Patent Publication Number: US-2006020906-A1

Title: Graphics preservation for spatially varying display device power conversation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation-in-part and claims priority under 35 U.S.C. §120 from commonly-owned and co-pending U.S. patent application Ser. No. 10/891,734, filed Jul. 15, 2004 and titled “SPATIAL-BASED POWER SAVINGS”, which claimed priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 60/487,761 filed on Jul. 16, 2003; each of these applications is incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION  
      This invention relates to systems and methods that reduce power consumed by an electronics device including a display. More particularly, the present invention relates to techniques for conserving power by altering video information for portions of a display area while preserving video information for graphical user interface items such as icons or toolbars.  
     BACKGROUND OF THE INVENTION  
      Video output consumes a significant amount of power for a laptop or desktop computer. Other computing systems and electronics devices—such as handheld computing devices, cellular telephones and music players—also devote a large fraction of their power budget to video. Power consumption sensitivity increases for portable devices that rely on a battery having limited energy supply.  
      Currently, commercially available power conservation techniques alter an entire image at once. Most techniques uniformly shut down a display or unvaryingly modify all video output in an image after some predetermined time. These techniques usually impede a person&#39;s ability to see graphics items and further use the computing device. Frequently, a person responds by reactivating the entire display—at full power. As a result, little power is saved.  
     SUMMARY OF THE INVENTION  
      The present invention provides systems and methods that reduce power consumption for an electronics device that includes a display device. The power conservation systems and methods alter video information outside a graphical user interface item and preserve video information for the graphical user interface item. The alteration decreases power consumption for the display device or electronics device. Preserving visual output for the graphical user interface item protects a person&#39;s ability to see and detect the graphical user interface item at a later time, even though other portions of the display area have been altered to conserver power.  
      The graphical user interface item may include a toggle, toolbar, icon, clock, and/or other small graphics component relevant to usage of the electronics device. Multiple graphical user interface items may be selected and preserved. After video information outside the graphical user interface item(s) has been altered to conserve power, a person may readily detect the graphical user interface items after a period of inactivity.  
      Some embodiments may alter video information for the graphical user interface item in addition to altering video information outside the item. In this case, video information for the graphical user interface item is altered less aggressively than the video information outside the item. This preferential treatment still allows a user to subsequently identify the graphical user interface item.  
      Since the graphical user interface items occupy a minor percentage of the display area, avoiding or minimizing power conservation video alterations for these relatively small elements does not contribute significantly to power consumption—but maintains a person&#39;s ability to subsequently detect and use these items.  
      In one aspect, the present invention relates to a method for reducing power consumed by an electronics device that includes a display device. The method comprises selecting at least one graphical user interface item. Each graphical user interface item occupies less than about 10 percent of a display area for the display device. The method also comprises altering the video information outside the at least one graphical user interface item, which produces altered video information, such that the display device will consume less power when displaying the altered video information than an amount of power that would be required to display the video information without the alteration. The method further comprises displaying the altered video information with the at least one graphical user interface item.  
      In another aspect, the present invention relates to a method for reducing power consumed by an electronics device that includes a display device. The method comprises altering video information for at least one graphical user interface item at a first rate. This produces altered video information for the at least one graphical user interface item, and the alteration reduces power consumption for the display device. The method also comprises altering the video information outside the at least one graphical user interface item at second rate that is greater than the first rate. This also reduces power consumption for the display device. The method further comprises displaying the altered video information for the at least one graphical user interface item and the video information outside the at least one graphical user interface item.  
      In yet another aspect, the present invention relates to a computer readable medium including instructions for reducing power consumed by an electronics device that includes a display device.  
      These and other features of the present invention will be presented in more detail in the following detailed description of the invention and the associated figures.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  illustrates video information output on a display device suitable for use with a laptop computer or desktop computer in accordance with one embodiment of the present invention.  
       FIG. 1B  illustrates the display device of  FIG. 1A  after video information alteration and graphical user interface item preservation in accordance with a specific embodiment of the present invention.  
       FIG. 2A  illustrates a handheld computer device in accordance with one embodiment of the present invention.  
       FIG. 2B  illustrates the handheld device of  FIG. 2A  after video information alteration and graphical user interface item preservation in accordance with a specific embodiment of the present invention.  
       FIG. 3  shows video information alteration for an exemplary pixel for an LCD device to conserve power in accordance with one embodiment of the present invention.  
       FIG. 4A  illustrates a process flow for reducing power consumed by a display device in accordance with one embodiment of the invention.  
       FIG. 4B  illustrates a process flow for reducing power consumed by a display device in accordance with another embodiment of the invention.  
       FIG. 5  illustrates an exemplary computer system suitable for implementing the invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.  
      Power conservation methods and systems described herein select at least one graphical user interface item and alter video information outside the graphical user interface item such that the alteration decreases power consumption for a display device or an electronics device. Often, these power conservation alterations degrade visual quality and/or perceptibility of the altered video information. Meanwhile, the graphical user interface item may be left untouched and unaltered. In another embodiment, video information for the graphical user interface item is also altered to decrease power consumption, albeit to a lesser extent or rate than alteration to the video information outside the graphical user interface item. In either case, the present invention preserves a person&#39;s ability to see and detect the graphical user interface item at a later time when information around the graphical user interface item has been altered.  
      For example, a person may stop using a handheld or laptop computer for some time. The present invention identifies at least one graphical user interface item that may be relevant to a person when the person returns to using the device. The graphical user interface item may be an icon or toolbar, for example, or any other small graphics item relevant to usage of the electronics device. Multiple graphical items may be selected. Video information for the graphical user interface item is then at least partially preserved so as to not degrade a person&#39;s ability to detect the graphics item while other video information in the display area is altered to conserve power.  
      The video information outside the graphical user interface item is altered at some time (e.g., due to inactivity in the display area) according to power conservation system design. This may include decreasing the brightness and luminance, altering color for the video information, etc. Several suitable alterations to conserve power are described below. Power conservation system designers and/or users may also vary the rate of video information alterations and/or set a lower limit for alterations and video information presentation. The alteration may occur once, multiple times, or continuously according to power conservation control. Often, alteration produces or progresses to a state where the video information outside the graphical user interface item is significantly visibly degraded—or even unrecognizable. For example, luminance for the video information outside the graphical user interface item may be reduced to black, or some minor fraction of its original luminance level, that compromises visual processing and recognition.  
