolution of the base print.
  • lenticular prints may have 9 or more views under each lens.
  • embodiments showing two views will generally be described. In general, a printed image will show more than two views of an image.
  • a directional printed image display apparatus comprising: a printed image surface having a plurality of images printed thereon with successive strips of each image being interlaced with each other in a regular order; a lens array having a structure which repeats at a pitch substantially equal to the pitch of the strips of one of said plurality of images, wherein the lens array is arranged such, that each respective section of the lens array at said pitch is formed to provide: at least one first region capable of directing light from the strips of the images aligned with the respective section into respective nominal viewing windows; and at least one second region capable of directing light from the strips of the images aligned with a section adjacent the respective section into the same respective nominal viewing windows.
  • Such an apparatus displays a printed image and provides directional viewing windows. It may be any type of directional printed image display apparatus, including in particular a three-dimensional autostereoscopic printed image display apparatus.
  • this invention serves to improve the image quality of the print by reducing artefacts, such as image cross-talk and image stripiness, and by increasing window uniformity.
  • the at least one second region has substantially the same imaging function as the at least one first region of said adjacent section and in this case, as compared to the prior art situation that all of a respective section of the lens directs light from the strips of the images aligned with the respective section into respective nominal viewing windows, adjacent sections may be considered as being interlaced.
  • the lens array of the present invention advantageously reduces the thickness of the lens array and thus the material usage and cost of the lens array.
  • the lens array may be formed as two layers, which may be made of polymer materials, by shaping the lens surface at the interface between the two layers, thus reducing the reflectivity of the lens surface, ⁇ n this case, the volume of material may be reduced by use of the present invention. Therefore relatively high cost materials may be used to optimise lens performance while used in small quantities, thus not increasing the device cost substantially. Similar advantages of reducing thickness could be achieved by use of Fresnel lenses in the lens array, but for the reasons discussed above, the present invention provides significantly reduced artefacts as compared to a Fresnel lens.
  • the structures of the present invention can be applied at the mastering stage of the lenses, rather than the replication stage.
  • the cost of the individual elements is not substantially affected by the complexity of the lens shape.
  • the lenses will further be more easily manufactured by means of roll processing compared to a conventional lens array, because of the lower thickness. Such lenses can thus be manufactured more cheaply.
  • Thinner lenses will be less prone to curving the base substrate and thus the substrate will be less easily deformed by the lens surface. Therefore, the lenticular print will be less prone to bending, and the window quality can thus be optimised.
  • the lenses will weigh less, and thus be more suitable for packaging applications for example.
  • a directional print apparatus comprising a printed surface arranged substantially in the focal plane of a lens array and comprising an array of groups of printed dots, the lens array being arranged to direct light into a first directional distribution, wherein: each lens of the lens array is arranged in alignment with a group of printed dots; each lens of the lens array comprises at least first and second imaging regions with respective first and second optical functions, the first imaging region being arranged to image light from a first group of dots to first viewing windows, the at least second imaging region being arranged to image light from a second group of dots to the first viewing windows, and the second imaging regions having substantially the same imaging function as the first imaging region of an adjacent lens.
  • the images may be illuminated from behind the printed image surface illuminated from in front of the printed image surface, edge illuminated, or any combination thereof.
  • Fig. Ia shows the generation of apparent depth in a 3D print for an object behind the print plane
  • Fig. Ib shows the generation of apparent depth in a 3D print for an object in front of the print plane
  • Fig. Ic shows the position of the corresponding homologous points on each image of a stereo pair of images
  • Fig. 2a shows schematically the formation of the right eye viewing window in front of an autostereoscopic 3D print
  • Fig. 2b shows schematically the formation of the left eye viewing window in front of an autostereoscopic 3D print
  • Fig. 3 shows in plan view the generation of viewing zones from the output cones of a 3D print
  • Fig. 4 shows the ideal window profile for an autostereoscopic print
  • Fig. 5 shows a schematic of the output profile of viewing windows from an autostereoscopic 3D print
  • Fig. 6 shows a first embodiment of the invention comprising a lens array in air and printed substrate
  • Fig. 7 shows a display comprising a prior art lens and printed substrate
  • Fig. 8 shows a display of the invention comprising an interlaced lens comprising first and second polymer materials and printed substrate;
  • Fig. 9 shows the use of an additional printed substrate
  • Fig. 10 shows the use of curved first and second imaging region pairs
  • Fig. 11 shows the use of plane first and second imaging region pairs;
  • Some of the various embodiments employ common elements which, for brevity, will be given common reference numerals and a description thereof will not be repeated.
  • the description of the elements of each embodiment applies equally to the identical elements of the other embodiments and the elements having corresponding effects, mutatis mutandis.
  • the figures illustrating the embodiments which are prints show only a portion of print, for clarity. In fact, the construction is repeated over the entire area of the print.
  • a cylindrical lens describes a lens in which an edge (which has a radius of curvature and may have other aspheric components) is swept in a first linear direction.
  • the term "cylindrical” as used herein has its normal meaning in the art and includes not only strictly spherical lens shapes but also aspherical lens shapes.
  • the geometric microlens axis is defined as the line along the centre of the lens in the first linear direction, i.e. parallel to the direction of sweep of the edge. In a 3D type print, the geometric microlens axis is vertical or at a slight angle to the vertical, so that it is generally parallel or at a slight angle to the columns of dots of the print.
  • a directional printed image display apparatus which constitutes a first embodiment of the invention is illustrated in Fig. 6.
  • a lens array 101 is formed by a lens surface 104 formed in a polymer material 100, on a substrate 102.
  • the substrate 102 and material 100 may be a single unitary element or may be separate elements of the same or different materials.
  • the substrate 102 and material 100 are transparent.
  • a plurality of interlaced images are printed on the rear surface (opposite from the lens array 104) of the substrate 102.
  • the images on the substrate 102 may be illuminated by at least one light source (not shown) which may be at the front or rear of the printed substrate.
  • at least one light source not shown
  • a printing apparatus (not shown) is used to form the plurality of images as an array 110 of dots.
  • the array 110 of dots may be formed in dye, pigment, toner or other printed materials as well known in the art.
  • the array 110 may be printed directly on to the substrate 102.
