Abstract:
Methods and control systems are provided for displaying an image electronically encoded in the form of illumination values using a two-dimensional matrix of image elements, each element adapted to covert energy to emit the light when an illumination value is written thereto. In accordance with one method, an array of elements including less than all of the elements in the matrix are defined to display the image so that the amount of energy consumed by the elements of the matrix when displaying an image using the elements of the array is lower than the amount of energy that the elements of the matrix would consume in displaying the image using all of the elements of the matrix.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuation of application Ser. No. 09/848,067, filed May 3, 2001. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a display driver and method for operating an emissive light video display.  
       BACKGROUND OF THE INVENTION  
       [0003]     Status displays are an important feature of electronic devices such as cellular telephones, global positioning systems (GPS), CD players, video cameras, digital cameras, conventional cameras, hybrid cameras and other devices. Status displays are used to inform the user of such a device about conditions that may impact the operation of the device. Examples of status displays include displays that indicate cellular telephone signal strength, battery status, and other warnings. These displays are typically active whenever the device is active. Because these displays are often in use, it is necessary that these displays consume little power.  
         [0004]     In the prior art, it is known to use Light Emitting Diodes, LEDs, and Liquid Crystal Displays, LCDs to present status information to the user of a hand held electronic device. These LEDs and LCDs are typically arranged or shaped in the form of icons that symbolically represent the status of the device. Using such displays, the status of the device can readily be ascertained by observing whether the LEDs or LCDs are active. Such LEDs and LCDs draw little power and are simple to operate. However, it will be appreciated that at least one separate LED or LCD must be incorporated into the portable electronic device for each status display. This increases the size and weight of the portable device, typically reducing the convenience and portability of the device.  
         [0005]     In the prior art, it is also known to provide video displays in hand held and portable devices. Such video displays are typically formed from a two dimensional matrix of image forming elements. In a preferred form of video display known as the Emissive Light Display, ELD, the image forming elements comprise discrete light emitting elements. An image to be displayed using an ELD is electronically captured and encoded into illumination values. The illumination values are written to the elements of the display and the elements illuminate at an intensity level that is called for in the illumination values. Variations in the intensity of light emitted by the elements create a contrast pattern that forms the image on the display.  
         [0006]     It will be appreciated that video displays can convey images including icons, graphics, text, still and motion images. This enables portable devices to communicate with users in a very effective fashion. Accordingly, video displays are increasingly being incorporated into portable electronic devices.  
         [0007]     However, the video displays of the prior art have consumed too much power to permit such video displays to be operated continuously. A certain portion of the power consumed is used to cause the elements of the display to emit light. Traditionally, it has taken substantial amounts of power to cause the elements of ELDs to emit light. However, with the advent of the Organic Light Emissive Display (OLED) it has become possible to substantially reduce the amount of power consumed in causing the elements of the display to emit light.  
         [0008]     The remaining portion of the power consumed in the operation of a video display is used by the electronic controls that control the elements of the display. These controls are collectively known as a display driver. The prior art has not provided a display driver or method for operating an OLED that is efficient enough to permit the near continuous operation of the OLED for the purposes of sustaining status displays.  
         [0009]     In the absence of such a display driver, it has become common for portable electronic devices that incorporate video displays to also incorporate separate LED and LCD displays to present status information. It will be appreciated that incorporating such a dual display scheme into a portable electronic devices increases the number of components of the device, the cost of designing the device, and the size and weight of the device. These factors increase the cost of portable electronic devices that incorporate both video and separate LED or LCD status displays.  
         [0010]     U.S. Pat. No. 5,977,704 recognizes that a need exists for a single display to present both video and status information. To meet this need, the &#39;704 patent shows a single Organic Light Emissive Display (OLED) having both a video display region and an icon region. The main limitation of this solution is that it is expensive to design and manufacture such an OLED. For example, any modification to the form, number, or arrangement of icons requires a modification to the physical structure of the display device. Accordingly, a display device designed for one product in accordance with the &#39;704 patent will not be readily adaptable for use in a second product.  