      The amount of power conserved will depend on the display device. OLED devices are current driven devices where electrical current flow to individual pixel elements varies with light output and video information for each pixel. Reducing RGB values for each pixel (or luminance, which then reduces RGB values) draws less current on a pixel-by-pixel basis. For many LCD devices, perceived luminance at each pixel of the LCD is a combination of backlight level and transmissivity of the video information using pixilated filters. To reduce power, one may alter video information so as to reduce transmissivity to the point where a lower backlight level may be used when displaying lower luminance video information. Hardware power consumption and conservation is described in further detail below  
      When the person returns to the display, even though video information outside the graphics item has been altered and degraded (and corresponding power savings achieved), the user may still readily detect and recognize a preserved graphical user interface item and use it to readily return to usage of the electronics device without any intermediate steps or without activating the entire display, e.g., just to check the time. The present invention thus preserves the person&#39;s ability to detect a graphical user interface item and maintains their ability to quickly return to usage of the device—after video information has been altered and degraded to conserve power. This also avoids annoyance by users that prefer to be able to see some active video at any time, informs a user that a computer has not entered a hibernate mode when it has not (entire screen shut-downs are often confused as a hibernate mode, very noticeable in their sudden luminance change, and commonly cause a user to re-activate the entire display to avoid entering the hibernate mode), and preserves visual perception for portions of a display area that are typically returned to after inactivity, such as icons and toolbars.  
      Some embodiments alter video information for the graphical user interface item in addition to altering video information outside the graphics item. In this case, video information for the graphical user interface item is altered less aggressively than the video information outside its boundaries. This preferential treatment allows a user to subsequently identify the graphical user interface item with visual salience and recognition relatively greater than the remainder of video information in the display area.  
      In one embodiment, the present invention alters video information for the graphical user interface item and the video information outside the graphical user interface item at different rates. For example, video information in a graphical user interface item may be altered at a slower rate and less aggressively than alterations to the background and/or one or more windows.  
      The present invention finds use with a wide array of display devices and electronics devices. For example, desktop and laptop computers with 12-20″ display areas, measured diagonally, are now common and may benefit from techniques described herein. The present invention is particularly useful for portable electronics devices powered from a battery or other limited source of energy. Video conservation techniques described herein may significantly extend battery longevity and useable time for the portable electronics device.  
       FIG. 1A  illustrates video information output on a display device  40  suitable for use with a laptop computer or desktop computer. While the present invention will now be described as video information, graphical user interface items, graphics components and hardware components, those skilled in the art will recognize that the subsequent description may also illustrate methods and discrete actions for reducing power consumption for a display device and associated electronics device.  
      Display device  40  displays video information, and may include a liquid crystal display (LCD) device, projector, or an organic light emitting diode (OLED) device. Other display devices and technologies are suitable for use with the present invention.  
      Display device  40  outputs video information for a laptop or desktop computer within a display area  44 . Display area  44  refers to a current image size of a display device. Pixel dimensions may characterize the size of display area  44 . Physical dimensions (e.g., inches) that span an image produced by the display device may also characterize the size of display area  44 . The display area  44  may be less than a maximum display area for the device, e.g., when a user manually alters horizontal and vertical expansion of a CRT image. Linear dimensions for display area  44  output by a projector will vary with the distance between the receiving surface and projector output lens and a splay angle for the projector. The physical dimensions may be measured on the projected image, usually after any keystone distortion has been suitably corrected for, which may also decrease the display area relative to the maximum display area. To facilitate discussion of LCD based power savings, device  40  will also be referred to as an LCD  40 .  
      An electronics device, such as a desktop, laptop or handheld computer, often runs a graphics-based user interface  42 . The graphics-based user interface  42  facilitates interaction between a user and the laptop computer and/or between the user and one or more programs run on the computer. Several suitable graphics-based user interfaces  42  are well known and commercially available, such as those provided by Microsoft of Redmond, Wash., and Apple Computer of Cupertino, Calif., for example. Interface  42  also controls video information output on LCD  40 .  
      The video information refers to data for display using the display device  40  to produce a visual representation of some form. The video information data is typically stored in a logical manner using values assigned to pixel locations. The pixel locations may correspond to a pixel arrangement used for device  40  or an arrangement used for storing the data. Exemplary color schemes suitable for assigning values to video information are described below. Stored video information may include a resolution that may or may not match a resolution for display device  40 . For example, picture video information used for background  48  may be stored as a bitmap having a resolution that does not match the resolution of LCD  40 .  
      Referring to  FIG. 1A , video information output on LCD  40  currently includes graphical user interface items  41  and  43 . A graphical user interface item refers to a graphics component for display as a discrete visual object on display device  40 . Each graphics component typically includes video information corresponding to a program run on the interface  42  or to visual output for an interactive feature of interface  42 . Popular programs include word processing programs, file navigation programs, Internet Browsers, drawing programs, music player programs, and video games, for example. Other programs are known in the art and the present invention is not limited by any particular graphics-based user interface  42  or program run thereon. Common graphical user interface items allow a user to select or initiate a program offered on the user interface  42 , use or select a feature offered with interface  42 , input data, display information, open programs, open and minimize windows, etc. In general, the present invention is not limited to any particular icon provided on a display device or function related thereto. As shown in  FIG. 1A , graphical user interface items  41  include icons related to programs offered by interface  42 , while graphical user interface item  43  includes a toolbar associated with interface  42 .  
      Icons  41  are popular graphical user interface items and include a characteristic graphics component that corresponds to a particular program. Some icons  41  provide an initiation shortcut to a program, while others initiate a menu for interface  42 . The examples shown include a trash bin icon  41   a  to help a user dispose of files for a file maintenance program offered by interface  42 , an envelope icon  41   b  to initiate an email program stored on the electronics device and offered by interface  42 , and a dollar icon  41   c  to initiate a money management program. Other icons may be used and are known to those of skill in the art. A user may select or initiate a program by positioning a pointer and selecting the visual icon  41  for a program.  
      Toolbar  43  is a visual tool provided by graphics-based user interface  42  that includes a number of graphics components to help a user interact with the electronics device and programs provided thereon. Toolbar  43  includes a toggle  43   a  for each program currently active in display area  44 , a pull-down menu  43   b  for accessing programs and options offered by the graphics-based user interface  42 , and a clock  43   c . Selecting a toggle  43   a  displays or minimizes a graphics item corresponding to the toggle  43   a.    
      Graphics items  45  and  47  are also shown in display area  44  and each correspond to video output for a program currently running on user interface  42 . Rectangular windows are common graphics items and may vary in size from a maximum size that roughly spans display area  44  (minus toolbar  43 ) to smaller sizes within display area  44 . The rectangular windows may also be operated in minimized states where the program is active but the graphics item is not visible. A toggle  43   a  for the program allows switching between these states. For  FIG. 1A , graphics item  45  includes a rectangular window that corresponds to a word processing program, while item  47  includes a window that corresponds to a file navigation program. Background  48  represents a backdrop graphics item for graphics-based user interface  42 , and may include a picture, single color or other backdrop graphics.  
