Patent Description:
Electronic devices include flat panel displays on which visual images may be shown. For example, a user of a computing device may view visual images on a flat panel display while watching a video or playing a video game. Display quality of flat panel displays can degrade over time.

<CIT> describes an apparatus for detecting variations in light output of an electroluminescent (EL) device is described. The EL device includes a transparent substrate having a first edge extending in a first direction and a plurality of EL emitters disposed over the face of the substrate in the first direction, and some of the light emitted by each EL emitter travels through the substrate and out of the first edge. A light sensor physically separated from the first edge senses the light travelling out of the first edge. A controller stored first sensed light at a first time and second sensed light at a later second time and computes a variation in light output of one or more of the EL emitters in the EL device using the stored first sensed light and second sensed light. At a time just before the first time, the controller can turn off all the EL emitters and receive a reading of sensed flare light from light sensor. The controller can subtract the sensed flare light from the first reading of first sensed light and store the difference in memory as the first sensed light.

<CIT> describes determining a light intensity level of emitted light from an illuminator of a display device and the ambient light surrounding the display device such that, for example, the display device may compensate for performance variations of the illuminator over time. During a calibration setup procedure, with the illuminators off, the light sensor may then sense an ambient light intensity level. Another calibration sample may be generated by the light sensor that captures both the controlled ambient light and the emitted light from the illuminators. Because the portion of the combined light intensity level attributable to the ambient light is known, that portion can be subtracted from the combined light intensity level to determine a light intensity level portion attributable to the illuminators. The calculated portion attributable to the illuminators can be saved as the expected light intensity level. A processor may generate an intensity offset corresponding to the difference between an emitted light intensity level and the expected light intensity level.

Aspects of the present invention are defined in the independent claims. Some preferred features are defined in the dependent claims.

Techniques are described for display burn-in compensation.

In flat panel display systems, such as organic light-emitting diode (OLED) displays, OLED material efficiency can degrade over time. Display degradation can be accelerated due to high current densities (e.g., high luminance), and ambient conditions such as high temperatures.

Display degradation can result in decreasing pixel brightness over time. For example, at a given driving voltage, an OLED of a pixel or sub-pixel may become dimmer over a period of days, weeks, and months. Pixel degradation over time can be referred to as "burn-in.

In order to extend OLED lifetime, luminance degradation can be estimated using statistical burn-in information. A display system can apply compensation based on a burn-in behavior model. Compensation can include raising the driving voltage over time in order to maintain consistent pixel brightness and color as the OLEDs degrade.

In some cases, actual display burn-in may not follow the burn-in model exactly. The display pixels may degrade at a faster or slower rate than the burn-in model. Thus, the compensation may raise the driving voltage to a value that is too high, or to a value that is not high enough, to maintain consistent brightness and color.

A display system can include sensors underneath the display. The sensors can include, for example, ambient light sensors (ALS) and red-green-blue (RGB) color sensors. The ALS and/or RGB sensors can receive and measure ambient light and color to adapt display brightness and color.

The ALS and/or RGB sensors under a display can also receive internally reflected OLED light. The sensors can measure a luminance of received light during both emission-on periods and emission-off periods. The display system can then compare the measured light from the sensors during the emission-on time to measured light from the sensors during the emission-off time to calculate a luminance of the internally reflected light.

The display system can compare the luminance of the internally reflected light to a reference luminance that is based on the burn-in model. Based on the difference between the reflected light luminance and the reference luminance, the display system can estimate the error of current burn-in compensation model. The display system can then update the burn-in model based on the estimated error. For example, the display system can apply a correction factor to the burn-in model that reduces the error to zero, or near zero.

The techniques described can improve flat-panel display quality. For example, the techniques described can maintain consistent brightness and color of the display. The techniques described can also extend OLED lifetime.

