Aging compensation method for active matrix organic light emitting diode (amoled) displays with a privacy mode
The method adjusts subpixel luminance in AMOLED displays to compensate for aging effects, ensuring consistent brightness and color across public and privacy modes by normalizing luminance with dimming factors and temperature compensation, addressing differential aging in AMOLED displays.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MERCEDES BENZ GROUP AG
- Filing Date
- 2025-09-08
- Publication Date
- 2026-05-21
AI Technical Summary
AMOLED displays experience pixel-related aging and burn-in effects, leading to inhomogeneous luminance due to differential degradation in public and privacy modes, which are exacerbated by area-specific luminance adjustments for privacy mode visibility.
A method to adjust the luminance of subpixel units by determining relative luminance loss and applying dimming factors to normalize luminance across all subpixels, with mode-specific thresholds and temperature compensation, ensuring homogeneous image appearance across public and privacy modes.
Maintains consistent brightness and color perception across public and privacy modes by compensating for subpixel-specific aging, extending display lifespan and improving visual homogeneity.
Smart Images
Figure EP2025075512_21052026_PF_FP_ABST
Abstract
Description
[0001] Mercedes-Benz Group AG
[0002] Methods for aging compensation of Active Matrix Organic Light Emitting Diode (AMOLED) displays with privacy mode
[0003] The invention relates to a method for adjusting the luminance of at least two subpixel units, wherein a subpixel unit comprises at least one subpixel of a pixel of an Active Matrix Organic Light Emitting Diode (AMOLED) display, and wherein the method is particularly suitable for compensating for aging processes in AMOLED displays that have a privacy mode.
[0004] Active Matrix Organic Light Emitting Diode (AMOLED) displays are self-illuminating, thin-film devices made of organic semiconducting materials. They comprise pixels arranged in a matrix. AMOLED displays designed for color image reproduction have pixels with at least one green, one blue, and one red subpixel each. However, AMOLED displays designed for monochromatic reproduction are also available. AMOLED displays with customer- or application-specific pixel arrangements and / or geometries are also known. Each pixel has its own contacts for electrically controlling the subpixels. This electrical control is achieved via an active matrix of regularly arranged thin-film transistors.
[0005] The light emitted by a pixel of an AMOLED display is perceived as a color mixture according to the luminance of the colored subpixels. Compared to conventional liquid crystal displays, AMOLED displays have lower power consumption and a higher refresh rate and are more versatile in their application.
[0006] AMOLED displays are subject to pixel-related aging and burn-in effects. Color-related subpixels within a pixel degrade depending on their exposure time (cumulative activation duration), their intensity (emitted luminance), and / or temperature. Consequently, aging depends on the image content displayed on the AMOLED display, either as a whole or on a portion of it. Aging or degradation leads to a reduced luminance of a subpixel, even with the same drive current. This results in inhomogeneous luminance across the display area, despite all pixels receiving the same current. Inhomogeneities are typically perceived visually when neighboring pixels differ in luminance by at least 2 to 3 percent.
[0007] Such aging effects are more pronounced in displays that can be switched between a public mode and a privacy mode. Using such switchable displays, the light distribution characteristics can be changed so that, for example, when installed in the dashboard area of a vehicle, content displayed in public mode is visible to all vehicle occupants, while content displayed in privacy mode is only visible to a front passenger. This prevents driver distraction.
[0008] Such a switchable display can be implemented by dividing the area of each subpixel into a privacy pixel area and a public pixel area. Light emitted from the privacy pixel area is displayed in privacy mode. Light emitted from the public pixel area is displayed in public mode. Thus, only a portion of a pixel's area is available for each mode. To achieve a brightness comparable to conventional (non-switchable) displays, the area-specific luminance must therefore be increased, which further accelerates aging processes. Furthermore, aging processes may affect the public and privacy modes differently because the respective pixel areas age at different rates.For example, a subpixel in Privacy Mode may appear comparatively darker (relative to the average brightness value of all identically addressed subpixels), and a subpixel assigned to the same pixel in Public Mode may appear comparatively brighter.
[0009] In a state-of-the-art method known as data counting for aging compensation, the grayscale value used to control a subpixel (corresponding to the value of a drive current for the subpixel) is changed subpixel-specifically so that the reduced luminance of degraded subpixels is no longer perceptible. Such pixel calibration can be performed during operation (for each video frame displayed on the screen).
