PATENT DOCUMENT

Publication Number: US-9666137-B2
Application Number: US-91151310-A
Country: US
Kind Code: B2

Title: OLED driving technique

Abstract:
Systems, methods, and devices for efficient brightness control for an organic light emitting diode (OLED) display are provided. In one embodiment, such a method may include receiving image data into a data driver of an organic light emitting diode display and transforming the image data into a logarithmic domain. A dimming control value may be subtracted from this log-encoded image data. The resulting log-encoded dimmed image data may represent a darker version of the originally received image data. Thereafter, a pixel of the organic light emitting diode display may be driven based at least in part on the dimmed image data.

Claims:
What is claimed is: 
     
       1. A method comprising:
 receiving image data into a data driver of an organic light emitting diode display; 
 transforming the image data into a logarithmic domain to obtain log-encoded image data using the data driver; 
 performing a subtraction operation comprising subtracting a logarithmic dimming control value from the log-encoded image data to obtain log-encoded dimmed image data using the data driver, wherein the log-encoded dimmed image data represents a darker version of the received image data; and 
 driving a pixel of the organic light emitting diode display based at least in part on the log-encoded dimmed image data using the data driver. 
 
     
     
       2. The method of  claim 1 , wherein the image data received into the data driver comprises data in a gamma-corrected domain and wherein the image data is transformed from the gamma-corrected domain to the logarithmic domain to obtain the log-encoded image data. 
     
     
       3. The method of  claim 1 , wherein the image data received into the data driver comprises data in a linear domain and wherein the image data is transformed from the linear domain to the logarithmic domain to obtain the log-encoded image data. 
     
     
       4. The method of  claim 1 , comprising refining the log-encoded dimmed image data by performing a system correction operation or a dithering operation, or a combination thereof, on the log-encoded dimmed image data. 
     
     
       5. The method of  claim 1 , comprising converting the log-encoded dimmed image data from the logarithmic domain to an organic light emitting diode pixel brightness control domain via a digital-to-analog converter to obtain an analog voltage, wherein the pixel is driven based at least in part on the analog voltage. 
     
     
       6. An organic light emitting diode display comprising:
 an organic light emitting diode panel having pixels configured to output light based at least in part on an analog driving signal; and 
 a data driver integrated circuit configured to provide the analog driving signal to the organic light emitting diode panel, wherein the data driver is configured to receive image data and a logarithmic dimming control value, to transform the image data from a non-logarithmic domain into a logarithmic domain to obtain log-encoded image data, to perform a subtraction operation comprising subtracting the logarithmic dimming control value from the log-encoded image data to obtain log-encoded dimmed image data, and to convert the log-encoded dimmed image data into the analog driving signal. 
 
     
     
       7. The display of  claim 6 , wherein the data driver integrated circuit is configured to convert the log-encoded dimmed image data into the analog driving signal via a digital-to-analog converter, wherein the digital-to-analog converter is programmed to transform the log-encoded dimmed image data from the logarithmic domain to an organic light emitting diode pixel brightness control domain. 
     
     
       8. The display of  claim 6 , wherein the data driver integrated circuit is configured to receive the image data, wherein the image data comprises a first plurality of bits, and to transform the image data from the non-logarithmic domain into the logarithmic domain to obtain the log-encoded image data, wherein the log-encoded image data encodes the same information as the image data using a second plurality of bits, wherein the second plurality of bits is less than the first plurality of bits. 
     
     
       9. The display of  claim 8 , wherein the log-encoded image data comprises additional bits added to the second plurality of bits to prevent a loss of precision when the logarithmic dimming control value is subtracted from the log-encoded image data. 
     
     
       10. The display of  claim 6 , wherein the data driver integrated circuit is configured to refine the log-encoded dimmed image data by replacing 2 or 3 real bits with 2 or 3 virtual bits before converting the log-encoded dimmed image data into the analog driving signal. 
     
     
       11. A data driver for an organic light emitting diode display comprising:
 circuitry configured to receive image data in a first domain from a framebuffer; 
 circuitry configured to transform the image data from the first domain to a second domain, wherein the second domain is a logarithmic domain, to obtain log-encoded image data; 
 circuitry configured to convert the log-encoded image data into log-encoded dimmed image data, wherein the log-encoded dimmed image data comprises a logarithmic representation of a darker version of the image, wherein the circuitry configured to convert the log-encoded image data into the log-encoded dimmed image data comprises circuitry configured to perform a subtraction operation by subtracting a logarithmic dimming control value from the log-encoded image data; and 
 a digital-to-analog converter programmed to transform the log-encoded dimmed image data from the second domain to a third domain to obtain an analog OLED pixel driving signal for driving a pixel of the organic light emitting diode display. 
 