In general, one innovative aspect of the subject matter described in this specification can be embodied in methods for compensating an image to be shown on a display including an array of light-emitting pixels, with a sensor being arranged to receive light transmitted by adjacent light-emitting pixels of the display. A method includes collecting, from the sensor, a luminance of light received by the sensor during an emission-on period during which the adjacent light-emitting pixels emit light; collecting, from the sensor, a luminance of light received by the sensor during an emission-off period during which the adjacent light-emitting pixels emit no light; calculating, by comparing the luminance of the light received during the emission-on period to the luminance of the light received during the emission-off period, a luminance of light internally reflected from the adjacent light-emitting pixels and received by the sensor during the emission-on period; determining that an error between the luminance of light internally reflected from the adjacent light-emitting pixels and a reference luminance equals or exceeds a threshold error; and adjusting a driving voltage for driving the light-emitting pixels to reduce the error.

The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some implementations, the array of light-emitting pixels includes an array of OLEDs.

In some implementations, the driving voltage drives the light-emitting pixels based on a burn-in model.

In some implementations, adjusting the driving voltage to reduce the error includes adjusting the burn-in model by a correction factor.

In some implementations, the correction factor includes an additive inverse of the error.

In some implementations, the sensor is one of an ambient light sensor or an RGB sensor.

In some implementations, the reference luminance includes an expected luminance of light internally reflected from the adjacent light-emitting pixels and received by the sensor.

In some implementations, determining that an error between the luminance of light internally reflected from the adjacent light-emitting pixels and the reference luminance equals or exceeds a threshold error includes accumulating the error over a period of time; averaging the error; and comparing the averaged error to the threshold error.

In some implementations, adjusting the driving voltage includes adjusting the driving voltage for all pixels of the array.

In some implementations, adjusting the driving voltage includes adjusting the driving voltage for a selection of pixels of the array.

Implementations of the above techniques include methods, apparatus, systems and computer program products. One such computer program product is suitably embodied in a non-transitory machine-readable medium that stores instructions executable by one or more processors. The instructions are configured to cause the one or more processors to perform the above-described actions.

<FIG> are diagrams of an example electronic device <NUM> with a display <NUM> and a light sensor <NUM>. <FIG> illustrates a front perspective view of the electronic device <NUM>. <FIG> illustrates an example cross section view of the electronic device <NUM>.

Referring to <FIG>, the electronic device <NUM> may be, for example, a smart phone, a television, a smart watch, or a handheld game console. The display <NUM> includes an array of light-emitting pixels. In operation, the display <NUM> can display an image by illuminating the light-emitting pixels. The display <NUM> may be, for example, an active matrix organic light-emitting diode (OLED), or a light-emitting diode (LED) liquid crystal display (LCD). The electronic device <NUM> includes the light sensor <NUM> adjacent to the display <NUM>. For example, the light sensor <NUM> may be located behind the display <NUM> from the front perspective view of the electronic device <NUM>.

An OLED display generally includes an array of pixels, each pixel including one or more OLEDs. An OLED display is typically driven by driver circuits including a row driver and a column driver. The row driver, e.g., a scan driver, sequentially selects each row of pixels in the display, and the column driver, e.g., a data driver, provides a driving voltage to pixel circuits in the selected row. The pixel circuits generate electric current that corresponds to the driving voltage. The pixel circuits provide the current to OLEDs of the pixel, enabling the selected OLEDs to emit light, and presenting an image on the display. Signal lines such as scan lines and data lines may be used in controlling the pixels to display images on the display.

Referring to <FIG>, the light sensor <NUM> is located adjacent to the display <NUM>. For example, the light sensor <NUM> may be located under the display <NUM>, from the cross section view of the electronic device <NUM>. In some examples, the light sensor <NUM> can be connected to a motherboard of the electronic device <NUM>. In some examples, the light sensor <NUM> can be connected to a back cover <NUM> of the electronic device <NUM>.

The light sensor <NUM> can receive ambient light <NUM> through the display <NUM>. The light sensor <NUM> can be, for example, an ambient light sensor (ALS) or a red-green-blue (RGB) color sensor. In some examples, the light sensor <NUM> can receive electromagnetic energy in a range of bands of the electromagnetic spectrum. In some examples, the electronic device <NUM> can include more than one light sensor <NUM>.

