Abstract:
A video system includes a video projector located in a housing a display screen disposed adjacent to the housing, wherein the display screen is capable of being tilted to expose the video projector, logic for generating a test image to display on the tilted display screen in order to calibrate the video projector, logic for projecting the test image onto the tilted display screen; and logic for calibrating the video projector using the test image. The test image is altered to fit the tilted display screen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application Ser. No. 60/703,433 filed on Jul. 29, 2005, the disclosure of which is incorporated in its entirety by reference herein. 

   FIELD 
   Aspects of the present invention generally relate to video display methods and systems. 
   BACKGROUND 
   Currently, in rear projection video systems in order to calibrate the projector of these systems, a user must open up an access panel in the system. Typically, the access panel is the display screen itself. The user must tilt the screen upwards to gain access to the video projector. The user must reach in the opening for the display screen and calibrate the projector. However, since display screen is tilted, the user cannot properly view the image from the projector in order to calibrate the projector. Further, the user must tilt the display screen back into its original position to view video and to determine if the calibration is successful. 
   Accordingly, the user cannot make adjustments to the video projector and simultaneous view the adjustments. Thus, the user must make adjustments to the projector and then step back from the video system, tilt the display screen back to its normal position, and view the adjustments. Since the user may not correctly calibrate the projector on the first try, the user may need to repeat these steps multiple times. 
   Other video system may place an access panel in the rear of video system. In video systems with this access panel, the video system must incorporate enough room for the user to get completely behind the system. Further, the user still cannot calibrate the video system without stepping out from behind the video system to view the calibration changes. 
   In other video systems, the access panel may be a large opening beneath the display screen. In video systems with this access panel, extra space must be incorporated into the video system below the display screen to accommodate the large access panel. Usually a central audio speaker is located beneath the screen and may interfere with this access panel. Further, the user still cannot calibrate the video system without stepping away from the video system to view the calibration changes. 
   SUMMARY 
   Aspects of the present invention concern a method for calibrating a video display system. The method includes tilting a display screen of the video display system to expose a video projector, generating a test image to display on the tilted display screen in order to calibrate the video projector, projecting the test image onto the tilted display screen, and calibrating the video projector using the test image. In the method, the test image is altered to fit the tilted display screen. 
   Additionally, aspects of the present invention concern a video system. The video system includes a video projector located in a housing a display screen disposed adjacent to the housing, wherein the display screen is capable of being tilted to expose the video projector, logic for generating a test image to display on the tilted display screen in order to calibrate the video projector, logic for projecting the test image onto the tilted display screen; and logic for calibrating the video projector using the test image. The test image is altered to fit the tilted display screen. 
   Additional aspects of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
   Further, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present invention, as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the present invention and together with the description, serve to explain the principles of the invention. 
       FIGS. 1   a  and  1   b  are diagrams illustrating a system for displaying a video consistent with aspects of the present invention; 
       FIG. 2  is a rear view diagram illustrating a system for displaying a video consistent with aspects of the present invention; 
       FIG. 3   a  is a diagram illustrating a DLP video projector consistent with aspects of the present invention; 
       FIGS. 3   b - f  are various views illustrating an integrated video projector and video source consistent with aspects of the present invention; 
       FIG. 3   g  is a diagram illustrating a DLP video projector consistent with aspects of the present invention; 
       FIGS. 4 and 5  are flow charts illustrating a method of calibrating a video system consistent with aspects of the present invention; and 
       FIG. 6   a - c  are diagrams illustrating a test image consistent with aspects of the present invention. 
   

   DETAILED DESCRIPTION 
   Aspects of the present invention relate to systems and methods which improve the operation of a video projection system. A video projection system includes a display screen that is capable of being titled upward. As such, a user can tilt the display screen upward and gain access to the video projector inside the system in order to calibrate the video projector. Further, the video projector is capable of altering a test image so that the test image may be properly viewed on the tilted display screen. Thus, a user can calibrate the video projection while looking at the altered test image on the titled display screen. 
   Accordingly, the user can calibrate the video projector easily without having to step back from the video system. Further, the user does not have to open and close the display screen multiple times in order to calibrate the video projector. Also, the video system may be compact since an additional access panel does not have to be included in the video system. 
   Reference will now be made in detail to various aspects of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 1   a  illustrates a video system  100  for displaying video consistent with aspects of the present invention. System  100  includes a housing  102 , a video projector  104 , a mirror  108 , and a display screen  110 . Housing  102  may be a separate portable housing capable of being moved such as a television set. Additionally, housing  102  may be integrated into another structure such as a wall. 
