A display pixel

Abstract

The display pixel is for a large multiview video screen for displaying a first image to a first viewing zone and a second image to a second viewing zone. It comprises a light source such as a light emitting diode and a light modulator including a first plurality of light valves such as liquid crystal cells arranged in front of said light source including a first light valve for modulating light to said first viewing zone and a second light valve for modulating light to said second viewing zone.

Description

[0001] A display pixel

[0002] DESCRIPTION

[0003] The present disclosure relates to a display pixel for a large multiview video screen as well as a module of display pixels for a large multiview video screen.

[0004] The pixels are to be observed from a much larger distance than for example a TV in a household, and the pixel pitch may be larger than a pupillary distance, which is typically in the range 50 to 80 mm.

[0005] A video screen is also termed a display or a monitor.

[0006] An example of a large video screen (albeit not a multiview screen) is the Sphere at The Venetian Resort in Las Vegas.

[0007] An example of a display pixel for a large multiview video screen is disclosed in WO22115320, which is incorporated in the present disclosure by reference.

[0008] A first aspect of the present disclosure is:

[0009] A display pixel for a large multiview video screen for displaying a first image to a first viewing zone and a second image to a second viewing zone, said display pixel comprising:

[0010] - a light source such as a light emitting diode,

[0011] - a light modulator including a first plurality of light valves such as liquid crystal cells arranged in front of said light source including a first light valve for modulating light to said first viewing zone and a second light valve for modulating light to said second viewing zone.

[0012] A second aspect of the present disclosure is:

[0013] A method for generating a pixel in a large multiview video screen, comprising: providing a light source such as a light emitting diode, providing a light modulator including a first plurality of light valves such as liquid crystal cells arranged in front of said light source including a first light valve for modulating light to a first viewing zone and a second light valve for modulating light to a second viewing zone.

[0014] A multiview display generates an image to a plurality of viewing zones. The plurality of images to the different viewing zones are different such that when an observer moves in front of the display different images will be observed.

[0015] With the term display pixel is meant one pixel of the overall display, e.g. the whole display has a plurality of display pixels defining the resolution of the display. Each display pixel generates / displays one image pixel of an image - the display pixel is arranged for displaying a single pixel of the first image and a single pixel of the second image.

[0016] The display pixel may be an RGB pixel, e.g. a pixel capable of generating any color at any light intensity. Light intensity (for a wavelength range such as a primary color) may also be referred to as “grey scale”.

[0017] When a driving signal to a light emitter is an impulse (Dirac delta function for example) a light burst is generated by the light emitter, e.g. the light signal will be similar to the driving signal, but not completely identical - it will differ, because the light emitter has inherent resistance, capacitance, and inductance.

[0018] Seen over a time window a number of impulses integrate to an amount of energy (Joule), e.g. in the time window the light emitter has an energy output. This energy output in the time window is input to the eye of the observer and integrated in the brain and determines the grey scale.

[0019] % Viewing zone

[0020] The first viewing zone may be to the right of the display pixel and the second viewing zone may be to the left of the display pixel. A viewing zone may also be termed viewing region or eye box, and it is a space in front of the display pixel.

[0021] In the following the term “viewing zone width” may refer to how large the space is.

[0022] An absolute measure for how large the space is may be the full width half maximum (FWHM) light intensity. Full width at half maximum is the difference between the two values of the independent variable (angle in this case) at which the dependent variable (light intensity) is equal to half of its maximum value. In other words, it is the width of a spectrum curve measured between those points which are half the maximum amplitude. Often the dependent variable is normalized with respect to its maximum, e.g. the maximum value is normalized to 1. Full width at half maximum is then 0.5. If the maximum (of a beam) is at an angle of 0 degrees and the beam has a value of 0.5 at the angles -15 degrees and 15 degrees, the FWHM is 30 degrees.

[0023] % Observation angle

[0024] Normally, an observation angle of an observer with respect to a display is defined as the angle between the normal to the display and a straight line between the display and the observer. The normal may for example be positioned at the center of the display, e.g. where the two diagonals of the display cross each other.

[0025] 3D displays and multiview displays are configured to emit light in specific angles or directions so that the light and thereby the image generated by such a display is only visible when the observer is positioned at such a specific angle or angle range. Outside that angle such a display may appear dark.

[0026] In the following specific examples according to aspects of the present disclosure will be explained in more detail with reference to the accompanying drawings. The present disclosure may, however, be embodied in different forms than depicted below, and should not be construed as limited to any examples set forth herein. Rather, any examples are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout. Like elements will, thus, not be described in detail with respect to the description of each figure.

[0027] Fig. 1 illustrates an example of a display pixel. The display pixel comprises a light source 1, and a light modulator 2 in front of the light source, e.g. between the light source and an observer 4 during intended use of the display pixel.

[0028] The display pixel may have a width in the range 1 cm to 4 cm such as 1 .5 cm, and the pitch / distance between display pixels when mounted in a large multiview video screen may be 2 cm.

[0029] % axis

[0030] It is contemplated that the display pixel is to have a much larger resolution of viewing zones along a primary axis than along a secondary axis. The primary axis may be horizontal, e.g. in a horizontal plane, and the secondary axis may be substantially orthogonal to the primary axis.

[0031] With substantially is meant + / - 10 degrees.

[0032] If a specific orientation of the primary axis is desired (which may be the case if the display pixel is to be mounted on a building structure such as a dome for example) the display pixel may be rotated such that the primary axis has the desired orientation, e.g. mounted on a building structure such that primary axis has the desired orientation - for example arranged vertically instead of horizontally.

