Patent Publication Number: US-2003222866-A1

Title: Display driver and method for driving an emissive video display in an image displaying device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] Cross reference to related application Ser. No. 09/848,067, entitled DISPLAY DRIVER AND METHOD FOR DRIVING AN EMISSIVE VIDEO DISPLAY filed in the name of David L. Funston on 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] Video displays are an important feature of electronic devices such as cellular telephones, global positioning systems (GPS), CD players, video cameras, digital cameras, hybrid cameras and other devices. Such video displays are typically formed from a two dimensional matrix of image elements. In a preferred form of video display known as the emissive light display, the image forming elements comprise discrete light emitting elements. An image to be displayed using an emissive light display 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. The intensity of light emitted by the elements varies within a range of observable intensity levels. The variations in intensity form a contrast pattern on the display that takes on the appearance of the image.  
       [0004] The emissive light display technologies of the prior art, such as the ubiquitous cathode ray tube and the electroluminescent display consume substantial amounts of power when displaying images. The energy requirements of such displays typically outstrip the power supply capacity of such portable electronic devices. Because of this, emissive light displays have not often been used in circumstances where it is desirable to present images in a lower power manner such as in portable electronic devices.  
       [0005] A new form of emissive light display technology, the organic light emissive display, has been developed which provides elements that emit light over a desired range of illumination intensities using substantially less power than is required by the emissive display technologies of the prior art See, for example, commonly assigned U.S. Pat. No. 5,276,380, entitled “ORGANIC ELECTROLUMINESCENT IMAGE DISPLAY DEVICE”, filed on Dec. 30, 1991 by Tang et al. and commonly assigned U.S. Pat. No. 5,294,870 entitled “METHOD OF MAKING AN ORGANIC ELECTROLUMINESCENT DEVICE” filed on Aug. 12, 1999 by Hryhorenko et al. Such organic light emissive displays are being rapidly developed for use in portable electronic devices and other low power applications.  
       [0006] Although the use of organic light emissive displays greatly reduces the power requirements of an emissive light display, there is a desire to further reduce the amount of power required to operate an emissive light display. This can be done, for example, to extend the operation of a handheld or portable device having a finite supply of electrical energy. For example, certain users of portable electronic devices have expressed dissatisfaction with the short life of batteries that are used in such devices and/or the need to frequently recharge the batteries in such devices. One example of an apparatus and method to further reduce the amount of power required to operate in emissive light display is described and claimed in commonly assigned and co-pending patent U.S. patent application Ser. No. 09/848,067, entitled “DISPLAY DRIVER AND METHOD FOR DRIVING AN EMISSION DISPLAY” filed in the name of David L. Funston on May 3, 2001, it is proposed to reduce the amount of power required to operate an emissive display by reducing the amount of power consumed by the driver of the display.  
       [0007] Another example of an apparatus that is used to reduce the power required to operate emissive display is shown in U.S. Pat. No. 5,977,704 entitled ORGANIC ELECTROLUMINESCENT DISPLAY WITH ICONS filed Oct. 28, 1996 in the name of Shi et al. which provides an organic electroluminescent device having a first display region for displaying icon information and a second display region for displaying other information. In the first region, the electroluminescent display elements are shaped in the form of the icons and therefore, when a particular display element illuminates, the user of the device sees the form of the icon. In the second region an array of pixilated display elements is provided for the display of images formed from a pattern of pixels. Using such a display, the illumination of icons can be maintained while the power consuming driver and individual elements of the pixilated display can be disabled.  
       [0008] It will be appreciated that additional and/or alternative methods for reducing the power consumed in presenting an image using an emissive light display remain desirable.  
       SUMMARY OF THE INVENTION  
       [0009] In accordance with one aspect of the present invention, what is provided is a method for displaying an image using a matrix display of picture elements that radiate light in response to the application of power. In this method, a display mode is selected from at least a first and a second mode. The image is presented on the display when the first mode is selected and the image is presented in a modified form when a second mode is selected. The image is modified so that presenting the image in the second mode consumes less power than presenting the image in the first mode.  
