Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N17/00—Diagnosis, testing or measuring for television systems or their details
  • H04N17/04—Diagnosis, testing or measuring for television systems or their details for receivers
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
  • G06F3/14—Digital output to display device ; Cooperation and interconnection of the display device with other functional units
  • G06F3/147—Digital output to display device ; Cooperation and interconnection of the display device with other functional units using display panels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3141—Constructional details thereof
  • H04N9/3147—Multi-projection systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3191—Testing thereof
  • H04N9/3194—Testing thereof including sensor feedback
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/02—Composition of display devices
  • G09G2300/026—Video wall, i.e. juxtaposition of a plurality of screens to create a display screen of bigger dimensions
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/001—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes using specific devices not provided for in groups G09G3/02 - G09G3/36, e.g. using an intermediate record carrier such as a film slide; Projection systems; Display of non-alphanumerical information, solely or in combination with alphanumerical information, e.g. digital display on projected diapositive as background

Definitions

• the present invention relates to electro-optical display apparatus.
• the invention is particularly useful in large interactive displays of the type enabling one or more persons to interact with the display, by adding to, deleting from, or otherwise changing the displayed information; and the invention is therefore described below with respect to such an application.
• electro-optical display apparatus comprising: a screen; a plurality of modular units each including a projector for receiving electrical signals, converting them to optical images, and projecting the optical images via an optical projection system onto the screen; the plurality of modular units being arranged in a side-by-side array such as to produce a combined display on the screen; the apparatus further comprising a calibration system for detecting distortions in the combined display caused by the projection system of each modular unit and for modifying the electrical signals applied to the projector of each modular unit to correct the combined display with respect to the detected distortions .
• each of the modular units further includes an image sensor for sensing an optical image on the screen and for converting the image to electrical signals; and an optical imaging system for imaging the screen on the image sensor.
• the calibration system also detects distortions in the combined display caused by the optical imaging system and modifies the electrical signals applied to the projector of each modular unit to correct the combined display also with respect to those detected distortions .
• the screen is a light-transmission screen of a size and configuration to overlie all the modular units.
• the calibration system may also include a two-dimensional array of reference points of known locations on the face of the screen.
• the two-dimensional array of reference points is defined by the intersection points of a plurality of horizontal reference lines and a plurality of vertical reference lines on the screen.
• the two- dimensional array of reference points are the ends of optical fibers on the screen.
• the reference lines may also be the joint border lines of the individual module screens.
• the selected calibration technique may be used for on-line calibration or only for off-line calibration.
• apparatus to be constructed from one or more modular units of the same design, size and configuration, and to be assembled according to the particular application.
• apparatus can be assembled with two modular units arranged in a straight line, four modular units arranged in a 2 X 2 array, nine modular units arranged in a 3 X 3 array, etc., according to the size of the screen desired for the particular application.
• the depth of the overall display will be the same irrespective of the size of the screen.
• Such an apparatus is capable of grabbing any image that appears on the screen, including images projected on the screen by a light projector or any hand-written script using dry-erase markers, electronic pens, etc.
• the apparatus can also grab the image of any object, e.g., documents, placed against the screen.
• the apparatus can be used not only for displaying documents, but also for storing or transmitting documents. Since the combined screen is not obstructed by the user, the user can conduct a natural flowing presentation. Since the system is modular, the configuration and the size of the combined screen can be fitted to any application; and since the system depth is relatively small, it may be used in office-like environments, or other space-limited environments, such as conference rooms, airport aisles (corridors), etc.
• the calibration system is preferably built into the apparatus as an integral part of the apparatus so that it can be conveniently used to recalibrate the system as frequently as may be desired, e.g., to compensate for the tendency of the opto-mechanical systems to drift with time and temperature. While the calibration system is particularly useful with respect to a large viewing area apparatus constructed of a plurality of modular units as described above, the calibration system could also be used in a single-unit setup.
• the calibration system generates an image path correction table for each unit for correcting discrepancies between the known locations of the two- dimensional array of reference points on the screen and the corresponding locations of the two-dimensional array of reference points as imaged on the screen. It also generates a projector-path correction table for each unit for correcting discrepancies between the known locations of the two-dimensional array of reference points on the screen and the corresponding locations of the two-dimensional array of reference points as projected on the screen.
