Privacy display device

Abstract

A control system for a switchable privacy display device includes an ambient light sensor and a display brightness controller, and the display brightness controller is arranged to control the brightness of a display in response to a measured illuminance. High image visibility is provided for common mode operation, while in the privacy mode, a visual safety level higher than a perceived privacy threshold can be obtained by controlling the image brightness in response to the output of the ambient light sensor.

Description

Technical Field

[0001] The present disclosure generally relates to illumination from a light modulation device, and more particularly to the control of privacy displays. Background Art

[0002] Privacy displays provide image visibility to a primary user (typically located in a coaxial position) and reduced visibility of the image content to a snoop (typically located in an off-axis position). The privacy function can be provided by a micro-louver optical film that transmits some light in the coaxial direction from the display and low luminance in the off-axis position. However, such films have high losses for front illumination, and due to pixel jitter of the spatial light modulator, the micro-louvers may cause Moiré artefacts. The pitch of the micro-louvers may need to be selected for the panel resolution, increasing inventory and cost.

[0003] A switchable privacy display can be provided by controlling the off-axis optical output.

[0004] The control can be provided by means of luminance reduction, for example by means of a switchable backlight for a liquid crystal display (LCD) spatial light modulator. Display backlights typically employ waveguides and edge-emitting sources. Some imaging directional backlights have the additional ability to direct illumination through the display panel to the viewing window. An imaging system can be formed between multiple sources and the corresponding window images. An example of an imaging directional backlight is an optical valve that can employ a folded optical system and can thus also be an example of a folded imaging directional backlight. Light can propagate through the optical valve with substantially no loss in one direction, while the light propagating in the reverse direction can be extracted by reflecting inclined facets, as described in U.S. Patent No. 9,519,153, which is incorporated herein by reference in its entirety.

[0005] In known privacy displays, the privacy mode is provided by adding a removable louver film such as that sold by 3M, which the user may not be able to install or remove reliably, and thus in practice, the user does not deliberately attach the louver film every time they are outside the office. In another known privacy display, the control of the privacy mode is electronically activated, but the control is attributed to the user who must perform a keystroke to enter the privacy mode. Summary of the Invention

[0006] According to a first aspect of the present disclosure, there is provided a privacy display device, the privacy display device comprising: a display device arranged to display an image, the display device being capable of providing a privacy function, wherein the visibility of the image to an off-axis viewer is reduced compared to the visibility of the image to an on-axis viewer; a control system arranged to control the display device; and an ambient light sensor arranged to detect an illumination level of ambient light, wherein the control system is arranged to control the brightness of the displayed image based on the detected level of the ambient light according to a transfer function, and when providing the privacy function, the transfer function maintains the relationship Y 最大 ≤Y 上限 ,wherein Y 最大 is the maximum output brightness of the display device, and Y 上限 is given by the following equation:

[0007]

[0008] wherein the equation for Y 上限 applies to an observation direction at a polar angle θ of 45° with respect to the normal of the display device at at least one azimuth angle around the normal of the display device, I is the detected level of the ambient light, the unit of I is the unit of Y 最大 multiplied by a solid angle in steradians, ρ(θ = 45°) is the reflectivity of the display device along the observation direction, P(θ = 45°) is the ratio of the brightness of the display device along the observation direction to the maximum output brightness Y 最大 of the display device, and S 最小 has a value of 1.0 or greater.

[0009] It is desirable to optimize the visibility of the displayed image to an on-axis viewer based on the detected level of the ambient light for the brightness control of the displayed image. By performing such control according to the transfer function that maintains the relationship Y 最大 ≤Y 上限 when providing the privacy function, even if the illumination level of the ambient light and the brightness of the display device change, the visual safety level of the operation of the display device can be maintained at the limit S 最小 or below in the observation direction. By maintaining the visual safety level at the limit S 最小 or below, an off-axis viewer in this observation direction cannot actually perceive the displayed image.

[0010] Advantageously, the value of S 最小 can be 1.5 or greater. Such an increased S 最小The limit achieves a higher level of visual security where the image is invisible to off-axis viewers, i.e., for most images and most viewers, even when the image is being displayed, the viewer cannot perceive it.

[0011] Advantageously, the value of S 最小 can be 1.8 or greater. Such an increased value of S 最小 The limit achieves a higher level of visual security where the image is invisible to all viewers, regardless of the image content.

[0012] where the display device has a symmetric major axis and minor axis, and the equation of Y 最大 can be applied to an observation direction at a polar angle θ of 45° with respect to the normal of the display device at an azimuth angle corresponding to either or both of the major axis (to achieve an advantage with respect to off-axis viewers when the display device is used in a landscape orientation) or the minor axis (to achieve an advantage with respect to off-axis viewers when the display device is used in a portrait orientation).

[0013] Advantageously, the control system is arranged such that when the privacy function is provided, it controls the brightness of the displayed image based on the detected level of the ambient light according to the transfer function maintaining the relationship Y 最大 ≥ Y 下限 where Y is given by the following equation: 下限 is given by:

[0014]

[0015] where the equation of Y 下限 is applicable to an observation direction at a polar angle θ of 10° with respect to the direction of the maximum output brightness of the display device at at least one azimuth angle around the direction of the maximum output brightness of the display device. ρ(Δθ = 10°) is the reflectance of the display device along the observation direction at a polar angle θ of 10° with respect to the direction of the maximum output brightness of the display device, P(Δθ = 10°) is the ratio of the brightness of the display device along the observation direction at a polar angle θ of 10° with respect to the direction of the maximum output brightness of the display device to the maximum output brightness Y 最大 of the display device, and the value of S 最大 is 0.1 or less.

[0016] By further controlling the brightness of the displayed image according to the transfer function maintaining the relationship Y 最大 ≥ Y 下限 when the privacy function is provided, the visibility of the displayed image to on-axis viewers is maintained.

[0017] In some cases, an ambient light sensor can detect the illuminance level of ambient light incident on the display device in a non-directional manner. In such cases, the detected level I represents an average level such that the effects of the technology of the present invention are achieved for off-axis viewers at different positions.

[0018] In other cases, the ambient light sensor can detect the ambient light illuminance level incident on the display device along the incident direction to be reflected to the viewing direction. In such cases, the effects of the technology of the present invention can be specifically optimized for off-axis viewers in the viewing direction.

[0019] The display device can be capable of operating at least in a public mode and in a privacy mode, where the privacy function is provided in the privacy mode, and compared with the public mode, the visibility of the image for off-axis viewers is reduced. The control system can selectively operate the display device in the public mode or the privacy mode for at least one area of the display device. This provides selective operation in the public mode or the privacy mode, depending on the use of the display device. By way of example, the privacy mode can be used in public places such as cafes or trains to enable the primary user to continue working, but prevent bystanders or snoops from being able to see or photograph data from the screen, and the public mode can be used, for example, when discussing the content on the screen with colleagues within a company office.

[0020] The control system can be arranged to selectively operate the display device in the public mode or the privacy mode in response to the detected level of the ambient light.

[0021] In the case where the display device includes a backlight and a transmissive spatial light modulator arranged to receive light from the backlight, the control system can be arranged to control the brightness of the displayed image by controlling the brightness of the backlight and / or by controlling the light transmission performed by the spatial light modulator.

[0022] In the case where the display device includes an emissive spatial light modulator, the control system can be arranged to control the brightness of the displayed image by controlling the light emission performed by the spatial light modulator.

[0023] According to a second aspect of the present disclosure, there is provided a display device, the display device comprising: a display means arranged to display an image and capable of operating at least in a public mode and in a privacy mode, wherein in the privacy mode, the visibility of the image to an off-axis viewer is reduced compared to the public mode; and the visibility of the coaxial image is maintained in the privacy mode; and a control system arranged to control the display means, the control system capable of selectively operating the display means in the public mode or the privacy mode includes an ambient light sensor arranged to detect the ambient light level.

[0024] The privacy mode can be used in public places such as cafes or trains to enable the primary user to continue working while preventing onlookers or snoops from being able to see or photograph data from the screen. The public mode can be used when discussing the content on the screen with colleagues, for example, within a corporate office.

[0025] Advantageously, the operation of the privacy mode can be independent of user preferences, such that control over the exposure of private data can be provided to an organization when used in a public place without the user's consent.

[0026] The control system can be arranged to selectively operate the display means in the public mode or the privacy mode in response to the detected level of the ambient light.

[0027] The control system can be arranged to selectively control any one or more of the brightness, contrast, white point, and spatial frequency of the image in the privacy mode in response to the detected level of the ambient light. The control system can be arranged to selectively control any one or more of the brightness, contrast, white point, and spatial frequency of the image in the public mode in response to the detected level of the ambient light. Advantageously, the visual safety level of the display operation can be optimized for the illuminated environment. Additional image appearance for the primary user during privacy display operation can be increased in response to the type of privacy image being displayed.

[0028] Taking into account the detected level of the ambient light, the control system can be arranged to selectively control the display means to display information representing the visibility of the image to an off-axis viewer. Advantageously, information about the visual safety of the environment can be provided to the display user to enable a reliable decision to be made about viewing confidential data.

[0029] The control system can be arranged to control the display means to display information representing a change in a user-controllable parameter that can reduce the visibility of the image to an off-axis viewer. Advantageously, the visual safety level can be reduced while achieving comfortable viewing of the image data for the primary user, depending on the user's preference for image viewing.

[0030] The control system may be arranged to selectively control the brightness of the displayed image in the public mode and in the privacy mode in response to the detected level of the ambient light, using different transfer functions that correlate the brightness level with the detected level of the ambient light in the public mode and in the privacy mode.

[0031] Compared to the transfer function in the privacy mode, the transfer function in the public mode may correlate a higher brightness level with the detected level of the ambient light. Advantageously, a high level of visual security can be provided to snoopers in the privacy mode for a wide range of ambient light conditions, and high image visibility can be provided to the user in the public mode for a wide range of ambient light conditions.

[0032] The control system may be arranged to selectively control the brightness of the displayed image in the privacy mode in response to the detected level of the ambient light, according to a transfer function that maintains the relationship Y 最大 / I ≥ 1 lux / nit, where Y 最大 is the maximum output brightness of the display device measured in nits, and I is the detected level of the ambient light measured in lux. Advantageously, a high level of visual security is observed for varying ambient light levels and desired image visibility is provided to the display user.

[0033] The control system may be arranged to selectively control the brightness of the displayed image in the privacy mode in response to the detected level of the ambient light, according to a transfer function that maintains the relationship Y 最大 ≤ Y 极限 , where Y 极限 is given by the following equation:

[0034]

[0035] where V 极限 has a value of 10, Rθ is the ambient illuminance reflected at an observation angle θ of 45 degrees lateral to the normal of the display device and a zero elevation angle, Kθ is the display black state brightness at the observation angle, and Pθ is the relative brightness at the observation angle θ compared to the maximum display output brightness Y 最大 .