An ALS sensor can measure ambient light to adapt display brightness. An ALS can detect overall light intensity surrounding the electronic device <NUM>. Based on the detected light intensity, the display <NUM> can adjust brightness and contrast. Adjusting brightness and contrast can improve visibility of images on the display <NUM> and can improve battery life of the electronic device <NUM>.

An RGB sensor can measure ambient color to adapt display color. An RGB sensor includes individual sensors that can detect red, green, and blue light. An RGB sensor can detect a proportion of each color in the light surrounding the electronic device <NUM>. Based on detected color, the display <NUM> can adjust color balance. Adjusting color balance can improve visibility and quality of images on the display <NUM>.

This specification describes burn-in compensation techniques primarily with reference to luminance of light emitted by pixels, as measured by an ALS sensor. However, the techniques described can also be applied to luminance of individual subpixels, e.g., RGB subpixels, as measured by an RGB sensor.

<FIG> show cross section views 200a, 200b of the example display <NUM> and the light sensor <NUM> in an emission-off ("OFF") condition and an emission-on ("ON") condition, respectively. In both the OFF condition and the ON condition, the sensor <NUM> receives ambient light <NUM> through adjacent pixels <NUM> of the display <NUM>.

<FIG> shows a cross section view of the example display <NUM> and the light sensor <NUM> in the OFF condition. In the OFF condition, the adjacent pixels <NUM> emit no light. Thus, the sensor <NUM> receives only the ambient light <NUM>.

<FIG> shows a cross section view of the example display <NUM> and the light sensor <NUM> in the ON condition. In the ON condition, the adjacent pixels <NUM> emit light.

Some of the light emitted from each of the pixels <NUM> is projected light <NUM>. The projected light <NUM> projects outward from a surface <NUM> of the display <NUM>, such that an image is shown on the display <NUM>.

Some of the light emitted from each of the pixels <NUM> is reflected light <NUM>. The reflected light <NUM> reflects away from the surface <NUM> of the display <NUM>. The reflected light <NUM> can reflect off of one or more internal layers of the display <NUM>. Some of the reflected light <NUM> may be received by the sensor <NUM>. Thus, in the ON condition, the sensor <NUM> receives both ambient light <NUM> and reflected light <NUM>. The reflected light <NUM> from the adjacent pixels <NUM> is a fraction of the total light emitted from the adjacent pixels <NUM>. The intensity, or luminance, of the reflected light <NUM> may be indicative of the intensity of light emitted from the pixel <NUM>. For example, the luminance of the reflected light <NUM> may be proportional to the luminance of light emitted from the pixels <NUM>.

The sensor <NUM> can receive and measure a luminance of received light while in the OFF condition, and while in the ON condition. The difference between received luminance while in the OFF condition and the ON condition is the luminance of the reflected light, and therefore indicates the luminance of light emitted from the pixels <NUM>. The luminance of light emitted from the pixels <NUM>, and therefore the luminance of reflected light, may change over time due to degradation, or burn-in. The luminance of light emitted from the pixels <NUM>, and therefore the luminance of reflected light, may also change over time due overcompensation or undercompensation by a burn-in model.

<FIG> is a diagram of a display system <NUM> of the electronic display <NUM>. The display system <NUM> is an OLED display system that includes an array <NUM> of light-emitting pixels. Each light-emitting pixel includes an OLED. The OLED display is driven by drivers including scan/emission drivers <NUM> and data drivers <NUM>. In general, the scan/emission drivers <NUM> selects a row of pixels in the display, and the data drivers <NUM> provide data signals (e.g. voltage data) to the pixels in the selected row to light the selected OLEDs according to the image data. Signal lines such as scan lines, emission lines, and data lines may be used in controlling the pixels to display images on the display. <FIG> illustrates the display system having the scan/emission drivers on one side of the system but the drivers can be placed on both left and right sides of the display improving the driving performance (e.g. speed).

