Patent Publication Number: US-11651719-B2

Title: Enhanced smoothness digital-to-analog converter interpolation systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Application No. 63/083,687, entitled “ENHANCED SMOOTHNESS DIGITAL-TO-ANALOG CONVERTER INTERPOLATION SYSTEMS AND METHODS,” filed Sep. 25, 2020, the disclosure of which is incorporated by reference in its entirety for all purposes. 
    
    
     SUMMARY 
     This disclosure relates to interpolation systems and methods for a digital-to-analog converter (e.g., a gamma bus generator) to enhance the smoothness of its output. 
     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. 
     To display an image, an electronic display generally controls light emission (e.g., luminance and/or color) of its display pixels based on corresponding image data. For example, an image data source may output image data as a stream of pixel data that indicates target luminance of display pixels located at a corresponding pixel positions. In some embodiments, image data may indicate target luminance per color component (e.g., a gray level for each color component), for example, via red component image data, blue component image data, and green component image data. Additionally or alternatively, image data may indicate target luminance in grayscale. 
     Current may be supplied by a gamma bus generator to drivers of display pixels at various analog voltage levels to achieve the desired luminance values (e.g., gray levels for each color component). For example, in some embodiments, the different voltage levels may be achieved via one or more digital to analog converters (DACs), amplifiers, and/or a resistor string. In some scenarios, the gamma bus may not provide the voltage levels associated with every gray level. Instead, the gamma bus may provide analog reference voltages that correspond to some but not all gray levels. In some embodiments, providing only a portion (e.g., the analog reference voltages) of the total analog voltage levels associated with the gamut of gray levels may reduce power consumption of the gamma bus generator, reduce the size of the gamma bus generator, and/or decrease the footprint of the data lines (e.g., gamma bus) carrying the analog voltages. As such, interpolation circuitry may be included, such as with the source amplifiers of the electronic display, to generate intermediate analog voltages (e.g., voltages between the analog reference voltages of the gamma bus) to make available a full range of analog voltage levels associated with a gamut of gray levels for driving the display pixels. 
     Additionally, in some embodiments, the interpolation circuitry may perform different levels of interpolation based on which gray level is desired. For example, in some embodiments, certain intermediate analog voltages may be determined by interpolating between two analog reference voltages having immediate proximity (e.g., in the range of discrete analog voltage levels) to the intermediate analog voltage. In other words, two analog reference voltages associated with gray levels (e.g., gray levels 5 and 7) immediately adjacent a desired gray level (e.g., gray levels 6) may be interpolated between to generate the intermediate analog voltage associated with the desired gray level (e.g., gray level 6). However, other desired gray levels may be interpolated at higher levels of interpolation. For example, in some embodiments, multiple different intermediate voltages having different desired gray levels (e.g., gray levels 64-66) may be interpolated based on the same two analog reference voltages having gray levels (e.g., gray levels 63 and 67) surrounding the multiple different intermediate voltages. In other words, the span of gray levels between tap points of the gamma bus (e.g., the analog reference voltages) may vary. In some embodiments, the level of interpolation may vary based on a likelihood of perceivable artifacts. For example, at lower gray levels (e.g., darker gray levels), where error in the gray level may have a more perceivable effect, a lower level interpolation may be used to increase the accuracy of the interpolation and reduce the likelihood of perceivable artifacts and increase smoothness of the transitions between gray levels. On the other hand, at higher gray levels (e.g., brighter gray levels), where error in the gray level may be less perceivable, a higher level interpolation may be used to save space, power, and/or additional resources. As should be appreciated, the number of gray levels, tap points, and/or which analog reference voltages are used to interpolate which intermediate voltages are given as examples and are non-limiting. 
    
    
     
       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 that includes an electronic display, in accordance with an embodiment; 
         FIG.  2    is an example of the electronic device of  FIG.  1   , in accordance with an embodiment; 
         FIG.  3    is another example of the electronic device of  FIG.  1   , in accordance with an embodiment; 
         FIG.  4    is another example of the electronic device of  FIG.  1   , in accordance with an embodiment; 
         FIG.  5    is another example of the electronic device of  FIG.  1   , in accordance with an embodiment; 
         FIG.  6    is a diagrammatic representation of a gamma bus generator in electrical communication with an electronic display via a gamma bus, in accordance with an embodiment; 
         FIG.  7    is a graph of gray levels and corresponding digital input signals in relation to analog reference voltages of a gamma bus, in accordance with an embodiment; 
         FIG.  8    is a block diagram of interpolation circuitry, in accordance with an embodiment; and 
         FIG.  9    is a flowchart of an example process for providing analog reference voltages to an electronic display, in accordance with an embodiment. 