[0036] The control system may be arranged to control the display device to display information representing the visibility of the image to off-axis viewers. Advantageously, the visual security level of the display device can be optimized.

[0037] In this document, public and private refer to the display mode, rather than the nature of the location. For example, the privacy (display) mode is usually selected in public places such as coffee shops, while the public (display) mode is usually selected in private places such as at home.

[0038] Any aspect of the present disclosure can be applied in any combination.

[0039] Embodiments of the present disclosure can be used in various optical systems. The embodiments can be included or used with a variety of projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, self - contained projector systems, vision and / or audio - visual systems, and electrical and / or optical devices. Various aspects of the present disclosure can actually be used with any device related to optical devices and electrical devices, optical systems, presentation systems, or any device that can contain any type of optical system. Thus, embodiments of the present disclosure can be used in optical systems, devices for visual and / or optical display, visual peripherals, etc., as well as in a variety of computing environments.

[0040] Before entering into the detailed disclosed embodiments, it should be understood that the present disclosure is not limited to the details of the specific settings shown in terms of its application or creation, as the present disclosure is capable of having other embodiments. In addition, various aspects of the present disclosure can be presented in different combinations and settings to define unique embodiments in terms of their own rights. Moreover, the terms used herein are for the purpose of description and not limitation.

[0041] By reading the entire content of the present disclosure, these and other advantages and features of the present disclosure will become obvious to those of ordinary skill in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments are shown by way of example in the drawings, where like reference numerals indicate like parts, and wherein:

[0043] Figure 1 is a schematic front - view showing a privacy display including a privacy control system operating in a privacy mode at a first visual security level;

[0044] Figure 2 is a schematic top - view showing a privacy display including a privacy control system operating in a privacy mode at a first visual security level;

[0045] Figure 3 is a schematic diagram showing the output brightness of a typical collimated backlight varying with the viewing angle, the collimated backlight being arranged to cooperate with a switchable retarder to provide a high visual security level for a wide range of snooper positions;

[0046] Figure 4is a schematic diagram showing the variation of the visual safety level with the off-axis relative luminance of a switchable privacy display operating in the privacy mode;

[0047] Figure 5 is a schematic diagram showing the reflectance of two types of privacy displays varying with the polar angle;

[0048] Figure 6 is a schematic diagram showing Figure 5 the visual safety levels of two types of privacy displays varying with the polar angle;

[0049] Figure 7A is a schematic diagram showing the transfer function between the front display luminance and the ambient illuminance;

[0050] Figure 7B is a schematic diagram showing the transfer function between the measured ratio of the ambient illuminance to the front display luminance and the ambient illuminance;

[0051] Figure 8A is a schematic diagram showing the safety factor of an illustrative privacy display operating in the privacy mode varying with the polar angle at a lux / nt ratio of 3.0;

[0052] Figure 8B is a schematic diagram showing the safety factor of an illustrative privacy display operating in the public mode varying with the polar angle at a lux / nt ratio of 0.5;

[0053] Figure 8C is a schematic diagram showing the safety factor of an illustrative privacy display operating in the public mode varying with the polar angle at a lux / nt ratio of 0.5;

[0054] Figure 8D is a schematic diagram showing the safety factor of an illustrative privacy display operating in the privacy mode varying with the polar angle at a lux / nt ratio of 3.0;

[0055] Figure 9A is a schematic diagram showing the user-selectable transfer function between the front display luminance and the ambient illuminance;

[0056] Figure 9B is a schematic flowchart showing the method for operating the user-selectable transfer function;

[0057] Figure 10 is a schematic diagram showing the perceived privacy varying with the visual safety level;

[0058] Figure 11 shows Figure 1-2 and Figure 3-4 the flowchart of the privacy control system;

[0059] Figure 12Ais a schematic diagram showing a top view of a privacy display and an off-axis ambient light sensor;

[0060] Figure 12B is a schematic diagram showing a polar region for ambient illuminance measurement for a privacy display;

[0061] Figure 12C 、 12D and 12E are schematic diagrams showing a top view of an off-axis ambient light sensor for measuring ambient illuminance in a polar region for Figure 12B ;

[0062] Figure 13 is a schematic diagram showing a switchable directional display device including a directional backlight and a switchable liquid crystal retarder in a previous perspective view;

[0063] Figure 14 is a schematic diagram showing an arrangement of a switchable liquid crystal retarder in a privacy operation mode in a perspective side view, the switchable liquid crystal retarder including a passive negative C-plate compensating retarder;

[0064] Figure 15A is a schematic diagram showing the polar and azimuthal variations of the output luminance of a collimated backlight and a spatial light modulator;

[0065] Figure 15B is a schematic diagram showing the polar and azimuthal variations of the transmittance of a switchable retarder arranged between parallel polarizers;

[0066] Figure 15C is a schematic diagram showing the polar and azimuthal variations of the relative reflectance of a switchable retarder arranged between a reflective polarizer and an absorptive polarizer;

[0067] Figure 15D is a schematic diagram showing Figure 13 the polar and azimuthal variations of the total display reflectance in a privacy operation mode;

[0068] Figure 15E is a schematic diagram showing Figure 13 the polar and azimuthal variations of the output luminance in a privacy operation mode;

[0069] Figure 15F is a schematic diagram showing for Figure 13 the polar and azimuthal variations of the visual safety level S of the front display luminance in a privacy operation mode, the value Y of the front display luminance measured in nits 最大 is half of the illuminance I measured in lux;

[0070] Figure 15G is a schematic diagram showing for Figure 13Schematic diagram of the extreme change in the zero-elevation visual safety level S of the front brightness of the display in the privacy operation mode, where the value Y of the front brightness of the display measured in nits 最大 is half of the illuminance value I measured in lux;

[0071] Figure 16 Schematic diagram showing the arrangement of the switchable retarder in the public operation mode in a perspective side view, where the switchable retarder includes a switchable liquid crystal layer with vertical alignment and a passive C-plate compensation retarder;

[0072] Figure 17A Shows Figure 13 Schematic diagram of the extreme change and azimuth change of the output brightness of the arrangement in the public operation mode;

[0073] Figure 17B Shows for Figure 13 Schematic diagram of the extreme change in the zero-elevation visual safety level S of the front brightness of the display of the arrangement in the public operation mode, where the value Y of the front brightness of the display measured in nits 最大 is half of the illuminance value I measured in lux;

[0074] Figure 17C Shows the maximum brightness Y 最大 Schematic diagram of the extreme change and azimuth change of the output brightness whose direction is not perpendicular to the backlight of the display;

[0075] Figure 18A Schematic diagram in a side view showing the propagation of the output light from the spatial light modulator through the Figure 13 optical stack in the privacy operation mode;

[0076] Figure 18B Schematic diagram in a top view showing the propagation of the ambient illumination light through the Figure 13 optical stack in the privacy operation mode;

[0077] Figure 19A Schematic diagram in a side view showing the propagation of the output light from the spatial light modulator through the Figure 13 optical stack in the public operation mode;

[0078] Figure 19B Shows Figure 19A Schematic diagram of the change in the output brightness of the transmitted light with the polar direction in;

[0079] Figure 19C Schematic diagram in a top view showing the propagation of the ambient illumination light through the Figure 13 optical stack in the public operation mode;

[0080] Figure 19Dis a schematic diagram showing Figure 19C the change in reflectance of the reflected light in

[0081] Figure 20 a perspective view showing a switchable directional display device including a directional backlight and two switchable liquid crystal retarders each disposed between a pair of polarizers;

[0082] Figure 21A is a schematic diagram showing the polar and azimuthal angle changes in the output luminance of an emission spatial light modulator;

[0083] Figure 21B is a schematic diagram showing the polar and azimuthal angle changes in the transmittance of a first switchable retarder disposed between a first pair of parallel polarizers;

[0084] Figure 21C is a schematic diagram showing the polar and azimuthal angle changes in the relative reflectance of a first switchable retarder disposed between a reflective polarizer and an absorptive polarizer;

[0085] Figure 21D is a schematic diagram showing Figure 20 the polar and azimuthal angle changes in the total display reflectance of

[0086] Figure 21E is a schematic diagram showing the polar and azimuthal angle changes in the transmittance of a second switchable retarder disposed between a second pair of parallel polarizers;

[0087] Figure 21F is a schematic diagram showing Figure 20 the polar and azimuthal angle changes in the output luminance of

[0088] Figure 21G is a schematic diagram showing for Figure 20 the polar and azimuthal angle changes in the visual safety level S of the front display luminance of 最大 in a privacy operation mode, where the value Y of the front display luminance measured in nits

[0089] Figure 21H is half of the illuminance of the value I measured in lux; and Figure 20 is a schematic diagram showing the polar angle change in the zero elevation visual safety level S of the front display luminance of 最大 in a privacy operation mode, where the value Y of the front display luminance measured in nits DETAILED DESCRIPTION

[0090] Terms related to the appearance of the privacy display will now be described.

[0091] The privacy operation mode of a display is a mode in which an observer sees a low contrast sensitivity such that the image is not clearly visible. Contrast sensitivity is a measure of the ability to distinguish between different brightness levels in a static image. Inverse contrast sensitivity can be used as a measure of visual security because a high level of visual security (VSL) corresponds to low image visibility.

[0092] For a privacy display that provides an image to an observer, visual security can be given as:

[0093] V = (Y + R) / (Y – K) Equation 1

[0094] where V is the visual security level (VSL), Y is the luminance of the white state of the display from the snooper's perspective, K is the luminance of the black state of the display from the snooper's perspective, and R is the luminance of the reflected light from the display.

[0095] The panel contrast is given as:

[0096] C = Y / K Equation 2

[0097] Therefore, the visual security level can be further given as:

[0098] V = (P.Y 最大 + I.ρ / π) / (P.(Y 最大 – Y 最大 / C)) Equation 3

[0099] where: Y 最大 is the maximum luminance of the display; P is the off-axis relative luminance, typically defined as the ratio of the luminance at the snooper's angle to the maximum luminance Y 最大 ; C is the image contrast; ρ is the surface reflectance; and I is the illuminance. The unit of Y 最大 is the unit of I divided by the solid angle in steradians.

[0100] The luminance of the display varies with angle, and thus the maximum luminance Y 最大 of the display occurs at a specific angle depending on the configuration of the display.

[0101] In many displays, the maximum luminance Y 最大 occurs in the front, i.e., perpendicular to the display. Any display device disclosed herein can be arranged to have the maximum luminance Y 最大 occur in the front, in which case the reference to the maximum luminance Y 最大 of the display device can be replaced by a reference to the luminance perpendicular to the display device.

[0102] Alternatively, any display described herein may be arranged to have a maximum luminance Y that occurs at a polar angle greater than 0° with respect to the normal of the display device. 最大 By way of example, the maximum luminance Y 最大 may occur at a non-zero polar angle and an azimuth angle having, for example, a zero lateral angle such that the maximum luminance is for a coaxial user looking down on the display device. For example, the polar angle may be 10 degrees and the azimuth angle may be in the north direction (90 degrees counterclockwise from the east direction). Thus, a viewer may expect to see high luminance at a typical non-vertical viewing angle.