• a method of producing an electro-optical display comprising: providing a plurality of modular units each including a projector for receiving electrical signals, converting them to optical images, and projecting the optical images via an optical projection system on a screen; arranging the plurality of modular units in a side-by-side array such as to combine their respective displays to produce a combined display; and calibrating the modular units by detecting distortions in the combined display caused by the optical projection system and modifying the electrical signals applied to the projector of each modular unit to correct the combined display with respect to the detected distortions .
• Electro-optical display apparatus constructed in accordance with the foregoing features may be used in a large number of applications, including conference rooms, control centers, and electronic bill-boards, as well as in front/rear large projection systems. Further features and advantages of the invention will be apparent from the description below.
• Fig. 1 diagrammatically illustrates one example of a display apparatus in accordance with the present invention including four modular units, and a combined screen overlying the screens of all the modular units;
• Fig. 2 diagrammatically illustrates one construction of a modular unit used in the display apparatus of Fig. 1 ;
• Fig. 3 diagrammatically illustrates the optical system in one of the modular units in the apparatus of Fig. 2;
• Fig. 4 more particularly illustrates the folded mirror arrangement in the optical system in one of the modular units
• Fig. 5 diagrammatically illustrates another type of optical system that may be used in each modular unit
• Figs. 6a-6e illustrate various types of distortions produced in the optical systems of the modular units which distortions are to be corrected by the calibration systems of the modular units;
• Fig. 7 illustrates a calibration grid on the combined screen used for calibrating the modular units
• Figs . 8a and 8b are longitudinal and transverse sectional views along lines 8a—8a and 8b—8b, respectively, of Fig. 7;
• Fig. 9 diagrammatically illustrates one technique for correcting non-uniformity in light intensity in the modular units
• Fig. 10 illustrates an alternative structure of a combined screen for calibrating the modular units for both distortions caused by the optical systems and non-uniformity in light intensity in the modular units;
• Figs. 11a and 11b diagrammatically illustrate one technique for correcting spatial distortions in the imaging systems of the modular units
• Figs. 12a and 12b diagrammatically illustrate one technique for correcting spatial distortions in the imaging- path optical system, and in the projector optical systems, respectively, of the modular units;
• Fig. 13 diagrammatically illustrates one technique for eliminating overlaps and gaps between the displays in the screens of the plurality of modular units
• Fig. 14 is a flowchart illustrating one example of the overall calibration technique, constituted of the four operations, A, B, C and D;
• Fig. 15 is a flowchart illustrating operation A in Fig. 14;
• Fig. 16 is a flowchart illustrating operation B in Fig. 14;
• Figs. 16a, 16b and 16c are flowcharts illustrating certain sub-operations of operation B;
• Fig. 18 is a flowchart illustrating operation D in Fig. 14 for correcting non-uniformity in light intensity between the various modular units;
• Fig. 19 illustrates electro-optical display apparatus including a plurality of projectors each equipped with a Fresnel lens, and having a common diffusive screen to produce uniformity from any viewing angle;
• Fig. 20 is a schematic view of the Fresnel lens array in the apparatus of Fig. 19;
• Figs. 21a, 21b and 21c diagramatically illustrate the front, side and top of a projector provided with mechanical means for making some of the mechanical corrections as an alternative to digital corrections;
• Figs. 22a, 22b and 22c are diagrams from the front, side and top, respectively, illustrating more particularly one manner of making some of the mechanical corrections of Figs. 21a-21c;
• Figs. 23a, 23b and 23c are diagrams illustrating different camera positioning arrangements to allow better distortion correction
• Fig. 24 is a flowchart illustrating one example of the operations involved in using the camera positioning arrangement of Fig. 23c for correcting color-convergence distortions in a single projector;
• Figs. 25 and 26 are diagrams helpful in explaining the flowchart of Fig. 24;
• Fig. 27 is a flowchart illustrating one example of the operations involved in similarly correcting geometrical distortions; and Fig. 28 is a diagram helpful in explaining the flowchart of Fig. 27;
• Fig. 1 illustrates one form of display apparatus constructed in accordance with the present invention and constituted of four modular units M.. -M, arranged in a 2 x 2 array in abutting relation such as to combine their respective displays to produce a combined display.
• the apparatus further includes a combined screen, generally designated 2, of a size and configuration to overlie all the modular units . All four modular units are of the same design, size and configuration so that they can be assembled to produce a combined screen of the size and configuration desired for any particular application.