[0010] Another known prior art method for aging compensation involves determining pixel calibration based on stored pixel data. This requires capturing parameters, such as a voltage threshold per pixel or block of pixels, and comparing them to reference values stored for the display in the form of a look-up table (LUT). Aging compensation is performed when the luminance or supply current falls below a threshold due to aging.
[0011] LUTs include reference data captured during development, for example a luminance characteristic curve dependent on the voltage threshold as a function of the operating temperature of the display.
[0012] The comparison of subpixel-related parameters (for example, the voltage threshold) with the reference values stored in a LUT and, if necessary, pixel calibration is performed periodically or manually triggered by the user.
[0013] From DE 102016006890 A1, a method for displaying a symbol on a display unit is known. The display unit comprises a plurality of pixels, and each pixel comprises a plurality of controllable subpixels, whose control values define a displayed color value of the pixel. The symbol is displayed using defined pixels of the display unit. The method comprises displaying the symbol using the defined pixels on the display unit; measuring a symbol-related display duration for which the symbol is displayed using the defined pixels on the display unit; and changing the control of the subpixels of each defined pixel as a function of the measured display duration such that the displayed color value of the corresponding pixel is maintained.
[0014] Furthermore, EP 2701 140 A1 describes a method for controlling a multi-pixel display, wherein the method comprises: displaying a plurality of test pattern images on a multi-pixel display; determining a respective value of the measured total electric current consumed by the multi-pixel display while each test pattern image from the plurality of test pattern images is displayed; determining a plurality of current value differences for each respective value of the total electric current, wherein each current value difference within the plurality of current value differences comprises a difference between a respective base current and the respective value of the total electric current, the respective base current being associated with a test pattern image that is displayed while determining the respective value of the total electric current;Determining a plurality of pixel aging characterization values based on the plurality of differences between the electrical current values and the pixel intensity values of pixels in each test pattern image, wherein each pixel aging characterization value within the plurality of pixel aging characterization values represents a respective decrease in the electrical current consumed by a respective group of at least one pixel of the multipixel display; and determining a display aging compensation matrix representing values by which pixel intensity values are to be compensated, based on the plurality of pixel aging characterization values.
[0015] Document US 2024 / 0257719 A1 describes a display surface and display device with surface sections comprising pixels and subpixels configured for different beam angles.
[0016] Document US 2024 / 0212600 A1 describes a method and device for compensating for age-related luminance changes of subpixels of display devices.
[0017] The invention is based on the objective of providing an improved method for adjusting the luminance of subpixel units comprising one or more subpixels of an AMOLED display that may degrade to different degrees during its operating life.
[0018] The problem is solved according to the invention by a method which has the features specified in claim 1.
[0019] Advantageous embodiments of the invention are the subject of the dependent claims. The invention relates to a method for adjusting the luminance of at least two subpixel units of an AMOLED display. Such displays have matrix-like arranged pixels, each pixel being assigned a geometric position (corresponding to a row and a column of the matrix-like arrangement) in an image. A pixel comprises at least one subpixel, for example, for AMOLED displays for color image reproduction, a red, a blue, and a green subpixel corresponding to the emitted light color. A pixel can also, for example, for a monochrome AMOLED display, comprise only one or more subpixels of a single emitted light color.
[0020] According to the invention, the AMOLED display is configured for display in a public mode and a privacy mode. The display modes differ in their spatial radiation characteristics. Preferably, an image displayed in privacy mode is only visible within a more limited solid angle range compared to public mode; however, disjoint (non-overlapping) solid angle ranges are also possible. Public mode subpixels are configured for display in public mode. Privacy mode subpixels are configured for display in privacy mode. Public mode subpixels and privacy mode subpixels are referred to as corresponding if they are displayed at geometrically identical pixel positions, that is, if they appear at the same positions in an image displayed in public mode or privacy mode, respectively.
[0021] A subpixel unit comprises at least one subpixel of a pixel or several pixels, which may, for example, be assigned to the same display mode and preferably arranged spatially adjacent to each other, or which may be assigned to different display modes and arranged spatially in the same or adjacent positions.
