Patent Publication Number: US-10762820-B2

Title: Inversion balancing compensation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Under 35 U.S.C. § 120, this application is a continuation of U.S. patent application Ser. No. 15/812,868 filed Nov. 14, 2017, which is a continuation of U.S. patent application Ser. No. 14/986,181 filed Dec. 31, 2015, which is a continuation-in-part of U.S. patent application Ser. No. 14/725,545 filed May 29, 2015, which claims priority to and benefit of U.S. Provisional Patent Application No. 62/017,081 filed Jun. 25, 2014, each of which is incorporated by reference herein in its entirety for all purposes. 
    
    
     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. 
     The present disclosure generally relates to improving quality of images displayed on an electronic display particularly when refresh rate of the electronic display is dynamic. More specifically, when the refresh rate is dynamic, the duration each successive image (e.g., frame) is displayed may vary. As such, when inversion exclusively alternates between applying positive and negative voltages, polarization may occur in the electronic display pixels and reduce image quality. 
     Accordingly, when the refresh rate is dynamic, the techniques described herein may reduce the possibility of polarizing the pixels in the electronic display by determining the polarity of the voltage applied to write each image and the duration each image is displayed. In some embodiments, the duration each image is displayed may be based on the number of lines included in image data corresponding with each image. For example, a timing controller (TCON) in the electronic display may count the number of vertical blank (Vblank) lines and active lines in image data received from an image source. Based on the count value, the timing controller may then determine whether to apply a positive polarity voltage or a negative polarity voltage in the next image (e.g., frame). 
     More specifically, the timing controller may count up when a positive voltage is applied to the electronic display pixels and count down with a negative voltage is applied to the electronic display pixels, or vice versa. In some embodiments, the possibility of polarizing the electronic display pixels may be reduced by maintaining the counter value towards zero. Thus, when the count value is a positive number, the timing controller may determine that the next image should be written with a negative voltage and, when the count value is a negative number, the timing controller may determine that the next image should be written with a positive voltage. In other words, the inversion techniques may balance the duration that opposite polarity voltages are applied to the electronic display pixels, which may reduce the possibility of polarization. 
    
    
     
       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 a computing device used to display images, in accordance with an embodiment; 
         FIG. 2  is an example of the computing device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 3  is an example of the computing device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 4  is an example of the computing device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 5  is block diagram of a portion of the computing device of  FIG. 1  used to display images, in accordance with an embodiment; 
         FIG. 6  is a flow diagram of a process for reducing the possibility of polarization, in accordance with an embodiment; 
         FIG. 7  is a flow diagram of a process for displaying an image (e.g., frame) based on a counter value, in accordance with an embodiment; 
         FIG. 8  is a flow diagram of a process for updating the counter value, in accordance with an embodiment; 
         FIG. 9  is an example of a counter value in relation to a hypothetical operation of an electronic display, in accordance with an embodiment; 
         FIG. 10  is a flow diagram of a non-linear process for updating the counter value, in accordance with an embodiment; and 
         FIG. 11  is an example of a non-linear counter value in relation to a hypothetical operation of an electronic display, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be 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 may nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     As mentioned above, an electronic display may display images by applying voltage to the pixels in a display panel. More specifically, the pixels may transmit light based at least in part on the magnitude of the voltage applied. However, when a direct current (DC) voltage is applied to the pixel for extended periods of time, the pixels may become polarized, which may reduce the displayed image quality. For example, when a positive voltage is applied to a pixel for an extended period of time, the pixel may begin to be polarized positive. As such, when a voltage is applied to the pixel, the positive polarization may cause the pixel to have a higher voltage than the applied voltage, which causes the pixel to inaccurately transmit light. 
     Thus, it may be beneficial to utilize inversion techniques by alternating the polarity of the voltage applied to the display panel to reduce the risk of pixels becoming polarized. For example, in a frame inversion technique, a first image may be written to the display panel by applying a positive voltage and a second image may be written to the display panel by applying a negative voltage. In other words, assuming that a constant refresh rate is used, applying a positive and a negative voltage in an alternating manner may enable the opposite voltages to cancel each other out and reduce the risk of polarization. 
     However, in some embodiments, an electronic display may have the capability to switch to a dynamic variable refresh rate. More specifically, the electronic display may switch from utilizing a constant refresh rate (e.g., 60 Hz per frame) to a dynamic variable refresh rate and vice versa, for example by using a control bit. For example, when a dynamic variable refresh rate is used, the refresh rate used to display a first image may be different from the refresh rate used to display a second image. In other words, the duration each image is displayed on the display panel may vary. In such embodiments, even alternating the polarity of the voltage applied to the display panel in each successively displayed image may still result in polarization of the pixels. For example, in an extreme case, a first image may be displayed at 30 Hz by applying a positive voltage, a second image may be displayed at 60 Hz by applying a negative voltage, a third image may be displayed at 30 Hz by applying a positive voltage, a fourth image may be displayed at 60 Hz by applying a negative voltage, and so on. In such a case, the positive voltage will be applied to the display panel for twice as long as the negative voltage. Thus, over an extended period of time, the pixels may still become polarized positive. 