• each modular unit M..-M. is a modular unit of each modular unit M..-M.
• Each modular unit includes a housing 3, and a rear projector 5 for receiving electrical signals, converting them to optical images, and projecting the optical images onto screen 2 via an optical projection system.
• the rear projector 5 is driven by a graphics computer 6 which receives the electrical signals via an input port 7 from a systems computer SC.
• Graphics computer 6 is preferably constructed as a separate unit and not built into the module.
• Each modular unit further includes an image sensor 8 for receiving an optical image on the screen of the respective unit via an optical imaging system and for converting the image to electrical signals. These electrical signals are supplied to the graphics computer 6 for driving the rear projector 5 to include also the images appearing on screen 2.
• Rear projector 5 is preferably an active color LCD (liguid crystal display) projector. However, it could be a Digital Micromirror Device Projector, or any other known type of projector.
• Image sensor 8 is preferably a CCD (charge coupled device) commonly used today in area cameras. However, it could be any other type of image sensor, such as a tube camera, a scanner, etc.
• the graphics computer 6 receives electrical signals from the image sensor 8, and from the systems computer SC via the input port 7, and generates the signals (e.g., video signals) driving the rear projector 5.
• Graphics computer 6 further includes a built-in calibration system for calibrating the modular unit with respect to distortions (e.g., spatial, intensity, and color) in the projected images in the respective modular unit so as to reduce these distortions as appearing in the combined screen 2 for all the modular units.
• the calibrating system also eliminates overlaps and gaps in the combined display on screen 2 of the four modular unit displays.
• Figs. 3 and 4 diagrammatically illustrate the optical projection system for projecting the image produced by the rear projector 5 of the respective modular unit on screen 2, and also the optical imaging system for imaging the screen 2 on the image sensor 8 of the respective modular unit.
• the optical projection system includes a lamp and reflector 10.
• This lamp may be of any known type (e.g., tungsten halogen lamp, silver halogen lamp, arc lamp, etc.) which illuminates, via a condensor lens 11 and IR/UV filter 11a, an LCD light modular panel 12 straddled by a pair of Fresnel lenses 13, magnified by a projection lens 14, and projected by folding mirrors 15a, 15b, 15c, onto the screen 2.
• the optical imaging system images the screen 2 onto the image sensor 16 via mirrors 15a-15c and a lens system 17.
• the light reflected from the screen 2 thus represents a combined image, namely a superposition of the image produced by the rear projector 5, and any image written or projected onto the front side of the screen and imaged onto the image sensor 8.
• the graphics computer 6 stores a replica of the rear-projected image and of the captured combined image. From these two images, the system can determine the user input, namely the image written or projected onto the screen from the front side of the screen.
• Another technique for grabbing the image written or projected on the front of the screen is by momentarily turning off the image produced by the rear projector, and subsequently reading the image written or projected on the front side. This technique simplifies the determination process of the user input since the grabbed image does not include the rear projected image.
• Both the optical projector system and the optical imaging system inherently produce distortions, which are detected and corrected by the graphics computer 6, as will be described more particularly below, so as to produce a more satisfactory display on screen 2 combining the images generated by each of the modular units M..-M..
• Fig. 5 diagrammatically illustrates another optical arrangement that may be used for each of the modular units M..-M..
• the modular unit is provided with a separate optical projection system diagrammatically illustrated at 18, and a separate optical imaging system diagrammatically illustrated at 19.
• Fig. 6a illustrates a rectangular undistorted or ideal image UI having a longitudinal axis LA and a transverse axis TA.
• Fig. 6a also illustrates a pin-cushion type distorted image PDI, wherein it will be seen that the amount of distortion varies with the distance from the longitudinal axis LA and transverse axis TA.
• Fig. 6b illustrates a barrel-type distorted image BDI with respect to the undistorted image UI .
• Fig. 6c illustrates how a display combining the displays of the four modular units
• Fig. 6d illustrates an undistorted straight, horizontal line UL, to be projected on the combined screen by the four modular units M.-M.; whereas Fig. 6e illustrates at DLpc how that line would be distorted by the pin-cushion effect, and DSI the resultant screen image gray level if the distortions are not corrected.