     
     
       12. The data driver of  claim 11 , wherein the first domain is a gamma-corrected domain and the third domain is an organic light emitting diode pixel brightness control domain. 
     
     
       13. The data driver of  claim 11 , wherein the first domain and the third domain are the same. 
     
     
       14. The data driver of  claim 11 , wherein the digital-to-analog converter comprises a resistor ladder having a plurality of taps and a multiplexer, the plurality of taps providing a respective plurality of voltages, wherein the multiplexer is configured to select from among the plurality of taps based on the log-encoded dimmed image data to obtain the analog OLED pixel driving signal, wherein the plurality of taps is configured to provide the respective plurality of voltages such that the digital-to-analog converter transforms the log-encoded dimmed image data from the second domain to the third domain to obtain the analog OLED pixel driving signal. 
     
     
       15. The data driver of  claim 14 , wherein a plurality of refinement taps is configured to provide a respective plurality of refinement voltages to the resistor ladder such that the plurality of taps provides the respective plurality of voltages. 
     
     
       16. An electronic device comprising:
 memory configured to store image data; and 
 an organic light emitting diode display configured to output light based at least in part on an analog driving signal, wherein the organic light emitting diode display is configured to determine the analog driving signal by receiving the image data from the memory, transforming the image data from a framebuffer-encoded domain into a logarithmic domain to obtain log-encoded image data, operating on the log-encoded image data, and converting the log-encoded image data from the framebuffer-encoded domain to an organic light emitting diode pixel brightness control domain to obtain the analog driving signal, wherein operating on the log-encoded image data comprises performing a subtraction operation comprising subtracting a logarithmic dimming control value from the log-encoded image data such that the resulting log-encoded image data encodes a darker version of the image data stored in the memory without a substantial change in color. 
 
     
     
       17. The electronic device of  claim 16 , wherein the image data has 8 bits, the log-encoded image data has 7 bits plus one or more additional precision bits before being operated on by the organic light emitting diode display and 9 real bits and 2 virtual bits after being operated on by the organic light emitting diode display. 
     
     
       18. The electronic device of  claim 16 , wherein the organic light emitting diode display is configured to convert the log-encoded image data into the analog driving signal via a digital-to-analog converter configured to transform the log-encoded image data to an organic light emitting diode pixel brightness control domain.