      In one embodiment, one or more of the graphical user interface items  41  and  43  are static, which implies that they do not change over time without specific user input to such effect (a user may intentionally move them, if desired). With the exception of clock  43   c , the exemplary graphical user interface items  41  and  43  shown in  FIG. 1A  are static. A static graphical user interface item allows a user to quickly return to the item based on previous use and memory of its location. Toolbar  43  is statically located at the bottom of display area  44 . Toolbar  43  may alternatively be located on a side or the top of display area  44 , or combinations thereof. Icons  41  can be located anywhere in display area  44 .  
       FIG. 1B  illustrates display area  44  as a result of inactivity in accordance with a specific embodiment of the present invention. The present invention alters video information outside a graphical user interface item such that a display device outputting the altered video information consumes less power than an amount of power required to display the video information without alteration. As shown, luminance for all pixels outside the graphical user interface items  41  and  43  are reduced. Additional power conservation alterations will be described in further detail below.  
      As shown in  FIG. 1B , toolbar  43  and any toggles included therein do not decrease in luminance over time. In addition, video information for icons  41  are not altered over time to conserve power. Since toolbar  43  and icons  41  represent a relatively small portion of display area  44 , and a likely place for subsequent user interaction, power conservation may be slightly sacrificed for the expected demand of toolbar  43  and icon  41  usage.  
      In another embodiment, the present invention alters video information for icons  41  such that border portions for each icon  41  are subsequently illustrated with increased contrast than internal portions of each icon. Thus, video information in internal portions of each icon  41  may be altered while outer portions of each icon  41  remain unmodified. Video information in background  48  that borders each icon may also be preserved to enhance border edge detection of each icon  41  and quick visual recognition. This allows icons  11  to be recognized based on the shape without requiring full video output from each icon.  
      Color information for toolbar  43  and icons  41  may also be preserved. Many icons include one or more characteristic colors that facilitate rapid recognition. In one embodiment, the present invention preserves the characteristic colors of a graphical user interface item. This maintains the ability to identify the graphical user interface item based on its color appearance.  
      The graphical user interface items are typically small relative to the size of the display area  44 . In one embodiment, each graphical user interface item occupies less than about 10 percent of a display area for the display device. This ratio may be determined by pixel count comparison between a graphical user interface item and display area  44 , for example. The exact ratio may vary and will depend on the graphical user interface item, display area, electronics device type (e.g., handheld, laptop, desktop, etc.) and a particular manufacturer. In a specific embodiment, the graphical user interface item occupies less than about 5 percent of a display area for the display device.  
      The present invention allows a user to see and readily use graphical user interface items  41  and  43  within display area  44 —which may constitute a relatively small proportion of display area  44 —while reducing video output and power consumption from the rest of the display area  44 . In contrast, conventional display devices and power conservation require the entire display area to be active and consume power. For larger display areas, displaying only graphical user interface items  41  and  43  and not the remainder of display area  44  may lead to a 70+ percent reduction in power consumption, which is particularly valuable when the display device is powered by a battery in a portable computer.  
       FIG. 2A  illustrates a handheld computer device  20  in accordance with one embodiment of the present invention.  FIG. 2B  illustrates handheld device  20  after video information alteration in accordance with a specific embodiment of the present invention.  
      Handheld computer device  20  includes a display device  22  that displays video information. Individual pixel locations within a display area  23  for device  22  permit allocation and addressing of video information displayed within a display area  23 . Pixel dimensions and resolution may characterize display area  23 . For example, display device  22  may comprise an OLED display device that offers pixel dimensions of 480×640. The OLED device permits video information changes for individual pixels to affect power consumption and conservation at pixel granularity.  
      Handheld device  20  runs a graphics-based user interface  24  within display area  23 . Interface  24  facilitates interaction between a user and device  20  and/or between the user and one or more programs run on computer device  20 . To do so, interface  24  outputs video information on display device  20 . As shown in  FIG. 2A , interface  24  currently displays a background  28  and a set of icons  26  that each correspond to a program available on device  20 . The icons  26  are displayed on background  28 , which includes its own set of background video information and provides a backdrop environment for graphics-based user interface  24 . Two toolbars  30  are output in display area: a top toolbar  30   a  that includes a pull-down toggle for interface  24  and a bottom toolbar  30   b  that includes a clock.  
       FIG. 2A  illustrates display area  23  before alteration of video information in display area  23 , while  FIG. 2B  shows display area  23  after alteration of video information. As shown in  FIG. 2B , video information in background  28  has been turned to black. Lesser alterations to the video information in background  28  may be used.  
      Notably, the present invention conserves power without substantially compromising usability of electronics device  20 . More specifically, the video information is altered such that the person may still see icons  26  and toolbars  30  in display area  23 . Thus, a user may still perceive visual information relevant for interaction after returning to the display after a period of non-usage.  
      In another embodiment, a program has been opened in display area  23  of device  20 . The program may correspond to a word processing program, for example. During usage, the word processing program dominates display area  23  such that the majority of video information output by display device  22  includes video information for the word processing program. For example, the word processing video information may constitute 80+% of the video information output in display area  23 . In this case, power conservation alters the word processing video information, which leaves the toolbars  30  still visible and discernable after the alterations, but conserves the majority of power output for display device  22 . In this case, for example, a user may still see the clock in toolbar  30   b.    
      While  FIGS. 1 and 2  illustrate two specific electronics devices, power conservation techniques described herein are also well suited for use with other electronics devices. Other exemplary devices include cellular telephones, portable music players, digital cameras, and other portable computing and electronics devices that include a video display.  
      Having discussed exemplary display devices and graphics, power conservation will now be expanded upon.  
      The present invention may implement a wide array of video alterations to conserve power. In general, the alteration reduces the amount of power that would be required to display the altered video information relative to the video information without the alteration. Alterations may vary according to the video information, time, usage of the electronics device, the display device and its power consumption characteristics, etc.  
      In one embodiment, video alteration occurs based on user activity—or lack thereof. Activity may comprise a) user input within a perimeter or outer boundary for a window for a program—as determined by the program associated with the window, b) program output to the user—as determined by the program, and/or c) user input in the background  48  or interaction with the graphics-based user interface  42 .  
