Patent Publication Number: US-2011065479-A1

Title: Portable Electronic Apparatus Having More Than one Display Area, and a Method of Controlling a User Interface Thereof

Description:
TECHNICAL FIELD 
     The present invention relates to the field of portable electronic equipment, and in particular to a portable electronic apparatus of a kind having more than one display area. The invention also relates to a method of controlling a user interface of such a portable electronic apparatus. 
     BACKGROUND 
     Portable electronic equipment of course exists in many different types. One common example is a mobile terminal, such as a mobile telephone for a mobile telecommunications system like GSM, UMTS, D-AMPS, CDMA2000, FOMA or TD-SCDMA. Other examples include personal digital assistants (PDAs), portable media players (e.g. DVD players), palmtop computers, digital cameras, game consoles, navigators, etc. A mobile terminal in the form of a mobile telephone will be used as a non-limiting example of a portable electronic apparatus in the following. 
     Conventionally, mobile terminals have been equipped with a single display. More recently, mobile terminals have been introduced which have both a main, front-mounted display and an auxiliary display, typically mounted either on a rear side of the terminal, or in a separate housing member hinged to the main terminal housing (such models are often referred to as foldable terminals or clamshell terminals). Since multi-media applications, based for instance on Internet services, are expected to continue to grow rapidly in popularity, it is likely that user demands for larger displays and/or more display areas will become stronger and stronger. 
     New, flexible display technologies may for instance make it feasible to provide a single physical display that extends across more than one housing side of the mobile terminal, thereby in effect offering a plurality of display areas, one at each housing side of the mobile terminal. Alternatively or additionally, multiple separate physical displays may be provided on different housing sides, thereby again offering a plurality of display areas at different locations on the housing of the mobile terminal. If the traditional mechanical keypad in the man-machine interface (MMI) is replaced by touch-sensitive display technologies, such multiple display areas may be even more feasible. 
     However, a problem to consider when a mobile terminal is provided with several display areas at different locations on the mobile terminal is that it will be difficult to know which particular display area(s) that the user is currently monitoring. This has to do with the portable nature of the mobile terminal. Since it is hand-held, it can be held in many different spatial orientations and can be viewed by the user from many different angles, not necessarily only the traditional straight-from-the-front approach. If the display areas are touch-sensitive and therefore also serve as input devices, it is even harder to predict which particular display area(s) may be used by the user at a given moment. 
     In turn, this may require the mobile terminal to keep all display areas activated, i.e. driven with full power to be capable to present information as required, and possibly also to accept hand-made input (when the display area is touch-sensitive). However, this poses a new problem; keeping all display areas activated will consume more electric power, and electric power is a limited resource in a portable, battery-driven electronic apparatus. 
     Therefore, there is a need for improvements in the way the user interface is controlled for a portable electronic apparatus that comprises more than one display area. 
     US 2007/0188450, US 2007/0232336 and US 2005/0140565 disclose mobile terminals with more than one display area. Presentation of information in the display areas depends on the rotation of the mobile terminal. 
     SUMMARY 
     It is accordingly an object of the invention to eliminate or alleviate at least some of the above problems referred to above. 
     As a conceptual idea behind the invention, the present inventor has realized that novel and beneficial use may be made of an orientation sensor or tilt sensor, for instance in the form of an accelerometer or similar external force-measuring device known as such, as a part of a selective control scheme for the different display areas which allows a kind of handover of the user interface from one currently active display area to another one which is to become active. The present inventor has further realized that image capturing and processing devices, for instance in the form of camera(s) in combination with an image processor having face detection functionality also known as such, may be used to enhance the accuracy of the selective control of the different display areas. 
     This conceptual idea has been reduced to practice at least according to the aspects and embodiments of the invention referred to below. 
     One aspect of the present invention therefore is a portable electronic apparatus having first and second display areas according to claim  1 , the apparatus thus being characterized, inter alia, by: 
     an orientation sensor configured to provide an orientation sensor output signal indicative of a spatial orientation of said apparatus; and 
     a display controller coupled to said first and second display areas and to said orientation sensor, said display controller being responsive to said orientation sensor output signal to selectively control said first display area and said second display area. 
     Thanks to this arrangement, the display controller can selectively drive one of the first and second display areas differently from the other one, and, consequently, make optimal use of the first and second display areas depending on the current spatial orientation of the portable electronic apparatus. Within the context of the present invention, “spatial orientation” refers to an orientation of the portable electronic apparatus in one or more dimensions in a two-dimensional or three-dimensional space. Moreover, “the orientation sensor output signal [being] indicative of a spatial orientation of the portable electronic apparatus” means that the orientation sensor output signal will contain information from which a current orientation, or change in orientation (i.e. movement), of the portable electronic apparatus can be derived. For embodiments where “spatial orientation” refers to at least two dimensions, the orientation sensor may either be composed of a single sensor unit capable of sensing the orientation (or movement) of the portable electronic apparatus in said at least two dimensions, or of a plurality of sensor units, each capable of sensing the orientation (or movement) of the portable electronic apparatus in a respective one of said at least two dimensions. 