[0033] In the following the reference is that the display pixel is arranged such that the primary axis is horizontal, and the secondary axis is vertical, e.g. in the figures it is illustrated that the primary axis is horizontal such that there is a horizontal resolution of viewing angles. If a vertical resolution of viewing angles is desired the mentioned display pixel should be rotated 90 degrees.

[0034] % light modulator

[0035] The light modulator extends from the bottom of the display pixel to the top of the display pixel. The light modulator may comprise a plurality of light valves such as liquid crystal cells or ferroelectric liquid crystal cells.

[0036] Each light valve is illustrated as being elongated along the secondary axis, e.g. having a height greater than width.

[0037] Each light valve may comprise a plurality of sub light valves operated in parallel such that each sub light valve opens and closes substantially simultaneously - for example two sub light valves / liquid crystal cells arranged in a column or four sub light valves / liquid crystal cells arranged in a square.

[0038] Each light valve may be controlled such that it switches between two states including a light transmitting state for transmitting light from the light source or a light shielding state for shielding light from the light source. Thus, the light valves may be binary operated (switching exclusively between these two states). A light valve is said to be open when it is in the light transmitting state and closed when it is in the light shielding state.

[0039] It is contemplated that the number of light valves for a display pixel is above 10 such as in the range 10 to 100 per mm such as 10 to 50, or 20 to 100, or 20 to 50, or 20 to 40, or 25 to 35 per mm.

[0040] Light from the light source will be visible at a given angle with respect to a normal of the display pixel depending on which light valve is open, e.g. each light valve may define a viewing zone / region in which light transmitted through the light valve is visible to an observer. Thus, light is visible in a respective viewing zone when the light valve for that respective viewing zone is open.

[0041] The width of a viewing zone may be controlled as a function of a number of neighboring light valves, e.g. the viewing zone may be made wider by opening more light valves for that viewing zone. Thus, a plurality of neighboring light valves may be controlled with the same driving signal for each viewing zone, e.g. the controller may receive pixel values for a number of viewing zones (which is less than the number of light valves), and the controller divides the light valves into a number of sets corresponding to the number of viewing zones. For example there may be 80 light valves and 8 viewing zones of equal width. Each set of light valves then comprises 10 light valves.

[0042] The number of light valves may be greater than the number of viewing Having a greater number

[0043] 100 light valves, vil styre p raecist hvor man skal skifte viewing zones, controller modta- ger 8 vaardier, hvordan skal de fordeles pa light valves

[0044] % light source

[0045] In the example, the light source comprises a tri-color light emitter, e.g. a light source having a red, a green and a blue emitter.

[0046] The three emitters are arranged vertically, e.g. with respect to the secondary axis. The light emitters may also be arranged in a square or on two lines next to each other.

[0047] The light source may have a width that is not greater than the width of a light valve, e.g. the light source may be arranged as a light emitter that is delimited with respect to the primary axis (a horizontally delimited light emitter in the example).

[0048] Specifically, the width of the light emitting area of the light source (along the primary axis) may be equal to or less than the width of a light valve. The width may be defined by the distance between the point emitting light at the far right and the point emitting light at the far left. The light source may arranged at the center of the backplane seen along the primary axis. Thus, the light source may be arranged approximately halfway between the sides of the display pixel, e.g. the distance from the center of the light source to the right edge of the light modulator (the projection of the right edge onto the backplane) is not more than 15 % different from the distance from the center of the light source to the left edge of the light modulator (the projection of the left edge onto the backplane).

[0049] In a contemplated solution the light source is also arranged at the center of the backplane seen along the secondary axis, e.g. the distance from the center of the light source to the top edge of the light modulator (the projection of the top edge onto the backplane) is not more than 15 % different from the distance from the center of the light source to the bottom edge of the light modulator (the projection of the bottom edge onto the backplane).

[0050] The height of the light source may be less than 25 % of the height of the light modulator such as less than 10 % or less than 5 %. In this case the light source constitutes a point light source (albeit not in the strict literal sense), because the area of the light source is much smaller than the area of the light modulator such as less than 10 %, or less than 5 % than the area of the light modulator.

[0051] The mounting of the light source is done to what is typically called a backplane (it is not necessarily a plane in the literal sense, but a print board such as a flex PCB).

[0052] % cor itroller

[0053] A controller 3 capable of controlling the light source 1 and the light modulator 2 receives an input signal from an image source (not shown).

[0054] The controller 3 may be located outside the light modulator 2, for example it may be a chip-on-flex integrated circuit mounted on a flexible printed circuit bonded to the light modulator 2, or it may be comprised in the light modulator 2, for example as a thin film circuit on an LCD substrate. The controller 2 may comprise a memory for storing a light modulation value and circuitry for controlling a light valve according to a stored value in the memory.

[0055] The controller 2 may comprise an input for inputting light modulation values to a memory. The input may for example be a matrix addressing circuit, for example an active matrix circuit for an LCD or FLCD light type light modulator.

[0056] There may be a plug 9 on the opposite side of the light source, e.g. the rear side of the back wall / backplane of the display pixel.

[0057] % gap between light valves

[0058] The light modulator does not comprise a black matrix having lines parallel to the secondary axis. Instead the light modulator 2 may be configured to have a minimum gap between light valves such as for example 4 or 2 micrometers. This may reduce light leakage between light valves causing crosstalk between colors of different angles.

[0059] The gap may be configured so a fringe field between liquid crystal cells in the light modulator 2 essentially ’’closes the gap”, i.e. orients liquid crystal molecules in a gap so light transmitted through the gap is modulated with a modulation which is in between the two neighboring light valves.