      Interaction that qualifies as activity is related to one or more programs being output, and may vary with power conservation system design. For example, user input and activity for a word processing program running on graphics component  45  of  FIG. 1A  may include: typing within the window  45 , positioning a pointer within the window  45 , clicking a button (e.g., using a mouse) within the window  45 , manipulating menus and scrollbars within the window  45 , a subset of these chosen by design, etc. User input for a music player program running on graphics component may include selecting songs to be played or manipulating volume and other audio output features. Video output for a music player program may include temporally-varying video that changes with the music based on program operation—without regular user input—such as an equalizer output or a clock that counts music time as a song plays. In one embodiment of the present invention, the music player program maintains an active graphics components status as a result of the temporally varying video output. In another embodiment, the power conservation system is designed such that temporally varying video output for the music player program does not qualify as activity. User input for an Internet browser window may include positioning a pointer within the window, typing addresses, and opening links, for example. In one embodiment, activity comprises temporally varying video output provided by a program whose video output intentionally varies over time without continued user input, such as a movie player. Video output is also common with Internet browsers and may or may not constitute interaction based on power conservation system design. User input for background  48  includes moving a pointer within background  48 , selecting (‘clicking’ or ‘double clicking’) an icon  41 , accessing individual items on control bar  43 , etc.  
      Inactivity for a graphics component implies a lack of interaction in the inactive portion. As activity described above depends on a program associated with the graphics component, so does inactivity. In one embodiment, inactivity is defined for an individual graphics component according to a lack of activity for the graphics component, which will depend on the program associated with the graphics component. Thus, inactivity for word processing graphics component  45  includes a lack of typing within the window boundary, a lack of positioning a pointer within the window boundary, a lack of manipulating menus and scrollbars within the window boundary, etc. Inactivity for background  48  may include a lack of positioning a pointer within the background  48  perimeter, a lack of initiating icons and menus, etc.  
      In one embodiment, the power conservation methods use a threshold inactivity time to determine when alterations to video information begin. The power conservation methods may alternatively alter immediately with inactivity in the display area. A user may set the threshold inactivity time via a graphics control. Once the threshold inactivity time has been reached, output power for the display device decreases according to one or more video manipulation techniques and the display device type.  
      In one embodiment, after the threshold inactivity time, video alterations and power conservation may continue at set power reduction intervals. The power reduction intervals determine specific times after the threshold inactivity time at which further video alterations are applied. This allows the altering video information to gradually change—and power conservation to gradually increase—over time and according to varying design or user preference. A user may set the power reduction intervals using a graphics control. In order for a power reduction interval to be met, inactivity continues in the display area or window for the duration of the interval. The threshold inactivity time and power reduction intervals are a matter of system design and user choice and may be different time periods.  
      Once the threshold inactivity time has past, the present invention alters video information outside a graphical user interface item such that a display device will consume less power than that which would be required without alteration. In addition, video information outside a graphical user interface item may continue to adapt as time proceeds to further reduce power consumption. An array of video manipulation techniques may be employed by the present invention to reduce power consumption.  
      Power conservation as shown in  FIG. 1B  reduces luminance for video information outside the graphical user interface items  41  and  43 . In one embodiment, the present invention reduces the luminance for all pixels outside the graphical user interface items  41  and  43  by the same amount. In other words, the altered video information becomes darker by subtracting a constant value from the luminance value for each pixel. This effectively shifts a luminance histogram for the altered video information to a darker state. Such a luminance reduction may be implemented at a threshold inactivity time and at each power reduction interval. The constant value may include a function of i) a maximum luminance for the video information outside the graphical user interface items  41  and  43  (such as a percentage), ii) a maximum luminance provided by the display device, iii) a mean, median or mode of luminance values for the video information outside the graphical user interface items  41  and  43 , or iv) a mean, median or mode of a luminance range values provided by the display device, etc. A suitable percentage of the maximum luminance for the video information outside the graphical user interface items  41  and  43  may range from about 2 percent to about 100 percent of the maximum luminance. Thus, a 100 percent reduction turns video information outside the graphical user interface items  41  and  43  black at the threshold inactivity time and maximizes energy conservation. A 5 percent luminance reduction at the threshold inactivity time and each power reduction interval thereafter steadily decreases luminance over time. Values less than 1 percent may be used for subtle and/or high frequency changes. While saving less power than a full 100 percent reduction, smaller alterations may be preferable to some users who prefer a less dramatic visual change. It is also understood that the percentage reduction at the threshold activity time and each power reduction interval may be different levels. For example, a 5 percent luminance reduction may be implemented at the threshold inactivity time, while a 2 percent, 10 percent, or escalating (0.25, 0.5, 1, 2, 4, 6, 8, 10 percent, etc.) reduction may be used at each power reduction interval.  
      In one aspect, the present invention builds a histogram for a set of pixels being altered and reduces power consumption for the pixels using one or more histogram-manipulation techniques. The histogram is a function showing, for each pixel value (e.g., luminance or chroma), the number of pixels in an image that have that pixel value. One embodiment alters pixel values by compressing and shifting a luminance histogram. More specifically, a luminance histogram is first constructed for a set of pixels to be altered. The luminance histogram is then compressed, e.g., about the mean, median or mode. A shift subsequently reduces the luminance values for all pixels in the compressed set by a constant. One suitable constant is a number that gives a pixel with the lowest luminance value in the new compressed histogram a zero luminance. The altered video information becomes darker since the final histogram luminance varies from zero luminance to a new maximum luminance produced as a result of the compression and shift.  
      A suitable amount of luminance compression may range from about 1 percent to about 50 percent of histogram luminance range. Another suitable compression may range from about 5 percent to about 20 percent of histogram luminance range. Compression and shifting may occur at the threshold inactivity time and at each power reduction interval, if desired. This process may repeat at subsequent power reduction intervals until the video information outside the graphical user interface item is almost black or until a predetermined cutoff is reached. Suitable cutoffs include: when the maximum luminance value outside the graphical user interface item reaches a predetermined minimum luminance, when the histogram reaches a minimum width, or when the difference between subsequent iterations is minimal.  
      The present invention may implement other compression and shift schemes. In one embodiment, the luminance histogram for a set of pixels is compressed only on one side, e.g., on the high end. If the histogram compression occurs just on the high end, the video information becomes darker for brighter pixels only. If the histogram compression occurs only on the low end of luminance values and then a shift is applied, the video information becomes darker for all pixels.  