• the optical distortions produced by the optical system can frequently be passed without notice; however, when producing a combined image wherein a plurality (in this case four) displays are "stitched" together in a “seamless” manner, distortions produced in each modular unit are very much noticeable in the combined display.
• the major distortions are:
• a calibration system is needed to detect these distortions and to correct the combined image with respect to these distortions.
• the calibration system to be described below corrects for most of the above distortions. While the calibration system can be provided as a separate system, to be used during the first setup of the display system or whenever else it may be desired to calibrate the system, the calibration system included in the apparatus to be described below is built into the system as an integral part. It therefore has the important advantages that it can be more frequently used in a convenient manner to correct for the tendency of optical-mechanical systems to drift with time and temperature .
• the built-in calibration system illustrated in Fig. 7 includes a plurality of horizontal reference lines 20 and a plurality of vertical reference lines 21 formed on the face of the combined screen 2 such that the intersection points of the two groups of reference lines define a two- dimensional array or grid of reference points 22 of precisely-known locations on the face of the combined screen 2.
• the reference lines 20 and 21 are produced by forming V-grooves 23 on the face of the combined screen 2 and filling the grooves with a luminescent material 24 which is excited by a horizontal light source 25 extending along one edge (the upper edge) of the combined screen 2, and a vertical light source 26 extending along one side (the left side) of the combined screen.
• Each of the two light sources 25, 26 is enclosed by a reflector 25a, 26a, formed with an opening 25b, 26b, facing the combined screen 2 so as to direct the light towards the luminescent material 24 carried by the combined screen.
• the luminiscent material 24 is an ultraviolet (UV) fluorescent material
• the light sources 25, 26 are UV light sources which cause the material 24 to fluoresce.
• the combined screen 2 may be constructed of a rigid light transmissive (translucent) panel 27 formed on its inner face 27a with the V-grooves 23 filled with the luminescent material 24 defining the grid of reference lines 20, 21, the opposite face 27b of the transparent panel serving as a write-on surface by a user.
• the combined screen 2 further includes a flexible plastic sheet 28, e.g., of "Mylar” sheet material having a rough surface, covering the grooved face 27a of the transparent panel 27 and the luminescent material 24 within the V-grooves 23.
• the two-dimensional array of reference points 22, defined by the intersections of the horizontal and vertical lines 20, 21, is used for detecting and correcting distortions caused by the optical systems in each modular unit, as described more particularly below.
• Fig. 9 diagrammatically illustrates a technique that may be used for calibrating for non-uniformity in the light intensity of the modular units M..-M..
• the combined screen 2 is provided with a plurality of optical fibers 30 having one of their ends 31 located on the inner face of the combined screen 2 to sense the light intensity at the respective location.
• the opposite end of each optical fiber 30 is connected to a light detector 32 producing an output corresponding to the light intensity at the respective location 31.
• the outputs of light detectors 32 are connected to a control circuit 33 which controls the intensity of the light sources in the rear projectors (5, Fig. 2), constituting the projection system designated by block 34 in Fig.
• the imaging system 35 including the light sensors 8 of the modular units, is separate from the projection system 34, similar to the arrangement of Fig. 5, and also controls the control circuit 33.
• Fig. 10 illustrates another technique that may be used for detecting and correcting not only distortions in the optical systems of the respective modular units M..-M., but also non-uniformity in the light intensities of the projector devices in these modular units.
• combined screen 2 includes a plurality of optical fibers 41 having one of their ends 42 embedded in the face of the combined screen at precisely-known locations to define the two-dimensional array of reference points of known locations on the face of the combined screen.
• the opposite end of each optical fiber 41 is connected to a light emitter 43 (e.g., a LED), and also to a light sensor 44 (e.g., a photodetector) via a beam splitter cube 45.
• the light emitter 43 and light sensor 44 of each optical fiber 41 are connected in parallel so as to be selectively enabled .
• optical fibers 41 are to be used for producing the two-dimensional array of reference points
• the light emitters 43 of the optical fibers 41 are energized; and when the optical fibers 41 are to be used for detecting and correcting non-uniformity in light intensity of the rear projectors in the modular units, the light sensors 44 are enabled.
• Fig. 14 is a general flowchart illustrating the overall calibration technique.
• the calibration is constituted of four main operations, designated Operations A, B, C and D, respectively, as appearing in blocks 51-54.
