Abstract:
A method and apparatus for calibration of a projection system, comprising projecting visible and non-visible images on at least one image plane, detecting said non-visible images projected on the image plane, and calibrating projection of the visible images using the non-visible images. The visible and non-visible images are simultaneously projected and the non-visible images are continually monitored for automatic calibration of composite displays, without taking the projection system off-line. In addition, calibration can be maintained through continuous automatic adjustment using invisible calibration patterns, even if the system is disturbed while it is operating.

Description:
FIELD 
       [0001]    This specification relates generally to projection systems, and specifically to a method and apparatus for automatic calibration of projection systems using non-visible light. 
       BACKGROUND 
       [0002]    It is known in the art to provide projection systems with multiple overlapping displays. Such systems may be used to create arbitrarily large and irregularly shaped composite displays suitable for use in immersive environments (e.g. simulators) and large venues such as shopping malls and amphitheatres. One challenge with such composite displays is maintaining calibration (e.g. geometrical alignment, brightness equalization, etc.) of the multiple displays. Manual calibration is often time consuming, and requires that the projection system be ‘off-line’ while calibration is being performed. In an effort to at least partially address this challenge, machine vision systems have been designed for automatically calibrating composite displays more quickly and accurately than is possible with manual calibration. Although such machine vision systems result in faster calibration than is possible with manual adjustment, the projection system must nonetheless continue to be taken off-line in order to project the calibration patterns required to effect the automatic calibration. It is also difficult to automatically determine when a system needs to be realigned without taking the system off-line. 
         [0003]    Projection systems are also known in the art for projecting non-visible light in addition to visible light. Such systems are used in applications, such as night vision (NVIS) applications, where projection of images in non-visible spectra is desirable. Such non-visible images are generally viewable through the use of special equipment. An example of a non-visible image is an image projected using infrared (IR) light and hence, in these instances, the non-visible images are viewable in the simulation/visualization environment through the use of NVIS goggles and/or IR image detectors. 
       SUMMARY 
       [0004]    The inventors have recognized that such prior art projectors may be used to simultaneously project visible and non-visible light and continually monitor patterns of invisible calibration patterns for automatic calibration of composite displays, without taking the projection system off-line. In addition, calibration can be maintained through continuous automatic adjustment using invisible calibration patterns, even if the system is disturbed (e.g. accidentally bumped) while it is operating. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0005]    The foregoing and other aspects of the invention are described in greater detail below, with reference to the following figures, in which: 
           [0006]      FIG. 1  is a block diagram showing a projection system for performing automatic calibration using non-visible light, according to a non-limiting embodiment; 
           [0007]      FIG. 2  is a block diagram showing details of the projection system in  FIG. 1 ; 
           [0008]      FIG. 3  is a block diagram showing details of a projector head assembly of the projection system of  FIG. 1 ; 
           [0009]      FIG. 4  is a flowchart showing an exemplary method of calibrating the projections system shown in  FIGS. 1-3 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0010]      FIG. 1  depicts a projection system  10  for projecting visible images from an image generator  11  and non-visible images from a calibration controller  12  on a display  13 . Although the calibration controller  12  is illustrated as being a separate component external to the projection system  10 , all or portions of the calibration controller  12  may be incorporated into the projection system  10  or image generator  11 . 
         [0011]    The calibration controller  12  triggers generation of at least one non-visible calibration pattern (either via the controller  12 , the image generator  11  or the projection system  10 ), for projection onto a display  13  (e.g. one of a plurality of displays comprising a composite display). The non-visible calibration pattern is projected via a non-visible light channel  15  simultaneously with projection of the video image via a visible light channel  14 . The non-visible light can be detected, for example, using off-the-shelf camera equipment. For example, a standard CCD-based camera  16  which is capable of detecting light in the near-IR portion of the spectrum can therefore be used to detect the non-visible light by filtering the visible light using a visible light filter  17 . 
         [0012]    The detected non-visible calibration patterns are transmitted back to the calibration controller  12  for performing calibration (and re-calibration) of the projection system  10  using known techniques. For example, warp-capable projection systems such as the Matrix™ series of projectors from Christie Digital Systems Canada, Inc. can perform calibration through geometry correction and edge blending algorithms. Alternatively, calibration can be performed through image correction at the image generator  11 . 
         [0013]    As discussed above, the re-calibration can be performed using non-visible calibration patterns without interrupting the visible light channel  14 . This is particularly advantageous for projections systems deployed in high usage environments such as theme parks, simulators, command and control centers, etc., where shutting down the system for calibration would be disadvantageous. 
         [0014]    One embodiment of projection system  10  for generating non-visible light patterns is set forth in greater detail below with reference to  FIGS. 2 and 3 . 
         [0015]    The projection system  10  comprises a projector head assembly  101  having a light source and modulator  105  for emitting visible light (i.e. light in the visible light spectrum from about 380 to 750 nm, or a subset of the visible light spectrum) and a non-visible light source for emitting non-visible light (i.e. light outside of the visible light spectrum, such as infrared and/or ultraviolet light). 
         [0016]    The image generator  11  and calibration controller  12  are shown connected to projection system  10  via data links  130  and  134 , respectively. The image generator  11  comprises a processing unit  131 , a communication interface  132  and a memory  133 . The processing unit  131  is enabled for receiving visible data representing the visible images  113  to be projected by the projector  101 . The visible data can represent color or monochrome images, as desired. The image generator includes an interface  132  for communicating with the projector head assembly  101 , and specifically for conveying the video data to the projector head assembly  101  via link  130 . 