     Accordingly, one embodiment of the present disclosure describes an electronic display that includes a display panel, which displays images with varying refresh rates, and a timing controller. More specifically, the timing controller receives image data from an image source, determines a counter value, and instructs a driver in the electronic display to apply a voltage to the display panel to write an image on the display panel based on the counter value. In some embodiments, the timing controller may instruct the driver to apply a negative voltage when the counter value is positive and a positive voltage when the counter value is less than or equal to zero or vice versa. Additionally, the timing controller updates the counter value based on the duration that the image is displayed on the display panel. In some embodiment, the timing controller may increase the counter value when the applied voltage is positive and decrease the counter value when the applied voltage is negative. 
     As will be described in more detail below, the counter value may be used to keep track of the duration positive voltage and negative voltage is applied to the display panel. As such, the counter value may be used to determine the polarity of voltage that should be applied to reduce the possibility of polarization. For example, when a first image is displayed at 30 Hz by applying a positive voltage, the counter value may indicate that a subsequent 60 Hz image should be displayed by applying a negative voltage. Additionally, the counter value may indicate that a second subsequent 60 Hz image should be displayed by applying a negative voltage. In other words, the techniques described herein allow for successively displayed images (e.g., frames) to be written using the same polarity voltage. 
     To help illustrate, a computing device  10  that utilizes an electronic display  12  to display images is described in  FIG. 1 . As will be described in more detail below, the computing device  10  may be any suitable computing device, such as a handheld computing device, a tablet computing device, a notebook computer, and the like. 
     Accordingly, as depicted, the computing device  10  includes the display  12 , input structures  14 , input/output (I/O) ports  16 , one or more processor(s)  18 , memory  20 , nonvolatile storage  22 , a network interface  24 , and a power source  26 , and image processing circuitry  27 . The various components described in  FIG. 1  may include hardware elements (including circuitry), software elements (including computer code stored on a non-transitory computer-readable medium), or a combination of both hardware and software elements. It should be noted that  FIG. 1  is merely one example of a particular implementation and is intended to illustrate the types of components that may be present in the computing device  10 . Additionally, it should be noted that the various depicted components may be combined into fewer components or separated into additional components. For example, the image processing circuitry  27  (e.g., graphics processing unit) may be included in the one or more processors  18 . 
     As depicted, the processor  18  and/or image processing circuitry  27  are operably coupled with memory  20  and/or nonvolatile storage device  22 . More specifically, the processor  18  and/or image processing circuitry  27  may execute instruction stored in memory  20  and/or non-volatile storage device  22  to perform operations in the computing device  10 , such as generating and/or transmitting image data. As such, the processor  18  and/or image processing circuitry  27  may include one or more general purpose microprocessors, one or more application specific processors (ASICs), one or more field programmable logic arrays (FPGAs), or any combination thereof. Additionally, memory  20  and/or non volatile storage device  22  may be a tangible, non-transitory, computer-readable medium that stores instructions executable by and data to be processed by the processor  18  and/or image processing circuitry  27 . In other words, the memory  20  may include random access memory (RAM) and the non-volatile storage device  22  may include read only memory (ROM), rewritable flash memory, hard drives, optical discs, and the like. By way of example, a computer program product containing the instructions may include an operating system (e.g., OS X® or iOS by Apple Inc.) or an application program (e.g., iBooks® by Apple Inc.). 
     Additionally, as depicted, the processor  18  is operably coupled with the network interface  24  to communicatively couple the computing device  10  to a network. For example, the network interface  24  may connect the computing device  10  to a personal area network (PAN), such as a Bluetooth network, a local area network (LAN), such as an 802.11x Wi-Fi network, and/or a wide area network (WAN), such as a 4G or LTE cellular network. Furthermore, as depicted, the processor  18  is operably coupled to the power source  26 , which provides power to the various components in the computing device  10 . As such, the power source  26  may includes any suitable source of energy, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter. 
     As depicted, the processor  18  is also operably coupled with I/O ports  16 , which may enable the computing device  10  to interface with various other electronic devices, and input structures  14 , which may enable a user to interact with the computing device  10 . Accordingly, the inputs structures  14  may include buttons, keyboards, mice, trackpads, and the like. Additionally, in some embodiments, the display  12  may include touch sensitive components. For example, the electronic display  12  may be a MultiTouch™ display that can detect multiple touches at once. 
     In addition to enabling user inputs, the display  12  may display images. In some embodiments, the images displayed may be a graphical user interface (GUI) for an operating system, an application interface, a still image, or a video. As depicted, the display is operably coupled to the processor  18  and the image processing circuitry  27 . Accordingly, the images displayed by the display  12  may be based on image data received from the processor  18  and/or the image processing circuitry  27 . 