[0060] For example, two neighboring light valves may be controlled to have an equal light modulation such that transmission of light in the gap between the two is also modulated to the same degree as the light through the two light valves.

[0061] % spacer beads

[0062] The light modulator 2 may comprise substantially randomly distributed spacer beads and may be configured to minimize clustering of spacer beads for reducing scattering and blocking of light. Such random or pseudo random structures may eliminate moiree between spacer structure and light emitters. Alternatively the light modulator 2 may comprise (pseudo) random photolithographic spacer structures and a black matrix substantially just covering the spacer structures as seen by the observer 4 within a selected vertical field of view, for example + / - 45 degress. Hence the black matrix may reduce scattering of light in one direction to other directions. Alternatively the light modulator 2 may have horison- tally oriented spacer columns being uniform in a horisontal direction (e.g. lines or stripes), such as photolithographic spacers. A vertical distance between centers of spacer columns may be configured to be substantially equal to an integer number times the height of a light emitter for reducing moiree between ligth emitters and spacers. Additionally a black matrix may be comprised, configured so it obscures spacer columns for the observer 4 within a selected vertical viewing angle range. The black matrix may be configured as horisontal stripes located over the horisontal spacer columns.

[0063] % compensation film

[0064] If light onto a light valve is not incident at a right angle, e.g. parallel to the normal of the surface of the light valve, the greyscale produced by the light valve may be different than the target.

[0065] A compensation film / wave retarder film may be comprised to improve performance of the spatial light modulator 2. A compensation film / layer may be comprised and configured for example as specified in European patent EP2259131 B1 (Sharp Corp) which is hereby incorporated in the description by reference.

[0066] A first compensation film / layer may be located in a first optical path from a first position of the observer 4 through a first light valve to the light source 1 and a second compensation film / layer may be located in a second optical path from a second position of the observer 4 through a second light valve. Hence light leakage from a set of observation angles may be minimized resulting in very good contrast from a wide range of viewing angles.

[0067] % electronic compensation Instead of using a compensation film to compensate for different lengths of travel through different light valves the compensation may be done electronically, e.g. the display pixel is controlled by the controller such that the driving signal to a light valve is a function of the position of the light valve. In this way the transmission of light through the light valves may be adjusted such that all light valves have substantially (+ / - 15 %) the same transmission independent of their different positions (and thereby the different lengths of travel through the different light valves). Thus, a first light valve is opened with a first driving signal, and a second light valve is opened with a second driving signal (different from the first).

[0068] A lookup table may be used comprising position of the light valves and the amount that the driving signal is to be changed. A mathematical function can also be used having the position of a light valve as input and a driving signal value as output or a change to a driving signal as output.

[0069] A lookup table may be optimized by calibrating a lookup table while observing the light source 1 through a corresponding light valve.

[0070] An output value of the lookup table corresponding to an input value representing black may be calibrated to appear as dark as possible. Such calibration may also be automated for example using a machine vision camera and a controller with an iterative loop software. This can also be used to determine the mathematical function.

[0071] In the same way as when a light valve is open, a signal compensating for the position of a light valve may be applied to the light valve when it is closed.

[0072] % width of light valves

[0073] The width of a light valve closer to the center of the display pixel than to the edge of the display pixel may be smaller than the width of a light valve closer to the edge of the display pixel than the center of the display pixel. Hence angular resolution for small viewing angles (relative to a line / normal perpendicular to the display plane) can be higher than a resolution for a larger viewing angle.

[0074] Hence with a given number of light valves a high angular resolution for small viewing angles can be achieved where off-axis angular resolution is less important, such as when a large display is mounted on an end wall in a room.

[0075] % detector

[0076] The display pixel may be part of a system comprising a detector / sensor for detecting if a person is approaching one of the display pixels in the system, e.g. for preventing that a person comes too close to a display pixel resulting in eye damage due to the high light intensity from the display pixel.

[0077] The sensor may be a passive infrared detector. It may be omni directional and operated at a threshold such as person closer than the threshold such as 2 m causes the display pixel to turn off.

[0078] % vertical resolution

[0079] The light modulator may comprise a grid of light valves, e.g. there may be a plurality of rows with light valves when the light source is a point light source. In fig. 1 it is illustrated that there is one row of light valves, e.g. a 1D grid. But in fig. 2 it is illustrated that there are 2 rows, e.g. each column comprises two light valves. Thus, there are two viewing zones along the secondary axis.

[0080] Fig. 2 illustrates an example of a display pixel with a light guide / rod 5.

[0081] The light guide may be configured / designed using optical design software such as for example Zemax OpticStudio, LTI Optics Photopia or SolidWorks LightTools.

[0082] The light guide may be designed to incouple light from the light source including comprising any incoupling structures such as a lens and / or a reflector and to outcouple light at an outcoupling area at an end of the light guide located between the light source and the light modulator, e.g. the free end of the light guide is closer to the light modulator than the base of the light guide which is at the light source.

[0083] The light guide may be configured to homogenize light by blending light from different emission areas of the light source.

[0084] The light guide may comprise a diffuser preferably at the outcoupling area.

[0085] The light guide may be tapered to allow for a light source having a larger width than the outcoupling area.

[0086] The light guide may for example be molded PMMA guiding light by total or frustrated internal diffusion and the diffuser may be molded structures in the outcoupling area.

[0087] The light guide may be fully or partially comprised in a low refractive index solid or a solid with a low refractive index coating between the solid and the light guide . The solid may fixate the light guide mechanically relative to the light modulator. Alternatively, the light guide may be a solid with a hollow structure coated with a reflective coating. In this configuration the solid may have a low reflectivity and may be for example black PMMA and the solid may likewise fixate the light guide relative to the light modulator.