     
    
    
     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. 
     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. Furthermore, the phrase A “based on” B is intended to mean that A is at least partially based on B. Moreover, the term “or” is intended to be inclusive (e.g., logical OR) and not exclusive (e.g., logical XOR). In other words, the phrase A “or” B is intended to mean A, B, or both A and B. 
     Electronic devices such as computers, mobile phones, portable media devices, tablets, televisions, virtual-reality headsets, and vehicle dashboards, among many others, often use one or more electronic displays to present information via one or more images (e.g., image frames). Such electronic displays may take the form of a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, a plasma display, or the like. In any case, to display an image, the electronic display generally controls light emission (e.g., luminance and/or color) of its display pixels based on corresponding image data. For example, an image data source (e.g., memory, an input/output (I/O) port, and/or a communication network) may output image data as a stream of pixel data that indicates target luminance of display pixels located at a corresponding pixel positions. In some embodiments, image data may indicate target luminance per color component, (e.g., a gray level for each color component), for example, via red component image data, blue component image data, and green component image data. Additionally or alternatively, image data may indicate target luminance in grayscale. 
     Digital values of the image data may be mapped to analog voltages to drive each of the display pixels at a target luminance level. For example, in some embodiments, the different voltage levels may be achieved via one or more digital to analog converters (DACs), amplifiers, and/or a resistor string of a gamma bus generator. In some embodiments, the gamma bus generator may output multiple different voltage levels corresponding to the digital values of the image data. For example, 8-bit image data per color component may correspond to a gamut of 256 different gray levels and, therefore, 256 different voltage levels per color component. As should be appreciated, the image data and corresponding voltage outputs may be associated with any suitable bit-depth and gray level values depending on implementation and the electronic display. Furthermore, the gamma bus generator may include more or fewer voltage outputs than the corresponding bit-depth of image data. For example, in some embodiments, the same voltage level may be used for multiple gray levels, and the current may be pulse-width modulated to obtain the different perceived luminance outputs. 
     Current may be supplied to the display pixels at various voltage levels generated by a gamma bus generator to achieve the desired luminance values (e.g., gray levels for each color component). In some scenarios, however, the gamma bus may not provide the voltage levels associated with every gray level. Instead, the gamma bus may provide analog reference voltages that correspond to some but not all gray levels. In some embodiments, providing only a portion of the total analog voltage levels associated with the gamut of gray levels may reduce power consumption of the gamma bus generator, reduce the size of the gamma bus generator, and/or decrease the footprint of the data lines (e.g., gamma bus) carrying the analog voltages. As such, interpolation circuitry may be included, such as with the source amplifiers of the electronic display, to generate intermediate analog voltages (e.g., voltages between the analog reference voltages of the gamma bus) to make available a full gamut of analog voltages for driving the display pixels. 
     Additionally, in some embodiments, the interpolation circuitry may perform different levels of interpolation based on which gray level is desired. For example, in some embodiments, certain intermediate analog voltages may be determined by interpolating between two analog reference voltages having immediate proximity to the intermediate analog voltage. In other words, two analog reference voltages associated with gray levels (e.g., gray levels 5 and 7) immediately adjacent a desired gray level (e.g., gray levels 6) may be interpolated between to generate the intermediate analog voltage associated with the desired gray level (e.g., gray level 6). However, other desired gray levels may be interpolated at higher levels of interpolation. For example, in some embodiments, multiple different intermediate voltages having different desired gray levels (e.g., gray levels 64-66) may be interpolated based on the same two analog reference voltages having gray levels (e.g., gray levels 63 and 67) surrounding the multiple different intermediate voltages. In other words, the span of gray levels between tap points of the gamma bus (e.g., the analog reference voltages) may vary. In some embodiments, the level of interpolation may vary based on a likelihood of perceivable artifacts. For example, at lower gray levels (e.g., darker gray levels), where error in the gray level may have a more perceivable effect, a lower level interpolation may be used to increase the accuracy of the interpolation, reduce the likelihood of perceivable artifacts, and increase the smoothness of the transitions between gray levels. On the other hand, at higher gray levels (e.g., lighter gray levels), where error in the gray level may be less perceivable, a higher level interpolation may be used to save space, power, and/or additional resources. As should be appreciated, the number of gray levels, tap points, and/or which analog reference voltages are used to interpolate certain intermediate voltages as discussed herein are given as examples and are non-limiting. Furthermore, although discussed herein as relating to interpolation of analog voltages for use in an electronic display panel, the techniques discussed herein may be applicable to additional scenarios where interpolation of analog voltages is of interest. For example, audio reproduction may have different sensitivities to the precision/accuracy of different analog voltages, and as such the different analog voltages may be interpolated differently. 