     As will be described in more detail below, the image data transmitted to the display  12  may determine the refresh rate with which images based on the image data are displayed. For example, the processor  18  and/or the image processing circuitry  27  may communicate the refresh rate to use based on the number of vertical blank (Vblank) lines include in the image data. Accordingly, once the image data is received, the display  12  may determine the refresh rate to use by determining the number of vertical blank lines and/or the number of active lines include in the image data. As will be described in more detail below, the number of lines (e.g., vertical blank and active lines) may directly correspond with duration an image is displayed because the time it takes for the display  12  to write one line is generally constant. For example, when a displayed image has a resolution of 2880×1800 and is displayed at 60 Hz, the image data may include 52 vertical blank lines and 1800 active lines. Thus, the duration the image is displayed may be described as 1852 lines. 
     As described above, the computing device  10  may be any suitable electronic device. To help illustrate, one example of a handheld device  10 A is described in  FIG. 2 , which may be a portable phone, a media player, a personal data organizer, a handheld game platform, or any combination of such devices. Accordingly, by way of example, the handheld device  10 A may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. 
     As depicted, the handheld device  10 A includes an enclosure  28 , which may protect interior components from physical damage and to shield them from electromagnetic interference. The enclosure  28  may surround the display  12 , which, in the depicted embodiment, displays a graphical user interface (GUI)  30  having an array of icons  32 . By way of example, when an icon  32  is selected either by an input structure  14  or a touch sensing component of the display  12 , an application program, such as iBooks® made by Apple Inc., may launch. 
     Additionally, as depicted, input structure  14  may open through the enclosure  28 . As described above, the input structures  14  may enable a user to interact with the handheld device  10 A. For example, the input structures  14  may activate or deactivate the handheld device  10 A, navigate a user interface to a home screen, navigate a user interface to a user-configurable application screen, activate a voice-recognition feature, provide volume control, and toggle between vibrate and ring modes. Furthermore, as depicted, the I/O ports  16  open through the enclosure  28 . In some embodiments, the I/O ports  16  may include, for example, an audio jack and/or a Lightning® port from Apple Inc. to connect to external devices. 
     To further illustrate a suitable computing device  10 , a tablet device  10 B is described in  FIG. 3 . By way of example, the tablet device  10 B may be a model of an iPad® available from Apple Inc. Additionally, in other embodiments, the computing device  10  may take the form of a computer  10 C as described in  FIG. 4 . By way of example, the computer  10 C may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. As depicted, the computer  10 C also includes a display  12 , input structures  14 , I/O ports  16 , and an enclosure (e.g., housing)  28 . 
     As described above, the display  12  may display images based on image data received from the processor  18  and/or the image processing circuitry  27 . More specifically, the image data may be processed by any combination of the processor  18 , the image processing circuitry  27 , and the display  12  itself. To help illustrate, a portion  34  of the computing device  10  that processes and communicates image data is described in  FIG. 5 . 
     As depicted, the portion  34  of the computing device  10  includes an image source  36 , a timing controller (TCON)  38 , and a display driver  40 . More specifically, the source  36  may generate image data and transmit the image data to the timing controller  38 . Accordingly, in some embodiments, the source  36  may be the processor  18  and/or the image processing circuitry  27 . Additionally, in some embodiments, the timing controller  38  and the display driver  40  may be included in the electronic display  12 . 
     As described above, the display  12  may display an image based at least in part on the received image data. As such, the timing controller  38  may analyze the received image data and instruct the driver  40  to write an image to the pixels by applying a voltage to the display panel of the electronic display  12 . To facilitate processing/analyzing the image data and/or performing other operations, the timing controller  38  may include a processor  42  and memory  44 . In some embodiments, the timing controller processor  42  may be included in the processor  18  and/or the image processing circuitry  27 . In other embodiments, the timing controller processor  42  may be a separate processing module. Additionally, in some embodiments, the timing controller memory  44  may be included in memory  20 , storage device  22 , or another tangible, non-transitory, computer readable medium. In other embodiments, the timing controller memory  44  may be a separate tangible, non-transitory, computer readable medium that stores instructions executable by the timing controller processor  42 . 
     More specifically, the timing controller  38  may analyze the received image data to determine the magnitude of voltage to apply to each pixel to achieve the desired image and instruct the driver  40  accordingly. Additionally, the timing controller  38  may analyze the received image data to determine the refresh rate with which to display an image described by the image data and instruct the driver  40  accordingly. More specifically, the timing controller  38  may determine the refresh rate based at least in part on the number of vertical blank (Vblank) lines and/or active lines included in the image data. 
     For example, when the display  12  displays images with a resolution of 2880×1800, the timing controller  38  may instruct the driver  40  to display a first image at 60 Hz when the timing controller  38  determines that corresponding image data includes 52 vertical blank lines and 1800 active lines. Additionally, the timing controller  38  may instruct the driver  40  to display a second image at 30 Hz when the timing controller  38  determines that corresponding image data includes 1904 vertical blank lines and 1800 active lines. 