[0022] For each subpixel unit, a relative luminance loss is determined based on an initial luminance. For example, the initial luminance of a subpixel unit is determined for a predetermined drive current when the AMOLED display is brand new. Similarly, an initial luminance can also be determined for any other point in time. Preferably, the initial luminance values, assigned to the respective subpixel units, are stored in non-volatile memory for all subpixel units of an AMOLED display, for example, in the form of a table or list.
[0023] Then, at a later time, the luminance emitted at the same drive current (typically reduced by aging) is determined as in the initial measurement. The difference between the initial luminance and the luminance measured at the later time, relative to the initial luminance, determines the relative luminance loss.
[0024] From among all subpixel units eligible for adjustment, the one exhibiting the highest relative luminance loss is selected. If this highest relative luminance loss exceeds a predetermined loss threshold, adjustment is performed; otherwise, no adjustment is made.
[0025] During the adjustment process, a dimming factor is determined for each subpixel unit, which is expressed as a ratio less than or equal to 100% (correspondingly, as a numerical value less than or equal to 1). The dimming factor is calculated such that the normalized luminance (i.e., the luminance relative to the initial luminance) of the respective subpixel unit, multiplied by the dimming factor, is equal to the normalized luminance of the most degraded subpixel unit, but at least equal to a predetermined normalized luminance threshold.
[0026] Each subpixel unit is then driven with a gray value and / or a drive current that is adjusted according to the respective dimming factor. For example, if the most degraded subpixel unit has a relative luminance loss of 5 percent (thus having a normalized luminance of 95%), each subsequent subpixel unit designated for adjustment has its luminance changed so that at maximum gray value (maximum drive current), 95% of the initial luminance of the respective subpixel unit is emitted.
[0027] The method enables the correction of subpixel-specific degradation such that, up to the predetermined normalized luminance threshold, subpixels with varying degrees of degradation appear at the same brightness. This results in a homogeneous image appearance. In one embodiment, at least one public mode subpixel unit and one corresponding privacy mode subpixel unit are selected for this purpose, with the corresponding privacy mode subpixel unit being configured for display at the same pixel position as the public mode subpixel unit. This ensures a homogeneous image appearance when switching between public mode and privacy mode. In other words, the same image content appears identical or very similar in color and brightness in public mode as in privacy mode.
[0028] In one embodiment, the entirety of all subpixel units configured for display in the same display mode is selected for adaptation. For example, all subpixel units designated for display in Public Mode are selected. Alternatively, all subpixel units designated for display in Privacy Mode are selected. Naturally, the method can also be performed for all Public Mode subpixel units as well as, independently, for all Privacy Mode subpixel units.
[0029] This embodiment improves the homogeneity of the display within a display mode.
[0030] In a further development of this embodiment, a first normalized luminance limit is predefined to adjust the subpixel units of the Public Mode display mode, and an independent second luminance limit is predefined to adjust the subpixel units of the Privacy Mode display mode. This allows aging effects, which manifest differently in different display modes (for example, due to different subpixel sizes), to be corrected independently. Thus, for instance, the display in Public Mode remains unaffected by the faster aging of some Privacy Mode subpixels.
[0031] In one embodiment, the relative luminance losses detected at a given time are stored in a stress profile, which assigns a relative luminance loss to each subpixel unit. For example, the detected relative luminance losses for all public mode subpixel units can be stored in a first table (or list), and the detected relative luminance losses for all privacy mode subpixel units can be stored in a second table (or list).
[0032] Such a stress profile, implemented as a table, can be continuously (cyclically) updated. For example, a table can be updated very quickly and in real time in volatile memory until one of the subpixel units it records experiences a luminance loss exceeding the assigned loss threshold. If the loss threshold is exceeded, the table is transferred to non-volatile memory. This ensures that it remains available for correction even after the AMOLED display has been restarted.
[0033] In one embodiment, the dimming factor is determined taking into account the current operating temperature of the AMOLED display. Using a look-up table (LUT) that records a voltage threshold-luminance characteristic as a function of the operating temperature, the current luminance can be determined by measuring a voltage threshold assigned to each subpixel unit. This embodiment enables a particularly fast, simple, and accurate determination of the current luminance and thus also of the relative luminance loss.
[0034] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.
[0035] This shows:
[0036] Fig. 1 schematically shows a pixel of a state-of-the-art AMOLED display.
[0037] Fig. 2 schematically normalized luminance profiles of subpixels of a pixel, Fig. 3 schematically corrected luminance profiles of subpixels of a pixel according to the state of the art,
[0038] Fig. 4 schematically shows a pixel with subpixels for a public mode and subpixels for a privacy mode in different size ratios.