         [0011]     Thus, what is needed is a display driver and method for displaying both icons and video images and that does not require the use of custom combination displays.  
         [0012]     U.S. Pat. No. 4,823,121 represents one effort to reduce the power consumed in generating an image using a light emissive display. The &#39;121 patent teaches a display control circuit for producing illumination values for controlling the illumination intensity level of light emissive display elements in an Electro-Luminescent (E-L) display panel. The &#39;121 patent teaches that each of the illumination values associated with a horizontal row of elements in an E-L display is to be written to a shift register and examined while in the shift register. If no element in the row is to be illuminated, the driver can omit the step of transmitting the illumination values to the elements in the row and the step of applying a maintenance charge to the row of elements. The &#39;121 patent, however, still requires that the display driver generates illumination values for all of the elements in the display, to examine the illumination values for each row to determine whether to write illumination values to each of the elements  14 in the display and to determine whether to apply a maintenance charge to the row of elements.  
         [0013]     Thus, the forgoing needs are not met by the prior art.  
       SUMMARY OF THE INVENTION  
       [0014]     According to a feature of the present invention, a method is provided for using a two-dimensional matrix of light emitting elements to display an image electronically encoded in the form of illumination values. An array of elements including less than all of the elements in the matrix to display the image is defined. A pixel rate for writing the illumination values for the elements in the array is determined, and a sweep signal having the illumination values for the elements in the array is generated, where the sweep signal writes illumination values for the elements in the array at the determined pixel rate.  
         [0015]     According to another embodiment of the present invention, a display driver generates an image encoded in the form of illumination values. The driver includes an image source and a controller receiving the image from the image source, said controller being adapted to (1) define an array of elements including fewer than all of the elements in the matrix for display of the image (2) determine a pixel rate for writing illumination values to the array of elements, and (3) generate images by writing illumination values to the elements in the array at the pixel rate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows a video display system operating in accordance with the method of the prior art.  
         [0017]      FIG. 2  shows another embodiment of a video display system operating in accordance with the method of the prior art.  
         [0018]      FIG. 3  shows a flow chart depicting one embodiment of the method of the present invention.  
         [0019]      FIG. 4A  shows a flow chart depicting one preferred embodiment of the method to define the elements to be included in an array.  
         [0020]      FIG. 4B  shows a flow chart depicting another preferred embodiment of the method to define the elements to be included in an array.  
         [0021]      FIG. 5  shows a detailed embodiment of the display driver of he present invention.  
         [0022]      FIG. 6  shows a representation of the operation of an ELD having row drivers and column drivers operated by the display driver of the present invention to display a status indicator image.  
         [0023]      FIG. 7  shows representation of the operation of an ELD having only row drivers and operated by another embodiment of the display driver of the invention to display a status indicator image.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]      FIG. 1  shows an ELD  10  operated by a display driver  20  according to the method of the prior art. Display  10  is fixed in device  12 . In this example, ELD  10  comprises an OLED having light emitting elements  14  that are organized into a vertical array of “n” horizontal rows  16 . Each horizontal row  16  is associated with one of a plurality of row drivers  26 . A device controller  17  controls display  10 , an image source  18 , and display driver  20 . Image source  18  provides illumination values to the display driver  20 . Image source  18  provides an image to display driver  20 . Display driver  20  receives the image and transmits illumination values to row drivers  26  as shown in  FIG. 1 , or directly to elements  14 . Where row drivers  26  are used, each row driver  26  received illumination values from display driver  20  and causes the elements  14  in the associated horizontal row  16  to illuminate at intensity levels that are characteristic of the illumination values. Image  22  appears on ELD  10  as a contrast pattern created by variations in the intensity of the light emitted by elements  14 .  
         [0025]     In the prior art, a method, known as the horizontal linear scanning method is used by display driver  20  to write illumination values. In this method, the illumination values are organized into “scan lines.” Each scan line contains illumination values associated with those elements  14  that are located in a horizontal row  16 . A sweep signal is used to write illumination values to elements  14 . The sweep signal writes illumination values to elements  14  one scan line at a time.  
         [0026]     It will be appreciated that, in the horizontal linear scanning method, illumination values are written to different elements  14  at different times. Thus, to form image  22  on ELD  10 , it is necessary that elements  14  emit an intensity of light defined by the illumination values that are written to row drivers  26  for a period of time after the illumination values that are written. The length of time during which elements  14  will emit a defined intensity of light in response to the writing of an illumination value is known as the persistence period of elements  14 .  
         [0027]     The persistence period of elements  14  is finite. To maintain the appearance of image  22  the sweep signal repeatedly writes element illumination values to the display drivers  26  that operate elements  14  of ELD  10 . This is known as refreshing the ELD  10 . It will be appreciated that the rate at which ELD  10  must be refreshed is inversely proportional to the persistence period of elements  14 .  
         [0028]     It will also be appreciated that the rate at which the sweep signal must write illumination values can be determined from the refresh rate. This rate is known as the pixel rate. The pixel rate can be calculated by multiplying the refresh rate by the number of elements  14  in ELD  10 . In the horizontal linear scanning method of the prior art, the number of elements  14  in ELD  10  is fixed and the persistence period of the elements  14  to be swept is also fixed. In the prior art, an image refresh clock  28  provides a clock signal having a period that is equal to the persistence period. The signal from image refresh clock  28  provides a timing signal to govern the writing of illumination values.  
         [0029]     In one embodiment of the horizontal linear scanning method, a horizontal clock rate is also defined and is used to determine when the sweep signal is to transition from writing the illumination values associated with one scan line to writing the illumination values associated with another scan line. The horizontal clock rate is calculated by dividing the pixel clock rate by the number of elements in each horizontal row  16 .  
         [0030]      FIG. 2  shows an ELD  10  wherein illumination values are written to row drivers  26  and column drivers  30  in accordance with the horizontal linear scanning method of the prior art. As is shown in  FIG. 2 , elements  14  of ELD  10  are arranged into a matrix of rows  16  and columns  32 . Each row  16  is operated by a row driver  26  and each column  34  is operated by a column driver  30 . The illumination intensity of elements  14  is controlled by action of both row drivers  26  and column drivers  30 . Here too, the method of choice for writing illumination values is typically the horizontal linear scanning method.  
         [0031]     It will be recognized that it is not necessary to use every element  14  in ELD  10  to form image  22 . However, the horizontal linear scanning method of the prior art still calls for sweeping illumination values into all of the elements  14  in ELD  10  regardless of the characteristics of the image. For example, if image  22  shown in  FIGS. 1 and 2  requires the use of only 10% of elements  14  in ELD  10 ,the horizontal linear scanning method of the prior art still requires that illumination values are generated for all of elements  14  in ELD  10 , the horizontal linear scanning method of the prior art still requires that illumination values are generated for all of elements  14  in ELD  10 . Further, scan lines containing these illumination values for unused elements must be composed and swept. Each of these steps is unnecessary and expends energy.  
         [0032]     Thus, the prior art does not meet the need for a more efficient display driver and method for presenting a partial image.  
         [0033]      FIGS. 3, 4A  and  4 B show flowcharts illustrating preferred embodiments of the present invention for displaying an image  22  using ELD  10 , row drivers  16 , device controller  17 , display driver  20 , image source  18  and column drivers  30 .  