       [0010] In another aspect, what is provided is a method for displaying an image using a matrix display of picture elements that radiate light in response to the application of power. In this method, the status of a display mode condition is detected and a display mode is selected from at least a first and second mode based upon the status of the display mode condition. The image is presented on the display when the first mode is selected. The image is presented in a modified form when a second mode is selected. The image is modified so that presenting the image in the second mode consumes less power than presenting the image in the first mode.  
       [0011] In another aspect what is provided is an image display driver for a matrix display of picture elements that radiate light in response to the application of power. The driver has a signal processor for receiving an image and processing the image for presentation on the display in accordance with one of at least a first mode and a second mode. The signal processor modifies the appearance of the image as presented in the second mode so that the presentation of the image in the second mode consumes less power than the presentation of the same image in the first mode. A device controller determines a display mode for displaying the image and generates a display mode selection signal. The signal processor processes the image in a mode indicated by the display mode selection signal.  
       [0012] In still another aspect what is provided is an image display driver for use with an image displaying device having an image source and a matrix display of light emitting elements. The image display driver has a set of element drivers adapted to control the illumination intensity of the elements. A signal processor receives an image from the image source and processes the image for presentation on the display in accordance with one of at least a first mode and a second mode, with the processor modifying the appearance of the image as presented in the second mode so that the presentation of the image in the second mode consumes less power than the presentation of the same image in the first mode. A device controller determines a display mode condition and generates a display mode selection signal based upon the display mode condition. The signal processor processes the image in a mode selected by the mode selection signal.  
       [0013] In accordance with a further embodiment of the present invention, an image display driver is provided for use in an imaging device having a matrix display of light emitting elements and an image source. The image display driver comprises a set of element drivers adapted to control illumination intensity of the elements. A signal processor receives an image from the image source and processes the image for presentation on the display. A device controller determines a display mode condition to generate the display mode selection signal based upon the display mode condition. A display controller controls the operation of the element driver and modifies the operation of the element driver in response to the display mode selection signal with the display controller being operable to control the element driver in at least a first mode and a second mode. The display controller modifies the operation of the set of element drivers in the second mode so that the presentation of an image in the second mode consumes less power in the presentation of the same image in the first mode. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 shows an example embodiment of an electronic device having a display driver and an emissive light display.  
     [0015]FIG. 2 shows an example of a method in accordance with the present invention.  
     [0016]FIG. 3 a  shows an image presented in a first mode.  
     [0017]FIG. 3 b  shows the image of FIG. 3 a  presented in a sub-scanned form.  
     [0018]FIG. 4 a  shows an image presented in a first mode.  
     [0019]FIG. 4 b  shows the image of FIG. 4 a  presented in a sub-scanned form.  
     [0020]FIG. 4 c  shows the image of FIG. 4 a  presented in another sub-scanned form.  
     [0021]FIG. 4 d  shows the image of FIG. 4 a  presented in still another sub-scanned form.  
     [0022]FIG. 5 a  shows an image presented in a first mode.  
     [0023]FIG. 5 b  shows the image of FIG. 5 a  presented in sub-scanned form.  
     [0024]FIG. 6 a  shows an example of an image presented in three colors.  
     [0025]FIG. 6 b  shows the image of FIG. 6 a  presented in one color.  
     [0026]FIG. 7 a  shows an image presented in a first mode associated with a display mode condition having a status in a first range.  
     [0027]FIG. 7 b  shows the image of FIG. 7 a  presented in a second mode associated with a display mode condition having a status in a second range.  