Description:
BACKGROUND 
     The present disclosure relates generally to electronic display brightness control and, more particularly, to brightness control for an organic light emitting diode (OLED) display. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Flat panel displays, such as liquid crystal displays (LCDs) organic light emitting diode (OLED) displays, are commonly used in a wide variety of electronic devices, including such electronic devices as televisions, computers, and hand-held devices (e.g., cellular telephones, audio and video players, gaming systems, and so forth). Such display panels typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, such devices typically use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to reduce power usage. 
     Electronic displays are not always used at a full brightness setting, but rather may operate at variable brightness levels. For example, since LCDs are backlit, brightness may be adjusted by increasing or decreasing an amount of light emitted by a backlight. The amount of light emitted by the backlight corresponds to the amount of light emitted through each of pixel of the LCD. On the other hand, OLED displays do not rely on a backlight, but rather each OLED may emit light individually. Thus, the brightness of an OLED display may be varied by changing the power supplied to each OLED. 
     While increasing or decreasing the amount of power may increase or decrease the amount of light emitted by each OLED, the precise amount of light emitted by each OLED may vary according to a nonlinear function. As such, many techniques for adjusting the brightness of OLED screens have conventionally involved performing complex calculations on image data to ensure that when a brightness-adjusted image is displayed on the OLED display, each pixel displays a proper color and brightness. For example, a nonlinear transfer function may be applied to framebuffer-encoded image data and a dimming value divided from the image data. This dimmed image data then may be converted to an analog OLED pixel brightness control signal that is used by the OLED display to output light from OLED pixels. These conventional techniques may consume excessive system resources and/or may be incompatible with existing LCD brightness control mechanisms. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     Systems, methods, and devices for efficient brightness control for an organic light emitting diode (OLED) display are provided. In one embodiment, such a method may include receiving image data into a data driver of an organic light emitting diode display and transforming the image data into a logarithmic domain. A dimming control value may be subtracted from this log-encoded image data. The resulting log-encoded dimmed image data may represent a darker version of the originally received image data. Thereafter, a pixel of the organic light emitting diode display may be driven based at least in part on the dimmed image data. 
     Various refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of an electronic device capable of performing the techniques disclosed herein, in accordance with an embodiment; 
         FIG. 2  is an embodiment of the electronic device of  FIG. 1  in the form of a handheld device, in accordance with an embodiment; 
         FIG. 3  is an embodiment of the electronic device of  FIG. 1  in the form of a computer, in accordance with an embodiment; 
         FIG. 4  is a schematic block diagram of an organic light emitting diode (OLED) display of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 5  is a schematic block diagram of a data driver integrated circuit (IC) of the OLED display of  FIG. 4 , in accordance with an embodiment; 
         FIG. 6  is a schematic diagram of a digital-to-analog converter (DAC) of the data driver IC of  FIG. 5 ; and 
         FIG. 7  is a flowchart describing an embodiment of a method for displaying dimmed image data on the OLED display of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Present embodiments relate to techniques for efficiently controlling the brightness of an organic light emitting diode (OLED) display. Since the amount of light output by an OLED pixel of an OLED display varies nonlinearly with the amount of power supplied to OLED pixel, increasing or decreasing the brightness of an OLED display cannot simply involve linearly increasing or decreasing the power supplied to these pixels. Embodiments of the present disclosure may avoid such distortion while retaining a relatively simplified manner of brightness control. Specifically, image data may be converted in the data driver integrated circuit (IC) from a framebuffer encoding (e.g., a gamma-corrected color space such as sRGB) to a logarithmic value (i.e., from an initial encoding domain to a logarithmic domain). As used herein, the terms “framebuffer encoding,” “framebuffer-encoded,” and the like refer to any suitable encoding of image data that may appear in a framebuffer. For example, the framebuffer encoding may include linear, non-gamma-corrected image data, such as may be obtained directly from an image capture device, or may include gamma-corrected image data, such as image data encoded in the sRGB color space. Image data in such a framebuffer encoding may be said to be in a framebuffer-encoded domain or, in corresponding situations, a linear domain or a gamma-corrected domain. 
     From this logarithmic value, a digital dimming control value may be subtracted rather than divided. This dimmed logarithmic image data then may be converted directly to an analog OLED pixel brightness control signal, without first being converted to a linear digital value, via a digital-to-analog converter (DAC) programmed to convert the logarithmic digital image data to the OLED pixel brightness control signal (i.e., from the logarithmic domain to an OLED pixel control domain). As used herein, the term “OLED pixel brightness control signal” and the like refer to a value that may be interpreted by an OLED display panel to cause an OLED pixel to emit a certain amount of photons. Such an OLED pixel brightness control signal may be said to be in a OLED pixel brightness control domain. 