     To help illustrate, an electronic device  10 , which includes an electronic display  12 , is shown in  FIG.  1   . As will be described in more detail below, the electronic device  10  may be any suitable electronic device  10 , such as a computer, a mobile phone, a portable media device, a tablet, a television, a virtual-reality headset, a vehicle dashboard, and the like. Thus, 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 an electronic device  10 . 
     The electronic device  10  may include the electronic display  12 , one or more input devices  14 , one or more input/output (I/O) ports  16 , a processor core complex  18  having one or more processor(s) or processor cores, local memory  20 , a main memory storage device  22 , a network interface  24 , a power source  26 , and one or more gamma bus generators  28  coupled to one or more respective gamma buses. The various components described in  FIG.  1    may include hardware elements (e.g., circuitry), software elements (e.g., a tangible, non-transitory computer-readable medium storing instructions), or a combination of both hardware and software elements. It should be noted that the various depicted components may be combined into fewer components or separated into additional components. For example, the local memory  20  and the main memory storage device  22  may be included in a single component. Additionally, the gamma bus generator  28  may be included in the electronic display  12 , such as part of a display driver, or implemented separately. 
     The processor core complex  18  may be operably coupled with local memory  20  and the main memory storage device  22 . Thus, the processor core complex  18  may execute instruction stored in local memory  20  and/or the main memory storage device  22  to perform operations, such as generating and/or transmitting image data. As such, the processor core complex  18  may include one or more general purpose microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable logic arrays (FPGAs), or any combination thereof. 
     In addition to instructions, the local memory  20  and/or the main memory storage device  22  may store data to be processed by the processor core complex  18 . Thus, in some embodiments, the local memory  20  and/or the main memory storage device  22  may include one or more tangible, non-transitory, computer-readable mediums. For example, the local memory  20  may include random access memory (RAM) and the main memory storage device  22  may include read only memory (ROM), rewritable non-volatile memory such as flash memory, hard drives, optical discs, and/or the like. 
     In some embodiments, the network interface  24  may facilitate data communication with another electronic device and/or a communication network. For example, the network interface  24  (e.g., a radio frequency system) may enable the electronic device  10  to communicatively couple 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. 
     In some embodiments, the power source  26  may provide electrical power to one or more components in the electronic device  10 , such as the processor core complex  18 , the electronic display  12 , and/or the gamma bus generator  28 . Thus, the power source  26  may include any suitable source of energy, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter. 
     Furthermore, in some embodiments, I/O ports  16  may enable the electronic device  10  to interface with other electronic devices. For example, when a portable storage device, computing system, and/or accessory is connected, the I/O port  16  may enable the processor core complex  18  to communicate data with the portable storage device, computing system and/or accessory. 
     In some embodiments, an input device  14  may facilitate user interaction with the electronic device  10 , for example, by receiving user inputs. Thus, an input device  14  may include a button, a keyboard, a mouse, a trackpad, and/or the like. Additionally, in some embodiments, an input device  14  may include touch-sensing components in the electronic display  12 . In such embodiments, the touch sensing components may receive user inputs by detecting occurrence and/or position of an object touching the surface of the electronic display  12 . 
