FIELD OF THE INVENTION

The invention relates to a display apparatus for enabling a user to experience a 3D perception when visual information is presented by the display apparatus.

BACKGROUND OF THE INVENTION

Display apparatuses for enabling a user to experience a 3D perception when visual information is presented by the display apparatus are known in various varieties. Some known systems require the user to wear glasses to, for example, separate the visual information presented to the left eye from the visual information presented to the right eye. The inconvenience of the need to wear glasses may be overcome with so-called

autostereoscopic systems. Some systems for 3D perception use lenticular lenses to spatially direct the visual information. An example of a lenticular system is described in C. van Berkel et al, "Multiview 3D - LCD" published in SPIE Proceedings Vol. 2653, 1996, pages 32 to 39. Other systems use parallax barriers. Some system approaches run into their design limits due to physical constraints. For example, some high-resolution small- size display systems would require lenticular lenses with a negative thickness. In some other systems, in particular with large display sizes, to allow the user to experience a high-quality 3D perception, a display apparatus using lenticular lenses or parallax barriers may need a significant distance between the lenticular lenses and the display panel with the two-dimensional array of image subpixels. Further, optical tolerances may require extra mechanical measures to define and maintain this distance, for example by using a solid transparent plate to provide the distance, which may lead to a significant increase in weight and cost. It would be advantageous to provide a display apparatus with better controllable design parameters, such as thickness, weight and cost.

SUMMARY OF THE INVENTION

The invention hereto provides a display apparatus for enabling a user to experience a 3D perception when visual information is presented by the display apparatus, wherein the display apparatus comprises an image forming unit comprising a two- dimensional array of image subpixels and an optical system comprising an array of diffractive optical elements. The two-dimensional array of image subpixels is arranged to emit light for presenting associated visual information. The array of diffractive optical elements is associated with respective ones of the array of image subpixels. Each diffractive optical element is arranged to diffract light from the associated image subpixel into a diffraction pattern comprising a plurality of diffraction orders to provide the visual information from the associated image subpixel to a plurality of directional viewing regions associated with the plurality of diffraction orders. The optical system may thus said to effectively duplicate the visual information presented by one subpixel to a plurality of directional viewing regions as the visual information is provided to each of the plurality of diffraction orders, such that the user may experience a 3D perception in each one of the plurality of directional viewing regions. The diffractive optical element may for example be a diffractive grating. The diffractive optical element may be thin. The diffractive optical elements may provide visual information for experiencing 3D perception without the need for additional spatial separation that is required in a display apparatus using conventional optics, such as lenticular lenses or parallax barriers, between the lenticular lenses or parallax barriers and the two-dimensional array if image subpixels in such systems The display apparatus may hereby be thinner, lighter and/or cheaper.

In an embodiment, each diffractive optical element of the array of diffractive optical elements is arranged to diffract light from the associated image subpixel into the diffraction pattern comprising the plurality of diffraction orders according to a plurality of predefined intensity ratios between the diffraction orders. The relative intensities of each of the directional viewing regions may hereby be defined to, for example, provide a higher intensity for the directional viewing regions at the most common viewing positions, i.e., at the central viewing region.

In a further embodiment, the plurality of predefined intensity ratios corresponds to a gradual variation of intensity from a central to outer diffraction orders, the gradual variation corresponding to Lambert's cosine law, to provide the corresponding directional viewing regions with corresponding predefined intensity ratios.

In an embodiment, the plurality of directional viewing regions are restricted one or more predefined limited directional ranges.

For example, in an embodiment, the plurality of directional viewing regions are restricted to a predefined limited directional range. The diffractive optical elements may hereto be designed such that the higher diffraction orders are suppressed. The predefined limited directional range may e.g. correspond to an angular range in the horizontal plane of - 60° to +60° or smaller, with 0° corresponding to the normal to the display apparatus.

Restricting to the predetermined limited directional range may allow for an increased brightness of the visual information as provided to the plurality of directional viewing regions. The predefined limited directional range may e.g. correspond to an angular range in the horizontal plane of -30° to +30° or smaller, with 0° corresponding to the normal to the display apparatus. Restricting to the predetermined limited directional range may

alternatively or additionally restrict the use of the display apparatus to only the user in the predefined limited directional range, and provide a reduced disturbance of other people and/or prevent other people to view the visual information.

In an embodiment, the plurality of directional viewing regions are restricted to two predefined limited directional ranges. The diffractive optical elements may hereto be designed such that central diffraction orders are suppressed. The two predefined limited directional range may e.g. correspond to a first angular range in the horizontal plane of -45° to -15° or narrower and a second angular range in the horizontal plane of +15° to +45° or narrower, with 0° corresponding to the normal to the display apparatus. Restricting to two predetermined limited directional ranges may allow two spatially separated regions wherein a user can experience 3D perception, such as e.g. a driver and a co-pilot in a car.

In embodiments, each diffractive optical element is a diffractive grating. The grating pitch and shape may be designed to provide the wanted directions and intensity ratios of the diffraction orders of the diffraction pattern of the light emitted by the associated subpixel. The diffractive gratings may thus be arranged to provide the diffraction orders with the plurality of predefined intensity ratios.

In embodiments, each diffractive optical element of the array of diffractive optical elements is arranged to diffract light from the associated image subpixel into the diffraction pattern comprising the plurality of diffraction orders, wherein adjacent non- suppressed diffraction orders of the plurality of diffraction orders associated with directional viewing regions are separated by one or more suppressed diffraction orders. Thus, the diffractive optical element does not diffract light into suppressed diffraction orders which are effectively not associated with respective visual information for directional viewing regions and diffraction orders which are associated with directional viewing regions. For example, every third diffraction order could be used for repeating visual information for directional viewing regions, with every two intermediate orders suppressed. This may allow additional design freedom for the diffractive optical element, such as additional design freedom in pitch and shape of diffractive gratings. In embodiments, the array of diffractive optical elements comprises a plurality of subsets of diffractive optical elements. The diffractive optical elements of each subset of diffractive optical elements may be arranged to provide the diffraction pattern from the associated diffractive optical element with an associated predetermined subset direction. The predetermined subset directions of different subsets are different to provide the visual information from the image subpixels associated with the different subsets to the directional viewing regions at different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions. The subsets of diffractive optical elements may thus provide visual information from subsets of associated subpixels to an associated plurality of different directions in each of the directional viewing regions. Each diffractive optical element may thus diffract the incoming light to provide the diffraction pattern, and provide the associated predetermined subset direction to the diffraction pattern.

In further embodiments, the diffractive optical elements of each subset of diffractive optical elements are arranged to provide the diffraction pattern from the associated diffractive optical element with an associated predetermined subset direction, adjacent diffraction orders of the plurality of diffraction orders associated directional viewing regions are separated by one or more suppressed diffraction orders, and the suppression is different for different subsets to provide the diffraction pattern from the associated diffractive optical element with the predetermined subset direction. Each diffractive optical element may thus diffract the incoming light to provide the diffraction pattern, and provide the associated predetermined subset direction to the diffraction pattern by suppression of diffraction orders in dependence of the predetermined subset direction for the associated subpixel.

In embodiments, the optical system further comprises an array of further optical elements associated with respective one or more diffractive optical elements of the array of diffractive optical elements. The array of further optical elements comprises a plurality of subsets of further optical elements, the further optical elements of each subset of further optical elements being arranged to provide the diffraction pattern from the associated one or more diffractive optical elements with an associated predetermined subset direction. The predetermined subset directions of different subsets are different to provide the visual information from the image subpixels associated with the different subsets to the directional viewing regions at different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions. The subsets of further optical elements may thus provide visual information from subsets of associated one or more subpixels to an associated plurality of different directions in each of the directional viewing regions. Using further optical elements next to the diffractive optical elements may facilitate design and/or manufacturing, and/or tolerances therein.

In embodiments, the further optical elements of the different subsets of the array of further optical elements comprise respective further diffractive components arranged to provide the associated diffraction pattern with the corresponding predetermined subset direction. In embodiments, the further diffractive optical components comprise, or are, blazed gratings. The blazed gratings may thus be arranged to provide the associated predetermined subset direction in an efficient manner.

In embodiments, the further optical elements of the different subsets of the array of further optical elements comprise respective refractive optical components arranged to provide the associated diffraction pattern with the corresponding predetermined subset direction. In embodiments, the refractive optical components comprise , or are, prisms. The refractive optical components may thus be arranged to provide the associated predetermined subset direction in an efficient manner. The refractive optical components may be relatively easy to handle. The prisms may for example be provided as a prism sheet.

The further optical elements may relate one to one to a subpixels. A single further optical element may relate to multiple subpixels, in particular to subpixels associated with a single full-color pixel or with adjacent subpixels corresponding to the same subset viewing direction.

In embodiments, the diffractive optical elements and the further optical elements may be separate elements. In alternative embodiments, the diffractive optical element and the associated further optical element are integrated as a single optical element. For example, in embodiments, the diffractive optical elements of each subset of diffractive optical elements have respective diffractive surfaces and opposite surfaces, and the respective diffractive surfaces arranged to diffract light from the associated image subpixel into the diffraction pattern comprising the plurality of diffraction orders are arranged at a subset- specific angle with respect to the respective opposite surfaces, where the subset-specific angle is selected to provide the associated predetermined subset direction. The diffractive surfaces and opposite surfaces hereby form the refractive optical elements, integrated with the diffractive optical elements. Each diffractive optical element may thus diffract the incoming light to provide the diffraction pattern, and provide the associated predetermined subset direction to the diffraction pattern.

In embodiments, the two-dimensional array of image subpixels is positioned in between the array of further optical components and the array of diffractive optical elements. In alternative embodiments, the array of further optical components is positioned in between the two-dimensional array of image subpixels and the array of diffractive optical elements. In embodiments, the array of diffractive optical elements is positioned at a front side of the display apparatus, i.e., the side facing a user during use.

In embodiments, the two-dimensional image forming unit is arranged for emitting light with a predefined angular intensity profile from the image subpixels of the two- dimensional array of image subpixels to the optical system. The diffractive optical components and/or the further optical components may be optimized for the predefined angular intensity profile. The predefined angular intensity profile may e.g. correspond to a slightly divergent beam. The predefined angular intensity profile may relate to the profile in the direction corresponding to the assumed parallax of the user, thus in the horizontal plane. The vertical profile may be a diffuse, Lambertian, profile or any other suitable profile.

In embodiments, the two-dimensional image forming unit is arranged for emitting light with the predefined angular intensity profile with a time-periodically varying angular profile direction and to provide associated visual information to the subpixels, to provide the visual information from the image subpixels associated with the different subsets to the directional viewing regions in periodically different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions. For example, the display apparatus may have a time- sequentially directional backlight illuminating a transmissive LCD panel. The spatial resolution if the two-dimensional array of image subpixels may hereby be fully used. The number and/or complexity of optical components may be reduced.

In embodiments, the array of diffractive optical elements is arranged to provide corresponding diffraction patterns for sets of image subpixels arranged to emit light with different colors to provide corresponding directional viewing regions associated with the plurality of diffraction orders of light with different colors. Hereby an improved quality of visual information in each directional viewing region is obtained.

It will be appreciated by those skilled in the art that two or more of the above- mentioned embodiments, implementations, and/or aspects of the invention may be combined in any way deemed useful. Modifications and variations of the display apparatus, that correspond to the described modifications and variations of the display apparatus, can be carried out by a person skilled in the art on the basis of the present description. The invention is defined in the independent claims. Advantageous options are defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings,

Fig. 1 schematically shows a presentation of visual information by a display apparatus;

Fig. 2a - 2d schematically show embodiments of a display apparatus;

Fig. 3 - 6 schematically show details of various embodiments; and

Fig. 7a - 7c schematically shows details of another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 schematically shows a presentation of visual information by a display apparatus 140. The display apparatus 140 can enable a user to experience a 3D perception when visual information is presented by the display apparatus 140. The display apparatus 140 comprises an image forming unit 142 comprising a two-dimensional array of image subpixels (in later Figures shown as 142b) and an optical system 144 comprising an array of diffractive optical elements 150. The two-dimensional array of image subpixels is arranged to emit light for presenting associated visual information. The two-dimensional image forming unit 142 is arranged for emitting light with a predefined angular intensity profile from the image subpixels of the two-dimensional array of image subpixels to the optical system. In the example shown, the two-dimensional image forming unit 142 is arranged for emitting slightly divergent light. The array of diffractive optical elements 150 is associated with respective ones of the array of image subpixels. Each diffractive optical element is arranged to diffract light from the associated image subpixel into a diffraction pattern 300 comprising a plurality of diffraction orders to provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders. The image subpixels of the array of image subpixels are provided as image subpixels arranged to emit light of specific colors for groups of image subpixels, such as red, green and blue light. Image subpixels may be referred to by the color of the light they emit, e.g., as red subpixels, green subpixels and blue subpixels. Alternative colors may be, for example, red, green, blue and yellow light. The array of diffractive optical elements is arranged to provide corresponding diffraction patterns for sets of image subpixels arranged to emit light with different colors to provide corresponding directional viewing regions associated with the plurality of diffraction orders of light with different colors. The diffractive optical elements may be diffractive gratings. The diffractive gratings associated with the image subpixels of the same color may have the same grating pitch. Thus, all gratings associated with red subpixels may have a first grating pitch, all gratings associated with green subpixels may have a second pitch, and all gratings associated with blue subpixels may have a third pitch, wherein the first, second and third pitch are designed to provide the pluralities of diffraction orders for light of the different colors to the same plurality of directional viewing regions. The image subpixels are organized in subsets of image subpixels associated with different visual information representing different perspective. The image subpixels are hereto provided with an image signal 122 from an image processor 120. The image processor 120 is arranged to provide the subpixels with drive signals to allow visual information to be presented allowing a 3D perception. Each subset is associated with a subset of visual information associated with a subset direction, indicated as 0, 1, 2, 3, 4 and 5, within a directional viewing region. When the user's eyes are in neighboring subsect- directions within a directional viewing region, e.g., as indicated with 110, the user may experience a 3D perception. The optical system may thus be said to effectively duplicate the visual information presented by one subpixel to a plurality of directional viewing regions 102, 104, 106 as the visual information is provided to each of the plurality of diffraction orders by the diffractive optical components. The duplication is indicated with the dotted area for subset direction number 3. The user may hereby experience a 3D perception in each one of the plurality of directional viewing regions 102, 104, 106. In the example shown, the number of diffraction orders schematically shown to be limited to three, with corresponding directional viewing regions 102, 104, 106, and a predetermined limited angular range covered by these directional viewing regions 102, 104, 106 and indicated as 100. The array of diffractive optical elements is arranged to diffract light from the associated image subpixel into the diffraction pattern comprising the plurality of diffraction orders according to a plurality of predefined intensity ratios between the diffraction orders. The optical system may effectively duplicate the visual information presented by one subpixel to the plurality of directional viewing regions 102, 104, 106 with predefined intensity ratios. Outer directional viewing regions, such as directional viewing regions 102, 106 in the example shown in Fig. 1 , may e.g. have intensity ratios according to a plurality predefined intensity ratios between the diffraction orders.

Fig. 2a schematically shows a display apparatus 140 comprising an image forming unit 142 comprising a backlight 142a and a two-dimensional array of image subpixels 142b, and an optical system 144 comprising an array of diffractive optical elements 150 and an array of further optical elements 160. The array of further optical components is 160 positioned in between the two-dimensional array of image subpixels 142b and the array of diffractive optical elements 150, and is thereby arranged to provide the light emitted by image subpixels of subsets of the two-dimensional array of image subpixels 142b with a respective subset direction before the emitted light is "duplicated" by the diffractive optical element into the plurality of diffraction orders of the diffraction pattern. The diffractive optical element associated with a subpixel and the associated further optical element may integrated as a single optical element.

Fig. 2b schematically shows another display apparatus 140 comprising an image forming unit 142 comprising a backlight 142a and a two-dimensional array of image subpixels 142b, and an optical system 144 comprising an array of diffractive optical elements 150 and an array of further optical elements 160. The two-dimensional array of image subpixels 142b is positioned in between the array of further optical components 160 and the array of diffractive optical elements 150 and is thereby arranged to provide the emitted light with a respective subset direction to subsets of the two-dimensional array of image subpixels 142b, after which the light is emitted by image subpixels of the subsets of the two- dimensional array of image subpixels 142b with the respective subset direction before the light is "duplicated" by the diffractive optical element into the plurality of diffraction orders of the diffraction pattern.

Fig. 2c schematically shows again another display apparatus 140 comprising an image forming unit 142 comprising a backlight 142a and a two-dimensional array of image subpixels 142b, and an optical system 144 comprising an array of diffractive optical elements 150 and an array of further optical elements 160. The array of further optical components is 160 and the array of diffractive optical elements 15 are positioned in between the backlight 142a and the two-dimensional array of image subpixels 142b. The array of diffractive optical elements 15 is positioned at a close distance to the two-dimensional array of image subpixels 142b. In this arrangement, the array of further optical components is 160 and the array of diffractive optical elements 15 are arranged to provide the light emitted from the backlight 142a with a respective subset direction and to "duplicated" into the plurality of diffraction orders before the light is delivered to the image subpixels of subsets of the two- dimensional array of image subpixels 142b. The diffractive optical element associated with a subpixel and the associated further optical element may integrated as a single optical element.

Fig. 2d schematically shows again other display apparatus 140 comprising an image forming unit 142 comprising a two-dimensional array of emissive image subpixels 142c, and an optical system 144 comprising an array of diffractive optical elements 150 and an array of further optical elements 160. The array of further optical components is 160 positioned in between the two-dimensional array of image subpixels 142b and the array of diffractive optical elements 150, and is thereby arranged to provide the light emitted by image subpixels of subsets of the two-dimensional array of emissive image subpixels 142c with a respective subset direction before the light is "duplicated" by the diffractive optical element into the plurality of diffraction orders of the diffraction pattern. The diffractive optical element associated with a subpixel and the associated further optical element may be integrated as a single optical element. The image forming unit 142 comprising the two- dimensional array of emissive image subpixels 142c may be an organic LED display.

Fig. 3 schematically shows a simplified embodiment of a display apparatus 140as shown in Fig. 2b. The display apparatus 140 comprises an image forming unit 142 comprising a backlight 142a and a two-dimensional array of image subpixels 142b, and an optical system 144 comprising an array of diffractive optical elements 150 and an array of further optical elements 160. Fig. 3 schematically shows three image subpixels 300R1, 300L1, 300R2 together with the corresponding optics. The backlight 142a illuminates the array of further optical elements 160 with a substantially parallel beam. The two-dimensional array of image subpixels 142b is positioned in between the array of further optical components 160 and the array of diffractive optical elements 150 and is thereby arranged to provide the light with a respective subset direction to subsets of the two-dimensional array of image subpixels 142b, after which the light is emitted by image subpixels of the subsets of the two-dimensional array of image subpixels 142b with the respective subset direction before the light is "duplicated" by the diffractive optical element into the plurality of diffraction orders of the diffraction pattern. An array of further optical elements 160 is provided as a prism sheet to provide the light received from the backlight 142a in two subset directions to the two-dimensional array of image subpixels 142a. The prism sheet has a prism angle a of 3,6°. The prisms extend along a full pixel, consisting of three colored subpixels, in this example a red, green and blue subpixel. The prism sheet is in contact with the a two- dimensional array of image subpixels 142b with its prism tops. The array of diffractive optical elements 150 comprises gratings having pitches of 5,2 μιη, 4,4 μιη and 3,6 μιη for the red, green and blue subpixel respectively, to enable an optimal 3D perception at a viewing distance of lm. The array of diffractive optical elements 150 is designed to a plurality diffraction orders corresponding to a plurality directional viewing regions of predetermined luminous intensity ratios. Fig. 4 schematically shows a presentation of visual information by a display apparatus 140 of an exemplary embodiment of the display apparatus 140 shown in Fig. 2a. The display apparatus 140 comprises a directional backlight 142a and a two-dimensional array of image subpixels 142b, of which three subpixels are shown. The display apparatus 140 comprises an array of diffractive optical elements 150, associated with respective ones of the array of image subpixels. Each diffractive optical element is arranged to diffract light from the associated image subpixel into a diffraction pattern. The display apparatus 140 comprises an array of further optical elements 160 associated with respective diffractive optical elements of the array of diffractive optical elements 150. The array of further optical elements 160 comprises a plurality of subsets of further optical elements. The further optical elements of each subset of further optical elements are arranged to provide the diffraction pattern from the associated one or more diffractive optical elements with an associated predetermined subset direction. The predetermined subset directions of different subsets are different to provide the visual information from the image subpixels associated with the different subsets to the directional viewing regions at different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions. The further optical elements of the different subsets of the array of further optical elements 160 comprise respective further diffractive components arranged to provide the associated diffraction pattern with the corresponding predetermined subset direction. In the example shown, the further diffractive optical components are blazed gratings, arranged to provide the