     The orientation sensor may comprise an accelerometer capable of sensing at least one of a static acceleration and a dynamic acceleration of said portable electronic apparatus. To this end, the orientation sensor may measure the static acceleration force on the portable electronic apparatus caused by gravity, and the orientation sensor output signal may thus be used to derive a tilt angle of the portable electronic apparatus with respect to a ground plane. Additionally or alternatively, the orientation sensor may measure the dynamic acceleration force on the portable electronic apparatus caused by movement of the apparatus, and the orientation sensor output signal may therefore be used to determine that the portable electronic apparatus is being moved. 
     In one or more embodiments where the portable electronic apparatus further has a memory, said display controller is configured to read from said memory a previous orientation of said apparatus, determine from said orientation sensor output signal a current orientation of said apparatus, and selectively control said first display area and said second display area based on a difference between said previous orientation and said current orientation of said apparatus. 
     In the portable electronic apparatus, the display controller is adapted to selectively control said first display area and said second display area by: 
     maintaining one of said first and second display areas in a first display state, and another of said first and second display areas in a second state, said second display state being a state with less display activity than said first display state; 
     determining, from said orientation sensor output signal, a movement of said portable electronic apparatus; and, in response, 
     causing said one of said first and second display areas to switch from said first display state to said second display state, and said other of said first and second display areas to switch from said second display state to said first display state. 
     The first display state may be a state where the particular display area is activated, i.e. with full capacity for visual presentation of information, whereas the second display state may be a state where the particular display area is deactivated (for instance powered off, or put in an idle or power-save mode), i.e. with no capacity for visual presentation of information, or at least with less than full capacity for visual presentation of information (for instance with reduced display brightness or color spectrum). 
     The display controller may be further adapted to compare the determined movement of said portable electronic apparatus to a threshold and to perform said causing to switch between first and second display states for said first and second display areas only if the determined movement exceeds said threshold. 
     In one or more embodiments of the portable electronic apparatus, the display controller is further adapted to perform said causing to switch between first and second display states by 
     first causing said other of said first and second display areas to switch from said second display state to said first display state; 
     then maintaining, during a transition time period, both of said first and second display areas in said first display state; and 
     finally, after said transition time period has lapsed, causing said one of said first and second display areas to switch from said first display state to said second display state, 
     wherein said transition time period is a function of a speed of said determined movement of said portable electronic apparatus. 
     Enhanced accuracy of the selective control of the first and second display areas is provided, wherein the portable electronic apparatus further comprises an image processor associated with said display controller, said image processor being configured to investigate a captured image of a surrounding of said portable electronic apparatus for any presence in said captured image of an object of a certain kind, and to indicate such presence in an image processor output signal, 
     wherein said display controller is responsive also to said image processor output signal for the selective control of said first display area and said second display area. 
     Aforesaid certain kind of object may be the face of one or more human individuals, wherein said image processor will be configured to execute a face detection algorithm in order to detect the presence of a user of said portable electronic apparatus. 
     The captured image will contain a surrounding of said other of said first and second display areas, and said display controller will be configured, after the determining of a movement of said portable electronic apparatus, to: 
     verify that said image processor has detected a face in said captured image and thus indicates presence of said user at said other of said first and second display areas, and 
     perform said causing of said other of said first and second display areas to switch from said second display state to said first display state, only upon an affirmative result from said verification by said image processor. 
     The provision of face detection functionality will therefore enhance the accuracy of the selective control of the first and second display areas, by verifying that the user is present at the particular display area which, according to the determined apparatus movement, the display controller intends to switch to. 
     In one or more embodiments, the display controller is adapted, after having performed said causing to switch between first and second display states, to: 
     receive a sequence of captured images of said surrounding of said portable electronic apparatus; 
     determine an angular change in the appearance of the face of said user, as detected in the sequence of captured images, and 
     control said other of said first and second display areas to switch from a first angular display mode to a second angular display mode. 
     The first angular display mode may for instance be a portrait mode (or a zero-degree rotated display mode), and the second angular display mode may be a landscape mode (or a mode where the display contents are rotated by, for instance, 90 degrees compared to the first angular display mode). This arrangement will allow a user to put down his portable electronic apparatus on a table or other steady surface, and move freely around the table (etc), with the angular display mode of the apparatus being automatically adjusted so that the display contents will continue to appear at a suitable orientation for the user. 