     As described above, a line (e.g., active or vertical blank) is used to describe the amount of time to write an image to one row of pixels. More specifically, since each row of pixels in the display panel is successively written, the duration an image is displayed includes the number of active lines in corresponding image data. Additionally, when a vertical blank line in the corresponding image data is received, the displayed image may continue to be displayed. As such, the total duration an image is displayed may be described as the sum of the number of vertical blank lines and the number of active lines in the corresponding image data. To help illustrate, continuing with the above example, the duration the first image is displayed may be 1852 lines and the duration the second image is displayed may be 3704 lines. 
     More specifically, as described above, the duration positive and negative voltages are applied to the display panel may be used to determine polarity of the voltage to use for writing the next image. Accordingly, the timing controller  38  may utilize a counter  46  to keep track. For example, in some embodiments, the counter  46  may count up when a positive voltage is applied and count down when a negative voltage applied. Additionally, the timing controller  38  may instruct the driver  40  to apply a negative voltage to the display panel when the counter value is positive and to apply a positive voltage to the display when the counter value is negative. In other words, the timing controller  38  may maintain the counter value towards zero. Thus, in some embodiments, the counter  46  may be sized such that the maximum positive and negative value is equal to the total number of lines in an image (e.g., frame). For example, the counter  46  may be 24 bits signed to accommodate refresh rates below 0.2 Hz. 
     As such, the possibility of polarizing the pixels may be reduced by applying positive voltages and negative voltages for approximately equal amounts of time. Thus, the timing controller  38  may determine the number of vertical blank lines and/or active lines to determine polarity of the voltage to apply to the display panel to write the next successive image when the image source  36  is in an active mode and communicate the determined polarity to the driver  40 , for example, using the Common Device Interface (CDI). However, in some embodiments, to further conserve power, the source  36  may utilize Advanced Link Power Management (ALPM). More specifically, the source  36  may enter a sleep mode when the source  36  determines that the next subsequent image to be displayed is the same as the previously displayed image. 
     However, when the source  36  stops transmitting image data, the voltage applied to display the previous image continues to be held in the pixels. In other words, the voltage continues to be applied to the pixels even when new images are not being written to the display panel. As such, the timing controller  38  may continue to account for the duration the voltage is being held by the pixels in the display panel using a timer  47 . More specifically, the timer  47  may continue to keep track of the duration that the voltage is held. Thus, since the time used to write a line is generally constant, the timing controller  38  may continue keeping track of duration voltage is held by dividing the timer value by the time generally used to write a line in an image. In some embodiments, the time used to write a line may be predetermined and stored in the timing controller memory  44 . Thus, as will be described in more detail below, the counter  46  may continue counting up while a positive voltage is being held in the display panel and continue counting down while a negative voltage is being held in the display panel based on the timer value. 
     Accordingly, even when the source  36  enters a sleep mode and ceases transmitting image data, the counter  46  may continue keeping track of duration positive voltages and negative voltages have been applied to the display panel. Thus, as described above, the timing controller  38  may determine the polarity of voltage to apply to write the next subsequent image based on the counter value and instruct the driver  40  accordingly. 
     To help illustrate, one embodiment of a process  48  for displaying images is described in  FIG. 6 . Generally, the process  48  includes determining a previous counter value (process block  50 ), displaying an image (process block  52 ), determining duration the image is displayed (process block  54 ), and updating the counter value (process block  56 ). In some embodiments, the process  48  may be implemented using instructions stored in the timing controller memory  44  and/or another suitable tangible non-transitory computer-readable medium and executable by the timing controller processor  42  and/or another suitable processing circuitry. 
     Accordingly, the timing controller  38  may determine the previous counter value by polling the counter  46  (process block  50 ). In some embodiments, the timing controller  38  may poll the counter  46  whenever image data is received from the source  36 . As described above, the previous counter value may then be used to determine polarity of voltage to use to write an image to the display panel. 
     Thus, the timing controller  38  may instruct the driver  40  to write an image to the pixels of the display panel based on the received image data and the previous counter value (process block  52 ). More specifically, the timing controller  38  may determine magnitude of voltage to apply to the pixels in the display panel based on the active lines included in the received image data and the polarity of the voltage to apply based on the previous counter value. As described above, the timing controller  38  may determine the magnitude of the voltage to apply to control brightness of each pixel. 
     Additionally, the timing controller  38  may determine the polarity of the voltage to use for applying the determined voltage magnitude based on the previous counter value. To help illustrate, one embodiment of a process  58  for determining polarity of the voltage to apply is described in  FIG. 7 . Generally, the process  58  includes determining whether the previous counter value is greater than zero (decision block  60 ) and when the counter value is greater than zero, displaying an image with a negative polarity (process block  62 ) and decreasing the counter value (process block  64 ). On the other hand, when the counter value is not greater than zero (e.g., less than or equal to zero), the process  58  includes displaying an image with a positive polarity (process block  66 ) and increasing the counter value (process block  68 ). In some embodiments, process  58  may be implemented using instructions stored in the timing controller memory  44  and/or another suitable tangible non-transitory computer-readable medium and executable by the timing controller processor  42  and/or another suitable processing circuitry. 
