GB2467898A

GB2467898A - Display with automatic screen parameter adjustment based on the position of a detected viewer

Info

Publication number: GB2467898A
Application number: GB0822151A
Authority: GB
Inventors: Andrew Kay; Marc Paul Servais; Benjamin John Broughton
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2008-12-04
Filing date: 2008-12-04
Publication date: 2010-08-18
Also published as: GB0822151D0

Abstract

A display screen 6 with an arrangement 2 for detecting the position of a viewer 3 relative to the screen 6, and a processing arrangement 5 for processing image data 7 for display by the screen 6, arranged to change angular colour correction based on the detected position of the viewer 3. The processing arrangement 5 may provide increased off-axis colour correction when the detected position is further from the screen 6 than a first threshold distance 8 or angle 10. It may also provide reduced angular colour correction, by varying the gamma curve, at the edges of the screen 6 when the detected position is further from the screen 6 than a second threshold distance or angle. When the user sensor 2 detects a plurality of viewers 3, the detected position may be that of the viewer nearest the screen 6 or an average of the viewer positions. The processing arrangement 5 may also process other image data, such as the aspect ratio, resolution, frame rate, bandwidth, scale, privacy strength, text size and perspective based on the detected position of the viewer 3. Audio data may also be directed towards the detected position of the viewer 3.

Description

DISPLAY

The invention relates to a display. Such a display may, for example, be used as, in or as part of, or may include, a television, mobile phone, advertising hoarding, digital photograph display device, computer display, image projector or other public or personal device.

Herein, a display is considered to be a device or any arrangement capable of processing and showing static or moving images, possibly with other outputs including sound. The term "viewer" denotes one capable of receiving one or more of the outputs of the display, whether these are images, sounds or other outputs, and the term "viewing" denotes such reception.

It is well understood that a viewer's experience of a display device depends on their geometrical relationship to it. Most obviously, the further you sit from a television, the smaller the image appears to be. The TV industry has created larger and larger displays, in part so that the viewer can sit further away and still receive a sufficiently large image to appreciate the content. However, viewers are free to watch from any distance, and sometimes this is dictated by the layout of a living room or, in the case of a mobile display such as might be in a mobile phone, the length of an arm. Given that viewing distance may change from moment to moment and from viewer to viewer over a large range of distances, it is a problem for the manufacturer to set the characteristics of the device so that viewers will achieve the best possible picture at all times.

Traditionally, this problem has been solved by giving the viewers control over brightness, contrast, image sharpness etc, by means of menus and/or buttons on remote controls. However, many viewers never adjust these parameters and certainly many more viewers do not adjust these parameters as necessary when viewing conditions change. A related problem is that conditions in a showroom where devices are selected are likely to be very different from conditions in the owner's own viewing situation.

Company Gateway 2000 Inc. in WO/1999/021356 describes a display device which detects the distance of a viewer from a video monitor, and indicates to the viewer when to adjust his or her position to achieve an optimal distance.

Inventor A. Pascal Mahvi in WO/2001/030070 describes a television set which switches itself off after it detects there is no living being in the vicinity, presumably to save power.

It is well known that the amount of sharpness, or other parameters, in a printed image depends on the viewing distance, as is mentioned for example in company Nik Multimedia Inc. publication WO/2002/025589.

It is well known that the sensitivity of the human visual system to contrast varies with spatial frequency of the stimulus, as for example explained at http://www.usd.edu/coqlab/CSFlntro.htm. Naturally as distance to an object increases, the spatial frequencies received at the eye from that object increase and so the sensitivity changes.

Some displays for games and virtual reality type applications track the player's or viewer's position and adjust the geometry of the scene displayed to present the illusion that the image on the display is a 3D reality. In this case, the image representing the scene is synthesised by the device for a given point of view, which is not the same thing as altering an image or video stream for display to provide best quality, readability or audibility.

British Patent Application No. 0803168.4 discloses a low power light directing display which tracks the viewer and beams the image only to the viewer to save light power.

However, the perceived quality of the image is not modified.

Privacy displays typically provide one image to the main viewer, and a secondary image (or blank image) to side viewers. However, they do not react to viewer position.

Examples of display arrangements which adjust displayed image parameters are disclosed in JP6237394, JP9247564, JP11352950, JP2006005418, JP2007057599, JP2007074130, JP2007212664, JP2008064971, JP200789000, JP2008072561, JP4249486, JP4127667, JP20051 84442, JP7007692 and JP2006005828.

According to first to tenth aspects of the invention, there are provided displays as defined in the appended claims 1,8, 17,21,26,30,34,38,42 and 46, respectively.

Embodiments of the invention are defined in the other appended claims.

Brief Description of the drawings

Figure 1 shows a plan view of the system with its main components and a single viewer.

Figure 2 shows an image with different amounts of sharpening.

Figure 3 illustrates increased text size for a more distant viewer.

Figure 4 is a table of possible parameter modifications and benefits with viewer distance.

Figure 5 is a table of possible parameter modifications and benefits with viewer angle.

Figure 6 illustrates perspective correction for an off-axis viewer.

Figure 7 illustrates a possible camera configuration for viewer position sensing.

Figure 8 illustrates a standard layout of sub-pixels.

Figure 9 illustrates how display angle relates to viewer distance.

Figure 10 illustrates the use of varying numbers of pixels for a privacy effect.

Figure 11 is a table of a possible method for selecting viewer distance parameter when there is more than one viewer.

Figure 12 is a table of a possible method for selecting viewer angle parameter when there is more than one viewer.

Figure 13 illustrates an embodiment of the invention for a mobile device.

In embodiments of the invention, the position of a viewer relative to the display device is determined to a given level of precision by any available means and this position information is used to modify the processing of the image in one or more ways to provide a better viewing experience or for some other gain such as reduced power consumption. It is supposed that the processing of the image and other outputs of the device is controlled by at least one parameter which can be varied and adjusted depending on the situation.

Embodiments of the invention may be used to modify a stream of video and/or audio data, perhaps from a broadcast or a camera or a DVD player or similar device, or received video as part of a video-conferencing system, which is to be shown on a display. The display may be a TV set, a computer monitor, a mobile phone, an advertising display, a portable video display, a digital photograph viewer, or other device.

On detection of at least one viewer, the device may optimise one or more of its parameters to provide the best performance with respect to them.

The table in Figure 4 shows some of the parameters that may be varied depending on viewer distance. For each parameter, a direction of change is suggested. However, in some circumstances, such as when several parameters are being adjusted at once, it may be advantageous to change some of them in a different way. For example, if the image is being scaled to a larger size for a more distant viewer, then it may be better to increase (or leave fixed) the amount of noise reduction at the same time rather than to decrease it.

When exactly one viewer is detected by the display, it may optimise its behaviour for that viewer. When more than one viewer is detected, there are several possibilities.

The most appropriate possibility may depend on the parameter being optimised, so each parameter may potentially be optimised for different target behaviour. Amongst these possibilities, the device may select the nearest detected viewer, the furthest, the most centrally placed viewer or some mean position determined from all detected viewers as a basis for parameter adjustment for any particular parameter.

Some parameters may best be optimised jointly, with reference to the viewer positions and also to each other.

The display may consider that the "closest" viewer is the detected viewer closest in angle to the central axis of the display, rather than the one with the smallest linear distance. Other definitions of closest are possible as will be apparent. The most suitable definition of "closest" may vary from parameter to parameter or may be varied by application or by user preference or by ambient conditions. Figures 11 and 12 give some possibilities for particular parameters.

Some parameters are naturally adjusted based not only on the position of the viewer or viewers but also on the material being displayed from moment to moment; and/or on the ambient conditions such as the amount of external light or the time of day (reducing volume late at night, perhaps); and/or the present application of the display; and/or the preferences of the viewer or the owner of the display. If the age or other attributes of the viewer can be determined, perhaps from an image of the face as for example disclosed in "Image-Based Human Age Estimation by Manifold Learning and Locally Adjusted Robust Regression" by Guodong Guo, Yun Fu, Dyer, C.R., and Huang, T.S.

in IEEE Transactions on Image Processing, Volume 17, issue 7, July 2008, this could also be used to estimate parameters, for example making text larger for older viewers, as well as based on distance.

If no viewer is detected, the display may revert to some preset parameters or user defined parameters, or to some average settings learnt over time, or it may keep the settings from when a viewer was last detected with sufficient certainty.

The viewer or device owner may be given a method of control over the various parameters so that some parameters are made to vary in a different way from their default method of variation. For example, the viewer may prefer the display not to react to viewer distance at all or may indicate that only the closest viewer is to be considered for parameter setting.

Some parameters may not require a precise distance measurement, but a more approximate, for example quantised, scale of distance, such as "near" or "far" or "central" or "non-central". These judgements may possibly be made using simpler viewer detection methods. The failure to detect a viewer may optionally be taken to indicate that the viewer is "far" rather than "near", for example.

It may be advantageous for some of the display parameters to exhibit some resistance to frequent change, for example by deliberately reacting only slowly to changes in the number of viewers detected, or at least one viewer position, or by adding artificial hysteresis to the algorithm describing the method of parameter variation.

Some existing display devices, including "dual view" devices, are capable of producing more than one output at a time in different viewing domains. These domains are either static or are able to track viewers as they move about, as is the case for the display disclosed in British Patent Application No. 0803168.4. Optionally, this kind of device may be configured to split the detected viewers into groups so that, for at least one parameter, at least one output domain is optimised for its particular group of viewers independently of viewers in other domains. Alternatively, at least one parameter for at least one domain may be optimised based on the total collection of viewers. For example, for the case of audio volume where sound may leak between the different domains, it may be preferred to keep volume low in one domain when there are viewers in an adjacent domain in order to reduce nuisance.

The display may be configured to increase the degree of sharpening applied to the image as the viewer distance increases, and vice versa. The design goal is simply that, from the point of view of a viewer moving around in front of the image, the sharpness of the image will appear to be approximately unchanged at any distance.

By examining Figure 2 from varying distances it will be evident (depending on how Figure 2 has been rendered) that different amounts of sharpening are preferred for different viewing situations.

For a closer viewer, the image processing unit may do more processing on the video content to remove compression noise. Such processing may be invisible to a more distant viewer and hence be a waste of power and other computing resources.

In many cases, a display is required to scale an image so that it fits well on the screen.

There are many different scaling algorithms. For a distant viewer, the pixel details are less visible so a lower quality scaling algorithm may be used, for example one which uses less power in its computation.

When a viewer is very close, the display fills a significant fraction of such a viewer's field of view. In this case, it may be better to perform less scaling so that pixels are unused at the edges of the display but the size of the displayed image is smaller.

Reduced magnification means that image noise is less obvious, so the perceived picture quality may be better.

Image displays are often required to change the aspect ratio of input video to make better use of the available pixels, for example, in distorting widescreen video onto a 4:3 display or vice versa. A viewer closer to the display can see fine details and a large display may fill a significant fraction of such a viewer's field of view. In this case, it may be better not to distort the image in this way, or to distort it to a lesser extent, thus wasting display area but achieving better picture quality for that viewer.

When the viewer is far away, the individual pixels may be too small to be seen with the unaided eye. The display could therefore be configured to provide spatially dithered colours in this case, to produce a larger number of available colours (compared to the display panel's natural ability) without degrading the perceived spatial resolution.

Conversely, for a near viewer, it may be advantageous to provide better spatial resolution by using less or no colour dithering.

When the viewer is closer, the display may be made dimmer, to save electrical power or to extend the lifetime of the display. This parameter may also vary with the ambient lighting conditions, as is known.

Displays typically display an image over a range of viewing angles. For a closer viewer, the viewing angle may be decreased, potentially leading to a power saving.

Displays often use methods for increasing the response to motion within the images displayed. One method is to drive the pixels in a special way to make them change more quickly. Another method is to make changes to the backlight illumination.

Another method is to create intermediate frames using image processing and to display these frames in between original frames at a higher rate. These methods may make motion smoother, at the cost of more electrical power for the image processing and/or the pixel driving and/or the backlight control. When the viewer is further away, these methods may be reduced or turned off to save power.

Displays often overlay text and other graphical items with video content, for example for displaying subtitles, menus, electronic programme guides, teletext and others. If the text is too small, the viewer cannot read it but, if it is too large, it may obscure too much of the video content. The present system may be configured to display larger text when the viewer is further away. It may then be necessary to provide a system of pages when there is too much text to be displayed at once at the larger sizes.

A computer display could be designed so that it passed information about viewer distance back to the operating system or other software of a computer. The operating system or software could then optimise the size of text and other graphical objects for best readability by a user at that distance. A particular example would be for a web browser, which could adjust its layout and text size depending on viewer distance. The same could be done for a display combining video and software applications, such as a web browser on a TV.

Displays for video often require audio output. Such a system may be configured so that when the "viewer" is further away the audio output is made louder so that it can still be heard. Conversely the volume may be turned down as the "viewer" approaches.

Some displays are required to fetch content interactively, for example over the internet and/or for a video conferencing application. When the image quality is higher, more bandwidth is used, which may be costly. In addition, a sufficient bandwidth may not be available at all times to download such data and there may be contention with other users or with audio quality, or (in the video conference case) with the bandwidth required to send a video image at the same time. The present system may be configured to request lower quality video data from the data provider when the viewer is further from the display. Then the perceived quality is no lower, as the viewer cannot see the finest details, but a better use of bandwidth is made. This may provide a better viewing experience overall, potentially giving better audio, less network congestion and lower network costs.

Some displays are designed to limit the image visible to the side, for example to create a private display. There may be a trade-off between the strength of privacy and the quality of the main (on-axis) image. The present system may be configured so that, as the viewer gets closer, the trade-off is made more in favour of image quality and less in favour of privacy strength. The rationale here is that a closer viewer sees more details, so needs more quality, and the nearness of the viewer naturally puts a lower bound on the angle from which a "spy" could possibly attempt to view the display, so that there is less need for extreme angle of restriction.

Some display technologies create colours which have an angular dependence. Thus, as the viewer moves around the display, the perceived colours will vary. There are several methods available to correct the colour variation, including image processing methods which trade resolution for colour accuracy. The present system may be configured so that, for a closer viewer, the trade-off is made in favour of good resolution In addition, when the viewer is very close to a large display, the edges of the display will be visible at an oblique angle and are therefore subject to colour or brightness distortions. This situation is illustrated in Figure 9. In such a case, the display could be configured to correct colour or brightness distortions at the edges of a display depending on the viewer position. Methods for correction include varying the gamma curve (which relates pixel data values to on-axis brightness) as a function of viewer position.

It may be advantageous to measure not the distance of the viewer, but the angle the viewer makes with the central axis of the display. This could be for reasons of cost or performance or both. For some parameters, such as colour correction, viewer angle may form a more natural basis for correction. Again, as with viewer distance, viewer angle may be quantised into rough categories, such as central and non-central. It may be preferable to consider the angular spread of detected viewers.

A viewer is said to be "on-axis" if his or her position lies close to the perpendicular drawn through the centre of the display screen. Otherwise, the viewer is said to be "off-axis". For many purposes, it is sufficient to consider only the lateral angle of the viewer and to ignore the vertical angle, and this makes the angle measurement problem simpler.

The table in Figure 5 shows some possibilities for adjusting parameters based on viewer angle.

It may be advantageous to optimise some parameters taking account of both viewer distance and angle, when the viewer distance and angle are both available or each is available to some degree of precision or certainty. For example, in a privacy display, so long as the viewer is on-axis, the display may adjust privacy strength with viewer distance. However, when the viewer is no longer on-axis at any distance, the privacy should be such that no private image is displayed at all.

Further, the display may react to failure to detect a viewer or to detect a viewer at a given range of distances or angles, using this to adjust parameters. For example, if no viewer is detected on-axis, the display may assume all viewers are off-axis and optimise the display for off-axis viewing, even though it has not detected an off-axis viewer.

The display may be configured so that aspect -ratio stretching is used to make the image fill more of the screen area when the viewer is off-axis. The distortion introduced by stretching is less visible off-axis and the effect of the extra image size gained may offset it.

The display may be configured so that the image is made brighter when the viewer is off-axis. This may be done to overcome lack of off-axis brightness in many display panel technologies.

The display may be configured to correct the apparent perspective distortion of the screen for an off-axis viewer, by enlarging the areas of the image on the screen which are further away from the viewer and/or shrinking areas of the image on the screen which are closer as illustrated in Figure 6. The uncorrected image 61 is seen from off-axis as a perspective rectangle. The corrected image 62 appears as a rectangle from the viewer's point of view.

The display may be configured so that displayed text, such as for menus, electronic programme guides, teletext and subtitles, is enlarged for an off-axis viewer.

The display may be configured so that audio output is panned left or right for an off-axis viewer. In the case of stereo, the far speaker can be boosted to give the viewer proper balance between left and right channels.

The display may be configured so that secure output remains secure when the viewer is off-axis. To do this, it may increase privacy strength and/or adapt the privacy function to steer the main image in the direction of the viewer and away from other directions. Alternatively, the main private image may be switched off altogether when the viewer is not in the appropriate on-axis position to view it.

Some displays trade off angle of view for image quality. Such a display may be configured so that image quality is favoured if the viewer is on-axis whereas angle of view is favoured if the viewer is off-axis.

Some displays trade off off-axis colour quality for image quality. Such a display may be configured so that image quality is favoured if the viewer is on-axis whereas off-axis colour quality is favoured if the viewer is off-axis. For a display which has colours with an angular dependence, such as an LCD, it is possible to process the image to correct the colours for viewing in any particular direction. For example, one way to do this is to adjust RGB pixels using the apparent colour matrix of the display as seen from that direction. Thus, if a single viewer is detected, colours may be adjusted to give the best colour image in that direction alone. For example, it is not necessary to maintain good colours in the on-axis direction if the viewer is off-axis. This gives more freedom for colour adjustment. More generally, if there are several viewers for which the angular spread is known, image processing may be used to give the best colour performance over that range, without making any concession to colour performance beyond that range.

When the viewer is close to the display at a large off-axis angle, then the near side of the screen is potentially much closer to the eye than the far side. It may in such a case be preferable to apply image processing to process the image with different parameters at different parts of the image. For example, as before, the near edge may be processed to give better scaling and less sharpness than the far edge.

Embodiment for TV Figure 1 illustrates an embodiment of the invention. At least one camera or other sensor 2 is mounted on a display panel 6, directed into the potential viewing area. The panel 6 receives video data 7 and panel control signals 9 from an image processing and control unit 5. The unit 5 obtains video source material from a video source 1 which may be a tuner, decoder, DVD player, or any other source of video material.

The unit 5 also receives sensor information 4 from the at least one sensor 2 and uses this to select parameter values for processing the video and controlling the panel. The position of the viewer 3 may be measured by distance 8 or by angle 10 or both. In reality, the processing components and video source may be located inside the body of the display. The at least one sensor need not be located on the display, but may be elsewhere in the environment, so long as it is capable of detecting at least one viewer and passing that information to the display.

Embodiment for Mobile Device Figure 13 illustrates another embodiment of the invention for a mobile device. Here the system is integrated with other components of the device, such as the panel 6 or camera to be used as viewer sensor 2. In reality, the video source 1 and processing unit 5 will usually be located inside the body 131 of the device.

Embodiment with sharpness Figure 2 illustrates the effects of another embodiment. In this embodiment, the display is configured to increase the sharpness of the displayed image as the viewer distance increases. This may be performed by adjusting the parameters of an image sharpening algorithm, such as an unsharp filter or other methods as will be well understood by those in the image processing field. The modified parameter is preferably the radius of the sharpening, but other parameters such as strength of sharpening may be modified instead of or as well as radius. In Figure 2 an image 21 is shown sharpened by increasing amounts to produce images 22, 23 and 24. Viewing Figure 2 from varying distances (distances depending on how the figure is rendered) should illustrate that the effect of distance on perceived sharpness is real.

Embodiment with text size Figure 3 illustrates the effect of another embodiment. In this embodiment, overlaid text of various origin is made to vary according to viewer distance. The text may be one of the available streams of information provided with a video (for example a subtitle stream from a DVD), or from a teletext service or from an electronic programme guide, or a menu system used to control the display, or some other source. The base image 31 seen from a near viewer has text 32 overlaid at a standard size. However, when the viewer is further away, the base image 33 appears smaller (though the base image actually displayed may be the same), so the overlaid text 34 is made larger to achieve sufficient apparent size to be easy to read.

This is simplest when the text data is in text format, since the display has anyway to render the text data into an image and scaling is then simply a matter of scaling in the rendering algorithm, as will be apparent to those skilled in the art.

If the text data is an image (as may be the case with a subtitles overlay), the display may need to scale the text 37 (shown in 3a) as an image to create a larger text image 38 (shown in 3b) together with wrapping text 36 which has gone off the edge of the visible area 35. This is possible by simply detecting all regions of text 36 and moving them into the visible area whilst keeping the text ordering the same (shown in 3c).

Some provision for text alignment and/or justification may be preferable for elegance.

Potentially, the display would have to know the direction of flow of the text, such as left to right or right to left. This could be guessed from analysing the characters of text themselves, and/or by providing a method, such as a menu option, for the viewer to provide an indication.

As part of this process, the text may preferably be re-coloured as necessary to provide good contrast with the background image for readability.

Embodiments for sensing distance The viewer position may be sensed optically, using at least one camera mounted on the display. Software or hardware in the display interprets the image at least to the extent of identifying at least one viewer in the image. The distance to the viewer may be estimated from the apparent size of the viewer or of parts of the viewer, such as distance between his or her eyes.

Eyes are particularly easy to detect by camera or infra-red sensor using the phenomenon of "red-eye", which makes human eyes glow red under certain conditions.

Eye separation may then be used to estimate distance.

Alternatively, two or more cameras may be used. Then the apparent discrepancy (known as disparity) in the position of a viewer as seen by the different cameras leads to an estimate of the distance. Figure 7 illustrates two cameras 71, 72 positioned with a wide separation on the display panel so that their respective fields of view 73, 74 overlap over the region where viewer detection is required. It is possible to integrate the cameras much more closely geometrically, as will be well understood, or to use 3D or multiple imaging cameras capable of estimating depth Active systems for estimating viewer distance include: measuring distance with a sonic (or ultrasonic) pulse, or pulse of electromagnetic radiation (including visible light, infrared and ultraviolet).

In some situations, the viewer may be assumed to be holding a remote control for at least some of the time and the remote control may be modified to be easy to detect by any available means, for example by adding at least one element to the remote to reflect or otherwise modify a given wavelength of electromagnetic radiation or sound.

For example, since its dimensions are known, distance may be estimated from its apparent size. As an alternative, distance may be estimated by signal level, since electromagnetic radiation signals reduce with the square of the distance.

Conversely, the remote control may measure the distance to the display, for example optically using a built-in camera. Since the display is relatively large and of known size, it is relatively easy to measure its distance from the remote control. Optionally, the display may temporarily show a calibration pattern during this step to make the processing easier. It may emit or reflect visual or non-visual signals from different parts of its surface.

Distance from the remote control may be estimated by the received signal strength in either or both directions, from remote control to display or from display to remote control.

Distance may be measured by triangulation, in which the angle to the viewer is determined from two or more known positions and trigonometry is used to calculate the viewer's actual position.

The display may show a special calibration pattern which the viewer would watch and, by monitoring changes in the viewer (perhaps as his or her gaze is directed to different parts of the display), the display may estimate distance.

The viewer may provide an estimate of viewing distance using any of the control methods available. This embodiment could be used alone as a method for reducing cost, or combined with any other methods to allow the viewer to override or augment an automatic distance sensing system Embodiments for estimating viewer angle It will be evident to an expert in the field that many of the above methods for estimating viewer distance also provide, inter alia, at least an indication of viewer angle. The preferred method is to use a single camera as in Figure 1, then use vision algorithms to detect a face or faces in the scene. The angle to the viewer may then be calculated simply, assuming that each face represents a viewer.

Embodiment for wide view versus resolution Some TVs divide each colour sub-pixel in two and output different amounts of light for each part. This is to provide accurate colours over a wide angle, by spatial averaging in the viewer's eye. The display may use the two halves of the sub-pixel to provide higher spatial resolution rather than wide angle when the viewer is known to be on-axis. Figure 8 shows how this may be achieved. In one standard arrangement, RGB pixels 82 are arranged as indicated 81. A single pixel thus has six controllable sub-regions r, g, b as well as r', g', b', giving rise to the equivalent of two independent pixels. By switching these pixels independently, either the on-axis resolution may be increased or off-axis colours may be corrected as is known from the prior art. In this embodiment, the device may switch between the two modes depending on the viewer position.

In another embodiment, this method may be enhanced further. When the viewer is at even longer distances, even single pixels can be too small to be seen unaided.

Therefore clusters of several pixels can be used to achieve the wide-angle colour averaging to produce more accurate colour perception.

Embodiment for privacy versus resolution Figure 10 illustrates how privacy may be increased at the expense of resolution when the viewer is known to be distant. In the kind of display here envisaged, each pixel has differing on-axis and off-axis luminance curves, where the luminance curve (often called gamma) is defined as the relationship between the pixel data value and the amount of light emitted. As is described in the prior art, four pixels 101 displaying a 2x2 region of luminance L = 0.75 may be replaced by four pixels 102 of which two are at L1.00 and two 105 are at L=0.5. When the viewer is far enough away to average the four pixels as a single source of light, the average brightness is the same on-axis.

However, due to the different off-axis luminance curves, an off axis viewer will see a different value and, in this way by varying the pattern across the screen, the main image can be concealed to some extent from an off-axis viewer. In the present embodiment, the display may be configured so that, as the viewer retreats even further, more pixels can be used to obtain a better privacy effect. For example, six pixels 103 of luminance L = 0.75 can be replaced by six pixels 104 such that four 106 are at L 1.0 and two are at L0.0. The mechanism is the same, but the use of more pixels means that more extreme pixel values can be used. More extreme values (such as 0.0 and 1.0) tend to lie in more non-linear regions of the off-axis luminance curve and so give rise to a larger privacy effect.

Embodiment for distance dependent display The table in Figure 4 indicates parameters which may optionally be adjusted according to the distance of the viewer. It will be readily appreciated that any of these could be implemented depending on the available processing and output capabilities of the display. The table in Figure 11 indicates one possible way to select viewer distance when there is more than one viewer. It may be advantageous to set a limit to viewing distance so that potential viewers beyond a certain distance or closer than a certain distance are discounted. It may be advantageous to allow display parameters to vary only slowly as the viewer or viewers are detected and/or move around, so as to limit annoying response to transitory events.

Those skilled in the art will readily appreciate that the selection of the precise mapping between viewer position and parameter values is simply a matter of preference and optimisation by testing and modification, and by knowledge of customer requirements.

Since each panel type will have its own characteristics, it is not possible to give a simple formula for each parameter. However, for concreteness, we could suggest that parameters may be allowed to vary linearly as a function of viewer distance as a first approximation, so that the limits of the range of variation are achieved at the determined limits of viewer distance.

Embodiment for angle dependent display The table in Figure 5 indicates parameters which may optionally be adjusted according to the angle of the viewer. It will be readily appreciated that any of these could be implemented depending on the available processing and output capabilities of the display. The table in Figure 12 indicates one possible way to select viewer angle when there is more than one viewer. It may be advantageous to set a limit to viewing distance so that potential viewers beyond a certain distance or closer than a certain distance are discounted.

It is thus possible to provide continuous optimisation of the perceived image or sound quality of the display to improve the viewer experience of the content. Power savings and bandwidth savings may be made in some viewing conditions. In some applications, it may provide better privacy, such as home on-line banking using a TV.

