Abstract:
Provided are methods and systems for reducing visual distortion in near-to-eye (“NTE”) visual display systems that is worn, at least partially, on a viewer&#39;s head. The movement rate of the viewer&#39;s head is sensed while an image that comprises individual content frames is displayed on the NTE using a vertically based raster scan. A characteristic of the raster scan is varied to mitigate distortion of the content frames due to the viewer&#39;s head movement.

Description:
TECHNICAL FIELD 
     The subject matter described herein relates to methods that reduce image distortion in near-to-eye (“NTE”) visual displays due to rapid head motion of the viewer wearing an NTE display device. 
     BACKGROUND 
     One of the more important features in a cockpit is the Heads Up Display (“HUD”) whereby flight control information is projected onto the wind screen of the aircraft so that the pilot may receive the information without taking his eyes from the airspace in front of him. However, there has been a growing interest in moving away from HUD systems to NTE or to NTE-HUD systems with head mounted viewing and sensor components that may be attached to a pilot&#39;s earphones or to his helmet. 
     A NTE system is characterized by a small display screen that is suspended directly in front of one or both of the pilot&#39;s eyes such that the displayed virtual object or image moves about the display screen as the pilot turns his head to look for other aircraft, look at his other controls and instrumentation, etc. The NTE display is otherwise transparent such that the pilot may see through or see past the display. 
     It would be disconcerting, disorientating and annoying to the pilot if information being sent to the NTE display was constantly visible in his display as he looks around him for other aircraft or for cockpit instrumentation. As such, a NTE display processor is programmed to register or be conformal with the NTE display information within a specific area within the cockpit such that when the pilot is looking at the area of image registration the NTE information is visible in his NTE display and when he turns, nods or cocks his head (i.e. yaw, pitch and roll), the NTE information moves in the opposite direction, and even out of view, until the pilot returns his head to a normal flight position. 
     The image registration is typically established by attaching one or more markers or marker bars to physical locations in the cockpit. The markers may have a particular shape or pattern, or may emit light at a particular frequency. The shape, pattern or emission frequency can be detected by the pilot&#39;s NTE headset and the detected position of the marker then causes the NTE processor to render the display on the NTE display screen only when the pilot&#39;s head is in a desired viewing position range relative to the marker. 
     However, the registration process as practiced in the art has not been perfect. It has been noticed that the majority of head movements are side-to-side (yaw) movements and the speed of the yaw movement has been determined to be in the 1000 degrees per second range compared to a nodding action (pitch) and cocking action (roll), which have been measured to be typically in the 400 degrees per second range. Pitch and roll movements are therefore of lesser concern. 
     Because of the relatively rapid side-to-side (yaw) speed, blurring and/or swimming of the NTE image or virtual object can occur when a pilot turns his head. Blurring is the loss of contrast due to multiple overlapping image rendering. Swimming is the phenomenon that occurs when different parts of an image move at different speeds. 
     Both blurring and swimming tend to occur because NTE head positioning sensor only periodically updates the position of a pilot&#39;s head. If a rapid yaw motion should occur during the interstitial time period between head position updates, sequential information frames will be presented with an abnormally large physical separation. The size of this separation which is a function of the head&#39;s travel time and velocity, and results in distortion such as horizontal blurring. The longer the latency between head position measurements the worse the distortion. 
     However, even in the absence of head sensor delays, some blurring and swimming will continue to occur due to the NTE display&#39;s inbuilt horizontal raster scan periodicities. Typical visual distortions due to horizontal raster scan periodicities include a blurring effect and/or a tilting of the virtual object image. Therefore, there is a need to improve an NTE display to minimize the distortion resulting from a pilot&#39;s head movement. 
     SUMMARY 
     It should be appreciated that this Summary is provided to introduce a selection of exemplary, non-limiting concepts. In one exemplary embodiment, a method for mitigating the distortion in a NTE raster scan video display due to rapid yaw head motion of a wearer is provided where a raster scan video display is configured such that its scan lines are rendered in a vertical orientation. At the completion of each of the plurality of vertical scan lines, the raster scan video display is advanced one column position horizontally. 
     In another exemplary embodiment, a computer readable medium is provided containing instructions that include determining a first column address, calculating a head yaw velocity, and determining a column address adjustment. 
     In another exemplary embodiment, an apparatus is provided comprising a processor and a video display screen that displays a plurality of raster scan lines. The video display screen is configured such that each of the plurality of the raster scan lines is rendered in a vertical orientation and is rendered serially and horizontally across the video display screen at the completion of each vertical scan line of the plurality in response to commands from the processor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified rendering of a NTE apparatus. 