[0103] The off-axis relative luminance P is sometimes referred to as the privacy level. However, such a privacy level P describes the relative luminance of the display at a given polar angle compared to the front luminance and is not actually a measure of the privacy appearance.

[0104] The illuminance I is the luminous flux per unit area incident on the display and reflected from the display towards the observer position. For Lambertian illuminance and a display with a Lambertian front diffuser, the illuminance I does not vary with the polar angle and azimuth angle. For an arrangement of a display with non-Lambertian front diffusion in an environment with directional (non-Lambertian) ambient light, the illuminance I varies with the observed polar angle and azimuth angle.

[0105] Thus, in a completely dark environment, the VSL of a high-contrast display is approximately 1.0. As the ambient illuminance increases, the perceived image contrast decreases, the VSL increases, and a privacy image is perceived.

[0106] For a typical liquid crystal display, the panel contrast C is higher than 100:1 for almost all viewing angles, thus allowing the visual safety level to be approximated as:

[0107] V = 1 + I.ρ / (π.P.Y 最大 ) Equation 4

[0108] In embodiments of the present invention, in addition to the exemplary definition of Equation 4, other measurements of the visual safety level V may be provided, such as including the visibility of the image to a snooper at the snooper's position, the image contrast, the image color and white point, and the effect on the size of the image features facing the image. Thus, the visual safety level may be a measure of the privacy degree of the display, but may not be limited to the parameter V.

[0109] The perceived image safety can be determined from the logarithmic response of the eye such that

[0110] S = log 10 (V) Equation 5

[0111] The desired limit of S is determined as follows. In a first step, a privacy display device is provided. The change P(θ) in the privacy level of a display device having a polar viewing angle and the change ρ(θ) in the reflectance of a display device having a polar viewing angle are measured using a bright vision measuring device. A light source such as a light box with substantially uniform brightness is arranged to provide illumination from an illuminated area, which is arranged to illuminate the privacy display device along the incident direction for reflection to a viewer position at a polar angle greater than 0° with respect to the normal of the display device. The change I(θ) in illuminance having a polar viewing angle of a substantially Lambertian emitting light box is determined by measuring the recorded change in reflected luminance with the polar viewing angle, taking into account the change in reflectance ρ(θ). The measurements of P(θ), r(θ), and I(θ) are used to determine the variation of the safety factor S(θ) with the polar viewing angle along the zero elevation axis.

[0112] In a second step, a series of high-contrast images are provided on the privacy display, including (i) a small text image having a maximum font height of 3 mm, (ii) a large text image having a maximum font height of 30 mm, and (iii) a moving image.

[0113] In a third step, each observer (with vision correction for viewing at 1000 mm where appropriate) views each image from a distance of 1000 m and adjusts their polar angle at zero elevation until image invisibility is achieved for one eye from a position on the display close to or near the centerline of the display. The polar position of the observer's eye is recorded. Based on the relationship S(θ), the safety factor at the said polar position is determined. The measurements are repeated for different images, for various display luminances Y 最大 、different light box illuminances I(θ = 0), for different background lighting conditions, and for different observers.

[0114] From the above measurements, S < 1.0 (V < 10) provides low visual safety or no visual safety, 1.0 ≤ S < 1.5 (10 ≤ V < 32) provides visual safety depending on the contrast, spatial frequency, and temporal frequency of the image content, 1.5 ≤ S < 1.8 (32 ≤ V < 63) provides acceptable image invisibility (i.e., no observable image contrast) for most images and most observers, and S ≥ 1.8 (V ≥ 63) provides complete image invisibility, independent of the image content for all observers.

[0115] In an actual display device, this means that it is desired to provide an S value for off-axis viewers that satisfies the relationship S ≥ S 最小 where: S 最小 has a value of 1.0 or greater to achieve the effect that the off-axis viewer cannot perceive the displayed image; S 最小has a value of 1.5 or greater to achieve the effect that the displayed image is invisible, that is, for most images and most observers, even when the image is being displayed, the viewer cannot perceive it; or S 最小 has a value of 1.8 or greater to achieve the effect that the displayed image is invisible to all observers, regardless of the image content.

[0116] Compared with the privacy display, the desired wide-angle display is easily observable under standard ambient illumination conditions. A measure of image visibility is given by the contrast sensitivity, such as the Michelson contrast given by the following equation:

[0117] M = (I 最大 – I 最小 ) / (I 最大 + I 最小 ) Equation 6

[0118] And thus:

[0119] M = ((Y + R) – (K + R)) / ((Y + R) + (K + R)) = (Y - K) / (Y + K + 2.R) Equation 7

[0120] Therefore, the visual safety level (VSL) V is equal to (but different from) 1 / M. In this discussion, for a given off-axis relative luminance P, the wide-angle image visibility W is approximately

[0121] W = 1 / V = 1 / (1 + I.ρ / (π.P.Y 最大 )) Equation 8

[0122] The above discussion focuses on reducing the visibility of the displayed image to an off-axis viewer as a snooper, but similar considerations apply to the visibility of the displayed image to the intended user of the display device, who is usually a coaxial user. In this case, a decrease in the level of the visual safety level (VSL) V corresponds to an increase in the visibility of the image to the viewer. During observation, S ≤ 0.1 (V ≤ 1.25, W ≥ 0.8) can provide an acceptable visibility of the displayed image. In an actual display device, this means that it is desirable to provide for a coaxial viewer who is the intended user of the display device to satisfy the relationship S ≤ S 最大 , where S 最大 has a value of 0.1.

[0123] It is desirable to provide control of a switchable privacy display.

[0124] Figure 1 is a schematic front view showing a privacy display device 200, which includes a privacy display device 100 controlled by a privacy control system 500 operating at a first visual safety level in a privacy mode. The display device 100 displays an image.

[0125] The display device 200 may include a display device 100 having a privacy mode and a control system 500. The display device 100 is arranged to display images and is capable of operating at least in a public mode and in a privacy mode, wherein in the privacy mode, a privacy function is provided, and compared with the public mode, the visibility of the image to off-axis viewers is reduced, and in both the privacy mode and the public mode, the visibility of the image to the primary user at the coaxial position remains visible. For at least one area of the displayed image, typically the entire displayed image, the control system 500 selectively operates the display device 100 in the public mode or the privacy mode.

[0126] The display device 100 may generally provide a privacy function in any manner. Examples of suitable types of display devices used as the display device 100 are further described below.

[0127] The manner for determining privacy mode operation will now be described.

[0128] For a front user in a typical ambient illumination environment, desirably the display device 100 provides a displayed image 101 having a luminance that achieves a high image visibility W both in the privacy operation mode and in the public operation mode.

[0129] The display device 200 may further include inputs related to desired situations to provide privacy images, or conversely include inputs related to undesired situations to provide public images. Such desired and undesired situations may be determined by, for example, a policy 240 provided by company policy, government policy, medical ethics policy, or user preferences.

[0130] The control system 500 may be arranged to selectively operate the display device 100 in the public mode or the privacy mode in response to a detected level of ambient light. The display device 200 has an ambient light sensor 232 that detects the illuminance level of the ambient light. The ambient light sensor 232 may be of any suitable type, such as a photodiode that may have a photopic filter or a photopic light-responsive current or voltage or digital value.

[0131] Some types of displays have multiple optical effects to improve privacy performance, and exemplary optical effects are described below. If more than one privacy optical effect is available, the control system 500 may select a mode that provides the widest viewing freedom for the primary user while still maintaining an adequate level of visual safety at the ambient light levels experienced. Privacy is advantageously protected and user productivity is maintained.

[0132] The flight mode 270 may be selected, indicating that there may be a low light level surrounding environment and accordingly adapting the visual safety level control.

[0133] Advantageously, in the common mode, the display device 100 can have greater image uniformity and viewing freedom for the primary user and be visible from multiple viewing positions.

[0134] A visual safety level indicator 280 can be provided on the display, and the visual safety level indicator is a measure of the achieved privacy level. In Figure 1 the illustrative example, the indicator 282 indicating that there may be some residual image visibility for off-axis snoops can be an amber privacy warning. When switched to the privacy mode, the control system 500 can be arranged to control the display device 100 to display the image 101 and the information such as the indicator 280 representing the visibility of the image to off-axis viewers, for example, to provide the visual safety level V. Advantageously, the user or their supervisor can be confident in the privacy level achieved in the specific environment in which they operate.

[0135] Now, the display appearance in the privacy mode as seen by a snoop and further inputs for controlling the visual safety level will be described.

[0136] Figure 2 FIG. is a schematic top view showing a privacy display including a privacy control system 500 operating in the privacy mode at a first visual safety level.

[0137] As will be described below, off-axis privacy can be provided by controlling the off-axis luminance, reflectivity, and image contrast of the image 103 provided by the switchable privacy display device 100 to an unwanted snoop.

[0138] In one example, the display device can include an emissive spatial light modulator. In this case, the privacy control system 500 can control the luminance of the displayed image by controlling the light emission by the spatial light modulator.

[0139] In another example, the display device can include a backlight and a transmissive spatial light modulator arranged to receive light from the backlight. In this case, the control system can be arranged to control the luminance of the displayed image by controlling the luminance of the backlight and / or by controlling the light transmission by the spatial light modulator.

[0140] In the operation in the privacy mode, a restricted output cone angle 402C centered generally on the optical axis 199 is provided, and the optical axis is generally perpendicular to the surface of the display device 100. The off-axis luminance is reduced. The ambient light source 604 illuminates the display surface with light rays 610. The reflected light 606 from the display provides an increased visual safety level V as described above.

[0141] Some of the light 608 may be incident on the ambient light sensor ALS 232. The ALS 232 may be a separate component or may be incorporated into the camera 230 detection system.

[0142] The ambient illuminance detection 234 provides a calculation of the ambient illuminance and is input into the control system 500. The VSL calculation 250 is used to determine the desired display setting characteristics and output to the display control 710. The display control 710 may control the display brightness setting 278 and may further be used to provide the visual safety level indicator 280 level 282. The display control 710 is further described below in connection with an example of a privacy display.

[0143] It can be assumed that the features of the Figure 2 embodiments not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0144] In the public display mode, a larger solid angle output light cone 402D as shown Figure 13 can be provided by the switchable privacy display device 100. The solid angle output light cone can be adjusted to be larger than in the privacy mode, such that the off-axis display brightness increases.

[0145] A visual safety level indicator 280 can be provided on the display, and the visual safety level indicator is a measure of the achieved privacy level.

[0146] Now, the switching between exemplary privacy and public brightness profiles will be described.

