Patent Publication Number: US-2013249936-A1

Title: Multi-level stochastic dithering with noise mitigation via sequential template averaging

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 12/121,706, filed May 15, 2008, entitled “SYSTEMS AND METHODS FOR OPTIMIZATION OF SYNCHRONIZATION MESSAGE TRANSMISSION INTERVALS IN A PEER-TO-PEER NETWORK,” which is incorporated by reference herein in its entirety and for all purposes, and which claims to U.S. Provisional Application 61/028,465, filed on Feb. 13, 2008. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The field of the invention relates to displays which have quantized display characteristics for each of the pixels, and more particularly to methods of display which improve the apparent resolution of the display. The invention also relates to optical MEMS devices, in general, and bi-stable displays in particular. 
     2. Description of the Related Technology 
     A function of electronic displays, regardless of whether they are monochrome or color displays or whether they are of self-luminous or reflective type, is the generation of graded intensity variations or gray levels. A large number of gray levels are required for high-quality rendering of complex graphic images and both still and dynamic pictorial images. In addition, color reproduction and smooth shading benefit from a relatively high intensity resolution for each primary color display channel. The de facto standard for “true color” imaging is 8 bits per primary color or a total of 24 bits allocated across the three (RGB) primary color channels. However, it is important to recognize that it is the perceived representation, or effective resolution of these bits (producing an effective intensity resolution) and not merely their addressability which ultimately determine display image quality. 
     Bi-stable display technologies pose unique challenges for generating displays with high quality gray scale capability. These challenges arise from the bi-stable and binary nature of pixel operation, which requires the synthesis of gray scale levels via addressing techniques. Moreover, high pixel density devices are often limited to relatively low temporal frame rates due to fundamental operational constraints and the need for high levels of synthesis for both gray scale and color. These challenges and constraints place emphasis on the need for novel and effective methods of spatial gray level synthesis. 
     SUMMARY OF CERTAIN EMBODIMENTS 
     The system, method, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Embodiments” one will understand how the features of this invention provide advantages over other display devices. 
     One aspect is a method of displaying a first image on a display. The method includes generating a first version of the first image according to a first spatial dither template, generating a second version of the first image according to a second spatial dither template, the second template being different from the first template, and displaying the first image by successively displaying the first and second versions of the first image on the display. 
     Another aspect is a method of displaying a first image on a display having a native resolution, the method including generating a first version of the first image according to a first template, generating a second version of the first image according to a second template, the second template being different from the first template, and displaying the first and second versions of the first image such that an effective resolution of the first image is higher than the native resolution of the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view depicting a portion of one embodiment of a bi-stable display, which is an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a relaxed position and a movable reflective layer of a second interferometric modulator is in an actuated position. 
         FIG. 2  is a diagram of movable mirror position versus applied voltage for one embodiment of the bi-stable display of  FIG. 1 . 
         FIGS. 3A and 3B  are system block diagrams illustrating an embodiment of a visual display device comprising a bi-stable display. 
         FIG. 4  is a block diagram of one embodiment. 
         FIG. 5  is a flow chart of a method of an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices. 
     Embodiments of the invention more particularly relate to displays which have quantized display characteristics for each of the pixels, and to methods of displaying images with the displays. The displays and methods relate to both spatially and temporally dithering images such that the effective resolution of the display is higher than the result of the native spatial resolution of the display (affected by pixel size and pitch), and the native intensity resolution affected by the number of quantization levels of each of the pixels. 
     An example of display elements which have quantized levels of brightness are shown in  FIG. 1 , which illustrates a bi-stable display embodiment comprising an interferometric MEMS display element. In these devices, the pixels are in either a bright or dark state. In the bright (“relaxed” or “open”) state, the display element reflects a large portion of incident visible light to a user. When in the dark (“actuated” or “closed”) state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the “on” and “off” states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white. 
       FIG. 1  is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In one embodiment, one of the reflective layers may be moved between two positions. In the first position, referred to herein as the relaxed position, the movable reflective layer is positioned at a relatively large distance from a fixed partially reflective layer. In the second position, referred to herein as the actuated position, the movable reflective layer is positioned more closely adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel. 