     [0028]FIG. 7 c  shows the image of FIG. 7 a  presented in a third mode associated with a display mode condition having a status in a third range. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0029]FIG. 1 shows an emissive light display system  10  of the present invention for use in an electronic device  12 . In this embodiment, emissive light display system  10  has a display driver  14  and an organic emissive light display  16  having light emitting elements  18 . In the embodiment shown in FIG. 1, light emitting elements  18  are organized into a vertical array of “n” horizontal rows  20 . Each horizontal row  20  of light emitting elements  18  is associated with one of a plurality of element drivers  22 . Each of the element drivers  22  causes light emitting elements  18  of one of horizontal rows  20  with which it is associated to illuminate in accordance with illumination values that are transmitted to the element driver  22 .  
     [0030] Electronic device  12  includes an image source  24 . Image source  24  can take a variety of forms including, but not limited to, an electronic, magnetic or optical image storing memory, an image capture device incorporating an image such as a Charge Coupled Device, CMOS sensor or Charge Injection Device, or a network connection such as an Ethernet or token ring network from which one or more images are supplied. A signal processor  36  receives images from image source  24  and processes the images to provide illumination values that can be transmitted to element drivers  22 . Where emissive light display  16  is called upon to present the same image over a period of time, it may be necessary to continually retransmit the illumination values for that image to the element drivers  22  that are used to present the image. This is referred to as refreshing the image. To simplify the task of refreshing an image, a refresh memory  35  is provided. Refresh memory  35  stores illumination values associated with an image so that the illumination values can be retransmitted to the element drivers  22  in order to refresh the images without requiring the signal processor  36  to repeatedly generate illumination values for the same image. In the embodiment shown, all illumination values that are transmitted to element drivers  22  pass through refresh memory  35 .  
     [0031] A device controller  28  is provided. The device controller  28  is an electronic system such as a microcomputer or microcontroller based electronic control system. In the embodiment shown, device controller  28  determines the status of at least one display mode condition and generates a display mode signal. Device controller  28  can be dedicated to the tasks of determining the status of at least one display mode condition and generating a display mode signal. Device controller  28  can also be used to control other systems of the electronic device  12 .  
     [0032] The display mode signal is transmitted to a signal processor  36 . As will be described in greater detail below in one embodiment, the signal processor  36  is operable in one of at least two modes, a first mode and at least one second mode. When signal processor  36  is operated in a mode other than the first mode, it converts an image to be displayed into a set of illumination values that cause emissive light display  16  to present a version of the image having an appearance that is modified so that presenting the image on the emissive light display  16  in the second mode consumes less power than presenting the image in the first mode. In this embodiment, the display mode signal is used by signal processor  36  to select from between the available modes.  
     [0033] The display mode signal is also transmitted to a display controller  34 . Display controller  34  generates signals that operate element drivers  22 . More specifically, in the embodiment that is shown, display controller  34  is defined so that it generates a signal that causes one of the element drivers  22  to become receptive to illumination values transmitted by refresh memory  35 . This signal is transmitted to the element drivers  22  using common bus  37 . Display controller  34  also transmits a signal to refresh memory  35  causing refresh memory  35  to transmit the illumination values for light emitting elements  18  of horizontal row  20  of elements with which the receptive one of element drivers  22  is associated. These illumination values are also transmitted along common bus  37 . The receptive one of element drivers  22  receives these code values and causes the individual light emitting elements  18  of horizontal row  20  with which the receptive row driver is associated to illuminate in accordance with the illumination values. The other element drivers  22  ignore the illumination values being transmitted by common bus  37 . This process is then repeated for each one of the element drivers  22 . In this way, the common bus  37  can be used to transmit illumination values to all of element drivers  22  and separate electrical connections between each of element drivers  22  and refresh memory  35  are not required.  
     [0034]FIG. 2 shows a method for operating display driver  14  in accordance with the present invention. As a shown in FIG. 2, display driver  14  receives at least one image for presentation on emissive light display  16 . (Step  41 ) A display mode condition is then determined. (Step  42 ) A display mode selection is made on the basis of the display mode condition. (Step  44 ) In one embodiment, the display mode condition is the status of a user interface  26  such as a switch, dial, or other transducer that converts an input action by a user into a condition that can be detected by device controller  28 . Device controller  28  detects the condition of user interface  26  and generates a mode selection signal in response. In this embodiment, the user of electronic device  12  can determine the display mode by altering the condition of user interface  26 .  