[0147] Figure 3 is a schematic diagram showing the output brightness of a typical collimated backlight varying with the viewing angle. The collimated backlight is arranged to cooperate with a plurality of retarders 300 to provide a high visual safety level to a wide range of snooper positions. It can be assumed that the features of the Figure 3 embodiments not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0148] Figure 3 shows the desired brightness profile 486 of the backlight 20 operating in the privacy mode to be used with the Figure 13 switchable liquid crystal retarder 300 in the privacy mode. The profile 486 is modified by the switchable liquid crystal retarder 300 to provide the illustrative profile 490, which advantageously achieves an off-axis relative brightness of less than 0.5% at a 45-degree lateral angle and a zero-degree elevation angle.

[0149] Now, the control of the visual safety level will be further described.

[0150] Figure 4is a schematic diagram showing the variation of the visual safety level with the off-axis relative luminance of a switchable privacy display operating in a privacy mode, and refers to the privacy display of Figure 13 as an exemplary embodiment of the switchable privacy display 100. It can be assumed that the features of the embodiments not further discussed in detail Figure 4 correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0151] Figure 4 shows the profile of the visual safety level V (calculated from Equation 4 above in each illustrative embodiment) and the exemplary embodiments shown in Table 1 for different privacy levels achieved at the target snooper viewing positions 26L, 26R. For a display including a reflective polarizer 302, a display reflectivity of 30% or higher can be achieved, while for a display without the reflective polarizer 302, a display reflectivity of approximately 5% can be achieved.

[0152]

[0153] Table 1

[0154] At a 0.5% privacy level, various visual safety level points 458 can be provided, depending on the display structure, ambient illumination, and display luminance. Embodiments of the present invention further provide an indicator 280 for displaying the visual safety level, which can be provided, for example, by a traffic light indicator.

[0155] Now, the variation of the display reflectivity with the viewing angle will be described.

[0156] Figure 5 is a schematic diagram showing the variation of the reflectivity of two types of privacy displays with the polar viewing angle (which can be the lateral angle at zero elevation angle). The profile 820 shows the Figure 13 variation of the reflectivity of the illustrative embodiment of Figure 13 and the profile 822 shows the variation of the reflectivity of the embodiment without the reflective polarizer 302 of

[0157] Now, the variation of the visual safety level V with the viewing angle will be described.

[0158] Figure 6 is a schematic diagram showing Figure 5 the variation of the visual safety level of two types of privacy displays with the polar viewing angle. The VSL profile 824 shows the output of the display of the Figure 13 type with the reflective polarizer 302, and the VSL profile 826 shows the output of the Figure 13Output of the display. The VSL profiles are shown for the same ambient illuminance I. The limit V above which there is no image visibility is described further below. 极限 The angular range 825 of the snooper positions of the profile 824 is thus greater than the angular range 827 of the profile 826. The reflective polarizer 302 achieves a visual safety level above the threshold in a wider polar range, thus advantageously enhancing protection against snooping. In addition, for a given ambient brightness, the frontal illuminance can be increased, thus increasing the image visibility for the display user.

[0159] Selective control of the relationship between the desired display brightness and the ambient illuminance will now be described.

[0160] The control system 500 controls the brightness of the displayed image based on the detected level of the ambient light according to a transfer function. The transfer function can be selected to optimize the visibility of the displayed image for a coaxial viewer. Similar techniques for optimizing the visibility of the displayed image based on the detected level of the ambient light are commonly used in display devices of portable devices such as mobile phones and can be applied here. However, as described below, when a privacy function is provided, the transfer function can be adapted to be used with the privacy display device 100.

[0161] Generally, the transfer function provides a higher brightness of the displayed image in the public mode than in the privacy mode. Some illustrative examples will now be described.

[0162] Figure 7A is a schematic diagram showing transfer function profiles 802, 804, 852, 854 of the frontal brightness of the display measured in nits and the detected ambient illuminance measured in lux; and Figure 7B is a schematic diagram showing transfer function profiles 803, 805, 853, 857 of the ratio of the ambient illuminance measured in lux per nit to the frontal display brightness and the ambient illuminance measured in lux.

[0163] The control system 500 is arranged to selectively control the brightness of the displayed image in the public mode and in the privacy mode in response to the detected level of the ambient light according to different transfer functions 802, 804, 852, 854, 856 that relate the brightness level to the detected level of the ambient light in the public mode and in the privacy mode, respectively.

[0164] Consider Figure 7A the profile 856 and Figure 7BThe corresponding profiles 857 provide a linear change in the display luminance Y0 as compared to the measured ambient illuminance, with a constant ratio of 0.5 lux / nit for all illuminance levels. In operation, such displays have a luminance higher than the background illuminance across all illuminance ranges.

[0165] Profiles 802 and 803 differ from profiles 856 and 857 in that they increase the lux / nit ratio as the luminance increases. Advantageously, such profiles achieve a visually comfortable image with high image visibility and low perceived glare across a wide illuminance range.

[0166] In the switchable privacy displays described below with respect to Figure 13 such profiles 856, 857 and 802, 803 may be desirable for the public operation mode. Profiles 856, 857, 802, 803 advantageously achieve high image visibility (desirably W≥0.8) and low image safety factor (desirably S≤0.1) for coaxial and off-axis viewing positions across a wide polar region, as will be further described below.

[0167] Considering Figure 7A profile 854 and Figure 7B the corresponding profile 855, provide a linear change in the display luminance Y0 as compared to the measured ambient illuminance, with a constant ratio of 3.0 lux / nit for all illuminance levels. In operation, such displays have a luminance lower than the background illuminance across all illuminance ranges as compared to displays with profiles 802, 803.

[0168] Profiles 804 and 805 differ from profiles 854 and 855 in that they increase the lux / nit ratio as the luminance increases for luminance levels below 150 nits.

[0169] In the switchable privacy displays described below with respect to Figure 13 such profiles may be desirable for the privacy operation mode. Profiles 856, 857, 802, 803 advantageously achieve high image visibility (desirably W≥0.8) and low image safety factor (desirably S≤0.1) for coaxial and off-axis viewing positions across a wide polar region, as will be further described below. Advantageously, such profiles 854, 855 and 804, 805 can achieve the desired luminance and image visibility for the display user at lower illuminance levels. Further, such profiles 856, 857, 802, 803 achieve increased image safety at higher illuminance levels.

[0170] When operating in privacy mode, the privacy transfer function 804 is selected and the control system uses the measured ambient light level to control the display brightness such that a desired visual safety level V is provided at at least one off-axis snooper viewing angle for different ambient illumination levels. Advantageously, display security can be maintained under different lighting conditions.

[0171] When operating in public mode, the public transfer function 802 can be selected to provide a desired image visibility W for different ambient illumination levels. Advantageously, display visibility can be maintained under different lighting conditions for off-axis observers.

[0172] The variation of the safety factor with display control and ambient illuminance level will now be further described.

[0173] Figure 8A is a schematic diagram showing the variation of the safety factor of an illustrative privacy display operating in privacy mode with the polar angle at a lux / nt ratio of 3.0; Figure 8B is a schematic diagram showing the variation of the safety factor of an illustrative privacy display operating in privacy mode with the polar angle at a lux / nt ratio of 0.5; Figure 8C is a schematic diagram showing the variation of the safety factor of an illustrative privacy display operating in public mode with the polar angle at a lux / nt ratio of 0.5; and Figure 8D is a schematic diagram showing the variation of the safety factor of an illustrative privacy display operating in public mode with the polar angle at a lux / nt ratio of 3.0.

[0174] Figure 8A The profile of -D is provided by the illustrative embodiments below Figure 13 for different ratios of illuminance to frontal brightness Y0 as will now be described. The primary display user is located in the polar region near a lateral angle of 0° and an elevation angle of 0°. Snoopers are typically located in polar positions with a lateral angle > 25°, and more typically in polar positions with a lateral angle > 35°.

[0175] In Figure 8A the display 100 is arranged to provide low off-axis brightness (as shown by the profile 490 of Figure 3 in the lateral direction) and high off-axis reflectivity (as shown by the profile 820 of Figure 5 in the lateral direction). The frontal display brightness Y0 is controlled by controlling the light source 15 of the backlight 20 such that the brightness Y0 measured in nits is one-third of the illuminance measured in lux (assuming the same for all polar angles). Around the coaxial direction, S ≤ 0.1 and an image with a high image visibility W ≥ 0.8 is seen. Advantageously, the arrangement 8A is the desired polar profile of the safety factor S for privacy operation.

[0176] By comparison withFigure 8A The way of making comparison Figure 8B shows the variation of the safety factor S with the polar angle for the luminance Y0 measured in nits, where the luminance is twice the illuminance measured in lux (i.e., the arrangement suitable for public-mode viewing). The polar regions where the safety factor S≥1.5 are undesirably substantially reduced. The off-axis display user can see more image data than Figure 8A the arrangement of

[0177] In Figure 8C , the display 100 is arranged by controlling the polar control retarder 300 to provide increased off-axis luminance (as shown by the profile 486 of Figure 3 in the lateral direction) and reduced off-axis reflectance (as shown by the profile 822 of Figure 5 in the lateral direction). The front luminance Y0 of the display in nits is controlled to be three times the illuminance measured in lux. Around the coaxial direction, S≤0.1 and an image with a high image visibility W≥0.8 is seen. The arrangement 8A is the desired polar profile of the safety factor S for privacy operation. Advantageously, the polar regions where S≤0.1 are significantly increased, enabling the off-axis observer to see an image with high image visibility on the display 100.

[0178] By way of comparison with Figure 8C the way of making comparison Figure 8D shows the variation of the safety factor S with the polar angle for the luminance Y0 measured in nits, where the luminance is one-third of the illuminance measured in lux (i.e., the arrangement suitable for privacy viewing). The polar regions where the safety factor S>1.5 are undesirably substantially reduced. The off-axis display user undesirably can see less image data than Figure 8C the arrangement of

[0179] Advantageously, the control system of the embodiments of the present invention achieves the desired performance in both privacy and public operation modes for different illuminance levels.

[0180] The user or the control system may desire to select a transfer function to achieve the desired luminance level for the front user, adjust the size of the polar region for the front user in the privacy mode, adjust the size of the polar region for safe viewing by off-axis snoops and / or adjust the size of the polar region for public operation, as will be described now.

[0181] Figure 9A is a schematic diagram showing the user-selectable transfer function between the front display luminance and the ambient illuminance. Compared with Figure 7ACompared with the arrangement, alternative profiles 830, 832, 834, 836, 838, 840, 842, 844, 846, 848 can be provided, where each profile is shaped as a step function in which the luminance of the displayed image increases with the detected level of ambient light.

[0182] Advantageously, due to the step function shape of the transfer function, profile control can be provided at low cost and complexity. Figure 9A The control system 500 can similarly provide a single profile to achieve the same benefits.

[0183] Illustrative examples of operation will now be described. The display can operate in a bright environment such as 450 lux. In such an environment, the display can default to its maximum peak luminance of 250 nits provided to the front user. If desired, the user can further reduce the display luminance. Advantageously, high visual safety can be provided for a wide range of ambient illuminances. A step function as shown can be used to select profiles to reduce the number of settings and drive costs by selecting different profiles. Alternatively, a smooth profile that varies continuously with ambient illuminance can be provided.