      Although the present invention has primarily been discussed so far with linear and simple reductions in luminance for pixel values in an inactive portion, a power conservation system designer may apply more complicated video alteration and power conservation schemes. The relationship between power reduction, video alterations, and time may be established according to system design. One suitable power conservation scheme applies stepwise reductions of predetermined values at predetermined times. Another power conservation scheme employs an exponential decrease in luminance values as time proceeds. In this case, luminance reduction starts slowly in an initial time span, increases gradually in some midpoint time span, and then increases sharply in a later time span. A linear reduction based on y=F(x 2 ), where y is a current luminance reduction, x represents the ith alteration in a number of alterations over time, and F(x 2 ) is some function that increases power conservation as inactivity time passes or increases exponentially with a number of alterations to the video information. Linear constants and other mathematical operators may be inserted into the equation to alter video alterations as desired. Logic may also be applied in the video information manipulation to achieve a desired luminance vs. time curve.  
      Logic that limits further alterations to video information in subsequent power reduction intervals may also be implemented. At this point, the entire display area may be turned off. One suitable logic applies a lower limit that values of individual pixels outside the graphical user interface items may be reduced to, such as a percentage of an initial luminance or chroma level. For example, luminance reductions may cease for a pixel once the pixel reaches from about 5 percent to about 50 percent of its initial level—regardless of how it reached this point. Time may also be used. For example, all video information outside the graphical user interface item may be turned off or turned black at a predetermined time. In addition, the entire display area, including the graphical user interface item, may be turned off at some second predetermined shut-off time.  
      In another embodiment, luminance reduction occurs gradually over time at smaller intermittent time intervals (e.g., less than a minute) and small luminance alterations, as opposed to larger and less frequent alterations. This technique provides a more gradual power reduction without sharp or noticeable changes in video content. For example, luminance in an inactive portion may decrease 1 percent every 10 seconds, thereby decreasing luminance by 60 percent over ten minutes without a large and obvious single change.  
      Advantageously, the present invention permits more aggressive alterations and power conservation, if desired, to video information outside the graphical user interface items since the video information being altered is often needed less by a user upon return to the device after inactivity.  
      In another embodiment, white video information is altered. This power conservation technique divides video information into white and non-white video information. ‘White video information’ refers to video information that has passed some threshold or criteria of whiteness. A power conservation system designer and/or user may define a white threshold—and thus specify what information is altered for white power conservation. Altering white video information to reduce power consumption may include reducing one or more RGB values for the white video information. This produces colors and shades that are ‘off-white’, or non-Full White. A ‘replacement’ shade of white (that consumes less power) may be used, such as Snow White (255-250-250), Ghost White (248-248-255), Floral White (255-250-240), White Smoke (245-245-245), or Old Lace (253-245-230).  
      Having discussed exemplary graphics, video information preservation, and video information alterations, video information representation and hardware power conservation will now be described in further detail. In general, video information alterations may include any changes to video information that decrease power consumption, and are not limited to any particular color scheme used by the hardware or by the software that implements power conservation.  
      Red, green, blue (RGB) color schemes are popular and suitable to characterize video information according to combinations of red, green and blue values. Video information is often stored according to an RGB scheme, while many display devices employ an RGB color scheme for video output. These display devices include a red, green, and blue optical modulation element for each pixel, such as individual RGB light emitting diode emitters for an OLED display device, individual RGB filters for an LCD device, or a digital micromirror element used in a projector that sequentially and selectively reflects incident red, green and blue light from a lamp and color wheel into a projection lens. In many RGB based devices, individual optical modulation elements receive commands for video output that include RGB values between 0 and 255 to produce a desired video output for a pixel. For example, one greenish color may initially comprise red/green/blue values of 45/251/62. According to luminance reduction techniques described above, the color may be darkened to 3/155/16, and subsequently darkened again to 2/90/9 (this maintains the relatively same hue for the greenish color).  
      In one embodiment, the present invention converts data to an HSL scheme and performs video alteration in the luminance domain. Converting RGB video information to and from HSL video information provides a simpler forum to implement luminance control. In a specific embodiment, the present invention sacrifices minor changes in color quality when performing luminance manipulation to achieve luminance targets and tailor video alteration changes. Depending on the size of the display device, the human eye generally detects changes in luminance more readily than changes in color. While the human eye can differentiate about 10 million colors, this level of differentiation is usually achieved by making side-by-side comparisons. The human eye can only identify about 300 different colors from memory. Luminance and luminance differences are often more detectable, but vary with size of the image.  
      Video information alterations may be applied in a number of color schemes, as one of skill in the art will appreciate. An HSL color scheme characterizes video output according to a wavelength or color (hue), degree of purity of the color—or degree of separation from gray having the same color (saturation), and degree of brightness for the color ranging from black to white (luminance). Cyan, magenta, yellow and black (CMYK) is another color scheme regularly used to characterize video output from display device according to combinations of cyan, magenta, yellow and black values. In general, power conservation techniques described herein may be implemented regardless of the color scheme used to store the video information or employed by a graphics-based user interface, video controller or display device. Alterations and video conservation as described herein may also apply to black and white video output.  
      Translation between the color schemes is well known to one of skill in the art. Thus, power conservation techniques described herein may be programmed or stored according to one color scheme, and output according to another color scheme for the display device. For example, video data manipulation techniques described herein may be implemented and stored in an HSL scheme, and then converted to and output by an RGB based display device.  
      Hardware power consumption and conservation will vary with display technology for the display device.  
      OLED display devices provide pixel granularity power consumption—and permit pixel granularity power conservation. OLED devices include a red, green, and blue individual light emitting diode or filter for each pixel. The amount of current sent to each light emitting diode or filter increases with each RGB color level between 0 and 255. Decreasing the RGB levels then reduces the amount of power for each diode and pixel. More specifically, altering white video information RGB values of 255/255/255 to a white shade of 235/235/235 reduces the amount of current sent to each individual light emitting diode for each pixel that emits the white shade. The amount of power conserved over the display area for the OLED display device can then be determined by summing the power saved for all pixels in the display area that have been altered.  
      LCD display device power consumption and conservation typically relates to backlight luminance. LCD devices provide two degrees of freedom for controlling luminance: 1) different luminance levels provided a backlight and 2) graduated filtering by optical modulation elements for each pixel.  FIG. 3  shows video information alteration for an exemplary pixel for an LCD device to achieve power conservation. Four luminance states  100   a - d  are shown at three different times: t=0, t=1 and t=2.  
      Scale  102  illustrates a number of backlight luminance levels  103  offered by a backlight used in an LCD device. As shown, the LCD provides ten discrete backlight levels  103 , numbered from 0 to 10, where 0 is off and 10 represents the maximum luminance for the backlight. In this simplified example, each increasing integer luminance level between 0 and 10 provides a proportionate increasing luminance (each level represents about 10% the maximum luminance) for the backlight. More complicated backlight levels are contemplated and suitable for use.  