   Video projector  104  produces video  106  to be displayed on display screen  110 . Video  106  projected onto display screen  102  may be moving video or still images. Video projector  104  may be any type of video projector capable of receiving a video signal and converting the video signal to a viewable image to be displayed on display screen  102 . For example, video projector  104  may be a digital light processing (“DLP”) video projector, a liquid crystal (“LCD”) video projector, or cathode-ray tube (“CRT”) projector. 
   As illustrated in  FIG. 1A , video projector  104  produces video  106  and projects video  106  onto mirror  108 . Mirror  108  reflects video  106  onto projection screen  110 . Video projector  104  produces video  106  based on a signal from a video source (not shown). The video source may be any standard video equipment capable of generating a video signal readable by video projector  104 . For example, the video source may be a Digital Versatile Disk (“DVD”) player, laser disk player, Compact Disk (“CD”) player, Video CD (“VCD”) player, VHS player/recorder, Digital Video Recorder (“DVR”), video camera, video still camera, cable receiver box, or satellite receiver box. The video source may also be a standard laptop or desktop computer. One skilled in the art will realize that the preceding list of standard video equipment is exemplary and the video source may be any device capable of generating a video signal readable by video projector  104 . Furthermore, the video source may be integrated with video projector  104 . Additionally, video projector  104  may be coupled to multiple video sources. 
   Display screen  110  may be any type of display screen capable of displaying video from a projector located behind display screen  110 . For example, display screen may be glass, glass coated with a diffusion material, glass embedded with a diffusion material, acrylic substrate, acrylic substrate coated with a diffusion material, or acrylic substrate embedded with a diffusion material. One skilled in the art will realize that the above list is exemplary and that display screen may be made of any material capable of displaying video from a projector located behind display screen  110 . 
   Further, as illustrated in  FIG. 1   a , display screen  110  is attached to housing  102  by a hinge  112 . As illustrated in  FIG. 1   b , hinge  112  allows display screen  110  to be tilted upward away from housing  102 . This allows access to video projector  104 . Hinge  112  may be any type of hinge capable of allowing display screen  110  to be tilted upward. Hinge  112  also includes a locking mechanize to allow display screen  110  to be secured once tilted upward. For example, hinge  112  may include a hydraulic cylinder. One skilled in the art will realize that hinge  112  may be any type of locking mechanism to hold display screen  110  in place once tilted. 
   Alternatively, hinge  112  may comprise a power assist system to allow display screen to be automatically tilted. For example, hinge  112  may include a powered hydraulic cylinder or a motor and gear system which may automatically tilt display screen  110  without force applied by a user. A user may activate the power assist system by a switch (not shown) on housing  102  or by remote control (not shown). 
     FIG. 2  is a back view of video projector  104  illustrating input/output ports  200  for sending and receiving signals consistent with aspects of the present invention. The video source may be coupled to one of the input/output ports  200 . As illustrated in  FIG. 2 , input/output ports  200  include a S-video input  202 , DVI-I input  204 , component video input  206 , VGA input  208 , audio input  210 , coaxial video input  212 , and coaxial audio input  214 . 
   Input/output ports  200  may include additional input and output ports. For example, input/output ports  200  may include ports any number of a S-video input, S-video output, composite video input, composite video output, component video input, component video output, DVI-I video input, DVI-I video output, coaxial video input, coaxial video output, audio input, audio output, infrared input, infrared output, RS-232 input, RS-232 output, VGA input, or VGA output. One skilled in the art will realize that the preceding list of input and output ports is exemplary and that input/output ports  200  may include any port capable of sending or receiving an electrical signal. Input/output ports  200  are coupled to the internal components of video projector  104 . 
     FIG. 3   a  illustrates an exemplary DLP video projector  300  which may be used as video projector  104 . DLP video projector  300  is an example of one type of projector which may be used with system  100 . One skilled in the art will understand that any type of video projector may be used with system  100  such as a CRT projector or an LCD projector. 
   DLP video projector  300  may include a controller  318  and a bus  324 . Controller  318  may include components to control and monitor DLP video projector  300 . For example, controller  318  may include a processor, non-volatile memory, and mass storage. All the components of DLP video projector  300  may be coupled to bus  324  to allow all the components to communicate with controller  318  and one another. DLP video projector  300  includes a fan  322  to cool DLP video projector  300 . Fan  322  may be coupled to bus  324 . DLP video projector  300  also includes a power supply (not shown) coupled to all the components. 