[0184] In the default setting 838, when the ambient illuminance drops, for example, between 250 lux and 175 lux, the display switches between 150 nits and 100 nits. The visual safety level of the snoopers is maintained above the threshold. A time constant can be applied to the switching of the profile such that the change is not visible in the form of display flicker. For example, the time constant can be several seconds.

[0185] At high illuminance levels, a single display front luminance Y can be provided for all the profiles shown, 最大 or the step function can continue to vary with luminance.

[0186] In some environments, the user may prefer a brighter front image and some limited reduction in visual safety, and thus can select profile 832 instead of the default setting. In other environments where a high level of visual safety is desired, profile 848 with a lower front luminance and increased visual safety level can be selected.

[0187] In other words, the user can change the default display brightness setting from the profile shown by the default profile 838 in the figure. If the ambient illuminance changes, the display can follow the selected brightness step profile, for example, profile 830 as shown.

[0188] During changes in ambient illuminance or changes in the user's selection of profiles, the switching between profiles can be provided over an extended period such as several seconds to achieve a seamless change in the appearance of the display.

[0189] Figure 9B is a schematic flow chart showing a method for operating a user-selectable transfer function.

[0190] A display device, such as a laptop computer, may have a system-level PWM (pulse width modulation) generator 860. The input of the system-level PWM generator 860 may include a setting of a global brightness 868 set by an operating system and may be used as an input to the output of a separate ambient light sensor (not shown).

[0191] The input to the global brightness 868 setting may also include a user input that may bias or adjust a default display brightness. The PWM input 878 is received by a timing controller (TCON) board 862, which may include a microcontroller for performing processing functions. The TCON board 862 also includes an input from a privacy enable 876 signal, which determines whether the display is in a privacy mode. If the display is not in the privacy mode, the PWM output 880 may follow the PWM input 878. The TCON board 862 further includes an input from an ambient light sensor ALS 872 that may be different from the ambient light sensor ALS provided by the system. Specifically, the ambient light sensor 872 may be provided as directly connected to the TCON 862 as shown. This connection may be independent of operating system control. The PWM output 880 sent to the LED controller 864 can be modified by the TCON 862. The time response function 874 takes an input from the ALS 872 and enables the TCON 862 to provide the PWM output 880 such that a change in ambient illuminance causes the signal to the LED controller 864 to change gradually over time, such that the user does not experience display brightness flicker or jumps. The time response function 874 may also suppress the effects of frequency components (e.g., 50 Hz or 60 Hz) of ambient lighting that may be caused by fluorescent tubes or the like.

[0192] The LED controller 864 is connected to an LED strip 15 of the privacy display 100, which may be a PCB or a flexible PCB incorporated within a backlight 20 of the privacy display 100 as shown, for example, below. Figure 13 In other arrangements (not shown), the LED controller 864 may be provided by a display controller arranged to control the brightness of an emissive spatial light modulator 48 such as an emissive OLED display or an emissive micro-LED display.

[0193] When a privacy function is provided in the privacy mode, the transfer function may maintain the relationship Y 最大 ≤ Y 上限 where Y 上限 is the maximum output brightness of the display device and Y 上限 is given by the following equation:

[0194]

[0195] where Y 上限 's equation is applicable to the viewing direction that forms a polar angle θ of 45° with the normal of the display device at at least one azimuth angle around the normal of the display device. I is the detected level of the ambient light, and the unit of I is Y 最大 's unit multiplied by the solid angle in steradians, ρ(θ = 45°) is the reflectivity of the display device along the viewing direction, and P(θ = 45°) is the ratio of the luminance of the display device along the viewing direction to the maximum output luminance Y 最大 of the display device, and S 最小 has a value of 1.0 or greater.

[0196] Y 上限 's formula is derived from Equation 4, considering both the reflectivity ρ and the ratio (relative luminance) P of the viewer along the viewing direction. The viewing direction forms a polar angle θ of 45° with the normal of the display device at at least one azimuth angle around the normal of the display device. By satisfying the relationship Y 最大 ≤Y 上限 , it can be ensured that the S value of the off-axis viewer for the snooper in the viewing direction satisfies the relationship S≥S 最小 , where S 最小 has a value of 1.0 or greater, regardless of the illuminance level of the ambient light and the luminance of the display device. By maintaining the relationship S≥S 最小 , where S 最小 has a value of 1.0 or greater, the off-axis viewer in this viewing direction can actually not distinguish the visual safety level at or below the limit S 最小 . Such an off-axis viewer cannot perceive the displayed image, as described above.

[0197] Advantageously, the value of S 最小 can be 1.5 or greater. Such an increased limit of S 最小 achieves a higher visual safety level, where for most images and most observers, such an image is effectively invisible to the off-axis viewer along the viewing direction.

[0198] Advantageously, the value of S 最小 can be 1.8 or greater. Such an increased minimum limit of S achieves a higher visual safety level, where the image is invisible to all observers, regardless of the image content.

[0199] where the display device has a symmetric major axis and minor axis, Y 最大The equation can be applied to an observation direction that forms a 45° polar angle θ with the normal of the display device at an azimuth corresponding to either or both of the major axis (to achieve an advantage for off-axis viewers when the display device is used in a landscape orientation) or the minor axis (to achieve an advantage for off-axis viewers when the display device is used in a portrait orientation).

[0200] The control system can also be arranged to, when the privacy function is provided, control the brightness of the displayed image based on the detected level of the ambient light according to the maintenance relationship Y 最大 ≥Y 下限 whose transfer function is based on the detected level of the ambient light, where Y 下限 is given by the following equation:

[0201]

[0202] where Y 下限 The equation is applicable to an observation direction that forms a 10° polar angle θ with the direction of the maximum output brightness of the display device at at least one azimuth around the direction of the maximum output brightness of the display device. ρ(Δθ = 10°) is the reflectivity of the display device along the observation direction that forms a 10° polar angle θ with the direction of the maximum output brightness of the display device, P(Δθ = 10°) is the ratio of the brightness of the display device along the observation direction that forms a 10° polar angle θ with the direction of the maximum output brightness of the display device to the maximum output brightness Y 最大 of the display device, and the value of S 最大 is 0.1 or less.

[0203] Y 下限 The formula for Y is derived from Equation 4, considering both the reflectivity ρ and the ratio (relative brightness) P with respect to the observation direction, which forms a 10° polar angle θ with the direction of the maximum output brightness of the display device at at least one azimuth around the direction of the maximum output brightness of the display device. The coaxial viewer will typically be positioned along such an observation direction or at a smaller polar angle with better visibility.

[0204] By satisfying the relationship Y 最大 ≥Y 下限 , it can be ensured that the S value of the coaxial viewer satisfies the relationship S ≤ S 最大 , where the value of S 最大 is 0.1 or less, regardless of how the illuminance level of the ambient light and the brightness of the display device change. By maintaining the relationship S ≤ S 最大 , where the value of S 最大 is 0.1 or less, the visibility of the displayed image for the coaxial viewer is maintained, as described above.

[0205] Now, the desired limit of the front brightness of the display operating in the privacy mode will be described.

[0206] Figure 10 It is a schematic diagram showing the change 806 of perceived visual security with the visual security level V at the viewing angle θ. The visual security level V is a measured quantity of any given display and varies with the polar viewing angle.

[0207] Compared with the visual security level V, perceived visual security is a subjective judgment of the visibility of the private image of the display generated by the response of the human visual system at the viewing angle.

[0208] In operation, it has been found that above the threshold limit V 极限 of the visual security level V, the image information is not perceived. This transition of the perceived visibility with the change of the visual security level V is very rapid, as shown by the steepness of the graph in Figure 7B around the threshold limit V 极限 . That is to say, as the visual security level V increases, the initially perceived visibility only gradually decreases, and the image is basically viewable. However, when reaching the threshold limit V 极限 , the perceived image quickly becomes invisible in a practically surprising way.

[0209] When observing the surprising result, for the text document image concerned by the privacy application, it is found that when V is 10, the perceived image seen by the snooper quickly becomes invisible. In the region 810 where the V value is higher than 10, the visibility of all the displayed text is zero. In other words, when V is 10 or greater, the perceived text quickly becomes invisible in a practically surprising way.

[0210] In the region 812 below V 极限 , the text is visible with low contrast, and in the region 814 below V', the text is clearly visible.

[0211] It is desired to maximize the positive display brightness to achieve high image visibility for the main display user. It is further desired to achieve a high image security level for the snooper at the viewing angle. Now, the selective control of the positive brightness will be described in more detail.

[0212] For the viewing angle θ, prevent the maximum display output brightness Y 最大 (usually the positive brightness) from exceeding the brightness limit Y 极限 at the threshold limit V 极限 of the visual security level V higher than the threshold limit V 极限 , so that the image is not perceived as visible at this viewing angle θ. The brightness limit Y

[0213]

[0214] where Rθ is the reflected ambient illumination at the viewing angle θ, Kθ is the display black state luminance at the viewing angle, and Pθ is the relative luminance at the viewing angle θ compared to the maximum display output luminance Y 最大 (usually the front luminance and measured in nits). For a display reflectivity ρθ and a Lambertian light source with the illumination Iθ reflected by the display at the viewing angle measured in lux, the luminance limit Y0 极限 is also given by the following equation:

[0215]

[0216] Since the illumination Iθ depends on the amount of ambient light, the luminance of the display device can be controlled by the control system 500 according to these relationships. Specifically, the privacy transfer function 804 used by the control system 500 as described above can be selected to maintain the relationship Y 最大 ≤Y 极限 , so that the image is not perceived as visible at the desired viewing angle θ, for example, at a viewing angle θ that is 45 degrees lateral and zero degrees elevation angle from the normal of the display device.

[0217] Subject to this limit, the luminance is preferably as high as possible to optimize the performance of the front view. Therefore, the privacy transfer function 804 used by the control system 500 as described above can be additionally selected to maintain the relationship Y 最大 / Iθ ≥ 1 lux / nit, as shown by the profile 805 in Figure 7B . The illumination Iθ can be the sensed ambient illumination averaged from the illuminated scene.

[0218] Advantageously, a display can be provided that has high image security for off-axis snoops while achieving high image visibility for front users at different illumination levels.

[0219] A further description of the control of the privacy display will now be described.

[0220] Figure 11 Shows Figure 1-2 and Figure 3-4 the flowcharts of the privacy control systems.

[0221] The display operating environment 261 can include (but is not limited to) network ID 201, date / time 262, GPS 206 data, ambient light sensor 232 detection, and flight mode 270 settings.

[0222] The company privacy policy 240 can include the definition of when the display should operate in privacy mode, including time and location; files and applications; and visual security level specifications.

[0223] Other inputs may include display design parameters 272 and information 274 about the viewed documents and applications.