         [0034]     As is shown in  FIG. 3 , the first step in the method of the present invention is the array definition step  34  wherein an array of elements  14  from ELD  10  is defined for use in displaying image  22 . Those elements  14  that are not defined for use in the array are not used to display image  22 .  FIGS. 4A and 4B , respectively, show two preferred embodiments of step  34 . In the embodiment of  FIG. 4A , those elements  14  to be included in the array are defined by analysis of image  22 . The first step in this embodiment is the Receive Image Step  44 . In the Receive Image step  44 , image  22  is transferred from image source  18  and received by display driver  20 . Where necessary, Step  44  can include transforming the image received into illumination values. Image  22  is analyzed in the Analyze Image Data Step  46 . This analysis can take many forms. For example, the analysis of image  22  can include an examination of the size and shape of image  22 . Alternatively, image  22  can be examined to determine the number of elements  14  required to display image  22 . In still another embodiment, image  22  is analyzed to determine the outline of image  22 .  
         [0035]     After the analysis of image  22  is complete, the method proceeds to a Select Array Elements step  48 . In step  48 , the analysis of the image  22  from step  46  is used to determine which of elements  14  are to be included in the array. Step  48  can be performed by selecting an array of elements  14  from a look-up table of predefined arrays based upon analysis of image  22 . Step  48  can also be performed by selecting a pattern of elements  14  to include in the array based upon the analysis of image  22 .  
         [0036]     In the embodiment of  FIG. 4B , the elements  14  to be included in the array are defined in response to a mode selection. The mode selection is made in the mode selection step  52 . The mode selection can be made by the user of the portable electronic device  12 . Alternatively, the mode selection can be made automatically by the device controller  17  or display controller  20 . In step  54  the mode selection is used to select the elements  14  to be included in the array. Step  54  is preferably performed by using the mode selection to select an array of elements  14  from a look-up table that associates each mode of operation with a preferred array of elements  14  for the display of images in that mode.  
         [0037]     It will be appreciated that other criteria can be used for selecting the elements to be included in the array. For example, in a further embodiment, (not shown) the selection of elements  14  to be included in the array is based on the content of image  22 .  
         [0038]     Returning now to  FIG. 3 , the next step in the method of the present invention is shown. This step is a Calculate Timing step  38  wherein the clock rate and the pixel rate are determined. As is discussed above, both the horizontal sweep rate and the pixel rate increase and decrease as a multiple of the number of elements  14  to which illumination values must be written. In the prior art, the number of elements  14  for which illumination values must be written is fixed. This is because in the horizontal linear scanning method of the prior art, the sweep signal writes illumination values to each of the elements  14  in ELD  10  during each sweep.  
         [0039]     However, in the method of the present invention, the pixel rate and horizontal clock rate are not fixed. This is because the number of elements  14  for which illumination values must be written during each sweep is limited to include only those elements  14  that are in the array. Where the array includes fewer than all of elements  14  in ELD  10 , a lower horizontal sweep rate and pixel rate can be used without degrading the appearance of image  22 . Thus, in the present invention, a minimum pixel rate and minimum horizontal clock rate that must be used to maintain an image in an array can be determined by calculation. In particular, the minimum pixel rate can be determined by multiplying the number of elements  14  in the array by the persistence rate. The minimum horizontal clock rate can be calculated by multiplying the sweep rate by the number of elements  14  of a horizontal row  16 . It will be appreciated that, consistent with the present invention, the pixel rate and horizontal clock rate can be operated at rates in excess of the minimum rates. However, operating at such increased rates reduced efficiency. It will be appreciated that the pixel rate and horizontal clock rate that are used in generating the sweep signal can be determined in other ways. For example, the pixel rate and horizontal clock rate for an array can be determined using a look-up table, that associates particular arrays with preferred pixel rates and horizontal clock rates.  
         [0040]     Step  38  of  FIG. 3  is the Sweep Signal Generation step, wherein a sweep signal is generated for writing illumination values. In the present invention, the sweep signal is defined to include only those illumination values associated with those elements  14  that are included in the array. No other illumination values are written by the sweep signal. The illumination values for those elements  14  in the array are incorporated into scan lines. The sweep signal transmits the scan lines to the row drivers  16  and column drivers  30  at the horizontal clock rate and the pixel rate.  