• Operation A involves the calibration of the imaging path in each module.
• the distortions in the optical imaging system, from the screen 2 to the image sensor 8 in the respective module are detected and corrected by the graphics computer 6 of the respective module. This operation is more particularly illustrated in the flowchart of Fig. 15.
• Operation B involves the calibration of the projector path in each module.
• distortions in the optical projection system from the rear projector 5 to the screen 2, are detected and corrected also by the graphics computer 6 of the respective module.
• This operation is more particularly illustrated in the flowcharts of Figs. 16, 16a, 16b and 16c.
• Operation C involves the calibration of the array of projectors in the plurality of modular units M 1 -M. to fine-tune the combined image projected on the combined screen 2, including eliminating overlaps and gaps between the displays in each of the modules caused by distortions in the optical sytems .
• This operation as well as the other previously-described distortion-correction operations, is performed by the graphics computer 6 in the respective modules M.-M. , and also by the systems computer SC which controls all the modules, and is illustrated in the flowcharts of Figs. 17 and 17a.
• Operation D involves the calibration for non-uniformity in light intensity levels among all the modules.
• this operation the light intensity levels of the images projected on the combined screen from all the modular units are detected and controlled to reduce non- uniformity.
• This operation is also performed by the graphics computer 6 of the modular units, as well as by the systems computer SC controlling all the modular units, and is illustrated in the flowchart of Fig. 18.
• the first step is to energize the two tubes 25, 26 (Fig. 7) of the first modular unit M 1 in order to produce in that modular unit the visual reference lines 20, 21 (Fig. 7) defining, at their intersections 22, the two-dimensional array of reference points of known locations on the face of the combined screen 2.
• This step is indicated by block 61 in Fig. 15.
• the ideal grid produced by these reference lines is shown by horizontal lines HL hinder-HL, and vertical lines VL ⁇ -VL,, respectively, in Fig. 11a.
• the image sensor 8 in the respective module grabs the image produced on the combined screen 2 for the respective module (block 62).
• the actual image "seen" by the image sensor is not the ideal grid illustrated in
• Fig. 11b That is, whereas all the horizontal and vertical lines in the ideal grid of Fig. 11a are straight and perpendicular to each other, in the distorted grid illustrated in Fig. 11b all the horizontal lines HL ⁇ 0 ⁇ -HL6, , and vertical lines VL' ⁇ -VL 1 , (except lines HL_. and VL-. along the longitudinal axis and the transverse axis TA) are distorted because of the inherent distortions of the imaging-path optics. These distortions increase with the distance of the respective line from the longitudinal axis LA and transverse axis TA.
• intersection points of the horizontal and vertical reference lines, defining the two-dimensional array of reference points are determined in the distorted grid of Fig. 11b (block 63), and are correlated with the known locations of the reference points in the ideal grid of Fig. 11a (block 64).
• the graphics processor 6 for the respective module then calculates a two-dimensional, best-fit cubic function for transforming the intersection points of the distorted grid to those of the ideal grid.
• Such calculations are well known; see for example "Image Reconstruction by Parametric Cubic Convolution" by Stephen K. Park and Robert A. Schowengerdt, published in "Computer Vision, Graphics and Image Processing" 23, 258-272. This procedure is performed for each horizontal pair of lines (box 65), and for each pair of vertical lines (box 66).
• a two-dimensional Image-Path Correction Table is then produced and stored in the graphics computer 6 for the respective module for each of the reference points in two- dimensional array reference points (block 67).
• the foregoing steps are the repeated for all the remaining modules M -M 4 (block 68).
• the result of blocks 65 and 66 is a set of distortion functions for each horizontal line 20 and each vertical line 21 of the stored ideal grid (Fig. 7), i.e., seven (in the described example of Fig. 11a) horizontal functions and seven vertical functions.
• the Image-Path Correction Table calculated in block 67 is a correction table which enables the system hardware to convert the grabbed distorted images of the imaging path into distortion-free images.
• the above-described technique for performing Operation A has a number of advantages, including the following:
• the calculation of a best-fit function filters out (smoothes) any local noise generated by the imaging path, or local error in the reference grid.
• the calculation of a cubic function for each reference line enables determination, by interpolation, of all the other points that are not on the reference grid.
• the representation of the distortation data by a cubic function (as distinguished from a table) enables handling and storing the data in a more compact manner .