   DLP video projector  300  contains a light source  302  for generating light to produce a video image. Light source  302  may be, for example, an ultra-high performance (“UHP”) lamp capable of producing from 50-500 watts of power. Light source  300  may be coupled to bus  324  to communicate with other components. For example, controller  318  or DLP circuit board  310  may control the brightness of light source  302 . 
   Light generated by light source  302  passes though optics  304 ,  308  and color filter  306 . Optics  304  and  308  may be, for example, a condenser and a shaper, respectively, for manipulating the light generated by light source  302 . Color filter  306  may be, for example, a color wheel capable of spinning at various speeds to produce various colors. 
   Video projector  300  also contains a DLP circuit board  310 . DLP circuit board  310  may include a digital micro-mirror device, a processor, and memory. For example, DLP circuit board  310  may be a DARKCHIP2 or DARKCHIP3 DLP chip manufactured by TEXAS INSTRUMENTS. DLP circuit board  310  is coupled to bus  324  to receive the video signal received from input/output ports  320  and to communicate with controller  318 . DLP circuit board  310  reflects light from light source  302  using the digital micro-mirrors and generates video based on the video signal to be displayed on video screen  202 . DLP circuit board  310  reflects light not used for the video onto light absorber  312 . Light reflected by DLP circuit board  310  used for the video passes through lens housing  314  and lens  316 . Lens  316  focuses the video to be displayed on display screen  102 . Lens housing  314  may include a manual lens moving mechanism or a motor to automatically move lens  316 . The manual lens moving mechanism or motor allows the position of lens  316  and, as a result, shift the position of the video displayed on display screen  102 . The shifting may be achieved by moving lens  316  in any combination of the x, y, or z directions. 
   DLP video projector  300  also includes input/output ports  320 . Input/output ports  320  may be a single port or multiple ports. Input/output ports  320  enables DLP video projector to receive video signals, receive signals from a remote control device, and output signals to other sources. For example, input/output ports  320  may include ports as illustrated in  FIG. 2  or any number of a S-video input, S-video output, composite video input, composite video output, component video input, component video output, DVI-I video input, DVI-I video output, coaxial video input, coaxial video output, audio input, audio output, infrared input, infrared output, RS-232 input, RS-232 output, VGA input, or VGA output. One skilled in the art will realize that the preceding list of input and output ports is exemplary and that input/output ports  320  may include any port capable of sending or receiving an electrical signal. Input/output ports  320  are coupled to bus  324 . Signals input into DLP video projector  300  may be transferred to the various components of DLP video projector  300  via bus  324 . Likewise, signals output of DLP video projector  300  may be transferred to input/output ports  320  via bus  324 . 
   As stated above, the video source may be integrated with video projector  104 .  FIGS. 3   b - f  are various views of a video projection system  350  which includes a video source and video projector integrated into a single housing  352  consistent with aspects of the present invention. Video projection system  350  may be utilized as system  104  in video system  100 .  FIG. 3   b  is a top view of video projection system  350  consistent with aspects of the present invention. As shown in  FIG. 3   b , video projection system  350  includes video projector  354  and a video source  358  in a single housing. For example, video projector  354  may be a DLP projector and video source  358  may be a DVD player. Video projection system  350  includes a lens housing  356  located in a front portion of video projector  354 . Lens housing  356  may include various lens used in projecting video onto a display screen. Further, video source  358  includes a tray  360  for housing media read by video source  358 . For example, if video source  358  is a DVD player, tray  360  may house DVD discs. 
   Further, as illustrated in  FIG. 3   b , video projection system  350  includes projector controls  362  for operating video projector  354 . For example, projector controls  362  may be a power switch, zoom controls, input/output select controls, and picture mode controls. Video projection system  350  also includes video source controls  364 . For example, video source controls  364  may be tray open/close controls, play/stop controls, and video search controls for operating video source  358 . Video projection system  350  may also be controlled by a remote device (not shown). For example, a remote device may include redundant projector controls  362  and video source controls  364 . Video projection system  350  also includes speakers  366  for presenting sounds corresponding to video generated by video projection system  350 . 
     FIG. 3   c  is a front view of video projection system  350 . As shown in  FIG. 3   c , lens housing  356  is located in the front portion of housing  352  of video projection system  350 . Further, video source  358  and tray  360  may be housed in the top portion of housing  352  of projection system  350 .  FIG. 3   d  is another front view of video projection system  350 .  FIG. 3   d  illustrates video projection system  350  when tray  360  is open for inserting media to be played by video source  358 . 