     Accordingly, once the previous counter value is received, the timing controller  38  may determine whether the previous counter value is greater than zero (decision block  60 ). When the previous counter value is greater than zero, the timing controller  38  may instruct the driver  40  to apply a negative polarity voltage at the determined magnitude (process block  62 ). On the other hand, when the previous counter value is not greater than zero, the timing controller  38  may instruct the driver  40  to apply a positive polarity voltage at the determined magnitude (process block  66 ). 
     Additionally, returning to  FIG. 6 , once the image is displayed, the timing controller  38  may determine the duration to display the image based on the received image data (process block  54 ). More specifically, when active lines are received, a corresponding image is written to the pixels in the display panel. Additionally, when vertical blank lines are received, the image is continued to be displayed. In other words, the voltage at the determined magnitude and polarity may be applied for a duration equal to the number of active lines and vertical blank lines in the image data. 
     As such, the counter value may be updated to keep track of the duration respective positive and negative polarity voltages are applied by increasing or decreasing the counter value (process block  56 ). More specifically, returning to  FIG. 7 , the counter  46  may be increased when a positive polarity voltage is applied (process block  68 ). On the other hand, the counter  46  may be decreased when a negative polarity voltage is applied (process block  64 ). Thus, the amount the counter value may be increased or decreased (e.g., updated or incremented) by the number of lines (e.g., vertical blank and/or active) included in the image data. 
     To help illustrate, one embodiment of a process  70  for determining the amount to increase or decrease the counter  46  is described in  FIG. 8 . Generally, the process  70  includes determining the number of active lines included in the image data (process block  72 ), determining the number of vertical blank (Vblank) lines included in the image data (process block  74 ), and determining whether new image data is received (decision block  76 ). When new image data is received, the number of vertical blank lines and active lines may again be determined based on the new image data. On the other hand, when new image data is not received, the process  70  includes starting a timer (process block  78 ), stopping the timer when new image data is received (process block  80 ), and determining the number of lines the timer was running for (process block  82 ). In some embodiments, process  70  may be implemented using instructions stored in the timing controller memory  44  and/or another suitable tangible non-transitory computer-readable medium and executable by the timing controller processor  42  and/or another suitable processing circuitry. 
     Accordingly, the timing controller  38  may determine the number of active lines in the received image data (process block  72 ). Generally, the image data includes one active line for each row of the display  12 . In other words, the number of active rows is generally equivalent to the height of the resolution of the displayed image. For example, when the displayed image has a resolution of 2880×1800, the image data may include 1800 active lines. Accordingly, in some embodiments, the timing controller  38  may count the number of active lines included in the image data. Additionally or alternatively, the number of active lines may be predetermined and stored in the timing controller memory  44 . 
     Additionally, the timing controller  38  may determine the number of vertical blank lines included in the received image data (process block  74 ). In some embodiments, the vertical blank lines may include a vertical front porch, a vertical sync pulse, and a vertical back porch. More specifically, the vertical front porch may include a number of blank (e.g., black) lines that are transmitted before the vertical sync pulse, which may also last for several lines. After the vertical sync pulse, the vertical back porch may transmitted, which also includes a number of blank (e.g., black) lines. Thus, the timing controller  38  may determine the number of vertical blank lines by counting the number of blank lines and the number of lines in the vertical sync pulse in the received image data. 
     Thus, the timing controller  38  may determine the duration an image corresponding with received image data is displayed by adding together the number of vertical blank lines and the number of active lines received from the source  36 . However, as described above, power consumption may be improved by placing the source  36  into sleep mode and ceasing transmission of image data, for example, when a subsequent image is the same as a previous image. More specifically, when the source  36  ceases transmission of the image data, the display  12  continues to hold the voltage in the pixels of the display panel. Thus, the duration the voltage is held in the pixels should also be accounted for. 
     As such, when new image data is not received, the timing controller  38  starts the timer  47  (process block  78 ). The timing controller  38  stops the timer  47  when new image data is received (process block  80 ), which indicates that the source  36  is no longer asleep. Thus, the timer  47  may indicate the amount of time the voltage was held in the pixels while the source  36  was asleep. 
     Since the duration to write a line is generally constant, the equivalent number of lines that the voltage is held in the pixels may be determined (process block  82 ). More specifically, the duration measured by the timer  47  may be divided by the time used to write one row (e.g., line) of an image. For example, if it takes one millisecond to write a row of an image and the timer  47  determines that the voltage was held for five milliseconds, the timing controller  38  may determine that voltage was held by the pixels for an equivalent of five lines. Additionally or alternatively, the counter  46  may simply count up or count down each time duration for writing one line passes. 
