WO2018115842A1

WO2018115842A1 - Head mounted virtual reality display

Info

Publication number: WO2018115842A1
Application number: PCT/GB2017/053803
Authority: WO
Inventors: Simon John Hall; James ANSWER; Ryan David BOWEN
Original assignee: Sony Interactive Entertainment Inc.; Sony Interactive Entertainment Europe Limited
Priority date: 2016-12-23
Filing date: 2017-12-19
Publication date: 2018-06-28
Also published as: GB201622170D0; GB2558278A

Abstract

A virtual reality system comprises a head mountable display (HMD) by which images are displayed to a user; a camera to capture images of the user; and an image processor to generate, for display to the user by the HMD, a representation of the user's body, the displayed representation moving in response to movements of the user's body.

Description

HEAD MOUNTED VIRTUAL REALITY DISPLAY

BACKGROUND

Field of the Disclosure

This disclosure relates to virtual reality systems and methods.

Description of the Prior Art

The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.

A head-mountable display (HMD) is one example of a head-mountable apparatus for use in a virtual reality system in which an HMD wearer views a virtual environment. In an HMD, an image or video display device is provided which may be worn on the head or as part of a helmet. Either one eye or both eyes are provided with small electronic display devices.

Some HMDs allow a displayed image to be superimposed on a real-world view. This type of HMD can be referred to as an optical see-through HMD and generally requires the display devices to be positioned somewhere other than directly in front of the user's eyes. Some way of deflecting the displayed image so that the user may see it is then required. This might be through the use of a partially reflective mirror placed in front of the user's eyes so as to allow the user to see through the mirror but also to see a reflection of the output of the display devices. In another arrangement, disclosed in EP-A-1 731 943 and US-A-2010/0157433, a waveguide arrangement employing total internal reflection is used to convey a displayed image from a display device disposed to the side of the user's head so that the user may see the displayed image but still see a view of the real world through the waveguide. Once again, in either of these types of arrangement, a virtual image of the display is created (using known techniques) so that the user sees the virtual image at an appropriate size and distance to allow relaxed viewing. For example, even though the physical display device may be tiny (for example, 10 mm x 10 mm) and may be just a few millimetres from the user's eye, the virtual image may be arranged so as to be perceived by the user at a distance of (for example) 20 m from the user, having a perceived size of 5 m x 5m.

Other HMDs, however, allow the user only to see the displayed images, which is to say that they obscure the real world environment surrounding the user. This type of HMD can position the actual display devices in front of the user's eyes, in association with appropriate lenses or other optical components which place a virtual displayed image at a suitable distance for the user to focus in a relaxed manner - for example, at a similar virtual distance and perceived size as the optical see-through HMD described above. This type of device might be used for viewing movies or similar recorded content, or for viewing so-called virtual reality content representing a virtual space surrounding the user. It is of course however possible to display a real-world view on this type of HMD, for example by using a forward-facing camera to generate images for display on the display devices.

Although the original development of HMDs and virtual reality was perhaps driven by the military and professional applications of these devices, HMDs are becoming more popular for use by casual users in, for example, computer game or domestic computing applications.

The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

Various aspects and features of the present disclosure are defined in the appended claims and within the text of the accompanying description and include at least a head mountable apparatus such as a display and a method of operating a head-mountable apparatus as well as a computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 schematically illustrates an HMD worn by a user;

Figure 2 is a schematic plan view of an HMD;

Figure 3 schematically illustrates the formation of a virtual image by an HMD;

Figure 4 schematically illustrates another type of display for use in an HMD;

Figure 5 schematically illustrates a pair of stereoscopic images;

Figures 6 and 7 schematically illustrate a user wearing an HMD connected to a Sony® PlayStation 3® games console;

Figure 8 schematically illustrates a change of view of user of an HMD;

Figures 9a and 9b schematically illustrate HMDs with motion sensing;

Figure 10 schematically illustrates a position sensor based on optical flow detection;

Figure 1 1 schematically illustrates image processing carried out in response to a detected position or change in position of an HMD;

Figure 12 schematically illustrates a virtual reality system;

Figure 13 is a schematic flowchart illustrating the operation of a background removal function;

Figure 14 schematically illustrates the capture of an image of a user;

Figure 15 schematically illustrates a captured image; Figure 16 schematically illustrates a depth image;

Figure 17 schematically illustrates the generation of an avatar representation;

Figure 18 schematically illustrates the generation of two avatar representations;

Figure 19 schematically illustrates the display of an error indication;

Figures 20 to 23 are schematic flowcharts illustrating methods; and

Figure 24 is a schematic flowchart illustrating a virtual reality processing method.

DESCRIPTION OF THE EMBODIMENTS

Referring now to Figure 1 , a user 10 is wearing an HMD 20 (as an example of a generic head-mountable apparatus or virtual reality apparatus). The HMD comprises a frame 40, in this example formed of a rear strap and a top strap, and a display portion 50.

Note that the HMD of Figure 1 may comprise further features, to be described below in connection with other drawings, but which are not shown in Figure 1 for clarity of this initial explanation.

The HMD of Figure 1 completely (or at least substantially completely) obscures the user's view of the surrounding environment. All that the user can see is the pair of images displayed within the HMD.

The HMD has associated headphone audio transducers or earpieces 60 which fit into the user's left and right ears 70. The earpieces 60 replay an audio signal provided from an external source, which may be the same as the video signal source which provides the video signal for display to the user's eyes. A boom microphone 75 is mounted on the HMD so as to extend towards the user's mouth.

The combination of the fact that the user can see only what is displayed by the HMD and, subject to the limitations of the noise blocking or active cancellation properties of the earpieces and associated electronics, can hear only what is provided via the earpieces, mean that this HMD may be considered as a so-called "full immersion" HMD. Note however that in some embodiments the HMD is not a full immersion HMD, and may provide at least some facility for the user to see and/or hear the user's surroundings. This could be by providing some degree of transparency or partial transparency in the display arrangements, and/or by projecting a view of the outside (captured using a camera, for example a camera mounted on the HMD) via the HMD's displays, and/or by allowing the transmission of ambient sound past the earpieces and/or by providing a microphone to generate an input sound signal (for transmission to the earpieces) dependent upon the ambient sound.

A front-facing camera 122 may capture images to the front of the HMD, in use. A Bluetooth® antenna 124 may provide communication facilities or may simply be arranged as a directional antenna to allow a detection of the direction of a nearby Bluetooth transmitter.

In operation, a video signal is provided for display by the HMD. This could be provided by an external video signal source 80 such as a video games machine or data processing apparatus (such as a personal computer), in which case the signals could be transmitted to the HMD by a wired or a wireless connection 82. Examples of suitable wireless connections include Bluetooth® connections. Audio signals for the earpieces 60 can be carried by the same connection. Similarly, any control signals passed from the HMD to the video (audio) signal source may be carried by the same connection. Furthermore, a power supply 83 (including one or more batteries and/or being connectable to a mains power outlet) may be linked by a cable 84 to the HMD. Note that the power supply 83 and the video signal source 80 may be separate units or may be embodied as the same physical unit. There may be separate cables for power and video (and indeed for audio) signal supply, or these may be combined for carriage on a single cable (for example, using separate conductors, as in a USB cable, or in a similar way to a "power over Ethernet" arrangement in which data is carried as a balanced signal and power as direct current, over the same collection of physical wires). The video and/or audio signal may be carried by, for example, an optical fibre cable. In other embodiments, at least part of the functionality associated with generating image and/or audio signals for presentation to the user may be carried out by circuitry and/or processing forming part of the HMD itself. A power supply may be provided as part of the HMD itself.

Some embodiments of the disclosure are applicable to an HMD having at least one electrical and/or optical cable linking the HMD to another device, such as a power supply and/or a video (and/or audio) signal source. So, embodiments of the disclosure can include, for example:

(a) an HMD having its own power supply (as part of the HMD arrangement) but a cabled connection to a video and/or audio signal source;

(b) an HMD having a cabled connection to a power supply and to a video and/or audio signal source, embodied as a single physical cable or more than one physical cable;

(c) an HMD having its own video and/or audio signal source (as part of the HMD arrangement) and a cabled connection to a power supply; or

(d) an HMD having a wireless connection to a video and/or audio signal source and a cabled connection to a power supply.

If one or more cables are used, the physical position at which the cable 82 and/or 84 enters or joins the HMD is not particularly important from a technical point of view. Aesthetically, and to avoid the cable(s) brushing the user's face in operation, it would normally be the case that the cable(s) would enter or join the HMD at the side or back of the HMD (relative to the orientation of the user's head when worn in normal operation). Accordingly, the position of the cables 82, 84 relative to the HMD in Figure 1 should be treated merely as a schematic representation.

Accordingly, the arrangement of Figure 1 provides an example of a head-mountable display system comprising a frame to be mounted onto an observer's head, the frame defining one or two eye display positions which, in use, are positioned in front of a respective eye of the observer and a display element mounted with respect to each of the eye display positions, the display element providing a virtual image of a video display of a video signal from a video signal source to that eye of the observer.

Figure 1 shows just one example of an HMD. Other formats are possible: for example an

HMD could use a frame more similar to that associated with conventional eyeglasses, namely a substantially horizontal leg extending back from the display portion to the top rear of the user's ear, possibly curling down behind the ear. In other (not full immersion) examples, the user's view of the external environment may not in fact be entirely obscured; the displayed images could be arranged so as to be superposed (from the user's point of view) over the external environment. An example of such an arrangement will be described below with reference to Figure 4.

In the example of Figure 1 , a separate respective display is provided for each of the user's eyes. A schematic plan view of how this is achieved is provided as Figure 2, which illustrates the positions 100 of the user's eyes and the relative position 1 10 of the user's nose. The display portion 50, in schematic form, comprises an exterior shield 120 to mask ambient light from the user's eyes and an internal shield 130 which prevents one eye from seeing the display intended for the other eye. The combination of the user's face, the exterior shield 120 and the interior shield 130 form two compartments 140, one for each eye. In each of the compartments there is provided a display element 150 and one or more optical elements 160. The way in which the display element and the optical element(s) cooperate to provide a display to the user will be described with reference to Figure 3.

Referring to Figure 3, the display element 150 generates a displayed image which is (in this example) refracted by the optical elements 160 (shown schematically as a convex lens but which could include compound lenses or other elements) so as to generate a virtual image 170 which appears to the user to be larger than and significantly further away than the real image generated by the display element 150. As an example, the virtual image may have an apparent image size (image diagonal) of more than 1 m and may be disposed at a distance of more than 1 m from the user's eye (or from the frame of the HMD). In general terms, depending on the purpose of the HMD, it is desirable to have the virtual image disposed a significant distance from the user. For example, if the HMD is for viewing movies or the like, it is desirable that the user's eyes are relaxed during such viewing, which requires a distance (to the virtual image) of at least several metres. In Figure 3, solid lines (such as the line 180) are used to denote real optical rays, whereas broken lines (such as the line 190) are used to denote virtual rays.

An alternative arrangement is shown in Figure 4. This arrangement may be used where it is desired that the user's view of the external environment is not entirely obscured. However, it is also applicable to HMDs in which the user's external view is wholly obscured. In the arrangement of Figure 4, the display element 150 and optical elements 200 cooperate to provide an image which is projected onto a mirror 210, which deflects the image towards the user's eye position 220. The user perceives a virtual image to be located at a position 230 which is in front of the user and at a suitable distance from the user.

In the case of an HMD in which the user's view of the external surroundings is entirely obscured, the mirror 210 can be a substantially 100% reflective mirror. The arrangement of Figure 4 then has the advantage that the display element and optical elements can be located closer to the centre of gravity of the user's head and to the side of the user's eyes, which can produce a less bulky HMD for the user to wear. Alternatively, if the HMD is designed not to completely obscure the user's view of the external environment, the mirror 210 can be made partially reflective so that the user sees the external environment, through the mirror 210, with the virtual image superposed over the real external environment.

In the case where separate respective displays are provided for each of the user's eyes, it is possible to display stereoscopic images. An example of a pair of stereoscopic images for display to the left and right eyes is shown in Figure 5. The images exhibit a lateral displacement relative to one another, with the displacement of image features depending upon the (real or simulated) lateral separation of the cameras by which the images were captured, the angular convergence of the cameras and the (real or simulated) distance of each image feature from the camera position.

Note that the lateral displacements in Figure 5 could in fact be the other way round, which is to say that the left eye image as drawn could in fact be the right eye image, and the right eye image as drawn could in fact be the left eye image. This is because some stereoscopic displays tend to shift objects to the right in the right eye image and to the left in the left eye image, so as to simulate the idea that the user is looking through a stereoscopic window onto the scene beyond. However, some HMDs use the arrangement shown in Figure 5 because this gives the impression to the user that the user is viewing the scene through a pair of binoculars. The choice between these two arrangements is at the discretion of the system designer.

In some situations, an HMD may be used simply to view movies and the like. In this case, there is no change required to the apparent viewpoint of the displayed images as the user turns the user's head, for example from side to side. In other uses, however, such as those associated with virtual reality (VR) or augmented reality (AR) systems, the user's viewpoint needs to track movements with respect to a real or virtual space in which the user is located.

Figure 6 schematically illustrates an example virtual reality system and in particular shows a user wearing an HMD connected to a Sony® PlayStation 3® games console 300 as an example of a base device. The games console 300 is connected to a mains power supply 310 and (optionally) to a main display screen (not shown). A cable, acting as the cables 82, 84 discussed above (and so acting as both power supply and signal cables), links the HMD 20 to the games console 300 and is, for example, plugged into a USB socket 320 on the console 300. Note that in the present embodiments, a single physical cable is provided which fulfils the functions of the cables 82, 84. In Figure 6, the user is also shown holding a pair of hand-held controller 330s which may be, for example, Sony® Move® controllers which communicate wirelessly with the games console 300 to control (or to contribute to the control of) game operations relating to a currently executed game program.

The video displays in the HMD 20 are arranged to display images generated by the games console 300, and the earpieces 60 in the HMD 20 are arranged to reproduce audio signals generated by the games console 300. Note that if a USB type cable is used, these signals will be in digital form when they reach the HMD 20, such that the HMD 20 comprises a digital to analogue converter (DAC) to convert at least the audio signals back into an analogue form for reproduction.

Images from the camera 122 mounted on the HMD 20 are passed back to the games console 300 via the cable 82, 84. Similarly, if motion or other sensors are provided at the HMD 20, signals from those sensors may be at least partially processed at the HMD 20 and/or may be at least partially processed at the games console 300. The use and processing of such signals will be described further below.

The USB connection from the games console 300 also provides power to the HMD 20, according to the USB standard.

Figure 6 also shows a separate display 305 such as a television or other openly viewable display (by which it is meant that viewers other than the HMD wearer may see images displayed by the display 305) and a camera 315, which may be (for example) directed towards the user (such as the HMD wearer) during operation of the apparatus. An example of a suitable camera is the PlayStation Eye camera, although more generally a generic "webcam", connected to the console 300 by a wired (such as a USB) or wireless (such as WiFi or Bluetooth) connection.

The display 305 may be arranged (under the control of the games console) to provide the function of a so-called "social screen". It is noted that playing a computer game using an HMD can be very engaging for the wearer of the HMD but less so for other people in the vicinity (particularly if they are not themselves also wearing HMDs). To provide an improved

experience for a group of users, where the number of HMDs in operation is fewer than the number of users, images can be displayed on a social screen. The images displayed on the social screen may be substantially similar to those displayed to the user wearing the HMD, so that viewers of the social screen see the virtual environment (or a subset, version or

representation of it) as seen by the HMD wearer. In other examples, the social screen could display other material such as information relating to the HMD wearer's current progress through the ongoing computer game. For example, the HMD wearer could see the game environment from a first person viewpoint whereas the social screen could provide a third person view of activities and movement of the HMD wearer's avatar, or an overview of a larger portion of the virtual environment. In these examples, an image generator (for example, a part of the functionality of the games console) is configured to generate some of the virtual environment images for display by a display separate to the head mountable display.

Figure 7 schematically illustrates a similar arrangement (another example of a virtual reality system) in which the games console is connected (by a wired or wireless link) to a so- called "break out box" acting as a base or intermediate device 350, to which the HMD 20 is connected by a cabled link 82, 84. The breakout box has various functions in this regard. One function is to provide a location, near to the user, for some user controls relating to the operation of the HMD, such as (for example) one or more of a power control, a brightness control, an input source selector, a volume control and the like. Another function is to provide a local power supply for the HMD (if one is needed according to the embodiment being discussed). Another function is to provide a local cable anchoring point. In this last function, it is not envisaged that the break-out box 350 is fixed to the ground or to a piece of furniture, but rather than having a very long trailing cable from the games console 300, the break-out box provides a locally weighted point so that the cable 82, 84 linking the HMD 20 to the break-out box will tend to move around the position of the break-out box. This can improve user safety and comfort by avoiding the use of very long trailing cables.

It will be appreciated that the localisation of processing in the various techniques described in this application can be varied without changing the overall effect, given that an HMD may form part of a set or cohort of interconnected devices (that is to say, interconnected for the purposes of data or signal transfer, but not necessarily connected by a physical cable). So, processing which is described as taking place "at" one device, such as at the HMD, could be devolved to another device such as the games console (base device) or the break-out box. Processing tasks can be shared amongst devices. Source signals, on which the processing is to take place, could be distributed to another device, or the processing results from the processing of those source signals could be sent to another device, as required. So any references to processing taking place at a particular device should be understood in this context. Similarly, where an interaction between two devices is basically symmetrical, for example where a camera or sensor on one device detects a signal or feature of the other device, it will be understood that unless the context prohibits this, the two devices could be interchanged without any loss of functionality.

As mentioned above, in some uses of the HMD, such as those associated with virtual reality (VR) or augmented reality (AR) systems, the user's viewpoint needs to track movements with respect to a real or virtual space in which the user is located. This tracking is carried out by detecting motion of the HMD and varying the apparent viewpoint of the displayed images so that the apparent viewpoint tracks the motion.

Figure 8 schematically illustrates the effect of a user head movement in a VR or AR system.

Referring to Figure 8, a virtual environment is represented by a (virtual) spherical shell

250 around a user. This provides an example of a virtual display screen (VDS). Because of the need to represent this arrangement on a two-dimensional paper drawing, the shell is represented by a part of a circle, at a distance from the user equivalent to the separation of the displayed virtual image from the user. A user is initially at a first position 260 and is directed towards a portion 270 of the virtual environment. It is this portion 270 which is represented in the images displayed on the display elements 150 of the user's HMD. It can be seen from the drawing that the VDS subsists in three dimensional space (in a virtual sense) around the position in space of the HMD wearer, such that the HMD wearer sees a current portion of VDS according to the HMD orientation.

Consider the situation in which the user then moves his head to a new position and/or orientation 280. In order to maintain the correct sense of the virtual reality or augmented reality display, the displayed portion of the virtual environment also moves so that, at the end of the movement, a new portion 290 is displayed by the HMD.

So, in this arrangement, the apparent viewpoint within the virtual environment moves with the head movement. If the head rotates to the right side, for example, as shown in Figure 8, the apparent viewpoint also moves to the right from the user's point of view. If the situation is considered from the aspect of a displayed object, such as a displayed object 300, this will effectively move in the opposite direction to the head movement. So, if the head movement is to the right, the apparent viewpoint moves to the right but an object such as the displayed object 300 which is stationary in the virtual environment will move towards the left of the displayed image and eventually will disappear off the left-hand side of the displayed image, for the simple reason that the displayed portion of the virtual environment has moved to the right whereas the displayed object 300 has not moved in the virtual environment.

Figures 9a and 9b schematically illustrated HMDs with motion sensing. The two drawings are in a similar format to that shown in Figure 2. That is to say, the drawings are schematic plan views of an HMD, in which the display element 150 and optical elements 160 are represented by a simple box shape. Many features of Figure 2 are not shown, for clarity of the diagrams. Both drawings show examples of HMDs with a motion detector for detecting motion of the observer's head.

In Figure 9a, a forward-facing camera 322 is provided on the front of the HMD. This may be the same camera as the camera 122 discussed above, or may be an additional camera. This does not necessarily provide images for display to the user (although it could do so in an augmented reality arrangement). Instead, its primary purpose in the present embodiments is to allow motion sensing. A technique for using images captured by the camera 322 for motion sensing will be described below in connection with Figure 10. In these arrangements, the motion detector comprises a camera mounted so as to move with the frame; and an image comparator operable to compare successive images captured by the camera so as to detect inter-image motion.

Figure 9b makes use of a hardware motion detector 332. This can be mounted anywhere within or on the HMD. Examples of suitable hardware motion detectors are piezoelectric accelerometers or optical fibre gyroscopes. It will of course be appreciated that both hardware motion detection and camera-based motion detection can be used in the same device, in which case one sensing arrangement could be used as a backup when the other one is unavailable, or one sensing arrangement (such as the camera) could provide data for changing the apparent viewpoint of the displayed images, whereas the other (such as an accelerometer) could provide data for image stabilisation.

Figure 10 schematically illustrates one example of motion detection using the camera

322 of Figure 9a.

The camera 322 is a video camera, capturing images at an image capture rate of, for example, 25 images per second. As each image is captured, it is passed to an image store 400 for storage and is also compared, by an image comparator 410, with a preceding image retrieved from the image store. The comparison uses known block matching techniques (so- called "optical flow" detection) to establish whether substantially the whole image has moved since the time at which the preceding image was captured. Localised motion might indicate moving objects within the field of view of the camera 322, but global motion of substantially the whole image would tend to indicate motion of the camera rather than of individual features in the captured scene, and in the present case because the camera is mounted on the HMD, motion of the camera corresponds to motion of the HMD and in turn to motion of the user's head.

The displacement between one image and the next, as detected by the image comparator 410, is converted to a signal indicative of motion by a motion detector 420. If required, the motion signal is converted by to a position signal by an integrator 430.

As mentioned above, as an alternative to, or in addition to, the detection of motion by detecting inter-image motion between images captured by a video camera associated with the HMD, the HMD can detect head motion using a mechanical or solid state detector 332 such as an accelerometer. This can in fact give a faster response in respect of the indication of motion, given that the response time of the video-based system is at best the reciprocal of the image capture rate. In some instances, therefore, the detector 332 can be better suited for use with higher frequency motion detection. However, in other instances, for example if a high image rate camera is used (such as a 200 Hz capture rate camera), a camera-based system may be more appropriate. In terms of Figure 10, the detector 332 could take the place of the camera 322, the image store 400 and the comparator 410, so as to provide an input directly to the motion detector 420. Or the detector 332 could take the place of the motion detector 420 as well, directly providing an output signal indicative of physical motion.

Other position or motion detecting techniques are of course possible. For example, a mechanical arrangement by which the HMD is linked by a moveable pantograph arm to a fixed point (for example, on a data processing device or on a piece of furniture) may be used, with position and orientation sensors detecting changes in the deflection of the pantograph arm. In other embodiments, a system of one or more transmitters and receivers, mounted on the HMD and on a fixed point, can be used to allow detection of the position and orientation of the HMD by triangulation techniques. For example, the HMD could carry one or more directional transmitters, and an array of receivers associated with known or fixed points could detect the relative signals from the one or more transmitters. Or the transmitters could be fixed and the receivers could be on the HMD. Examples of transmitters and receivers include infra-red transducers, ultrasonic transducers and radio frequency transducers. The radio frequency transducers could have a dual purpose, in that they could also form part of a radio frequency data link to and/or from the HMD, such as a Bluetooth® link.

Figure 1 1 schematically illustrates image processing carried out in response to a detected position or change in position of the HMD.

As mentioned above in connection with Figure 10, in some applications such as virtual reality and augmented reality arrangements, the apparent viewpoint of the video being displayed to the user of the HMD is changed in response to a change in actual position or orientation of the user's head.

With reference to Figure 1 1 , this is achieved by a motion sensor 450 (such as the arrangement of Figure 10 and/or the motion detector 332 of Figure 9b) supplying data indicative of motion and/or current position to a required image position detector 460, which translates the actual position of the HMD into data defining the required image for display. An image generator 480 accesses image data stored in an image store 470 if required, and generates the required images from the appropriate viewpoint for display by the HMD. The external video signal source can provide the functionality of the image generator 480 and act as a controller to compensate for the lower frequency component of motion of the observer's head by changing the viewpoint of the displayed image so as to move the displayed image in the opposite direction to that of the detected motion so as to change the apparent viewpoint of the observer in the direction of the detected motion.

Figure 12 schematically illustrates a virtual reality system or apparatus comprising: an HMD 1200 which may include an orientation detector 1205, for example of the type discussed above with reference to Figures 9A-1 1 , one or more user controls 1210, a data processor 1220 such as a game engine, an image processor 1230, a camera 1240 and optionally a social screen 1250 of the type discussed above. Storage media 1280 is optionally provided to store (and to allow retrieval by the data processor of) displayable content and/or game data.

In use, the user wears the HMD 1200 and can operate the one or more controls or controllers 1210. Examples of suitable user controls include the controller 330 shown in Figures 6 and 7. The game engine 1220 provides images and other content such as audio content to the HMD via a wired or wireless connection 1260 and receives input from the controllers 1210 via the connection 1260 or via the camera 1240.

The camera 1240 is directed towards the HMD and/or controllers in use. The camera

1240 can therefore capture a current position and/or orientation of the HMD 1200 and a current position and/or orientation of the controllers 1210, each of which is detected from the captured images by the image processor 1230. These captured positions and/or orientations can be used to control data processing operations of the game engine 1220, such as game control operations.

Similarly, the orientation detector 1205 can provide orientation information (such as a data defining a current orientation and/or data defining a detected change in orientation) to the data processor 1220 via the link 1260.

Therefore, in examples, there are various types of control input to the game engine 1220, such as control inputs 1270 derived by the image processor 1230 from captured images captured by the camera 1240 and/or control inputs received from the controls 1210 via the wired or wireless connection 1260. The image processor 1230 provides an example of an image processor to detect, from one or more images captured by the camera 1240, one or more of: (i) a current orientation of the HMD 1200; and (ii) a current location of the HMD 1200. The game engine 1220 provides an example of a data processor to direct a data processing function according to the detection by the image processor. In some examples, the data processing function is a gameplay function.

Figure 13 is a schematic flowchart illustrating the operation of a background removal function of the image processor 1230.

At a high level, the image processor 1230 carries out the following steps. At a step 1300, the background removal module detects images received from the camera 1240. At a step 1310, the background removal module detects and stores image data relating to a background region, for example in an image data store. At a step 1320 the background removal module subtracts the stored background from the detected images.

Techniques by which the background removal module can operate to remove

background image material from the captured images can vary according to the type of camera used, for example. In some examples, the camera 1240 is a so-called depth camera. An example is a stereoscopic camera, but other types of cameras using structured infrared light (for example, a projected grid of infrared light from which depth information can be acquired using an infrared sensor) are also capable of detecting the depth parameter of image material in a captured image. The step 1310 can be carried out by the background removal module detecting background image material as image material having a greater image depth than other (foreground) image material in the captured images. So, in such examples, the foreground is taken to be image material or item (for example, of at least a threshold size, in pixels) which is closest to the camera. In other examples, the user could indicate an image region in which the foreground material is the closest of any material within that image region to the camera. In other examples, the step 1310 can be implemented by the background removal module detecting background image material as that image material which is static with respect to a plurality of captured images. Therefore, in at least some examples, the image processor is configured to detect, as background image material, one or more of: initially calibrated background image material; image material which remains static; and image material having a greater depth than other image material.