• Fig. 16 illustrates the steps of Operation B (block 52, Fig. 14) involving the calibration of the projector path in each module. This operation detects the distortions produced in the projector path optics, i.e., from the rear projector 5 of the respective module to the combined screen 2, and produces a Projector Path Correction Table for correcting these distortions.
• the stored ideal grid (Fig. 11a) is projected onto the combined screen 2 (block 71), which image is distorted by the projector path optics.
• the projected image is partially reflected from the screen onto the image sensor (8, Fig. 2) of the respective module (block 72), which grabbed image is distorted by the distortions in the imaging-path optics.
• This distorted image of the grid is illustrated in Fig. 11b.
• the graphics processor (6, Fig. 2) of the respective module corrects the intersection points (reference points) in the distorted grid (block 73) according to the flowchart illustrated in Fig. 16a.
• a calculation is made from the Image-Path Correction Table (produced in Operation A according to the flowchart of Fig. 15) of the four surrounding grid reference points; and then by using bi-linear interpolation (block 73b), each such pixel is relocated to the correct location.
• the graphics computer of the respective module has now an image of the projected screen that is free of the distortions of the imaging-path optics, and includes only the distortions of the projection-path optics.
• a Projection-Path Correction Table is then calculated for the projection path optics (block 74) .
• the Projector-Path Correction Table provides, for every ideal-grid reference location, the correct locations of the projected reference points in the distorted grid.
• the manner in which the Projector-Path Correction Table (block 74) is calculated is more particularly illustrated by steps 74a-74f in Fig. 16b.
• a check is made as to whether the distortion is smaller than the threshold (block 75). If not (i.e., the distortion is larger than the threshold) the correct location of the reference point is determined and stored according to the flowchart illustrated in Fig. 16c and the diagram of Fig. 12b.
• Operation C (block 53, Fig. 14) is now performed to calibrate the array of projectors to form one combined projector image.
• the projector displays of the four modular units are treated as four tiles with parallel coordinate systems on the plane of the combined screen 2, and are electronically moved vertically and horizontally until they cover the face of the combined screen 2 with no overlaps and no gaps .
• This operation is more particularly described in Figs. 17 and 17a, and is illustrated in the diagram of Fig. 13.
• the horizontal lines are projected from the first module (block 81 ) , and the image of the horizontal lines from the imaging path of the first module is grabbed (block 82).
• the horizontal lines from the second module are then projected (block 83), and the image of the horizontal lines from the imaging path of the first module are grabbed (block 84).
• the location of the stored image in the projector of the second module is then moved laterally by a horizontal offset, and vertically by vertical offset, until the lines are aligned (block 85).
• the foregoing steps are repeated for the third and fourth modules by calculating the horizontal offset and vertical offset for these modules (block 86).
• Operation D is performed (block 54, Fig. 14) for detecting and correcting non-uniformity in the light intensity among all the modules.
• This operation is more particularly illustrated in the flowchart of Fig. 18, and uses the light intensity detectors (optical fibers 30 of Fig. 9, or 41 of Fig. 10) for this purpose.
• Illumination differences between the modules are global in nature, meaning that the non-uniformity profiles of the modules are similar in shape, but non- similar in amplitude.
• the difference beween the ampliudes is a result of differences in the brightness of the lamps in each module and differences in the optical attenuation of each module .
• the variation of illumination within each module are gradual at very low spatial frequency.
• the non-unformity of the illumination of the screen of each module may behave according to a known physical behavior, e.g., according to the following:
• This non-uniformity will be corrected, for each module, by adjusting the gray level of each module stored image.
• the adjustment of the gray level uses the light- modulator's capacity to modulate its transparency in an almost continuous way.
• the graphics processor will generate an image which has a value of 255*( 1 -0.314) , or 175 gray levels in the middle pixels of the screen, and 255 in the corner pixels.
• the gray level of the other pixels will be calculated in accordance with Eq. 1. These values will cause the light modulator to attentuate the transmitted light in such proportion that the illumination on the module's screen will be flat (uniform) over the entire face of the screen.
• the system uses sensing detectors in each module which are capable of reading the average brightness level of light projected on the screen.
• the light sensors are comprised of optic fibers whose tips are attached to the face of the screen, shown at 31 in Fig. 9, and at 42 in Fig. 10. Each fiber tip collects a fraction of the light projected on the screen and transfers this light to the light detector.