[0039] Fig. 5 schematically shows a pixel with subpixels for a public mode and subpixels for a privacy mode in the same size ratio,
[0040] Fig. 6 schematically shows a stress profile for subpixel units of a public mode and a privacy mode; Fig. 7 schematically shows luminance profiles corrected for adjusting the display in a public mode and in a privacy mode.
[0041] Fig. 8 schematically shows luminance profiles corrected for adjusting the display within a mode, as well as
[0042] Fig. 9 shows a schematic flowchart for correcting luminance.
[0043] Corresponding parts are marked with the same reference numerals in all drawings.
[0044] Figure 1 schematically shows a pixel P of a prior art AMOLED display (not shown in detail). In the embodiment shown here only as an example and purely schematically, the pixel P comprises a red light-emitting red subpixel R, a green light-emitting green subpixel G, and a blue light-emitting blue subpixel B arranged side by side. In other embodiments, pixel P is possible that comprises subpixels R to G of only a single emitting light color, in other geometric shapes, and in other arrangements.
[0045] Figure 2 schematically shows a first to third normalized luminance profile L1, L2, L3 of a normalized luminance LN of the subpixels R, G, B over the operating time T for the pixel P shown in Figure 1. Starting at a normalized luminance LN of 100 percent, the luminance profiles L1, L2, L3 decrease linearly over the operating time T, whereby the normalized luminance LN of the different subpixels R, G, B changes in different ways due to the different burn-in behavior.
[0046] The normalized luminance LN of the blue subpixel B decreases more than the normalized luminance LN of the red subpixel R. In the graph shown here, which is merely an example and purely schematic, the normalized luminance LN of the red subpixel R decreases more than the normalized luminance LN of the green subpixel G. In other words, with increasing operating time T, despite the same supply current, the green subpixel G appears brighter than the red subpixel R, and the red subpixel R appears brighter than the blue subpixel B. The overall perceived color and brightness across pixel P also change accordingly.
[0047] Of course, in addition to the example shown here, other normalized luminance (LN) profiles are possible, for example, a profile in which the normalized luminance (LN) of the green subpixel G decreases more than the normalized luminance (LN) of the red subpixel R. As already explained, the specific characteristics of the normalized luminance (LN) profiles of the various subpixels R, G, and B depend on their past exposure, in particular on the respective brightness values (grayscale values) and / or temperatures to which each subpixel R, G, and B was exposed over time.
[0048] A method for compensating this subpixel-specific aging is illustrated in Figure 3. At time points T1 to T3, the blue subpixel B, which is showing the strongest degradation, emits with normalized luminance values LN1, LN2, and LN3, respectively, where 100% > LN1 > LN2 > LN3. The less degraded green and red subpixels G and R are dimmed at each of time points T1 to T3 so that all subpixels R, G, and B emit with the same normalized luminance values LN1, LN2, and LN3. This dimming can be achieved, for example, by driving the subpixels with a reduced grayscale level (and thus a correspondingly reduced supply current).
[0049] If the measured standardized luminance value LN1, LN2, LN3 falls below a luminance limit value LNG, further dimming would reduce the brightness to such an extent that the display's readability would be impaired. At that point, compensation for aging is no longer possible, and the display's lifespan has reached its end.
[0050] Figure 4 schematically shows a pixel P with a total of six non-overlapping subpixels R1, R2, G1, G2, B1, B2, of which two subpixels are configured in pairs to emit the same color: a first and second red subpixel R1, R2, a first and second green subpixel G1, G2, and a first and second blue subpixel B1, B2. The two subpixels R1 to B2 of the same color can be addressed independently of each other, thus enabling a display in a public mode (in this case, with the first red, green, and blue subpixels R1, G1, B1) and, independently, a display in a privacy mode (in this case, with the second red, green, and blue subpixels R2, G2, B2). By way of example, the emitting area of the second subpixels R2, G2, B2 intended for privacy mode is approximately one-third of the emitting area of the first subpixels R1, G1, B1 intended for public mode.To achieve approximately the same brightness in Privacy and Public Mode, the luminance (and therefore also the current density of the supply current) of a second subpixel R2, G2, B2 intended for Privacy Mode must be higher than the luminance of the respective first subpixel R1, G1, B1 of the same color intended for Public Mode.
