Locally different gamma mapping for multi-pixel density OLED display

A method for driving an organic light emitting diode (OLED) display having a first area with a first pixel density and a second area with a second pixel density higher than the first pixel density, the method includes receiving image content that specifies a grayscale value for both a first pixel in the first area and a second pixel in the second area, providing, based on the grayscale value, a first voltage to the first pixel in the first area, and providing, based on the grayscale value, a second voltage that is different from the first voltage to the second pixel in the second area, where the second voltage causes the second pixel to emit light less brightly than the first voltage causes the first pixel to emit light.

BACKGROUND

Electronic devices include displays that can change in brightness.

SUMMARY

This specification describes techniques, methods, systems, and other mechanisms for locally different gamma mapping for multi-pixel density organic light-emitting diode (OLED) displays. Gamma mapping may change gamma values of pixels in images to compensate for various luminance effect of displays. For example, gamma mapping may include gamma correction to account for non-linear human perceptive bias of brightness, i.e., humans being more sensitive to changes in brightness at low levels than at high ones.

An OLED display that has areas with different pixel densities across the display may vary in brightness. For example, a first area of the display may have pixels that are a similar size to a second area of the display but only have half the number of pixels per unit area in comparison to the second area. Accordingly, if the two areas of the display are both showing a completely white image, the first area may appear dimmer than the second area as fewer pixels per unit area in the first area may emit light compared to the second area.

In order to keep luminance of the lower pixel density region similar to the higher pixel density region, the luminance of each pixel in the lower pixel density region may be increased. For example, each of the pixels in the lower pixel density region may be made to be twice as bright as each pixel in the higher pixel density region.

Increasing the brightness of each pixel may be done through gamma mapping based on whether the pixels are in the first area or the second area. For example, image content may be provided for display where a pixel in the first area and a pixel in the second area may both have a same digital grayscale value of G255 (the highest gray level in 8-bit grayscale), a pixel data voltage, VDATA, of 1.5 volts (V) may then be provided to the pixel in the first area, and a voltage of 2.5 V may then be provided to the pixel in the second area, where providing a voltage of 1.5 V to pixels may result in the pixels emitting light brighter than providing a voltage of 2.5 V to the pixels due to p-channel transistor behavior in the pixel circuit.

Accordingly, locally different gamma mapping for multi-pixel density OLED displays may enable multi-pixel density OLED displays to have a uniform luminance even between areas of the OLED displays that have different pixel densities. Having a uniform luminance may hide the difference in pixel density of areas of the display from viewers and users may not even realize the display has areas with different pixel densities from a distance.

Additionally, in some implementations, matching luminance between areas of the OLED displays that have different pixel densities may limit a maximum luminance of the displays. For example, at high display brightness settings a maximum brightness of pixels in the lower pixel density region may be insufficient to produce an overall luminance in the lower pixel density region that matches the luminance that could otherwise be produced in the higher pixel density region. Accordingly, the brightness of the pixels in the different pixel density areas may be further adaptively adjusted based on display brightness settings to increase a maximum luminance of the displays.

In general, one innovative aspect of the subject matter described in this specification can be embodied in a method for driving an organic light emitting diode (OLED) display having a first area with a first pixel density and a second area with a second pixel density higher than the first pixel density, the method including receiving image content that specifies a grayscale value for both a first pixel in the first area and a second pixel in the second area, providing, based on the grayscale value, a first voltage to the first pixel in the first area, and providing, based on the grayscale value, a second voltage that is different from the first voltage to the second pixel in the second area, where the second voltage causes the second pixel to emit light less brightly than the first voltage causes the first pixel to emit light.

These and other embodiments can each optionally include one or more of the following features. In some aspects, providing, based on the grayscale value, a second voltage that is different from the first voltage to the second pixel in the second area includes determining a remapped grayscale value for the second pixel based on the value and providing the second voltage based on the remapped grayscale value. In certain aspects, determining a remapped grayscale value for the second pixel based on the grayscale value includes determining that a location of the second pixel is within the second area and in response to determining that the location of the second pixel is within the second area, determining the remapped value for the second pixel based on the grayscale value and a lookup table for the second area.