[0088] An outcoupling area of the light guide may be a small rectangle, for example 100 micrometers wide and 1000 micrometers high. Hence the small width of the outcoupling area relative to widths of the light valves enable sharp transitions between observed pixel colors from different angles, and the small height relative to the height of the pixel enables a wide vertical angle. The height of the outcoupling area may be an integer number times a distance between horizontal spacer columns in the light modulator. Hence, assuming that the observer is at a long distance from a display pixel relative to the height of the outcoupling structure, a substantially equal fraction of the outcoupling area may be visible from any vertical viewing angle, hence eliminating Moiree pattern due to gradually changing viewing angles over a display surface as observed by the observer.

[0089] The light guide may have a length (in the direction parallel to a normal to the light modulator) that is up to 50 % of the thickness of the display pixel such as up to 35 %, or 25 %.

[0090] % Temperature dependent operation

[0091] Below a certain temperature threshold, such as 15 degrees Celsius or 10 or 5 or 0 degrees Celsius, it is contemplated that the display may switch to a single view operation, e.g. the controller receives input from a temperature sensor in order to control the display.

[0092] Below the temperature threshold the light valves could all be open - they are all in the light transmitting state.

[0093] To avoid DC imbalance / offset in the light valves they may all be closed in the same amount of time as they were open, e.g. they alternate between being open and closed substantially simultaneously (within a time window). And when they are open an image is generated and this image is visible in all viewing zones (because there is no modulation by the light valves).

[0094] Further, below a certain temperature threshold, a heating operation of the light modulator may be initiated. Such heating operation may comprise heating an ITO layer or other conducting layer in the light modulator, for example by inducing a (de) current through the layer for example by applying a voltage difference to opposing ends of the layer or by applying an AC voltage across liquid crystal cells in the light modulator, said AC voltage preferably having a frequency being high relative to an RC component of opposing cell electrodes, hence inducing a high current.

[0095] A temperature sensor may be provided to measure the temperature of the environment, such as the air temperature, or some other temperature of a component of the display. Fig. 3 illustrates an example of a display pixel.

[0096] % vertical light source

[0097] In the example the light source comprises 12 light emitters of each color arranged with respect to the secondary axis (vertically in the example), e.g. a sequence alternating between a red light emitter, a green light emitter, and a blue light emitter.

[0098] The light source may have an extent / height along the secondary axis, e.g. arranged for emitting light from an area defined by a height being greater than the width such as a rectangular area. The radiation pattern in a horizontal plane is Lambertian.

[0099] The height of the light source from the bottom light emitter to the top light emitter is at least 50 %, or 80 %, or 90 % of the height of the light modulator.

[0100] An elongated light source may be made using an assembly of an LED optically coupled to a light guide being transmissive on one side along the length of the light guide. Or it could be made using plurality of light emitters such as LEDs arranged in a column with a vertical diffuser in front. The vertical diffuser may have a full width half maximum (FWHM) light intensity in a range 10 to 60 degrees in a vertical plane. OLEDs could also be used. In this case the OLED may comprise a Fabry Perot cavity.

[0101] % reflective surface

[0102] A pair of reflective surfaces including a first reflective surface and a second reflective surface 6a, 6b may be located at the top and bottom of the display pixel.

[0103] The pair is arranged between the light source and the light modulator, e.g. between the plane of the light source and the plane of the light modulator. For a horizontal resolution of viewing zones the first reflective surface is at the top of the display pixel in a substantially horizontal plane between the backplane (which is vertical) and the light modulator plane (which is also vertical). The second reflective surface is at the bottom of the display pixel in a substantially horizontal plane between the backplane and the light modulator plane. The two reflective surfaces face each other such that the light source appears as extending infinitely along the secondary axis, e.g. it appears to fill out the full height of the light modulator as seen from the observer independent of the (vertical) viewing angle of the observer.

[0104] When a plurality of display pixels are arranged in a module the reflective surfaces may be arranged at the top and bottom of the module as described for fig. 7, e.g. in that case the individual display pixels in the module does not need reflective surfaces.

[0105] Instead of a reflective surface at the top, the light source may have a part that extends along the top of the display pixel towards the light modulator, e.g. the light source may be L-shaped (having a part extending along the backpanel and a part extending along the top side of the display pixel.

[0106] Instead of a reflective surface at the bottom, the light source may have a part that extends along the bottom of the display pixel towards the light modulator, e.g. the light source may be L-shaped (having a part extending along the backpanel and a part extending along the bottom side of the display pixel.

[0107] A reflective surface may extend from the back of the display pixel towards the front, but preferably not all the way to the front, e.g. a reflective surface may stop before the front. The stop may be at a distance to the light modulator- for example the distance may be up to 25 % or 50 % of the distance between the light source and the light modulator.

[0108] % light guide

[0109] A diffuser / l ight guide may be arranged in front of the elongated light source.

[0110] The diffuser may be tapered, e.g. having a smaller area at the free end than at the base where the light source is.

[0111] Fig. 4 illustrates an example of a timing diagram for a Hybrid Modulation scheme, where the light source is monochrome and is modulated by cycling it through a series of pulses. Three timing diagrams are shown in fig. 4, e.g. the display pixel can display different pixel values to three different viewing zones (A, B and C). Thus, there is a timing diagram for the one or more light valves (A, B and C) for each of the three viewing zones (each viewing zone may be so wide that more than one light valve modulates light for each viewing zone). In the following it is assumed that one or more light valve modulates light per viewing zone.