• the fiber by itself interferes minimally with the projected image due to the fact that the fiber is extremely thin (around 100 ⁇ m) and the fact that only the fiber tip is close to the screen, whereas most of the fiber length is away from the screen and out of focus.
• the light sensors readout (of the light level projected on the screen) will be inputs to the graphics processor.
• the graphics processor will use this input to calculate the difference between the modules and to control the attenuation of the light modulators, as described in step (1) of the calibration.
• Figs. 19 and 20 illustrate four projectors 100 (only two of which are seen in the top view of Fig. 19), each having a drive 102 providing six degrees of movement.
• Each projector includes a Fresnel lens 104 which collimates the light from the respective projector. All the Fresnel lenses are covered by common screen 106, e.g. constructed with a lenticular or a diffusing surface, for scattering the light and thereby providing more uniformity from any viewing angle.
• a blocking element 108 is mounted by a member 110 to underlie the junctures between adjacent Fresnel lenses 104 in order to reduce overlapping of the light from the projectors and thereby to produce a seamless combined display.
• Figs. 21a-21c also illustrate how the drives 102 of the projectors 100 can be controlled for correcting translation distortions (x, y), rotation distortions (R), magnification distortions (M) , and also distortions due to the Keystone effect (KSx, KSy) .
• Pin cushion (PC) and barrel distortions can.be corrected by using curved mirrors, e.g. for one or more of the folding mirrors 15a-15c in Fig. 4.
• Color convergence distortions may be corrected digitally by moving the respective pixel elements the required sub-pixel distances as described earlier.
• Figs. 22a-22c are front, side and top views, respectively illustrating one manner of providing each projector drive 102 with six degrees of movement. Thus, the arrangement illustrated in Figs.
• 22a-22c includes seven plates 111-117 supported one on top of the other, the upper most plate 117 supporting the projector 100.
• Plate 112 is movable vertically with respect to plate 111 to correct for y-translation distortions; plate 113 is slidable horizontally on plate 112 to correct for magnification differences (M) ; plate 114 is movable on plate 113 along the x-axis to correct for X-translation distortions (X); plate 115 is pivotally mounted to plate 114 about axis 115a (Fig.
• plate 116 is pivotally mounted about a central axis 116a to plate 115 to correct for the Keystone distortions KSy; and plate 117 is pivotal about pivot 117a to plate 116 to correct for rotational distortions (R) .
• Figs. 23a-23c illustrate different camera positionings with respect to the screens (preferably normal to the screen in a symmetric way) for the four projectors.
• Fig. 23a illustrates four cameras 121-124 each located to image the center of the respective projector screen 131-134
• Fig. 23b illustrates the four cameras 141-144 located to image the edges of the four screens 151-154
• Fig. 23c illustrates five cameras 161-165 located to image the corners of the four screens 171-174.
• the edge positioning arrangement illustrated in Fig. 23b, and the corner positioning arrangement illustrated in Fig. 23c allow better distortion correction, since the same camera views more than one module image and can be centred around a more problematical region.
• the correction of color distortions is done by modifying the R/G/B components of each projected pixel. Intensity uniformity correction is done by the same mechanism and is practically a side effect of the color correction mechanism. For example, if G and B (i.e. the Green and Blue components, respectively) are not changed and R (the Red component) is multiplied by 0.5, then the pixel becomes less "reddish”. However, If G, B and R are all multiplied by 0.5 then the hue is unchanged but the intensity decreases.
• each projector uses its own lamp to project the image, and each lamp has a unique emitted spectra signature which is determined by the exact manufacturing conditions and which is also changed over time (generally, the emitted light gets "redder” and the intensity gets lower as time evolves; this is true for metal-halide lamps which are commonly used in projectors. Thus each projector produces slightly different colors relative to its neighbours.
• the second reason (which mainly applies to intensity corrections) is a non-uniform light intensity (generally the center of the image is more illuminated than the outer parts) emitted from the projector due to the internal optical system.
• the color distortions estimation is done as part of the system calibration phase. It is based on using the video cameras (CCDs) as color measuring tools. Each camera is aimed towards the border of a plurality of adjacent regions, e.g., as shown in Fig. 23b or Fig. 23c. Thus the camera is used first of all to measure the relative color differences between neighboring projectors. This is done by repeating several times the following basic step (which is comprised of the following operations) :
• ( 2 ) Capture a snapshot of the area covered by the projectors. This step may be repeated several times to improve the SNR by averaging the snapshots .
