Patent Publication Number: US-2016234481-A1

Title: Method for indicating a sweet spot in front of an auto-stereoscopic display device, corresponding auto-stereoscopic display device and computer program product

Description:
TECHNICAL FIELD 
     The present disclosure relates to the field of multi-views auto-stereoscopic display devices. 
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present disclosure that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Auto-stereoscopic display devices (either based on the use of a parallax barrier, or based on the use of a micro-lens array) enables the display of multi-view content. As mentioned in the document US 2014/0168390, when a user is positioned at an “optimal distance”, he perceives only a first view from one eye, and a second view from another eye (see FIG. 5 of document US 2014/0168390, and the optimal viewing distance “OVD”). Therefore, he perceives a 3D effect, without having to wear 3D glasses (either passive or active glasses). The set of positions at an optimal viewing distance define regions in space named sweet spots or also viewing spots, i.e. these regions located in front of auto-stereoscopic display device are regions where a user can only perceive one view per eye, enabling the viewing of a 3D content without interferences (see for example the article entitled “Comparative study of auto-stereoscopic displays for mobile devices” by A. Boev and A. Gotchev). It should be noted that, the higher a number of views an auto-stereoscopic display devices provide, the smaller the sweet spots are. Moreover, when the user is not positioned at the “optimal distance” (that defines the sweet spots), he can perceive from at least one eye, an additional view. The perception of an additional view alters the rendering of the 3D effect. 
     Therefore, it is important to help a user to position him correctly in a sweet spot. 
     To achieve such objective, it can be possible to use tracking systems, using cameras that can track the position of the eyes of the user and adapt the content consequently. The main drawback of this solution is that it can only work with one user. 
     The present technique does not limit the number of users and can work in the case of a family sitting on a couch watching the same content. 
     In order to inform a user/viewer for finding out a position enabling him to see a 3D content without troubles (i.e. to indicating him the sweet spots), one skilled in the art could also use one of the techniques described in the documents WO2012143836 or FR2888000. Indeed, techniques of documents WO2012143836 ( FIG. 4 a - e   ), and FR2888000 (see the arrow indicating a direction in  FIG. 2  in views  12  and  18 ) furnish such information. 
     However, the techniques of documents WO2012143836 and FR2888000 incorporate such information in the 3D image data itself. Indeed, in document WO2012143836, the indicator generator device, referenced  140 , generates a signal combining 3D image data and an indicator, and then such signal is displayed. In document FR2888000, it is mentioned that the indicator can be removed during the display. Therefore, it means that the signal received by the display device is also a combination of 3D image data and an indicator (as in document WO2012143836). 
     The proposed technique is an alternative of the ones cited previously, that does not need to modify the 3D content data (i.e. two different views) itself. 
     SUMMARY 
     References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     The present disclosure is directed to an auto-stereoscopic display device comprising a display panel configured to deliver n different images views, with n a integer greater or equal to two; and an optical filter which is configured to control diffusion directions of said n different images views. Such auto-stereoscopic display device is remarkable in that it comprises opaque materials positioned in said display panel in such way that a content indicating a direction that a user should follow in order to be in a correct sweet spot, is delivered on an edge of different views, when said display panel is on. 
     More precisely, it is proposed to modify the structure of a multi-view auto stereoscopic display devices by adding an opaque material in particular positions of the display panel (also named an electroluminescent display). Therefore, when the user is positioned at the extreme borders of opposite sweet spots, an image (or a logo, or a symbol) appears indicating in which direction the viewer has to move. Hence, such technique enables a user to be placed correctly in front of a multi-view auto stereoscopic display device. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said opaque material has fixed opacity properties, and that said edge of different views is an edge of extreme views. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said opaque materials are smart glasses of which light transmission properties can be changed under application of either a voltage and/or a light and/or heat. 
     The opaque materials can be derived from the document US 2010/0046060 which describes an optical filter that can be controlled by the intensity of a voltage or a current. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said edge of different views is an edge of extreme views. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said opaque materials are positioned below color filter of sub-pixels comprised in said display panel. 
     It should be noted that in such embodiment, the photolithographic process has to be modified in order to position the opaque materials below the color filter. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said opaque materials are positioned on color filter of sub-pixels comprised in said display panel. 
     The photolithographic method used in order to manufacture an auto-stereoscopic display device having these features is unchanged versus classical method. Indeed, only the photolithography masks are modified to enlarge black matrix size on selected sub-pixels and to decrease the color filter size on those same sub-pixels. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said optical filter comprises at least one parallax barrier. 
     In another embodiment of the present disclosure, it is proposed an auto-stereoscopic display device in which said optical filter comprises at least one lenticular array. 
     In a preferred embodiment, the auto-stereoscopic display device is remarkable in that said optical filter comprises at least one integral photography plate with a fly&#39;s-eye lens array. 
     In another embodiment, it is proposed a method for indicating, in front of an auto-stereoscopic display device, a correct sweet spot. Such method is remarkable in that it comprises displaying on extreme views delivered by said auto-stereoscopic display device, a content indicating a direction that a user should follow in order to be located in a correct sweet spot. 
     In a preferred embodiment, such method is remarkable in that said displaying is done during a first period of time, and in that when such first period of time has exceeded, displaying on said extreme views content related to content displayed on other views instead of said content indicating a direction that a user should follow in order to be located in a correct sweet spot. 
     In another embodiment, it is proposed a method for indicating, in front of an auto-stereoscopic display device, a correct sweet spot. The method is remarkable in that it comprises controlling light transmission properties of materials positioned in a display panel in said auto-stereoscopic display device according to a voltage and/or a light and/or heat; and displaying on edge of different views a content indicating a direction that a user should follow in order to be located in a correct sweet spot. 
     In another embodiment, the method for indicating is remarkable in that said displaying is done during a first period of time, and in that when such first period of time has exceeded, displaying on said edge of different views content related to content displayed on other views instead of said content indicating a direction that a user should follow in order to be located in a correct sweet spot. 
     According to an exemplary implementation, the different steps of the methods are implemented by a computer software program or programs, this software program comprising software instructions designed to be executed by a data processor of a relay module according to the disclosure and being designed to control the execution of the different steps of this method. 
     Consequently, an aspect of the disclosure also concerns a program liable to be executed by a computer or by a data processor, this program comprising instructions to command the execution of the steps of a method as mentioned here above. 
     This program can use any programming language whatsoever and be in the form of a source code, object code or code that is intermediate between source code and object code, such as in a partially compiled form or in any other desirable form. 
     The disclosure also concerns an information medium readable by a data processor and comprising instructions of a program as mentioned here above. 
     The information medium can be any entity or device capable of storing the program. For example, the medium can comprise a storage means such as a ROM (which stands for “Read Only Memory”), for example a CD-ROM (which stands for “Compact Disc-Read Only Memory”) or a microelectronic circuit ROM or again a magnetic recording means, for example a floppy disk or a hard disk drive. 
     Furthermore, the information medium may be a transmissible carrier such as an electrical or optical signal that can be conveyed through an electrical or optical cable, by radio or by other means. The program can be especially downloaded into an Internet-type network. 
     Alternately, the information medium can be an integrated circuit into which the program is incorporated, the circuit being adapted to executing or being used in the execution of the method in question. 
     According to one embodiment, an embodiment of the disclosure is implemented by means of software and/or hardware components. From this viewpoint, the term “module” can correspond in this document both to a software component and to a hardware component or to a set of hardware and software components. 
     A software component corresponds to one or more computer programs, one or more sub-programs of a program, or more generally to any element of a program or a software program capable of implementing a function or a set of functions according to what is described here below for the module concerned. One such software component is executed by a data processor of a physical entity (terminal, server, etc.) and is capable of accessing the hardware resources of this physical entity (memories, recording media, communications buses, input/output electronic boards, user interfaces, etc.). 
     Similarly, a hardware component corresponds to any element of a hardware unit capable of implementing a function or a set of functions according to what is described here below for the module concerned. It may be a programmable hardware component or a component with an integrated circuit for the execution of software, for example an integrated circuit, a smart card, a memory card, an electronic board for executing firmware etc. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The above and other aspects of one or more embodiments of the invention will become more apparent by the following detailed description of exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1(A)  presents a part of an auto-stereoscopic display device that can deliver four different views; 
         FIG. 1(B)  illustrates that the auto-stereoscopic display device of  FIG. 1(A)  can deliver four different views via four sub-pixels defining four viewing cones; 
         FIG. 1(C)  depicts the intersection of the viewing cones shown in  FIG. 1(B) ; 
         FIG. 1(D)  depicts an embodiment where the eyes of a viewer can perceive 3D content; 
         FIG. 1(E)  depicts an alternate embodiment where the eyes of a viewer can also perceive 3D content; 
         FIG. 1(F)  depicts an instance where the viewer is not positioned correctly in front of an auto-stereoscopic device; 
         FIG. 1(G)  depicts a second instance where the viewer is not positioned correctly in front of an auto-stereoscopic device; 
         FIG. 2  details a part of a display panel according to one embodiment of the invention; 
         FIGS. 3(A) and 3(B)  represent images of arrows that are perceived by a viewer in the case that one eye of the viewer is on the edge of a sweet spot; 
         FIG. 4  presents an example of a device that can be used to perform one or several steps of methods disclosed in the present document. 
     
    
    
     DETAILED DESCRIPTION 
     An auto-stereoscopic display device comprises, for example:
         a display panel which is an array of pixels (such display panel can be for example a TFT LCD screen (for Thin-film-transistor liquid-crystal display screen)) that can be viewed as an image forming means, and   an optical filter positioned in front of such display panel that controls the diffusion directions of rays of light emitted by the display panel. The optical filter can be either a parallax barrier (or a combination of parallax barriers, that intend to block light in some directions), or a lenticular sheet (that intends to refract the received light from pixels), or an integral lens sheet (as in document EP 0780727).       

     More precisely, a pixel comprises several sub-pixels as explained for example in document US 2014/0226205. As detailed in the  FIG. 3  of document US 2014/0226205, a pixel can be made of three sub-pixels, and each of these sub-pixels is associated with a primary color (blue, red or green) and with an image view. An example of an arrangement of these sub-pixels in a display panel is depicted in the  FIG. 4  of document US 2014/0226205, in the case that three images views are delivered by the auto-stereoscopic display device. At last, when all the sub-pixels associated to one view (as in the  FIG. 5  of document US 2014/0226205, with a view  1 ) are perceived by an eye of a viewer, an image associated with the view  1  is visualized by the viewer. It is the goal of the optical filter to deviate correctly the light emitted by the sub-pixels in such way that a viewer can correctly see the different images views. In the case that the auto-stereoscopic display device can handle n different images views, with n an integer greater or equal to two, it is possible to generate such n different images views from only two views (named stereoscopic images) as explained in the document US 2013/0050187. 
     It should be noted that the display panel can be positioned in front of a light source and that the sub-pixels are commanded in order to modulate the light via controlling means that can handle addressing schemes (in the case of a reflective LCD, the light source is not positioned in front of a light source). Moreover, each sub-pixel is associated with a switching element (that is usually a transistor, such as a TFT (for Thin Film Transistor). 
     These examples of panel display can obviously be modified in order to handle n different views, with n an integer greater or equal to two. 