     Based on the above described techniques, the duration positive and negative voltages are applied/held may be balanced to reduce possibility of polarizing the pixels. To help illustrate the techniques, a hypothetical display operation  84  is described in  FIG. 9 . More specifically, the hypothetical display operation  84  describes image data received by the display  12  between t 0  and t 9 . 
     As depicted, first image data  86  begins to be received at to. To display a first image corresponding with the first image data  86  the timing controller  38  may analyze the first image data  86  to determine the magnitude of the voltage to apply to write the first image. More specifically, the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the first image data  86 . Additionally, in response to receiving the first image data  86 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is zero. Thus, the timing controller  38  may determine that a positive polarity voltage should be applied to the pixels in the display panel to write the first image. 
     Furthermore, the timing controller  38  may determine the refresh rate based on the total number of lines (e.g., vertical blank and active) included in the image data. For example, in the depicted example, the timing controller  38  may determine that the first image should be displayed at 60 Hz because the first image data  86  includes 52 vertical blank lines and 1800 active lines (e.g., 1852 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a positive voltage at the determined magnitude at 60 Hz to display the first image. Additionally, since a positive voltage is applied, the counter  46  will count up 1852 lines. Thus, at t 1 , the counter value may be 1852. 
     Subsequently, as depicted, second image data  88  begins to be received at t 1 . Similar to displaying the first image, to display a second image corresponding with the second image data  88 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the second image data  88 . Additionally, in response to receiving the second image data  88 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is 1852. Thus, the timing controller  38  may determine that a negative polarity voltage should be applied to the pixels in the display panel to write the second image. 
     Furthermore, the timing controller  38  may determine that the second image should be displayed at 30 Hz because the second image data  86  includes 1904 vertical blank lines and 1800 active lines (e.g., 3704 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a negative voltage at the determined magnitude at 30 Hz to display the second image. Additionally, since a negative voltage is applied, the counter  46  will count down 3704 lines. Thus, at t 2 , the counter value may be −1852. 
     Then, as depicted, third image data  90  begins to be received at t 2 . Similar to displaying the first and second images, to display a third image corresponding with the third image data  90 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the third image data  90 . Additionally, in response to receiving the third image data  90 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is −1852. Thus, the timing controller  38  may determine that a positive polarity voltage should be applied to the pixels in the display panel to write the third image. 
     Furthermore, the timing controller  38  may determine that the third image should be displayed at 60 Hz because the third image data  90  includes 52 vertical blank lines and 1800 active lines (e.g., 1852 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a positive voltage at the determined magnitude at 60 Hz to display the third image. Additionally, since a positive voltage is applied, the counter  46  will count up 1852 lines. Thus, at t 3 , the counter value may be zero. 
     As depicted, fourth image data  92  begins to be received at t 3 . Similar to displaying the first through third images, to display a fourth image corresponding with the fourth image data  92 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the fourth image data  92 . Additionally, in response to receiving the fourth image data  92 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is zero. Thus, the timing controller  38  may determine that a positive polarity voltage should again be applied to the pixels in the display panel to write the fourth image. As such, two positive polarity voltages are applied to write successive images. In other words, the voltages applied using the present techniques do not necessarily alternate in successive images. 
     Furthermore, the timing controller may determine that the fourth image should be displayed at 45 Hz because the fourth image data  86  includes 978 vertical blank lines and 1800 active lines (e.g., 2778 total lines). In other words, the refresh rate with which images may be displayed is not limited to 30 Hz and 60 Hz and can be any refresh rate suitable for the display  12 . In fact, in some embodiments, the refresh rate may be anywhere from 0.2-75 Hz. The timing controller  38  may then instruct the driver  40  to use a positive voltage at the determined magnitude at 45 Hz to display the fourth image. Additionally, since a positive voltage is applied, the counter  46  will count up 2778 lines. Thus, at t 4 , the counter value may be 2778. 
     Then, as depicted, fifth image data  94  begins to be received at t 4 . Similar to displaying the first through fourth images, to display a fifth image corresponding with the fifth image data  94 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the fifth image data  94 . Additionally, in response to receiving the fifth image data  94 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is 2778. Thus, the timing controller  38  may determine that a negative polarity voltage should be applied to the pixels in the display panel to write the fifth image. 
     Furthermore, the timing controller  38  may determine that the fifth image should be displayed at 60 Hz because the fifth image data  94  includes 52 vertical blank lines and 1800 active lines (e.g., 1852 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a negative voltage at the determined magnitude at 60 Hz to display the fifth image. Additionally, since a negative voltage is applied, the counter  46  will count down 1852 lines. Thus, at t 5 , the counter value may be 926. 
     At t 5 , the source  36  may go into a sleep mode and cease transmitting image data. As such, the display  12  may continue to hold the negative voltage used to display the fifth image in the display panel pixels. Thus, in response to detecting that new image data is not received, the timing controller  38  may start the timer  47  at t 5 . Subsequently, at t 6 , sixth image data may be received. Thus, in response to detecting that a new image has been received, the timing controller  38  may stop the timer  47  at t 6 . 