         FIG. 2   a  is an exemplary rendering of a virtual object image as presented in a horizontally oriented raster display with no head movement. 
         FIG. 2   b  is an exemplary rendering of a virtual object image as presented in a horizontally oriented raster display with head movement to the right. 
         FIG. 3  is an exemplary rendering of a virtual object image as presented in a vertically oriented raster display with head movement to the right. 
         FIG. 4  illustrates an exemplary flow chart of an exemplary method to reduce tilting by adding or deleting raster image lines. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure is merely exemplary in nature and is not intended to limit the invention, the application or the uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     The subject matter now will be described more fully below with reference to the attached drawings which are illustrative of various embodiments disclosed herein. Like numbers refer to like objects throughout the following disclosure. The attached drawings have been simplified to clarify the understanding of the systems, devices and methods disclosed. The subject matter may be embodied in a variety of forms. The exemplary configurations and descriptions, infra, are provided to more fully convey the subject matter disclosed herein. 
     The subject matter herein will be disclosed below in the context of an aircraft. However, it will be understood by those of ordinary skill in the art that the subject matter is similarly applicable to many vehicle types and activities as human head movement is the same in any environment. Non-limiting examples of other vehicle types in which the subject matter herein below may be applied includes aircraft, spacecraft, watercraft and terrestrial motor vehicles. Non-limiting non-vehicle environments may include virtual reality simulators. 
     The subject matter disclosed herein may be incorporated into any suitable navigation, flight control system, or virtual reality system that currently exists or that may be developed in the future. Without limitation, terrestrial motor vehicles may also include military combat and support vehicles of any description. 
     Turning now to  FIG. 1 , an exemplary embodiment of an NTE display system  100  that may be used, for example, in a vehicle is depicted. No matter the particular end-use vehicle, the display system  100  includes at least a near-to-eye (NTE) display device  102 , a tracking sensor  104 , a processor  106 , and a memory  130  in operable communication with the processor  106 . 
     The NTE display device  102  is preferably mounted on a headset  108 . The headset  108  may be variously configured, but in the depicted embodiment the headset  108  is configured to be worn by a user (or viewer)  110 , and may include one or more earphones  112  and a microphone  114 . The earphones  112  are adapted to generate audio signals in response to signals received from, for example, a suitable non-illustrated interface. It will be appreciated that the non-illustrated interface may receive signals from, for example, a non-illustrated vehicle radio, the processor  106 , and/or one or more other non-illustrated devices. It will additionally be appreciated that the earphones  112  may be variously implemented. For example, the earphones  112  may be implemented as active noise reduction (ANR) devices or passive devices. 
     The microphone  114  is adapted to detect viewer utterances or other vehicle noises and to transmit signals representative of the detected utterances or noises via, for example, a suitable non-illustrated interface. It will be appreciated that the non-illustrated interface may supply the signals to, for example, the non-illustrated vehicle radio, the processor  106 , and/or one or more other non-illustrated devices. The microphone  114  may include, for example, a noise cancelling microphone or any one of numerous other suitable devices. In some embodiments, headset  108  also may include a non-illustrated push-to-talk (PTT) switch which, when depressed, causes the non-illustrated vehicle radio to transmit pilot utterances detected by the microphone  114  over the air. In other embodiments, a PTT switch may be disposed at a location remote from the headset  108 . 
     The NTE display device  102 , as noted above, is preferably mounted on the headset  108 , and may include a monocular or binocular set of displays  116 . Although the configuration of the displays  116  may vary, in one embodiment each display  116  includes a transparent display panel (e.g., a liquid crystal on silicon display), a light source (e.g., light emitting diodes), one or more prisms adapted to deflect light generated by the light source, one or more polarizers, and one or more lenses. With this configuration, the NTE display device  102  may display one or more virtual images to the viewer  110 . That is, the one or more displayed images appear to the viewer  110  to overlie (or otherwise be disposed in proximity to) another surface, such as a vehicle windshield  118 , and/or one or more non-illustrated vehicle instruments, and/or one or more non-illustrated vehicle control components. It is noted that in some embodiments the NTE display device  102  may be adjustably mounted on the headset  108 . By adjustably mounting the NTE display device  102  on the headset  108 , the NTE display device  102  may be moved into and out of the field of view of the viewer  110 . 
     The sensor  104  is preferably mounted on the headset  108  and is configured to sense movements of at least the viewer&#39;s head  122  and/or the NTE display device  102 . More specifically, the sensor  104  is configured to sense movement of the NTE display device  102 , and to supply a signal representative of the sensed movement to the processor  106 . In one particular embodiment, the sensor  104  is configured to sense, either directly or indirectly (e.g., derived from sensed position), at least a movement rate of the NTE display device  102  by sensing the movement rate of the viewer&#39;s head  122 , and to supply a signal representative of the sensed movement to the processor  106 . In any case, the movement that the sensor  104  senses preferably includes both translational movements and angular movements. The sensor  104  may also be configured, at least in some embodiments, to sense the position and orientation of the NTE display device  102  and/or the viewer&#39;s head  122 . 