     [0035] Alternatively, the display mode condition can comprise an electrical or other signal that is generated by a component of electronic device  12 . For example, device controller  28  can monitor the use of electronic device  12  and can develop a profile of the way in which the display is typically used. This profile can be used to help device controller  28  select a display mode signal. In one embodiment of this type, device controller  28  determines whether to select a particular mode based upon the current pattern of use of electronic device  12  and the patterns that are recorded in the profile.  
     [0036] In another example, a display mode condition is generated based upon the elapse of time. Electronic device  12  has a device controller  28  that is adapted to determine when a period of time has elapsed. In this example, the device controller  28  determines the elapse of the time period and generates a mode selection signal that causes signal processor  36  to process images in accordance with the second mode. The time period can be reset by, for example, manipulation of user interface  26 . In another example, the signal processor  36  can be adapted to detect when a new image has been provided by image source  24  and can generate a new image signal which is transmitted to the device controller  28 . In this embodiment, device controller  28  detects the new image signal and resets the time period when the new image signal is received. When the time period is reset, the output signal ceases and signal detector  32  generates an output signal that causes signal processor  36  to display images in a first mode.  
     [0037] In still another alternative embodiment, the display mode condition is derived from the amount of energy available to electronic device  12 . In one example of this type, electronic device  12  has a power supply  38  such as a battery and an available energy detector  40 . Available energy detector  40  is an electronic device that monitors the amount of energy available in power supply  38  and generates a signal that is representative of the available energy in the power supply  38 . This available energy signal is then supplied to the device controller  28 . Available energy detector  40  can, for example, comprise a voltage detector that monitors the voltage level provided by power supply  38 . However, it will be appreciated that the amount of energy remaining in a power supply  38  can be determined in other ways.  
     [0038] In the embodiment shown in FIG. 2, and the above described examples, the display driver  14  is operable in two modes. In a first mode, an image is transmitted to display driver  14 , is presented on emissive light display  16  in a form that is intended to accurately represent the image, and presented to display driver  14 . (Step  46 ) In a second mode the image is modified. (Step  48 ) The modification changes the appearance of the image so that the amount of electrical power used to display the modified image on emissive light display  16  is less than the amount of power that is required to present the same image on display  16  in the first mode. The modified image is then presented on emissive light display  16 . (Step  50 ) The display mode that is selected is a function the state of the display mode condition. Where it is possible that the state of the display mode condition can change during the presentation of an image on emissive light display  16 , the state of the display mode condition is repeatedly tested while the image is displayed. (Step  52 ) Emissive light display  16  remains in the selected mode and the image is periodically refreshed unless the display mode condition changes. (Step  54 ) In the embodiment shown, the display mode can also be changed by receipt of the new image for presentation on emissive light display  16  or by instructions to display no image. (Step  56 )  
     [0039] There are various way in which the appearance of an image can be modified to reduce the power that is consumed by emissive light display  16  during the presentation of an image. In this regard it will be appreciated that in order to form and sustain an image on an emissive light display  16 , it is necessary to supply electrical power to each of the picture elements  18  that are illuminated to form the image. The total amount of electrical power that is required to present an image on emissive light display  16  is therefore the sum of the amount of electrical power provided to each of light emitting elements  18 . It will be appreciated from this that it is possible to reduce the total amount of power required to present an image using emissive light display  16  by reducing the number of light emitting elements  18  used to present the image on emissive light display  16  and/or by reducing the a amount of light emitted by light emitting elements  18  The following embodiments detail methods for modifying the appearance of an image so that the amount of power required to present the modified image on emissive light display  16  is lower than the amount of power required to present the same image in a non-modified form.  