  • the substrate 102 may be optimised for adhesion of the printed dots to its surface, or diffusion in to the substrate.
  • the material 100 may be separately optimised for its optical properties; for example the quality of the replication - and refractive index.
  • the lens material 100 and substrate material 102 may advantageously be different materials.
  • the dots are formed in groups 140, 142, 144 of dots. Each image represents one view to be displayed. To interlace the images, the images are divided into strips and each group 140, 142, 144 of dots successively across the substrate comprises a successive strip 131-139 of each image.
  • the strips 131-139 of respective images are arranged in the same order within each group 140, 142, 144, so that the order is regular across the substrate 102.
  • Each strip 131-139 may comprise a single dot, but often comprises plural dots.
  • the lens array 101 has a structure which repeats across the lens array at a predetermined pitch to form a plurality of substantially identical, adjacent, elongate lenses 101, 103, 104.
  • the term "lens" is used to refer to a section of the lens array 101 at the predetermined pitch, that is the repeating unit of the structure of the lens array 101.
  • each lens of the lens array 101 has regions which have different optical functions.
  • the predetermined pitch at which the structure of the lens array 101 repeats is substantially equal to the pitch of the strips 131-139 of a single one of the images (ie the pitch of the groups 140, 142, 144 of dots), although in fact slightly less than the pitch of the strips 131-139 of a single one of the images by an amount providing viewpoint correction.
  • Each lens 101, 103, 104 has a plurality of regions, for,example five regions 106, 108, 110, 112, 114 in this embodiment.
  • First regions 106, 108, 110 are interlaced altcrnately with, second regions 112, 114 and will now be described specifically in respect of lens 103, it being noted that the other lenses 101, 104 have the same structure.
  • the first regions 106,108,110 comprise regions of a notional continuous lens surface 116.
  • the first regions 106,108,110 serve to direct light from the strips 131 : 139 of the images aligned with the given lens 103 (ie from group 142 of dots) into respective nominal viewing windows. This is illustrated in Fig. 6 which shows rays 118 of light from the strip 135 in the aligned group 142 of dots being directed towards the zero order lobe. Light from the other strips 131-134 and 136-139 is similarly directed into respective viewing windows in slightly different directions although this is not shown in Fig. 6 for clarity.
  • the strip 135 is the central one of the strips 131-139 and due to viewpoint correction will underlie the optical axis of the lens 103 in the middle of the substrate 102, but will be offset from the optical axis of the lens in regions towards the edge of the substrate 102.
  • the second regions 112, 114 serve to direct light from the strips 131-139 of the images aligned with a lens 101, 104 adjacent a given lens 103 (ie from groups 140, 144 of dots) into the same respective viewing windows into which the first regions 106, 108, 110 direct light from the strips 131-139 of the images aligned with the given lens 103 (ie from group 142 of dots). This is illustrated in Fig.
  • the second regions 112, 114 have substantially the same imaging function as the first regions 1O6, 108, 110 ofthe adjacent lens 101, 104. To provide the best effect, the second regions 112, 114 have an amount of curvature, but in practice as the second regions 112, 1 14 are relatively narrow they may comprise straight, tilted surfaces which thus operate in a similar manner to prisms.
  • the second regions 112, 114 direct light differently from the first regions 106, 108, 110, they could be thought of as being different "lenses” in particular by considering the second regions 112, 114 as part of the same "lens" as the first regions 106, 108, 110, but herein the term "lens" is used in a different manner to refer to the lens 103 as a whole, that is a section of the lens array 101 at the predetermined pitch at which the lens array 101 repeats.
  • each lens 103 of the lens array 101 serves to collect light firstly from strips 131-139 of the image aligned with the given lens 103 and secondly from strips 131-139 of the image aligned with the adjacent lenses 101, 104, and to direct all that light into the same viewing windows.
  • This mixing improves image quality by reducing artefacts, such as image stripiness, and by increasing window uniformity. All the light is collected so the mixing does not cause any reduction in the brightness of the observed image.
  • the structure can have the same sag as a standard lens with a single imaging regions across its aperture, but can be thinner.
  • a thinner lens uses less material 100 and is thus cheaper to manufacture and easier to handle.
  • the lens may be more suitable for roll processing, as the thickness of the optical surface is reduced.
  • the lens array may also distort less than a conventional lenticular screen. The printed image will thus produce higher quality window images across its width.
  • the aberrations of the lens may vary with viewing angle so that the size of the spot at the dot plane may vary for each of the imaging regions.
  • the lens design may be compensated for an intermediate off-axis viewing position, rather than being tuned for the central viewing position, so as to increase the range of average lens performance for off-axis viewing positions.
  • FIG. 7 shows the use of a conventional Fresnel lens in a printed'image display apparatus which is not in accordance with the present invention.
  • a lens array is formed in a material 146 on a substrate 148 with a plurality of images printed in the form of an array of groups of printed dots 140,142,144 on the rear surface of the substrate 148, in the same manner as in the apparatus of Fig. 6 described above.
  • the lens array comprises conventional Fresnel lenses 150 designed for use with on-axis windows.
  • the Fresnel lenses 150 have substantially vertical surfaces 156, 160 within each lens 150 and thus have the advantage of reduced thickness for on-axis imaging, such as for rays 152.
  • the Fresnel lenses 150 provide a reduced thickness in a similar manner to the present invention, for example if the first regions 106, 108, 110 in the apparatus of Fig. 6 are compared to the main facets of the Fresnel lenses 150.
  • the image quality ⁇ vith the Fresnel lenses 150 is worse than the present invention for at least the following reasons.
  • the off-axis behaviour of the Fresnel lenses 150 can be considered as follows. Light striking the vertical surfaces 156, 160 is deflected in directions which cause aberrations in the image. For example as shown in Fig. 7, light output along ray 154 will see a total internal reflection at the surface 156 and similarly light output along the ray 158 undergoes a high angle refraction at the surface 160, with the effect that the origin of the rays 154, 158 is thus substantially different to the required view data. Such rays 154, 158 may cause patterning in the final image appearance, as they may contain data from incorrect views or the gaps 141 between the groups 140, 142, 144.