      Transmissivity refers to the amount of light passage provided by optical modulation elements for a pixel. Many LCD devices include red green and blue (RGB) filters that act as optical modulation elements, where each filter regulates passage of white light produced by the backlight through a colored filter element to produce red, green and blue light, respectively. Transmissivity may then be expressed using RGB values sent on control signals to each RGB filter. LCD devices including modulation elements that respond to RGB transmissivity values ranging from 0 to 255 are common. The video information and transmissivity may also be expressed and converted from another video data scheme, such as HSL luminance. For example, luminance for each pixel may be provided at integers between 0 and 240, where zero represents black (full filtering and blocking of light provided by the backlight for each RGB filter) and 240 represents white (no filtering and blocking of light provided by the backlight).  
      As the term is used herein, ‘aggregate luminance’ refers to a luminance output to a viewer of an LCD device. This aggregate luminance combines luminance effects provided by a) the backlight and b) filtering provided by the optical modulation elements for each pixel. The aggregate luminance is typically limited to a maximum determined by the backlight level since the pixelated filters only reduce light currently offered by the backlight. For  FIG. 3 , maximum luminance for the LCD device corresponds to a backlight level of 10 and luminance transmissivity of 240. At backlight luminance level 9, the maximum aggregate luminance for video data corresponds to a luminance transmissivity of 240 (t=2). Aggregate luminance for the pixel is designated as  104   a - d  for  FIG. 3  at each time instance.  
      Both the backlight level and the luminance transmissivity are controllable. In one embodiment, LCD power conservation leverages the two degrees of freedom in luminance control to reduce power for the LCD device.  
      At time t=0, the illustrated high luminance pixel (a white pixel) includes a backlight level of 10 and luminance transmissivity of 240, which corresponds to a maximum for the aggregate luminance and is designated as  104   a.    
      LCD power conservation alters video information for the pixel. This reduces transmissivity and luminance for the pixel and/or the backlight level. For the example at time t=1, the backlight level remains at level  10  but the video information is altered to reduce the luminance transmissivity to 228. This provides an aggregate luminance of  104   b  (a less white shade). In this case, information has been altered but without a backlight change, and no power conservation has yet been achieved.  
      At time t=2, the backlight level still remains at level 10 but the video information is altered to reduce the luminance transmissivity to 224 (an even less white shade). This provides an aggregate luminance of  104   c . Aggregate luminance of  104   c  is noteworthy because it approximately corresponds to the aggregate luminance of  104   d  provided by the LCD device for the pixel when the backlight level drops to level 9 and the luminance transmissivity returns to 240 (its original level). At this luminance, the backlight level may drop from level 10 to level 9 and the luminance transmissivity increases from 224 to 240—without changing the aggregate luminance of  104  output to the viewer—or as perceived by a viewer. Thus, a person may not notice the backlight change. Power consumption for the backlight and LCD device reduces when the backlight level changes from level 10 to level 9.  
      For an LCD, aggregate luminance is then manipulated for all pixels affected by a backlight (some LCD devices include more than one). Video information for the image is altered to produce a new maximum luminance that is less than the next or largest available luminance at the next backlight level. Then, the LCD switches to the next backlight level.  
      Although the above example has been simplified to illustrate two degree of freedom luminance control and power conservation using and LCD, power conservation as described herein is not limited to such simple expressions of backlit luminance levels and pixel transmissivity. The above example employed ten backlight luminance levels; other numbers of backlight luminance levels are contemplated. In general, the LCD device may include any number of backlight luminance levels. As the granularity of backlit luminance levels increases, so does power conservation and the ability to more readily use a lower backlight level. The backlight luminance levels also need not correspond to simple fractions of the maximum luminance or integer levels as described above. In addition, luminance transmissivity is not limited to expression using a range of 1-240. Other luminance transmissivity and color schemes, such as normalized scales, are also suitable for use. As one of skill in the art will appreciate, the number and characterization of backlight luminance levels will depend on the LCD used, while the number and characterization of video information will depend on the video scheme used to represent the video data.  
      Aggregate luminance thus allows a designer to relate backlight luminance levels and pixel transmissivity for an LCD device, which permits a designer to alter the video information and direct the modifications towards backlight luminance reductions. An aggregate luminance model may be built for a device that estimates luminance perceived by a user as a combination of backlight and pixilated transmissivity. For example, the aggregate luminance may be used to provide a ratio (or another suitable mathematical relationship) between the backlight luminance levels and pixel transmissivity.  
      One video alteration embodiment for LCD use sets a high luminance limit for a histogram of luminance after an alteration. The high luminance limit refers to a reference luminance level for video information in the display area that may be used to guide alteration, e.g., before changing a next backlight luminance on an LCD device. The edge detection video information may rest near the high luminance limit, while the remaining video information other than the edge detection video information is altered to a lesser aggregate luminance. This maintains visible salience of the edge detection video information relative to the remaining video information, and allows stepwise decreases in backlight luminance. This also allows luminance for any pixel in the image to remain relatively constant at the moment of each backlight level change (to produce little perceptible change). Further description of LCD based power conservation suitable for use with the present invention is described in commonly owned pending patent application Ser. No. 11/122,313 and entitled “LCD Plateau Power Conservation”, which is incorporated herein in its entirety for all purposes.  
       FIG. 4A  illustrates a process flow  200  for reducing power consumed by an electronics device and/or display device in accordance with one embodiment of the invention. While the present invention will now be described as a method and separable actions for reducing power consumption, those skilled in the art will recognize that the subsequent description may also illustrate hardware and/or software systems and items capable of performing the method and actions.  
      Process flow  200  begins by selecting at least one graphical user interface item ( 202 ). Selection may vary. In one embodiment, a power conservation program run on the electronics device automatically selects the graphical user interface item(s) according to system design. In another embodiment, a user toggles a class of graphical user interface items using a power conservation graphics control offered by a graphical user interface. Some classes include icons, toolbars, shortcut icons, and active window or program representations, for example. This allows the user to determine what items are preserved.  
      Process flow  200  proceeds by altering the video information outside the at least one graphical user interface item ( 204 ). The video information is altered such that the display device will consume less power when displaying the altered video information than an amount of power that would be required to display the video information without the alteration.  
      In a specific embodiment, video information outside the graphical user interface item alters immediately upon inactivity in the display area. One suitable luminance reduction scheme decreases luminance incrementally and alters video information at power reduction intervals that begin immediately upon user inactivity and have a frequency of greater than 1 alteration every 5 seconds. In this case, the incremental reductions decrease luminance by a tiny amount each time such that any individual alteration is not readily noticeable to a user. Cumulatively, however, the incremental alterations may accumulate to produce a significant change, such as a 50 percent reduction in luminance for the background and graphics components over five minutes for example. The gradual rate of alteration may be established according to power conservation system design or user preference, and advantageously allows video information to alter without substantially noticeable momentous changes. A magnitude for each incremental alteration may be determined by dividing a desired total alteration over a period of time by the number of intervals in the time period. For example, the progressive changes may occur as often as desired to produce a backlight luminance level change in an LCD device every 30 seconds. The backlight luminance level change may then occur without changing aggregate luminance perceived by a user.  
      The altered video information and at least one graphical user interface item are then displayed together on the display device ( 206 ).  
      Altered video information returns—or reactivates—to its original state from an altered state after user activity with the display area, or as otherwise designated by a power conservation program designer. Reactivation displays the display area as it was initially displayed before any alterations. In a specific embodiment, positioning a pointer onto an area of a display area triggers reactivation. Reactivation may also include initiating graphics window via its corresponding toggle on toolbar  43 . Power conservation system designers may also customize reactivation rules. For example, reactivation may be designed such that solely positioning and moving a pointer within a window or background does not satisfy reactivation criteria. In this case, clicking a button on a mouse while the pointer is within the window, or another explicit action within the graphics component, may satisfy reactivation.  
      In another embodiment, inactivity within the display area may be monitored and timed. The graphics-based user interface may include a global power saving tool that initiates after a predetermined time of inactivity throughout the entire display area. In this case, the global power saving tool turns off video display for the entire display area, including the graphical user interface items being preserved, when inactivity reaches the global power saving tool time limit, e.g., such as 5 minutes.  
       FIG. 4B  illustrates a process flow  210  for reducing power consumed by a electronics device and/or display device in accordance with another embodiment of the invention. Process flow  210  begins by setting a power conservation scheme ( 211 ). A power scheme refers to a collection of power options that dictate how and when video information is altered to reduce power consumption. In one embodiment, a power conservation system is stored on a computer and implements a power conservation scheme without user input. In another embodiment, a graphics control allows a user to set a power scheme or one or more power options corresponding to techniques described herein, e.g., select one or more types of graphical user interface item for video preservation.  
      For process flow  210 , the power conservation scheme uses a threshold inactivity time to determine when alterations to video data begin. The threshold inactivity time may beset by a user via a graphics control, or automatically with power conservation system design. Once the threshold inactivity time has been reached, video information is altered to reduce power consumption.  
      After the power conservation scheme has been established, process flow  200  monitors user activity within the display area ( 213 ). Process flow  210  continues to monitor activity over time and reacts according to any user activity or lack thereof ( 216 ). If user activity occurs in the display area, process flow  210  then resets the inactivity monitor clock and returns to  213 . If user inactivity continues until the threshold inactivity time, then process flow  210  alters video information.  
      In this embodiment, video information for the graphical user interface items is also altered. In this case, alterations to video information for the graphical user interface items occur at a lesser rate than that for video information alterations outside the graphical user interface items. Process flow  200  proceeds by altering the video information for the graphical user interface item at a first rate ( 220 ). The change may include reducing the luminance for the graphical user interface item such that a next luminance level in an LCD device may be employed.  
      Power conservation also alters the video information outside the at least one graphical user interface item ( 204 ). Since the graphical user interface item(s) occupy a minor amount of space, alteration of video information outside the at least one graphical user interface item leads to the majority of power conservation. Suitable techniques for altering video information outside the graphical user interface item were described above.  
      In this case, the video information for the graphical user interface item alters at a lesser rate than video information outside the graphical user interface item. In one temporally varying embodiment, alterations to video information occur at set power reduction intervals. The power reduction intervals determine specific regular times at which minor but additive video alterations are applied. In this case, alterations to the graphical user interface item may occur less frequently (at larger intervals) than for video information outside the graphical user interface item. For example, progressive and stepwise changes to RGB values of the graphical user interface item may occur every twenty seconds while progressive and stepwise changes to RGB values of video information outside the graphical user interface item may occur every ten seconds. Other intervals may be used. In one embodiment, a power reduction interval from one second to about 3 minutes is suitable. In another embodiment, a power reduction interval from about 1 second to about 10 seconds is suitable. It is understood that power reduction intervals are a matter of system design and user choice and may be include different time periods that those specifically provided herein.  
      The difference in rate of alteration may also include changes at the same frequency—but by different amounts at each interval. In this case, the video information outside the graphical user interface item is altered more aggressively at each interval than that of each graphical user interface item.  
      In one embodiment, power conservation as described herein is implemented without user input. In another embodiment, a computer system provides a user the ability to turn on/off power conservation or tailor the power conservation to personal preferences that include the ability to preserve video information for one or more graphical user interface items.  
      The present invention may also include controls for implementing power conservation. Graphics-based user interfaces employ what are referred to as graphics “controls”. A graphics control is a discrete video object, for display by a display device, which can be manipulated by a user to alter one or more graphics outputs or effects and/or to initiate an action in an the graphical user interface. The graphics control often includes its own bitmap comprising an array of pixel values. For the present invention, the graphics control includes visual tools that allow a user to turn on/off visual preservation for graphical user interface items in general, or for one or more classes of graphical user interface items as described above. Further description of graphics controls suitable for use with the present invention is provided in commonly owned U.S. patent application Ser. No. 10/891,734, which was incorporated by reference above.  
      The present invention may also relate to systems for reducing power consumed by a display device. The power conservation system may comprise any combination of software and hardware for carrying out actions described herein. In a specific embodiment, general-purpose computer processing units, instead of dedicated hardware, implement the monitoring and video alteration techniques. Further description of power conservation systems suitable for use with the present invention is provided in commonly owned U.S. patent application Ser. No. 10/891,734, which was incorporated by reference above.  
      The present invention finds use with computer systems such as desktop and laptop computers, personal digital assistants (PDAs), cellular telephones, digital cameras, portable computer systems, and the like.  FIG. 5  schematically illustrates an exemplary general-purpose computer system  300  suitable for implementing the present invention.  
      Computer system  300  comprises a processor, or CPU,  302 , one or more memories  314  and  316 , input/output (I/O) circuitry  306 , display device  308 , input device  310 , and system bus  312 . System bus  312  permits digital communication between system processor  302  and ROM  314 , as well as permits communication between other components within system  300  and processor  302  and/or ROM  314 .  