     [0040]FIG. 3 a  shows an original image  60 , presented on emissive light display  16 . FIG. 3 b  shows a modified image  62  that represents image  60  after modification to reduce the amount of power required to present the image on the emissive light display  16 . In this embodiment, the step of modifying the appearance of the image, (step  48 ) is performed by reducing the overall number of light emitting elements  18  required to present the image on the emissive light display  16 . In this example, FIG. 3 a  shows an image  60  presented in a first mode. In this mode, the display of image  60  requires the use of an array of 480 rows of 640 light emitting elements  18 . In the second mode, shown in FIG. 3 b , image  60  is modified by the signal processor  36  to form a modified image  62  that is presented using an array of 240 rows of 320 light emitting elements  18 . As displayed, modified image  62  uses one-fourth as many light emitting elements  18  as are used display image  60 . This reduces the number of light emitting elements  18  to which power is supplied and reduces the overall amount of power required to present the image on the emissive light display  16 . In this embodiment, the illumination values contained in image  60  have been compressed for presentation in the second mode. This can be done, for example, by electronically undersampling the imaging information used in the formation of image  60 . Modified image  62  is undersampling the illumination values of image  60  on a four to one basis. Other compression schemes and strategies can be used. It will be appreciated that other ratios of compression can be used. It will be appreciated that an advantage of such compression is that the overall information content of image  60  is essentially preserved in modified image  62 .  
     [0041] The step of modifying the appearance of the image (step  48 ) can also be performed by reducing the number of light emitting elements  18  used in presenting the image by sub-scanning the original image  60  to present a limited portion of an original image. Various sub-scanning approaches can be used. In the embodiment of FIGS. 4 a  and  4   b , image  64  is sub-scanned to form a modified image  66  that is limited by blocking selected ones of light emitting elements  18  from illuminating. The embodiment shown in FIG. 4 b , one-half of light emitting elements  18  of emissive light display  16  are not used to present the modified image  66 . In the embodiment of FIG. 4 b  these unused elements are arranged in rows of elements distributed throughout the display. An advantage of this embodiment is that this embodiment provides a modified image  66  having the same overall size as image  64  and thus is more easily seen at a distance. As is shown in FIGS. 4 c , and  4   d , a variety of sub-scanning patterns can be used to effectively reduce the number elements that are illuminated when image  64  is presented on emissive light display  16 .  
     [0042]FIGS. 5 a  and  5   b  show yet another sub-scanning method. In this method a subject  72  of image  64  is determined and the image is sub-scanned so that only the subject area  72  is shown.  
     [0043] As is shown in FIG. 6 a , color light emissive display  16 , a color image  64  is typically formed for presentation on the light emitting display  16  by combining light from three adjacent light emitting elements  18 , each radiating light in one of three primary colors such as red, blue and green. Because light emitting elements  18  are in close proximity, their individual colors appear to blend. Thus, by varying the intensity of the light radiated in each primary color, it is possible to provide an image  74  having an apparent range of colors that is very broad. However, this means that every such color image  68  is formed from a set of three differently colored images, a red image  76 , a green image  78  and a blue image  80 . The step of modifying the appearance of the image (step  48 ) can comprise presenting modified image  84  having, for example, only those elements of image  74  that radiate one of the primary colors. For example, because the human eye is most sensitive to green, a green image can be provided as is shown in FIG. 6 b . In this embodiment, only the green image  80  is formed on emissive light display  16 . Under certain circumstances, this change effectively reduces the amount of power required to display modified image  84  by a factor of 66% as compared to the amount of power that is required to display the image in an unmodified form. It will be recalled that the amount of power required to present an image on emissive light display  16  of light emitting elements  18  is a function of both the number of elements used in the presentation of the image and the amount of light emitted by the elements. The power required to illuminate light emitting element  18  increases as the amount of light radiated by element increases. Thus, in an alternative embodiment of the present invention, the step of modifying the appearance of the image (step  48 ) can also comprise reducing the luminous output of the light emitting elements  18  of the emissive light display  16  used to present an image. In one example, the upper limit of the range of illumination intensities used in presenting an image can be reduced. The upper limit can be reduced to an arbitrary level so that none of light emitting element  18  will radiate light above a certain level. In another example, the overall brightness of the image can be lowered.  