  • Fig. 8 shows a further directional printed image display apparatus which constitutes an embodiment of the invention, and which is the same as the apparatus of Fig.6 except that the lens array 101 is replaced by a lens array comprising two layers 164, 166 having a lens surface 162 formed at the interface between the two layers 164, 166.
  • the two layers have different refractive indices and may be formed of polymer materials. This configuration has an important advantage because the reflectivity of the surface is substantially reduced, because the Fresnel reflectivity of the surface pair formed by the two layers 164, 166 is lower than for a leas surface placed directly in air like the lens surface 104 in Fig. 6.
  • the outer layer 166 has a plane surface 168 on its outer side.
  • the reflections from the plane surface 168 are different in nature to the reflections from the lens surface 162.
  • the plane surface 168 will provide a specular reflection which is easily avoided by the user by tilting tlie print away from direct ambient light.
  • the reflection from the lens surface 162 produces a much wider distribution and is thus less easily avoided. Thus, more lens visibility will be present to a user in ambient lighting conditions if the lens surface is in air rather than between two polymer surfaces as shown.
  • the lenses of Fig. 8 allow a wide range of polymer materials 164,166 to be used to provide such a reduction in the surface reflectivity, as follows.
  • the sag of the lenses must be increased compared to the equivalent lens in air to obtain the same optical power.
  • lower volume of material can be used and the cost is reduced. Therefore, more expensive materials with a wider range of refractive indices may be used.
  • high refractive index materials may tend to be more yellow in colour. If the thickness of material is lower, the overall colouration of the image will be reduced. Such advantages are obtained while optimizing the image quality at the window plane.
  • the use of polymer materials on both sides of the lens surface 168 serves to increase the critical angle of light in the medium. Total internal reflection from surfaces between imaging regions may cause an increase in the stray light in the printed image, and thus should be minimised to reduce visibility of the lens structure and to reduce cross talk in the images. Increasing the critical angle advantageously reduces such stray light.
  • Fig. 8 further shows that the lens thickness may be further reduced by introducing more imaging regions (which may be done independently of forming the lens array of two layers 164, 166).
  • more imaging regions which may be done independently of forming the lens array of two layers 164, 166.
  • a total of seven first imaging regions and six second imaging regions are used.
  • Each of the second imaging regions is used to direct light from adjacent image lobes to the zero order lobe.
  • the intermediate imaging regions form an extension of the adjacent lens element, as they have a common focus.
  • the lenses can thus be considered as being interleaved.
  • the lens array 162 with lenses 170,171 and 172 can be considered as producing overlapping ray bundles 174,175,176.
  • ray bundle 174 is formed from the imaging of lens 170 of ray bundle 178, by imaging of lens 171 of ray bundle 180 and by imaging of lens 172 of ray bundle 182.
  • the lens may be considered in terms of the ray bundles 174, 175, 176 they produce rather than the physical extent of the repeat unit. The lenses are thus overlapping, or interlaced.
  • the lens form may be tuned to optimise the aberrations of the system.
  • the composite surface may be aspheric.
  • the aperture size of the imaging regions may be set so as to minimise diffractive spreading of the output spot.
  • the height of the imaging region may be set to optimise the phase profile of the output illumination from the lens, thus minimizing spot size at the dot plane.
  • the lens arrays of Figs. 6 and 8 may be manufactured by conventional techniques similar to those used to manufacture the known Fresnel lens of Fig. 7.
  • the structure may be replicated into a polymer material as well known in the art.
  • Fig. 9 shows that the printed surface may comprise an additional substrate 184.
  • the additional substrate may comprise a material for printing directly on to and post- registering to the lenticular sheet, or may be a reflective layer which may also be a diffuser for optimising the brightness of the printed image.
  • a lens surface 514 comprises a central spherical portion 509 and two imaging region pairs 511,513.
  • On-axis rays 517 are incident on the lens surface 514 and are imaged to sppts 516, 518 and 520 at the pixel plane 515.
  • the on-axis spot comprises light from the central spherical portion 509 and one imaging region of each of the two imaging region pairs 511,513 as described elsewhere in the application.
  • the other imaging regions image light to positions 518 and 520, coincident with the central spot of the adjacent lens (not shown).
  • the imaging region pairs have spherical surface profiles, and blurring of the spot is due to chromatic aberration in the lens.
  • intensity of the spot at the pixel plane can be derived from an intensity addition of light from each of the imaging regions.
  • the lens is also shown to function for imaging of light from the centre of the first lobe, as shown by ray directions 522.
  • the spherical lens portion images light to position 520, while the imaging region pairs image light to positions 516,524.
  • chromatic aberration effects are not shown, so the spot 524 appears to be smaller than the spot 518.
  • the angle of the planar surface is set to approximate the tilt of the equivalent curved surface, such that the spot falls at the appropriate position at the pixel plane as described elsewhere.
  • the size of the spot at the pixel plane may be substantially the same as the width of the imaging region. Small increases in the spot size will be produced by diffraction at the aperture of the imaging region.
  • the imaging region width should advantageously be of similar size to the size of the eye spot imaged by the spherical portion of the lens at the pixel plane. This is illustrated for the ray trace of Fig. 11.
  • On-axis light is image to spots 528,530,532 and off-axis light to spot 534.
  • the spots can be seen to blur somewhat, but the overall size of the central spot 528 is little charLged. This is particularly true as the relative area of the imaging regions is small compared to the central spherical region.
  • the lenses can be conveniently formed using known manufacturing techniques.
  • Such a lens may be formed by means of thermal embossing, UV casting, injection molding or other polymer moulding techniques as well known in the art.
  • the second polymer material may be applied subsequent to the formation of the first polymer material.
  • the tool may be conveniently mastered using known mastering techniques including photoresist processing and diamond machining.
  • the directional printed image display apparatuses of Figs.6 and 8 may be autosterescopic display apparatuses in which images displayed in at least two adjacent viewing windows are a left eye view and a right eye view respectively.
  • the apparatus may be used to provide any other directional effect, for example a non- stereoscopic multi-view application in which a series of images is printed.
  • a non- stereoscopic multi-view application in which a series of images is printed.
  • the image can change, and a series of 2D images presented.