     In one or more embodiments, the first and second display areas are two physically different displays on said apparatus. Alternatively, the first and second display areas may be different parts of one common display of said apparatus. The portable electronic apparatus may have additional display area(s), such as a third display area, a fourth display area, etc. Such additional display area(s) may be controlled by said display controller in the same way as the first and second display areas. 
     The portable electronic apparatus may advantageously, but not necessarily, be embodied as a mobile terminal, such as a mobile telephone for a mobile telecommunications system, including but not limited to GSM, UMTS, D-AMPS, CDMA2000, FOMA or TD-SCDMA. 
     A second aspect of the invention is a method according to claim  9  of controlling a user interface of a portable electronic apparatus having first and second display areas, the method involving, inter alia: 
     determining a spatial orientation, or change in spatial orientation, of said apparatus; and 
     selectively controlling said first display area and said second display area in response to the determined spatial orientation, or change in spatial orientation, of said apparatus. 
     Aforesaid determining may involve:
         determining a current orientation of said apparatus; and   reading a stored previous orientation of said apparatus,       

     wherein said first display area and said second display area are selectively controlled based on a difference between said previous orientation and said current orientation of said apparatus. 
     Said first display area and said second display area are selectively controlled by: 
     maintaining one of said first and second display areas in a first display state, and another of said first and second display areas in a second state, said second display state being a state with less display activity than said first display state; 
     determining a movement of said apparatus from the determined spatial orientation, or change in spatial orientation, of said apparatus; and, in response, 
     causing said one of said first and second display areas to switch from said first display state to said second display state, and said other of said first and second display areas to switch from said second display state to said first display state. 
     One or more embodiments may further involve comparing the determined movement of said apparatus to a threshold and performing said causing to switch between first and second display states for said first and second display areas only if the determined movement exceeds said threshold. 
     In one or more embodiments, said causing to switch between first and second display states involves: 
     causing said other of said first and second display areas to switch from said second display state to said first display state; 
     calculating a transition time period as a function of a speed of said determined movement of said portable electronic apparatus; 
     maintaining, during said transition time period, both of said first and second display areas in said first display state; and 
     after said transition time period has lapsed, causing said one of said first and second display areas to switch from said first display state to said second display state, 
     Functionality for enhancing the accuracy of the selective control of the first and second display areas involves: 
     receiving a captured image of a surrounding of said portable electronic apparatus; and 
     investigating said captured image for any presence therein of an object of a certain kind, 
     wherein said first display area and said second display area are selectively controlled also based on a result of said investigating of said captured image. 
     Said certain kind of object is the face of one or more human individuals, and said investigating of said captured image thus involves executing a face detection algorithm in order to detect the presence of a user of said portable electronic apparatus. 
     The captured image contains a surrounding of said other of said first and second display areas, wherein the method involves: 
     verifying, after the determining of a movement of said portable electronic apparatus, that a face has been detected in said captured image and thus indicates presence of said user at said other of said first and second display areas, and 
     performing said causing of said other of said first and second display areas to switch from said second display state to said first display state, only upon an affirmative result from said verifying. 
     One or more embodiments further involve: 
     receiving, after said causing to switch between first and second display states, a sequence of captured images of said surrounding of said portable electronic apparatus; 
     executing said face detection algorithm to detect faces in said sequence of captured images; 
     determining an angular change in the appearance of the face of said user, as detected in the sequence of captured images, and 
     controlling said other of said first and second display areas to switch from a first angular display mode to a second angular display mode. 
     It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Objects, features and advantages of embodiments of the invention will appear from the following detailed description, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a schematic illustration of a non-limiting example of an environment in which embodiments of the present invention may be exercised; 
         FIGS. 2   a - c  are a schematic front view, rear view and partially sectional side view, respectively, of a portable electronic apparatus according to a first embodiment of the present invention, embodied as a mobile terminal having a first display area in the form of a front-mounted display, and a second display area in the form of a rear-mounted display; 
         FIG. 3  is a schematic block diagram representing the major components, within the context of the present invention, of a portable electronic apparatus according to one embodiment; 
         FIG. 4  is a schematic flowchart of a method according to one embodiment of the present invention; 
         FIGS. 5   a - c  illustrate different spatial orientations of a portable electronic apparatus according to one embodiment, and how different display areas thereof are selectively controlled in accordance with the inventive concept; 
         FIG. 6   a - b  are schematic perspective views of a portable electronic apparatus according to a second embodiment of the present invention, having a display which extends to all six sides of the apparatus housing, each side thus accommodating a respective display area forming part of said display; and 
         FIGS. 7 and 8  schematically illustrate images captured by a front-mounted and a rear-mounted camera, respectively, of the portable electronic apparatus according to one embodiment, wherein faces of human individuals are included in the illustrated images. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention will be now described with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the particular embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. 