     Logarithmically encoding the image data may enable both simplified dimming and digital-to-analog conversion with fewer bits. As mentioned above, dimming the image data may involve simply subtracting, rather than dividing, a dimming value. Additionally, logarithmically encoding image data may encode more information using fewer bits. For example, 8-bit image data may be logarithmically encoded using 7 bits. To account for losses in precision that could be brought about by subtracting the dimming value, 4 additional bits may be added for a total of 11 real bits. After applying certain image refinement techniques such as system correction and/or dithering, the resulting log-encoded image data may hold approximately 9 real bits and 2 virtual bits, for a total effective number of 11 bits. It should be appreciated that this example involving 8 bit image data logarithmically encoded to 7 bits, discussed in greater detail below, is intended only as one possible application of the techniques disclosed herein. Indeed, image data of any suitable data size, which may incorporate any suitable number of additional precision bits, may be used with the present techniques. 
     With the foregoing in mind,  FIG. 1  represents a block diagram of an electronic device  10  employing an organic light emitting diode (OLED) display  18  employing the improved brightness controls disclosed herein. Among other things, the electronic device  10  may include processor(s)  12 , memory  14 , nonvolatile storage  16 , the display  18 , input structures  20 , an input/output (I/O) interface  22 , network interface(s)  24 , and/or a light sensor  26 . In alternative embodiments, the electronic device  10  may include more or fewer components. 
     In general, the processor(s)  12  may govern the operation of the electronic device  10 . In some embodiments, based on instructions loaded into the memory  14  from the nonvolatile storage  16 , the processor(s)  12  may respond to user touch gestures input via the display  18 . In addition to these instructions, the nonvolatile storage  16  also may store a variety of data. By way of example, the nonvolatile storage  16  may include a hard disk drive and/or solid state storage, such as Flash memory. 
     The display  18  may be an organic light emitting diode (OLED) display. As mentioned above, the amount of light output by a pixel of an OLED display varies with the power supplied to the OLED. Thus, to dim image data displayed on the display  18 , framebuffer-encoded image data (e.g., linear image data or gamma-corrected image data sRGB) may be converted in a data driver integrated circuit (IC) of the display to a logarithmic value, from which a digital dimming control value may be subtracted rather than divided. Additionally, a digital-to-analog converter (DAC) associated with the data driver IC of the display  18  may be programmed to convert the logarithmic digital image data to an OLED pixel control value analog value, avoiding an additional linearization step. 
     The display  18  also may represent one of the input structures  20 . Other input structures  20  may include, for example, keys, buttons, and/or switches. The I/O ports  22  of the electronic device  10  may enable the electronic device  10  to transmit data to and receive data from other electronic devices  10  and/or various peripheral devices, such as external keyboards or mice. The network interface(s)  24  may enable personal area network (PAN) integration (e.g., Bluetooth), local area network (LAN) integration (e.g., Wi-Fi), and/or wide area network (WAN) integration (e.g., 3G). 
     The light sensor  26  of the electronic device  10  may measure ambient light for advanced brightness control. Specifically, in some embodiments, when the light sensor  26  detects that the amount of light surrounding the electronic device  10  increases or decreases beyond a threshold amount for a threshold amount of time, the brightness of the display  18  may be adjusted up or down by changing a dimming control value. In this way, image data shown on the display  18  may be brighter when the ambience is brighter, and darker when the ambience is darker. 
       FIG. 2  illustrates an electronic device  10  in the form of a handheld device  30 , here a portable phone. It should be noted that while the handheld device  30  is provided in the context of a portable phone, other types of handheld devices (such as media players for playing music and/or video, personal data organizers, handheld game platforms, and/or combinations of such devices) may also be suitably provided as the electronic device  10 . Further, the handheld device  30  may incorporate the functionality of one or more types of devices, such as a media player, a cellular phone, a gaming platform, a personal data organizer, and so forth. 
     For example, in the depicted embodiment, the handheld device  30  is in the form of a cellular telephone that may provide various additional functionalities (such as the ability to take pictures, record audio and/or video, listen to music, play games, and so forth). As discussed with respect to the general electronic device of  FIG. 1 , the handheld device  30  may allow a user to connect to and communicate through the Internet or through other networks, such as local or wide area networks. The handheld device  30  also may communicate with other devices using short-range connections, such as Bluetooth and near field communication (NFC). By way of example, the handheld device  30  may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. 