corresponding predetermined subset direction. Figure 4 schematically shows three subpixels of the array of image subpixels. The three subpixels belong to three different subsets, corresponding to subset directions 2, 3 and 4 (refer to Fig. 1). The further diffractive optical components 160 provide the light emitted from the associated subpixels 142b with a subset direction and then emit the light to the associated diffractive optical element 150. As indicated, the three further diffractive optical components 160 shown each provide a different subset direction to the emitted light. The further diffractive components 160 associated with subpixels of the same subset and arranged to emit light of different colors are designed to provide equal subset directions. Each diffractive optical element 150 diffract lights from the associated image subpixel into a diffraction pattern comprising a plurality of diffraction orders indicated as -1, 0, 1, to provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders. Fig. 5 schematically shows details of another embodiment. The embodiment of Fig. 5 differs from the embodiment of Fig. 4 at least in that the further optical elements 160 are not further diffractive optical components but refractive optical components arranged to provide the associated diffraction pattern with the corresponding predetermined subset direction. In the example shown, the refractive optical components are prisms, arranged to provide the corresponding predetermined subset direction. Thus, the refractive optical components 160 provide the light emitted from the associated subpixels 142b with a subset direction and then emit the light to the associated diffractive optical element 150. Each diffractive optical element 150 diffracts light from the associated image subpixel into a diffraction pattern comprising a plurality of diffraction orders indicated as -1, 0, l,to provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders.

Fig. 6 schematically shows details of again another embodiment. In the embodiment shown in Fig 6, the array of diffractive optical elements 151 is arranged to diffract light from the associated image subpixel into the diffraction pattern comprising the plurality of diffraction orders, wherein adjacent non-suppressed diffraction orders of the plurality of diffraction orders associated directional viewing regions are separated by one or more suppressed diffraction orders. In the schematic example of Fig. 6, five adjacent diffraction orders are suppressed and one out of six diffraction orders is used for visual information, where the suppression is dependent on the viewing direction associated with a subpixel. Fig. 6 shows the selective suppression in a schematic manner: three subpixels are associated with directions labelled 2, 3 and 4; the left diffractive optical element 151 is designed to diffract light from the associated image subpixel into a diffraction pattern comprising a plurality of diffraction orders indicated as -7, -1, 5 to provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders; the middle diffractive optical element 151 is designed to diffract light from the associated image subpixel into a diffraction pattern comprising a plurality of diffraction orders indicated as -6, 0, 6 to provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders; and the left diffractive optical element 151 is designed to diffract light from the associated image subpixel into a diffraction pattern comprising a plurality of diffraction orders indicated as -5, -1, 7 to provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders. The diffractive optical elements of each subset of diffractive optical elements is thus arranged to provide the diffraction pattern from the associated diffractive optical element with an associated predetermined subset direction, with the predetermined subset directions of different subsets being different to provide the visual information from the image subpixels associated with the different subsets to the directional viewing regions at different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions. The suppression is different for different subsets to provide the diffraction pattern from the associated diffractive optical element with the predetermined subset direction.

Fig. 7a - 7c schematically shows details of again another embodiment. The display apparatus 140 shown on Fig. 7a - 7c comprises a time-sequential directional backlight 142aS and a two-dimensional array of image subpixels 142b, of which three subpixels are shown. The display apparatus 140 comprises an array of diffractive optical elements 150, associated with respective ones of the array of image subpixels. Each diffractive optical element is arranged to diffract light from the associated image subpixel into a diffraction pattern. In the example shown, each diffractive optical element diffracts light into a diffraction pattern of three orders, -1, 0 and 1, and any other others are suppressed. The diffractive optical components thus provide the visual information from the associated image subpixel to a plurality of directional viewing regions 102, 104, 106 associated with the plurality of diffraction orders. The two-dimensional image forming unit 142 is arranged for emitting light with the predefined angular intensity profile with a time- periodically varying angular profile direction and to provide associated visual information to the subpixels 142b to provide the visual information from the image subpixels associated with the different subsets to the directional viewing regions in periodically different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions.

Fig 7a - 7c show three successive moments in time. In Fig. 7a, the time- sequential directional backlight 142aS emits lights with a first predefined angular intensity profile having a first profile direction associated with viewing direction 2; in Fig. 7b, the time-sequential directional backlight 142aS emits lights with a second predefined angular intensity profile having a second profile direction associated with viewing direction 3, substantially perpendicular to the screen; in Fig. 7c, the time- sequential directional backlight 142aS emits lights with a third predefined angular intensity profile having a third profile direction associated with viewing direction 4. The viewing directions associated with the different profile directions are different to provide the visual information from the image subpixels associated with the different profile directions to the directional viewing regions at different directions, to enable the user to view with 3D perception in each of the plurality of directional viewing regions. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.