         [0041]     The method of the present invention shown in  FIGS. 3, 4A  and  4 B has been described as being used in conjunction with an ELD  10  having row drivers  26  and column drivers  32  to control the illumination status of elements  14 . It will be appreciated that the array may not include any of elements  14  from certain of the rows  16  or columns  30 . Thus, the method of  FIG. 3  includes the optional step  39  of disabling those row drivers  26  and column drivers  30  that do not control the operation of any of the elements  14  in the array. It will also be appreciated that other discrete electronic components in display driver  20  such as a video memory (not shown) may not be necessary when the array incorporates less than all of elements  14  in ELD  10 . Accordingly, optional steps of disabling these components can be performed to reduce the power consumed during operation of display  10 .  
         [0042]     Step  40  is the Continue Inquiry step. In step  40 , it is determined whether it is necessary to continue refreshing the display of image  22  on ELD  10 . Where a new image is to be displayed, the process returns to step  34 . Where no image is to be displayed the process ends. If the same image  22  is to be displayed, then step  42 , an Image Refresh step, repeats the sweep signal. It will be appreciated that by continually repeating the same sweep signal, it is not necessary to repeat the steps of receiving the image, determining the elements in the array or determining the pixel rate and/or horizontal clock rate. This conserves power.  
         [0043]     The method of  FIGS. 3, 4A  and  4 B has been shown and described in conjunction with a sweep signal that sweeps data into the display according to the horizontal linear scanning method. However, this has been done for the purpose of example only. It is not necessary to use the horizontal linear scanning method to practice the present invention in connection with a display of elements  14  operated by row drivers  26  and column drivers  30 . This is because elements  14  can be individually addressed and therefore illumination values can be written to elements  14  in any order. Thus, any sweep signal that writes illumination values to elements  14  in the array can be used so long as illumination values are written to elements  14  in the array at least once during the persistence period. In such methods, the step of calculating a horizontal sweep rate can be omitted or modified as appropriate.  
         [0044]     The method of  FIGS. 3, 4A  and  4 B has also been shown and described in conjunction with row drivers  26  and column drivers  30 . It will be appreciated however, that this method will also work in conjunction with an ELD  10  that uses only row drivers  26  to cause elements  14  to illuminate in response to the illumination values. An embodiment of the present method that uses only row drivers, the array is defined to include all of the elements  14  of each horizontal row  16  that will be used to display image  22  and illumination values and scan lines are generated only for those elements  14  of ELD  10  that are within the horizontal rows  16  of elements  14  associated with the array. The horizontal clock rate and pixel rate are then determined so that all of the scan lines and illumination values can be written within the persistence period. In such a method, a further power savings can be obtained by the further step of enabling only those horizontal row drivers that will be used in to operate elements within the array.  
         [0045]      FIG. 5  shows a detailed embodiment of the display driver  20  of the present invention. As is shown in  FIG. 5 , image source  18  delivers image  22  to an image processor  60 . Image processor  60  analyzes image  22  and defines at least one array A of elements  14  for displaying image  22 . In this embodiment of display driver  20 , array A is defined as a function of a number “N” of horizontal rows  16  and a number “K” of columns  32  assigned to each horizontal row  16  in array A. Where necessary, image processor  60  also converts image  22  into illumination values.  
         [0046]     As is shown in  FIG. 5 , a sweep signal generator  62  is used to generate a sweep signal to write illumination values to elements  14  within array A. Toward this end, sweep signal generator  62  receives illumination values and array information from image processor  60 . Sweep signal generator  62  converts this information into a sweep signal that writes illumination values only to those elements  14  within array A. The sweep signal generator  62  generates “N” scan lines containing “K” pixel illumination values on each line. The sweep signal generator  62  combines the scan lines to form a sweep signal.  