Abstract

A directional printed image display apparatus comprises a printed image surface on a substrate (102) having a plurality of images printed thereon with successive strips (131-139) of each image being interlaced with each other in a regular order. The apparatus has a lens array (101) having a structure which repeats- at a pitch substantially equal to the pitch of the strips (131-139) of one of said plurality of images. Each respective section (103) of the lens array (101) at said pitch is formed to provides at least one first region 106, 108, 110 and at least one second region (112, 114), the first regions) (106, 108, 110) directing light from the strips of the images aligned with the respective section (103) into respective nominal viewing windows the second regions) (112, 114) directing light from the strips of the images aligned with a section (101, 104) adjacent the respective section (103) into the same respective nominal viewing windows. The second region(s) (112, 114) have substantially the same imaging function as the first region(s) (106, 108, 110) of said adjacent: sections (101, 104). By provision of the second regions (112, 114), the image quality is improved and the thickness of the lens array (101) is reduced.

Description

Directional Printed Image Display Apparatus
The present invention relates to a directional print apparatus. Such an apparatus may be used in a three dimensional (3D) autostereoscopic print apparatus. Such systems may be used for printed output from computer systems. Normal human vision is stereoscopic, that is each eye sees a slightly different image of the world. The brain fuses the two images (referred to as the stereo pair) to give the sensation of depth. Three dimensional stereoscopic prints replay a separate, generally planar, image to each of the eyes corresponding to that which would be seen if viewing a real world scene. The brain again fuses the stereo pair to give the appearance of depth in the image.
Fig. Ia shows in plan view a print surface in a print plane 1. A right eye 2 views a right eye homologous image point 3 on the print plane and a left eye 4 views a left eye homologous point 5 on the print plane to produce an apparent image point 6 perceived by the user behind the print plane. Fig. Ib shows in plan view a print surface in a print plane 1. A right eye 2 views a right eye homologous image point 7 on the print plane and a left eye 4 views a left eye homologous point 8 on the print plane to produce an apparent image point 9 in front of the print plane.
Fig. Ic shows the appearance of the left eye image 10 and right eye image 11. The homologous point 5 in the left eye image 10 is positioned on a reference line 12.
The corresponding homologous point 3 in the right eye image 11 is at a different relative position 3 with respect to the reference line 12. The separation 13 of the point 3 from the reference line 12 is called the disparity and in this case is a positive disparity for points which will lie behind the print plane. For a generalised point in the scene there is a corresponding point in each image of the stereo pair as shown in Fig. Ia. These points are termed the homologous points. The relative separation of the homologous points between the two images is termed the disparity; points with zero disparity correspond to points at the depth plane of the print. Fig. Ib shows that points with uncrossed disparity appear behind the print and Figl c shows that points with crossed disparity appear in front of the print. The magnitude of the separation of the homologous points, the distance to the observer, and the observer's interocular separation gives the. amount of depth perceived on the print. Stereoscopic type prints are well known in the prior axt and refer to prints in which some kind of viewing aid is worn by the user to substantially separate the views sent to the left and right eyes. For example, the viewing aid may be colour filters in which the images are colour coded (e.g. red and green); or polarising glasses in which the images are encoded in orthogonal polarisation states. Autostereoscopic prints operate without viewing aids worn by the observer. In autostereoscopic prints, each of the views can be seen from a. limited region in space as illustrated in Fig. 2.
Fig. 2a shows a print device 16 with an attached parallax optical element 17. The print device produces a right eye image 18 for the right eye channel. The parallax optical element 17 directs light in a direction shown by the arrow 19 to produce a right eye viewing window 20 in the region in front of the print. An observer places their right eye 22 at the position of the window 20. The position of the left eye viewing window 24 is shown for reference. The viewing window 20 may also be referred to as a vertically extended optical pupil. Fig. 2b shows the left eye optical system. The print device 16 produces a left eye image 26 for the left eye channel. The parallax optical element 17 directs light in a direction shown by the arrow 28 to produce a left eye viewing window 30 in the region in front of the print. An observer places their left eye 32 at the position of the window 30. The position of the right eye viewing window 20 is shown for reference. The system comprises a print and an optical steering mechanism. The light from the left image 26 is sent to a limited region in front of the print, referred to as the viewing window 30. If an eye 32 is placed at the position of the viewing window 30 then the observer sees the appropriate image 26 across the whole of the print 16. Similarly the optical system sends the light intended for the right image 18 to a separate window 20. If the observer places their right eye 22 in that window then the right eye image will be seen across the whole of the print. Generally, the light from either image may be considered to have been optically steered (i.e. directed) into a respective directional distribution.
Fig. 3 shows in plan view a print device 16,17 in a print plane 34 producing the left eye viewing windows 36,37,38 and right eye viewing windows 39,40,41 in the window plane 42. The separation of the window plane from the print is teπrxed the nominal viewing distance 43. The windows 37,40 in the central position with respect to the print are in the zeroth lobe 44. Windows 36,39 to the right of the zeroth lobe 44 are in the +1 lobe 46, while windows 38,41 to the left of the zeroth lobe are in the -1 lobe 48.
The viewing window plane 42 of the print represents the distance from the print at which the lateral viewing freedom is greatest. For points away from the window plane, there is a diamond shaped autostereoscopic viewing zone, as illustrated in plan view in Fig. 3. As can be seen, the light from each of the points across the print is beamed in a cone of finite width to the viewing windows. The width of the cone may be defined as the angular width.
If an eye is placed in each of a pair viewing zones such as 37,40 then an autostereoscopic image will be seen across the whole area of the print. To a. first order, the longitudinal viewing freedom of the print is determined by the length of these viewing zones.
The variation in intensity 50 across the window plane of a print (constituting one tangible form of a directional distribution of the light) is shown with respect to position 51 for idealised windows in Fig. 4. The right eye window position intensity distribution 52 corresponds to the window 41 in Fig. 3, and intensity distribution 53 corresponds to the window 37, intensity distribution 54 corresponds to the window 40 and intensity distribution 55 corresponds to the window 36. -A-
Fig. 5 shows the intensity distribution with position schematically for more realistic windows. The right eye window position intensity distribution 56 corresponds to the window 41 in Fig. 3, and intensity distribution 57 corresponds to the window 37, intensity distribution 58 corresponds to the window 40 and intensity distribution 59 . corresponds to the window 36.