The display system <NUM> includes the pixel array <NUM> that includes a plurality of light-emitting pixels, e.g., the pixels P11 through P43. A pixel is a small element on a display that can change color based on the image data supplied to the pixel. Each pixel within the pixel array <NUM> can be addressed separately to produce various intensities of color. The pixel array <NUM> extends in a plane and includes rows and columns. A row extends horizontally across the array. For example, the first row of the pixel array <NUM> includes pixels P11, P12, and P13. A column extends vertically down the display. For example, the first column of the pixel array <NUM> includes pixels P11, P21, P31, and P41. Only a few pixels are shown in <FIG> for simplicity. In practice, there may be several million pixels in the pixel array <NUM>. Greater numbers of pixels can result in higher image resolution.

The display system <NUM> includes scan/emission drivers <NUM> and data drivers <NUM>. The scan/emission drivers <NUM> are integrated, i.e., stacked, row line drivers that supply signals to rows of the pixel array <NUM>. For example, the scan/emission drivers <NUM> supply scan signals S1 to S4, and emission signals E1 to E4, to the rows of pixels. The data drivers <NUM> supply signals to columns of the pixel array <NUM>. For example, the data drivers <NUM> supply data signals D1 to D4 to the columns of pixels.

Each pixel in the pixel array <NUM> is addressable by a horizontal scan line and emission line, and a vertical data line. For example, the pixel P11 is addressable by the scan line S1, the emission line E1, and the data line D1. In another example, the pixel P32 is addressable by the scan line S3, the emission line E3, and the data line D2.

The display system <NUM> includes a display driver integrated circuit (DDIC) <NUM> that receives display input data <NUM> from a system-on-chip (SoC) <NUM>. The DDIC <NUM> may include a graphic controller and a timing controller. The DDIC <NUM> generates the timing of the signals for delivery to the display. The DDIC <NUM> provides the input signals (e.g. clock signals, start pulses) to the scan/emission drivers <NUM>, and the image data to the data drivers <NUM>.

The scan/emission drivers <NUM> and the data drivers <NUM> provide signals to the pixels enabling the pixels reproduce the image on the display screen. The scan/emission drivers <NUM> and the data drivers <NUM> provide the signals to the pixels via the scan lines, the emission lines, and the data lines. To provide the signals to the pixels, the scan/emission drivers <NUM> select a scan line and control the emission operation of the pixels. The data drivers <NUM> provides data signals to the pixels addressable by the selected scan line to light the selected OLEDs according to the image data.

Although <FIG> illustrates an OLED display, the technique for burn-in compensation may be applied to any flat panel display that includes an array of pixels. For example, the technique for burn-in compensation may be applied to light-emitting diode (LED) liquid crystal displays (LCD) and plasma electronic displays (PDP).

<FIG> is an example operating timing diagram for the example display <NUM> with the light sensor <NUM>. <FIG> shows a graph of pixel emission <NUM>, and a graph of sensor output luminance <NUM>, over time <NUM>.

The pixel emission <NUM> can represent operation, e.g., a driving voltage, of one of the pixels <NUM> that is adjacent to the sensor <NUM>. The pixel emission <NUM> can also represent operation of a row of multiple pixels <NUM> that are adjacent to the sensor <NUM>. The pixel emission <NUM> shows the pixel alternating between a high value <NUM> and a low value <NUM>.

At time <NUM>, the pixel turns off for a duration of an emission-off period <NUM>, illustrated by the pixel emission <NUM> dropping from the high value <NUM> to the low value <NUM>. During the emission-off period <NUM>, the pixel emits no light. At time <NUM>, the pixel turns on for a duration of an emission-on period <NUM>, illustrated by the pixel emission <NUM> rising to the high value <NUM>. During the emission-on period <NUM>, the pixel emits light. At time <NUM>, the pixel turns off again.

The pixel may turn on an off at designated intervals, e.g., corresponding to a frame rate of the display system. During the emission-off period, the display system may program the pixel with image data for a next frame.

