Abstract:
Sensor independent display characterization system spectrally characterizes a display system to measure radiant power emitted by the display system that displays a video image to a trainee pilot during sensor stimulation. A sensor spectral response for each wavelength produced by the stimulated sensor is determined. A stimulated luminance for each color level of the displayed image or for a range of color levels is computed. A color look up table that maps computed stimulated luminance to a set of stimulating color values is generated. When a trainee pilot looks at the displayed image using a sensor having a sensor response that was used in computing the stimulated luminance, the pilot will see an image that was created by simulated spectral rendering. The displayed image is an accurate, display and sensor independent image that the pilot can see during the real flight.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to providing computerized simulations of real-world views. In particular, the present invention is directed towards a sensor and display-independent quantitative per-pixel stimulation system. 
     2. Description of the Related Art 
     Pilots of aircrafts or other pilot-controlled vehicles sometimes guide their aircraft over a given terrain with the assistance of vision-augmenting equipment known as sensors, including, for example, Night Vision Goggles (NVG&#39;s) and Low Level Light Television Cameras (LLLTV&#39;s). Sensors typically are used to convert hard-to-see imagery in one or more of the visible and/or invisible spectral bands into imagery that is more clearly visible to the human eye. Sensors often display imagery that is different from the one a pilot may be accustomed to seeing naturally with his or her own eyes (also known as an out-the-window view). Therefore, it is desirable to train pilots ahead of time so that they can correctly interpret what they see with sensors during actual flights. 
     Flight simulators are commonly used to simulate flight training environments. Flight simulators typically include one or more video display screens onto which video images are projected by one or more projectors. Two known approaches are used in pilot training: simulation systems and stimulation systems. 
     Simulation systems display images as they would appear to a pilot using a given sensor. For example, if NVGs are being simulated, the display shows an image on a head-mounted display as it might appear to a pilot wearing NVGs. Since the displayed image already incorporates the wavelength translations performed by the sensor—i.e. the system displays simulated images—these types of systems do not allow the pilot to use actual vision-augmenting equipment during training. This is considered a drawback of simulated systems, because a pilot&#39;s experience using the simulator will differ from that during actual flight-for example, wearing NVGs, a pilot may see a sensor-based image occupying most of his field of vision, but may see a regular out-the-window image using his peripheral vision. Since in a simulated system only a sensor-adjusted image is displayed, and is based on head tracking, the experience differs from that of the real world. The disparity between the simulator and the real world experience is further augmented by the pilot not being able to wear the sensor equipment. 
     Stimulated systems, on the other hand, provide a pilot with a stimulated image that can be viewed using an appropriate sensor, e.g., one that can be worn by the pilot. Again using the example of NVGs, with a stimulated system the images displayed will match the spectral wavelengths to which the NVGs are sensitive, allowing the pilot to use a real pair of NVGs and thus provide a more realistic experience. However, because display systems vary widely in their display characteristics, the spectra emitted by one system might appear drastically different than those emitted by a second system, and the real world image different still. Accordingly, stimulated systems are generally of lower fidelity than simulated systems, providing only a qualitative experience versus the more quantitative experience of simulated systems. 
     Accordingly, what is needed is a system and method for providing high-quality stimulated imaging. 
     SUMMARY OF THE INVENTION 
     The present invention enables a sensor-independent per-pixel stimulating spectral method and apparatus that is configurable across different display systems and which combines quantitative simulated sensor rendering with a stimulated system. 
     Initially, a display system to be used with a system of the present invention is characterized according to the particulars of its emissions. An image generator (IG) generates a test pattern that is then displayed by the display system to be characterized. A spectroradiometer measures radiant power emanating from the display and stores the data. The process is repeated for various combinations of test pattern images—for example, for a color-independent RGB display, each value of red, each value of green, and each value of blue is measured. 
     Once the display has been characterized (also known as calibrated), the present invention creates color lookup tables that map simulated luminance to stimulating color values. This mapping is specific to the display that has been characterized and to the sensor that will be used with the display. 
     Once the display has been characterized and the color lookup tables created, the present invention is ready to be used for flight (or other) simulation. A simulated image stream is received by the present invention, and using the color lookup tables, for each luminance value provided in the stream, a set of RGB values (or other input values, depending on the display technology involved) is determined that will produce the equivalent stimulated image on the display system. Those color values are then provided to the display system by the IG, and displayed for use with the appropriate sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a method for performing sensor and display-independent sensor stimulation in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates a system for providing stimulated images in accordance with an embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a display characterization function in accordance with an embodiment of the present invention. 