Arrangements to be described below make use of the subtraction of background material to detect image portions relating to the user's body. This or other techniques may be used, so that the body can be detected (for example) in image portions by one or more of the image portions moving; and the image portions not relating to background image material.

Figure 14 schematically illustrates the capture of an image of a user 1400 by, for example, the camera 1240 of Figure 12. The user is positioned in front of a background 1410 and is wearing an HMD 1200. It can be seen that the user is facing the camera 1240 by the fact that the HMD 1200 is on the front side of the user's face.

In some examples, the camera 1240 is a depth camera as discussed above. This allows the camera to distinguish between images of the user (which may be moving, whereas the background may be stationary, and which are likely to be closer to the camera in depth terms than the background 1410) and of the background itself.

Figure 15 schematically illustrates a captured image acquired by the camera 1240 showing the user 1400 facing the camera 1240, in front of the background 1410.

Once the background subtraction process described with reference to Figure 13 above has been carried out, the resulting depth image of Figure 16 contains regions of foreground (representing the user 1400) of different depths, generally corresponding to the user's limbs 1600. The configuration of those limbs, and changes in that configuration, may be used in the process which is described below.

Referring to Figure 17, the generation of an avatar representation 1700 of the user 1400 is illustrated. The avatar representation 1700 is visible by the user 1400 using the HMD 1200. Its virtual position in space relative to the user 1400 has been shown; however, it will be appreciated that this simply indicates the position at which the user 1400 perceives the avatar 1700 to be present.

Using techniques to be described below, the avatar 1700 is generated so as to be facing the same way as the user 1400 and is positioned in front of the user 1400 in the virtual environment visible by the user. The avatar 1700 may, for example, be partially transparent (for example, 50% transparent) so that the virtual environment may be at least partially viewed through the avatar 1700. In this way, the avatar 1700 can provide the user 1400 with an indication of the user's own activities relative to the virtual world viewed by the user using the HMD 1200.

An avatar representation 1700 is employed because the view which the camera 1240 has of the (real) user 1400 is a view of the front of the user 1400, because the user 1400 is facing the camera 1240. However, the view presented to the user 1400 through the HMD 1200 is of the back of the avatar 1700 so that the user 1400 may perceive that the user is looking over the (avatar) user's shoulder. For example, the user's left arm corresponds to the left arm as seen in the avatar 1700.

Again, using techniques to be described below, physical movements by the user 1400 may be represented by corresponding movements of the same limb or limbs by the avatar 1700. As mentioned, this can provide the user 1400 with useful indications and/or feedback on the user's 1400 own physical movements relative to the virtual world viewed by the user through the HMD 1200.

Therefore, the apparatus of Figure 12, acting in this manner, provides an example of a virtual reality system comprising a head mountable display (HMD) by which images are displayed to a user; a camera to capture images of the user; and an image processor to generate, for display to the user by the HMD, a representation of the user's body, the displayed representation moving in response to movements of the user's body.

In examples, the representation is an avatar representation.

Figure 18 schematically illustrates the representation of two avatar representations 1700 (as discussed above, representing the user's physical movements in corresponding avatar movements) and 1710, which is an avatar indicating a desired or required body configuration of the user. In some examples, the two avatars 1700, 1710 can be similarly sized and arranged next to one another (in the user's viewpoint), in front of one another (that is to say, one of the avatars 1700, 1710 is stood in front of the other of the avatars 1700, 1710 from the user's viewpoint), one above the other or in any desired relative configuration. One example use of the pair of avatars is to train the user 1400 in particular movements such as dance movements, military operational movements and the like for use in engaging with a virtual world. The avatar 1700 can indicate a required body configuration and the user can see, by observing the avatar 1700, whether the user is achieving the required body configuration. In the example of Figure 18, therefore, the image processor is configured to generate a further representation of an avatar indicating a required body configuration of the user.

In a further example arrangement, shown schematically in Figure 19, an error indication is also displayed. In the example shown, the avatar 1710 indicating a required body

configuration has one arm 1900 partially raised, whereas the corresponding arm 1910 off the avatar 1700 (representing the arm 1920 of the user 1400) is not raised. The data processor 1220 can detect this disparity between the two avatars and indicate an error, for example if the disparity is greater than a certain threshold disparity. An error indication can be provided, for example, by displaying the relevant body part of one or both of the avatars 1700, 1710 in a different colour to normal and/or a different colour to the remainder of the avatars 1700, 1710.

In the example of Figure 19, therefore, the image processor is configured to detect a difference between the required body configuration and the current body configuration of the user. In such an example, the image processor is configured to display an indication of the detected differences between the required body configuration and the current body

configuration of the user.