     FIG. 3   e  is a rear view of video projection system  350 . As illustrated in  FIG. 3   e , input/output ports  368  are located in a rear portion of housing  352  of video projection system  350 . For example, input/output ports  368  may include an S-video input  370 , DVI-I input  372 , component video input  374 , VGA input  376 , composite video input  378 , RS-232 port  380 , audio input  382 , audio output  384 , and optical audio output  386 , and power input  388 . Input/output ports  368  may include additional input and output ports (not shown). For example, input/output ports  368  may include ports any number of a S-video input, S-video output, composite video input, composite video output, component video input, component video output, DVI-I video input, DVI-I video output, coaxial video input, coaxial video output, audio input, audio output, infrared input, infrared output, RS-232 input, RS-232 output, VGA input, or VGA output. One skilled in the art will realize that the preceding list of input and output ports is exemplary and that input/output ports  368  may include any port capable of sending or receiving an electrical signal. 
   Further, as illustrated in  FIG. 3   e , speakers  366  are located in the sides of the rear portion of housing  352  of video projection system  350 . Of course, speakers  366  may also be located in other portions of housing  352 . In addition, video projection system  350  may be coupled to other speakers (not shown) that are external to housing  352 . 
     FIG. 3   f  is a block diagram illustrating internal components of video projection system  350  consistent with aspects of the present invention. As illustrated in  FIG. 3   f , video projection system  350  includes a DLP video projector  354  and a DVD player  358  integrated into a single housing  352 . DLP video projector  354  is an example of one type of projector which may be used with video projection system  350 . One skilled in the art would understand that any type of video projector may be used with video projection system  350  such as a CRT projector or an LCD projector. Further, DVD player  358  is an example of one type of video source which may be used with video projection system  350 . One skilled in the art will understand that any type of video source may be used with video projection system  350 . 
   DLP video projector  354  may include a controller  318  and a bus  324 . Controller  318  may include components to control and monitor DLP video projector  354 . For example, controller  318  may include a processor, non-volatile memory, and mass storage. All the components of DLP video projector  354  may be coupled to bus  324  to allow all the components to communicate with controller  318  and one another. DLP video projector  354  includes a fan  322  to cool DLP video projector  354 . Fan  322  may be coupled to bus  324 . DLP video projector  354  also includes a power supply (not shown) coupled to all the components. 
   DLP video projector  354  contains a light source  302  for generating light to produce a video image. Light source  302  may be, for example, an UHP lamp capable of producing from 50-500 watts of power. Light source  300  may be coupled to bus  324  to communicate with other component. For example, controller  318  or DLP circuit board  310  may control the brightness of light source  302 . 
   Light generated by light source  302  passes though optics  304 ,  308  and color filter  306 . Optics  304  and  308  may be, for example, a condenser and a shaper, respectively, for manipulating the light generated by light source  302 . Color filter  306  may be, for example, a color wheel capable of spinning at various speeds to produce various colors. 
   DLP projector  354  also contains a DLP circuit board  310 . DLP circuit board  310  may include a digital micro-mirror device, a processor, and memory. For example, DLP circuit board  310  may be a DARKCHIP2 or DARKCHIP3 DLP chip manufactured by TEXAS INSTRUMENTS. DLP circuit board  310  is coupled to bus  324  to receive the video signal received from input/output ports  320  and to communicate with controller  318 . DLP circuit board  310  reflects light from light source  302  using the digital micro-mirrors and generates video based on the video signal to be displayed on display screen  102 . DLP circuit board  310  reflects light not used for the video onto light absorber  312 . Light reflected by DLP circuit board  310  used for the video passes through lens housing  356  and lens  316 . Lens  316  focuses the video to be displayed on display screen  102 . Lens housing  356  may include a manual lens moving mechanism or a motor to automatically move lens  316 . The manual lens moving mechanism or motor allows the position of lens  316  and, as a result, shift the position of the video displayed on display screen  102 . The shifting may be achieved by moving lens  316  in any combination of the x, y, or z directions. 