         FIG. 4  illustrates a method for automatic display calibration in accordance with an embodiment of the present invention. 
         FIG. 5  illustrates an example spectral radiance graph in accordance with an embodiment of the present invention. 
     
    
    
     The figures depict preferred embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates three steps of a method for performing sensor and display-independent sensor stimulation. First, the display system that will be used in conjunction with the sensor is characterized  102  according to the particulars of its emissions. Next, sensor-dependent color lookup tables that map simulated luminance to stimulating color values are created  104 . This mapping is specific to the display that has been characterized and to the sensor that will be used with the display. Finally, a simulated image stream is received by the present invention, and using the color lookup tables, for each luminance value provided in the stream, a set of RGB values (or other input values, depending on the display technology involved) is determined  106  that will produce the equivalent stimulated image on the display system. Those color values are then provided to the display system for use with the appropriate sensor. Each of these steps is described further below. 
     System Architecture 
       FIG. 2  illustrates a system  200  for providing stimulated images in accordance with an embodiment of the present invention. System  200  includes an image generator (IG)  202  and its calibration engine  206 , a simulator engine  204 , and color lookup tables  208 . Each of these components is further described below.  FIG. 2  also includes a simulated data stream  210 , a display system  212 , a sensor  214 , and a pilot  216 , meant to represent a user of system  200 . 
     Calibration 
     Because each display system has its own particular characteristics, the exact spectral emissions from the display system will vary between systems receiving the same input. Indeed, even a single display system may develop different characteristics over time, for example as the projector ages. Consequently, it is preferable to first calibrate system  200  for use with a particular display system  212 . 
       FIG. 3  illustrates a way in which display characterization is preferably performed. Image generator  202  creates or displays a color video image assigned to a given color or video level. For display calibration, image generator  202  preferably includes a test pattern generator. IG  202  sends images for display to display system  212 . Display system  212  is a monitor, screen, video projector, rear projector, dome, or any other device adapted to display an image. During display calibration, display system  212  receives images from IG  202  and displays the images. The display is then measured by a spectroradiometer  330 . That is, the radiant power or energy per wavelength emanating from display system  212  is measured by the spectroradiometer  330 . In one embodiment, spectroradiometer  330  is the PR-715 spectroradiometer, by Photo Research Inc. of Chatsworth, Calif.; in an alternative embodiment, spectroradiometer  330  is the Minolta R-1000 by Konica Minolta of Japan. Spectroradiometer  330  returns the results of its measurements to IG  202 , which stores the data sets, e.g., in database  304 . 
     The result of the display calibration is a series of power spectral tables or datasets for each measured color video level, or for each of the display input levels. 
       FIG. 4  is a trace diagram of a method for automatic display calibration performed by system  200  in accordance with one embodiment of the present invention. Initially, at step  400 , calibration engine  206  sets intensity values for red, green and blue to a minimum value, e.g., 0 intensity. IG  202  generates  410  an image such as a test pattern and sends it to display system  212 , which then displays  490  the image. A test pattern in a preferred embodiment corresponds to specified red, green and blue values. The example of  FIG. 4  illustrates the case in which initially only red values are displayed, and then green and then blue data values are added in as described below. Calibration engine  206  next activates  412  spectroradiometer  330  to perform spectral measurements. Spectroradiometer  330  measures  492  emissions from display system  412  and sends  420  the measurements back to calibration engine  206 . Assuming for purposes of the illustrated example that there are 256 possible values of red intensity, calibration engine  206  increments  430  the value (intensity) of the image being displayed by a delta amount. If  440  the new red-value does not exceed a maximum red value, the process returns to step  410  and the image with the new red value is then measured by spectroradiometer  330 . Once all of the red intensity values have been measured, the red intensity value is reset  450  to its original value, and values are then measured for each green intensity value (i.e. for each intensity value of green, 256 values of red intensity are measured). Once  460  the value of green intensity reaches its maximum, blue values are then measured  470  for each intensity value of red and green. At the conclusion of all steps, emissions for intensity values for each combination of red, green and blue have been measured and stored by calibration engine  206 . In this example, 256×256×256=16,777,216 measurements. 
     In an alternative embodiment using display systems that feature true color independence, such as on CRT RGB video projectors, the number of measurements taken can be reduced. Because of their color independence, there is no need to measure all color parameter combinations—only the independent values of each color. In the case of RGB color parametric space, if 256 levels are used, only 256+256+256=768 measurements will be required, compared the 16,777,216 measurements required when a display system lacks color independence. 
