A display driver and method for controlling image reproduction in a micro-led display

Abstract

An apparatus and a method for controlling image reproduction on a colour display having a pixel array are disclosed. The method comprises receiving pixel data corresponding to an image to be displayed by the pixel array, the pixel data comprising brightness data for pixels in each of a plurality of colour space primaries. For each colour space primary, brightness data is loaded and output for display in a band of n rows that progresses across the pixel array such that each row of the pixel array is activated in a given colour space primary for the same amount of time. The value of n is different for the respective colour space primaries such that the duty cycle differs for each colour space primary.

Description

[0001] A DISPLAY DRIVER AND METHOD FOR CONTROLLING IMAGE REPRODUCTION IN A

[0002] MICRO-LED DISPLAY

[0003] The present application relates to an apparatus and a method for controlling image reproduction on a colour display. In particular, a display driving method for a micro light emitting diode (micro-LED) display that reduces motion blur and colour breakup is disclosed.

[0004] BACKGROUND TO THE INVENTION

[0005] Conventional display driving methods typically use a sustain-and-hold driving scheme to update the pixels in a display from frame to frame of image data. This scheme may also be referred to as a sample-and-hold driving scheme, and it involves loading data into each row of a pixel array of the display and sequentially turning on each row of the display so that all pixels are simultaneously activated in order to display the desired image frame. Data is then loaded for the next image frame into each row of the pixel array, and so on. Typically, a memory element is associated with each pixel so that the whole array can be addressed row by row with the driving data for each pixel being retained. The memory element may be implemented in the form of an SRAM cell, or a storage capacitor that stores the voltage or current to be passed through the diode(s) of a pixel.

[0006] This display driving scheme is typically configured for a long duty cycle for the respective pixels, which is optimised for counteracting the slow switching and settling speed (and therefore extended downtime during data load times) of displays using liquid crystal material to control the brightness of each pixel. By maintaining this high duty cycle, the maximum brightness can be achieved for the liquid crystal display (LCD), with the overall switching time for each frame of image data minimised. It will be appreciated that this process can be repeated for subsequent image frames, which may together represent a moving image I video data.

[0007] The speed with which data can be buffered and loaded into the pixel array of a display depends on the transistor process node design used in the backplane of the display. If the data load time for each row is assumed to be 20 ns, then the time to load data into a 1080p display would be 21.6 us. Brightness of a given pixel can be controlled using pulse width modulation (PWM) with a constant applied voltage or current. 21.6 us can be considered to be the time required to display the lowest brightness signal. Typically, the PWM uses 8- bit encoding, which provides 256 values, with the first of these being a zero I off brightness. As such, the brightest signal would correspond to the pixel emitting for all 255 units of time in the PWM window, which can be equated to 5.5 ms.

[0008] For single panel displays, the frame is typically split into respective subframes for colour sequential update, i.e. the brightness data for the pixels in one colour channel is loaded and displayed, and then subsequently the brightness data for the pixels in another colour channel is loaded and displayed, and so on. This field sequential colour update would therefore take 16.5 ms in the above example for a display using three colour space primaries, for example red, green, and blue (RGB) colour spaces. For a refresh rate of 60 Hz, the time available for each refresh is approximately 16.7 s, and so it can be seen that the duty cycle for this arrangement is very high.

[0009] However, eye tracking movements across a display can result in blurring of the perceived image in such configurations due to the long duty cycle. This is due to an image frame being statically displayed across the whole of a refresh cycle, even for objects that the observer’s eye is tracking during a smooth pursuit, while the observer’s eye moves across this period of time. This is known as motion blur. For displays using colour field sequential update, the respective colours of a single frame are also displayed at different times within their own subframes. Accordingly, this can also lead to separation of the RGB components of a given colour at the edges of different colour areas, which is referred to as colour breakup.

[0010] This is particularly relevant in displays that are configured to occupy a large proportion of an observer’s field of view, for example in displays that are used in augmented reality (AR) and / or virtual reality (VR). While a modest smooth pursuit eye tracking speed may be considered to be approximately 120 degrees per second, saccadic eye movements can be expected to be more common in such AR and VR displays, which could be at speeds of approximately 500 degrees per second. The faster the eye tracking movement is, the greater the motion blurring I colour breakup effects will be.