[0112] % frequency

[0113] At the top in the figure is shown how the light source is controlled / pulsed during a cycle / time window - the duration of which is illustrated by the time axis below the pulses, e.g. during a time window (of length T) the light source is pulsed 8 times. The time window corresponds to a frame, e.g. the time window in which an image is presented to an observer. Typically, a display has a frame rate of 60 frames per second, but it may be higher. If it is lower flickering may be observed.

[0114] The frequency f (how many times the cycle / time window is repeated per unit of time) may be fast enough for the received light to be integrated on a retina of the observer so it appears steady illuminated. It is the inverse of the length of the time window (f = 1 / T). The duration of the time window is from the raising edge of the first pulse in the timing diagram to the raising edge (shown as dotted line) of the next time window.

[0115] The number of steps in a multiplexing cycle for the display pixel may defined by the number of times the light source is switched on, e.g. eight times in the example.

[0116] Each time the light emitter is switched on it may be switched on by a signal having a different pulse width and / or amplitude.

[0117] The maximum number of viewing zones is defined by the number of light valves in the display pixel. % pulses

[0118] The 8 pulses each have an optical energy (x) being a power of 2, e.g. xA2. This means that the light source emits 8 light flashes with 8 different energies (measured in Joules).

[0119] Above each pulse is stated a number representing the optical energy.

[0120] The optical power of a pulse may be calibrated / defined either by a duration of the pulse or an amplitude of a pulse or by a combination, e.g. each time the light source is switched on it may be switched on by a signal having a different pulse width and / or different pulse amplitude.

[0121] % zones A, B, C

[0122] What can be observed / measured in the three zones during the time window is illustrated below each timing diagram.

[0123] A timing diagram depends on the brightness value that the display pixel is to display (for a viewing zone), e.g. each pixel in a monochrome image comprises a brightness value.

[0124] For light valve(s) A the timing diagram shows 7 pulses (the light valve(s) is open during a pulse - not withstanding raise and fall transitions, e.g. each pulse is comprised within a time interval during which light valves are either fully open or fully closed, e.g. light pulses fall outside of light valve transition intervals.

[0125] Thus, when a light valve is open during the same time interval as the light source generates a light flash that light flash can be detected in viewing zone A.

[0126] For viewing zone A the 7 flashes are integrated by the observer’s brain and this integral is the perceived grey scale of the display pixel in viewing zone A, e.g. for a viewing zone the sum of the optical energies (of each pulse / light flash) multiplied by the duration of the time window substantially equals an optical power corresponding to a brightness value.

[0127] 4 light flashes are transmitted to viewing zone B, and 3 light flashes are transmitted to viewing zone C.

[0128] % grey scale space

[0129] Thus, the grey scale value to be perceived in the different viewing zones may be found as a function of how the light valve for a respective viewing zone is controlled during the time window, e.g. during the time window in which the light source is switched on a number of times with different pulse widths and / or amplitudes the light valves may be switched between being open and closed a number of times - depending on the grey scale value to be perceived in the different viewing zones.

[0130] If the light valve for a respective viewing zone is open for all the pulses during the whole cycle / time window a pixel having maximum brightness will be observed when observing the display pixel in that respective viewing zone.

[0131] If the light valve for a respective viewing zone is closed during the whole cycle / time window a pixel being dark (light intensity / grey scale being 0) will be observed when observing the display pixel in that respective viewing zone, e.g. an observer in the respective viewing zone will observe a black pixel when observing the respective display pixel.

[0132] A grey scale / light intensity between zero and maximum for a respective viewing zone can thus be achieved by synchronizing the light valve for that viewing zone with the pulsing of the light source, e.g. selecting or determining by a controller at which pu Ises / I ight flashes that a light modulator is to be open.

[0133] The example shows 8 pulses corresponding to 8 bits (binary digits). Thus, the grey scale range / space comprises 2A8 = 256 values. For each of the bits the controller may set a light valve to open during a corresponding pulse if the bit is 1 and to closed if the bit is 0.

[0134] The grey scale space may be increased, e.g. it is assumed that a number of light valves modulates light for a viewing zone, and a sub number of these light valves (such as every other) generates a first possible grey scale value, and the rest of the light valves generates a second possible grey scale value. The observer in the viewing zone will then perceive an average of the two generated grey scale values, e.g. there may be a target grey scale value, the first grey scale value may be below the target and the second may be above the target.

[0135] If each pulse has the same amplitude, but different widths the pulse widths can for example be:

[0136] 2A0*tt, 2A1*tt, 2A2*tt, 2A3*tt, 2A4*tt, 2A5*tt, 2A6*tt, 2A7*tt. where tt for example could be 1 ms. In that case the absolute values of the pulse widths are in ms:

[0137] 1 , 2, 4, 8, 16, 32, 64, 128

[0138] % DC balance

[0139] After a light valve has been open or closed during a time interval the controller may set it to the opposite state for a substantially equal time interval during which the light source is dark, to maintain a DC balance over liquid crystals in the light valve.

[0140] % skips a pulse

[0141] The light source may be pulsed a different number of times in one time window than in another, for example one time window may comprise 8 pulses and another time window may comprise less than 8 pulses such as 7. This may achieve a better dark level for observation angles where deep dark is desired, even if the contrast of a practical implementation of the light modulator 1 is limited.

[0142] % example In the following is given an example with three different pulse widths, e.g. a time window with three steps. The pulses are 1 ms in the first step / first pulse, 2 ms in the second step / second pulse and 4 ms in the third step / third pulse.

[0143] For three different pulses there are 2A3 = 8 combinations of brightness / light in- tensities / grey scale values, because a light valve is operated binary.