     As described above, using the timer value, the timing controller  38  may update the counter  46 . More specifically, the timing controller  38  may update the counter value by dividing the timer value by time generally used to write a line of an image. For example, assuming that it generally takes 1 ms to write one line of an image and the timer value at t 6  is 2222, the timing controller  38  may determine that between t 5  and t 6  a negative voltage is held in the display panel pixels for 2222 lines. Thus, the counter value at t 6  may be −1296. In some embodiments, the timing controller  38  may update the counter value while the timer  47  measures the duration. In other words, the counter  46  may count down every 1 ms between t 5  and t 6 . Additionally or alternatively, the timing controller  38  may update the counter value when new image data is received (e.g., at t 6 ). 
     As depicted, sixth image data begins to be received at t 6 . Similar to displaying the first through fifth images, to display a sixth image corresponding with the sixth image data  96 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the sixth image data  96 . Furthermore, in response to receiving the sixth image data  96 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is −1296. Thus, the timing controller  38  may determine that a positive polarity voltage should be applied to the pixels in the display panel to write the sixth image. 
     Furthermore, the timing controller  38  may determine that the sixth image should be displayed at 30 Hz because the sixth image data  96  includes 1904 vertical blank lines and 1800 active lines (e.g., 3704 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a positive voltage at the determined magnitude at 30 Hz to display the sixth image. Additionally, since a positive voltage is applied, the counter  46  will count up 3704 lines. Thus, at t 7 , the counter value may be 2408. 
     Subsequently, as depicted, seventh image data  98  begins to be received at t 7 . Similar to displaying the first through sixth images, to display a seventh image corresponding with the seventh image data  98 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the seventh image data  98 . Furthermore, in response to receiving the seventh image data  98 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is 2408. Thus, the timing controller  38  may determine that a negative polarity voltage should be applied to the pixels in the display panel to write the seventh image. 
     Furthermore, the timing controller  38  may determine that the seventh image should be displayed at 35 Hz because the seventh image data  98  includes 1375 vertical blank lines and 1800 active lines (e.g., 3175 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a negative voltage at the determined magnitude at 35 Hz to display the seventh image. Additionally, since a negative voltage is applied, the counter  46  will count down 3175 lines. Thus, at t 8 , the counter value may be −767. 
     Then, as depicted, eighth image data  100  begins to be received at t 8 . Similar to displaying the first through seventh images, to display an eighth image corresponding with the eighth image data  100 , the timing controller  38  may determine the magnitude of the voltage to apply based on the active lines included in the eighth image data  100 . Furthermore, in response to receiving the eighth image data  100 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is −767. Thus, the timing controller  38  may determine that a positive polarity voltage should be applied to the pixels in the display panel to write the eighth image. 
     Furthermore, the timing controller  38  may determine that the eighth image should be displayed at 60 Hz because the eighth image data  100  includes 52 vertical blank lines and 1800 active lines (e.g., 1852 total lines). Accordingly, the timing controller  38  may instruct the driver  40  to use a positive voltage at the determined magnitude at 60 Hz to display the eighth image. Additionally, since a positive voltage is applied, the counter  46  will count down 1852 lines. Thus, at t 9 , the counter value may be 1085. 
     Based on the above hypothetical operation  84 , the duration that positive voltages and negative voltages are applied/held may be balanced such that the possibility of polarizing pixels in the display panel may be reduced. More specifically, the above example assumes a linear relationship between duration a voltage is applied and the possibility of polarization. In other words, a positive voltage applied for one line should exactly cancel out a negative voltage applied for one line. However, in other embodiments, the relationship may be non-linear. To implement a non-linear embodiment, the amount the counter  46  counts up or down may be adjusted. For example, the longer a voltage is applied/held the less the counter  46  may count up or down. In other words, a non-linear counter may be used. 
     To help illustrate, one embodiment of a process  102  for using a non-linear counter is described in  FIG. 10 . Generally, the process  102  includes increasing/decreasing the counter value (process block  104 ), determining whether the counter value has reached a duration threshold (decision block  106 ), and, when the duration threshold has not been reached, continuing the increase/decrease the counter (arrow  108 ). On the other hand, when the duration threshold is reached, the process  102  includes changing the counter divider (process block  110 ) and returning to increasing/decreasing the counter (arrow  112 ). In some embodiments, process  102  may be implemented using instructions stored in the timing controller memory  44  and/or another suitable tangible non-transitory computer-readable medium and executable by the timing controller processor  42  and/or another suitable processing circuitry. 
     As in the linear embodiments described above, the timing controller  38  may update (e.g., increase or decrease) the counter value based on the duration an image is displayed (process block  104 ). However, once the timing controller  38  determines that a duration threshold has been reached (decision block  106 ), a counter divider value may be applied (process block  110 ). More specifically, in some embodiments, a counter divider may be applied so that the counter value adjusts at smaller increments. For example, a counter divider value of two may be applied once a duration threshold is reached. In such an embodiment, the counter  46  may be adjusted one unit for every two lines. 