[0011] One option to mitigate motion blur and colour breakup in video is to increase the frame rate, thus reducing the persistence time of each constituent image. However, this is highly technically challenging and LCDs, such as Liquid Crystal on Silicon (LCOS) displays typically have an upper limit frame rate of around 360 Hz, while successful mitigation of colour breakup using refresh rate alone can be expected to require refresh rates in excess of 700 Hz. Alternatively, black frames can be inserted between colour data frames in order to double the frame rate of the video in a simple manner; however, it will be appreciated that this will also reduce the overall brightness and / or contrast of the display.

[0012] The inventor has appreciated that the above display driving schemes are not well suited to display technologies that do not use liquid crystals, and that motion blur and colour breakup may be mitigated in alternative manners.

[0013] SUMMARY OF THE INVENTION

[0014] The invention is defined in the independent claims to which reference should now be directed. Advantageous features are set out in the dependent claims.

[0015] In a first aspect of the present disclosure, the invention relates to an apparatus for controlling image reproduction on a colour display having a pixel array. The apparatus comprises an input configured to receive pixel data corresponding to an image to be displayed by the pixel array (the pixel data comprising brightness data for each pixel in each of a plurality of colour space primaries) and a processor configured to receive the pixel data and to iteratively load and output for display the brightness data in a first colour space primary corresponding to a plurality of rows of the pixel array such that n1 rows of the pixel array are progressively activated to simultaneously output brightness data in the first colour space primary. The processor is further configured to iteratively load and output for display the brightness data in the first colour space primary in any remaining rows such that, for the first colour space primary, no more than n1 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time.

[0016] The processor is further configured to iteratively load and output for display the brightness data in a second colour space primary corresponding to a plurality of rows of the pixel array such that n2 rows of the pixel array are progressively activated to simultaneously output brightness data in the second colour space primary; and to iteratively load and output for display the brightness data in the second colour space primary in any remaining rows such that, for the second colour space primary, no more than n2 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time. The value of n1 is an integer greater than n2, and n2 is a positive real integer. In this manner, a number of rows can be activated in a given colour space primary simultaneously to create a band of rows that are on and that progress down the display until all rows have been activated for the same amount of time for that colour space primary. By varying the number of rows in the band for each colour space primary, the first aspect advantageously provides a display driving scheme in which the duty cycle can be easily and simply varied for the respective primaries of the chosen colour space to normalise the brightness levels of the respective light sources providing the light.

[0017] It will be appreciated that the same effect could be achieved by activating rows that are not adjacent to each other, although this would lead to a more complicated driving scheme. In this context, a row of the pixel array is considered to be activated when it is outputting the relevant brightness data, which may be a zero brightness. In this sense, the row will be considered to be activated even if the brightness data indicates that the light sources associated with the entire row should be turned off.

[0018] Optionally, the processor may be further configured to iteratively load and output for display the brightness data in a third colour space primary corresponding to one or more rows of the pixel array such that n3 rows of the pixel array are progressively activated to simultaneously output brightness data in the third colour space primary; and to iteratively load and output for display the brightness data in the third colour space primary in any remaining rows such that, for the third colour space primary, no more than n3 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time. The value of n2 may be greater than n3, and n3 is a positive real integer. This advantageously provides an implementation of the first aspect of the present disclosure with three colour space primaries to provide the colour gamut. Implementations with two colour space primaries can be configured to provide a full colour range for an image where a peak emission wavelength of at least one of the colour space primaries can be set on the fly, i.e. adapted between different image frames and from pixel to pixel. It will be appreciated that this process could also be repeated for further colour space primaries in implementations where more than three colour space primaries are used to form a given colour output from the pixel.

[0019] Optionally, the processor may be further configured to, for each colour space primary, load and output brightness data to adjacent rows of the pixel array such that a band of rows is activated to simultaneously output brightness data that progresses through the rows of the pixel array. The use of a band of adjacent rows advantageously simplifies the addressing scheme for the update.

[0020] Optionally, the processor may be further configured to output brightness data for each colour space primary colour sequentially in respective subframes that are non-overlapping. This advantageously minimises the instantaneous power requirement for driving the display.

[0021] Optionally, the processor may be further configured to simultaneously activate respective rows of the pixel array with brightness data for two or more of the plurality of colour space primaries. In this manner, rows of the pixel array may be activated for a second colours space primary before all of the rows have ceased outputting brightness data for a first colour space primary. While this increases the instantaneous power requirement for driving the display, it advantageously reduces the amount of colour breakup perceived in the resulting image or video data.

[0022] The processor may be further configured to control the duty cycle of the respective colour space primaries by setting the respective values of n1 , and n2.

[0023] Optionally, n1 may be set equal to the number of rows in the pixel array, such that the duty cycle for the first colour space primary is set to a maximum value. Optionally, the colour space primary corresponding to the greatest wavelength of light is chosen for the first colour space primary. In one example, the first colour space primary corresponds to red, the second colour space primary corresponds to green, and the third colour space primary corresponds to blue. In this manner, the red emission has the longest duty cycle and the blue emission has the shortest duty cycle, which can be used to balance the relative brightness of the red and blue light sources.

[0024] Optionally, the colour display may be a micro light emitting diode display. Optionally, each pixel of the pixel array may be formed from a plurality of light sources of the same type, wherein each light source has a peak emission wavelength that is dependent on the drive current such that each light source can reproduce light with a peak wavelength at each of the plurality of colour space primaries. This advantageously simplifies the structure and fabrication of the pixel array, and is particularly suited to the first aspect of the present disclosure. A second aspect of the present disclosure relates to a method for controlling image reproduction on a colour display having a pixel array. The method comprises receiving pixel data corresponding to an image to be displayed by the pixel array, the pixel data comprising brightness data for each pixel in each of a plurality of colour space primaries; iteratively loading and outputting for display the brightness data in a first colour space primary corresponding to a plurality of rows of the pixel array such that n1 rows of the pixel array are progressively activated to simultaneously output brightness data in the first colour space primary; and further iteratively loading and outputting for display the brightness data in the first colour space primary in any remaining rows such that, for the first colour space primary, no more than n1 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time.

[0025] The method further comprises iteratively loading and outputting for display the brightness data in a second colour space primary corresponding to a plurality of rows of the pixel array such that n2 rows of the pixel array are progressively activated to simultaneously output brightness data in the second colour space primary; further iteratively loading and outputting for display the brightness data in the second colour space primary in any remaining rows such that, for the second colour space primary, no more than n2 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time. The value of n1 is an integer greater than n2, and n2 is a positive real integer.

[0026] By varying the number of rows in the band for each colour space primary, the second aspect advantageously provides a method for driving a display in which the duty cycle can be easily and simply varied for the respective primaries of the chosen colour space to balance the brightness levels of the respective light sources providing the light. In particular, the desired white point can be set by adjusting the brightness of the respective colour channels in this manner.

[0027] Optionally, the method may further comprise iteratively loading and outputting for display the brightness data in a third colour space primary corresponding to one or more rows of the pixel array such that n3 rows of the pixel array are progressively activated to simultaneously output brightness data in the third colour space primary; and further iteratively loading and outputting for display the brightness data in the third colour space primary in any remaining rows such that, for the third colour space primary, no more than n3 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time. The value of n2 may be greater than n3, where n3 is a positive real integer.

[0028] Optionally, brightness data is iteratively loaded and output to adjacent rows of the pixel array for each colour space primary such that a band of rows is activated to simultaneously output brightness data that progresses through the rows of the pixel array. The use of a band of adjacent rows advantageously simplifies the addressing scheme for the update.

[0029] Optionally, brightness data for each colour space primary is output colour sequentially in respective subframes that are non-overlapping. This advantageously minimises the instantaneous power requirement for driving the display.

[0030] Optionally, brightness data for two or more of the plurality of colour space primaries are activated for respective rows simultaneously. In this manner, rows of the pixel array may be activated for a second colours space primary before all of the rows have ceased outputting brightness data for a first colour space primary. While this increases the instantaneous power requirement for driving the display, it advantageously reduces the amount of colour breakup perceived in the resulting image or video data.

[0031] The duty cycle of the first and second colour space primaries may be controlled by the relative values of n1 , and n2.

[0032] Optionally, n1 is equal to the number of rows in the pixel array such that the duty cycle for the first colour space primary is set to a maximum value. Optionally, the colour space primary corresponding to the greatest wavelength of light is the first colour space primary. In one example, the first colour space primary is red, the second colour space primary is green, and the third colour space primary is blue.

[0033] Optionally, the colour display is a micro light emitting diode display. Optionally, each pixel of the pixel array is formed from a plurality of light sources of the same type, wherein each light source has a peak emission wavelength that is dependent on the drive current such that each light source can reproduce light with a peak wavelength at the first colour space primary, at the second colour space primary, and at the third colour space primary. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0035] Figure 1 is a block diagram illustrating an example controller apparatus according to the first aspect of the present disclosure;

[0036] Figure 2 illustrates a scrolling update scheme for a pixel array of a display;

[0037] Figures 3A to 3C illustrate bands of different widths for respective colour space primaries in a scrolling update scheme for a pixel array of a display;

[0038] Figure 4 illustrates the shearing effect caused by a scrolling update scheme for a pixel array of a display during eye motion; and

[0039] Figure 5 is a flowchart illustrating an example method according to the second aspect of the present disclosure.

[0040] DETAILED DESCRIPTION

[0041] Colour displays are typically formed from an array of pixels, with each pixel having the ability to emit light of any desired colour within the colour gamut of the display. This is usually achieved by each pixel being formed from a plurality of subpixels, with respective subpixels being dedicated to a given colour space primary of the colour display. In emissive light emitting diode (LED) displays, the individual subpixels emit light having the wavelength of the given colour space primary, without the need for colour filters. For example, red, green, and blue colour space primaries may be used with LEDs that are configured to emit light having a peak wavelength at these colour points.

[0042] Conventional LEDs can be configured to emit light in a given narrow band of wavelengths by selection of the semiconductor material and diode construction used to form the LED in combination with the appropriate voltage applied to the LED structure. These differences in construction can lead to differences in the brightness I luminance of the light emitted for the respective colour space primaries. For LEDs being driven at a constant voltage or current, pulse width modulation (PWM) can be used to control the time averaged dimming of the light emitted for each colour space primary. Accordingly, techniques for balancing these differences in brightness between the respective colour space primaries include the use of PWM to even out I normalise these brightness differences, as well as to provide the dimming required to reproduce the required colour and brightness of the resultant pixel for the desired image to be reproduced by the display. Figure 1 is a block diagram illustrating an example controller apparatus 10 for controlling image reproduction on a colour display having a pixel array according to the first aspect of the present disclosure. The apparatus 10 comprises an input interface 12, a processor 14, and an output interface 16. The input 12 is configured to receive pixel data corresponding to an image to be displayed by the pixel array of the colour display. The pixel data will be processed into brightness data for each pixel of the pixel array in each of a plurality of colour space primaries. These colour space primaries can be combined such that each pixel can produce light in any colour of the colour gamut of the display. This brightness data is then output by the output interface 16 and loaded into the framebuffer / column latches above the pixel array. These column latches may be double buffered such that data for the next row is stored in a first column latch while pixels of one row are being loaded, and at the end of the row time, data from the first column latch is transferred to the second column latch so that the brightness data for the given colour space primary is ready to be displayed by the pixels of the array.

[0043] The inventor has appreciated that an alternative means for controlling the brightness of the LEDs associated with the respective colour space primaries is to vary the respective duty cycle of the LEDs by using a scrolling update for the pixel array. In the scrolling update, a band of rows are progressively activated and then the band of activated rows scrolls down the display. By configuring the number of rows in the band to be different for each of the respective colour space primaries, the duty cycle and time averaged brightness of the LEDs associated with each colour space primary can be adjusted.

[0044] The concept of a scrolling update scheme for a pixel array of a display is illustrated in Figure 2. Initially, the brightness data for a given colour space primary is loaded into the pixel memories of the pixel array. Then at time t = 0, subpixels of a given colour space primary in the first row of the pixel are activated for a first time interval. In this context, a row of the pixel array is considered to be activated when it is outputting the relevant brightness data, which may be a zero brightness depending on the desired colour of the pixel in question. In this sense, the row will be considered to be activated even if the brightness data indicates that the light sources associated with the entire row should be turned off. The brightness of each of the pixels in the row is controlled by using PWM across this first time interval. For the second time interval, the second row of the pixel array is activated while the first row remains activated. This is repeated until the nth time interval, at which point n rows of the pixel array will be simultaneously activated. This is illustrated as time t = ti in Figure 2. In the (n+1)th time interval, row 1 will be deactivated and row n+1 will be activated. This process is repeated such that with each subsequent time interval, the band of n activated rows progresses down the pixel array as illustrated in times t = t2 and t = ts of Figure 2. In this manner, the band of activated rows scans or scrolls down the display until the last row of the pixel row of the pixel array is activated. Then, in the next time interval the band of activated rows starts to scroll off of the display by deactivating the top row. This continues by successively deactivating the top row in each subsequent time interval until only the last row of the array is activated, and then finally the last row of the array is also deactivated.

[0045] In this manner, each row of the array of pixels will have been activated with brightness data for a first colour space primary for n time intervals. This process can then be repeated, sequentially activating the rows of the pixel array with brightness data for a second colour space primary. The inventor has appreciated that by changing the number of rows n that are simultaneously activated (and therefore the n time intervals that each row is activated for across the subframe) for each colour space primary, the respective duty cycles can be differed. As such an n value of ni may be used for the first colour space primary, and a value of n2 may be used for the second colour space primary. By setting the n value smaller for the colour space primary associated with an inherently brighter LED colour than the n value for the colour space primary associated with an inherently dimmer LED colour, the overall brightness of the respective LED colours can be equalised within the subpixels of each pixel of the array.

[0046] This technique can be used to equalise the brightness of light emitted by the respective colour subpixels in each pixel in a simple manner, and by orders of magnitude, without impacting the number of dimming levels provided by the PWM during each image frame or subframe. For example, a colour display having a resolution of 1080p will comprise 1 ,080 rows of pixels - by setting ni to be 1,080 and n2 to be 1, the persistence and overall brightness for the second colour space primary can be reduced by up to three orders of magnitude in comparison to the overall brightness for the first colour space primary.

[0047] In one example, this control scheme could be used with a pixel array formed from pixels having LEDs that have a variable peak wavelength of emission. WO 2023 / 007174 describes a variable wavelength LED having a peak emission wavelength that may be continuously controllable, over a given peak emission wavelength range, by varying the magnitude of a drive current applied to the variable wavelength LED. In the described LED configuration, the peak emission wavelength range over which the variable wavelength LED can be controlled to emit may be configured to be up to approximately 450 nm (for example ranging between approximately 400 nm and 850 nm). These techniques can be used to create an LED that can be driven to emit a red, green, and blue peak emission wavelength depending on the magnitude of the applied drive current. Relatively speaking, the red peak emission wavelength is produced when applying a low drive current, the green peak emission wavelength is produced when applying a medium drive current, and the blue peak emission wavelength is produced when applying a high drive current.

[0048] Due to the differences in drive current required for the variable wavelength LED to produce red light and blue light, the blue light emitted is significantly brighter than the red light emitted. Accordingly, the drive scheme of the present disclosure is particularly suited to a driving such variable wavelength LEDs.

[0049] Figures 3A to 3C illustrate bands of different widths for respective colour space primaries in a scrolling update scheme for a pixel array of a display. In line with the above discussion, Figure 3A may represent the scrolling band associated with a red colour space primary, Figure 3B may represent the scrolling band associated with a green colour space primary, and Figure 3C may represent the scrolling band associated with a blue colour space primary. In this manner, the duty cycle of the blue LED emission can be reduced in comparison to that of the green and red LED emissions.

[0050] In one example implementation of a colour display formed from pixels having such a variable wavelength LEDs, the value of n for the red emission is set to be equal to the number of rows in the colour display, which will be referred to as a 100% duty cycle; however, the skilled person will appreciate that this does not mean that every row of the pixel array is activated for the entire red subframe as certain rows will be deactivated I inactive while the band is scrolling onto and off of the pixel array. In such an example, the value of n may be set to be around 10% to 12% of the number of rows in the display for the green emission, and to 1 % (or less) of the number of rows in the display for the blue emission. For example, in a 1080p display the value of n for the red emission may be 1 ,080, while the value of n for the blue emission may be 1. These numbers are simply provided as one illustration of the level of brightness normalisation that may be required with such LED constructions and that may be provided by implementations of the present disclosure.

[0051] An advantage of such a driving scheme for a colour display is that the activation of only a single row (or small number of rows) of LEDs emitting blue light significantly reduces the instantaneous power I current requirements for the pixel array. For example, if each blue LED emission is considered to require approximately 10 uA of current, then activating every single pixel with blue light in a 1080p display would require an instantaneous current of more than 20 A. By reducing the total instantaneous current requirements with the methods of the present disclosure, the design and manufacture of a suitable display backplane can be simplified.

[0052] The above discussion has been in the context of a conventional colour display colour space that reproduces colour using three colour space primaries that are produced by three different LED subpixels. It will be appreciated that where a display pixel includes one or more variable wavelength LEDs, the colour gamut could be produced by two subpixels, for example, a red subpixel and a blue-green subpixel. Accordingly, a white point could be reproduced by the red subpixel being activated to emit red light and the blue-green subpixel being activated to emit cyan light. By varying the peak wavelength emitted by the blue-green subpixel, a full range of colours may be reproduced. However, it may be necessary to dynamically vary the value of n for the blue-green LED depending on the peak wavelength of light being emitted at any given point in time.

[0053] Taking this one step further, a pixel having a single variable wavelength LED may be configured to reproduce the colour gamut by emitting the respective colour space primaries in separate time intervals I subframes. In this manner, the pixel LED could be flashed red for ni time intervals in a first subframe, then green for n2 time intervals in a second subframe, and finally flashed blue for ns time intervals in a third subframe.

[0054] While the band of rows (or row if n is set to 1) has been illustrated in Figure 2 as progressing down the array, it will be appreciated that the band could instead progress up or across the array of the display in alternative configurations. Alternatively, the plurality of rows simultaneously activated may not be adjacent rows forming a band, and could instead be interlaced alternate rows or another appropriate pattern of rows. A further advantage of the display driving scheme of the present disclosure is that, by reducing the temporal persistence of the light emissions for each frame I subframe, motion blurring during eye tracking movements may be reduced. However, this motion blurring during eye tracking movement may be replaced with an observed shearing effect in the perceived image frame. This is because, during eye tracking movement, different rows of the display will be activated at different times and will be incident on a different portion of the observer’s retina. This leads to a slanting perceived image as illustrated in Figure 4 for a scrolling update scheme, which may be considered analogous to the rolling shutter effect in image capture of a moving target. The magnitude of the shearing effect increases with increasing eye velocity.

[0055] In a colour display, the sequential display of colour channels means that colour breakup will also occur in the perceived image for the same reason when the observer’s eye is moving, for example during tracking of an object within the content displayed by the pixel array of the display. These effects are particularly problematic for displays that are configured to occupy a large angular region of an observer’s field of view, for example in augmented reality (AR) or virtual reality (VR) use cases, since greater eye movement velocities can be expected as the observer’s gaze shifts across the field of view.

[0056] When implementing the method of the present disclosure to control of the duty cycle of respective colour emissions, the red colour channel will have a longer duty cycle and therefore a longer persistence than the green and blue colour channels. Consequently, the impact of colour breakup will be more pronounced for the red colour channel than the green colour channel, with the blue colour channel having the least pronounced colour breakup effect.

[0057] While the above discussion has assumed that the rows of the pixel array will be activated for respective colour space primaries in sequential and non-overlapping subframes, the inventors have appreciated that two or more colour space primaries may be activated for respective row(s) of the array simultaneously in order to reduce the amount of time between a respective row being activated in one colour space primary and another colour space primary, and thus to reduce the effects of shearing and colour breakup. In one example of this implementation, once the red band has grown to n1 rows and starts progressing down the display, the first row of the display may be activated with brightness data for the green channel, with a green band of n2 rows subsequently growing and starting to progress down the display (potentially) while one or more rows of the display are still activated with brightness data for the red channel. In some example implementations, red, green and blue colour channels may be simultaneously activated in different rows of the display.

[0058] This use of overlapping subframes reduces the total amount of time between rows being activated for the respective colour channels, which reduces the impact of any colour breakup effects. In this manner, colour breakup artifacts have been found to be reduced to acceptable levels without the need to increase the frame rate beyond 60 Hz, which represents a significant improvement over conventional update schemes for displays based on liquid crystal implementations.

[0059] In configurations in accordance with the present disclosure, colour breakup has been found to become noticeable to a user as the duty cycle for the colour channel exceeds approximately 10%. Accordingly, minimal colour breakup may be observable for the green colour channel, with the red colour channel being the colour channel mainly affected.

[0060] While colour breakup can be expected to be more pronounced during saccadic eye movement in comparison to smooth pursuit eye movement, the observer’s visual acuity is also reduced during saccadic eye movement, which may reduce the overall observed impact.