     The  FIG. 1( a )  presents a part of an auto-stereoscopic display device that can deliver four different views. More precisely,  FIG. 1(A)  illustrates that an auto-stereoscopic display device, referenced  100 , can deliver for different views via four sub-pixels positioned in a first part of the display panel, defining four viewing cones in space. The  FIG. 1(B)  illustrates that the auto- stereoscopic display device  100  can deliver four different views via four different sub-pixels positioned in a second part of the display panel, defining four other viewing cones in space. The intersection of these viewing cones is depicted in  FIG. 1(C) . For the sake of explanation, only these intersections of viewing cones is represented, but it should be noted that when all sub-pixels are emitting light, all the intersection of viewing cones should be taken into account in order to define sweet spots. In the  FIG. 1(C) , the diamond zones referenced  101 ,  102 ,  103  and  104  correspond to sweet spots. It should be noted that in that case the views  1  and views  4  are considered as being extreme views. It should be noted that the expression “extreme views” is well known for one skilled in the art. Indeed, it is used in numerous documents such as the U.S. Pat. No. 7,126,598 or the document “ Toward the Light Field Display: Autostereoscopic Rendering via a Cluster of Projectors ” by Ruigang Yang et al., or the document EP 1955553. The other zones (i.e. not the sweet spot) are a mixture of views, and are location where content cannot be viewed correctly. For example, the zone referenced  105  is a zone where both views  1  and  2  are mixed. In the same way, the zone referenced  106  is a zone where both views  3  and  4  are mixed. 
     For example, when the eyes of a viewer, referenced  107  and  108 , are positioned as depicted in  FIG. 1(D) , i.e. the eyes  107  and  108  are respectively positioned in zones  101  and  102 , the viewer is positioned in a correct sweet spot in the sense that he can perceive 3D content. In the same way, when the eyes  107  and  108 , are positioned as depicted in  FIG. 1(E) , i.e. the eyes  107  and  108  are respectively positioned in zones  103  and  104 , the viewer is positioned in a correct sweet spot in the sense that he can also perceive 3D content. 
     Obviously, if the eyes  107  and  108  are also positioned in zones  102  and  103 , the viewer can also perceive 3D content. 
       FIGS. 1(F) and 1(G)  depict some cases where the viewer is not correctly positioned in front of an auto-stereoscopic device. Indeed, in these cases, the two eyes  107  and  108  are not both comprised in the diamond zones (for example the eye  107  is located outside or at the edge of the diamond zone  101  in  FIG. 1(F) , and the eye  108  is located outside or at the edge of the diamond zone  104  in  FIG. 1(G) ). 
     The present technique enables a viewer to correctly position his eyes in sweet spots (i.e. to put his eyes in diamond zones  101  to  104 ). 
     The  FIG. 2  details a part of a display panel according to one embodiment of the invention. 
     In this  FIG. 2 , some sub-pixels of a display panel are represented: each sub-pixel comprises an ITO (Indium Tin Oxide) film, referenced  203 , and they are linked by the use of black matrix elements, referenced  204 , and these sub-pixels are positioned on a glass substrate referenced  205 . Color filters are either red (noted R), green (noted G) or blue (noted B). More precisely, in this embodiment, it is proposed to add, at the display panel level, a particular material on sub-pixels of extreme views (for example the views  1  and  4  in the case of an auto-stereoscopic display device as depicted in  FIGS. 1(A)-1(G) ). Such particular material is in one embodiment an opaque material. In another embodiment, such opaque material is a smart glass, which is a functional glass material. For example, the opaque material to be included in a part of a classical color filter can be a tunable plasmonic filter as defined in the document US 2010/0046060. In the case that the opaque material is a smart glass, it is not necessary to position it on sub-pixels of extreme views. Indeed, as it is possible to control the opacity of these materials, individually by using a variation of voltage for example, it enables a better flexibility for the positioning of these elements. 