     The depicted portion of the pixel array in  FIG. 1  includes two adjacent pixels  12   a  and  12   b.  In the pixel  12   a  on the left, a movable reflective layer  14   a  is illustrated in a relaxed position at a predetermined distance from an optical stack  16   a,  which includes a partially reflective layer. In the pixel  12   b  on the right, the movable reflective layer  14   b  is illustrated in an actuated position adjacent to the optical stack  16   b.    
     With no applied voltage, the gap  19  remains between the movable reflective layer  14   a  and optical stack  16   a,  with the movable reflective layer  14   a  in a mechanically relaxed state, as illustrated by the pixel  12   a.  However, when a potential (voltage) difference is applied to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable reflective layer  14  is deformed and is forced against the optical stack  16 . A dielectric layer (not illustrated in this Figure) within the optical stack  16  may prevent shorting and control the separation distance between layers  14  and  16 , as illustrated by actuated pixel  12   b  on the right in  FIG. 1 . The behavior is similar regardless of the polarity of the applied potential difference. Because the pixels  12   a  and  12   b  are stable in either of the states shown, they are considered bi-stable, and, accordingly, have selective light reflectivity characteristics corresponding to each of the two stable states. Therefore, the display has a native intensity resolution corresponding to two stable states and a native spatial resolution corresponding to the pitch of the pixels. 
       FIG. 2  illustrates one process for using an array of interferometric modulators in a bi-stable display. 
     For MEMS interferometric modulators, the row/column actuation protocol may take advantage of a hysteresis property of these devices as illustrated in  FIG. 2 . An interferometric modulator may require, for example, a 10 volt potential difference to cause a movable layer to deform from the relaxed state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the embodiment of  FIG. 2 , the movable layer does not relax completely until the voltage drops below 2 volts. There is thus a range of voltage, about 3 to 7 V in the example illustrated in  FIG. 2 , where there exists a window of applied voltage within which the device is stable in either the relaxed or actuated state. This is referred to herein as the “hysteresis window” or “stability window.” For a display array having the hysteresis characteristics of  FIG. 2 , the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be relaxed are exposed to a voltage difference of close to zero volts. After the strobe, the pixels are exposed to a steady state or bias voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the “stability window” of 3-7 volts in this example. This feature makes the pixel design illustrated in  FIG. 1  stable under the same applied voltage conditions in either an actuated or relaxed pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or relaxed state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. 
       FIGS. 3A and 3B  are system block diagrams illustrating an embodiment of a display device  40 , in which bi-stable display elements, such as pixels  12   a  and  12   b  of  FIG. 1  may be used with driving circuitry configured to spatially and temporally dither images such that the effective resolution of the display is higher than the result of the native spatial and intensity resolutions of the display. The display device  40  can be, for example, a cellular or mobile telephone. However, the same components of display device  40  or variations thereof are also illustrative of various types of display devices such as televisions and portable media players. 
     The display device  40  includes a housing  41 , a display  30 , an antenna  43 , a speaker  44 , an input device  48 , and a microphone  46 . The housing  41  is generally formed from any of a variety of manufacturing processes, including injection molding, and vacuum forming. In addition, the housing  41  may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing  41  includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols. 
     The display  30  of display device  40  may be any of a variety of displays, including a bi-stable display, as described herein. In some embodiments, the display  30  includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device. However, for purposes of describing certain aspects, the display  30  includes an interferometric modulator display. 
     The components of one embodiment of display device  40  are schematically illustrated in  FIG. 3B . The illustrated display device  40  includes a housing  41  and can include additional components at least partially enclosed therein. For example, in one embodiment, the display device  40  includes a network interface  27  that includes an antenna  43  which is coupled to a transceiver  47 . The transceiver  47  is connected to a processor  21 , which is connected to conditioning hardware  52 . The conditioning hardware  52  may be configured to condition a signal (e.g. filter a signal). The conditioning hardware  52  is connected to a speaker  45  and a microphone  46 . The processor  21  is also connected to an input device  48  and a driver controller  29 . The driver controller  29  is coupled to a frame buffer  28 , and to an array driver  22 , which in turn is coupled to a display array  30 . A power supply  50  provides power to all components as required by the particular display device  40  design. 