     In addition to enabling user inputs, the electronic display  12  may include a display panel with one or more display pixels. The electronic display  12  may control light emission from its display pixels (e.g., via the gamma bus generator  28 ) to present visual representations of information, such as a graphical user interface (GUI) of an operating system, an application interface, a still image, or video content, by displaying frames based at least in part on corresponding image data (e.g., pixel data corresponding to individual pixel positions). 
     The electronic display  12  may be operably coupled to the processor core complex  18  and the gamma bus generator  28 . In this manner, the electronic display  12  may display images based at least in part on image data received from an image data source, such as the processor core complex  18  and/or the network interface  24 , an input device  14 , and/or an I/O port  16 . To facilitate accurately representing an image, image data may be processed before being supplied to the electronic display  12 , for example, via a display pipeline implemented in the processor core complex  18  and/or image processing circuitry. 
     The display pipeline may perform various processing operations, such as spatial dithering, temporal dithering, pixel color-space conversion, luminance determination, luminance optimization, image scaling, and/or the like. Based on the image data from the image data source and/or processed image data from the display pipeline, target luminance values for each display pixel may be determined. Moreover, the target luminance values may be mapped to analog voltage values (e.g., generated by the gamma bus generator  28 ), and the analog voltage value corresponding to the target luminance for a display pixel at a particular location may be applied to that display pixel to facilitate the desired luminance output from the display. For example, a first display pixel desired to be at a lower luminance output may have a lower voltage applied than a second display pixel desired to be at a higher luminance output. 
     As described above, the electronic device  10  may be any suitable electronic device. To help illustrate, one example of a suitable electronic device  10 , specifically a handheld device  10 A, is shown in  FIG.  2   . In some embodiments, the handheld device  10 A may be a portable phone, a media player, a personal data organizer, a handheld game platform, and/or the like. For illustrative purposes, the handheld device  10 A may be a smart phone, such as any iPhone® model available from Apple Inc. 
     The handheld device  10 A may include an enclosure  30  (e.g., housing) to protect interior components from physical damage and/or shield them from electromagnetic interference. Additionally, the enclosure  30  may surround the electronic display  12 . In the depicted embodiment, the electronic display  12  is displaying a graphical user interface (GUI)  32  having an array of icons  34 . By way of example, when an icon  34  is selected either by an input device  14  or a touch-sensing component of the electronic display  12 , an application program may launch. 
     Furthermore, input devices  14  and/or the I/O ports  16  may be accessed through openings in the enclosure  30 . As described above, the input devices  14  may enable a user to interact with the handheld device  10 A. For example, the input devices  14  may enable the user to 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/or toggle between vibrate and ring modes. 
     To further illustrate, another example of a suitable electronic device  10 , specifically a tablet device  10 B, is shown in  FIG.  3   . For illustrative purposes, the tablet device  10 B may be any iPad® model available from Apple Inc. A further example of a suitable electronic device  10 , specifically a computer  10 C, is shown in  FIG.  4   . For illustrative purposes, the computer  10 C may be any Macbook® or iMac® model available from Apple Inc. Another example of a suitable electronic device  10 , specifically a watch  10 D, is shown in  FIG.  5   . For illustrative purposes, the watch  10 D may be any Apple Watch® model available from Apple Inc. The tablet device  10 B, the computer  10 C, and/or the watch  10 D each may also include an electronic display  12 , input devices  14 , I/O ports  16 , and an enclosure  30 . 
     As described above, an electronic device  10  may utilize a gamma bus to provide a spectrum of analog reference voltages to the electronic display to facilitate illumination of the display pixels at target luminances. To help illustrate, a schematic diagram of a portion of the electronic device  10 , including a gamma bus generator  28  and the electronic display  12  is shown in  FIG.  6   . As described in more detail below, the electronic device  10  may utilize one or more gamma bus generators  28  (e.g., a gamma bus generator  28  for each color component) and one or more respective gamma busses for transmitting analog reference voltages  36  to an electronic display  12 . A single gamma bus generator  28  with a single gamma bus is discussed herein for brevity. 