     [0044] In any of these sub-scanning embodiments, the sub-scanning can be performed by using signal processor  36  to modify the way in which it converts an image into illumination values. Alternatively, it is possible to perform sub-scanning by programming element drivers  22  so that they are operable in a first mode to illuminate a full set of the elements of emissive light display  16  that are used in displaying an image, and in a second mode where element drivers  22  illuminate less than all of light emitting elements  18  in the full set. Signal processor  36  or display controller  34  can transmit a signal to such element drivers  22  to select their mode of operation. Where element drivers  22  are operated in this manner, it is not necessary to use signal processor  36  to modify the way in which the image is converted into illumination values.  
     [0045] It will be appreciated that consistent with the present invention, more than one power saving mode can be selected. This can be done, for example, to indicate the state of a display mode condition. Such an embodiment can be useful in indicating, for example, when the amount of energy remaining in a power supply is within a relatively high range. In one embodiment of this type, an image  90  is displayed using a first set of light emitting elements  92  of the light emitting elements  18  of emissive light display  16  In this embodiment, when the amount of energy remaining is within a second range, a second set of light emitting elements  94  of light emitting elements  18  are used as is shown in FIG. 7 b.    
     [0046] When the amount of energy remaining in power supply  38  reaches a third range, a third set of light emitting elements  96  of light emitting elements  18  is used to display image  90 . In this embodiment, the third set of light emitting elements  96  of light emitting elements  18  is a sub-set of second set  94  of light emitting elements  18 . Second set  94  is a sub-set of the first set of light emitting elements  92  of light emitting elements  18 .  
     [0047] A useful embodiment of this type can be used where electronic device  12  comprises a camera for capturing images of a scene using an image source  24  such as a CCD or CMOS imager. In such an embodiment, user input  26  comprises a shutter switch that is movable from a non-image capture position, to a viewfinder position and into an image capture position. Device controller  28  monitors the position of the switch when the switch is moved from the non-image capture position to the viewfinder position. Controller  28  causes image source  24  to capture a stream of images of a photographic scene. Device controller  28  also generates a display mode signal causing a sub-sampled version of the image in the stream to appear on light emissive display  16 . This allows the user to use emissive light display  16  as a viewfinder but without consuming an undue amount of power. Movement of the switch into the capture position is also detected by device controller  28 . In response, device controller  28  causes an image from the stream of images to be stored, and generates a display mode signal causing the stored image to be displayed in an unmodified form.  
     [0048] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
                               PARTS LIST                                                10   Emissive Light Display System           12   Electronic Device           14   Display Driver           16   Emissive Light Display           18   Light Emitting Elements           20   Horizontal Row           22   Element Driver           24   Image Source           26   User Interface           28   Device Controller           30   Image           32   Signal Detector           34   Display Controller           35   Refresh Memory           36   Signal Processor           37   Common Bus           38   Power Supply           40   Available Energy Detector           41   Receive Image Step           42   Display Mode Condition Determination Step           44   Display Mode Selection Step           46   Display Image In First Mode Step           48   Modifying Image Step           50   Display Modified Image Step           52   Test Condition Step           54   Refresh Displayed Image Step           56   New Image Step           60   Image           62   Modified Image           64   Image           66   Modified Image           68   Color Image           72   Subject           74   Image           76   Red Image           78   Green Image           80   Blue Image           84   Modified Image           90   Image           92   First Set of Light Emitting Elements           94   Second Set of Light Emitting Elements           96   Third Set of Light Emitting Elements