     The network interface  27  includes the antenna  43  and the transceiver  47  so that the display device  40  can communicate with one ore more devices over a network. In one embodiment the network interface  27  may also have some processing capabilities to relieve requirements of the processor  21 . The antenna  43  is any antenna for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 standard, including IEEE 802.11(a), (b), or (g). In another embodiment, the antenna transmits and receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS, W-CDMA or other known signals that are used to communicate within a wireless cell phone network. The transceiver  47  pre-processes the signals received from the antenna  43  so that they may be received by and further manipulated by the processor  21 . The transceiver  47  also processes signals received from the processor  21  so that they may be transmitted from the display device  40  via the antenna  43 . 
     In an alternative embodiment, the transceiver  47  can be replaced by a receiver. In yet another alternative embodiment, network interface  27  can be replaced by an image source, which can store or generate image data to be sent to the processor  21 . For example, the image source can be a digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data. 
     Processor  21  generally controls the overall operation of the display device  40 . The processor  21  receives data, such as compressed image data from the network interface  27  or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor  21  then sends the processed data to the driver controller  29  or to frame buffer  28  for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level. 
     In one embodiment, the processor  21  includes a microcontroller, CPU, or logic unit to control operation of the display device  40 . Conditioning hardware  52  generally includes amplifiers and filters for transmitting signals to the speaker  45 , and for receiving signals from the microphone  46 . Conditioning hardware  52  may be discrete components within the display device  40 , or may be incorporated within the processor  21  or other components. 
     The input device  48  allows a user to control the operation of the display device  40 . In one embodiment, input device  48  includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone  46  is an input device for the display device  40 . When the microphone  46  is used to input data to the device, voice commands may be provided by a user for controlling operations of the display device  40 . 
     In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver  22 . 
     Power supply  50  can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply  50  is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply  50  is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, power supply  50  is configured to receive power from a wall outlet. The power supply  50  may also have a power supply regulator configured to supply current for driving the display at a substantially constant voltage. In some embodiments, the constant voltage is based at least in part on a reference voltage, where the constant voltage may be fixed at a voltage greater than or less than the reference voltage. 
     The driver controller  29  takes the raw image data generated by the processor  21  either directly from the processor  21  or from the frame buffer  28  and reformats the raw image data appropriately for high speed transmission to the array driver  22 . Specifically, the driver controller  29  reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array  30 . Then the driver controller  29  sends the formatted information to the array driver  22 . Although a driver controller  29 , such as a LCD controller, is often associated with the system processor  21  as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor  21  as hardware, embedded in the processor  21  as software, or fully integrated in hardware with the array driver  22 . 
     Typically, the array driver  22  receives the formatted information from the driver controller  29  and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display&#39;s x-y matrix of pixels. 
     In one embodiment, the driver controller  29 , array driver  22 , and display array  30  are appropriate for any of the types of displays described herein. For example, in one embodiment, driver controller  29  is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, array driver  22  is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller  29  is integrated with the array driver  22 . Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, display array  30  is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators). In some embodiments, display array  30  is another display type. One or both of the driver controller  29  and the array driver  22  may be configured to spatially and temporally dither the displayed images such that the effective resolution of the display is higher than the result of the native spatial and intensity resolutions of the display. 
     Those of skill in the art will recognize that the above-described architecture may be implemented in any number of hardware and/or software components and in various configurations 
     The driver circuitry uses novel and flexible methods for synthesis of a large number of intensity gradations or gray levels on displays with a limited number of native intensity gradations while reducing the visibility of image noise generated by the synthesis process. The methods combine multi-level stochastic spatial dithering with noise mitigation via temporal averaging of images generated using spatial dither templates with varying spatial patterns of threshold template values. The result is a solution to gray-level synthesis in which the number of effective intensity levels may be substantially increased with a minimized impact on visible spatial pattern noise. Such methods can exploit the trade off between display spatial resolution and gray level synthesis while minimizing the introduction of spatial pattern noise or other artifacts which could compromise display image quality. 
     Spatial dithering is a methodology which trades spatial area (or spatial resolution) for intensity (or gray level) resolution. The methodology consists of a variety of techniques which increase the effective number of “perceived” gray levels and/or colors for devices with a limited number of native gray levels and/or colors. These methods take advantage of the limited spatial resolution of the human visual system (HVS) as well as limitations in HVS contrast sensitivity, especially at high spatial frequencies. Spatial dither originated as an enabling methodology for gray level synthesis in bi-level printing technologies and is currently implemented in one form or another in most printing devices and applications. Since the methodology can provide excellent image quality for imaging devices with high spatial resolution and limited native gray scale capability, it has seen use in both monochrome and color matrix display devices. 