[0061] Figure 5 is a flowchart illustrating an example method according to the second aspect of the present disclosure. In step 50, the method comprises receiving pixel data corresponding to an image to be displayed by the pixel array, the pixel data comprising brightness data for pixels in each of a plurality of colour space primaries. At step 51 , the brightness data for a first colour space primary is iteratively loaded and output for display on a display having a pixel array. This iterative process is repeated such that n1 rows of the pixel array are progressively activated to simultaneously output respective brightness data in the first colour space primary for the relevant pixels. The value of n1 is an integer that defines the maximum number of rows that are simultaneously activated for the first colour space primary.

[0062] Then at step 52, the method further comprises iteratively loading and outputting for display the brightness data in the first colour space primary in any remaining rows. For each further row that is activated, the row that has been activated for the longest duration is deactivated such that, no more than n1 rows are activated to simultaneously output brightness data for the first colour space primary, and each row is activated for the same total duration of time.

[0063] The process of steps 51 and 52 is then repeated for a second colour space primary, but with a different value set for the number of rows that may be activated simultaneously. In particular, at step 53 the method comprises iteratively loading and outputting for display the brightness data in the second colour space primary corresponding to a plurality of rows of the pixel array such that n2 rows of the pixel array are progressively activated to simultaneously output brightness data in the second colour space primary. The value of n2 is also an integer, but n2 is smaller than n1. Then at step 54, the method comprises further iteratively loading and outputting for display the brightness data in the second colour space primary in any remaining rows such that, for the second colour space primary, no more than n2 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time.

[0064] In drive schemes for displays having three or more colour space primaries, this process may then be repeated again for the third colour space primary, again with a different value set for the number of rows that may be activated simultaneously. In particular, at step 55 the method comprises iteratively loading and outputting for display the brightness data in the third colour space primary corresponding to one or more rows of the pixel array such that n3 rows of the pixel array are progressively activated to simultaneously output brightness data in the third colour space primary. The value of n3 is also an integer, but n3 is smaller than n2. Then at step 54, the method comprises, further iteratively loading and outputting for display the brightness data in the third colour space primary in any remaining rows such that, for the third colour space primary, no more than n3 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time.

[0065] For completeness, it is noted that the flowchart of Figure 5 illustrates the operation of an example implementation of a method according to the present disclosure. Each block in the flowcharts may represent a module comprising one or more executable computer instructions, or a portion of an instruction, for implementing the relevant logical function specified in the block. Each block in the flowchart may be implemented in software, hardware or a combination of software and hardware. As will be appreciated by the skilled person, the subject matter described herein may be embodied in whole or in part as a method, a system, or a computer program product including computer readable instructions. Accordingly, the subject matter of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software, firmware, hardware and / or any other suitable approach or apparatus.

[0066] Any computer readable program instructions may be stored on a non-transitory, tangible computer readable medium. The computer readable storage medium may include one or more of an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk.

Claims

CLAIMS1. An apparatus for controlling image reproduction on a colour display having a pixel array, the apparatus comprising: an input configured to receive pixel data corresponding to an image to be displayed by the pixel array, the pixel data comprising brightness data for each pixel in each of a plurality of colour space primaries; a processor configured to receive the pixel data and to iteratively load and output for display the brightness data in a first colour space primary corresponding to a plurality of rows of the pixel array such that n1 rows of the pixel array are progressively activated to simultaneously output brightness data in the first colour space primary; the processor further configured to iteratively load and output for display the brightness data in the first colour space primary in any remaining rows such that, for the first colour space primary, no more than n1 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time; the processor further configured to iteratively load and output for display the brightness data in a second colour space primary corresponding to a plurality of rows of the pixel array such that n2 rows of the pixel array are progressively activated to simultaneously output brightness data in the second colour space primary; and the processor further configured to iteratively load and output for display the brightness data in the second colour space primary in any remaining rows such that, for the second colour space primary, no more than n2 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time; wherein n1 is an integer greater than n2, and n2 is a positive real integer.

2. The apparatus of claim 1 , wherein the processor is configured to iteratively load and output for display the brightness data in a third colour space primary corresponding to one or more rows of the pixel array such that n3 rows of the pixel array are progressively activated to simultaneously output brightness data in the third colour space primary; and the processor is further configured to iteratively load and output for display the brightness data in the third colour space primary in any remaining rows such that, for the third colour space primary, no more than n3 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time; wherein n2 is greater than n3, and n3 is a positive real integer.