     In some embodiments, the electronic display  12  may use analog reference voltages  36  to power display pixels  38  at various voltages that correspond to different luminance levels. For example, digital image data  40  may correspond to original or processed image data and contain target luminance values for each display pixel  38  in an active area of the electronic display  12 . Moreover, display circuitry  42 , such as column drivers  44 , also known as data drivers and/or display drivers, may include source latches  46 , source amplifiers  48 , and/or any other suitable logic/circuitry to utilize the appropriate analog reference voltage(s)  36 , based on the digital image data  40 . The display circuitry  42  may apply power at the corresponding voltage to the display pixel  38  to achieve the target luminance output from the display pixel  38 . Such power, at the appropriate voltage for each display pixel  38 , may travel down analog datalines  50  to display pixels  38  of the active area. As should be appreciated, the active area of the electronic display  12  may be all or a portion of the electronic display  12  utilized to display an image. 
     As discussed above, the different analog reference voltages  36  supplied by the gamma bus may correspond to at least a portion of the values of the digital image data  40 . For example, 8-bit digital image data  40  per color component may correspond to 256 different gray levels and, therefore, 256 different analog voltages per color component. Further, digital image data  40  corresponding to 8-bits per color component may yield millions or billions of color combinations as well as define the brightness of the electronic display  12  for a given frame. As should be appreciated, the digital image data  40  and corresponding voltage outputs may be associated with any suitable bit-depth depending on implementation and/or may use any suitable color space (e.g., RBG (red/blue/green), sRBG, Adobe RGB, HSV (hue/saturation/value), YUV (luma/chroma/chroma), Rec. 2020, etc.). Furthermore, the gamma bus may include more or fewer analog reference voltages  36  than the corresponding bit-depth of digital image data  40 . Indeed, in some embodiments, the same analog reference voltages  36  may be used for multiple gray levels, for example, via interpolation between analog reference voltages  36  and/or pulse-width modulated of current flow to obtain the different perceived luminance outputs. In some embodiments, the gamma bus generator  28  and/or display circuitry  42  may provide the display pixels with a negative voltage relative to a reference point (e.g., ground). As should be appreciated, the positive and negative voltages may be used in a similar manner to operate the display pixels  38 , and they may have mirrored or different mappings between voltage level and target gray level. 
     Additionally, in some embodiments, different color components of display pixels  38  (e.g., a red sub-pixel, a green sub-pixel, a blue sub-pixel, etc.) may have different mappings between voltage level and target gray level. For example, display pixels  38  of different color components may have different luminance outputs given the same driving voltage/current. As such, in some embodiments, one or more gamma buses may be used for each color component and/or voltage polarity. As should be appreciated, the mappings between voltage level and target gray level may depend on the type of display pixels (e.g., LCD, LED, OLED, etc.), a brightness setting, a color hue setting, temperature, contrast control, pixel aging, etc., and, therefore, may depend on implementation. 
     The different analog reference voltages  36  may be generated by the gamma bus generator  28  via one or more DACs  52 , amplifiers  54 , and/or a resistor string (not shown). However, in some scenarios, the gamma bus generator  28  may not provide the entire range of voltage levels associated with the entire gamut of gray levels. Instead, the gamma bus generator  28  may provide analog reference voltages  36  that correspond to some, but not all, gray levels. In some embodiments, providing only a portion of the total range of analog voltage levels associated with the gamut of gray levels may reduce power consumption of the gamma bus generator  28 , reduce the size of the gamma bus generator  28 , and/or decrease the footprint of the gamma bus carrying the analog reference voltages  36 . 
     To make available a satisfactory range (e.g., the full range, a subset of the full range that is being utilized in the current frame, or other subset of the full range) of discrete analog voltage levels for driving the display pixels  38 , intermediate analog voltages (e.g., voltages between the analog reference voltages of the gamma bus) may be interpolated via interpolation circuitry. Furthermore, different intermediate analog voltages may be interpolated using different levels of interpolation to improve the smoothness of transitions (e.g., with reduced likelihood of visual artifacts) between gray levels, while maintaining a reduced number of analog reference voltages  36  that may help save space, power, and/or additional resources. 