     Before turning to a detailed description of the disclosed embodiments, an exemplifying environment in which they may be exercised will now be briefly described with reference to  FIG. 1 . 
     In  FIG. 1 , a portable electronic apparatus in the form of a mobile terminal  100  is part of a cellular telecommunications system. A user  1  of the mobile terminal  100  may use different telecommunications services, such as voice calls, Internet browsing, video calls, data calls, facsimile transmissions, still image transmissions, video transmissions, electronic messaging, and e-commerce. These described telecommunication services are however not central within the context of the present invention; there are no limitations to any particular set of services in this respect. 
     The mobile terminal  100  connects to a mobile telecommunications network  110  over a radio link  111  and a base station  112 . The mobile terminal  100  and the mobile telecommunications network  110  may comply with any commercially available mobile telecommunications standard, including but not limited to GSM, UMTS, D-AMPS, CDMA2000, FOMA and TD-SCDMA. As already mentioned, embodiments of the mobile terminal  100  will be described in more detail later with reference to the remaining drawings. 
     A conventional public switched telephone network (PSTN)  130  is connected to the mobile telecommunications network  110 . Various telephone terminals, including a stationary telephone  131 , may connect to the PSTN  130 . 
     The mobile telecommunications network  110  is also operatively associated with a wide area data network  120 , such as the Internet. Server computers  121  and client computers  122  may be connected to the wide area data network  120  and therefore allow communication with the mobile terminal  100 . 
     An embodiment  200  of the mobile terminal  100  is illustrated in more detail in  FIGS. 2   a - c . The mobile terminal  200  has a housing that includes a front side  201   F , a rear side  201   R  and a lateral side  201   S . The front side  201   F  has a first user interface or MMI that involves a speaker or earphone  202 , a microphone  205 , a first display  203 , and a set of keys  204  which may include an ITU-T type keypad  204   a  (i.e., an alpha-numerical keypad representing keys 0-9, * and #) and certain special keys such as soft keys  204   b ,  204   c.  A joystick  211  or similar navigational input device (e.g. scroll keys, touchpad, or navigation key) is also provided. Furthermore, a first camera  206  is mounted on the front side  201   F . Other well-known external components may be provided, such as power switch, battery, charger interface, accessory interface, volume controls and external antenna, but are not indicated in  FIGS. 2   a - c  for the sake of clarity. 
     The rear side  201   R  has a second user interface or MMI with a second display  213 , which, in contrast to the first display  203 , is touch-sensitive and allows user operation by way of a stylus  214 . Also, even if not indicated in  FIG. 2   b , the second user interface may involve a second speaker and/or a second microphone. A second camera  216  is mounted on the rear side  201   R . 
     The internal component structure of a portable electronic apparatus according to one embodiment will now be described with reference to  FIG. 3 . The embodiment of  FIG. 3  may, but does not have to, be the mobile terminal  200  of  FIGS. 2   a - c . The portable electronic apparatus  300  of  FIG. 3  has a display controller  301 , which is configured for selective control  304  of a first display area  321  (for instance the first display  203  of the mobile terminal  200 ) and a second display area  322  (for instance the second display  213  of the mobile terminal  200 ) via a display controller output signal  302 . Even when shown as an electrical switch symbol in  FIG. 3 , the selective control  304  performed by the display controller  301  is rather to be regarded in functional terms. The functionality of this selective control  304  will appear clearly from the description of  FIG. 4  below. 
     The number of display areas is not necessarily limited to two. On the contrary, additional display areas  323  . . .  32   n  may be provided in some embodiments, as is schematically indicated as dashed boxes in  FIG. 3 . 
     To facilitate the display controller&#39;s  301  selective control of the first and second display areas  321 ,  322 , the apparatus  300  contains an orientation sensor  310  which is coupled to the display controller  301  and serves to provide the latter with an orientation sensor output signal  312  indicative of a current spatial orientation, or change in such spatial orientation (i.e. movement), of the apparatus  300  with respect to its surroundings. In the disclosed embodiment of  FIG. 3 , the orientation sensor  310  is an external force-measuring device known as an accelerometer. 
     The display controller  301  includes, is coupled to or otherwise associated with a memory  330 . The memory  330  stores data  332  representing a previous orientation of the portable electronic apparatus  300 , as detected by the orientation sensor  310  at an earlier point in time. 