3. The apparatus of claim 1 or 2, wherein the processor is further configured to, for each colour space primary, load and output brightness data to adjacent rows of the pixel array such that a band of rows is activated to simultaneously output brightness data that progresses through the rows of the pixel array.

4. The apparatus of any of claims 1 to 3, wherein the processor is further configured to output brightness data for each colour space primary colour sequentially in respective subframes that are non-overlapping.

5. The apparatus of any of claims 1 to 3, wherein the processor is further configured to simultaneously activate respective rows of the pixel array with brightness data for two or more of the plurality of colour space primaries.

6. The apparatus of any of claims 1 to 5, wherein the processor is further configured to control the duty cycle of the first and second colour space primaries by setting the respective values of n1 and n2.

7. The apparatus of any of claims 1 to 6, wherein n1 is set equal to the number of rows in the pixel array.

8. The apparatus of any of claims 1 to 7, wherein the colour space primary corresponding to the greatest wavelength of light is the first colour space primary.

9. The apparatus of any of claims 2 to 8, wherein the first colour space primary corresponds to red, the second colour space primary corresponds to green, and the third colour space primary corresponds to blue.

10. The apparatus of any of claims 1 to 9, wherein the colour display is a micro light emitting diode display.

11. The apparatus of any of claims 1 to 9, wherein each pixel of the pixel array is formed from a plurality of light sources of the same type, wherein each light source has a peak emission wavelength that is dependent on the drive current such that each light source can reproduce light with a peak wavelength at each of the plurality of colour space primaries.

12. A method for controlling image reproduction on a colour display having a pixel array, the method comprising: receiving pixel data corresponding to an image to be displayed by the pixel array, the pixel data comprising brightness data for each pixel in each of a plurality of colour space primaries; iteratively loading and outputting for display the brightness data in a first colour space primary corresponding to a plurality of rows of the pixel array such that n1 rows of the pixel array are progressively activated to simultaneously output brightness data in the first colour space primary; further iteratively loading and outputting for display the brightness data in the first colour space primary in any remaining rows such that, for the first colour space primary, no more than n1 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time; iteratively loading and outputting for display the brightness data in a second colour space primary corresponding to a plurality of rows of the pixel array such that n2 rows of the pixel array are progressively activated to simultaneously output brightness data in the second colour space primary; and further iteratively loading and outputting for display the brightness data in the second colour space primary in any remaining rows such that, for the second colour space primary, no more than n2 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time; wherein n1 is an integer greater than n2, and n2 is a positive real integer.

13. The method of claim 12, further comprising iteratively loading and outputting for display the brightness data in a third colour space primary corresponding to one or more rows of the pixel array such that n3 rows of the pixel array are progressively activated to simultaneously output brightness data in the third colour space primary; and further iteratively loading and outputting for display the brightness data in the third colour space primary in any remaining rows such that, for the third colour space primary, no more than n3 rows are activated to simultaneously output brightness data and each row is activated for the same duration of time; wherein n2 is greater than n3, and n3 is a positive real integer.

14. The method of claim 12 or 13, wherein, for each colour space primary, brightness data is iteratively loaded and output to adjacent rows of the pixel array such that a band ofrows is activated to simultaneously output brightness data that progresses through the rows of the pixel array.

15. The method of any of claims 12 to 14, wherein brightness data for each colour space primary is output colour sequentially in respective subframes that are nonoverlapping.

16. The method of any of claims 12 to 14, wherein brightness data for two or more of the plurality of colour space primaries are activated for respective rows simultaneously.

17. The method of any of claims 12 to 16, wherein the duty cycle of the first and second colour space primaries is relative to the value of n1 , and n2 respectively.

18. The method of any of claims 12 to 17, wherein n1 is equal to the number of rows in the pixel array.

19. The method of any of claims 12 to 18, wherein the colour space primary corresponding to the greatest wavelength of light is the first colour space primary.

20. The method of any of claims 13 to 18, wherein the first colour space primary is red, the second colour space primary is green, and the third colour space primary is blue.

21. The method of any of claims 12 to 20, wherein the colour display is a micro light emitting diode display.

22. The method of any of claims 12 to 20, wherein each pixel of the pixel array is formed from a plurality of light sources of the same type, wherein each light source has a peak emission wavelength that is dependent on the drive current such that each light source can reproduce light with a peak wavelength at each of the plurality of colour space primaries.

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