     In some scenarios, the range of discrete analog voltage levels may have a non-linear (e.g., logarithmic, exponential, piecewise, etc.) relation with the gamut of gray levels. Moreover, the curvature (e.g., second derivative) of the relation may correspond to the smoothness of the perceived gray level transitions. As such, in some embodiments, the discrete positions (e.g., tap points) of the analog voltage levels may be selected to increase the perceived smoothness of transitions between gray levels by placing more tap points at locations where the curvature is greater (e.g., where voltage errors may have a higher likelihood of perceivable artifacts). Additionally, in some embodiments, different interpolations may be accomplished based on what gray level is associated with the analog voltage level being interpolated. For example, interpolations with less potential error may be performed where the curvature of the relation between analog voltage levels and gray levels is greater, and interpolations where error is less likely to be perceived and/or less error is likely to occur may utilize less resource intensive interpolations to increase efficiency (e.g., size efficiency, power efficiency, etc.). 
     To help illustrate,  FIG.  7    is a graph  56  of gray levels  58  and corresponding digital input signals  60  in relation to the analog reference voltages  36  of the gamma bus. In the depicted example, the gray level  58  ranges from 0 to 255, corresponding to digital input signals  60  from 0 to 255, and the gamma bus provides  81  analog reference voltages  36 . As should be appreciated, the graph  56  is shown as a non-limiting example, and the gamut of gray levels  58  and the number of analog reference voltages  36  may vary based on implementation. As depicted, certain gray levels  58  (e.g., GL5, GL7, GL 63, and GL 67) may be directly related to corresponding analog reference voltages  36  (e.g., V&lt;3&gt;, V&lt;4&gt;, V&lt;32&gt;, and V&lt;33&gt;, respectively). The range of the analog voltage levels  62  may include additional intermediate voltages  64  that do not have directly relating analog reference voltages  36  from the gamma bus. Furthermore, although shown as generally linear, the changes in analog voltage levels  62  from one gray level  58  to another may be non-linear (e.g., logarithmic, exponential, piecewise, etc.). For example, the voltage jump  66  in the analog voltage level  62  from GL0 to GL1 may be greater than the change in analog voltage level  62  from GL1 to GL2. 
     To generate the intermediate voltages  64  for gray levels  58  that are not directly associated with an analog reference voltage  36 , analog reference voltages  36  for nearby gray levels  58  may be interpolated between using either linear or non-linear interpolation. For example, because GL6 does not have a directly associated analog reference voltage  36 , the analog voltage levels  62  corresponding to GL5 and GL 7 may be used to generate the intermediate voltage  64  corresponding to GL6. In some embodiments, the interpolation may be generally linear, while the changes in analog voltage level  62  from one gray level  58  to the next may be non-linear. As such, gray levels  58  associated with analog voltage levels  62  where the concavity of the non-linear relation is greater may be interpolated differently from gray levels associated with analog voltage levels  62  where the concavity of the non-linear relation is less. Indeed, in some scenarios, closer initial interpolation points to the desired intermediate voltage  64  may result in reduced interpolation error, particularly at gray levels  58  associated with analog voltage levels  62  where the concavity of the non-linear relation is greater (e.g., at gray levels  58  where linear interpolation error may be greater and/or more likely to produce a perceivable artifact). Furthermore, while any set of analog reference voltages  36  may be used in interpolating the intermediate voltages  64 , in some embodiments, it may be desirable to utilize the two most proximate analog reference voltages  36  for a given intermediate voltage  64 . 
     Low level interpolation may utilize analog reference voltages  36  that are associated with gray levels  58  immediately proximate the gray level  58  to be interpolated. In the above example, the intermediate voltage  64  for GL6 is interpolated using analog reference voltages  36  (e.g., V&lt;3&gt; and V&lt;4&gt;) that are associated with immediately proximate gray levels  58  (e.g., GL5 and GL6). Such low level interpolation may decrease interpolation error and increase smoothness between gray levels  58 . In some embodiments, the interpolation of each intermediate voltage  64  may be performed via low level interpolation. 
     In some scenarios, it may not be feasible to perform low level interpolation for each intermediate voltage  64 . For example, in order to have an analog reference voltage  36  immediately proximate each intermediate voltage  64 , the number of analog reference voltages  36  and associated data lines of the gamma bus may be increased and/or the number of gray levels  58  may be decreased, which, in turn, may decrease operational efficiency, take up more space within the electronic device  10 , and/or decrease the color fidelity of the electronic display  12 . As such, in some embodiments, interpolation at gray levels  58  where interpolation error may have an increased likelihood of producing a visual artifact (e.g., color blockiness, banding, decreased visual smoothness, visible lines between color transitions, etc.) may use lower level interpolation, and gray levels  58  where interpolation error may be less likely to result in perceivable artifacts may utilize higher level interpolation. For example, in some embodiments, low level interpolation may be utilized for gray levels  58  below a threshold  68  (e.g., darker than a threshold gray level or lower than a threshold voltage). 