• ( 3 ) Analyze the captured image to estimate R./G./B. of the two (or more) projectors, as seen by the camera e.g., in the Fig. 23b or 23c arrangement. This is done by simply averaging the pixels which were projected by each projector separately.
• This basic step is repeated many times for various R/G/B configurations subject to the limitation that only one color component takes a non-zero value. There is no need to measure complex R/G/B configurations since they are all linear combinations of the basic R/O/O, 0/G/0 and O/o/B patterns .
• the next step is to convert the R./G./B.
• Transformation A simple linear transformation (using a 3x3 matrix) which result in a new R/G/B triplet.
• the flowchart of Fig. 24 illustrates the foregoing steps involved in the correction for color convergence distortions in a single projector, and the diagram of Figs. 25 and 26 illustrate this operation. Completion of the four steps set forth in the flowchart of Fig. 24 results in a correction table in which each color pixel has been moved the required sub-pixel value to correct for color convergence distortions.
• This alternative embodiment is based on the existance, and the possibility to detect, fixed reference lines which are located exactly between the adjacent Fresnel lenses. By adjusting the shape of each projected image to fill precisely into the rectangle formed by the reference lines, the need in global adjustment (i.e. the above mentioned operation C) is avoided.
• the detection of the reference lines is enabled by the fact that the camera receives light emitted from the back side of element 108 (in Fig. 19).
• Image shape adjustment is done digitally by implementing a well known resampling algorithm (as in the above mentioned operation B) .
• the resampling is done on each projected image separately in exactly the same manner.
• the resampling is done using a non-varying non-homogenous non-linear pixel distribution.
• the location of each resampled pixel is pre-determined once using a complex formula which takes into account the pixel desired location on the screen, and various distortion parameters which characterize the projector.
• each projected pixel int he reshaped image is resampled 0.5 pixel to the left of the corresponding original pixel.
• the actual formula in this embodiment similarly takes into account vertical shift (denoted as Y) , zoom factor (M) , axial rotation (R) , horizontal and vertical keystone (KSx,KSy) and the Pin Cushion effect (PC) or barrel effect.
• the algorithm starts by setting all the distortion parameters of the current module (which are initially known) to zero (step 201, Fig. 27). This results in projecting images just as they are, with no reshaping.
• the algorithm uses only one type of image, which is a rectangle internal to the reference lines (as can be seen in Fig. 28). The distance between the points forming the internal rectangle to the external rectangle (formed by the reference lines) is constant. The algorithm is iterative, trying to improve the values of the distortion parameters in each iteration.
• step 202 (Fig. 27) an image forming an internal rectangle, corrected using the current values of the distortion parameters, is projected.
• step 203 the image is captured and the distances shown in Fig. 28 are measured.
• step 204 the corrections to the distortion parameters (i.e., dX, dY, dM, etc.) are computed using the distances measured in step 203.
• the following is the heart of this algorithm: if the distortion parameters are correct, the internal rectangle is projected properly; hence all the distances measured in step 203 are equal, and the quantities calculated in step 204 are all zero.
• the exact expressions are specific to the iterative algorithm used to control the convergence of the distortion parameters.
• One possible algorithm is the "Direction Set” (or “Conjugates Gradient”) technique (such as described in “Numerical Recipies in C” by W.H. Press, B.P. Flannery, S.A. Teukalsky and W.T. Betterling, Cambridge University Press, ISBN-0-521 -35465-X, Chapter 10 (Minimization or Maximization of Functions), First Edition, 1988).
• step 206 the relative change in the distortion parameters is evaluated. If this value is close enough to zero, then the algorithm stops. Otherwise, a new iteration is started by going back to step 202. However, this time the internal rectangle is resampled in a different way than in the previous iteration. Hence it is projected in a form which is closer to a perfect rectangle as it should be.
• each modular unit could include its own screen, with a separate combined screen applied to overlie all the screens of the modular units.
• the calibration operations can be performed by an external computer.

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• 1998
  • 1998-08-24 AU AU88830/98A patent/AU743173B2/en not_active Ceased
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