     Techniques for spatial dither can be divided into two principal categories, point-process methods and neighborhood-operations methods. 
     Point-process methods are independent of the image and pixel neighborhood resulting in good computational efficiency for displays and video applications. Among the most prominent point-process techniques for spatial dithering are noise encoding, ordered dither and stochastic pattern dither. Noise encoding consists of the addition of a random value to the value of a multi-level pixel input, followed by a thresholding operation to determine the final pixel output value. While effective in increasing the number of effective gray levels, noise encoding generates a spatial pattern with “white noise” characteristics and resulting visible graininess from low spatial frequencies in the noise signal. 
     Ordered dither is a family of techniques in which a fixed pattern of numbers within a pre-defined X-by-Y region of pixels determines the order or pattern for activating pixels prior to a thresholding operation. The two most notable variations of ordered dither are cluster-dot dither and dispersed-dot dither. They can provide good results but are prone to generating visible, periodic spatial artifacts which interact or beat with the structure of images. 
     Stochastic pattern dither is similar to ordered dither but the stochastic pattern of the spatial dither template generates a “blue noise” characteristic with minimal spatial artifacts and a pleasing appearance. 
     Spatial dither methods which rely on neighborhood operations are typified by the technique of error diffusion. In this technique image-dependent pixel gray level errors are distributed or diffused over a local pixel neighborhood. Error diffusion is an effective method of spatial dither which, like stochastic pattern dither, results in a spatial dither pattern with “blue noise” characteristics and minimal spatial or structural artifacts. The drawbacks of error diffusion are that the method is image dependent and computationally intensive and also prone to a peculiar visible defect known as “worming artifacts.” Error diffusion is generally not amenable to real-time display operations due to the computationally-intensive, image-dependent nature of the operations. 
     Multi-level stochastic pattern dither is a somewhat effective approach to gray level synthesis for electronic displays with limited native gray scale capability. Such techniques use dither templates having certain stochastic characteristics to generate dithered versions of the displayed images. The stochastic characteristic of the dither templates is generated by the process in which the dither pattern is created. Two methods for creating stochastic dither patterns with “blue noise” characteristics are the blue-noise mask method and the void and cluster method. The blue noise mask method is based on a frequency domain approach while the void and cluster method relies on spatial domain operations. The void and cluster method of dither template generation relies on circular convolution in the spatial domain. This results in the ability to create small stochastic templates which may be seamlessly tiled to fill the image space of the displayed image. 
     While multi-level stochastic pattern dither can result in improvement in image quality for displays with limited native gray scale capability, there still remains a problem with residual apparent graininess resulting from the spatial dither pattern. This residual graininess is most visible in the darkest synthesized grade shades and where the display has a relatively small number of native gray levels (e.g., 3 bits or 8 levels). 
     In order to overcome this limitation, improved multi-level stochastic dither methodologies may be used. The methods mitigate residual pattern noise via temporal averaging of a series of template dithered images in which the synthesized gray levels are generated by different stochastic dither templates. Temporal averaging is achieved by taking advantage of the limited temporal resolution of the human visual system (HVS). Multiple versions of an image are displayed in rapid succession, such that, to an observer, the multiple versions of the image appear as a single image. To the observer, the intensity at any pixel is the average intensity of all of the displayed versions. Accordingly, the observer perceives gray levels between the actually displayed gray levels. 
     For example, a monochrome display may have pixels which are each either on or off, where the data for each pixel is one bit. Two versions of the image may be created with two different templates. Each of the versions may be displayed in rapid succession, such that the two images appear as a single image. Those pixels which are off in both images will appear dark to the observer, and those pixels which are on in both images will appear with maximum brightness to the observer. However, those pixels which are on in one version and off in the other version will appear with about half the maximum brightness. Accordingly, the observer perceives smoother gray levels across the image. 
     The multiple versions of the image can be generated using templates which represent mathematical operations to be performed on each pixel of the source image. Different types of templates have various effects on the spatial noise of the displayed image, and on temporal noise of a series of displayed images in the case of video. Therefore, the effect on noise may be considered when determining templates for use. 