     To utilize lower level interpolation while maintaining a reduced number of analog reference voltages  36 , a portion of the analog voltage levels  62  may be interpolated using higher level interpolation. For example, gray levels  58  above a threshold (e.g., threshold  68 ) may be interpolated by analog reference voltages  36  that may not be immediately proximate the intermediate voltage  64 . Higher level interpolation may utilize the same set (e.g., pair) of analog reference voltages  36  to interpolate multiple intermediate voltages  64 . For example, each of the intermediate voltages  64  corresponding to GL64, GL65, and GL66 may be interpolated using analog reference voltages V&lt;32&gt; and V&lt;33&gt; corresponding to GL63 and GL67. In some embodiments, the portion of analog voltage levels  62  interpolated by higher level interpolation may correspond to gray levels  58  that are less likely to produce perceivable artifacts in response to interpolation errors such as brighter gray levels  58 . In the depicted example, the high level interpolation utilizes two analog reference voltages  36  to interpolate three different intermediate voltages  64 . However, a given set of analog reference voltages  36  may be used to interpolate any suitable number (e.g., one, two, three, five, seven, or more) of intermediate voltages  64  depending on the level of interpolation. 
     As discussed above, it may be desirable to interpolate intermediate voltages  64  rather than generate the entire range of analog voltage levels  62  within the gamma bus generator  28 . As such interpolation circuitry  70  may receive the analog reference voltages  36 , generate the intermediate voltages  64  and output the analog voltage levels  62  to the display pixels  38 , as shown in  FIG.  8   . In some embodiments, the interpolation circuitry  70  may include low level interpolation circuitry  72  and high level interpolation circuitry  74 . Additionally or alternatively, the interpolation circuitry  70  may use the same circuitry for both low level interpolation circuitry  72  and high level interpolation circuitry  74 , and the level of interpolation used may be based on the digital input signal  60  of the digital image data  40 . For example, the low level interpolation circuitry  72  may be a subset of the high level interpolation circuitry  74  and/or include high level interpolation circuitry  74  operating in a low level interpolation mode. Moreover, the interpolation circuitry may use any suitable method of interpolation such as transistor-based interpolation (e.g., using differential pairs), switch-capacitor interpolation, resistor strings, etc. In some embodiments, the interpolation circuitry  70  may be disposed within the electronic display  12  such as within the display circuitry  42 . Furthermore, in some embodiments, the interpolation circuitry  70  may be integrated with amplifiers such as the source amplifiers  48 . 
     In some embodiments, the interpolation circuitry may interpolate each of the intermediate voltages  64  constantly such that the entire range of analog voltage levels  62  are constantly available during operation. However, in some embodiments, the interpolation circuitry  70  may interpolate the intermediate voltages  64  on demand in response to the digital image data  40 , which may reduce the size of and/or increase the efficiency of the display circuitry  42 . For example, in response to a digital input signal  60  representative of a particular gray level  58 , the interpolation circuitry  70  may modulate between passing through an analog reference voltage  36  and interpolating and outputting an intermediate voltage  64 . In some embodiments, the interpolation circuitry  70  may use the digital input signal  60 , either fully or in part, to determine the applicable analog reference voltages  36  and the least significant bit(s) of the digital input signal  60  to determine interpolations. 