     The handheld device  30  may include an enclosure  32  or body that protects the interior components from physical damage and shields them from electromagnetic interference. The enclosure  32  may be formed from any suitable material, such as plastic, metal or a composite material, and may allow certain frequencies of electromagnetic radiation to pass through to wireless communication circuitry within handheld device  30  to facilitate wireless communication. The enclosure  32  may also include user input structures  20  through which a user may interface with the device. Each user input structure  20  may be configured to help control a device function when actuated. For example, in a cellular telephone implementation, one or more input structures  20  may be configured to invoke a “home” screen or menu to be displayed, to toggle between a sleep and a wake mode, to silence a ringer for a cell phone application, to increase or decrease a volume output, and so forth. 
     The display  18  may display a graphical user interface (GUI) that allows a user to interact with the handheld device  30 . Icons of the GUI may be selected via a touch screen included in the display  18 , or may be selected by one or more input structures  20 , such as a wheel or button. The handheld device  30  also may include various I/O ports  22  that allow connection of the handheld device  30  to external devices. For example, one I/O port  22  may be a port that allows the transmission and reception of data or commands between the handheld device  30  and another electronic device, such as a computer. Such an I/O port  22  may be a proprietary port from Apple Inc. or may be an open standard I/O port. Another I/O port  22  may include a headphone jack to allow a headset  34  to connect to the handheld device  30 . 
     In addition to the handheld device  30  of  FIG. 2 , the electronic device  10  may also take the form of a computer or other type of electronic device. Such a computer may include a computer that is generally portable (such as a laptop, notebook, and/or tablet computer) and/or a computer that is generally used in one place (such as a conventional desktop computer, workstation and/or servers). In certain embodiments, the electronic device  10  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. In another embodiment, the electronic device  10  may be a tablet computing device, such as an iPad® available from Apple Inc. By way of example, a laptop computer  36  is illustrated in  FIG. 3  and represents an embodiment of the electronic device  10  in accordance with one embodiment of the present disclosure. Among other things, the computer  36  includes a housing  38 , a display  18 , input structures  20 , and I/O ports  22 . 
     In one embodiment, the input structures  22  (such as a keyboard and/or touchpad) may enable interaction with the computer  36 , such as to start, control, or operate a GUI or applications running on the computer  36 . For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on the display  18 . Also as depicted, the computer  36  may also include various I/O ports  22  to allow connection of additional devices. For example, the computer  36  may include one or more I/O ports  22 , such as a USB port or other port, suitable for connecting to another electronic device, a projector, a supplemental display, and so forth. In addition, the computer  36  may include network connectivity, memory, and storage capabilities, as described with respect to  FIG. 1 . 
     As noted briefly above, the display  18  represented in the embodiments of  FIGS. 1-3  is an organic light emitting diode (OLED) display. As shown, the display  18  may include an OLED panel  40  having unit pixels  42  disposed in a pixel array or matrix. In such an array, each unit pixel  42  may be defined by the intersection of rows and columns, represented here by the illustrated scanning lines  44  and data lines  46 , respectively. Although only six unit pixels  42  are shown for purposes of simplicity, it should be understood that in an actual implementation, each data line  46  and scanning line  44  may include hundreds or thousands of such unit pixels  42 . Moreover, in some embodiments, three unit pixels  42  of three different colors may be stacked atop each other rather than side-by-side. 
     As shown in the present embodiment, each unit pixel  42  includes an organic light emitting diode (OLED) capable of emitting light of a particular color. Each unit pixel  42  may be electrically connected to one scanning line  44  and one data line  46 . A scanning driver integrated circuit (IC)  48  may control when the pixels  42  become activated and able to receive image data signals. When a signal is provided across a scanning line  44 , the unit pixels  42  coupled to the scanning line  44  become active and able to receive an analog pixel brightness control signal from a data line  46 . A data driver IC  50  then may provide the pixel brightness control value across the data line  46  that, when received by a unit pixel  42 , causes the OLED of the pixel  42  to emit a specific amount of light. 
     The data driver IC  50  may provide an image data signal that has been dimmed from a maximum brightness level. As shown by  FIG. 5 , framebuffer-encoded (e.g., sRGB or any other suitable image processing value) image data  60  from a framebuffer of the electronic device  10  may enter the data driver IC  50 , which may modify the brightness of the image data and perform various other refinements before outputting an analog pixel brightness control value to the OLED panel  40 . The data driver IC  50  may adjust the brightness of the image data  60  after its conversion to a logarithmic encoding, allowing a dimming value to simply be subtracted, rather than divided, to produce dimmed image data. 