[0224] The data processor 290 is used to analyze the display operating environment 261, the display design parameters 272, the viewed documents and applications 274 and compare them with the company privacy policy 240. The output determines whether to operate the display in privacy mode or public mode, such that the switch 292 is set for privacy mode or public mode operation based on the output of the data processor 290.

[0225] In the case of privacy mode operation, settings are provided that are applied to the display device 100 using the display control system 710 and the image 101 using the image control system 296 to achieve a desired level of visual security. Further indication of the level of visual security may be provided using the indicator 280.

[0226] In the case of public mode operation, appropriate illumination control including the cone angle change by the display control system 710 and the brightness using the LED driver 715 is provided to the display device 100.

[0227] The controller 500 may continue to monitor the state of the display operating environment 261 and appropriate changes in the policy 240 and appropriately adjust the display device 100 and the image 101 to maintain the target level of visual security.

[0228] Advantageously, the control system 500 can enable a level of visual security that can be reliably calculated and compared with the level of the company policy 240 set for the current environment of the device. The level of visual security can be adjusted to the level required for the display device 100 environment such that the primary user maintains an optimal viewing freedom and comfort consistent with achieving the privacy level of the prescribed company privacy policy.

[0229] It may be assumed that the features of the Figure 11 embodiments not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0230] The ambient light sensor 232 may be of the type that detects the illuminance level of ambient light incident on the display device in a non - directional manner. In such cases, the detected illuminance level I represents an average level such that the effects described above are achieved for off - axis viewers at different positions.

[0231] Alternatively, the ambient light sensor 232 can be of a type that detects the ambient light illumination level incident on the display device along an incident direction and reflected to an observation direction. In this case, the ambient illumination can be measured in a direction corresponding to a position where the ambient light reflectance contributes to the snoopers' safety. This allows the effects described above to be particularly optimized for off-axis viewers in the observation direction. Some examples of this method are as follows.

[0232] Figure 12A is a schematic top view showing a privacy display and an off-axis ambient light sensor. The ambient light source 604 is reflected by the privacy display 100 to the snooper 45. The ambient light sensor 232 is arranged to measure the ambient illumination in the light cone 605R. In operation, the output of the ambient light sensor 232 is arranged to adjust the brightness for the user 47 to achieve a desired visual safety level of the ambient illumination. In operation, for a typical display without or with a limited diffuser (e.g., a front surface diffuser with an AG of 50 or less diffuser), the snooper only sees the reflected ambient light from the area around the direction of the light cone 605R.

[0233] Figure 12B is a schematic diagram showing the polar regions for ambient illumination measurement for a privacy display. Figure 12B Thus, the polar positions 605R, 605L are indicated, in which the ambient light source can be arranged to contribute to the visual safety level as observed by off-axis snoopers. Ambient light sources located elsewhere do not contribute to the visual safety factor. It is not desirable to provide a reduction in front brightness to compensate for the ambient illumination that does not provide an increased visual safety level, i.e., light sources outside the regions 605L, 605R.

[0234] Now, an ambient light sensor that preferentially measures the illumination in the polar regions 605L, 605R will be described.

[0235] Figure 12C -E is a schematic top view showing an off-axis ambient light sensor for measuring the ambient illumination in the polar regions Figure 12B thereof.

[0236] Figure 12C shows the ambient light sensor 232, which includes a mask 237 having holes 241R, 241L separated from the mask 237 by spacers 239. The sensor 235L measures the ambient illumination from the off-axis ambient light source 604L, while the sensor 235R measures the ambient illumination from the off-axis ambient light source 604R. Advantageously, in the privacy operation mode, the visual safety level provided to the snooper can be increased in response to appropriately placed ambient light sources 604R, 605L.

[0237] Figure 12D Similar to Figure 12C, except that the two sensors 235L and 235R are replaced by a single sensor 235C. Advantageously, the cost is reduced.

[0238] Figure 12E An embodiment is shown in which the sensors 235L, 235R and the masks 237L, 237R are inclined with respect to the normal direction of the display device 100, wherein the optical axes 299L, 299R point to the centers of the regions 605L, 605R. Advantageously, compared with Figure 12C the arrangement of, stray light can be reduced and the measurement accuracy can be improved.

[0239] In Figure 12C -E embodiment, the holes 241 and the sensors 232 can be shaped to achieve a measurement direction that matches the pole positions 605L, 605R of Figure 12B .

[0240] The ALS can include, for example, multiple detectors or detection channels capable of detecting different spectral bands or infrared rays. One channel can also be used to detect the flicker effect from, for example, pulsed LEDs or fluorescent lighting. The single detector described above can be multiplexed to an analog-to-digital converter to reduce costs.

[0241] Illustrative examples of a display capable of switching between a privacy mode and a public mode will now be described.

[0242] Figure 13 is a schematic diagram showing a switchable directional display device 100 including a backlight 20, a switchable liquid crystal retarder 300, and a spatial light modulator 48 in a front perspective view.

[0243] The display device 100 includes a directional backlight 20, such as a collimated backlight arranged to output light, the backlight 20 including a directional waveguide 1; and a plurality of light sources 15 arranged to input input light into the waveguide 1, and the waveguide 1, a rear reflector, and a light control film 5 are arranged to guide the light from the light sources 15 into a solid angle range 402A. The light control film 5 can include, for example, a turning film and a diffuser.

[0244] In the present disclosure, the solid angle range is the solid angle of an optical cone within which the luminance is greater than a given relative luminance of the peak luminance. For example, the luminance roll-off can be to a relative luminance of 50%, such that the solid angle range has the same angular width as the full width at half maximum (FWHM) in a given direction (such as the lateral direction).

[0245] The backlight 20 can be arranged to provide an angular light solid angle range 402A having a reduced luminance for off-axis viewing positions compared to the front luminance.

[0246] The display control system 710 is arranged to provide control of the light source driver 715. The brightness of the LED 15 can be controlled by the control system such that the absolute off-axis brightness for a snoop can be controlled.

[0247] The spatial light modulator 48 can include a liquid crystal display including substrates 212, 216 and a liquid crystal layer 214 having red, green, and blue pixels 220, 222, 224. The spatial light modulator 48 has an input display polarizer 210 and an output display polarizer 218 on its opposite sides. The output display polarizer 218 is arranged to provide a high extinction ratio for light from the pixels 220, 222, 224 of the spatial light modulator 48. Typical polarizers 210, 218 can be absorption polarizers, such as dichroic polarizers.

[0248] Optionally, a reflective polarizer 208 can be provided between the dichroic input display polarizer 210 and the backlight 210 to provide recycled light and improve display efficiency. Advantageously, the efficiency can be increased.

[0249] An optical stack for providing control of off-axis brightness will now be described.

[0250] The reflective polarizer 302, the plurality of retarders 300, and the additional polarizer 318 are arranged to receive the output light from the spatial light modulator 48.

[0251] The plurality of retarders 300 are arranged between the reflective polarizer 302 and the additional polarizer 318. The polarizers 210, 218, 318 can be absorption polarizers, such as iodine polarizers, while the reflective polarizer 302 can be a stretched birefringent film stack, such as APF from 3M Corporation or a wire grid polarizer.

[0252] The plurality of retarders 300 include a switchable liquid crystal retarder 301 including a liquid crystal material layer 314 and substrates 312, 316 arranged between the display polarizer 302 and the additional polarizer 318. The retarder 300 further includes a passive retarder 330, as will be further described below.

[0253] As described below, the plurality of retarders 300 do not affect the brightness of light passing through the reflective polarizer 302, the retarders 300, and the additional polarizer 318 along an axis normal to the plane of the retarders 300, but the retarders 300 do reduce the brightness of light passing through them along an axis inclined to the normal of the plane of the retarders 300 at least in one of the switchable states of the switchable retarder 301. This is due to the presence or absence of a phase shift introduced by the retarders 300 to light along axes at different angles with respect to the liquid crystal material of the retarders 300.

[0254] The transparent substrates 312, 316 of the switchable liquid crystal retarder 301 include electrodes that are arranged to provide a voltage across the layer 314 of liquid crystal material 414 therebetween. A control system 752 is arranged to control the voltage applied across the electrodes of the switchable liquid crystal retarder 301 by the voltage driver 350.

[0255] It may be assumed that the features of embodiments not further discussed in detail Figure 13 correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0256] As will be further described below, additional polarizers 318, a plurality of retarders 300, and a reflective polarizer 302 may be arranged to provide polar control of the output luminance and front reflectance from ambient illumination 604.

[0257] An example of an optical stack providing off-axis luminance control will now be described.

[0258] Figure 14 is a schematic perspective side view showing the arrangement of a plurality of retarders 300 in a privacy operation mode, the plurality of retarders including a negative C-plate passive retarder 330 and a switchable liquid crystal retarder 301 that is vertically aligned in the privacy operation mode. In Figure 14 For clarity, some layers of the optical stack are omitted. For example, the switchable liquid crystal retarder 301 is shown with the substrates 312, 316 omitted.

[0259] The switchable liquid crystal retarder 301 includes two surface alignment layers that are disposed on the electrodes 413, 415 and adjacent to the layer of liquid crystal material 414 and on opposite sides thereof, and each is arranged to provide homeotropic alignment in the adjacent liquid crystal material 414. The layer 314 of liquid crystal material 414 of the switchable liquid crystal retarder 301 includes a liquid crystal material having a negative dielectric anisotropy. The liquid crystal molecules 414 may be provided with a pretilt of, for example, 88 degrees with respect to the horizontal to remove degeneracy in switching.

[0260] The electric vector transmission direction of the reflective polarizer 302 is parallel to the electric vector transmission direction of the output polarizer 218. Further, the electric vector transmission direction 303 of the reflective polarizer 302 is parallel to the electric vector transmission direction 319 of the additional polarizer 318.

[0261] The switchable liquid crystal retarder 301 includes a layer 314 of liquid crystal material 414 having a negative dielectric anisotropy. The passive retarder 330 includes a negative C-plate having an optical axis perpendicular to the plane of the retarder 330, as schematically shown by the orientation of the disclike material 430.

[0262] The liquid crystal retarder 301 further includes transmissive electrodes 413, 415 which are arranged to control a liquid crystal material, and the liquid crystal material layer can be switched by adjusting the voltage applied to the electrodes. Electrodes 413, 415 can span layer 314 and are arranged to apply a voltage for controlling the liquid crystal retarder 301. The transmissive electrodes are located on opposite sides of the liquid crystal material layer 414 and can be, for example, ITO electrodes.

[0263] Alignment layers can be formed between the electrodes 413, 415 and the liquid crystal material 414 of layer 314. The orientation of the liquid crystal molecules in the x - y plane is determined by the pre - tilt direction of the alignment layer, such that each alignment layer has a pre - tilt, where the pre - tilt of each alignment layer has components 417a, 417b in the plane of layer 314 that are parallel or anti - parallel or orthogonal to the electric vector transmission direction 303 of the reflective polarizer 302.