Figure 20 is a schematic flow chart illustrating a method of generating the avatar 1700 described above.

At a step 2000, the background is removed from a depth image of the scene including the user 1400, and at a step 2010 the limb orientations of the user 1400 are detected from the remaining depth information of the form shown in Figure 16. The limb orientations are detected (in at least some examples) by mapping portions of the depth map of Figure 16 onto an expected configuration of a user (for example, a vertical standing position) so that sections of the depth map are mapped to corresponding limbs of the user. The depth value along the length of a limb then indicates the orientation of that limb. For example, a portion of the depth image representing a leg may have a depth value which decreases (indicating a closer position to the camera) along the length of the limb from the trunk to the distal end (foot). This indicates that the limb is oriented towards the camera with the foot nearest to the camera.

Then, at a step 2020, an avatar representation such as the representation 1700 is generated for display to the user via the HMD 1200 which the user is wearing.

An optional step 2015 is indicated schematically in Figure 21 , disposed between the steps 2010 and 2020, in which the orientation of the avatar 1700 is reversed with respect to the orientation of the user 1400, so that the user sees the avatar 1700 facing the same way as (away from) the user.

These steps provide an example in which the image processor is configured to detect a current orientation of the user's limbs in a captured image and to generate the representation so that the representation, as displayed to the user, is facing away from the user. All of Figures 17 to 19 represent examples in which the image processor is configured to detect a current orientation of the user's limbs in a captured image and to generate the representation so that the representation, as displayed to the user, is in front of the user.

Figure 22 is a schematic flow chart representing a method of generating the avatar 1710, in which at a step 2200 a required body configuration is determined, then at a step 2210 the required body configuration is oriented to be facing away from the user. At a step 2220 an avatar representation such as the avatar 1710 is generated for display to the user via the HMD 1200.

An optional step 2300, to follow the step 2220 is shown schematically in Figure 23, in which differences between the avatar 1700 representing the user and avatar 1710 representing the required body position are detected and indicated to the user, for example by colouring, illumination, flashing colour and the like.

Figure 24 is a schematic flowchart illustrating a virtual reality processing method comprising:

displaying (at a step 2400) images to a user using a head mountable display (HMD); capturing (at a step 2410) images of the user; and

generating (at a step 2420), for display to the user by the HMD, a representation of the user's body, the displayed representation moving in response to movements of the user's body.

It will be appreciated that example embodiments can be implemented by computer software operating on a general purpose computing system such as a games machine. In these examples, computer software, which when executed by a computer, causes the computer to carry out any of the methods discussed above is considered as an embodiment of the present disclosure. Similarly, embodiments of the disclosure are provided by a non-transitory, machine-readable storage medium which stores such computer software.

It will also be apparent that numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practised otherwise than as specifically described herein.

Claims

1 . A virtual reality system comprising:

a head mountable display (HMD) by which images are displayed to a user;

a camera to capture images of the user; and

an image processor to generate, for display to the user by the HMD, a representation of the user's body, the displayed representation moving in response to movements of the user's body.

2. A system according to claim 1 , in which:

the representation is an avatar representation.

3. A system according to claim 1 or claim 2, in which the image processor is configured to detect a current orientation of the user's limbs in a captured image and to generate the representation so that the representation, as displayed to the user, is facing away from the user.

4. A system according to any one of the preceding claims, in which the image processor is configured to detect a current orientation of the user's limbs in a captured image and to generate the representation so that the representation, as displayed to the user, is in front of the user.

5. A system according to any one of the preceding claims, in which the image processor is configured to generate a further representation of an avatar indicating a required body configuration of the user.

6. A system according to claim 5, in which the image processor is configured to detect a difference between the required body configuration and the current body configuration of the user.

7. A system according to claim 6, in which the image processor is configured to display an indication of the detected differences between the required body configuration and the current body configuration of the user.

8. A system according to any one of the preceding claims, in which the camera is a depth camera.

9. A system according to claim 8, in which the image processor is configured to detect image portions relating to the user's body by one or more of:

the image portions moving;

the image portions not relating to background image material.

10. A system according to claim 9, in which the image processor is configured to detect, as background image material, one or more of:

initially calibrated background image material;

image material which remains static; and

image material having a greater depth than other image material.

1 1 . A virtual reality processing method comprising:

displaying images to a user using a head mountable display (HMD);

capturing images of the user; and

generating, for display to the user by the HMD, a representation of the user's body, the displayed representation moving in response to movements of the user's body.

12. Computer software which, when executed by a computer, causes the computer to perform the steps of claim 1 1 .

13. A machine-readable, non-transitory storage medium which stores computer software according to claim 12.