Claims

CLAIMS: 1. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to change angular colour correction in accordance with the detected position of the at least one viewer.
2. A display as claimed in claim 1, in which the processing arrangement is arranged to provide increased off-axis colour correction when the detected position is further from the screen than a first threshold distance.
3. A display as claimed in claim 1 or 2, in which the processing arrangement is arranged to provide increased off-axis colour correction when the detected position is further from the screen axis than a first threshold angle.
4. A display as claimed in any one of the preceding claims, in which the processing arrangement is arranged to provide reduced angular colour correction at edges of the screen when the detected position is further from the screen than a second threshold distance.
5. A display as claimed in any one of the preceding claims, in which the processing arrangement is arranged to provide reduced angular colour correction at the edges of the screen when the detected position is further from the screen axis than a second threshold angle.
6. A display as claimed in claim 2 or 4, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer nearest the screen.
7. A display as claimed in claim 3 or 5, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is an average of the viewer positions.
8. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to scale the image data with a scaling parameter which is dependent on the detected position of the at least one viewer.
9. A display as claimed in any one of claims 1 to 7, in which the processing arrangement is arranged to scale the image data with a scaling parameter which is dependent on the detected position of the at least one viewer.
10. A display as claimed in claim 8 or 9, in which the detecting arrangement is arranged to detect the distance of the at least one viewer from the display.
11. A display as claimed in claim 10, in which the scaling parameter comprises scaling quality.
12. A display as claimed in claim 11, in which the processing arrangement is arranged to apply a scaling algorithm having a first quality when the detected position is at a first distance from the screen and having a second quality less than the first quality when the detected position is at a second distance from the screen greater than the first distance.
13. A display as claimed in claim 12, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer nearest the screen.
14. A display as claimed in any one of claims 10 to 13, in which the scaling parameter comprises a scaling amount.
15. A display as claimed in claim 14, in which the processing arrangement is arranged to apply a first scaling amount when the detected position is at a third distance from the screen and a second scaling amount greater than the first scaling amount when the detected position is at a fourth distance from the screen greater than the third distance.
16. A display as claimed in claim 15, in which, in the case where the detecting arrangement detects a plurality of viewers, the third and fourth distances are an average of the detected viewer distances.
17. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to change the displayed image aspect ratio in accordance with the detected position of the at least one viewer.
18. A display as claimed in any one of claims ito 16, in which the processing arrangement is arranged to change the displayed image aspect ratio in accordance with the detected position of the at least one viewer.
19. A display as claimed in claim 17 or 18, in which the processing arrangement is arranged to stretch the image when the detected position is further from the screen than a third threshold distance or further from the screen axis than a third threshold angle.
20. A display as claimed in any one of claims 17 to 19, in which the processing arrangement is arranged to fill the screen when the detected position is further from the screen than a fourth threshold distance or further from the screen axis than a fourth threshold angle.
21. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to change the image colour resolution in accordance with the detected position of the at least one viewer.
22. A display as claimed in any one of claims 1 to 20, in which the processing arrangement is arranged to change the image colour resolution in accordance with the detected position of the at least one viewer.
23. A display as claimed in claim 21 or 22 in which the processing arrangement is arranged to increase the image colour resolution when the detected position is further from the screen than a fifth threshold distance.
24. A display as claimed in claim 23, in which the processing arrangement is arranged to increase the image spatial resolution when the detected position is nearer the screen than a sixth threshold distance which is less than or equal to the fifth threshold distance.
25. A display as claimed in claim 23 or 24, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer nearest the screen.
26. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to change the frame rate in accordance with the detected position of the at least one viewer.
27. A display as claimed in any one of claims 1 to 25, in which the processing arrangement is arranged to change the frame rate in accordance with the detected position of the at least one viewer.
28. A display as claimed in claim 26 or 27, in which the processing arrangement is arranged to increase the frame rate when the detected position is nearer the screen than a seventh threshold distance.
29. A display as claimed in claim 28, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer nearest the screen.
30. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, an input for receiving image data from a data communication medium, and a processing arrangement for processing the image data for display by the screen, the processing arrangement being arranged to change the bandwidth of the image data received at the input in accordance with the detected position of the at least one viewer.
31. A display as claimed in any one of claims 1 to 29, comprising an input for receiving image data from a data communication medium, the processing arrangement being arranged to change the bandwidth of the image data received at the input in accordance with the detected position of the at least one viewer.
32. A display as claimed in claim 30 or 31, in which the processing arrangement is arranged to reduce the bandwidth when the detected position is further from the screen than an eighth threshold distance.
33. A display as claimed in claim 32, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer nearest the screen.
34. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to change the privacy strength of an image for restricted viewing in accordance with the detected position of the at least one viewer.
35. A display as claimed in any one of claims 1 to 33, in which the processing arrangement is arranged to change the privacy strength of an image for restricted viewing in accordance with the detected position of the at least one viewer.
36. A display as claimed in claim 34 or 35, in which the processing arrangement is arranged to increase the privacy strength when the detected position is further from the screen than a ninth threshold distance or further from the screen axis than a fifth threshold angle.
37. A display as claimed in claim 36, in which, in the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer nearest the screen or nearest the screen axis.
38. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to change the image data perspective in accordance with the detected position of the at least one viewer so as to reduce viewer-perceived distortion.
39. A display as claimed in any one of claims 1 to 37, in which the processing arrangement is arranged to change the image data perspective in accordance with the detected position of the at least one viewer so as to reduce viewer-perceived distortion.
40. A display as claimed in claim 38 or 39, in which the processing arrangement is arranged to change the image data perspective in accordance with the direction of the at least one viewer with respect to the screen.
41. A display as claimed in claim 40, in which, in the case where the detecting arrangement detects a plurality of viewers, the direction is an average of the viewer directions.
42. A display comprising a display screen, an arrangement for detecting the position of at least one viewer with respect to the screen, and a processing arrangement for processing audio data for accompanying image display, the processing arrangement being arranged to pan the audio data towards the detected position of the at least one viewer.
43. A display as claimed in any one of claims 1 to 41, in which the processing arrangement is arranged to process audio data for accompanying image display be panning the audio data towards the detected position of the at least one viewer.
44. A display as claimed in claim 42 or 43, in which the processing arrangement is arranged to pan the audio data in accordance with the direction of the at least one viewer with respect to the screen.
45. A display as claimed in claim 44, in which, in the case where the detecting arrangement detects a plurality of viewers, the direction is an average of the viewer directions.
46. A display comprising a display screen, an arrangement for detecting the position of the at least one viewer with respect to the screen, and a processing arrangement for processing image data for display by the screen, the processing arrangement being arranged to display text with a text size which is dependent on the detected position of the at least one viewer.
47. A display as claimed in any one of claims 1 to 45, in which the processing arrangement is arranged to display text with a text size which is dependent on the detected portion of the at least one viewer.
48. A display as claimed in claim 46 or 47, in which the processing arrangement is arranged to increase the text size when the detected position is further from the screen than a tenth threshold distance.
49. A displays claimed in claim 48, in which, is the case where the detecting arrangement detects a plurality of viewers, the detected position is that of the viewer furthest from the screen.
50. A display as claimed in any one of claims 46 to 49, in which the processing arrangement is arranged to wrap the text such that all of the text is displayed in a correct order.