     The viewer&#39;s head position may be represented, for example, in terms of offsets from a static, default point in the vehicle. The viewer head orientation may be represented, for example, in terms of angles of rotation about a set of orthogonal reference axis (e.g., axis  124 ,  126 ,  128 ). For example, viewer head movements to the left or right may be represented in terms of angular rotation about axis  124 , viewer head movements up or down (e.g., nods) may be represented in terms of angular rotation about axis  126 , and viewer head tilts to the left or right may be represented in terms of angular rotation about axis  128 . 
     It will be appreciated that although  FIG. 1  depicts the sensor  104  as a single sensing device, the sensor  104  may be implemented, if needed or desired, as a plurality of sensing devices. Moreover, the particular type and configuration of the sensor  104  may vary, and may be implemented as any one of numerous suitable devices including, for example, an inertial movement unit (IMU), an inertial navigation unit (INU), one or more magnetometers, or auxiliary cameras locking on reference signals, just to name a few. 
     The NTE display device  102  and the sensor  104  are both in operable communication with the processor  106 . The processor  106  may be implemented as one or more processors and/or other suitable electronic components, and may be configured to implement one or multiple functions. At least one function that the processor  106  implements is a display generator that renders one or more images on the NTE display device  102 . The processor  106  may render the one or more images on the NTE display device  102  in response to various signals it receives from one or more non-illustrated external systems, subsystems, devices, or components. It will be appreciated that the processor  106  may be mounted on the headset  108 , or it may be disposed remote from the headset  108  and form part of one or more other non-illustrated systems. 
     Processor  106  may be any suitably type of processor of sufficient speed. The processor  106  may be a general purpose processor or a special purpose processor. The processor  106  may be a single processor, multiple co-processors or processors distributed within a wireless or a wired network. Processor  106  is also a non-limiting example of a computer readable medium. 
     Memory  130  is in operable communication with the processor  106 , and may be any type of suitable volatile or non-volatile memory. As discussed more thoroughly below, memory  130  may store display pixel information that may be used as pseudo or generic raster line information to mitigate distortion resulting from rapid movements of the pilot&#39;s head. 
     Memory  130  may comprise any or combination of memory or memory devices currently existing or that may exist in the future. Non-limiting examples of memory devices include random access memory (RAM), read-only memory (ROM), flash memory, programmable logic devices (PLD), magnetic disks, and optical disks. The preceding memory devices are also non-limiting examples of computer readable media. 
       FIG. 2   a  depicts display  116  rendering an image  220   a  when the tracker  104  measures little or no head motion. Thus, the image  220   a  is not distorted. The image  220   a  rendered in the viewing screen appears to be conformed or registered to a physical location within the cockpit in relation to the marker bar  230 , which is physically attached somewhere in the external background  118  (i.e. the cockpit). 
       FIG. 2   b  is an example of an overlapping image  220   b  that is rendered while the viewer  110  moves his head to the right. In such a case the processor  106  causes the overlapping image  220   b  to move left in the display  116 . The overlapping image  220   b  also appears tilted because a conventional display  116  utilizes a conventional raster scan  240   a  that begins at the top left of the display and proceeds to the right in rows and then down the display  116 . 
     In a conventional raster system, the time that it takes to move the active pixel from left to right across the display  116  is much faster than the time it takes to proceed from the top of the screen to the bottom of the screen. A horizontal traversal of the raster pattern  240   a  may be measured in microseconds while a complete vertical traversal may be measured in milliseconds. Because of the relatively slow vertical traversal speed, the bottom row of pixels is naturally the last to be rendered. As such, this may occur at the furthest point in the head movement such that that the bottom row of pixels appears to lead and the top line appears to lag because the top pixels were the first to be rendered and because the blurred image  220   b  is actually moving in the direction in the display  116  opposite from the direction of head movement  124 . 
       FIG. 3  illustrates an exemplary, non-limiting embodiment that at least mitigates the blurring and/or tilting effects resulting from a yawing movement  124  of the pilot&#39;s head  122  in which the raster pattern  240   b  in the display, is turned 90° in either direction to change the scanning pattern from horizontal to vertical. By using a raster scan  240   b  with a vertical orientation, the rate of travel of the raster in the vertical direction is now much faster than it would have been if the raster scan in a horizontal orientation  240   a . As such, the vertical movement of the raster  240   b  is also much faster relative to the fastest yaw movement  124  of a pilot&#39;s head  122 . The increase in speed in the vertical direction may be on the order of 10×-1000× or more. 