The quality of the separation of images and the extent of the lateral and longitudinal viewing freedom of the print is determined by the window quality, as illustrated in Fig. 4. Fig. 4 shows the ideal viewing windows while Fig. 5 is a schematic of the actual viewing windows that may be outputted from the print. Several artefacts can occur due to inadequate window performance. Cross talk occurs when light from the right eye image is seen by the left eye and vice versa. This is a significant 3D image degradation mechanism which can lead to visual strain for the user. Additionally, poor window quality will lead to a reduction in the viewing freedom of the observer. The optical system is designed to optimised the performance of the viewing windows. A printed image is typically composed of an array of dots printed on to a surface of an image bearing substrate.
A type of parallax optic well known in the art for use in stereoscopic prints is called the lenticular screen, which is an array of vertically extended cylindrical microlenses. The image bearing substrate is positioned substantially at the focus of the lenses of the lenticular screen so that the curvature of the lenses is set substantially so as to produce an image of the printed dots at the window plane. The image bearing substrate may comprise one surface of the lenticular screen or may be a separate substrate attached to the lenticular screen.
As the lenses collect the light in a cone from the dot and distribute it to the windows, lenticular prints have the full brightness of the base print.
In order to steer the light from each dot to the viewing window, the pitch of the lenticular screen is slightly smaller than an integer multiple of the pitch of the dot array where the integer multiple generally represents the number of views in each viewing lobe. This condition is known as "viewpoint correction". In a two view print, the resolution of each of the stereo pair images is half of the horizontal resolution of the base print.
In a lenticular screen type print, the columns directly under the lenses are imaged to a first set of windows in the zeroeth lobe of the print. The adjacent dot columns are also imaged to viewing windows, in +1 and -1 lobes of the print. Thus as can be seen in Fig. 3, if the user moves laterally outside the orthoscopic zone then light from the incorrect image will be sent to each eye. In a two view print, when the right eye sees the left eye view and yice versa, the image is termed 'pseudoscopic', compared to the correct orthoscopic condition.
In order to increase the lateral viewing freedom of the print, more than two dot columns can be placed under each lens. For example, four columns will create four windows in which the view is changed for each window. For example in Fig. 3, windows 38,41,37,40,36,39 may represent views 1,2,3,4,5,6 respectively. Such a print will give a 'look-around' appearance as the observer moves. The longitudinal freedom is also increased by such a method. However, in this case, the resolution of the print is limited to one quarter of the resolution of the base print. Typically lenticular prints may have 9 or more views under each lens. However, for ease of description in this application, embodiments showing two views will generally be described. In general, a printed image will show more than two views of an image.
Lenticular prints are described in T.Okoshi "Three Dimensional Imaging Techniques", Academic Press, 1976.
According to the present invention, there is provided a directional printed image display apparatus comprising: a printed image surface having a plurality of images printed thereon with successive strips of each image being interlaced with each other in a regular order; a lens array having a structure which repeats at a pitch substantially equal to the pitch of the strips of one of said plurality of images, wherein the lens array is arranged such, that each respective section of the lens array at said pitch is formed to provide: at least one first region capable of directing light from the strips of the images aligned with the respective section into respective nominal viewing windows; and at least one second region capable of directing light from the strips of the images aligned with a section adjacent the respective section into the same respective nominal viewing windows.
Such an apparatus displays a printed image and provides directional viewing windows. It may be any type of directional printed image display apparatus, including in particular a three-dimensional autostereoscopic printed image display apparatus.
Advantageously this invention serves to improve the image quality of the print by reducing artefacts, such as image cross-talk and image stripiness, and by increasing window uniformity. These advantages results from the fact that the second region(s) of the a given section of the lens array serve to image light from the strips of the images aligned with an adjacent section to the on-axis viewing windows for example. In particular, the at least one second region can be considered as cooperating with the first region of the adjacent section, and vice versa. Preferably, the at least one second region has substantially the same imaging function as the at least one first region of said adjacent section and in this case, as compared to the prior art situation that all of a respective section of the lens directs light from the strips of the images aligned with the respective section into respective nominal viewing windows, adjacent sections may be considered as being interlaced. These advantages are achieved without reducing the brightness of the image.
In addition, the lens array of the present invention advantageously reduces the thickness of the lens array and thus the material usage and cost of the lens array. For example, the lens array may be formed as two layers, which may be made of polymer materials, by shaping the lens surface at the interface between the two layers, thus reducing the reflectivity of the lens surface, ϊn this case, the volume of material may be reduced by use of the present invention. Therefore relatively high cost materials may be used to optimise lens performance while used in small quantities, thus not increasing the device cost substantially. Similar advantages of reducing thickness could be achieved by use of Fresnel lenses in the lens array, but for the reasons discussed above, the present invention provides significantly reduced artefacts as compared to a Fresnel lens.
The structures of the present invention can be applied at the mastering stage of the lenses, rather than the replication stage. Thus, the cost of the individual elements is not substantially affected by the complexity of the lens shape.
The lenses will further be more easily manufactured by means of roll processing compared to a conventional lens array, because of the lower thickness. Such lenses can thus be manufactured more cheaply.
Thinner lenses will be less prone to curving the base substrate and thus the substrate will be less easily deformed by the lens surface. Therefore, the lenticular print will be less prone to bending, and the window quality can thus be optimised. The lenses will weigh less, and thus be more suitable for packaging applications for example.
According to another aspect of the present invention, there is provided a directional print apparatus comprising a printed surface arranged substantially in the focal plane of a lens array and comprising an array of groups of printed dots, the lens array being arranged to direct light into a first directional distribution, wherein: each lens of the lens array is arranged in alignment with a group of printed dots; each lens of the lens array comprises at least first and second imaging regions with respective first and second optical functions, the first imaging region being arranged to image light from a first group of dots to first viewing windows, the at least second imaging region being arranged to image light from a second group of dots to the first viewing windows, and the second imaging regions having substantially the same imaging function as the first imaging region of an adjacent lens. In general, the images may be illuminated from behind the printed image surface illuminated from in front of the printed image surface, edge illuminated, or any combination thereof.