The sensor output luminance <NUM> can represent output of the sensor <NUM>. The sensor <NUM> can measure and output luminance (L) of received light over time <NUM>. During the emission-off period <NUM>, the sensor <NUM> only receives ambient light. The sensor <NUM> therefore measures ambient luminance (Lamb) <NUM> of received light during the emission-off period <NUM>.

During the emission-on period <NUM>, the sensor <NUM> receives both ambient light and light internally reflected from the adjacent pixels of the display. Reflected OLED luminance LOLED <NUM> is a luminance of light internally reflected from the adjacent pixels and received by the sensor <NUM> during the emission-on period <NUM>.

The sensor <NUM> measures a total luminance Ltot <NUM> of received light during the emission-on period <NUM> that is a combination of ambient luminance Lamb <NUM> and reflected OLED luminance LOLED <NUM>. By subtracting the ambient luminance Lamb <NUM> from the total luminance Ltot <NUM>, a display system can calculate the reflected OLED luminance LOLED <NUM>. The reflected OLED luminance LOLED <NUM> may be a function of pixel intensity, e.g., may be proportional to pixel luminance. Thus, based on the reflected OLED luminance LOLED <NUM>, the display system can estimate pixel luminance.

<FIG> is a diagram of an example system <NUM> for display burn-in compensation. The system <NUM> compensates an image to be shown on a display, e.g., the display <NUM>. The system <NUM> includes the display <NUM> with the sensor <NUM>, an OLED model error calculator (OMEC) <NUM>, and a burn-in compensator <NUM>. The OMEC <NUM> includes an OLED reference calculator <NUM> and an error accumulator <NUM>. The burn-in compensator <NUM> includes a burn-in model <NUM>. In some examples, the OMEC <NUM>, the burn-in compensator <NUM>, or both, can be components of the DDIC or the SoC, e.g., the DDIC <NUM> or the SoC <NUM> of the display system <NUM>.

The burn-in model <NUM> is a model of expected degradation over time for the pixels of the display <NUM>. The burn-in model <NUM> can include expected average pixel and/or subpixel luminance as a function of time, e.g., time of operation. In general, pixel luminance is expected to decrease over time. The burn-in model <NUM> can be pre-programmed and may be based on historical trends and statistical data.

The burn-in compensator <NUM> can compensate the display <NUM> according to the burn-in model <NUM>. For example, at a certain time of operation, the burn-in model <NUM> may predict that pixels of the display <NUM> will be <NUM>% dimmer, on average, than the initial programmed luminance level. The burn-in compensator <NUM> can therefore provide a compensating signal COMP <NUM> to the display <NUM> to increase the luminance of the pixels by <NUM>%. The compensating signal COMP <NUM> may include, for example, an adjustment to the driving voltage provided by the DDIC <NUM>. The adjusted driving voltage causes the average pixel luminance to rise <NUM>%, returning to the initial programmed luminance level.

In operation, pixel degradation might not follow the burn-in model <NUM> exactly. For example, the burn-in model <NUM> may be based on an expected usage time, expected environmental conditions, e.g., temperature, and other factors. Actual conditions of usage may differ from the expected conditions. Thus, actual pixel luminance at a certain time may be more or less than predicted by the burn-in model <NUM>. The difference between predicted pixel luminance and actual pixel luminance can be considered luminance error.

Due to luminance error, the burn-in compensator <NUM> may overcompensate or undercompensate the display <NUM>. If the burn-in rate is less than predicted by the burn-in model <NUM>, the burn-in compensator <NUM> will likely overcompensate the display <NUM>. This can result in actual pixel luminance exceeding the programmed pixel luminance. If the burn-in rate is greater than predicted by the burn-in model <NUM>, the burn-in compensator <NUM> will likely undercompensate the display <NUM>. This can result in actual pixel luminance being less than the programmed luminance.

The system <NUM> can mitigate undercompensation and overcompensation of burn-in. The system <NUM> can measure errors between expected pixel luminance and actual pixel luminance, and can apply a correction to the burn-in model <NUM>.