     In particular, a framebuffer-encoded-to-logarithmic block  62  of the data driver IC  50  may apply a framebuffer-encoded-to-logarithmic function  64  to the image data  60  to produce log-encoded image data  65  using, for example, a digital lookup table (LUT). Such a lookup table may be precalculated and may indicate the conversion of each possible value of the image data  60  in the framebuffer-encoded domain to each possible value of the log-encoded image data  65  in the logarithmic domain. In other words, the log-encoded image data  65  output by the framebuffer-encoded-to-logarithmic block  62  may be understood to have been converted from a framebuffer-encoded domain to a logarithmic domain. 
     As noted above, logarithmically encoding image data may encode more information using fewer bits. For example, the framebuffer-encoded image data  60  may be 8-bit image data that, when logarithmically encoded, takes up only 7 bits. However, to account for losses in precision that could be brought about by subtracting a dimming value, 4 additional bits may be added for a total of 11 bits in the log-encoded image data  65 . In other embodiments, more or fewer precision bits may be added to produce the log-encoded image data  65 . For example, other embodiments may add no additional bits, or may add 1, 2, 3, 5, 6, or more bits, depending on the level of precision desired. Moreover, the above example involving 8-bit image data logarithmically encoded to 7 bits, discussed in greater detail below, is intended only as one possible application of the techniques disclosed herein. Indeed, image data of any suitable data size, which may incorporate any suitable number of additional precision bits, may be used with the present techniques. Regardless of the size of the framebuffer-encoded image data  60 , when the framebuffer-encoded image data  60  is logarithmically encoded, the log-encoded image data  65  may require fewer bits to encode the same data. Thus, even without dimming the log-encoded image data according to the techniques disclosed herein, transforming the log-encoded image data  65  into an analog signal may involve a digital-to-analog converter (DAC) having fewer resistors than otherwise. 
     Subtracting one logarithmic value from another has the same effect as dividing one linear value by another. Thus, rather than divide a linear dimming control value from a linearized value of the image data  60  to obtain dimmed image data, which could involve complex calculations and/or consume substantial resources, a logarithmic digital dimming control value  66  may be simply subtracted from the log-encoded image data  65  in a subtraction block  68  to obtain log-encoded digitally dimmed image data  69 . This log-encoded digitally dimmed image data  69  represents an image signal that, if transformed from the logarithmic domain to the OLED pixel brightness control domain and output to the OLED panel  40 , would represent a darker version of the same color as the original input image data  60 . The resulting log-encoded digitally dimmed image data  69  may include the same number of bits as the log-encoded image data  65 , or may include additional bits to offset losses in precision that could be induced by the subtraction block  68 . 
     The logarithmic digital dimming control value  66  may represent a logarithmic encoding of any dimming signal associated with any suitable dimming control system, such as those used for dimming an LCD display. Rather than supply a dimming control value to a backlight control to reduce the amount light output by a backlight, which may not be present in the OLED display  18 , such a dimming control value may be converted to a logarithmic value and provided as the digital dimming control value  66 . The dimming control value may be converted to a logarithmic value via, for example, a digital lookup table (LUT) in the manner of the framebuffer-encoded-to-logarithmic block  62 . 
     Other processes to refine the log-encoded digitally dimmed image data  69 , such as a system correction block  70  or a dithering block  72 , may be applied to the log-encoded digitally dimmed image data  69  to produce refined log-encoded image data  73 . For example, the system correction block  70  may provide a color correction that may be unique to the OLED panel  40  or to the vendor of the OLED panel  40 . This system correction block  70  may neither add nor subtract any bits of the log-encoded digitally dimmed image data  69 . The dithering block  72  may, by spatial, temporal, or spatiotemporal dithering, compensate for some of the least significant bits of the image data output by the system correction block  70 . For example, in some embodiments, the dithering block  72  may output 9 real bits, down from the 11 bits it received, as the refined log-encoded image data  73 . Still, as a result of the dithering provided by the dithering block  72 , the refined log-encoded image data  73  may be understood to include 9 real bits and 2 virtual bits, for an effective total number of 11 bits, or a logarithmic value of 2 11 . 
     In some embodiments, this log-encoded image data may be linearized (e.g., applied in an inverse transfer function and converted from a logarithmic value to a linear value) before being converted to an analog voltage in a digital-to-analog converter (DAC). However, doing so would require the DAC to accommodate the additional bits represented by the linearized rather than logarithmic value. Thus, in the embodiment of  FIG. 5 , a logarithmic-to-OLED-pixel-brightness-control-domain DAC  74  may convert the refined log-encoded image data  73  from the logarithmic domain to the OLED pixel brightness control domain by effectively applying a function to output an OLED pixel brightness control signal  78 . The OLED pixel brightness control signal  78  output by the DAC  74  may be approximately equal to the OLED pixel brightness control signal that would be output by a linear DAC that received a linearized value of the refined log-encoded image data  73 . When the OLED panel  40  receives the OLED pixel brightness control signal  78  output by the DAC  74 , the OLED panel  40  may drive OLED pixels  80  based on the OLED pixel brightness control signal  78 . The OLED pixels  80  may output an amount of photons  81  associated with the OLED pixel brightness control signal  78 . 