[0051] Accordingly, the first subpixels R1, G1, B1 and the second subpixels R2, G2, B2 age differently (and are also additionally influenced by the different, hardly predictable usage behavior).
[0052] Figure 5 shows an embodiment of a pixel P analogous to Figure 4, with the difference that the emitting area of the subpixels R2, G2, B2 intended for Privacy Mode is approximately the same size as the emitting area of the subpixels R1, G1, B1 intended for Public Mode. In such an embodiment, differences in aging behavior are possible due to different usage patterns, for example, different operating times for Public and Privacy Mode and / or different brightness or color of the respective displayed image content.
[0053] The invention is based on the idea of individually compensating each of the subpixels R1 to B2 by monitoring and individually controlling its respective luminance and / or supply current. To simplify the required control electronics and reduce the memory requirements, pixels P or subpixels R1 to B2 of the display can be grouped into blocks.
[0054] Figure 6 illustrates in more detail the differences in the aging behavior of the first subpixels R1, G1, B1 intended for Public Mode compared to the second subpixels R2, G2, B2 intended for Privacy Mode. In the upper right part of Figure 6, a luminance loss AL is plotted for various Public Mode subpixel units S1, Sn.
[0055] A public mode subpixel unit S1, Sn is defined as a subpixel R1, G1, B1 or a block of subpixels R1, G1, B1 that are intended for activation in public mode. A block can, for example, be formed by a set of spatially adjacent subpixels R1, G1, B1. For each such public mode subpixel unit S1, Sn, a luminance loss AL is determined as the difference between the luminance of the respective subpixel unit S1, Sn in an initial state and a luminance measured at a later time T1, T2, T3 during the operating time T.
[0056] The totality of the luminance losses AL of all public mode subpixel units S1, Sn (shown here only as examples) forms a public mode stress profile of the display.
[0057] In the lower right part of Figure 6, a luminance loss AL for Privacy Mode subpixel units ST, Sn', which are intended for activation in Privacy Mode, is shown analogously. Public Mode subpixel units S1, Sn and Privacy Mode subpixel units ST, Sn' shown one above the other correspond to subpixels R1 to B2 or sets of subpixels R1 to B2 that emit in the same color and at corresponding positions in an image displayed in Public Mode or Privacy Mode on an AMOLED display.
[0058] The totality of the luminance losses AL of all Privacy Mode subpixel units ST, Sn' (shown here only as examples) forms a Privacy Mode stress profile of the display.
[0059] Figure 6 illustrates that aging processes in Public Mode and Privacy Mode display at the same locations (corresponding to the subpixel units S1, Sn, ST, Sn' displayed vertically) have different effects (corresponding to different luminance losses AL). Therefore, different compensation must be applied for Public Mode and Privacy Mode.
[0060] The control current of an OLED thin-film transistor (not shown in detail in Figure 6) determines the luminance of a subpixel R1 to B2, pixel P, or subpixel unit S1, Sn, ST, Sn' that it controls. Since the thin-film transistor circuits are voltage-programmable, the thermal load profile of the display tends to alter the voltage-current characteristic of the OLED thin-film transistor. This affects the display's lifespan. Furthermore, temperature represents an additional accelerating factor that contributes to the aging of organic materials. Therefore, it is necessary to monitor the display's temperature throughout its operation. The temperature can be measured either across the entire display or individually (referenced to a subpixel R1 to B2, a pixel P, or a subpixel unit S1, Sn, ST, Sn' formed from it).
[0061] The stress profile of the display, which determines its aging (degradation), can be recorded using additional sensors, monitoring of the image content, and / or pixel current analysis. The aim of this recording is to determine the stress on each pixel P, subpixels R1 to B2, or any subpixel unit S1, Sn, ST, Sn' formed from them.
[0062] Aging detection and / or compensation can be performed automatically or manually (triggered by a user).
[0063] The luminance is cyclically measured with respect to pixel P, subpixels R1 to B2, or subpixel units S1, Sn, ST, Sn', and the total luminance loss AL determined from this is temporarily stored as a stress profile in a temporary memory of the display, for example, in a flash memory (not specified). Storage is performed separately for Public Mode subpixels R1, G1, B1, or subpixel units S1, Sn and for Privacy Mode subpixels R2, G2, B2, or subpixel units ST, Sn'.