         [0017]    The calibration controller  12  comprises a processing unit  135 , a communication interface  136  and a memory  137 . The processing unit  135  is enabled for generating and transmitting calibration patterns to the projection system  10  via a data link  134  and for receiving the non-visible light signals from camera  16  representing the calibration patterns projected onto image plane  13 . 
         [0018]    The processing unit  117  then merges or replaces a portion of the visible data received from image generator  11  with at least a portion of the non-visible data received from calibration controller  12  such that the visible images  113  and the non-visible images  114  are co-projected by the projector head assembly  101 . For example, in one embodiment visible data is received from image generator  11  at 60 Hz and an image is projected at 120 Hz alternating between non-visible calibration patterns and visible images. 
         [0019]    Upon receipt of the non-visible light signals from camera  16 , processing unit  135  determines whether re-calibration is required and if so performs image calibration or re-calibration in accordance with known algorithms and transmits calibration control signals to the projections system  10  via data link  138 . 
         [0020]    The video signal (comprising the combined visible data and the non-visible data) from processing unit  117  is applied to light source and modulator  105  to modulate the visible and non-visible light and thereby generate and/or transmit visible and non-visible light in a sequence that is coordinated by the processing unit  117 . The visible images  113  and non-visible images  114  are then both projected onto the image plane  13  by the projection optics  116 . 
         [0021]    Attention is now directed to  FIG. 3  which depicts a non-limiting embodiment of the projector head assembly  101 comprising a processing unit  117  and an interface  118 . The projector head assembly  101  further comprises projection optics  116  for projecting visible images  113  and non-visible images  114  onto image plane  13 . 
         [0022]    The projector head assembly  101  further comprises a broadband light source  109  and a spectrum splitter  410  for splitting light from the broadband light source  109  into non-visible light (e.g. IR light) and respective components of visible light, for example red, green and blue components. In some embodiments, the spectrum splitter  410  comprises, at least one of a prism and one or more dichroic filters (not pictured). 
         [0023]    The projector head assembly  101  further comprises a plurality of light modulators  415   r,    415   g,    415   b  for receiving and modulating a respective component of visible light from the spectrum splitter  410  to form a respective component ( 413   r,    413   g,    413   b ) of visible images  113 . The projector head assembly  101  further comprises at least one non-visible light modulator  416  for receiving and modulating non-visible light from the spectrum splitter to form the non-visible images  114  independent of the visible images  113 . For example, the non-visible light modulator  416  can be enabled to modulate infrared (IR) and/or ultraviolet (UV) light. In some embodiments, the projector head assembly  101  can comprise a plurality of non-visible light modulators, which can be similar to non-visible light modulator  416 , each of the plurality of non-visible light modulators enabled to modulate different (and/or the same) spectra of non-visible light. In these embodiments, the spectrum splitter  410  is further enabled to split the broadband light into a plurality of non-visible light spectra. For example, the projector head assembly  101  can comprise at least a first non-visible light modulator for modulating IR light, and a second non-visible light modulator for modulating UV light. Other combinations of non-visible light modulators for modulating non-visible light (e.g. different ranges of IR and/or UV light) are within the scope of present the illustrated embodiments. 
         [0024]    The projector head assembly  101  further comprises an optical combiner  420  enabled for combining the non-visible images  114  and respective components ( 413   r ,  413   g,    413   b ) of the visible images  113  from the light modulators  416  and  415   r,    415   g ,  415   b,  respectively and directing the combined images to the projection optics  116 . The projection optics  116  are enabled to focus the non-visible images  114  and visible images  113  onto the image plane  13 . For example, in some embodiments, the optical combiner  420  can comprise at least one of a dichroic filter and a beam splitter, each used in a combining mode. Other suitable optical combiners are within the scope of present embodiments. As in  FIG. 1 , while  FIG. 4  depicts the visible images  113  and the non-visible images  114  as being projected in different directions, it is understood that they have been depicted as such for clarity only. Indeed, it is further understood that each of the visible images  113  and the non-visible images  114  is projected in the image plane  13  and the visible and non-visible images are substantially aligned. Each of light modulators  415   r,    415   g,    415   b  and the non-visible light modulator  416  can be controlled to operate in parallel or in sequence as desired. 
         [0025]    Additional details of the projection system  10  are set forth in co-pending patent application Ser. No. 12/289,701, filed Oct. 31, 2008, entitled METHOD, SYSTEM AND APPARATUS FOR PROJECTING VISIBLE AND NON-VISIBLE IMAGES, the contents of which are incorporated herein by reference. 
         [0026]    Attention is now directed to  FIG. 4  which depicts a method for automatic calibration of the projection system  10  using non-visible light. At step  400 , visible images from image generator  11  and non-visible images from calibration controller  12  are projected onto an image plane  13  via the projection system  10 , as discussed above. 
         [0027]    Next, at step  410 , the camera  16  detects the non-visible images (i.e. calibration patterns). The detected non-visible calibration patterns are transmitted back to the calibration controller  12  for performing calibration (and re-calibration) of the projection system  10  at step  420  using geometry correction and/or edge blending algorithms, as is known in the art. As discussed above, the re-calibration can be performed using non-visible calibration patterns without interrupting the visible light channel  14 . 
         [0028]    Persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible for implementing the embodiments, and that the above implementations and examples are only illustrations of one or more embodiments. The scope, therefore, is only to be limited by the claims appended hereto.