In some implementations, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes determining that a location of the first pixel is within the first area and in response to determining that the location of the first pixel is within the first area, determining a remapped grayscale value for the first pixel based on the grayscale value and a lookup table for the first area. In certain aspects, providing the second voltage based on the remapped grayscale value includes providing the remapped grayscale value to a driver integrated circuit and providing, by the driver integrated circuit, the second voltage to the second pixel, where the driver integrated circuit is configured to output voltages in response to grayscale values that are input irrespective of locations of pixels that are driven by the voltages output.

In some aspects, the number of digital bits for the remapped grayscale value is higher than or equal to grayscale bit numbers for the grayscale value. In some implementations, providing, based on the grayscale value, a second voltage that is different from the first voltage to the second pixel in the second area includes receiving, by a driver integrated circuit, the grayscale value for the second pixel and providing, by the driver integrated circuit to the second pixel, the second voltage based on both the grayscale value and the second pixel being in the second area. In some aspects, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes receiving, by the driver integrated circuit, the grayscale value for the first pixel and providing, by the driver integrated circuit to the first pixel, the first voltage based on both the grayscale value and the first pixel being in the first area.

In certain aspects, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes providing the first voltage to the first pixel in the first area where the first voltage results in the first area having a unit area brightness that is less than a unit area brightness of the second area and a brightness setting for the display satisfies a criteria. In some aspects, actions include receiving second image content that also specifies the grayscale value for the first pixel in the first area and providing a third voltage that is different than the first voltage to the first pixel in the first area and the brightness setting for the display does not satisfy the criteria.

In some implementations, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes providing the first voltage to the first pixel in the first area where the first voltage results in the first area having a unit area brightness that is similar to a unit area brightness of the second area and a brightness setting for the display does not satisfy a criteria.

DETAILED DESCRIPTION

FIG.1is a block diagram of an example system100that includes a multi-pixel density OLED display panel110using locally different gamma mapping. The system100also includes a gamma mapper120that performs locally different gamma mapping on image content to generate remapped image content, and includes a driver integrated circuit130that receives the remapped image content and outputs voltages to the display panel110based on the remapped image content.

The display panel110includes a first area112and a second area114, where the first area112includes a pixel density that is lower than a pixel density of the second area114. For example, as shown inFIG.1, the first area112and the second area114may include pixels that have the same sizes between the areas, but the first area112may have a lower pixel density than the second area114as a pattern of pixels in the first area112may correspond to the pattern of the pixels in the second area114where three out of four pixels in the pattern of the pixels in the second area is missing, in other words, the first area112has a quarter pixels per unit area (a quarter pixel density) of the second area114.

The pixels in the display panel110may be configured to emit light at different brightness based on voltages received by the pixels. For example, each of the pixels in the display panel110may be configured to emit light at a first brightness in response to receiving 2.5 V and emit light at four times the first brightness in response to receiving 1.5 V.

The gamma mapper120may receive image content to be shown on the display panel110and generate remapped image content based on image content. For example, the gamma mapper120may receive image content with a grayscale value of G255 for both a pixel in the first area112and a pixel in the second area114and, in response, generate remapped image content with a grayscale value of G1023 for the pixel in the first area and G767 for the pixel in the second area.

The gamma mapper120may generate remapped image content based on locally different gamma mapping. For example, the gamma mapper120may map the grayscale value of G255 to G1023 for all pixels in the first area112and map the grayscale value of G255 to G767 for all pixels in the second area114. In another example, the gamma mapper120may the grayscale value of G127 to G511 for all pixels in the first area112and map the grayscale value of G127 to G383 for all pixels in the second area114.

The gamma mapper120may generate the remapped image content based on remapping a value for each pixel based on the location of the pixel in the display panel. The gamma mapper120may receive a digital grayscale value for a pixel, determine which area that the pixel is located, and then remap the grayscale value for the pixel based on a remapping range for the corresponding area.