In order to measure and mitigate undercompensation and overcompensation of burn-in, the OLED reference calculator <NUM> can calculate a reference luminance LREF <NUM>. The reference luminance LREF <NUM> can be an expected reflected OLED luminance, e.g., a luminance level of reflected light that the sensor <NUM> is expected to receive at a given time. Since the reflected light from each pixel is a fraction of the total light emitted from the pixel, the reference luminance LREF <NUM> is a luminance value that is less than the expected pixel luminance.

The OLED reference calculator <NUM> can be calibrated to the particular display <NUM>. For example, upon assembly, the pixels may emit light at a known, programmed, luminance, given certain display brightness values (DBVs) <NUM>, RGB values <NUM>, and environmental conditions, e.g., ambient temperature (TEMP) <NUM>. The sensor <NUM> can measure the total luminance Ltot <NUM> and the ambient luminance Lamb <NUM>. The OMEC <NUM> can collect, from the sensor <NUM>, data indicating the total luminance Ltot <NUM> and the ambient luminance Lamb <NUM>. The OMEC <NUM> can compare the total luminance Ltot <NUM> to the ambient luminance Lamb <NUM> to calculate the reflected luminance for the known conditions. The OLED reference calculator <NUM> can then be calibrated to correlate the calculated reflected luminance with the known emitted luminance.

Once calibrated, the OLED reference calculator <NUM> can calculate the reference luminance LREF <NUM> based on a number of factors. For example, the OLED reference calculator <NUM> can calculate the reference luminance LREF <NUM> based on programmed DBV <NUM>, RGB values <NUM>, and ambient temperature <NUM>.

During operation, the sensor <NUM> collects sensor data <NUM>. The sensor data <NUM> can include luminance of received light over time, as shown in <FIG>. The sensor data <NUM> can also include the total luminance Ltot <NUM>, measured during emission-on periods, and the ambient luminance Lamb <NUM>, measured during emission-off periods.

The OMEC <NUM> can compare the total luminance Ltot <NUM> to the ambient luminance Lamb <NUM> to calculate the reflected OLED luminance LOLED <NUM>. The OMEC <NUM> can then compare the reflected OLED luminance LOLED <NUM> to the reference luminance LREF <NUM>, e.g., by subtracting LREF <NUM> from LOLED <NUM>, to calculate reflected luminance error ΔL <NUM>.

The reflected luminance error ΔL <NUM> represents a difference between the luminance of light internally reflected from the adjacent pixels and received by the sensor during the emission-on period, and the reference luminance LREF <NUM>. The reflected luminance error ΔL <NUM> can be a positive value or a negative value. A positive ΔL <NUM> can indicate overcompensation, while a negative ΔL <NUM> can indicate undercompensation.

The error accumulator <NUM> can accumulate and average the reflected luminance error ΔL <NUM> over a time period <NUM>. The time period <NUM> can be, for example, a number of hours, days, weeks, or months. The error accumulator <NUM> outputs an average error ΔLavg.

The OMEC <NUM> can compare the average error ΔLavg to a luminance threshold error ΔLthr. The luminance threshold error ΔLthr can be, for example, an error value that may cause visible display effects, e.g., +/-<NUM>% of the programmed luminance.

The OMEC <NUM> may determine that the average error ΔLavg between the luminance of light internally reflected from the adjacent pixels and the reference luminance exceeds the threshold error ΔLthr. If the average error ΔLavg equals or exceeds the luminance threshold error ΔLthr, the OMEC <NUM> can output the average error ΔLavg to the burn-in compensator <NUM>.

The burn-in compensator <NUM> updates the burn-in model <NUM> based on the average error ΔLavg. In some examples, the burn-in compensator <NUM> can update the burn-in model <NUM> by offsetting the burn-in model <NUM> by a correction factor. The correction factor may be, for example, an additive inverse of the average error ΔLavg. For example, the average error ΔLavg may be +<NUM>%. The burn-in compensator <NUM> may update the burn-in model <NUM> by offsetting the burn-in model <NUM> by -<NUM>%, to return the pixel luminance to the programmed value.