[0144] In the table a “0” means that a light modulator is closed, and a “1” means that it is open. The table shows the 8 different possible light intensities that 8 zones can have.

[0145] It is assumed that a given pulse width applied to the light emitter causes the light source to emit light at an intensity being a factor X times the pulse width.

[0146] Since the display pixel can achieve different brightness to different zones a collection of display pixels can display different images to different zones. For example, half of the zones could show one image and the other half could show another image.

[0147] % puls modula

[0148] Instead of driving the light source with a plurality of different signal pulses during a frame, the light source may be operated / controlled with substantially identical signal pulses.

[0149] In this latter case the light flashes / energy transmitted through a light valve may be generated by different signal pulses to the light valves, e.g. during the frame a light valve is open a plurality of times - each time it is open in a different amount of time. Thus, a first light valve may be open a first plurality of times during the frame and a second light valve may be open a second plurality of times during the frame. They may also be open the same plurality of times, but in on of them the first light valve may be open for a longer or shorter amount of time than the other light valve.

[0150] % blanking period

[0151] Each time a light valve has been open for an amount of time it may be closed for the same amount of time immediately after it has been open for maintaining a DC balance in the light valve.

[0152] Fig. 5 illustrates an example of a time window with a timing diagram for one viewing zone for a configuration for a full color pixel.

[0153] In this case the light source comprises three “sub” light sources such as a tricolor LED - each emitting light at different wavelengths. It could be primary colors such as red, green and blue. The three light sources could be made using a monochrome light emitter with three different color filters in front.

[0154] Each light source may be operated as described above for fig. 4. The brain of the observer will then integrate the light flashes in the different colors to a perceived light intensity and perceived color at that light intensity.

[0155] Thus, each light source is pulsed a number of times with different amplitudes and / or pulse widths during a time window, e.g. each light source may be operated as described above for fig. 4.

[0156] The pulses for each color is shown at the top of the figure. Below is the timing diagram. In this case the time window comprises three times as many pulses as for the monochrome version.

[0157] In the figure the red light source is pulsed 8 times followed by pulsing the green light source 8 times and finally pulsing the blue light source 8 times.

[0158] For the frame / time window the specific light valve is open for 7 of the red pulses, 4 of the green pulses and 4 of the blue pulses. This produces an RGB value / color of (R,G,B)=(191 ,39,83).

[0159] The order / sequence of the pulses for the different colors may be different, e.g. in general, during a time window the light sources may be controlled to emit a sequence of light flashes comprising light flashes in different colors. The sequence may comprise a first number of light flashes in a first color, a second number of light flashes in a second color and a third number of light flashes in a third color.

[0160] In fig. 6 the light-flashes in different colors alternates between each other, e.g. first a red light flash is generated, then a green followed by a blue whereafter a red light flash is generated and so forth. The light valve has a timing diagram producing an RGB value / color of (R,G,B)=(97,10,196). Fig. 7 illustrates a perspective view from top-back of an example of a module with a plurality of display pixels.

[0161] The module comprises 9 display pixels.

[0162] The light source comprises a light guide.

[0163] The light source is arranged to the side / at the edge of the backplane, specifically the light source comprises a part at the left edge and a part at the right edge, e.g. two light emitters. The two parts of the light source are optically coupled to the light guide.

[0164] The light guide comprises a number of outcoupling structures including a first outcou- pling structure 7 (where light is emitted from the light guide). In the example there are three vertical extending outcoupling structures (extending from top to bottom of the module).

[0165] Instead of having a light guide, the light source may comprise three elongated light emitters extending from the top to bottom of the module.

[0166] Instead of having an elongated light source, each pixel may comprise a point light source as the display pixel in fig. 1.

[0167] At the top and bottom of the display module may be located reflective surfaces such as mirrors or silver coating (not shown in fig. 11) to make the light guide outcoupling areas appear to fill out the light modulator fully vertically. The reflective surfaces are arranged between the light source and the light modulator. Such reflective surfaces may be omitted in the case of point light sources for each display pixel.

[0168] % operation oclulle in general

[0169] All the display pixels in a module (whether it is the module in fig. 7, 9 or 11) may be controlled in parallel, e.g. generate the same pixel value for each viewing zone. Only a part of the display pixels in a module may be active for decorative purposes for example, e.g. the active display pixels may be the 8 display pixels along the sides (the center display pixel not being active). Fig. 8 illustrates an example of a display pixel.

[0170] As for the examples previously mentioned this example also comprise a flex PCB. For example, having an L-shape (a bottom and a side extending upwards from the bottom). At the bottom of the display pixel is the controller (mounted to the bottom of the flex PCB).

[0171] The light source is at the back (mounted to the side of the PCB extending upwards from the bottom), and the light modulator is at the front of the display pixel.

[0172] The light source is not a point light source but elongated as the light source for fig. 3. Preferably the light source extends from the bottom to the top of the display pixel.

[0173] In the example of fig. 8 the light source emits mono chrome (white) light which may be generated by an alternating pattern of red, green and blue light emitters. All of the light emitters may be arranged in a (single) column. In fig. 12 there are 12 sets of light emitters (a set having one red, one green and one blue light emitter).

[0174] The three different colors could also be placed side by side horizontally, e.g. one column with red light emitters, one column with green light emitters, and one column with blue light emitters.

[0175] In front of the light source is a vertical diffuser or light guide 8. It has an extent along the secondary axis and the base is above the area of the light source. It may have a cross section in the shape of a cone with the base facing the light source.

[0176] % light modulator

[0177] Contrary to the previous examples the light modulator comprises three sets or pluralities of light valves.