     It is preferable that the vertical speed of the raster  240   b  be at least 10 to 100 times faster than the vertical speed of the raster  240   a . It is more preferable that the vertical speed of the raster  240   b  be 100 to 1000 times faster than the vertical speed of the raster  240   a . It even more preferable the vertical speed of the raster  240   b  be over 1000 times faster than the vertical speed of the raster  240   a . At faster vertical speeds, the movement of the pilot&#39;s head  122  from side to side  124  during the several microseconds required to update an entire column of pixels is negligible and the image blurring therefore is diminished. 
     Even after changing the orientation of the raster scan, a blurred image  220   b  may continue to appear blurred toward the direction of the pilot&#39;s head movement  124  than if the pilot&#39;s head was stationary. This blurring effect may be reduced by electronically inserting (i.e. “stuffing”) or removing vertical image lines with the raster  240   b  in vertical configuration. Specifically, if the pilot&#39;s head movement  124  is in the direction of the raster scan  240   b , vertical image lines may be electronically removed from the image to counteract the blurring effect in one direction. Conversely, if the pilot&#39;s head movement  124  is in the direction opposite from that of the raster scan  240   b , then vertical image lines may be electronically inserted, or stuffed, into the space between the actual vertical image lines. The inserted vertical image lines may be image lines duplicated from the last actual vertical image line rendered or the inserted vertical image lines may comprise pseudo or generic lines that are stored in the memory  130 . Duplicated vertical image lines may be used in opaque images and pseudo or generic vertical image lines may be used for see through or translucent images. The number of removed or inserted vertical image lines may be proportional to the speed of the pilot&#39;s head movement although other relationships may be used as well. 
       FIG. 4  is an exemplary, non-limiting logic diagram of an embodiment that may be used to implement the insertion and removal of vertical image lines. In this embodiment the raster scan is moving column by column from the top right of the display to the bottom left. However, the process may be implemented in the reverse or converse orientations as well with the commensurate changes of direction throughout the process. 
     It will be recognized by those of ordinary skill in the art that the embodiment disclosed below is merely exemplary in that some of the process may be broken out into sub-processes, that sub-processes and processes may be combined into combined processes and that functionally equivalent processes may be substituted. It will also be recognized that the method is not direction dependent. The method is just as applicable whether the scan pattern  240   b  is rotated 90° to the left or to the right from a conventional horizontal raster scan pattern  240   a.    
     The method begins at process  300  with the pilot&#39;s head position being at a starting position. At process  308 , a first yaw position is detected as the pilot turns his head  122 . At process  316  a first column address is determined that corresponds with the first yaw position. At process  324  the first vertical column of pixels in the display is rendered at the first column address. At process  332 , a second yaw position is determined and a yaw velocity is then calculated, at process  340 , using the first yaw position and the second yaw position and the elapsed time period between the first and second determinations. 
     At process  348 , the number of raster or pixel columns that would fit in the gap between the first column address where the display raster is currently located in the NTE to where the raster  240   b  would begin its next column after the head movement  324  is calculated. This gap may be termed a “Column Address Adjustment”. As a non-limiting example, the Column Address Adjustment may be determined by calculating the integral number of vertical image lines (N) that will fit (or removed from) between two vertical image lines. The Column Address Adjustment may be calculated to be the closest integer produced by the formula:
 
 N=m*R*T *Ω( t )/ W  
 
where,
 
     m=the number of pixel columns in the display 
     R=the distance from the eye to the display image 
     T=the image refresh period 
     Ω(t)=a function of the head movement over time 
     W=width of the display 
     At decision point  356 , it is determined if the yaw movement was to the left. If so, then the NTE display would be commanded to decrement (or drop) the number of columns equal to the Column Address Adjustment. In this case actual vertical image lines equal to the Column Address Adjustment will be deleted. If the yaw movement was not to the left, then it would be determined at decision point  372  if the head movement was to the right. If so, then the NTE display would be commanded to increment (or advance) the column address in which the pixels are being rendered by the number determined by the Column Address Adjustment. In such a case, vertical image lines would be added or stuffed into the space equal to the Column Address Adjustment. If the head movement was negligible or indeterminate, then the NTE display column display scan is advanced to the next programmed column and the method proceeds back to process  324 . When vertical image lines are added, previous vertical image lines may be copied in to the Column Address Adjustment space created by the head movement. Alternatively, stored or pseudo vertical image lines may be added instead. 
     The subject matter described above is provided by way of illustration only and should not be construed as being limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.