In some examples, the burn-in compensator <NUM> may update the burn-in model <NUM> for all of the pixels of the display <NUM>. For example, in smaller displays, the display system may assume that burn-in rates for all of the pixels of the array are approximately equal. Thus, though the sensor <NUM> might only be adjacent to a fraction of pixels of the array, the burn-in model update can be applied to all of the pixels of the display.

In some examples, the burn-in compensator <NUM> may update the burn-in model <NUM> for a selection of the pixels of the display <NUM>. For example, some displays may have more than one sensor, e.g., a first sensor adjacent to a top region of the display and a second sensor adjacent to a bottom region of a display. Thus, the burn-in compensator <NUM> may update the burn-in model <NUM> for pixels of the display that are nearer to the first sensor with model updates calculated using sensor data <NUM> from the first sensor. The burn-in compensator <NUM> may update the burn-in model <NUM> for pixels of the display that are nearer to the second sensor with model updates calculated using sensor data <NUM> from the second sensor.

In some examples, the OMEC <NUM> may continuously calculate luminance error. In some examples, the OMEC <NUM> may calculate luminance error at designated time intervals or in response to an event. For example, the OMEC may calculate luminance error at an interval of once per hour, once per day, or once per week. In some examples, the OMEC may calculate luminance error in response to the display turning on, or in response to receiving input from a user.

The burn-in compensator <NUM> sends the compensation signal COMP <NUM> to the display <NUM>. The compensation signal COMP <NUM> includes an adjusted driving voltage based on the burn-in model, including the applied correction factor based on luminance error. Adjusting the driving voltage by the correction factor can reduce the error to zero, or near zero.

<FIG> is an example graph <NUM> of luminance error over time for the display <NUM> with burn-in compensation. Specifically, <FIG> shows a graph of average error ΔLavg <NUM> over time <NUM>. The burn-in compensator <NUM> maintains the average error ΔLavg <NUM> between a positive update threshold <NUM> and a negative update threshold <NUM>. The positive update threshold <NUM> and/or the negative update threshold <NUM> may be, for example, the luminance threshold error ΔLthr of <FIG>. The burn-in compensator <NUM> prevents the average error ΔLavg <NUM> from reaching either a positive visible threshold error <NUM> or a negative visible threshold error <NUM>.

In some examples, the positive update threshold <NUM>, the negative update threshold <NUM>, the positive visible threshold error <NUM>, and the negative visible threshold error <NUM> can each be a percentage error of the programmed luminance. For example, the positive update threshold <NUM> and the negative update threshold <NUM> may be +<NUM>% and -<NUM>%, respectively. The positive visible threshold error <NUM> and the negative visible threshold error <NUM> may be +<NUM>% and -<NUM>%, respectively.

At time <NUM>, the average error ΔLavg <NUM> is at a value of zero error <NUM>. At zero error <NUM>, the reflected OLED luminance LOLED <NUM> is equal to the reference luminance LREF <NUM>, on average. The display operates for a period of time <NUM>. The time <NUM> may be, for example, multiple weeks or months of operation. Between time <NUM> and time <NUM>, the average error ΔLavg <NUM> increases. The average error ΔLavg <NUM> may increase, for example, due to overcompensation of burn-in.

At time <NUM>, the average error ΔLavg <NUM> reaches the positive update threshold <NUM>. When the average error ΔLavg <NUM> reaches the positive update threshold <NUM>, the OMEC <NUM> outputs the average error ΔLavg <NUM> to the burn-in compensator <NUM>. The burn-in compensator <NUM> updates the burn-in model <NUM> based on the average error ΔLavg <NUM>, e.g., by offsetting the burn-in model by a correction factor of (-ΔLavg). When the burn-in compensator <NUM> updates the burn-in model <NUM>, the average error ΔLavg <NUM> drops <NUM> to zero error <NUM>.