         [0047]     As is noted above, illumination values must be written for each of the elements  14  in the array A at a rate defined by the refresh rate and the number of elements  14  in the array A. In the embodiment of  FIG. 5 , the sweep signal generator  62  defines a sweep signal that writes illumination values for elements  14  within array A at a pixel rate that is defined by a pixel rate clock signal. The pixel rate clock signal is defined at a rate that is a function of a vertical clock signal and a horizontal clock signal.  
         [0048]     In the embodiment shown in  FIG. 5 , image refresh clock  28  provides a vertical clock signal which runs at a rate that is at least equal to the refresh rate. The horizontal clock signal is calculated by multiplying the vertical clock signal by the number of lines “N” associated with array A. The number of lines “N” is calculated by the image processor  60  and transmitted to a horizontal clock signal generator  56 . The horizontal clock signal generator  56  comprises a phase detector  66  which receives the vertical clock signal and the output of the clock divider circuit  64 . The clock divider circuit  64  receives the output of the voltage controlled oscillator  70  which is driven by the phase detector  66  and integrator  68 . Since the clock divider circuit  64  is set to divide the output of the voltage controlled oscillator  70  by “N” which it receives from the image processor  60 , the effect is to multiply the vertical clock signal rate by “N” and it becomes the horizontal clock.  
         [0049]     Because the vertical and horizontal sweep rates must be maintained in phase, horizontal clock signal generator  56  also comprises a phase locked loop arrangement using a phase detector  66 , an integrator  68  and a voltage controlled oscillator  70 . Phase detector  66  has, as its inputs, the vertical clock signal and the divided horizontal clock signal. The output from the phase detector  66  is fed into an integrator  68  and the resulting output of the integrator  68  drives a voltage controlled oscillator  70 . The output from voltage controlled oscillator  70  is the horizontal clock signal.  
         [0050]     The horizontal clock signal is used as an input for the sweep signal generator  62  and as an input into pixel rate clock signal generator  58  which is also a phase locked loop. The pixel rate clock signal generator comprises a second phase detector  72 , a second clock signal divider  74 , a second integrator  76  and a second voltage controlled oscillator  78 . A second clock signal divider  74  receives the number of pixel illumination values “K” and divides the pixel rate clock signal by “K” which has the effect of multiplying the horizontal clock signal rate by “K”. The second phase detector  72  has the inputs of the horizontal clock signal and an output from the second clock divider whose output is the voltage controlled oscillator  78  signal which has been divided by K. The second phase detector  72  drives the second integrator  76  whose output controls the voltage controlled oscillator  78 . The output of second voltage controlled oscillator  78  is a pixel rate clock signal whose frequency is “K” times the horizontal clock signal. This signal is fed into the sweep signal generator  62 .  
         [0051]     Sweep signal generator  62  generates a sweep signal for writing illumination values for each of elements  14  in array A. Pixel illumination values are swept one scan line at a time into each of the “N” rows of array A. One scan line is written during every horizontal clock signal cycle. Consistent with this, the illumination values are written to the individual elements  14  of array A at the rate defined by the pixel rate clock signal. The sweep signal generated by the sweep signal generator  62  therefore conducts a full sweep of the elements  14  in array A at least once during every vertical clock signal.  
         [0052]     It will be understood that image processor  60  may determine that certain of the row drivers  26  and/or column drivers  30  are unnecessary for display of an image using array A. Accordingly, image processor  60  is fixed to the row drivers  26  and column drivers  30  for disabling selected ones of row drivers  26  or selected ones of column drivers  30  for disabling selected ones of row drivers  26  or selected ones of column drivers  30  that are not required for the display of image  22 .  