     The disclosed embodiment of  FIG. 3  provides enhanced accuracy for the selective control of the first and second display areas  321  and  322 , by the provision of face detection functionality which is indicated as an image processor  340  in  FIG. 3 . To this end, the  FIG. 3  embodiment of the apparatus  300  has first and second cameras  341 ,  342  which are positioned to capture images of the surroundings around the first and second display areas  321  and  322 , respectively. (However, the face detection functionality need not be present in all possible embodiments of the invention; therefore the elements  340 - 342  are indicated as dashed boxes in  FIG. 3 ). 
     When the apparatus  300  is realized as the mobile terminal  200  of  FIGS. 2   a - c , the first camera  341  will thus be the first camera  206  on the front side  201   F  of the terminal&#39;s housing, and it will be positioned to capture images of a surrounding of the terminal&#39;s first display  203 . The purpose of this image capturing will be to register when a user  1  is present in front of the first display  203 , as detected by the presence of at least a part of the user  1 —typically his face—in the images captured by the first camera  206 . Correspondingly, the second camera  342  will be the second camera  216  on the rear side  201   R  of the housing of the mobile terminal  200 , the second camera  216  being positioned to register when the user  1  is instead present at the second display  213 . 
     The image processor  340  is thus coupled to receive images captured by the first and second cameras  341  ( 206 ) and  342  ( 216 ) and to perform a face detection algorithm so as to detect the presence of a user&#39;s face in any of the captured images. The results of the face detection algorithm will be communicated in an image processor output signal  343  to the display controller  301 . Further details on how these results may be used by the display controller  301  will be given later with reference to  FIG. 4 . 
     The display controller  301 , which is responsible for the selective control of the first and second display areas  321 ,  322 , may be implemented by any commercially available and suitably programmed CPU (“Central Processing Unit”) or DSP (“Digital Signal Processor”), or alternatively by any other electronic logic device such as an FPGA (“Field-Programmable Gate Array”), an ASIC (“Application-Specific Integrated Circuit”) or basically any combination of digital and/or analog components which, in the mind of a skilled person, would be a natural choice in order to implement the disclosed functionality. In some embodiments it may be combined with, i.e. realized by, a main controller that is responsible for the overall operation of the apparatus. 
     The memory  330  may be realized by any available kind of memory device, such as a RAM memory, a ROM memory, an EEPROM memory, a flash memory, a hard disk, or any combination thereof. In addition to storing the previous orientation  332 , the memory  302  may be used for various purposes by the display controller  301  as well as by other controllers in the portable electronic apparatus (such as the aforementioned main controller), including but not limited to storing data and program instructions for various software in the portable electronic apparatus. 
     Particularly for embodiments where the portable electronic apparatus  300  is a mobile terminal, like the mobile terminal  200  referred to above, the software stored in memory  330  may include a real-time operating system, drivers for the user interface (MMI), an application handler as well as various applications. The applications may include applications for voice calls, video calls and messaging (e.g. SMS, MMS, fax or email), a phone book or contacts application, a WAP/WWW browser, a media player, a calendar application, a control panel application, a camera application, video games, a notepad application, etc. 
     Furthermore, still with reference to embodiments where the portable electronic apparatus is a mobile terminal, the apparatus typically has a radio interface. The radio interface comprises an internal or external antenna as well as appropriate electronic radio circuitry for establishing and maintaining a wireless link to a base station (for instance the radio link  111  and base station  112  in  FIG. 1 ). As is well known to a man skilled in the art, the electronic radio circuitry comprises analog and digital components which constitute a radio receiver and transmitter. Such components may include band pass filters, amplifiers, mixers, local oscillators, low pass filters, AD/DA converters, etc. The radio interface typically also includes associated communication service software in the form of modules, protocol stacks and drivers. 
     Typically but optionally, the apparatus also includes one or more interfaces for short-range supplemental data communication, such as a Bluetooth interface, an IrDA (infrared) interface or a wireless LAN (WLAN) interface. 
     The orientation sensor  310  may, as already indicated, be implemented as a tilt sensor or accelerometer. As such, accelerometers are commonly available in several types, operating in one, two or three dimensions (one-axis, two-axis and three-axis accelerometers, respectively). For instance, three-axis accelerometers suitable for portable or hand-held applications are commercially available from manufacturers like Analog Devices, Honeywell, STMicroelectronics and Freescale Semiconductor; therefore, the selection of an appropriate accelerometer when exercising the invention is believed to be well within reach for a person of ordinary skill, and no further details are believed to be required herein. 