Embodiments of, the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Fig. Ia shows the generation of apparent depth in a 3D print for an object behind the print plane;
Fig. Ib shows the generation of apparent depth in a 3D print for an object in front of the print plane; Fig. Ic shows the position of the corresponding homologous points on each image of a stereo pair of images;
Fig. 2a shows schematically the formation of the right eye viewing window in front of an autostereoscopic 3D print;
Fig. 2b shows schematically the formation of the left eye viewing window in front of an autostereoscopic 3D print;
Fig. 3 shows in plan view the generation of viewing zones from the output cones of a 3D print;
Fig. 4 shows the ideal window profile for an autostereoscopic print;
Fig. 5 shows a schematic of the output profile of viewing windows from an autostereoscopic 3D print;
Fig. 6 shows a first embodiment of the invention comprising a lens array in air and printed substrate;
Fig. 7 shows a display comprising a prior art lens and printed substrate;
Fig. 8 shows a display of the invention comprising an interlaced lens comprising first and second polymer materials and printed substrate;
Fig. 9 shows the use of an additional printed substrate;
Fig. 10 shows the use of curved first and second imaging region pairs;
Fig. 11 shows the use of plane first and second imaging region pairs; Some of the various embodiments employ common elements which, for brevity, will be given common reference numerals and a description thereof will not be repeated. Furthermore the description of the elements of each embodiment applies equally to the identical elements of the other embodiments and the elements having corresponding effects, mutatis mutandis. Also, the figures illustrating the embodiments which are prints show only a portion of print, for clarity. In fact, the construction is repeated over the entire area of the print.
A cylindrical lens describes a lens in which an edge (which has a radius of curvature and may have other aspheric components) is swept in a first linear direction. The term "cylindrical" as used herein has its normal meaning in the art and includes not only strictly spherical lens shapes but also aspherical lens shapes. The geometric microlens axis is defined as the line along the centre of the lens in the first linear direction, i.e. parallel to the direction of sweep of the edge. In a 3D type print, the geometric microlens axis is vertical or at a slight angle to the vertical, so that it is generally parallel or at a slight angle to the columns of dots of the print.
A directional printed image display apparatus which constitutes a first embodiment of the invention is illustrated in Fig. 6. A lens array 101 is formed by a lens surface 104 formed in a polymer material 100, on a substrate 102. The substrate 102 and material 100 may be a single unitary element or may be separate elements of the same or different materials. The substrate 102 and material 100 are transparent.
A plurality of interlaced images are printed on the rear surface (opposite from the lens array 104) of the substrate 102. The images on the substrate 102 may be illuminated by at least one light source (not shown) which may be at the front or rear of the printed substrate. In this embodiment there are nine images. In general, there could by any plural number of images, although there are typically at least eight.
A printing apparatus (not shown) is used to form the plurality of images as an array 110 of dots. The array 110 of dots may be formed in dye, pigment, toner or other printed materials as well known in the art. The array 110 may be printed directly on to the substrate 102. The substrate 102 may be optimised for adhesion of the printed dots to its surface, or diffusion in to the substrate. Thus advantageously, the material 100 may be separately optimised for its optical properties; for example the quality of the replication - and refractive index. Thus the lens material 100 and substrate material 102 may advantageously be different materials.
The dots are formed in groups 140, 142, 144 of dots. Each image represents one view to be displayed. To interlace the images, the images are divided into strips and each group 140, 142, 144 of dots successively across the substrate comprises a successive strip 131-139 of each image. The strips 131-139 of respective images are arranged in the same order within each group 140, 142, 144, so that the order is regular across the substrate 102. Each strip 131-139 may comprise a single dot, but often comprises plural dots.
There may advantageously be a gap 141 between each group of dots. The gap 141 may comprise a black printed area. In this way, the central viewing lobe may be clearly identified to a user, and the pseudoscopic viewing zones may be avoided. The lens array 101 has a structure which repeats across the lens array at a predetermined pitch to form a plurality of substantially identical, adjacent, elongate lenses 101, 103, 104. In this specification, the term "lens" is used to refer to a section of the lens array 101 at the predetermined pitch, that is the repeating unit of the structure of the lens array 101. As described in more detail below, each lens of the lens array 101 has regions which have different optical functions.
The predetermined pitch at which the structure of the lens array 101 repeats is substantially equal to the pitch of the strips 131-139 of a single one of the images (ie the pitch of the groups 140, 142, 144 of dots), although in fact slightly less than the pitch of the strips 131-139 of a single one of the images by an amount providing viewpoint correction.
Each lens 101, 103, 104 has a plurality of regions, for,example five regions 106, 108, 110, 112, 114 in this embodiment. First regions 106, 108, 110 are interlaced altcrnately with, second regions 112, 114 and will now be described specifically in respect of lens 103, it being noted that the other lenses 101, 104 have the same structure.
The first regions 106,108,110 comprise regions of a notional continuous lens surface 116. The first regions 106,108,110 serve to direct light from the strips 131:139 of the images aligned with the given lens 103 (ie from group 142 of dots) into respective nominal viewing windows. This is illustrated in Fig. 6 which shows rays 118 of light from the strip 135 in the aligned group 142 of dots being directed towards the zero order lobe. Light from the other strips 131-134 and 136-139 is similarly directed into respective viewing windows in slightly different directions although this is not shown in Fig. 6 for clarity. The strip 135 is the central one of the strips 131-139 and due to viewpoint correction will underlie the optical axis of the lens 103 in the middle of the substrate 102, but will be offset from the optical axis of the lens in regions towards the edge of the substrate 102.
The second regions 112, 114 serve to direct light from the strips 131-139 of the images aligned with a lens 101, 104 adjacent a given lens 103 (ie from groups 140, 144 of dots) into the same respective viewing windows into which the first regions 106, 108, 110 direct light from the strips 131-139 of the images aligned with the given lens 103 (ie from group 142 of dots). This is illustrated in Fig. 6 which shows light rays 120 from strip 135 in one of the adjacent group 140 of dots being directed by one of the second regions 112 tOΛvards the centre of the zero order lobe of lens 103, and light rays 122 from strip 135 in the other of the adjacent group 144 of dots 140 being directed by the other of the second regions 114 towards the centre of the zero order lobe of lens 103.