         [0053]     Device controller  17  is shown in  FIG. 5  connected to image processor  60 . Device controller  17  is connected to image processor  60  to disable operation of the image processor  60 , when the ELD  10  is not in use. An optional connection between device controller  17  and sweep signal generator  62  is shown. The purpose of this connection is to allow the device controller  17  to instruct sweep signal generator  62  to repeat the temporarily fixed sweep signal in a continuous fashion. In this regard, an optional sweep signal memory (not shown) within the sweep signal generator  62  can retain a sweep signal and permit the sweep signal to be repeated in a continuous fashion until display controller  17  instructs sweep signal generator  62  to cease the continual repetition. In this manner, where it is determined that a single image, such as a “power on” status indicator  72  is to be displayed on the ELD in a near-continuous fashion, image  22  can be maintained for extended periods without regenerating the sweep signal and recalculating array parameters such as “N” and “K” for the display of the indicator. It will be appreciated that this conserves power.  
         [0054]      FIG. 6  shows a similar representation of the operation of an ELD  10  operated by a display driver of the present invention to display a status indicator image  22 . As is shown in  FIG. 5 , the array A of elements  14  used to display image  22  comprises only a portion of the elements  14  of ELD  10 . Elements  14  that are not incorporated into array A are not used. Those elements  14  that are not used incorporated into array A are shown shaded in  FIG. 6 . It will be apparent then that the shaded row drivers  26  and column drivers  30  can be disabled during the presentation of image  22  as they do not operate any elements  14  within array A.  
         [0055]     For example,  FIG. 7  shows a representation of the operation of an ELD  10  having only row drivers  26  and operated by a display driver  20  of the present invention to display image  22 . As is shown in  FIG. 7 , the array A of elements  14  used to display image  14  includes not only those elements  14  that are necessary to form image  22 , but also all of the other elements  14  associated with any of the horizontal rows  16  which include elements  14  that are used to display image  22 . Here too, the elements  14  that are not incorporated into array A are not used. Those elements  14  that are not used are shown shaded in  FIG. 7 . It will be apparent from  FIG. 7  that those row drivers  26  that are shown shaded in  FIG. 7  can be disabled during the presentation of image  22  as they do not operate any elements  14  within array A.  
         [0056]     It will also be understood that the principles of the present invention can be used to define an array A with a variable number of “K” elements  14  in each horizontal row  16 . Thus, for example, the first of “N” rows of array A can contain a first number of elements  14  while the second row can contain, for example, a second, lower number of elements  14 . In such a circumstance the horizontal clock rate will be modified in accordance with the number of elements  14  in each horizontal row  16 .  
         [0057]     It will also be understood that display driver  20  can be used to display more than one image  22 . In this embodiment, image processor  60  defines more than one array A to display the images. Alternatively, a single array A can be defined to display all of the more than one image  22 . Where more than one image is displayed, further power savings can be accomplished by (what do we need here?) images to use common drivers and/or column drivers. This reduces the number of active row and column drivers.  
         [heading-0058]     Parts List  
         [none]    
       
           10  Emissive Light Display  
           12  Electronic Device  
           14  Light Emitting Elements  
           16  Horizontal Rows  
           17  Device Controller  
           18  Image Source  
           20  Display Driver  
           22  Image  
           26  Row Drivers  
           28  Image Refresh Clock  
           30  Column Driver  
           32  Column  
           24  Array Definition Step  
           36  Calculate Timing Step  
           38  Generate Sweep Signal Step  
           39  Disable Unnecessary Electronics Step  
           40  Continue Inquiry  
           42  Refresh Image Step  
           44  Receive Image Step  
           46  Analyze Image Step  
           48  Select Elements Step  
           52  Mode Selection Step  
           54  Select Elements Step  
           56  Horizontal Clock Signal Generator  
           58  Pixel Clock Signal Generator  
           60  Image Processor  
           62  Sweep Signal Generator  
           64  Clock Signal Divider  
           66  Phase detector  
           68  Integrator  
           70  Voltage Controlled Oscillator  
           72  Second Phase Detector  
           74  Second Clock Signal Divider  
           76  Second Integrator  
           78  Second Voltage Controlled Oscillator  
          A Array  
          N Number of Horizontal Rows in array A  
          K Number of Columns in array A  
          N Number of Horizontal Rows