     The image processor  340  may be a separate device, or the functionality thereof may be integrated with the display controller  301  or another processing device in the apparatus  300 , such as a main controller thereof. In embodiments where it is a separate device, the image processor  340  may be implemented by any commercially available CPU, DSP, FPGA, ASIC or basically any combination of digital and/or analog components which, in the mind of a skilled person, would be a natural choice in order to implement the disclosed functionality. In embodiments where it is integrated with the display controller  301 , the image processor  340  may be implemented wholly or partly as software executed by the display controller  301 , and its output signal  343  may be realized as a function call, program flag, semaphore, assignment of a certain global data variable, or any other suitable way of conveying the results of the face detection algorithm to the display controller  301  for use in the latter&#39;s selective control  304  of the first and second display areas  321 ,  322 . 
     The face detection functionality performed by the image processor  340  may be implemented by any suitable face detection algorithm. A variety of face detection algorithms are known which operate on a digital image to detect one or more faces or facial features contained therein, while ignoring other objects in the image, such as buildings, trees, cars and bodies. One common approach involves removing a mono-color background and deriving the face boundaries. Other approaches are to search for a typical skin color in order to find face segments, or to determine an image area that contains movements between subsequent images (using the fact that a human face is almost always moving in reality). Hybrids of these approaches are also known. More sophisticated face detection algorithms are also capable of detecting faces that are rotated horizontally, vertically, or both, in the image. 
     Two commonly used face detection algorithms are the Viola-Jones algorithm (“Rapid Object Detection Using a Boosted Cascade of Simple Features”, Viola, P.; Jones, M., Mitsubishi Electric Research Laboratories, TR2004-043, May 2004) and the Schneiderman-Kanade algorithm (“A Statistical Method for 3D Object Detection Applied to Faces and Cars”, Henry Schneiderman and Takeo Kanade, Robotics Institute, Carnegie Mellon University, Pittsburgh, Pa. 15213, USA). 
     It is therefore well within reach for a man skilled in the art to choose any of the various existing face detection algorithms and implement it for a portable electronic apparatus according to the invention; therefore no further particulars are believed to be necessary herein. 
     The functionality according to the invention for providing selective control of different display areas of a portable electronic apparatus depending on the orientation of the apparatus will now be exemplified in more detail with reference to  FIGS. 4 and 5   a - c .  FIG. 4  thus discloses a method of controlling a user interface, which includes the first and second display areas  321  and  322 , in response to information about the current spatial orientation, or change in orientation, provided by the orientation sensor  310 . 
     The method of  FIG. 4  starts with steps  400  and  402 , in which the display controller  301  receives the orientation sensor output signal  312  from the orientation sensor  310  and determines a current orientation of the apparatus  300 . Thus, at this stage the orientation sensor output signal  312  reflects a current orientation of the apparatus  300 . Assuming that the apparatus  300  is the afore-described mobile terminal  200 , this current orientation may be like the one illustrated in  FIG. 5   a : The mobile terminal  200  is currently held in a slightly inclined orientation, the first display area  203  facing upwardly at an angle to the user  1 . In other words, in the situation of  FIG. 5   a , the user interface (MMI) that the user is currently using is the one that includes the first display area  203  and the keypad  204 . The currently active display  203  is marked with a shadowed filling in  FIG. 5   a.    
     In a following step  404 , the display controller  301  reads the previous orientation of the apparatus  300 , as stored at  332  in memory  330 . Then, in step  406 , the display controller  301  calculates a movement of the apparatus  300  as the difference between the current orientation and the previous orientation  332 . As a filter against accidental movements of the apparatus  300 , for instance caused by a trembling hand, the calculated movement is compared in step  408  to a threshold, and if the threshold is not met, the execution ends. 
     Otherwise, if the calculated movement is found in step  408  to exceed the threshold, the movement is analyzed in step  410 . This analysis will be made in one, two or three dimensions depending on the dimensional scope of the current orientation as available from the orientation sensor output signal  312  (i.e., when a three-axis accelerometer implements the orientation sensor  310 , the analysis in step  410  may occur in three dimensions, etc). A conclusion is drawn in the following step  412  as to whether a handover of the user interface (MMI) from the currently active display area  321  or  322  to the other one ( 322  or  321 ) is appropriate given the determined and analyzed movement of the apparatus  300 . 
     For instance, referring again to the examples in  FIGS. 5   a - c , if the previous orientation of the mobile terminal  200  was as shown in  FIG. 5   a  (where, consequently, the first, front-mounted display  203  was activated), and the current orientation is as shown in  FIG. 5   b , it may be concluded in step  412  that a handover to the second, read-mounted display  213  is appropriate (based on the assumption that the user  1  has remained stationary). The concluded handover is executed in step  414  by activating the new display area (second display  213  in the example of  FIG. 5   b ) and deactivating the old, hitherto activated display area (first display  203  in the example of  FIG. 5   a ). 