For example, the gamma mapper120may determine that pixel data in an image is to be displayed in the first area112of the display panel110, in response, obtain a lookup table for the first area112that maps grayscale values from a first range of 0-255 to a second range of 0-1023. In another example, the gamma mapper120may determine that a pixel data in an image is to be displayed in the second area114of the display panel110, in response, obtain a lookup table for the second area114that maps grayscale values from a first range of 0-255 to a third range of 0-767. The lookup table may include rows for each grayscale value in the first range of 0-255 and, for each row, a corresponding remapped grayscale value.

In some implementations, the gamma mapper120may remap image content through circuitry. For example, the gamma mapper120may be implemented entirely in hardware circuitry that receives grayscale values for pixels and outputs remapped grayscale values differently based on the locations of the pixels in the display panel110, where the circuitry is arranged based on which pixels are located in which of the first area112and the second area114. In another implementation, the gamma mapper120may be implemented by software and use a formula that receives a grayscale value for a pixel and a location of the pixel as a paired input, and outputs a remapped grayscale value for the pixel as output. In yet other implementations, the gamma mapper120may be implemented by software and use the lookup tables as described above. In still another implementations, the gamma mapper120may be implemented by a combination of circuitry and software.

The driver integrated circuit130may be circuitry that is configured to provide voltage signals to pixels in a display panel110based on digital grayscale values received from a gamma mapper120for the pixels. For example, the driver integrated circuit130may be configured to provide a voltage of 2.5 V in response to receiving a grayscale value of G767 and a voltage of 1.5 V in response to receiving a grayscale value of G1023. The driver integrated circuit130may receive other control factors that affect the final output voltage signal level of a same grayscale data for a pixel, such as display brightness control, display uniformity calibration, color calibration, and pattern loading effect control.

WhileFIG.1shows a display with two areas with different pixel density, the gamma mapper120may similarly remap image content for a display panel with three, four, or more areas with different pixel densities based on providing drive signals with different pulse widths to the corresponding areas. For example, the gamma mapper120may include a map that defines which of four areas that each pixel is within, for each area, a lookup table for remapping grayscale values for the area, and then remap image content based on determining which of the four areas each pixel in the image content corresponds based on the map and then applying the lookup table for the determined area to the grayscale values to obtain remapped grayscale values.

FIG.2is a visualization200of locally different gamma mapping.FIG.2may represent locally different gamma mapping based on the system100shown inFIG.1. As shown inFIG.2, a grayscale value of G255 for all pixels in a normal pixel density area, e.g., the second area114, may be remapped by the gamma mapper120to G767 which results in the driver integrated circuit130providing 2.5 V to pixels which results in fifty nanoamps (nA) which results in four hundred fifty nit brightness. Additionally, as shown inFIG.2, a grayscale value of G255 for all pixels in a quarter pixel density area, e.g., the first area112, may be remapped by the gamma mapper120to G1023 which results in the driver integrated circuit130providing 1.5 V to pixels which results in four times higher pixel current, two hundred nanoamps (nA), which results in four hundred fifty nit brightness for the quarter pixel density area.

In some implementations, the gamma mapper120may generate remapped image content based on a same scale as the received image content. For example, the gamma mapper120may use the same 8-bit scale for image content and remapped image content but use different ranges for the different areas such that G255 is remapped to G191 for pixels in the second area114and remapped to G255 for pixels in the first area112.

While the examples describe locally different gamma mapping on grayscale values, locally different gamma mapping may independently be applied to red, green, blue (RGB) values. For example, a grayscale value of G255 of red pixels in the second area114may be remapped as G767 while a grayscale value of G255 of blue pixels in the second area114may be remapped as G760 by a gamma mapper120by independent different look-up tables of each color.

FIG.3is block diagram of another example system300that includes a multi-pixel density OLED display110using locally different gamma mapping. The system300may be similar to the system100in using locally different gamma mapping and having the display panel110with a first area112with less pixel density than a second area114. However, the system300may have gamma mapping integrated into the driver integrated circuit310instead of by a gamma mapper that is separate from the driver integrated circuit310.