     Certain embodiments use multi-level stochastic dither templates, which mitigate residual pattern noise via the temporal averaging of the series of the dithered image versions. As illustrated in  FIG. 4 , a block diagram of one embodiment shows a multi-level spatial dither methodology in which a series of dithered image versions is generated with different dither templates. Since each of the dither templates will result in a different noise or grain pattern, when these versions are temporally averaged, the result will be a decrease in the pattern noise or an increase in the signal-to-noise ratio. 
     As shown, for each version, the input image IL[x,y] is operated on according to a normalized dither template D[x′,y′], creating a dithered version of the image S[x,y]. In this embodiment, the dithered version of the image S[x,y] is quantized to create the output image OL[x,y]. The result is a series of N versions of the input image IL[x,y], where each version is created with a different template. The final output image is displayed as a sequence of the N versions, displayed in rapid succession such that the versions are temporally averaged. In some embodiments, the sequence of versions may be repeatedly displayed. In some embodiments, the order of the sequence may be altered between re-displayed sequences. 
     If uncorrelated stochastic templates are used on sequential frames, then the signal-to-noise ratio increases as the square root of the number of averaged dithered images. A variable number of templates from 2 up to N may be used according to the application and the image quality requirements. It is also possible to utilize pre-computed, correlated templates which have a mathematical relationship to one another. Such templates may increase the image signal-to-noise ratio with a smaller number of temporally averaged frames. One example of such a set of templates is the use of pairs of stochastic templates in which the threshold values at each pixel location are inverses of one another. 
     The method may be readily applied to a variety of display technologies, for example for use in both direct-view and projection applications. The result is a highly effective solution to gray-level synthesis in which the number of effective intensity levels is substantially increased with a high image signal-to-noise ratio. 
       FIG. 5  is a flowchart illustrating an embodiment of a method  100  of displaying an image. The method includes receiving data, generating first and second versions of the image based on the received data, and displaying the image by successively displaying the first and second versions. 
     In step  110  data representing the image is received. The data has a certain quantization associated therewith. For example, the data may have 24 bits, 8 bits each for the three colors of a single pixel. Other data formats can also be used. If necessary, the data is converted to a format which can be further manipulated as described below. 
     In steps  120  and  130 , first and second versions of the image are generated based on the data received in step  110 . The data received in step  110  for each pixel may be modified according to a spatial dither template. The first and second versions are generated based on first and second templates, respectively, where the first and second templates are different. In some embodiments, the first and second templates are algorithmically related. 
     In some embodiments, a separate template is used for each component of the pixels. For example, a value can be added to the data set for each of the color components of a pixel based on a template used for that component. 
     In step  140  the image is displayed by successively displaying the first and second versions of the image so as to temporally average the first and second versions. In some embodiments, the image is a still image, and the first and second versions of the image may be repeatedly displayed for the entire time that the image is to be shown on the display. The first and second versions may be repeatedly shown in the same order, or the order may be altered. In some embodiments, more than two versions of the image are generated and displayed. In some embodiments, which of the versions is to be displayed next is randomly or pseudo-randomly determined. In some embodiments, a sequence of all or some of the versions is determined and repeatedly displayed, where the sequence may sometimes be changed. 
     In some embodiments, the image is part of a series of images, which for example, cooperatively form a video stream. In such embodiments, if the frame rate of the display is 30 frames per second, each frame image may be displayed for about 1/30 second. Accordingly, during the 1/30 second for an image, the first and second versions of each image may each be displayed for about half of the 1/30 second. In some embodiments, the frame rate is different, and in some embodiments, more than two versions are displayed during the frame period. 
     In some embodiments, all frames use the same dither templates to generate multiple versions of the image of the frame. Alternatively, different templates may be used for sequential frame images. For example, a first frame may use dither templates  1  and  2  to generate first and second versions of the image of the frame, and a next frame may use either or both of templates  1  and  2 , or may use either or both of additional templates  3  and  4 . 
     In some embodiments, each of the series of images is displayed by displaying only one version of each image. To create the one version of each image, one of a plurality of templates may be used, such that versions of images adjacent in time are created using different templates. Because images adjacent in time are often similar, using different templates to create dithered versions of each of the images will result in appearance improvement similar to that discussed above where each image is displayed as multiple dithered versions. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.