     In this context, an activated display area may be where the particular display area is driven at full capacity for visual presentation of information, whereas a deactivated display area may mean no capacity for visual presentation of information (by, for instance, powering off the deactivated display area, or putting it in an idle or power-save mode), or at least less than full capacity for visual presentation of information (for instance by driving the deactivated display area with a reduced display brightness or color spectrum). 
     In some embodiments, there may be a transition time period in the MMI handover step  414 , during which both the old and the new display areas are active, until subsequently the old display area is deactivated. The display controller  301  may be configured to calculate the duration of the transition time period as a function of the speed the determined movement of the apparatus. This will adapt the handover of the MMI to the behavior of the user, so that a rapid tilting of the apparatus will trigger a rapid switch of the display areas, whereas the MMI handover will be performed during a longer transition time period for a slower tilting of the apparatus. Keeping both display areas active during a longer transition time period when the apparatus is tilted slowly will be beneficial to the user, since he may continue to monitor the old display area at least for a part of the transition time period and decide for himself when to move his eyes to the new display area. 
     After the MMI handover step  414 , the current orientation replaces the previous orientation by storing in step  416  the current orientation at the memory location  332  in memory  330 . Then, the execution ends. The next time the display controller  301  executes the method of  FIG. 4 , the memory location  332  will thus represent the previous orientation for use in steps  404  and  406 . This time, the example may continue as shown in  FIG. 5   c , where the mobile terminal  200  is moved into an orientation where, again, the first display  203  is deemed to be the one that best suits the user  1 , and a switch back to this display is therefore performed in step  414 . 
     It was mentioned above that the decision made in step  412 —as to whether or not an MMI handover between display areas  321  and  322  is appropriate—would be based on the assumption that the user  1  remains stationary. Since this may not always be the case in reality, the embodiment of  FIGS. 3 and 4  provides enhanced accuracy in the selective control of the display areas  321  and  322  by the provision of the face detection functionality provided by the image processor  340  in cooperation with the cameras  341  and  342 . This functionality is performed as steps  420 - 424  in  FIG. 4 , in the form of a branch performed after the MMI handover determination step  412  but prior to the actual execution of the MMI handover in step  414 : 
     In step  420 , image(s) of the surrounding of the apparatus  300  is/are received by the image processor  340  from the camera  341  and/or  342 . In one embodiment, the image processor  340  only performs the face detection algorithm of a following step  422  for an image captured in front of the new display area  321  or  322  that, according to the MMI handover determination step  412 , is intended to be activated in the MMI handover step  414 . In this case, the image processor  340  only needs to receive, in step  420 , an image from the particular camera  341  or  342  that is positioned to capture images of the surrounding of this new display area  321  or  322 . In other words, in the example of  FIGS. 5   a - b  where the terminal  200  is moved from the orientation shown in  FIG. 5   a  to the orientation of  FIG. 5   b , the new display area will be the rear-mounted second display  213 , and accordingly the image processor  340  will receive in step  420  an image captured by the rear-mounted second camera  216  and perform in step  422  the face detection algorithm for this image. 
     The results of the face detection algorithm will be provided to the display controller  301  in the image processor output signal  343 . In step  424 , the display controller  301  thus determines whether a face has been detected in the image analyzed in step  422 . If the answer is affirmative, the display controller  301  concludes that the head of the user  1  is likely apparent in front of the new display area and that the intended MMI handover, as determined in step  412 , can be performed in step  414  as planned. If, on the other hand, no face was detected by the face detection algorithm in step  424 , the display controller  301  concludes that the intended MMI handover shall not be performed, since it has not been verified that the user  1  is actually monitoring the new display area, and the execution ends without performing the intended activation of the new display area in the MMI handover step  414 . 
     In other embodiments, images from both cameras  341  and  342  are used in the face detection functionality of steps  420 - 424  in  FIG. 4 . This allows for a further improved accuracy in the selective control of the display areas  321  and  322 , since a situation can be handled where more than one individual appears in the surrounding of the apparatus  300 . For instance, in the examples of  FIGS. 5   a - c , the display controller  301  may use the image processor  340  and both cameras  341 / 206  and  342 / 216  to check for presence of individuals both at the first display area  321 / 203  and at the second display area  322 / 213 . 
     This means that situations where faces appear both in the image from the first camera  341 / 206  and in the image from the second camera  342 / 216  must be handled. One such situation is illustrated in  FIG. 7 , where a face  701  appears in an image  700  captured by the first camera  341 / 206 , and another face  711  appears in an image  710  captured by the second camera  342 / 216 . In this case, the display controller  301  may be configured to use information of the size of the respective face  701  and  711 , as reported by the image processor  340 , and to give preference to the image in which the largest face appears, indicative of the corresponding individual being positioned closer to the apparatus  300  and therefore likely being the user  1 . “Giving preference” will in this context mean that if the largest face  701  appears in the new display area, step  424  will be in the affirmative. 