[0264] The driver 350 supplies a voltage V across layer 314 of the switchable liquid crystal material 414 to the electrodes 413, 415, such that the liquid crystal molecules are tilted at an angle with respect to the vertical. The plane of the tilt is determined by the pre - tilt direction of the alignment layer formed on the inner surfaces of the substrates 312, 316.

[0265] In a typical use of switching between a common mode and a privacy mode, the liquid crystal material layer can be switched between two states. The first state is the common mode, such that the display can be used by multiple users, and the second state is the privacy mode, for use by a primary user with minimum visibility to snoopers. The switching can be done by applying a voltage across the electrodes. Generally, such a display can be considered to have a first wide - angle state and a second reduced off - axis brightness state.

[0266] It can be assumed that the features of Figure 14 the embodiments not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0267] Now, the polar profiles of the various elements of the Figure 13 illustrative embodiment of the stack will be described.

[0268] Figure 15A is a schematic diagram showing the polar and azimuthal variations of the output brightness of a collimated backlight and a spatial light modulator.

[0269] Figure 15B is a schematic diagram showing the polar and azimuthal variations of the transmission of a switchable retarder arranged between parallel polarizers for the exemplary embodiment of Table 2.

[0270]

[0271] Table 2

[0272] Figure 15C It is a schematic diagram showing the polar change and azimuthal change of the relative reflection of a switchable retarder arranged between a reflective polarizer and an absorptive polarizer for an exemplary embodiment of Table 2.

[0273] Figure 15D It is showing Figure 13 the polar change and azimuthal change of the total display reflectance in the privacy operation mode of the arrangement of, that is, the polar contour of the reflectance ρ(θ, φ), where θ is the polar angle and φ is the azimuthal angle.

[0274] Figure 15E It is showing Figure 13 the polar change and azimuthal change of the output luminance in the privacy operation mode of the arrangement of, that is, the polar contour of the privacy level P(θ, φ).

[0275] Figure 15F It is a schematic diagram showing the polar change and azimuthal change of the visual safety level S(θ, φ) of the front - face luminance of the display in the privacy operation mode for Figure 13 the arrangement of, the value Y of the front - face luminance of the display measured in nits 最大 is half of the illuminance I measured in lux. Contour lines of S = 1.0, S = 1.5, and S = 1.8 are shown to indicate the polar regions of image privacy and image invisibility. The contour line of S = 0.1 is shown to indicate the polar region of high image visibility.

[0276] Figure 15G It is a schematic diagram showing the polar change of the zero - elevation - angle visual safety level S of the front - face luminance of the display in the privacy operation mode for Figure 13 the arrangement of, the value Y of the front - face luminance of the display measured in nits 最大 is half of the illuminance I measured in lux. At 45 degrees, the display is controlled such that the I / Y 最大 ratio (lux / nit) of the display is set to 2.0, and the image is invisible at polar angles of + / - 45 degrees.

[0277] Now, the operation of the Figure 13 display in the public mode will be described.

[0278] Figure 16 It is a schematic diagram showing the arrangement of the retarder 300 in the public operation mode in a perspective side view. In this embodiment, zero volts is applied across the liquid - crystal retarder 301, as shown in Table 2.

[0279] Compared with the Figure 14 arrangement of, no voltage is applied and the molecules of the liquid - crystal material 414 are arranged substantially perpendicular to the alignment layer and the electrodes 413, 415.

[0280] It can be assumed that the features of the embodiments not further discussed in detail Figure 16 correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0281] Figure 17A is a schematic diagram showing Figure 13 the extreme change and azimuthal change of the output luminance of the arrangement in the common operation mode; and Figure 17B is a schematic diagram showing for Figure 13 the extreme change of the zero elevation visual safety level S of the front luminance of the display in the common operation mode, where the value Y of the front luminance of the display measured in nits 最大 is half of the illuminance of the value I measured in lux. Compared with Figure 15F the arrangement, the display remains visible to the user over a wide polar region and has the highest visibility near the axis.

[0282] Figure 17C is a schematic diagram showing the extreme change and azimuthal change of the output luminance where the maximum luminance Y 最大 is not perpendicular to the backlight of the display. Compared with having Y at the position 890 of the display normal 最大 of Figure 17A compared, Figure 17C shows Y 最大 at the position 892 above the axis. Advantageously, for a user looking down at the display, the display luminance can be increased. The viewing direction with a 10° polar angle θ from the direction of the maximum output luminance of the display device described in Equation 10 is shown by the polar region 894. Desirably, at least within the region 894, the visibility of the image for the primary user is high, i.e., the safety factor S is less than 0.1.

[0283] Now, the propagation of the polarized light from the output polarizer 218 will be considered for the coaxial and off-axis directions of the display operating in the privacy mode.

[0284] Figure 18A is a side view showing the propagation of the output light from the spatial light modulator through Figure 13 the optical stack in the privacy operation mode.

[0285] When the layer 314 of the liquid crystal material 414 is driven to operate in the privacy mode, the retarder 300 does not provide an overall transformation of the polarization component 360 to the output light ray 400 passing through it along the axis perpendicular to the plane of the switchable retarder, but provides an overall transformation of the polarization component 361 to the light ray 402 passing through it for certain polar angles that form an acute angle with the perpendicular to the plane of the retarder.

[0286] The polarization component 360 from the output polarizer 218 is transmitted by the reflective polarizer 302 and incident on the retarder 300. The coaxial light has a polarization component 362 that is not modified from the component 360, while the off-axis light has a polarization component 364 that is transformed by the retarder 300. At least, the polarization component 361 is converted into a linearly polarized component 364 and absorbed by the additional polarizer 318. More generally, the polarization component 361 is converted into an elliptically polarized component that is partially absorbed by the additional polarizer 318.

[0287] Figure 15B The polarity distribution of the light transmission shown changes the polarity distribution of the luminance output of the underlying spatial light modulator 48. In the case where the spatial light modulator 48 includes the directional backlight 20, the off-axis luminance can be further reduced as described above.

[0288] Embodiments that may be assumed without further detailed discussion Figure 18A have features corresponding to those with equivalent reference numerals as discussed above, including any potential variations in the features.

[0289] Advantageously, a privacy display is provided that has low luminance for off-axis snoops while maintaining high luminance for coaxial observers.

[0290] The operation of the reflective polarizer 302 on light from the ambient light source 604 will now be described for a display operating in a privacy mode.

[0291] Figure 18B is a schematic top view showing the propagation of ambient illumination light through Figure 13 the optical stack in the privacy operation mode.

[0292] The ambient light source 604 illuminates the display device 100 with unpolarized light. The additional polarizer 318 transmits light rays 410 perpendicular to the display device 100 with a first polarization component 372, which is a linearly polarized component parallel to the electrical vector transmission direction 319 of the additional polarizer 318.

[0293] In both operating states, the polarization component 372 remains unmodified by the retarder 300, and thus the transmitted polarization component 382 is parallel to the transmission axes of the reflective polarizer 302 and the output polarizer 218, so the ambient light is guided through the spatial light modulator 48 and lost.

[0294] In comparison, for the light ray 412, the off-axis light is guided through the retarder 300 such that the polarization component 374 incident on the reflective polarizer 302 can be reflected. Such a polarization component is reconverted to the component 376 after passing through the retarder 300 and transmitted through the additional polarizer 318.

[0295] Accordingly, when the liquid crystal material layer 314 is in the second of the two states, the reflective polarizer 302 does not provide reflected light of ambient light 410 that passes through the additional polarizer 318 and then through the retarder 300 along an axis perpendicular to the plane of the retarder 300, but rather provides reflected light rays 412 of ambient light that pass through the additional polarizer 318 and then through the retarder 300 at certain polar angles that are acute with respect to the perpendicular to the plane of the retarder 300; wherein the reflected light rays 412 return through the retarder 300 and are then transmitted by the additional polarizer 318.

[0296] Accordingly, the retarder 300 does not provide an overall transformation of the polarization component 380 to the ambient light 410 that passes through the additional polarizer 318 and then through the retarder 300 along an axis perpendicular to the plane of the switchable retarder, but rather provides an overall transformation of the polarization component 372 to the ambient light rays 412 that pass through the absorptive polarizer 318 and then through the retarder 300 at certain polar angles that are acute with respect to the perpendicular to the plane of the retarder 300.

[0297] Accordingly, Figure 15C the polarity distribution of the light reflection shown in provides a high reflectivity at typical snooper positions that can be achieved by the privacy state of the retarder 300. Accordingly, in the privacy operation mode, the reflectivity at off-axis viewing positions increases as shown in Figure 15C and the brightness of the off-axis light from the spatial light modulator decreases as shown in Figure 15B .

[0298] In the public operation mode, the control systems 710, 752, 350 are arranged to switch the switchable liquid crystal retarder 301 to a second retarder state in which a phase shift is introduced to the polarization component of light passing therethrough along an axis inclined with respect to the normal to the plane of the switchable liquid crystal retarder 301.

[0299] By comparison, the solid angle range 402D can be substantially the same as the solid angle range 402B in the public operation mode. This control of the output solid angle ranges 402C, 402D can be achieved by synchronous control of the light source groups 15, 17 and at least one switchable liquid crystal retarder 300.

[0300] Advantageously, for off-axis viewing, a privacy mode with low image visibility can be achieved, and for the public operation mode, a larger solid angle range with high efficiency can be provided for sharing a display image among multiple users and increasing image spatial uniformity.

[0301] An additional polarizer 318 is arranged on the same output side of the spatial light modulator 48 as the display output polarizer 218, which may be an absorption dichroic polarizer. The display polarizer 218 and the additional polarizer 318 have parallel transmission directions 219, 319 of the electric vectors. As described below, such parallel alignment provides high transmission for the central viewing position.

[0302] The transmissive spatial light modulator 48 is arranged to receive output light from the backlight source; the input polarizer 210 is arranged on the input side of the spatial light modulator in the space between the backlight source 20 and the spatial light modulator 48; the output polarizer 218 is arranged on the output side of the spatial light modulator 48; the additional polarizer 318 is arranged on the output side of the output polarizer 218; and the switchable liquid crystal retarder 300 includes a liquid crystal material layer 314 arranged between at least one additional polarizer 318 and the output polarizer 318, in this case, the additional polarizer 318 is arranged on the output side of the output polarizer 218; and the control system 710 is arranged to synchronously control the light sources 15, 17 and at least one switchable liquid crystal retarder 300.

[0303] The control system 710 further includes control of a voltage controller 752, which is arranged to provide control of a voltage driver 350 to effect control of the switchable liquid crystal retarder 301.

[0304] It may be assumed that the features of the Figure 18B embodiments not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0305] Advantageously, a privacy display is provided that has a high reflectivity for off-axis snoops while maintaining a low reflectivity for coaxial observers. As described above, such increased reflectivity provides enhanced privacy performance for the display in the surrounding lighting environment.

[0306] The operation in the common mode will now be described.