[0064] The individually measured luminance loss AL is compared with a loss limit G, G'. The Public Mode loss limit G, which applies to the luminance loss AL of Public Mode subpixel units S1, Sn, can be chosen differently from the Privacy Mode loss limit G', which applies to the luminance loss AL of Privacy Mode subpixel units ST, Sn'.
[0065] If the respective loss limit G, G' is not exceeded, the currently recorded luminance loss AL (which describes the aging accumulated over the previous operating time T of the display) is stored in the assigned temporary memory.
[0066] If the respective loss limit G, G' is reached or exceeded, aging compensation is performed in a manner described in more detail below. The luminance loss AL values recorded as a stress profile in the assigned temporary memory are transferred to a permanent memory (not shown in detail in Figure 6) and then deleted from the temporary memory. Aging compensation for the luminance loss AL can be achieved by pixel-specific adjustment of the image content displayed on the screen. For this purpose, the grayscale value assigned to an individual subpixel R1 to B2, depending on a single frame of a video stream, is transformed in real time.
[0067] For this purpose, the individual frames of the video stream intended for Public Mode are analyzed separately from the individual frames of the video stream intended for Privacy Mode in real time, compared with the respective assigned stress profile and, as explained in more detail below with reference to Figures 7 and 8, adjusted if necessary.
[0068] A first embodiment of the method for compensating subpixel-specific aging is explained in more detail with reference to Figure 7, which shows a first and a second luminance profile L1, L2 over the operating time T (in a similar manner to that already explained in Figure 3). For illustrative purposes only, the first luminance profile L1 is assigned to a public mode subpixel unit S1, Sn, while the second luminance profile L2 is assigned to a private mode subpixel unit ST, Sn' corresponding in color and location of representation.
[0069] Both the first and second luminance curves L1, L2 exhibit age-induced degradation, which can be simplified as a linear decrease in the normalized luminance value starting from an initial normalized luminance value of 100 percent. By way of example, the private mode subpixel unit ST, Sn' shows a greater degradation (a steeper decrease in luminance) than the corresponding public mode subpixel unit S1, Sn.
[0070] Without compensation for the different degradation, the brightness and / or color perception of an image displayed on the screen would change when switching from public mode to private mode. According to the invention, the respective drop in luminance relative to the initial value (normalized luminance LN) is therefore measured as luminance loss AL at certain, preferably equidistant, times T1 to T5. The greater drop (i.e., the lower current value of the normalized luminance LN) determines the compensation by dimming the less degraded element (in this case, the public mode subpixel unit S1, Sn). The dimming occurs inversely proportional to the current values of the normalized luminance LN.
[0071] For example, if at a third time point T3 the normalized luminance LN of the private mode subpixel unit ST, Sn' has dropped to a value of 70 percent and the normalized luminance LN of the public mode subpixel unit S1, Sn has dropped to a value of 80 percent, then the public mode subpixel unit S1, Sn is dimmed by a dimming factor of 7 / 8 = 0.875 (or to 87.5 percent). As a result, the corresponding subpixel units S1 and ST (or Sn and Sn') of both modes appear equally bright, albeit at a brightness reduced by 20 percent compared to the initial state (i.e., an unaged display).
[0072] Such compensation can be performed stepwise (at each of the time points T1 to T5) or continuously depending on the operating time T, by extrapolating the previous degradation profile to the subsequent time points T2 to T5. In the simplified linear representation shown here, this is achieved by continuously applying the dimming factor 7 / 8. In this way, a luminance profile LT of the first subpixel unit S1, Sn, corrected by the compensation, is obtained, which overlaps the second luminance profile L2 of the Privacy Mode subpixel unit ST, Sn' until the fifth time point T5. As a result, displays in Public Mode and Privacy Mode appear equally bright and in the same color.
[0073] When the luminance of the most degraded element (in this case, the second luminance profile L2 of the Privacy Mode subpixel unit ST, Sn') reaches a luminance threshold LNG (here, purely by way of example, at the fifth time point T5), the compensation is terminated. For the less degraded element (in this case, the Public Mode subpixel unit S1, Sn), the luminance threshold LNG is maintained. In other words, the dimming factor, which describes the artificial reduction of the remaining residual luminance of the less degraded element, is increased over time starting at the fifth time point T5.