The second regions 112, 114 have substantially the same imaging function as the first regions 1O6, 108, 110 ofthe adjacent lens 101, 104. To provide the best effect, the second regions 112, 114 have an amount of curvature, but in practice as the second regions 112, 1 14 are relatively narrow they may comprise straight, tilted surfaces which thus operate in a similar manner to prisms.
In that the second regions 112, 114 direct light differently from the first regions 106, 108, 110, they could be thought of as being different "lenses" in particular by considering the second regions 112, 114 as part of the same "lens" as the first regions 106, 108, 110, but herein the term "lens" is used in a different manner to refer to the lens 103 as a whole, that is a section of the lens array 101 at the predetermined pitch at which the lens array 101 repeats.
By virtue of the second regions 112, 114, each lens 103 of the lens array 101 serves to collect light firstly from strips 131-139 of the image aligned with the given lens 103 and secondly from strips 131-139 of the image aligned with the adjacent lenses 101, 104, and to direct all that light into the same viewing windows. Thus to an observer in a viewing window this effectively causes mixing of light between adj acent strips 131-139 of a single one of the images. This mixing improves image quality by reducing artefacts, such as image stripiness, and by increasing window uniformity. All the light is collected so the mixing does not cause any reduction in the brightness of the observed image.
Of particular advantage is that the structure can have the same sag as a standard lens with a single imaging regions across its aperture, but can be thinner. A thinner lens uses less material 100 and is thus cheaper to manufacture and easier to handle. In particular, the lens may be more suitable for roll processing, as the thickness of the optical surface is reduced. The lens array may also distort less than a conventional lenticular screen. The printed image will thus produce higher quality window images across its width.
The aberrations of the lens may vary with viewing angle so that the size of the spot at the dot plane may vary for each of the imaging regions. The lens design may be compensated for an intermediate off-axis viewing position, rather than being tuned for the central viewing position, so as to increase the range of average lens performance for off-axis viewing positions.
By way of comparison, Fig. 7 shows the use of a conventional Fresnel lens in a printed'image display apparatus which is not in accordance with the present invention. A lens array is formed in a material 146 on a substrate 148 with a plurality of images printed in the form of an array of groups of printed dots 140,142,144 on the rear surface of the substrate 148, in the same manner as in the apparatus of Fig. 6 described above. The lens array comprises conventional Fresnel lenses 150 designed for use with on-axis windows. Thus the Fresnel lenses 150 have substantially vertical surfaces 156, 160 within each lens 150 and thus have the advantage of reduced thickness for on-axis imaging, such as for rays 152. In this manner, the Fresnel lenses 150 provide a reduced thickness in a similar manner to the present invention, for example if the first regions 106, 108, 110 in the apparatus of Fig. 6 are compared to the main facets of the Fresnel lenses 150. However the image quality Λvith the Fresnel lenses 150 is worse than the present invention for at least the following reasons.
The off-axis behaviour of the Fresnel lenses 150 can be considered as follows. Light striking the vertical surfaces 156, 160 is deflected in directions which cause aberrations in the image. For example as shown in Fig. 7, light output along ray 154 will see a total internal reflection at the surface 156 and similarly light output along the ray 158 undergoes a high angle refraction at the surface 160, with the effect that the origin of the rays 154, 158 is thus substantially different to the required view data. Such rays 154, 158 may cause patterning in the final image appearance, as they may contain data from incorrect views or the gaps 141 between the groups 140, 142, 144. The visibility of the surfaces between imaging regions increases as the angle of observation of the lenses 150 increases, so that the artefact will appear to vary as the observer moves laterally with respect to the print surface. In contrast, the artefacts in the image are not experienced with the present invention in which the second regions 112, 114 in fact improve the image quality as described above.
Fig. 8 shows a further directional printed image display apparatus which constitutes an embodiment of the invention, and which is the same as the apparatus of Fig.6 except that the lens array 101 is replaced by a lens array comprising two layers 164, 166 having a lens surface 162 formed at the interface between the two layers 164, 166. The two layers have different refractive indices and may be formed of polymer materials. This configuration has an important advantage because the reflectivity of the surface is substantially reduced, because the Fresnel reflectivity of the surface pair formed by the two layers 164, 166 is lower than for a leas surface placed directly in air like the lens surface 104 in Fig. 6. The outer layer 166 has a plane surface 168 on its outer side. The reflections from the plane surface 168 are different in nature to the reflections from the lens surface 162. The plane surface 168 will provide a specular reflection which is easily avoided by the user by tilting tlie print away from direct ambient light. However, the reflection from the lens surface 162 produces a much wider distribution and is thus less easily avoided. Thus, more lens visibility will be present to a user in ambient lighting conditions if the lens surface is in air rather than between two polymer surfaces as shown.
Advantageously, the lenses of Fig. 8 allow a wide range of polymer materials 164,166 to be used to provide such a reduction in the surface reflectivity, as follows. The sag of the lenses must be increased compared to the equivalent lens in air to obtain the same optical power. As the lenses have reduced thickness, lower volume of material can be used and the cost is reduced. Therefore, more expensive materials with a wider range of refractive indices may be used. Additionally, high refractive index materials may tend to be more yellow in colour. If the thickness of material is lower, the overall colouration of the image will be reduced. Such advantages are obtained while optimizing the image quality at the window plane.
Further, the use of polymer materials on both sides of the lens surface 168 serves to increase the critical angle of light in the medium. Total internal reflection from surfaces between imaging regions may cause an increase in the stray light in the printed image, and thus should be minimised to reduce visibility of the lens structure and to reduce cross talk in the images. Increasing the critical angle advantageously reduces such stray light.
Fig. 8 further shows that the lens thickness may be further reduced by introducing more imaging regions (which may be done independently of forming the lens array of two layers 164, 166). In this example, a total of seven first imaging regions and six second imaging regions are used. Each of the second imaging regions is used to direct light from adjacent image lobes to the zero order lobe. In effect in each of the lenses of the present invention, the intermediate imaging regions form an extension of the adjacent lens element, as they have a common focus. The lenses can thus be considered as being interleaved. Thus the lens array 162 with lenses 170,171 and 172 can be considered as producing overlapping ray bundles 174,175,176. For example, ray bundle 174 is formed from the imaging of lens 170 of ray bundle 178, by imaging of lens 171 of ray bundle 180 and by imaging of lens 172 of ray bundle 182. Thus the lens may be considered in terms of the ray bundles 174, 175, 176 they produce rather than the physical extent of the repeat unit. The lenses are thus overlapping, or interlaced.