      System  300  memory includes read only memory (ROM)  314  and random access memory (RAM)  316 . Other memories may be included. ROM  314  stores a basic input/output system  318  (BIOS), containing basic routines that help to transfer information between elements within computer system  300 , such as during start-up. Computer system  300  may also include a hard disk drive and an optical disk drive, for example. The optical disk drive reads from and may write to a CD-ROM disk or other optical media. The drives and their associated computer-readable media provide non-volatile storage for system  300 . A number of program modules may be stored in the drives, ROM  314 , and/or RAM  316 , including an operating system, one or more application programs, other program modules, and program data. Although data storage above refers to a hard disk and optical disk, those skilled in the art will appreciate that other types of storage are suitable for use with a computer system, such as magnetic cassettes, flash memory cards, USB memory sticks, and the like. In addition, not all computer systems, such as PDAs and other portable devices may include multiple external memory options.  
      Processor  302  is a commercially available microprocessor such as one of the Intel or Motorola family of chips, or another suitable commercially available processor. Processor  302  digitally communicates with ROM  314  via system bus  312 , which may comprise a data bus, control bus, and address bus for communication between processor  302  and memory  314 . CPU  302  is also coupled to the I/O circuitry  306  by system bus  312  to permit data transfers with peripheral devices.  
      I/O circuitry  306  provides an interface between CPU  302  and such peripheral devices as display device  308 , input device  310 , audio output  334  and/or any other I/O device. For example, a mouse used as input device  310  may digitally communicate with processor  302  through a serial port  306  that is coupled to system bus  312 . Other interfaces, such as a game port, a universal serial bus (USB) or fire wire, may also provide digital communication between a peripheral device and processor  302 . I/O circuitry  306  may also include latches, registers and direct memory access (DMA) controllers employed for interface with peripheral and other devices. Audio output  334  may comprise one or more speakers employed by a headphone or speaker system.  
      Display device  308  outputs video information—both unaltered and altered—including graphics components, backgrounds, graphics controls such as those described herein, graphics-based user interfaces, and other visual representations of data. For example, display device  308  may comprise a cathode ray tube (CRT), liquid crystal display (LCD), organic light emitting diode (OLED), or plasma display, of the types commercially available from a variety of manufacturers. Display device  308  may also comprise one or more optical modulation devices, or the like, used in projecting an image. Projection display devices that project an image onto a receiving surface are becoming more popular, less expensive, more compact; and may employ one or more optical modulation technologies as well as a wide variety of individual designs. Common optical modulation devices include those employing liquid crystal display (LCD) technology and digital mirror device (DMD) technology. When used as a display device for a computer, these projection devices provide the potential for a much larger image size and user interface. In general, the present invention is not limited to use with any particular display device.  
      The present invention is independent of any particular display device, any mechanism of light generation for a display device, or any power consumption scheme for a display device, and only assumes that power consumption for display device  158  may vary with video information. In a specific embodiment, display device  158  can vary power consumption spatially on a pixel by pixel basis.  
      Display device  308  may also digitally communicate with system bus  306  via a separate video interface, such as a video adapter  346 . Video adapter  346  is responsible for assisting processor  302  with video graphics processing including power conservation alterations described herein. Video adapter  346  may be a separate graphics card or graphics processor available from a variety of vendors that are well known in the art.  
      Input device  310  allows a user to enter commands and information into the computer system  300 , and may comprise a keyboard, a mouse, a position-sensing pad on a laptop computer, a stylus working in cooperation with a position-sensing display on a PDA, or the like. Other input devices may include a remote control (for a projector), microphone, joystick, game pad, scanner, or the like. As used herein, input device refers to any mechanism or device for entering data and/or pointing to a particular location on an image of a computer display. Input as described herein may also come through intermediary devices. For example, a remote control may communicate directly with processor  302 , or through an intermediary processor included in another device such as a hybrid entertainment device such as a set-top box or projector. The user may then input information to computer system  300  using an infrared remote control device that communicates first with the intermediary device, and then to processor  302 .  
      In one embodiment, a graphics-based user interface implemented by computer system  300  displays a graphics control such as control described above. To display a power conservation graphics control, processor  302  issues an appropriate command, followed by an identification of data that is to be used to construct the graphics control. Such data may include a number of power conservation control tools that allow a user to change how video data is altered. ROM  314  also stores a number power conservation commands and instructions for implementing the techniques described herein. In one embodiment, the present invention is practiced in the context of an application program that runs on an operating system implemented by computer system  300  or in combination with other program modules on computer system  300 .  
      The present invention may be implemented on a range of computer systems. In addition to personal computers such as desktop computers and laptop computers, a variety of other computer systems and computer devices employing a digital processor, memory and a display device may implement the present invention. Handheld computers and other small portable digital devices such as cell phones and digital cameras are increasingly integrating video display and computer functionality. One current trend is hybrid entertainment devices that integrate the functionality of computer systems, audio devices, and televisions. Any of these devices may employ and benefit from the power conservation methods and systems described herein. The scope of digital computer systems is expanding hurriedly and creating new devices that may employ the present invention. In general, any digital device employing an output display device that varies output power with video content may benefit from the present invention. Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, multiple display device systems, multi-processor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like.  
      The present invention is particularly useful to portable computing devices run with battery power. Most handheld devices are designed to rely on battery power. In addition, although the present invention has been discussed with respect to reduced power consumption, energy and power are relatively interchangeable in a discussion of the benefits of conservation.  
      Embodiments of the present invention further relate to computer readable media that include program instructions for performing power conservation techniques described herein. The media and program instructions may be those specially designed and constructed for the purposes of the present invention, or any kind well known and available to those having skill in the computer software arts. Examples of computer-readable media include, but are not limited to, magnetic media such as hard disks, semiconductor memory, optical media such as CD-ROM disks; magneto-optical media such as optical disks; and hardware devices that are specially configured to store program instructions, such as read-only memory devices (ROM), flash memory devices, EEPROMs, EPROMs, etc. and random access memory (RAM). Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher-level code that may be executed by the computer using an interpreter.  
      Graphics controls and graphics-based user interfaces such as those described herein may be implemented using a number of computer languages and in a number of programming environments. One suitable language is Java, available from Sun Microsystems of Sunnyvale, Calif. Another suitable programming environment is the Microsoft Windows™ programming environment, which provides a series of operating systems suitable for implementing the present invention both on laptop computers and handheld computers.  
      Although the foregoing invention has been described in some detail for purposes of clarity of understanding, those skilled in the art will recognize that various modifications may be made within the scope of the appended claims. In addition, although power consumption and conservation has not been detailed for every type of display device, the present invention is suitable with any display technology that can vary power output with video information. Projectors, for example, consume power based on the amount of light produced, which may be reduced using techniques described herein. The invention is, therefore, not limited to the specific features and embodiments described herein and claimed in any of its forms or modifications within the scope of the appended claims.