[0074] With continued use, the dimming factor gradually increases from 7 / 8 and reaches a value of 1 (or 100 percent) at a time not shown in Figure 7, when the luminance of the Public Mode subpixel unit S1, Sn has degraded to the luminance limit LNG. During this time T (i.e., from the fifth time point T5), differences in brightness and / or color of the display occur between Public Mode and Privacy Mode.
[0075] In other words, the embodiment of the method shown in Figure 7 avoids differences in brightness and / or color between a display in Public Mode and a display in Privacy Mode, as long as the aging of none of the subpixel units S1, Sn, ST, Sn' has progressed to such an extent that the luminance limit LNG is reached or fallen below.
[0076] An alternative second embodiment of the method for compensating subpixel-specific aging is explained in more detail with reference to Figure 8. In this embodiment, luminance losses AL are compensated only with respect to the respective mode (Public Mode or Privacy Mode). Here, the degradation is determined separately for different subpixels R1, G1, B1 of Public Mode and for different subpixels R2, G2, B2 of Privacy Mode.
[0077] The degradation of all subpixels R1, G1, B1 of the Public Mode is determined. Less degraded subpixels R1, G1, B1 are dimmed until all subpixels R1, G1, B1 exhibit the same reduced normalized luminance LN as the most degraded subpixel R1, G1, B1 of the Public Mode. The time-dependent profile of the resulting normalized luminance LN of a subpixel R1, G1, B1 of the Public Mode, as a function of operating time T, is shown as the first luminance profile L1.
[0078] Similarly, the degradation of all subpixels R2, G2, B2 of the Privacy Mode is determined. Less degraded subpixels R2, G2, B2 are dimmed so that all subpixels R2, G2, B2 exhibit the same reduced normalized luminance LN as the most degraded subpixel R2, G2, B2 of the Privacy Mode. The time-dependent profile of the resulting normalized luminance LN of a subpixel R2, G2, B2 of the Privacy Mode, as a function of operating time T, is shown as the second luminance profile L2.
[0079] In this way, homogeneity of all pixels P in Public Mode and homogeneity of all pixels P in Privacy Mode is achieved; however, differences in brightness and / or color may occur when switching between Public Mode and Privacy Mode. The determination and subsequent compensation of luminance losses AL takes place at various times T1 to T5 in essentially the same way as already described for Figure 7, although the compensation is based on different subsets of subpixels R1 to B2 (namely, separately for Public Mode and Privacy Mode).
[0080] If the normalized luminance LN of the most degraded subpixel R1 to B2 (referring to either Public Mode or Privacy Mode) reaches a luminance threshold LNG1, LNG2, other (less degraded) subpixels R1 to B2 are no longer dimmed. The applicable luminance thresholds LNG1, LNG2 can be selected differently depending on the mode. In this case, the first luminance threshold LNG1, applicable to Public Mode, is set higher than the second luminance threshold LNG2, applicable to Privacy Mode. These mode-specific luminance thresholds LNG1, LNG2 can be determined based on a model of display aging and / or the vehicle in which the display is installed.
[0081] Once the respective luminance limit values LNG1 and LNG2 are reached (here shown purely as an example at time point T5 – however, the luminance limits LNG1 and LNG2 can also be reached at different times T1 to T5), the dimming of the less degraded subpixels R1 to B2 is gradually reduced. This maintains the respective luminance limit values LNG1 and LNG2 for as long as the pixel-specific degradation allows.
[0082] In other words, the embodiment of the method illustrated in Figure 8 avoids differences in brightness and / or color within a Public Mode representation and within a Privacy Mode representation, as long as the aging of none of the subpixels R1 to B2 has progressed to the point where the respective luminance limit LNG1, LNG2 is reached or falls below the threshold. This embodiment thus enables compensation of inhomogeneities in one mode even when such compensation is no longer possible in the other mode (due to the luminance limit LNG1, LNG2 already being reached there). Figure 9 shows a flowchart for a method for pixel-specific compensation of luminance losses AL. The method comprises steps 1 to 6, which are arranged between a start point SP and an end point EP.
[0083] In the first step, parameters of the display are read. For example, pixel-specific luminance losses AL are recorded.
[0084] In the second step 2, the recorded parameters are stored in a temporary memory, for example in a flash memory.