The lens form may be tuned to optimise the aberrations of the system. For example, the composite surface may be aspheric. The aperture size of the imaging regions may be set so as to minimise diffractive spreading of the output spot. The height of the imaging region may be set to optimise the phase profile of the output illumination from the lens, thus minimizing spot size at the dot plane.
The lens arrays of Figs. 6 and 8 may be manufactured by conventional techniques similar to those used to manufacture the known Fresnel lens of Fig. 7. For example the structure may be replicated into a polymer material as well known in the art. Fig. 9 shows that the printed surface may comprise an additional substrate 184.
The additional substrate may comprise a material for printing directly on to and post- registering to the lenticular sheet, or may be a reflective layer which may also be a diffuser for optimising the brightness of the printed image.
An example ray trace for one type of lens that uses spherical first and second imaging regions for all parts of the lens is shown in Fig. 10. A lens surface 514 comprises a central spherical portion 509 and two imaging region pairs 511,513. On-axis rays 517 are incident on the lens surface 514 and are imaged to sppts 516, 518 and 520 at the pixel plane 515. The on-axis spot comprises light from the central spherical portion 509 and one imaging region of each of the two imaging region pairs 511,513 as described elsewhere in the application. The other imaging regions image light to positions 518 and 520, coincident with the central spot of the adjacent lens (not shown). In this case, the imaging region pairs have spherical surface profiles, and blurring of the spot is due to chromatic aberration in the lens. As the imaging regions are substantially incoherent, intensity of the spot at the pixel plane can be derived from an intensity addition of light from each of the imaging regions.
The lens is also shown to function for imaging of light from the centre of the first lobe, as shown by ray directions 522. In this case, the spherical lens portion images light to position 520, while the imaging region pairs image light to positions 516,524. In this case, chromatic aberration effects are not shown, so the spot 524 appears to be smaller than the spot 518.
In the case that the imaging region pairs 511,513 have planar surfaces, the angle of the planar surface is set to approximate the tilt of the equivalent curved surface, such that the spot falls at the appropriate position at the pixel plane as described elsewhere. The size of the spot at the pixel plane may be substantially the same as the width of the imaging region. Small increases in the spot size will be produced by diffraction at the aperture of the imaging region. The imaging region width should advantageously be of similar size to the size of the eye spot imaged by the spherical portion of the lens at the pixel plane. This is illustrated for the ray trace of Fig. 11. On-axis light is image to spots 528,530,532 and off-axis light to spot 534.- As the imaging region is plane, the spots can be seen to blur somewhat, but the overall size of the central spot 528 is little charLged. This is particularly true as the relative area of the imaging regions is small compared to the central spherical region. The lenses can be conveniently formed using known manufacturing techniques.
Such a lens may be formed by means of thermal embossing, UV casting, injection molding or other polymer moulding techniques as well known in the art. In the case.of a lens incorporating two polymer materials, the second polymer material may be applied subsequent to the formation of the first polymer material. The tool may be conveniently mastered using known mastering techniques including photoresist processing and diamond machining.
The directional printed image display apparatuses of Figs.6 and 8 may be autosterescopic display apparatuses in which images displayed in at least two adjacent viewing windows are a left eye view and a right eye view respectively. However, the apparatus may be used to provide any other directional effect, for example a non- stereoscopic multi-view application in which a series of images is printed. Thus, as the apparatus is rotated, the image can change, and a series of 2D images presented.

Claims

Claims
1. A directional printed image display apparatus comprising: a printed image surface having a plurality of images printed thereon with successive strips of each image being interlaced with each other in a regular order; a lens array having a structure which repeats at a pitch substantially equal to the pitch of the strips of one of said plurality of images, wherein the lens array is arranged such that each respective section of the lens array at said pitch is formed to provide: at least one first region capable of directing light from the strips of the images aligned with the respective section into respective nominal viewing windows; and at least one second region capable of directing light from the strips of the images aligned with a section adjacent the respective section into the same respective nominal viewing windows.
2. A directional printed image display apparatus according to claim 1, wherein the lens array is arranged such that at least one second region is capable of directing light from the strips of the images aligned with sections adjacent the respective section on opposite sides of said respective section into the same respective nominal viewing windows.
3. A apparatus according to claim 1 or 2, wherein the lens array is arranged such that each respective section of the lens array is formed to provide a plurality of said first regions arranged alternately with a plurality of said second regions.
4. A directional printed image display apparatus according to any one of the preceding claims, wherein each respective section of the lens array has at least one lens surface shaped to provide said first and second regions.
5. A directional printed image display apparatus according to claim 4, wherein said at least one lens surface has no vertical facets between said first and second regions.
6. A directional printed image display apparatus .according to claim 4 or 5, wherein the lens array includes two adjacent layers having different refractive indices, said at least one surface being the interface between the two layers.
7. A directional printed image display apparatus according to claim 6, wherein the two layers are formed of polymer materials.
8. A directional printed image display apparatus according to any one of the preceding claims, wherein said printed image surface has at least eight images printed thereon.
9. A directional printed image display apparatus according to any one of the preceding claims, wherein the printed image surface is a surface of a substrate.
10. A directional printed image display apparatus according to any one of the preceding claims, wherein the at least one second region has substantially the same imaging function as the at least one first region of said adjacent section.
PCT/GB2005/003802 2004-10-08 2005-10-03 Directional printed image display apparatus WO2006037987A1 (en)

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GB0422408.5 2004-10-08

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WO2017072162A1 (en) * 2015-10-27 2017-05-04 Continental Automotive Gmbh Head-up display

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JPS6349742A (en) * 1986-08-19 1988-03-02 Mitsubishi Rayon Co Ltd Manufacture of transmission type screen
US6084713A (en) * 1995-01-18 2000-07-04 Rosenthal; Bruce A. Lenticular optical system
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WO2017072162A1 (en) * 2015-10-27 2017-05-04 Continental Automotive Gmbh Head-up display

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