[0178] There is a first plurality of light valves for modulating a light intensity from the light source to a plurality of viewing zones for a first primary color / wavelength range. And there is a second plurality of light valves for modulating a light intensity from the light source to a plurality of viewing zones for a second primary color / wavelength range. And there is a third plurality of light valves for modulating a light intensity from the light source to a plurality of viewing zones for a third color / wavelength range. The light valves in a set are arranged next to each other in a row (along the primary axis for a resolution of viewing zones along the primary axis), and there are three rows. In each row there are light valves from one (single) set of light modulators, e.g. a row comprises exclusively light modulators for one primary color.

[0179] The top row is for red color, the middle row is green color, and the bottom row is for blue color. However, any order can be contemplated as long as the sets are arranged vertically / along the secondary axis, e.g. on top of each other - on set positioned higher than the other.

[0180] It could be said that this example has RGB subpixels arranged along the secondary axis.

[0181] Either in front or behind the light valves of the first set is a first color filter (for transmitting a first wavelength range - red color in the example). And either in front or behind the light valves of the second set is a second color filter. And either in front or behind the light valves of the third set is a third color filter.

[0182] % analog light valves

[0183] Contrary to the examples in figs. 1 to 7 the light valves are not binary operated, but analog operated, and the light source is not pulsed with different pulses but constant (for examples pulsed with the same pulse at each clock pulse).

[0184] Thus, the signal to a light valve is not some factor multiplied to 0 and 1 (or 1 and -1), but a scale ranging from for example 0 to 256 (8 bit space). Thus, the light valve transmission is not 0 or 1 , but 256 points between 0 and 1 . This is illustrated by the following table where the light modulation / the transmitted light intensity for three light valves modulating light for each color for a first zone (zone 1) and three light valves modulating light for each color for a second zone (zone 2): Each light modulator is elongated in a vertical direction, e.g. having a height greater than a width. A quadratic geometry may also be contemplated.

[0185] The height of the display pixel (measured from the bottom of the lowest positioned set of light valves to the top of the highest positioned set of light valves) is greater than the distance between the light source and the light valves - when measured in a horizontal plane.

[0186] % upper and lower band Each set of light valves may be arranged in two rows, e.g. a top row and a bottom row. A top light valve and a light value it may modulate light at two different values and an average of these two values may be observed such that the color space is increased.

[0187] % passive matrix The display pixel may comprise three scan lines, one for each set of light valves, for driving the light valves according to a passive matrix driving scheme.

[0188] Fig. 9 illustrates a front view of an example of a module with a plurality of display pixels.

[0189] The module comprises 9 display pixels. Each display pixel corresponds to the display pixel described in connection with fig. 8 with the exception that there is no mirror chamber at each display pixel. Instead there is a reflective surface at the top of the module and a reflective surface at the bottom of the module - the two reflective surfaces facing each other.

[0190] The light source may comprise a light guide with three elongated outcoupling structures, e.g. a light source as the one described for fig. 7 with the exception how the light source is operated. For fig. 7 it is pulsed with different pulses and for fig. 9 it is constant.

[0191] The module may comprise a bezel, e.g. black area between an edge of a display pixel and the edge of the module. The reflective surfaces may be arranged before the bezel or the light source may extend across the bezel in which case a reflective surface is optional if the bezel is wide enough. If it is not wide enough the reflective surface may be arranged at the end of the light source, e.g. at the other side of the bezel than a display pixel.

[0192] Fig. 10 illustrates an example of a display pixel.

[0193] The display pixel has three sub pixels, a red, green and blue.

[0194] Each sub pixel is made in the same way as the display pixel of fig. 3, e.g. with an elongated light source and a light modulator in front. The difference being that each sub pixel is mono chrome, e.g. emitting light in a wavelength range corresponding to a primary color.

[0195] The sub pixels are arranged in a column, e.g. the red sub pixel is at top, the green sub pixel is below the red, and the blue sub pixel is lowest (below the green). Another or- der / sequence along the secondary axis may be contemplated.

[0196] The sub pixels are divided / separated by reflective surfaces, e.g. each sub pixel comprise a pair of reflective surfaces facing each other. Such reflective surfaces have also been described for fig. 3, and the reflective surfaces in the example of fig. 10 serves the same purpose as described for fig. 3. Each light source emits light in a wavelength range, e.g. the red subpixel has a light source emitting red light, the green subpixel has a light source emitting green light, and the blue subpixel has a light source emitting blue light. The light sources may be made using a white light emitter with a color filter in front. The color filters may also be placed in front of the light modulators.

[0197] Each light modulator comprises a plurality of light valves - each light valve preferably being elongated in the same direction as the light source.

[0198] The display pixel may be operated as described in connection with fig. 4, e.g. each light source is pulsed with a different pulse width and / or pulse height from one pulse to another, and each light valve is binary operated.

[0199] As an alternative, the display pixel may be operated as described in connection with fig. 8, e.g. each light source emits a constant light intensity during a frame, and each light valve modulates the light intensity to a shade / value - it is operated “analog’Vquan- tized to more than 2 values.

[0200] Fig. 11 illustrates a front view of an example of a module with a plurality of display pixels.

[0201] The module comprises 9 display pixels. Each display pixel corresponds to the display pixel described in connection with fig. 10.

[0202] An overview of the different solutions can be seen in the below table.

[0203] Now follows a set of items, which constitute aspects of the present disclosure which may be considered independently patentable and as such the following sets form basis for possible future sets of claims:

[0204] 1. A display pixel for a large multiview video screen for displaying a first image to a first viewing zone and a second image to a second viewing zone, said display pixel comprising:

[0205] - a light source such as a light emitting diode,

[0206] - a light modulator including a first plurality of light valves such as liquid crystal cells arranged in front of said light source including a first light valve for modulating light to said first viewing zone and a second light valve for modulating light to said second viewing zone.