[0085] In a third step, it is checked whether the parameters are outside a permissible range. For example, it is checked whether an individual luminance loss AL of a subpixel R1 to B2 or a subpixel unit S1, Sn, ST, Sn' reaches or exceeds an assigned loss limit G, G'. Similarly, it can be checked whether a value of an individual normalized luminance LN reaches or falls below an assigned luminance limit LNG, LNG1, LNG2. If the respective parameter is within the permissible range, the procedure ends at endpoint EP. Otherwise, steps four to six are executed sequentially.
[0086] In the fourth step, the temperature of the display is read.
[0087] In step 5, a pixel-specific aging compensation process is performed, as illustrated in Figures 7 and 8. This process begins with aging compensation based on individual pixels P or blocks of pixels P. As a result of this aging compensation, visually perceptible brightness differences may occur. These brightness differences are then compensated for or reduced by dimming, as shown in Figures 7 and 8.
[0088] In step six, a status diagnosis is stored in a temporary memory.
Claims
Mercedes-Benz Group AG Patent claims 1. Method for adjusting the luminance of at least two subpixel units (S1, Sn, ST, Sn'), wherein a subpixel unit (S1, Sn, ST, Sn') comprises at least one subpixel (R, G, B, R1, G1, B1, R2, G2, B2) of a pixel (P) of an Active Matrix Organic Light Emitting Diode (AMOLED) display, wherein - the AMOLED display includes public mode subpixel units (S1, Sn) configured for display in a public mode display mode and privacy mode subpixel units (ST, Sn') configured for display in a privacy mode display mode, - for each subpixel unit (S1, Sn, ST, Sn') a relative luminance loss (AL) is determined in relation to an initial luminance of the respective subpixel unit (S1, Sn, ST, Sn'), - the most degraded subpixel unit (S1, Sn, ST, Sn') is determined to be the subpixel unit (S1, Sn, ST, Sn') with the highest relative luminance loss (AL), characterized in that, - if the relative luminance loss (AL) of the most degraded subpixel unit (S1, Sn, ST, Sn') exceeds a loss limit (G, G'), a dimming factor less than or equal to 100 percent is determined for each subpixel unit (S1, Sn, ST, Sn') such that the normalized luminance (LN) of the respective subpixel unit (S1, Sn, ST, Sn') multiplied by the dimming factor is equal to the normalized luminance (LN) of the most degraded subpixel unit (S1, Sn, ST, Sn'), but at least equal to a predetermined normalized luminance limit (LNG, LNG1, LNG2), - each subpixel unit (S1, Sn, ST, Sn') is controlled with a gray value and / or drive current adapted to the respective dimming factor and, - if the relative luminance loss (AL) of the most degraded subpixel unit (S1, Sn, ST, Sn') does not exceed the loss limit (G, G'), no subpixel unit (S1, Sn, ST, Sn') is adjusted with a dimming factor.
2. Method according to claim 1 characterized in that at least one Public Mode subpixel unit (S1, Sn) and one corresponding Privacy Mode subpixel unit (ST, Sn') are selected for adaptation, wherein the corresponding Privacy Mode subpixel unit (ST, Sn') is set up for display at the same pixel position as the Public Mode subpixel unit (S1, Sn).
3. Method according to claim 1 , characterized in that, for adaptation, the entirety of all subpixel units (S1, Sn, ST, Sn') is selected which are set up for display in the same display mode.
4. Method according to claim 3, characterized in that a first normalized luminance limit value (LNG1) is predefined for adapting the Public Mode subpixel units (S1, Sn) and a second luminance limit value (LNG2) independent of this is predefined for adapting the Privacy Mode subpixel units (ST, Sn').
5. Method according to any one of the preceding claims, characterized in that the relative luminance losses (AL) recorded at a time (T 1 to T5) are stored in a stress profile which assigns a relative luminance loss (AL) to each subpixel unit (S1, Sn, ST, Sn'), wherein the stress profile is stored in a volatile memory if the assigned loss limit (G, G') is not exceeded, and is stored in a non-volatile memory if the assigned loss limit (G, G') is exceeded.
6. Method according to any one of the preceding claims, characterized in that the dimming factor is determined taking into account the operating temperature of the AMOLED display using a reference table (look-up table). Table LUT) is determined, which captures a voltage threshold-luminance characteristic curve assigned to the AMOLED display as a function of the operating temperature.