[0307] Figure 19A is a schematic view showing the propagation of the output light from the spatial light modulator through the Figure 1 optical stack in the common operating mode in a side view; and Figure 19B is a schematic view showing Figure 19A the output brightness of the transmitted light varying with the polar direction in

[0308] It may be assumed that the features of the Figure 19A and Figure 19B embodiments not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0309] When the liquid crystal retarder 301 is in the first of the two states, the retarder 300 does not provide a total transformation of the polarization components 360, 361 to the output light that passes perpendicularly to the plane of the switchable retarder 301 or at an acute angle to the perpendicular of the plane of the switchable retarder 301. That is, the polarization component 362 is substantially the same as the polarization component 360, and the polarization component 364 is substantially the same as the polarization component 361. Thus, Figure 19B the angular transmission profile of

[0310] Figure 19C is shown in a top view of the propagation of ambient illumination light through Figure 1 the optical stack in the common operating mode; and Figure 19D is a schematic view showing Figure 19C the reflectance of the reflected light in

[0311] Therefore, when the liquid crystal retarder 301 is in the first of the two states, the retarder 300 does not provide a total transformation of the polarization component 372 to the ambient light 412 that passes through an additional polarizer 318 and then through the retarder 300, i.e., perpendicular to the plane of the retarder 300 or at an acute angle to the perpendicular of the plane of the retarder 300.

[0312] In the operation in the common mode, the input light 412 has a polarization state 372 after passing through the additional polarizer 318. For the front direction and the off-axis direction, no polarization transformation occurs, and thus the reflectance of the light 402 from the reflective polarizer 302 is low. The light 412 is transmitted by the reflective polarizer 302 and is lost in the optical isolators 218, 518 in the backlight of Figure 1 or Figure 2 the emission spatial light modulator 38 of

[0313] It can be assumed that the features of the embodiments of Figure 19C and Figure 19D not discussed further in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0314] Advantageously, in the common operating mode, high brightness and low reflectance are provided over a wide viewing field. Such a display can be conveniently viewed by multiple observers with high contrast.

[0315] A display device including an emissive display will now be described.

[0316] Figure 20Schematic diagram of a switchable directional display device shown in a perspective view including a directional backlight and two switchable liquid crystal retarders each disposed between a pair of polarizers. Compared with Figure 13 the arrangement of, emissive displays such as OLED displays or micro-LED displays include an additional quarter-wave plate 202 between the pixel layer 214 and the output polarizer 218. Advantageously, the unwanted reflectivity from the backplane 214 is reduced.

[0317] It can be assumed that the features of the embodiments of Figure 20 not further discussed in detail correspond to the features with equivalent reference numerals as discussed above, including any potential variations in the features.

[0318] Figure 21A Schematic diagram showing the polar and azimuthal variations of the output luminance of an emissive spatial light modulator.

[0319] Figure 21B Schematic diagram showing the polar and azimuthal variations of the transmission of a first switchable retarder disposed between a first pair of parallel polarizers for an exemplary embodiment of Table 3.

[0320]

[0321] Table 3

[0322] Figure 21C Schematic diagram showing the polar and azimuthal variations of the relative reflection of a first switchable retarder 300A disposed between a reflective polarizer 302 and an absorptive polarizer 318A for an exemplary embodiment of Table 3.

[0323] Figure 21D Schematic diagram showing Figure 20 the polar and azimuthal variations of the total display reflectivity ρ(θ, φ) in the privacy operation mode of the arrangement of

[0324] Figure 21E Schematic diagram showing the polar and azimuthal variations of the transmission of a second switchable retarder 300B disposed between a second pair of parallel polarizers for an exemplary embodiment of Table 3.

[0325] Figure 21F Schematic diagram showing Figure 20 the polar and azimuthal variations of the output luminance P(θ, φ) in the privacy operation mode of the arrangement of

[0326] Figure 21G Schematic diagram showing Figure 20 the polar and azimuthal variations of the visual safety level S of the display front luminance in the privacy operation mode for the arrangement of, the value Y of the display front luminance measured in nits最大 It is half of the illuminance value I measured in lux.

[0327] Figure 21H It shows for Figure 20 the schematic diagram of the extreme change of the zero-elevation visual safety level S of the front display brightness in the privacy operation mode for the arrangement of, where the value Y of the front display brightness measured in nits 最大 It is half of the illuminance value I measured in lux. Desirably, the safety level S is greater than 1.8 at + / -45°.

[0328] Now, other types of switchable privacy displays will be described.

[0329] The display device 100 that can be switched between the privacy operation mode and the public operation mode includes an imaging waveguide and a light source array, as described in U.S. Patent No. 9,519,153, which is incorporated herein by reference in its entirety. The imaging waveguide images the light source array onto an optical window, and the optical window can be controlled to provide high coaxial brightness and low off-axis brightness in the privacy mode, and high brightness with a large solid angle cone for public operation.

[0330] Switchable angle contrast profile liquid crystal displays are described in Japanese Patent Publication No. JPH1130783 and U.S. Patent Publication No. 2017-0123241, both of which are incorporated herein by reference in their entirety. Such displays can provide out-of-plane tilting of liquid crystal molecules in the liquid crystal layer 214 of the liquid crystal display and can achieve reduced off-axis image contrast in the privacy operation mode. The control system 500 of the display device 100 can further include control of the out-of-plane tilting of the liquid crystal molecules.

[0331] As can be used herein, the terms "substantially" and "about" provide an industry-acceptable tolerance for the correlation between their corresponding terms and / or items. Such industry-acceptable tolerance ranges from zero percent to ten percent and corresponds to, but is not limited to, component values, angles, etc. The range of such correlation between items is between about zero percent and ten percent.

[0332] Although various embodiments in accordance with the principles disclosed herein have been described above, it should be understood that these embodiments are presented by way of example only and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with any claims issued from the present disclosure and their equivalents. Additionally, the above advantages and features are provided in the described embodiments, but the application of such issued claims should not be limited to the processes and structures that achieve any one or all of the above advantages.

[0333] In addition, the section headings provided herein are for consistency with the recommendations under 37 CFR 1.77 or to provide organizational cues. These headings should not limit or characterize the embodiments set forth in any claims that may be issued from this disclosure. Specifically and by way of example, although the heading refers to "Technical Field", the claims should not be limited by the language selected under the heading to describe the so-called field. Additionally, the technical descriptions in the "Background Art" should not be construed as admitting that certain techniques are prior art to any embodiments in this disclosure. The "Summary of the Invention" is also not considered to be a characteristic of the embodiments set forth in the issued claims. Further, any reference to the singular form of "the invention" in this disclosure should not be used to argue that there is only a single novel point in this disclosure. Multiple embodiments may be set forth in accordance with the limitations of the multiple claims issued from this disclosure, and such claims accordingly define the embodiments protected thereby and their equivalents. In all cases, the scope of these claims should be considered in light of this disclosure on its own merits and should not be limited by the headings set forth herein.

Claims

1. A privacy display device, the privacy display device comprising: A display device, the display device being arranged to display an image, the display device being capable of providing a privacy function, wherein Compared with the visibility of the image to an on-axis viewer, the visibility of the image to an off-axis viewer is reduced; A control system, the control system being arranged to control the display device; And An ambient light sensor, the ambient light sensor being arranged to detect the illuminance level of ambient light, wherein the control system is arranged to control the luminance of the displayed image based on a detected illuminance level of the ambient light according to a transfer function, and when the privacy function is provided, the transfer function maintains the relationship Y 最大 ≤Y 上限 , where Y 最大 is the maximum output luminance of the display device, and Y 上限 is given by the following equation: Wherein Y 上限 The equation is applicable to an observation direction that forms a polar angle θ of 45° with the normal of the display device at at least one azimuth angle around the normal of the display device. I is the detected illuminance level of the ambient light, and the unit of I is Y 最大 The unit of which is multiplied by the solid angle in steradians, ρ(θ = 45°) is the reflectivity of the display device along the observation direction, P(θ = 45°) is the ratio of the luminance of the display device along the viewing direction to the maximum output luminance Y of the display device 最大 and S 最小 The value is 1.0 or greater.

2. The privacy display device according to claim 1, wherein S 最小 has a value of 1.5 or greater.

3. The privacy display device according to claim 1, wherein S 最小 has a value of 1.8 or greater.

4. The privacy display device according to any one of the preceding claims, wherein the display device has a symmetric major axis and minor axis, and the equation of Y 上限 is applicable to an observation direction having a polar angle θ of 45° with respect to the normal of the display device at an azimuth angle corresponding to at least one of the major axis and the minor axis.

5. The privacy display device according to claim 1, wherein the control system is arranged to control the brightness of the displayed image based on the detected illuminance level of the ambient light according to a transfer function that maintains the relationship Y 最大 ≥Y 下限 where Y 下限 is given by the following equation: Wherein Y 下限 The equation applies to an observation direction that forms a polar angle θ of 10° with the direction of the maximum output luminance of the display device at at least one azimuth angle in the direction around the maximum output luminance of the display device. ρ(Δθ = 10°) is the reflectivity of the display device along the observation direction at a polar angle θ of 10° with respect to the direction of the maximum output brightness of the display device; P(Δθ=10°) is the ratio of the luminance in the viewing direction of the display device at a polar angle θ of 10° with respect to the direction of the maximum output luminance of the display device to the maximum output luminance Y of the display device 最大 and S 最大 The value is 0.1 or less.

6. The privacy display device according to claim 1, wherein the transfer function is shaped as a step function in which the brightness of the displayed image increases with the detected illuminance level of the ambient light.

7. The privacy display device according to claim 1, wherein I is the detected illuminance level of the ambient light incident on the display device in the incident direction and reflected to the observation direction.

8. The privacy display device according to claim 1, wherein the display device is capable of operating in at least a public mode and a privacy mode, wherein the privacy function is provided in the privacy mode, and compared with the public mode, the visibility of the image to an off-axis viewer is reduced, and the control system is capable of selectively operating the display device in the public mode or the privacy mode for at least one area of the display device.

9. The privacy display device according to claim 7, wherein the display device is capable of operating in at least a public mode and a privacy mode, wherein the privacy function is provided in the privacy mode, and compared with the public mode, the visibility of the image to an off-axis viewer is reduced, wherein the control system is arranged to selectively operate the display device in the public mode or the privacy mode in response to the detected illuminance level of the ambient light.

10. The privacy display device according to claim 8 or 9, wherein the transfer function provides a higher brightness of the displayed image in the public mode than in the privacy mode.

11. The privacy display device according to claim 1, wherein The display device includes a backlight and a transmissive spatial light modulator arranged to receive light from the backlight, and The control system is arranged to control the brightness of the displayed image by controlling the brightness of the backlight and / or by controlling the light transmission performed by the spatial light modulator.

12. The privacy display device according to claim 1, wherein The display device includes an emissive spatial light modulator, and The control system is arranged to control the brightness of the displayed image by controlling the light emission performed by the spatial light modulator.

13. The privacy display device according to claim 1, wherein the maximum output brightness of the display device is along the normal of the display device.

Images