     When performing low level interpolation (e.g., via low level interpolation circuitry  72 ) the interpolation circuitry  70  may select the appropriate analog reference voltages  36  from which to interpolate the intermediate voltage  64  based on the digital input signal  60  or a portion (e.g., most significant bit(s)) thereof. Furthermore, in some embodiments, low level interpolation may use one or more bits (e.g., the least significant bit(s)) of the digital input signal  60  to decide whether to interpolate between the analog reference voltages  36  and return an intermediate voltage  64  or return one of the analog reference voltages  36 . For example, in keeping with the example from  FIG.  7   , low level interpolation circuitry  72  may receive analog reference voltages  36 , such as V&lt;3&gt; and V&lt;4&gt;, and have the ability to output the analog voltage levels  62  (e.g., L5, L6, and/or L7) associated with GL5, GL6, and/or GL7. Moreover, based on the digital input signal  60  (e.g., the least significant bit of the digital input signal  60 ), the low level interpolation circuitry  72  may determine whether to perform an interpolation and output the intermediate voltage  64  (e.g., L6 associated with GL6) or output one of the analog reference voltages  36  (e.g., V&lt;3&gt; or V&lt;4&gt; as L5 or L7, respectively). 
     Similarly, the high level interpolation circuitry  74  may utilize the digital input signal  60  to determine which analog reference voltages  36  are applicable, and two or more bits (e.g., two or more least significant bits) of the digital input signal to determine whether to interpolate an intermediate voltage  64  and, if so, which intermediate voltage  64  to generate. For example, the high level interpolation circuitry  74  may receive analog reference voltages  36 , such as V&lt;32&gt; and V&lt;33&gt;, and have the ability to output the analog voltage levels  62 , such as L63, L64, L65, L66, and/or L67 associated with GL63, GL64, GL65, GL 66, and/or GL67, respectively. The high level interpolation circuitry  74  may utilize two or more bits of the digital input signal  60  to determine whether to interpolate and, if so, which of the intermediate voltages  64  (e.g., the analog voltage levels  62  or L64, L65, or L66 associated with GL64, GL66, or GL67, respectively) to generate. 
     In some embodiments, common interpolation circuitry may be utilized for both low level interpolation and high level interpolation. For example, a portion of the digital input signal  60  may be used to determine whether to use low level interpolation or high level interpolation and the least significant bits of the digital input signal  60  may be used to modulate the output interpolation circuitry  70 . Furthermore, even higher level interpolation may be accomplished using additional bits of the digital input signal  60 . For example, the interpolation circuitry  70  may utilize three or more least significant bits of the digital input signal  60  to perform higher level interpolation having four or more intermediate voltages  64  between consecutive analog reference voltages  36 . 
       FIG.  9    is a flowchart  76  of an example process of the interpolation circuitry  70 . The interpolation circuitry  70  may receive analog reference voltages  36  (process block  78 ) and digital input signals  60  of digital image data  40  (process block  80 ). The interpolation circuitry  70  may also interpolate intermediate voltages  64  (process block  82 ), for example, to provide analog voltage levels  62  not included in the analog reference voltages  36 . Interpolating may include utilizing low level interpolation (process block  84 ) and/or utilizing high level interpolation (process block  86 ) based on the digital input signal  60 . For example, low level interpolation may be utilized for gray levels  58  where interpolation error may be more likely to result in perceivable artifacts, and high level interpolation may be utilized for gray levels  58  where interpolation error may be less likely to result in perceivable artifacts. Using either low level or high level interpolation, the interpolation circuitry  70  may determine intermediate voltages  64  and/or passthrough analog reference voltages  36  based on the digital input signal  60  (process block  88 ). For example, the least significant bit(s) of the digital input signal  60  may be used to determine whether to interpolate an intermediate voltage  64  and/or which intermediate voltage  64  to generate. The analog voltage levels  62  corresponding to the digital input signal  60  may then be output (process block  90 ), for example, to the analog datalines  50  to the display pixels  38 . 
     As discussed herein, the use of variable interpolation (e.g., via interpolation circuitry  70 ) along the gamut of gray levels  58  may help reduce the likelihood of perceivable artifacts, while increasing efficiency. For example, the increased accuracy of the interpolation may increase the smoothness of transitions between gray levels  58  where error in the gray level  58  may have a more perceivable effect. Further, where error in the gray level  58  may be less perceivable, a higher level interpolation may be used to save space, power, and/or additional resources. Moreover, although the above referenced flowchart  76  is shown in a given order, in certain embodiments, process blocks may be reordered, altered, merged, deleted, and/or occur simultaneously. Additionally, the referenced flowchart  76  is given as an illustrative tool and further decision and process blocks may also be added depending on implementation. 
     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. 
     The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).