[0207] 2. The display pixel according to any of the preceding items, comprising: a controller arranged for controlling said display pixel.

[0208] % light modulator

[0209] 3. The display pixel according to any of the preceding items, said first plurality of light valves arranged along a primary axis.

[0210] 4. The display pixel according to any of the preceding items, said first plurality of light valves comprising at least 10 light valves.

[0211] 5. The display pixel according to any of the preceding items, each light valve being elongated along a secondary axis substantially orthogonal to said primary axis.

[0212] 6. The display pixel according to any of the preceding items, said controller arranged for controlling a plurality of neighboring light valves with a first driving signal.

[0213] % light source

[0214] 7. The display pixel according to any of the preceding items, said light source being elongated along a secondary axis substantially orthogonal to said primary axis, and having an extent at least 50 % of the extent of said light modulator along said secondary axis.

[0215] 8. The display pixel according to any of the preceding items, said light source having a width not greater than the width of said first light valve.

[0216] % PWM and / or PAM

[0217] 9. The display pixel according to any of the preceding items, each light valve switching between two states including a light transmitting state for transmitting light from said light source or a light shielding state for shielding light from said light source.

[0218] 10. The display pixel according to any of the preceding items, said controller arranged such that said display pixel generating a first image pixel in said first image during a time window and generating a second image pixel in said second image during said time window, said light source switched on a plurality of times during said time window by a plurality of signal pulses, said plurality of signal pulses being different from each other such that said light source emitting light at different Joules each time said light source being switched on during said time window, and during said time window said first light valve being in said light transmitting state a different number of times than said second light valve when said first image pixel and said second image pixel having pixel values different from each other.

[0219] % analog operation

[0220] 11. The display pixel according to any of the preceding items, said light modulator comprising a second plurality of light valves for modulating a light intensity from said light source, and a third plurality of light valves for modulating a light intensity from said light source.

[0221] 12. The display pixel according to any of the preceding items, comprising: a first color filter for transmitting a first wavelength range of light to or from said first first plurality of light valves, a second color filter for transmitting a second wavelength range of light to or from said second plurality of light valves, and and a third color filter for transmitting a third wavelength range of light to or from said third plurality of light valves.

[0222] 13. The display pixel according to any of the preceding items, said first plurality of light valves positioned higher than said second plurality of light valves, and said second plurality of light valves positioned higher than said third plurality of light valves.

[0223] % mirror chamber

[0224] 14. The display pixel according to any of the preceding items, comprising: a first reflective surface for reflecting light from said light source, and a second reflective surface for reflecting light from said light source, said second reflective surface preferably facing said first reflective surface.

[0225] 15. The display pixel according to any of the preceding items, said first reflective surface arranged between said light source and said light modulator, and said second reflective surface arranged between said light source and said light modulator.

[0226] 16. The display pixel according to any of the preceding items, said light source arranged between said first reflective surface and said second reflective surface.

[0227] 17. The display pixel according to any of the preceding items, said display pixel having a top and a bottom, said first reflective surface arranged at said top, and said second reflective surface arranged at said bottom. % module

[0228] 18. A module for a large multiview video screen for displaying a first image to a first viewing zone and a second image to a second viewing zone, comprising: a plurality of the display pixels according to any of the preceding items.

[0229] 19. The module according to any of the preceding items, comprising: a top, and a bottom, and a first reflective surface at said top, and a second reflective surface at said bottom, said second reflective surface facing said first reflective surface.

[0230] 20. The module according to any of the preceding items, comprising: a controller arranged for controlling said plurality of display pixels in parallel such that each display pixel in said module generating the same pixel value for each viewing zone.

Claims

Claims1 . A display pixel for a large multiview video screen for displaying a first image to a first viewing zone and a second image to a second viewing zone, said display pixel comprising:- a light source such as a light emitting diode,- a light modulator including a first plurality of light valves such as liquid crystal cells arranged in front of said light source including a first light valve for modulating light to said first viewing zone and a second light valve for modulating light to said second viewing zone, said first plurality of light valves comprising at least 10 light valves arranged along a primary axis, each light valve switching between two states including a light transmitting state for transmitting light from said light source or a light shielding state for shielding light from said light source,- a controller arranged such that said display pixel generating a first image pixel in said first image during a time window and generating a second image pixel in said second image during said time window, said light source switched on a plurality of times during said time window by a plurality of signal pulses, said plurality of signal pulses being different from each other such that said light source emitting light at different Joules each time said light source being switched on during said time window, and during said time window said first light valve being in said light transmitting state a different number of times than said second light valve when said first image pixel and said second image pixel having pixel values different from each other.

2. The display pixel according to any of the preceding items, said light source having a width not greater than the width of said first light valve.

3. The display pixel according to any of the preceding items,said light source being elongated along a secondary axis substantially orthogonal to said primary axis, and having an extent at least 50 % of the extent of said light modulator along said secondary axis.

4. A module for a large multiview video screen for displaying a first image to a first viewing zone and a second image to a second viewing zone, comprising: a plurality of the display pixels according to any of the preceding items.

5. The module according to any of the preceding items, comprising: a top, and a bottom, and a first reflective surface at said top, and a second reflective surface at said bottom, said second reflective surface facing said first reflective surface.

6. The module according to any of the preceding items, comprising: a controller arranged for controlling said plurality of display pixels in parallel such that each display pixel in said module generating the same pixel value for each viewing zone.

Images