Method for controlling an augmented reality display device

Abstract

A method for controlling a colour display device comprising a plurality of variable wavelength LED pixels for use in an augmented reality system and a corresponding augmented reality system are disclosed. An image to be output over an environmental scene by the variable wavelength LED pixels is received and a light sensor detects colour data for the scene. The variable wavelength LED pixels are then controlled to display the image in a colour that is complementary to the colour data for the scene by adjusting an electrical parameter of the display itself. If the colours of the scene change then the colour of the image can be updated by changing the electrical parameter of the display without the need to change the data of the image.

Description

[0001] Method for Controlling an Augmented Reality Display Device

[0002] The present invention relates to a system and method for controlling a colour display device comprising a plurality of variable wavelength LED pixels for use in an augmented reality system. In particular for controlling the colour output by the augmented reality display device for display over an environmental scene based on a sensed colour of at least one portion of the environmental scene.

[0003] BACKGROUND lll-V semiconductor materials are of particular interest for semiconductor device design, in particular the family of Ill-nitride semiconductor materials.

[0004] “Ill-V” semiconductors include binary, ternary and quaternary alloys of Group III elements, such as Ga, Al and In, with Group V elements, such as N, P, As and Sb, and are of great interest for a number of applications, including electronics and optoelectronics.

[0005] Of particular interest is the class of semiconductor materials known as “Ill-nitride” materials, which includes gallium nitride (GaN), indium nitride (InN) and aluminium nitride (AIN), along with their ternary and quaternary alloys. (AI n)GaN is a term encompassing AIGaN, InGaN and GaN. Ill-nitride materials have not only achieved commercial success in solid-state lighting and power electronics, but also exhibit particular advantages for quantum light sources and light-matter interaction.

[0006] While a variety of Ill-nitride materials are commercially interesting, Gallium nitride (GaN) is widely regarded as one of the most important new semiconductor materials, and is of particular interest for a number of applications.

[0007] The present invention may be realised using LEDs formed from GaN and InGaN, but may advantageously be applicable to LEDs containing alternative Ill-nitride material combinations. It will be appreciated that the present invention may also be realised using conventional LED display technologies.

[0008] It is known that the introduction of pores into bulk Ill-nitrides, such as GaN can profoundly affect its material properties (optical, mechanical, electrical, and thermal, etc.). The possibility of tuning a wide range of material properties of GaN and Ill-nitride semiconductors by altering its porosity therefore makes porous GaN of great interest for optoelectronic applications. In a significant improvement over conventional three-colour LED displays, Poro Technologies Ltd, the present applicant, has developed variable-wavelength LEDs formed from Ill-nitride semiconductor materials grown over a porous region of Ill-nitride material. Instead of a conventional LED which emits at a single colour, these variable-wavelength LEDs can emit a broad spectrum of different emission wavelengths in response to variations in the driving conditions provided to the variable-wavelength LED. These variable-wavelength LEDs, and their method of manufacture, are disclosed in international patent application no. PCT / GB2022 / 051997, published as W02023 / 007174.

[0009] As the peak emission-wavelength of such variable-wavelength LEDs can be tuned by varying the driving conditions, a single variable-wavelength LED can take the place of multiple “single-colour” subpixels. In particularly preferred embodiments, the same variablewavelength LED can be tuned to emit any one of red, green or blue light by tuning the driving conditions provided to that LED. This means that a colour display can be formed from an array of variable-wavelength LEDs, with each variable-wavelength LED acting as a colour-variable pixel, or alternatively as a colour-variable subpixel in a subpixellated display.

[0010] SUMMARY OF THE INVENTION

[0011] The invention is defined in the independent claims, to which reference should now be directed. Preferred or advantageous features of the invention are defined in the appended dependent claims.

[0012] The present invention may be carried out with a display device comprising a plurality of variable-wavelength LEDs. In some embodiments, such display devices comprise an array of variable-wavelength LEDs, with each variable-wavelength LED forming a pixel of the display device.

[0013] An example of variable-wavelength LEDs usable in the present invention are known as dynamic-pixel-tuning (DPT®) variable-wavelength LEDs from Poro Technologies Ltd, which are disclosed in international patent application no. PCT / GB2022 / 051997, published as WG2023 / 007174.

[0014] A continuum of different emission wavelengths across an emission wavelength range can be emitted directly from a variable-wavelength LED by varying the driving conditions (the magnitude of the driving current and / or driving voltage) supplied to that LED. In CIE xy colourspace, the variable-wavelength LED can emit any colour along a continuous curved line of wavelengths. The length and shape of the emittable-wavelengths line in CIE xy colourspace is determined by the LED composition and structure, as described in W02023 / 007174.

[0015] One way of controlling the wavelength of light emitted by a variable-wavelength LED would be to provide a continuously-variable driving current to the LED. When the display device receives a signal identifying the target colour to be displayed by a given variablewavelength LED, the driving current to that pixel could then be delivered at whatever magnitude is required for the LED to emit a particular wavelength from its continuum of emittable wavelengths. Downsides of this approach, however, are the difficulty of precisely controlling the variable driving current at all times, and the limitation that the variablewavelength LED could only display chromaticities which are on the continuous line of emission wavelengths directly-emittable by that LED.

[0016] An alternative approach to driving variable-wavelength LEDs is to choose a set of predetermined “primaries” (primary wavelengths) from the continuum of emission wavelengths which are emittable by the variable-wavelength LED. Instead of controlling the emission wavelength to any point across the entire range of emittable colours, a limited set of operating points can be created by selecting a plurality of N primary wavelengths from the range of emittable colours. Each of the N primaries is then used as a pre-determined operating point for the variable-wavelength LED, and the N respective driving conditions required to generate those N primary wavelengths are programmed into a display device incorporating the variable-wavelength LED.

[0017] The N primary wavelengths which are selected from the LED’s range of emittable wavelengths form a palette of N available primaries, so that at any time the variablewavelength LED can be controlled to emit light at one of these N predetermined primary wavelengths. The N available primaries define a colour gamut of a plurality of displayable colours, as any colour within this gamut can be displayed by the variable-wavelength LED by mixing the available primary wavelengths.

[0018] When the display device receives a signal identifying the target colour to be displayed by a given variable-wavelength LED, the device can select, out of the palette of N available primaries, a smaller set of 2 or more primaries which are mixable to render the target colour. Which primaries are selected from the N available primaries will depend on the wavelength of the target colour to be displayed. By driving the LED to emit light at only a plurality of “primary” wavelengths instead of any wavelength from the continuum of directly-emittable wavelengths, the display device can display additional chromaticities which are not directly-emittable by the variable-wavelength LED. Primary wavelengths can be mixed using colour-mixing techniques known for conventional displays, such that the overall colour observed by a viewer is a temporal and / or spatial combination of the emitted primaries, rather than a single colour which is emitted “directly” by a single variable-wavelength LED. Driving variable-wavelength LEDs to emit light at predetermined “primary” wavelengths may also advantageously simplify driving requirements, as instead of having to provide a continuously-variable driving current, the display device can be calibrated to deliver a more manageable set of N predetermined driving conditions which generate the N available primaries.

[0019] The number “N” of available primaries can be selected depending on the size of the colour gamut which is desired, and the desired complexity of the control system. The larger the number of N, the larger the displayable colour gamut, but the larger the number of required driving conditions and the more complex the control requirements. As the variablewavelength LED can emit a continuous range of wavelengths, N can be selected to be any number up to infinity (N = infinity being equivalent to continuous driving to any point within the range of emittable wavelengths). N is preferably greater than 3, so that the displayable colour gamut is sufficiently large to render a wide range of colours. Particularly preferably N is greater than or equal to 4, or 5, or 6, to encompass a large colour gamut while keeping the control requirements relatively straightforward. Preferably N may be less than or equal to 8, or 10, or 12, to prevent the control requirements from becoming overly complex.

[0020] In one embodiment of a display device, each variable-wavelength LED is a pixel of the device, and the display device is a field-sequential display. In this embodiment, the same variable-wavelength LED pixel is driven to emit a plurality of discrete primary emission wavelengths in sequential subframes, by driving the LED pixel with the discrete driving conditions which correspond to those primary wavelengths.

[0021] In a sequential-field display, the same variable-wavelength LED may be controlled to emit multiple discrete primary emission wavelengths one after the other, by supplying different driving conditions to the LED in sequential subframes of a display frame. In this way, the same variable-wavelength LED may be a pixel that emits a plurality of selected “primary emission wavelengths” one after another within the duration of a single display frame. During each individual subframe, only one primary emission wavelength is emitted by the pixel. Thanks to the persistence of vision of human observers, the primary wavelengths emitted during sequential subframes temporally-average, so that the resulting colour observed by a person viewing the display at a normal viewing distance is the mixture of the colours emitted during a display frame.

[0022] In a subpixellated display, different primary emission wavelengths can be emitted by separate subpixels. The subpixels may all be variable-wavelength LEDs, or some subpixels may be non-variable-wavelength LEDs.

[0023] The brightness, or greyscale, of the emitted light can be varied by shortening or lengthening the duty cycle (pulse width) of the driving current pulses supplied to the LEDs in the display, which varies the “on time” of the LEDs. In a field-sequential display, the maximum duty cycle is achieved when the driving current is supplied to a variablewavelength LED for 100% of the duration of the display frame, or subframe, allocated to the colour being emitted. While controlling the magnitudes of the driving currents provided to the variable-wavelength LEDs determines the emitted wavelengths, to achieve variable display brightness the duty cycles of the pulses of driving current must also be variable, which adds an additional layer of complexity to device control.

[0024] In Poro Technologies Ltd’s dynamic-pixel-tuning (DPT®) variable-wavelength LEDs, the peak emission wavelength of variable-wavelength LEDs is strongly dependent on the magnitude of the electrical driving signal provided to a given LED, and longer-wavelength emission colours require lower-magnitude driving currents / voltages which inherently produce a lower luminance. This presents a challenge for those situations where a high display brightness is desired, and also a challenge for colour-balance when naturally-bright shorter wavelengths must be mixed with naturally-dimmer longer wavelengths.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0027] Figure 1 is a CIE xy colour space plot showing an example of the wavelengths of light emittable by a variable-wavelength LED;

[0028] Figure 2 is a CIE xy colour space plot showing an example of the wavelengths of light emittable by a variable-wavelength LED overlaid with example points representing emission wavelength primaries; Figure 3 shows the CIE xy colour space plot of Figure 2 with dashed lines showing the linear mixing of pairs of emission wavelength primaries to create a reduced palette of displayable colours;

[0029] Figure 4 illustrates part of an example augmented reality system according to the present invention;

[0030] Figure 5 is a flowchart illustrating an example method for controlling a colour display device according to the present invention;

[0031] Figure 6 is a CIE xy colour space plot showing an example of how complementary colours could be determined;

[0032] Figure 7 illustrates a plot of the characteristic curve of an example variable wavelength LED pixel showing the emitted wavelength of light as a function of voltage driving signal;

[0033] Figure 8 illustrates a plot of the characteristic curve of an example variable wavelength LED pixel showing the peak emitted wavelength of light as a function of a current driving signal; and

[0034] Figure 9 is a CIE xy colour space plot showing an example of the wavelengths of light that could be produced by an example variable wavelength LED pixel when driven by the illustrated currents.

[0035] DETAILED DESCRIPTION

[0036] Figure 1 illustrates a CIE xy colour space plot 100, on which the wavelengths of light emittable by a variable-wavelength LED are indicated as a continuous black line 101 . By varying the driving conditions, such as the magnitude of the driving current or the driving voltage, provided to the LED, the wavelength of light which is directly emitted by the LED may be tuned to any wavelength along line 101 .

[0037] Figure 2 is a CIE xy colour space plot 200 which illustrates the same emission line 101 as shown in Figure 1 , overlaid with 6 points representing “primaries” P1 , P2, P3, P4, P5, P6. These six primaries are specific emission wavelengths which have been selected from the continuous line of emittable-wavelengths 101. The six respective driving conditions required to be supplied to the variable-wavelength LED to result in these six emission wavelengths can be easily found, and those six driving conditions can be programmed into a display device. During operation, those six driving conditions can be supplied to the variable-wavelength LED, leading to the LED emitting light at any one of the six primary wavelengths. The space bounded by the six primaries is the colour gamut of colours which are displayable using the variable-wavelength LED and these six primary wavelengths.

[0038] By driving the variable-wavelength LED using field-sequential driving, different driving conditions can be supplied to the LED during discrete subframe time periods. Thus during a first subframe time period, a first driving condition can be supplied to the LED so that the LED emits light at primary wavelength P1. During a subsequent subframe time period, a different driving condition can be supplied to the LED so that the LED emits light at a different primary wavelength (one of P2-P6). In one embodiment, each display frame contains only two subframes, each of which is assigned to the emission of a different primary. The overall colour which will be observed by an observer viewing the variablewavelength LED will be a temporal average of the two primary wavelengths emitted during the display frame.

[0039] It is possible to divide a display frame into any number of shorter subframes. For example one display frame could be divided into six subframes, so that each of the six primaries could be emitted one after the other within a display frame. However, the use of only two of the available primaries during a given display frame can be advantageous, as doing this simplifies colour mixing and reduces the power that is consumed in switching between driving conditions. In order to render a given target colour, two primary wavelengths are selected from the available palette of 6 primaries P1 -P6, and the two selected primaries are then mixed proportionally to give a temporal average which appears to an observer to be the target colour.

[0040] As illustrated in Figure 3, the palette of 6 available primaries P1 -P6 can be divided into a plurality of different pairs. Each pair of primaries can then be linearly mixed with one another to display any colour along the straight lines 301 between the two primary wavelengths.

[0041] As is also evident from Figure 3, however, using a limited set of primaries (N = 6 for example) means that not all colours inside the colour gamut are positioned on a linear mixing line 301 between a pair of primaries. Thus with such a small palette of available primaries, not all of the colours in the gamut can be formed from only a pair of primaries.

[0042] One application of micro LED technology is in the field of augmented reality devices. Such devices may be configured to be worn if the user is expected to be mobile, for example in a head mounted fashion, or alternatively may be configured to be within a field of view of a stationary user, for example within the field of view from a cockpit of an aircraft or other vessel, or a driving seat in a car.

[0043] These devices are configured to project information content as images within the user’s field of view, such that they are overlaid over an environmental scene in order to display the relevant information, which may be important or urgent notifications for the user’s attention. This environmental scene is the scene within the field of view of the user. It will be appreciated that the colours of the environmental scene may change over time, for example as the user (or a vehicle / vessel they are within) moves around the environment. The notifications or other information content may be configured to be displayed / projected in a certain area of the field of view and the changing colours of this certain area of the environmental scene will impact the visual clarity of the information content being conveyed. Specifically, where there is a low colour contrast (such as the presence of similar colours) between the colour of the information content and the colour of the area of the environmental scene that is being overlaid with the information content then the detail of the information content becomes hard to see and understand. For example, a green icon displayed over a green patch of grass may be unintelligible to the user.

[0044] In order to overcome this issue, the inventors have appreciated that a light or image sensor (such as a camera) may be provided to capture details of the colour and / or brightness of the environmental scene and that these details can be used to modify the colour and / or brightness of the information content to be displayed / projected by the device. Specifically, it has been identified that the colour of the information content can advantageously be modified to be a complementary colour (as defined by known colour theory) with respect to the colour captured by the light or image sensor from the environmental scene. Where a display is only capable of producing a limited set of colours, it will be appreciated that the information content would be modified to the colour of this limited set of colours that most closely matches the identified complementary colour.

[0045] This technique would obviously not be possible in a monochrome display, such as those used for some augmented reality applications. In a conventional colour display each pixel unit comprises three subpixels, for example a red subpixel, a green subpixel, and a blue subpixel and the colour of each pixel to create a desired image is set by adjusting the respective brightness of each of these three subpixels. Accordingly, an input signal with red, green, and blue components must be identified and processed (for example by a system on chip processor or an application specific integrated circuit) to generate the driving signals required to set the relative brightnesses of these respective subpixels to generate the image in the desired colour. If the desired colour changes as proposed above, then it would be necessary for the output image to be recomputed / rebuilt and the driving signals required to adapt the relative brightnesses of these respective subpixels to generate the image in the newly desired colour would need to be determined.

[0046] However, the inventors have appreciated that this concept could be further improved by the use of a display having pixels with an emission wavelength that varies with an electrical driving signal, for example by current or by voltage driving signal, as illustrated with the dynamic-pixel-tuning variable wavelength LED pixel technology described above. With a display device formed from a plurality of such variable wavelength LED pixels, the colour of image content in an augmented reality system could be adapted by simply controlling the relevant electrical parameter of the display once the desired colour has been determined, for example based on the analysis of the colour content of the environmental scene.

[0047] Figure 4 illustrates part of an example augmented reality system 400 that comprises an image processor 410, a light sensor 420, a memory 430, a panel driving system 440, and a display panel 450 that comprises a plurality of variable wavelength LEDs. The display panel 450 may be configured to output image content over the environmental scene of a user’s field of view, and the light sensor may be configured to capture colour and / or brightness data of the environmental scene.

[0048] Figure 5 is a flowchart illustrating an example method 500 for controlling a colour display device comprising a plurality of variable wavelength LED pixels for use in an augmented reality system 400. At step 510, the processor 410 of the system 400 receives the information content to be displayed by system, this may be in the form of pixel data corresponding to an image to be output by the plurality of variable wavelength LED pixels 450 over the environmental scene.

[0049] At step 520, the processor 410 receives colour data of at least one portion of the environmental scene from the light sensor 420. The light sensor 420 may be an image sensor, such as a camera, and the image obtained may represent the whole field of view or only a portion of it. The colour data of interest may be an average for the whole of the imaged area, or only for a portion of the imaged area / field of view. For example, the colour data may represent the predominant colour of the specific area of the field of view that the information content is to be displayed over. In some examples, this may be achieved by cropping a larger imaged area prior to analysing the colour data.

[0050] At step 530, the processor 410 determines the relevant electrical parameter for controlling the plurality of variable wavelength LED pixels 450 (or a subset thereof) based on the colour data of the at least one portion of the environmental scene. This electrical parameter will be that which causes the plurality of variable wavelength LED pixels 450 to output light of a colour that is complementary to the colour data of the at least one portion of the environmental scene. This electrical parameter may relate to a current driving signal or to a voltage driving signal (depending on the configuration of the variable wavelength LED pixels 450) that the panel driving system 440 should use to drive the variable wavelength LED pixels 450.

[0051] Next, at step 540, the processor controls (via the panel driving system 440) the variable wavelength LED pixels 450 of the display panel based on the determined electrical parameter. In this manner, any colour content of the information content received by the processor 410 may be ignored as the output colour of the pixels will be set directly based on the colour from the sensor data in accordance with the above method. Accordingly, the information content data simply provides the shape to be displayed.

[0052] As the environmental scene changes, different colour data may be received from the light sensor 420 and the processor 410 will then determine a new electrical parameter for the panel driving system 440 to drive the display panel pixels 450 such that the light output by the pixels 450 changes to a new colour that is complementary to the different colour now being received from the light sensor 420. In this manner, the image data does not need to be re-calculated as the colour can be immediately changed to the identified complementary colour by simply adjusting the electric parameter (e.g. a driving voltage or current) of the display panel directly.

[0053] As noted above, the colour data received from the light sensor 420 may be averaged to determine the predominant colour of the environmental scene / field of view, or a specific area thereof. Figure 6 is a CIE xy colour space plot 600 showing an example of how the relevant complementary colour to be emitted by the variable wavelength LED pixels 450 could be determined. The predominant colour identified, which may be referred to as the background colour, is illustrated by point 610 and can be taken to have CIE coordinates (,xb>yb)- For a white point (xw,yw), the (x,y) of the complementary colour may be found by solving the below equation in combination with the single spectrum curve of the colour map:

[0054] Colour curve 620 identifies the range of colours that may be emitted by each variable wavelength LED pixel 450 in one example. Accordingly, the point at which a line passing through both the identified predominant colour and the white point intersects the colour curve 620 will be complementary colour to be displayed and thus the wavelength W compensation of this complementary colour may be identified. It will be appreciated that the mapping between colours sensed by the light sensor 420 and their complementary colours may be determined in advance and stored in a lookup table. This lookup table may be stored in the memory 430 for recall by the processor 410.

[0055] Figure 7 illustrates a plot 700 of the characteristic curve of an example variable wavelength LED pixel 450 that plots the wavelength of light emitted by the pixel as a function of a voltage driving signal. Enrepresents an initial driving signal for causing the variable wavelength LED pixels 450 to emit light with a wavelength Wn. As the background changes, it is determined that the complementary colour now has a wavelength of W compensation, and thus the variable wavelength LED pixels 450 should now be driven by a voltage driving signal Ecompensation. Again, it will be appreciated that the mapping between the wavelength of light desired to be emitted by the variable wavelength LED pixels 450 and the relevant driving voltage (or other relevant electrical parameter) may be determined in advance and stored in a lookup table, which may be stored in the memory 430 for recall by the processor 410.

[0056] Moreover, it has been appreciated that instead of storing a first lookup table mapping the colour sensed by the light sensor 420 to its complementary colour, and a second lookup table mapping the wavelength of the complementary colour to a corresponding electrical parameter for driving the variable wavelength LED pixels 450, a single lookup table could be stored in the memory 430 that maps directly from the colour sensed by the light sensor 420 to the electrical parameter corresponding to its complementary colour.

[0057] In some examples, the electrical parameter used to drive the variable wavelength LED pixels 450 is current. Figure 8 illustrates a plot 800 of the data points that form the characteristic curve of an example variable wavelength LED pixel 450 showing the peak emitted wavelength of light as a function of a current driving signal applied to the variable wavelength LED pixel 450. In this example, the number of colours that the variable wavelength LED pixels 450 can produce may be limited by the accuracy with which the drive current can be controlled.

[0058] Figure 9 is a CIE xy colour space plot 900 showing an example of the wavelengths 910 that could be produced by an example variable wavelength LED pixel 450 when driven by the currents shown on the right hand side. The 0.1 mA drive current corresponds to the red light of the data point on the right hand side of the arc of data points. Conversely, the 30 mA drive current corresponds to the green light of the data point on the left hand side of the arc of data points. The white point 920 has been included in plot 900 for ease of reference.

Claims

CLAIMS:1 . A method for controlling a colour display device comprising a plurality of variable wavelength LED pixels for use in an augmented reality system, the method comprising: receiving pixel data corresponding to an image to be output by the plurality of variable wavelength LED pixels over an environmental scene; receiving, from a light sensor, colour data of at least one portion of the environmental scene; determining an electrical parameter for controlling at least a subset of the plurality of variable wavelength LED pixels based on the colour data of the at least one portion of the environmental scene; and controlling at least the subset of the plurality of variable wavelength LED pixels based on the determined electrical parameter such that the subset of the plurality of variable wavelength LED pixels output light of a first colour that is complementary to the colour data of the at least one portion of the environmental scene.

2. The method of claim 1 further comprising: receiving, from the light sensor, second colour data of the at least one portion of the environmental scene corresponding to a subsequent moment in time, the second colour data being different to the colour data; determining a second electrical parameter for controlling the at least a subset of the plurality of variable wavelength LED pixels based on the second colour data; and controlling at least the subset of the plurality of variable wavelength LED pixels based on the determined second electrical parameter such that the light output by the subset of the plurality of variable wavelength LED pixels changes from the first colour to a second colour that is complementary to the second colour data of the at least one portion of the environmental scene.

3. The method of claim 2 wherein the light output by the subset of the plurality of variable wavelength LED pixels changes from the first colour to the second colour without modifying the image to be output by the subset of the plurality of variable wavelength LED pixels.