     Another situation is illustrated in  FIG. 8 . Here, two faces  801  and  802  appear in an image  800  captured by the first camera  341 / 206 , whereas four faces  811 - 814  appear in an image  810  captured by the second camera  342 / 216 . In this case, the display controller  301  may be configured to count the number of faces appearing in the respective image, and to give preference to the image in which the largest number of faces appear, based on the assumption that the user  1  is more likely to be positioned where the crowd is. 
     Combinations of and alternatives to these situations may of course also be used in embodiments of the invention. For instance, preference may be given to an image from one camera, where a single face appears which is considerably larger than any of a plurality of faces appearing in an image from the other camera. Consideration may also be given to the brightness, sharpness or color with which a face appears in an image compared to the appearance of other face(s) in the same and/or other image. 
     The display controller  301  may be configured to repeat the method of  FIG. 4  at a certain periodicity, for instance each n:th second or millisecond. Alternatively, the performance of the method may be triggered by the orientation sensor  310  detecting a movement of the apparatus  300  ( 200 ). Embodiments are possible where the orientation sensor  310  detects movement (i.e. change in orientation) of the apparatus  300  and reports such movement, rather than the current orientation, as the orientation sensor output signal  312 . In effect, for such embodiments, steps  400  to  406 , or even  408 , can be performed by the orientation sensor  310  rather than the display controller  301 . 
     Also, it is to be noticed that initially (i.e. prior to the first iteration of the method of  FIG. 4 , for instance right after power-on), the previous orientation  332  may be assigned an assumed default orientation, and the active display area may be set, by default, to for instance the first display area  321 , or the display area belonging to the user interface used by the user  1  for powering on the apparatus  300 . 
     In one embodiment, in response to a detected user input, the active display area is automatically set to the display area belonging to the input device used (e.g. display  203  in  FIG. 2   a - c  and  5 , when the user  1  has made an input on the keypad  204 ). Thus, in this embodiment, detection of a user input will override the method of  FIG. 4 . 
     One embodiment offers a further convenience to the user  1  even after the user has stopped moving the apparatus  300  and put it in a spatially steady state (for instance by putting the apparatus on the surface of a table). Thus, after completion of step  416  in the method of  FIG. 4 , the display controller  301  will repeatedly receive a sequence of images from at least the camera  341  or  342  that is located to capture images of the surrounding of the currently activated display area (i.e. the new display area activated in step  414 ). In the sequence of captured images the display controller  301  will determine an angular change in the appearance of the face of the user  1 , and control the currently activated display area to switch from a first angular display mode (for instance a portrait mode or a zero-degree rotated display mode) to a second angular display mode (for instance a landscape mode or a mode where the display contents are rotated by, e.g., 90 degrees compared to the first angular display mode). The user  1  may therefore move conveniently around the steadily oriented apparatus  300 , with the angular display mode of the apparatus being automatically adjusted so that the display contents will continue to appear at a suitable orientation for the user. 
     In the embodiments disclosed above, the portable electronic apparatus of the invention has been described as a mobile terminal, in particular a mobile telephone. Generally, however, the portable electronic apparatus of the invention may be embodied as or included in various portable electronic equipment, including but not limited to a personal digital assistant (PDA), a portable media player (e.g. a DVD player), a palmtop computer, a digital camera, a game console, or a navigator. 
     Also, in the embodiment disclosed above in  FIGS. 2   a - c , the first and second display areas  321  and  322  are two physically different displays  203  and  213  on said apparatus. In other embodiments, however, the first and second display areas  321  and  322  may be different parts of one common display of the portable electronic apparatus. As previously mentioned, the portable electronic apparatus may have additional display area(s), such as a third display area  323 , a fourth display area, etc. Such additional display area(s)  323 - 32   n  may be controlled by the display controller  301  in the same way as the first and second display areas  321  and  322 . An example of such an alternative embodiment is shown in  FIGS. 6   a  and  6   b . Here, the portable electronic apparatus  200 ′ has a housing shaped much like a rectangular box having a front side A, a rear side D, a top side F, a bottom side C, and lateral sides B and E. A respective display area may be located on two, three, four, five or even all of the sides A, B, C, D, E and F of this apparatus housing. 
     The invention has, consequently, been described above with reference to some embodiments thereof. However, as is readily understood by a skilled person, other embodiments are also possible within the scope of the present invention, as defined by the appended claims.