   DLP video projector  354  also includes input/output ports  368 . Input/output ports  368  may be a single port or multiple ports. Input/output ports  368  enables DLP video projector  354  to receive video signals, receive signals from a remote control device, and output signals to other sources. For example, input/output ports  368  may include ports as illustrated in  FIG. 3   e  or any number of a S-video input, S-video output, composite video input, composite video output, component video input, component video output, DVI-I video input, DVI-I video output, coaxial video input, coaxial video output, audio input, audio output, infrared input, infrared output, RS-232 input, RS-232 output, VGA input, or VGA output. One skilled in the art will realize that the preceding list of input and output ports is exemplary and that input/output ports  368  may include any port capable of sending or receiving an electrical signal. Input/output ports  368  are coupled to bus  324  and to audio bus  336 . Signals input into DLP video projector  354  may be transferred to the various components of DLP video projector  354  via bus  324 . Likewise, signals output of DLP video projector  354  may be transferred to input/output ports  368  via bus  324 . 
   DLP video projector  354  also includes DVD player  358 . DVD player  358  is composed DVD reader  326 . DVD reader  326  may include a spindle motor for turning a DVD disc, a pickup head, and a head amplifier equipped with an equalizer. DVD reader  326  is coupled to a decoder/error correction circuit  328 , a content scrambling system  330  for copy protecting DVD contents, a program stream demultiplexer (“PS demultiplexer”)  332 . 
   DVD player reads a DVD disc with DVD reader  326  by emitting laser light from the pickup head in order to irradiate the DVD disc with a predetermined wavelength. The reflected light is converted to an electric signal which is then output to the head amplifier. The head amplifier serves to perform signal amplification, waveform shaping and digitization while decoder/error correction circuit  328  serves to perform 8-16 decoding and error correction. Next, content scrambling system  330  performs mutual authentication of the DVD disc and DVD player  358  in order to confirm the authorization. 
   When the authorization is successfully finished, PS demultiplexer  332  separates the program stream (“PS”) as read from the DVD disc into sound and video data in the form of packetized elementary streams (“PES”). Audio stream decoder  334  decodes the PES sound stream with sound compression encoding technology in order to output audio signals. For example, audio stream decoder may utilize sound compression formats such as AAC, AC3, and MPEG. DLP circuit board  310  decodes and processes the video PES which would include video, sub-picture, and navigation data. For example, DLP circuit board  310  may utilize video compression formats such as MPEG 2. The decoded sound stream is transferred to DLP circuit board  310  and DLP circuit board  310  synchronizes sounds, which is transferred to speakers  366  via sound bus  336  and video, which is generated by DLP video projector  354 . 
   One skilled in the art will realize that controller  318  may be utilized in combination with DLP circuit board  310  for producing video and sound from DVD player  358 . Further, DLP circuit board  310  or controller  318  may perform audio decoding functions similar to the functions as performed by audio stream decoder  334 . 
     FIG. 3   f  is a block diagram illustrating internal components of DLP video projector  390  consistent with aspects of the present invention. DLP video projector  390  includes all the components of DLP video projector  300 . In addition, video projection system  390  includes a temperature sensor  392 . Temperature sensor  392  may be any type of senor capable of measuring the temperature inside of DLP video projector  390 . For example, temperature sensor  392  may be a thermocouple. DLP video projector  390  also includes an air pressure sensor  394 . Air pressure sensor  394  may be any type of sensor capable of measuring the air pressure inside DLP video projector  390 . For example, air pressure sensor  394  may be a piezoelectric crystal sensor. Both temperature sensor  392  and air pressure sensor  394  may be coupled to bus  324 . Temperature sensor  392  and air pressure sensor  394  may be controlled by controller  318  or DLP circuit board  310 . One skilled in the art will realize that DLP video projector  350  may include a temperature sensor  392  and air pressure sensor  394 . 
     FIG. 4  illustrates a method  400  for calibrating video system  100  consistent with aspects of the present invention. In video system  100 , display screen  110  may be tilted up to gain access to video projector  104 . Method  400  may be performed by any control and processing hardware, software, or combination thereof contained in video projector  104 . For example, if DLP projector  300  is utilized, method  400  may be performed by a user manipulating controller  318 , DLP circuit board  310 , software stored in controller  318 , software stored in DLP circuit board  310 , or any combination thereof. One skilled in the art will realize that method  400  is merely exemplary and that method  400  may be performed by any hardware, software, or combination thereof capable of performing processing and control functions of the various components of video projector  104 . 
   Method  400  begins with display screen  110  being tilted upward (stage  402 ). Display screen  110  may be tilted far enough so that a user may gain access to video projector  104 . Next, user may operate video projector  104  to generate a test image that is to be displayed on display screen  110  (stage  404 ). Since display screen  110  is titled, the test image is configured or altered so that the test image appears normally on the titled display screen. For example, if the screen is tilted upward, the image may be altered to correct trapezoidal or keystoning distortion caused by the angle between the video path and the screen. 