4. The method of any one of claims 1 to 3 wherein the plurality of variable wavelength LED pixels are controlled by adjusting the electrical parameter for the colour display device directly.

5. The method of any one of claims 1 to 4 wherein the electrical parameter is a voltage level for driving the at least a subset of the plurality of variable wavelength LED pixels.

6. The method of any one of claims 1 to 5 wherein the first colour that is complementary to the colour data of the at least one portion of the environmental scene is determined from a lookup table based on the colour data of the at least one portion of the environmental scene.

7. The method of any one of claims 1 to 5 wherein the electrical parameter for controlling the at least a subset of the plurality of variable wavelength LED pixels is determined from a lookup table.

8. The method of claim 7 wherein the electrical parameter for controlling the at least a subset of the plurality of variable wavelength LED pixels is determined from a lookup table based on the colour data of the at least one portion of the environmental scene.

9. The method of any one of claims 1 to 8 further comprising receiving, from the light sensor, brightness data of the at least one portion of the environmental scene, wherein the electrical parameter is determined based on the colour data and the brightness data of the at least one portion of the environmental scene.

10. The method of any one of claims 1 to 9 wherein the augmented reality system is a head mountable augmented reality system.

11. An augmented reality system for outputting images over an environmental scene, the system comprising: a colour display device comprising a plurality of variable wavelength LED pixels for outputting the images over the environmental scene; an input for receiving pixel data corresponding to an image to be output by the plurality of variable wavelength LED pixels; a light sensor configured to measure colour data of at least one portion of the environmental scene; and a processor configured to determine an electrical parameter for controlling at least a subset of the plurality of variable wavelength LED pixels based on the colour data of the at least one portion of the environmental scene;wherein the processor is further configured to control at least the subset of the plurality of variable wavelength LED pixels based on the determined electrical parameter such that the subset of the plurality of variable wavelength LED pixels output light of a first colour that is complementary to the colour data of the at least one portion of the environmental scene.

12. The augmented reality system of claim 11 wherein: the light sensor is further configured to receive second colour data of the at least one portion of the environmental scene corresponding to a subsequent moment in time, the second colour data being different to the colour data; the processor is further configured to determine a second electrical parameter for controlling the at least a subset of the plurality of variable wavelength LED pixels based on the second colour data; and the processor is further configured to control at least the subset of the plurality of variable wavelength LED pixels based on the determined second electrical parameter such that the light output by the subset of the plurality of variable wavelength LED pixels changes from the first colour to a second colour that is complementary to the second colour data of the at least one portion of the environmental scene.

13. The augmented reality system of claim 12 wherein the processor is configured to change the light output by the subset of the plurality of variable wavelength LED pixels from the first colour to the second colour without modifying the image to be output by the subset of the plurality of variable wavelength LED pixels.

14. The augmented reality system of any one of claims 11 to 13 wherein the processor is configured to control the plurality of variable wavelength LED pixels by adjusting the electrical parameter for the colour display device directly.

15. The augmented reality system of any one of claims 11 to 14 wherein the electrical parameter is a voltage level for driving the at least a subset of the plurality of variable wavelength LED pixels.

16. The augmented reality system of any one of claims 11 to 15 wherein processor is configured to identify the first colour that is complementary to the colour data of the at least one portion of the environmental scene from a lookup table based on the colour data of the at least one portion of the environmental scene.

17. The augmented reality system of any one of claims 11 to 15 wherein the processor is configured to identify the electrical parameter for controlling the at least a subset of the plurality of variable wavelength LED pixels from a lookup table.

18. The augmented reality system of claim 17 wherein the processor is configured to identify the electrical parameter for controlling the at least a subset of the plurality of variable wavelength LED pixels from a lookup table based on the colour data of the at least one portion of the environmental scene.

19. The augmented reality system of any one of claims 11 to 18 wherein the light sensor is further configured to receive brightness data of the at least one portion of the environmental scene, and wherein the processor is configured to determine the electrical parameter based on the colour data and the brightness data of the at least one portion of the environmental scene.

20. The augmented reality system of any one of claims 11 to 19 wherein the augmented reality system is a head mountable augmented reality system.

Images