Just after time <NUM>, the average error ΔLavg <NUM> is at a value of zero error <NUM>. At zero error <NUM>, the reflected OLED luminance LOLED <NUM> is equal to the reference luminance LREF <NUM>, on average. Between time <NUM> and time <NUM>, the average error ΔLavg <NUM> decreases. The average error ΔLavg <NUM> may decrease, for example, due to undercompensation of burn-in.

At time <NUM>, the average error ΔLavg <NUM> reaches the negative update threshold <NUM>. When the average error ΔLavg <NUM> reaches the negative update threshold <NUM>, the OMEC <NUM> outputs the average error ΔLavg <NUM> to the burn-in compensator <NUM>. The burn-in compensator <NUM> updates the burn-in model <NUM> based on the average error ΔLavg <NUM>, e.g., by offsetting the burn-in model by the correction factor of (-ΔLavg). In this example, ΔLavg has a negative error value, and (-ΔLavg) has a positive value that is the additive inverse of ΔLavg. When the burn-in compensator <NUM> updates the burn-in model <NUM>, the average error ΔLavg <NUM> rises <NUM> to zero error <NUM>.

The process for burn-in compensation can be used throughout display operation to maintain consistent pixel brightness and color in displays. The system <NUM> can continue to measure luminance error and to update the burn-in model when luminance error reaches designated thresholds. The techniques described can improve display quality and can increase OLED lifetime.

Embodiments of the subject matter and the functional operations described in this specification can be implemented in any suitable electronic device such as a personal computer, a mobile telephone, a smart phone, a smart watch, a smart TV, a mobile audio or video player, a game console, or a combination of one or more of these devices.

The electronic device may include various components such as a memory, a processor, a display, and input/output units. The input/output units may include, for example, a transceiver which can communicate with the one or more networks to send and receive data. The display may be any suitable display including, for example, a cathode ray tube (CRT), liquid crystal display (LCD), or light-emitting diode (LED) display, for displaying images.

Embodiments may be implemented as one or more computer program products, e.g., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium may be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The apparatus may include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) may be written in any form of programming language, including compiled or interpreted languages, and it may be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A program may be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program may be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

Elements of a computer may include a processor for performing instructions and one or more memory devices for storing instructions and data. However, a computer may not have such devices. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks.

Claim 1:
A method of compensating an image to be displayed on a display (<NUM>) comprising a display surface (<NUM>), an array of light-emitting pixels, and a sensor being arranged adjacent the display so as to be behind the display in a front view; the method comprising:
driving the display with driving voltage signals that are compensated according to a burn-in model that represents predicted pixel degradation over time;
collecting, from the sensor, a luminance of light received by the sensor during an emission-on period during which light-emitting pixels (<NUM>) adjacent to the sensor (<NUM>) emit light according to the compensated driving voltage signals, the sensor receiving, during said emission-on period, both an ambient light (<NUM>) passing through the display surface (<NUM>) and light emitted by the adjacent light-emitting pixels (<NUM>) internally reflected away from the display surface (<NUM>);
collecting, from the sensor, a luminance of light received by the sensor during an emission-off period during which the adjacent light-emitting pixels emit no light so that the sensor (<NUM>) receives only the ambient light;
calculating, by comparing the luminance of the light received by the sensor during the emission-on period to the luminance of the light received by the sensor during the emission-off period, a luminance of light internally reflected away from the display surface (<NUM>) and received by the sensor during the emission-on period;
determining a reference luminance that is based on the burn-in model, the reference luminance comprising an expected luminance of light internally reflected from the display surface (<NUM>) that the sensor (<NUM>) is expected to receive;
determining whether an error between the luminance of light internally reflected away from the display surface (<NUM>) and received by the sensor during the emission-on period and the reference luminance based on the burn-in model equals or exceeds a threshold error, the error being indicative of an error in the burn-in model;
responsive to determining that the error equals or exceeds the threshold, updating the burn-in model based on the error;
and
adjusting the driving voltage signals for driving the light-emitting pixels based on the updated burn-in model to reduce the error.