   Other parameters of the image may need to be altered to fit display screen  110 . The image may be altered mechanically using such image settings as focus, pitch, yaw, and roll. The image may also be mechanically altered using projector position settings such as projector shift up, down, left, right, forward, and backward. The image may also be electronically altered using such settings as digital image shift. 
   The test image may be any type of video image used in calibrating video projector  104 . For example, the test image may be a constant image of color bars or a grid pattern ( FIG. 6   a - c ). The test image may be generated by video projector  104 . Further, the test image may be stored in memory located in video projector  104 . Additionally, the test image may be supplied by a video source coupled to video projector  104  such as video as a video source mentioned above. 
   After generation, the test image is projected onto tilted display screen  110  (stage  406 ). Finally, video projector  104  is calibrated using the test image. Video projector  104  may be calibrated in any number of ways. For example, the user may manipulate settings of video projector  104  to alter the focus, color, contrast, brightness etc. 
     FIGS. 5 and 6   a - c  illustrate a method  500  for generating a test image in stage  404  to be displayed on tilted display screen  110 . Since display screen  110  is tilted with respect the video beginning projected from video projector  104 , the test image is configured to fit on the tilted display screen  110 . Specifically, since display screen  110  is tilted upward, the test image is configured to compensate for trapezoidal or keystoning distortion caused by the tile of display screen  110 . Additionally, the image may as be altered mechanically or electronically to fit the display screen. 
   Method  500  may be performed by any control and processing hardware, software, or combination thereof contained in video projector  104 . For example, if DLP projector  300  is utilized, method  500  may be performed by controller  318 , by DLP circuit board  310 , by software stored in controller  318 , by software stored in DLP circuit board  310 , or any combination thereof. One skilled in the art will realize that method  500  being performed by the components of DLP projector  300  is exemplary and that method  500  may be performed by any hardware, software, or combination thereof capable of performing processing and control functions of the various components of video projector  104 . 
   Method  500  begins by determining if the test image is stored in memory (stage  502 ). If the test image is stored in memory, the test image is projected on display screen  110  (stage  504 ). Then, the test image may need to be further altered (stage  506 ). The test image may need to be further altered if display screen  110  or video projector  104  has moved since the last time the test image was used. Otherwise, the test image may be projected onto the display screen and the projector calibrated (stages  404  and  406 ). 
   If the test image is not stored, a default (or unaltered) test image may be provided or retrieved and then projected onto tilted display screen  110  (stage  508 ). The test image may be generated by video projector  104 . Additionally, the test image may be supplied by a video source coupled to video projector  104  such as video as a video source mentioned above. The test image may be the size and shape that would be normally display on an un-tilted display screen  110 . Thus, this default test image would not properly fit tilted display screen  110 .  FIG. 6   a  illustrates the display of the unaltered test image on display screen  110 . Since display screen is tilted upward, the image would appear larger near the bottom of the test image. 
   Next, the test image is altered to fit tilted display screen  110  (stage  510 ). Since display screen  110  is titled upward, the bottom portion of test image must be shrunk inward so that it fits display screen  110 .  FIG. 6   a  illustrates the alteration to the test image to correct the trapezoidal distortion.  FIG. 6   b  illustrates the view of the altered test image on tilted display screen  110 .  FIG. 6   c  illustrates the view of the altered test image on display screen  110  in a un-tilted configuration. 
   The pre-projected image may be modified line by line to correct for the trapezoidal distortion or the lens inside video projector may be moved to alter the test image. To size the test image to fit the screen, the angle of the screen tilt may be input into video projector  104  to determine the alteration of the test image. Likewise, the default image may be displayed on tilted display screen  110  and then modified using controls on video projector  104  until the test image properly fits tilted display screen  110 . 
   Additionally, other parameters of the image may need to be altered to fit display screen  110 . The image may be altered mechanically using such image settings as focus, pitch, yaw, and roll. The image may also be mechanically altered using projector position settings such as projector shift up, down, left, right, forward, and backward. The image may also be electronically altered using such settings as digital image shift. 
   Optionally, after the test image is altered, the altered test image may be stored in memory (stage  512 ). Afterwards, video projector may be calibrated using the test image (stage  406  and  408 ). 
   Other aspects of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.