     To help illustrate, an example of a duration threshold versus counter divider relationship is described below. 
                     TABLE 1                  Duration threshold vs. Counter Divider                             Duration               threshold   Counter Divider                       1852   2           3704   3           5556   4           7408   5           9260   6                        
In the described example, the duration thresholds and the counter dividers are set in a monotonically increasing fashion. However, in other embodiments, the duration threshold and the counter dividers may be set in any suitable manner. Furthermore, in other embodiments, additionally duration thresholds and counter dividers may be used.
 
     To help illustrate the use of the duration threshold versus counter divider relationship, the relationship is described with regard to the hypothetical display operation  114  described in  FIG. 11 . As depicted, first image data  116  begins to be received at t 0 . In response to receiving the first image data  116 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is zero. Accordingly, the timing controller  38  may determine that a positive polarity voltage should be applied to the pixels in the display panel to write a first image corresponding with the first image data  116 . Thus, the counter  46  may begin to count up based on the number of lines included in the first image data  116 , which includes 52 vertical blank lines and 1800 active lines (e.g., 1852 total lines). Since the duration thresholds have not been reached, the counter value may increase one unit per line for the duration the first image is displayed. Thus, the counter value at t 1  may be 1852. 
     Then, as depicted, second image data  118  begins to be received at t 1 . In response to receiving the second image data, the timing controller  38  may poll the counter  46  and determine that the previous counter value is 1852. Accordingly, the timing controller  38  may determine that a negative polarity voltage should be applied to the pixels in the display panel to write the second image. Thus, the counter  46  may begin to count down based on the number of lines included in the first image data  116 , which includes 9312 vertical blank lines and 1800 active lines (e.g., 11,112 total lines). 
     Based on the duration threshold versus counter divider relationship described above, the duration thresholds may be reached. More specifically, as depicted, the counter  46  may count down one unit per line until the first duration threshold (e.g., 1852) is reached. Thus, at t 2 , the duration the second image has been displayed is 1852 lines and the counter value is zero. 
     At t 2 , since the first duration threshold has been reached, the timing controller  38  may apply the corresponding counter divider, which as described above is two. As such, the counter  46  may count down one unit every two lines until the second duration threshold (e.g., 3704) is reached. Thus, at t 3 , the duration the second image has been displayed is 3704 lines and the counter value is −926. 
     At t 3 , since the second duration threshold has been reached, the timing controller  38  may again apply the corresponding counter divider, which as described above is three. As such, the counter  46  may count down one unit every three lines until the third duration threshold (e.g., 5556) is reached. Thus, at t 4 , the duration the second image has been displayed is 5556 lines and the counter value is −1543. 
     At t 4 , since the third duration threshold has been reached, the timing controller  38  may again apply the corresponding counter divider, which as described above is four. As such, the counter  46  may count down one unit every four lines until the fourth duration threshold (e.g., 7408) is reached. Thus, at t 5 , the duration the second image has been displayed is 7408 lines and the counter value is −2006. 
     At t 5 , since the fourth duration threshold is reached, the timing controller  38  may again apply the corresponding counter divider, which as described above is five. As such, the counter  46  may count down one unit every five lines until the fifth duration threshold (e.g., 9260) is reached. Thus, at t 6 , the duration the second image has been displayed is 9260 lines and the counter value is −2376. 
     At t 6 , since the fifth duration threshold is reached, the timing controller  38  may again apply the corresponding counter divider, which as described above is six. As such, the counter  46  may count down one unit every six lines. Thus, at t 7 , the counter value may be −2684. 
     Subsequently, as depicted, third image data  120  begins to be received at t 7 . In response to receiving the third image data  120 , the timing controller  38  may poll the counter  46  and determine that the previous counter value is −2684. Accordingly, the timing controller  38  may determine that a positive polarity voltage should be applied to the pixels in the display panel to write a third image corresponding with the third image data  120 . Thus, the counter  46  may begin to count up based on the number of lines included in the third image data  120 , which includes 52 vertical blank lines and 1800 active lines (e.g., 1852 total lines). Since the duration thresholds have not been reached, the counter value may increase one unit per line for the duration the third image is displayed. Thus, the counter value at t 8  may be −832. 
     Accordingly, the technical effects of the present disclosure include improving inversion techniques used by an electronic display particularly when the electronic display uses a dynamic variable refresh rate. More specifically, the likelihood of polarizing pixels in the electronic display may be reduced by using a counter. In some embodiments, the counter may keep track of duration that positive voltages are applied to the pixels and the duration that negative voltages are applied to the pixels. As such, the duration each polarity is applied may offset one another, which reduces the possibility of one being applied for substantially longer durations and polarizing the pixels. 
     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.