The driver integrated circuit310may receive image content and then provide voltages based on the image content and locally different gamma mapping. For example, the driver integrated circuit310may receive G255 for a first pixel in the first area112, in response, provide 1.5 V, receive G255 for a second pixel in the second area114, and, in response, provide 2.5 V. In another example, the driver integrated circuit310may receive G255 for a third pixel in the first area112, in response, provide 1.5 V, receive G255 for a fourth pixel in the second area114and, in response, provide 2.5 V.

In some implementations, the driver integrated circuit310provides voltages on different ranges between the different areas. For example, the driver integrated circuit310may receive a digital grayscale value for pixels, determine a data voltage level for a pixel in the second area114based on the grayscale value in a range between 6.5 V and 2.5 V, and determine a data voltage level for a pixel in the first area112based on the grayscale value in a range between 6.5 V and 1.5 V (or a range between 6.3 V and 1.5 V).

In some implementations, the driver integrated circuit310may provide integrated gamma mapping through circuitry. For example, the driver integrated circuit310may include circuitry that receives grayscale values for pixels and outputs voltage differently based on the locations of the pixels in the display panel110, where the circuitry is arranged based on which pixels are located in which of the first area112and the second area114. In another implementation, the driver integrated circuit310may use a formula that receives a grayscale value for a pixel and a location of the pixel as a paired input, and outputs a voltage as output.

FIG.4Ais a visualization400of locally different gamma mapping.FIG.4may represent locally different gamma mapping based on the system300shown inFIG.3. As shown inFIG.4A, a grayscale value of G255 for all pixels in a normal pixel density area, e.g., the second area114, may result in the driver integrated circuit310providing 2.5 V to pixels which results in fifty nanoamps (nA) of OLED pixel current and corresponding four hundred fifty nit brightness. Additionally, as shown inFIG.4A, a grayscale value of G255 for all pixels in a quarter pixel density area, e.g., the first area112, may result in the driver integrated circuit310providing 1.5 V to pixels which results in four times higher OLED pixel current, two hundred nanoamps (nA), and corresponding four hundred fifty nit brightness for the quarter pixel density area.

FIG.4Bis a visualization450of adaptive locally different gamma mapping. In some implementations, matching luminance between areas of the OLED displays that have different pixel densities may limit a maximum luminance of the displays. For example, at high display brightness settings a maximum brightness of pixels in the lower pixel density region may be insufficient to produce an overall luminance in the lower pixel density region that matches the luminance that could otherwise be produced in the higher pixel density region. Accordingly, the brightness of the pixels in the different pixel density areas may be further adaptively adjusted based on display brightness settings to increase a maximum luminance of the displays.

InFIG.4B, IOLEDNORMAL refers to current to a pixel in a normal pixel density area of the display, LOLED NORMALrefers to a unit area brightness of the normal pixel density area, PLOLED NORMALrefers to a luminance of a pixel in the normal pixel density area, IOLED LOWrefers to current to a pixel in a low pixel density area of the display, LOLED LOWrefers to a unit area brightness of the low pixel density area, PLOLED LOWrefers to a luminance of a pixel in the low pixel density area.

A unit area brightness may refer to a perceived luminance for a unit area. For example, a group of four pixels in a two pixel size by two pixel size area may have a unit area brightness that is the same as the luminance of each pixel, and a group of two pixels in a two pixel size by two pixel size area may have a unit area brightness that is half the luminance of each pixel.

In the example shown inFIG.4B, a multi-pixel density OLED display may have a maximum pixel brightness of seven hundred twenty nits and the pixels in the lower density area are half as dense as the pixels in the higher density area/the normal pixel density area. Accordingly, if the luminance of unit areas in the normal pixel density area and the lower density area were to always have matching unit area brightness, the unit area brightness of the normal pixel density area would be limited to three hundred sixty nits as the pixels in the lower density area may only be able to reach seventy hundred twenty nits per pixel to provide a unit area brightness of three hundred sixty nits.

With adaptive locally different gamma mapping, the normal pixel density area and the lower density area may have non-matching unit area brightness. For example, as shown inFIG.4B, for the value of G255 and a display brightness setting of 100%, the normal pixel density area may have a unit area brightness of four hundred fifty nits and the lower density area may have a unit area brightness of three hundred sixty nits. In another example, for the value of G254 and a display brightness setting of 100%, the normal pixel density area may have a unit area brightness of four hundred forty seven nits and the lower density area may have a unit area brightness of three hundred fifty eight nits.

Display brightness setting may be a global setting for a brightness of a display, and may also be referred to as a brightness setting. For example, a user may set a display brightness setting of a device that includes the display to 0% while the user is using the device in the dark, then set the display brightness setting of a device to 50% while the user is using the device under a lamp, and then set the display brightness setting of a device to 100% while the user is using the device under a lamp.

The display brightness may control a brightness that images are displayed on the display. For example, G255 may be displayed in a normal pixel density area with ninety nits at 20% display brightness setting and displayed in a normal pixel density area with four hundred fifty nits at 100% display brightness setting. Similarly, G254 may be displayed in a normal pixel density area with eighty nine nits at 20% display brightness setting and displayed in a normal pixel density area with four hundred forty eight nits at 100% display brightness setting.

Adaptive locally different gamma mapping may have unit area brightnesses of the low pixel density area and the normal pixel density area match or not match based on a brightness setting of the display brightness. For example, adaptive locally different gamma mapping may have unit area brightnesses of the low pixel density area and the normal pixel density area match for a brightness setting of 50%. In another example, adaptive locally different gamma mapping may have unit area brightnesses of the low pixel density area and the normal pixel density area not match for a brightness setting of 90%

Adaptive locally different gamma mapping may be implemented within a gamma mapper separate from a driver integrated circuit or within a driver integrated circuit with integrated gamma mapping. For example, the gamma mapper120ofFIG.1or the driver integrated circuit310ofFIG.3with integrated gamma mapping may have different gamma lookup tables for the normal pixel density area for different display brightness settings, and have different gamma lookup tables for the normal pixel density area for different display brightness settings.

The gamma lookup tables for brightness settings that do satisfy the criteria may result in a unit area brightness in the low pixel density area that is less than the unit area brightness of the low pixel density area. For example, for a criteria of 80% or brighter, each pair of gamma lookup tables for the low pixel density area and the normal pixel density area for brightness settings from 80% to 100% may result in a unit area brightness in the low pixel density area that is less than the unit area brightness in normal pixel density area. The gamma lookup tables for brightness settings that do not satisfy the criteria may result in a unit area brightness in the low pixel density area that is equal to the unit area brightness of the low pixel density area. For example, for a criteria of 80% or brighter, each pair of gamma lookup tables for the low pixel density area and the normal pixel density area for brightness settings from 0% to 79% may result in a unit area brightness in the low pixel density area that is equal to the unit area brightness in the normal pixel density area.

FIG.5is a flowchart that shows a process500for locally different gamma mapping. The process500may be performed by the system100or the system300. The process500includes receiving image content that specifies a grayscale value for both a pixel in the first area and a pixel in the second area (510). For example, the gamma mapper120may receive image content that specifies G255 for all pixels in the display panel110. In another example, the driver integrated circuit310may receive image content that specifies G255 for all pixels in the display panel110.

The process500includes providing, based on the grayscale value, a first voltage to the first pixel in the first area (520). For example, the driver integrated circuit130may provide a voltage of 1.5 V for the first pixel in the first area112.

In some implementations, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes providing the first voltage to the first pixel in the first area, where the first voltage results in the first area having a unit area brightness that is less than a unit area brightness of the second area and a brightness setting for the display satisfies a criteria. For example, as shown inFIG.4B, for a value of G255 and a display brightness setting of 100%, a voltage may be provided to a pixel in a lower density area that results in a unit area brightness of three hundred sixty nits which is less than a unit area brightness of four hundred fifty nits for a unit area brightness of a normal pixel density area for a same value of G255.

In some implementations, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes providing the first voltage to the first pixel in the first area, where the first voltage results in the first area having a unit area brightness that is similar to a unit area brightness of the second area and a brightness setting for the display does not satisfy a criteria. For example, as shown inFIG.4B, for a value of G255 and a display brightness setting of 20%, a voltage may be provided to a pixel in a lower density area that results in a unit area brightness of ninety nits which is the same unit area brightness of ninety nits for a unit area brightness of a normal pixel density area for a same value of G255.

The process500includes providing, based on the grayscale value, a second voltage to the second pixel in the second area (530). For example, the driver integrated circuit130may provide a voltage of 2.5 V for the second pixel in the second area114.

In some implementations, providing, based on the grayscale value, a second voltage that is different from the first voltage to the second pixel in the second area includes determining a remapped grayscale value for the second pixel based on the grayscale value and providing the second voltage based on the remapped grayscale value. For example, the gamma mapper120may determine a remapped grayscale value of G767 based on the grayscale value of G255 and the driver integrated circuit130may provide a voltage of 2.5 V based on the remapped grayscale value of G767.

In some implementations, determining a remapped grayscale value for the second pixel based on the grayscale value includes determining that a location of the second pixel is within the second area and, in response to determining that the location of the second pixel is within the second area, determining the remapped grayscale value for the second pixel based on the grayscale value and a lookup table for the second area. For example, the gamma mapper120may determine that the second pixel is within the second area114and, in response, determine the remapped grayscale value of G767 based on a lookup table for the second area114that maps G255 to G767.

In some implementations, providing, based on the grayscale value, a first voltage to the first pixel in the first area includes determining that a location of the first pixel is within the first area and in response to determining that the location of the first pixel is within the first area, determining a remapped grayscale value for the first pixel based on the grayscale value and a lookup table for the first area. For example, the gamma mapper120may determine that the first pixel is within the first area112and, in response, determine the remapped grayscale value of G1023 based on a lookup table for the first area112that maps G255 to G1023.

In some implementations, providing the second voltage based on the remapped grayscale value includes providing the remapped grayscale value to a driver integrated circuit and providing, by the driver integrated circuit, the second voltage to the second pixel, where the driver integrated circuit is configured to output voltages in response to grayscale values that are input irrespective of locations of pixels that are driven by the voltages output. For example, the gamma mapper120may provide the remapped grayscale value of G767 to the driver integrated circuit130that provides a voltage of 2.5 V any time the driver integrated circuit130receives an input of G767.

In some implementations, the remapped grayscale value is a 10-bit value and the grayscale value is an 8-bit value. For example, the gamma mapper120may receive values represented in 8-bits and output remapped values represented in 10-bits.

In some implementations, providing, based on the grayscale value, a second voltage that is different from the first voltage to the second pixel in the second area includes receiving, by a driver integrated circuit, the grayscale value for the second pixel and providing, by the driver integrated circuit to the second pixel, the second voltage based on both the grayscale value and the second pixel being in the second area. In the implementation, providing, based on the grayscale value, a first voltage to the first pixel in the first area may also include receiving, by the driver integrated circuit, the grayscale value for the first pixel and providing, by the driver integrated circuit to the first pixel, the first voltage based on both the grayscale value and the first pixel being in the first area. For example, the driver integrated circuit310may receive a grayscale value of G255 for both a pixel in the first area112and a pixel in the second area114and, in response, provide a grayscale value of 2.5 V to the pixel in the second area114and a grayscale value of 1.5 V to the pixel in the first area112.

In some implementations, actions include receiving second image content that also specifies the grayscale value for the first pixel in the first area and providing a third voltage that is different than the first voltage to the first pixel in the first area and the brightness setting for the display does not satisfy the criteria. For example, the display brightness setting may be changed from 100% to 20% and, for the same value of G255, a lower pixel density area may be provided a lower voltage.