     In other embodiments, the logarithmic-to-OLED-pixel-brightness-control-domain DAC  74  may be represented by two distinct functional blocks. That is, a first block may digitally convert the refined log-encoded image data  73  into a digital signal in the pixel brightness control domain and a second block may convert this digital signal into an analog signal. In still other embodiments, the OLED panel  40  may be capable of being controlled via a digital signal in the pixel brightness control domain rather than an analog signal. 
     In the embodiment illustrated in  FIG. 5 , the DAC  74  may effectively transform the information encoded in the refined log-encoded dimmed image data  73  from the logarithmic domain to the OLED pixel brightness control domain through a one-time factory programming. One embodiment of the DAC  74  appears in  FIG. 6 . As illustrated in  FIG. 6 , the DAC  74  may include a resistor ladder  82  with a series of taps  84  (e.g., 512 taps). The resistor ladder  82  may couple between two voltages (e.g., V MAX  and V MIN ), the taps  84  each providing a slightly different voltage. A multiplexer  86  (or several multiplexers  86 ) may couple to taps  84  of the resistor ladder  82  based on the bits of a digital input  88 , which may receive, for example, a 9-bit refined log-encoded dimmed image data  73  signal. That is, depending on the log-encoded dimmed image data  73  signal provided by the digital input  88 , the multiplexer  86  will select one of the taps  84  of the resistor ladder  82 , the voltage of which will be output as the OLED pixel brightness control signal  78 . 
     The taps  84  may be approximately equidistant from one another on the resistor ladder  82 , but certain refinement taps  89  may “bend” the voltages of the taps  84  to effectively transform the log-encoded dimmed image data  73  signal from the logarithmic domain into the pixel brightness control domain. Any suitable number of refinement taps  89  may be employed. For example, when 512 taps  84  are used, the DAC  74  may include between 5 and 30 refinement taps  89 . In one embodiment, 16 refinement taps  89  may be present. The refinement taps  89  may not necessarily be spaced equidistant of one another or equidistant to the taps  84  of the resistor ladder  82 . Instead, the placement of the refinement taps  89  and the voltages supplied by the refinement taps  89  may be selected so as to “bend” the voltages of the taps  84  such that when the bits of the digital input  88  correspond to the refined log-encoded dimmed image data  73 , the multiplexer  86  outputs the OLED pixel brightness control signal  78  equal to the OLED pixel brightness control signal that would be output by a linear DAC that received a linearized value of the refined log-encoded image data  73 . Once the location and/or voltage values of the refinement taps  89  have been programmed once, supplying different values for the digital input  88  (e.g., various values of the refined log-encoded dimmed image data  73 ) should consistently effectively result in the transformation from the logarithmic domain to the OLED pixel brightness control domain of such different values. 
     A flowchart  90  of  FIG. 7  represents an embodiment of a method for performing brightness control of the OLED display  18 . The flowchart  90  may begin when image data  60  in a framebuffer encoding (e.g., sRGB) for a given pixel is provided to the data driver IC  50  (block  92 ). The data driver IC  50  next may transform the image data from the framebuffer-encoded domain to the logarithmic domain using, for example, a lookup table (LUT) (block  94 ). To dim the resulting log-encoded image data  65 , a dimming control value  66  may be simply subtracted, rather than divided, from this logarithmic value (block  96 ). Additional processes next may be performed to refine the image data, such as system correction or dithering as shown by blocks  70  and  72  of  FIG. 5  (block  98 ). The resulting refined log-encoded dimmed image data  73  may enter, for example, the logarithmic-to-OLED-pixel-brightness-control-domain DAC  74 , which may effectively transform the refined log-encoded dimmed image data  73  from the logarithmic domain to the OLED pixel brightness control domain when the OLED pixel brightness control signal  78  is output (block  100 ). This OLED pixel brightness control signal  78  may be used to drive the OLED pixels  80  of the OLED panel  40 , which may output an amount of photons  81  corresponding to the OLED pixel brightness control signal  78  (block  102 ). 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Metadata:
Filing Date: 20101025
Publication Date: 20170530
Grant Date: 20170530
Priority Date: 20101025
Inventors: BARNHOEFER ULRICH T.
LEE YONGMAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3275", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0626", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2044", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0276", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2044", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0626", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0276", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3275", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 45972651