     More precisely, in one embodiment, an opaque material referenced  201  is positioned close to a part of a sub-pixel associated with the first view (the view  1 ). An opaque material referenced  202  is positioned close to a part of a sub-pixel associated with the final view (the view  4 ). It should be that, in one embodiment of the invention, not all the sub-pixels associated with the view  1  have such opaque material, and that not all the sub-pixels associated with the view  4  have such opaque material. Indeed, the opaque materials are positioned in such way that the collection of the opaque material provides information to the viewer, when the display panel is on. Such information is intended to help the viewer to correctly position himself in front of an auto-stereoscopic display device. 
     In another embodiment of the invention, opaque materials are comprised in the ITO film  203  and are position in suitable positions in order to provide a similar effect as the one of the previous embodiment. 
     In another embodiment of the invention, the opaque materials are positioned in some of the color filters of a TFT LCD panel (see the figure describing the vertical structure of a color TFT LCD panel) in the white paper entitled “ Overview of the theory and construction of TFT display panels ” published by Sequoia Technology Ltd, in December 2003. 
     An example of a result of a repartition of opaque material  201  is given in  FIG. 3(A) . Indeed,  FIG. 3(B)  represents an arrow that is perceived by a viewer in the case that the eye  107  is on the edge of the zone  101 . Such information enables to avoid the situation depicted in  FIG. 1(F) . 
     An example of a result of a repartition of opaque material  202  is given in  FIG. 3(B) . Indeed,  FIG. 3(B)  represents an arrow that is perceived by a viewer in the case that the eye  108  is on the edge of the zone  104 . Such information enables to avoid the situation depicted in  FIG. 1(G) . 
     In order to achieve such result, in one embodiment of the invention, such opaque material can be integrated in the color filter of sub-pixels. For example, the proposed technique proposes to modify the classical structure of sub-pixels as depicted in U.S. Pat. No. 7,292,294 by introducing an opaque material in the edge of a color filter associated with a sub-pixel, for some sub-pixels. Hence, a part of the color filter is dedicated to the delivering of the information to correctly position a viewer in front of the auto-stereoscopic display device. 
     In another embodiment of the invention, the use of an opaque material is substituted by the display on some of the views delivered by the auto-stereoscopic display device of the placement information (as the arrows described in  FIGS. 3(A) and 3(B) ). In such embodiment, the use of some of the views to deliver such placement information is done during a limited period of time, and then, these views are reassigned to the delivering of content. 
       FIG. 4  presents an example of a device that can be used to perform one or several steps of methods disclosed in the present document. 
     Such device referenced  400  comprises a computing unit (for example a CPU, for “Central Processing Unit”), referenced  401 , and one or more memory units (for example a RAM (for “Random Access Memory”) blocks in which intermediate results can be stored temporarily during the execution of instructions a computer program, or a ROM block in which, among other things, computer programs are stored, or an EEPROM (“Electrically-Erasable Programmable Read-Only Memory”) block, or a flash block) referenced  402 . Computer programs are made of instructions that can be executed by the computing unit. Such device  400  can also comprise a dedicated unit, referenced  403 , constituting an input-output interface to allow the device  400  to communicate with other devices. In particular, this dedicated unit  403  can be connected with an antenna (in order to perform communication without contacts), or with serial ports (to carry communications “contact”). It should be noted that the arrows in  FIG. 4  signify that the linked unit can exchange data through buses for example together. 
     In an alternative embodiment, some or all of the steps of the method previously described, can be implemented in hardware in a programmable FPGA (“Field Programmable Gate Array”) component or ASIC (“Application-Specific Integrated Circuit”) component. 
     In an alternative embodiment, some or all of the steps of the method previously described, can be executed on an electronic device comprising memory units and processing units as the one disclosed in the  FIG. 4 . 
     At last, it should be noted that the present technique can be applied to auto-stereoscopic display devices that are based on parallax barriers, or lenticular arrays or techniques that intend to reproduce a light field such as integral photography plate with a fly&#39;s-eye lens array.