       FIG. 5  illustrates an example spectral radiance graph  500  for a measurement taken with a red value of 255, and blue and green values of 0 each. 
     Color Lookup Table Determination 
     System  200  uses color lookup tables  208  to map simulated luminance to stimulating color values. That is, color lookup tables  208  indicate for a particular simulated luminance that is part of simulated data stream  210  what corresponding color values of a stimulated image would produce that simulated luminance given a particular sensor and a particular display device. Once the stimulated color values are known they can be sent by image generator  202  to display system  212  and viewed by pilot  216  using sensor  214 . 
     As is known by those of skill in the art, a sensor  214  such as NVGs enables increased perception of the environment by amplifying and translating the wavelengths captured by the sensor. A particular sensor has a spectral response that is characteristic of that sensor and can be determined experimentally using methods known to those of skill in the art, or obtained from the manufacturer of the sensor. The spectral response of the sensor is the response of the sensor to a power at a given wavelength (or range of wavelengths). 
     Thus, simulator engine  204  constructs a color lookup table by iterating through the various color value combinations, e.g., RGB values from 0 to 255. For each color value, simulator engine  204  determines the actual image that would be displayed by the particular display system  212 , and the stimulated luminance value that would be produced by the sensor from the displayed image values. Performing this step for each color value and then sorting by resulting luminance provides a color lookup table  208  that system  200  then can use to map from a luminance value to a color value set that can be used with the specified sensor on the calibrated display system. 
     In an alternative embodiment, luminance values that result in deviant colors—i.e. those colors that vary substantially from grayscale values—are excluded from the lookup table. This has the effect of producing images that while still stimulating the sensor create less distracting colors for an observer not wearing a sensor such as NVGs, as well as being less distracting through peripheral vision of an observer who is wearing a sensor like NVGs, which only covers a subset of the field of view. This takes advantage of the fact that unaided human vision at night or at low light levels is not very perceptive of small color deviations from gray scale. 
     Run-Time Operation 
     System  200  uses color lookup table  208  to render pixels or texels appropriate to the display system  212  and sensor  214  in use in the simulator. Simulator engine  204  takes as input a simulated data stream  210  provided by conventional real-time sensor simulation software or hardware, determines a corresponding stimulating color value set by referring to color lookup table  208 , and generates an image using IG  202  that is then displayed by display system  212 . Because the color lookup table  208  is specific to the display system  212  in use as well as to the sensor in use, the stimulated image generated by IG  202  will look to a pilot  216  using sensor  214  and display system  212  essentially identical to the simulated image originally provided by the simulated stream  210 . However, because the image is stimulated instead of simulated, the pilot has the advantage of being able to participate in a much more real-world simulation, e.g., by wearing NVGs that correctly account for peripheral vision effects, head motion, and the like—and because the stimulated image is accurate for the display system and the sensor in use, the lack of fidelity that previously plagued stimulated image systems is not present when using system  200 . 
     The present invention has been described in particular detail with respect to a limited number of embodiments. Those of skill in the art will appreciate that the invention may additionally be practiced in other embodiments. First, the particular naming of the components, capitalization of terms, the attributes, data structures, or any other programming or structural aspect is not mandatory or significant, and the mechanisms that implement the invention or its features may have different names, formats, or protocols. Further, the system may be implemented via a combination of hardware and software, as described, or entirely in hardware elements. Also, the particular division of functionality between the various system components described herein is merely exemplary, and not mandatory; functions performed by a single system component may instead be performed by multiple components, and functions performed by multiple components may instead performed by a single component. For example, the particular functions of the image generator and so forth may be provided in many or one module. 
     Some portions of the above description present the feature of the present invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are the means used by those skilled in the art of sensor simulation to most effectively convey the substance of their work to others skilled in the art. These operations, while described functionally or logically, are understood to be implemented by computer programs. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules or code devices, without loss of generality. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the present discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     Certain aspects of the present invention include process steps and instructions described herein in the form of an algorithm. It should be noted that the process steps and instructions of the present invention could be embodied in software, firmware or hardware, and when embodied in software, could be downloaded to reside on and be operated from different platforms used by real time network operating systems. 
     The present invention also relates to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, application specific integrated circuits (ASICs), or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus. Furthermore, the computers referred to in the specification may include a single processor or may be architectures employing multiple processor designs for increased computing capability. 
     The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may also be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description above. In addition, the present invention is not described with reference to any particular programming language. It is appreciated that a variety of programming languages may be used to implement the teachings of the present invention as described herein, and any references to specific languages are provided for disclosure of enablement and best mode of the present invention. 
     Finally, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention.