GB2280059A - Display - Google Patents

Description

1 2280059

FIELD OF THE INVENTION

The present invention relates to video output devices and more particularly to video displays.

BACKGROUND OF THE INVENTION

A variety of video display devices is known in the art. Cathode ray tubes are the most well known display devices, but suffer from well known limitations including cost, depth, and maximum practicable size.

Flat panel displays have recently become available based on various technologies such as liquid crystal technology. Such displays suffer from various limitations including directionality, and cost.

U.S. Patent 4,641,182 proposes systems and components for detecting electromagnetic radiation and displaying images produced thereby and describes the provision of a rotating planar array of optical display elements which creates the impression of a continuous output image. No commercial product currently exists based on the proposals contained in U. S. Patent 4,641,182.

1 1 SUMMARY OF THE INVENTION n- The present invention seeks to provide an improved video display. There is thus provided, in accordance with a preferred embodiment of the present invention, video display apparatus comprising a multiplicity of light emitters, moving in an endless loop, each of the multiplicity of light emitters being arranged so that it undergoes a travel path which differs from the travel path of any other light emitter at most by lying in a different plane parallel thereto, and apparatus for governing the light output of each of the light emitters in accordance with information contained in a video signal, thereby to provide a visible image of the information contained in the video signal.

There is also provided, in accordance with a preferred embodiment of the present invention, video display apparatus including at least one row of light emitters extending in a first direction, apparatus for displacing the at least one row of light emitters in a second direction perpendicular to the first direction, and apparatus for modulating the light output of each of the light emitters in accordance with information contained in a video signal, thereby to provide a visible image of the information contained in the video signal.

The light emitters may comprise light sources or, alternatively, light modulators.

In accordance with one embodiment of the invention, the at least one row of light emitters includes a plurality of rows of light emitters which are arranged in an endless loop configuration.

Preferably, the loop is displaced so that each of the plurality of rows undergoes a looping displacement.

In accordance with a preferred embodiment of the invention, the endless loop configuration is configured to define at least one flat surface. Preferably, the endless loop configuration defines a pair of generally flat, opposite facing surfaces.

Alternatively, the endless loop configuration may define a circular cylindrical configuration.

2 BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings in which:

Fig. 1A is a simplified plan view illustration of a video display constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 1B is a side view illustration of the video display of Fig. 1A; Fig. 2 is an isometric illustration of a video display constructed and operative in accordance with another preferred embodiment of the present invention; Fig. 3 is a simplified block diagram illustration of the circuitry employed in a video display constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 4A is a detailed illustration of an array driver forming part of the apparatus of Fig. 3 which is constructed and operative in accordance with one embodiment of the present invention; Fig. 4B is a detailed illustration of an array driver forming part of the apparatus of Fig. 3 which is constructed and opprative in accordance with an alternative embodiment of the present invention; Fig. 4C is a detailed illustration of an array driver forming part of the apparatus of Fig. 3 which is constructed and operative in accordance with a second alternative embodiment of the present invention; Fig. SA is a simplified illustration of a portion of a video signal transmission channel forming part of the apparatus of Fig. 3, including stationary circuit elements and an optical coupler; Fig. 5B is a simplified illustration of the moving circuit elements of the video signal transmission channel partially shown in Fig. SA; 3 Fig. 6A is a simplified illustration of a grating strip useful in conjunction with the apparatus of the present invention; Fig. 6B is a simplified side view illustration of the grating strip of Fig. 6A in conjunction with an optical position sensor; Fig. 6C is a simplified plan view illustration of the back side of one of the arrays of Fig. 1A; Fig. 6D is a simplified side view illustration of the array shown in Fig. 6C in association with an optical position sensor; Figs. 7A and 7B are simplified illustrations of part of a video display constructed and operative in accordance with alternative embodiments of the present invention; and Fig. 8 is a simplified illustration of part of a video display constructed and operative in accordance with yet another alternative embodiment of the present invention.

4 DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Reference is now made to Figs. 1A and 1B, which illustrate a video display constructed and operative in accordance with a preferred embodiment of the present invention. The video display preferably comprises a plurality of rows of light emitters 12, such as light emitting diodes (LED's), extending generally along an axis indicated by arrows 14. The plurality of rows are arranged for rapid displacement, preferably in a direction indicated by one of arrows 16, perpendicular to the axis indicated by arrows 14.

More generally, the video display may include from one to any suitable number of rows of light emitters. The light emitters may include any suitable light sources, or alternatively, light modulators, which modulate light from a separate source in response to an electrical signal. If the video display is a color display, light emitters providing light outputs in at least three primary colors are required and may be distributed along the rows in any suitable manner.

As noted above, the rows of light emitters 12 preferably extend along longitudinal axes which are perpendicular to the direction of displacement of the rows. Alternatively, the rows need not be perpendicular to the direction of displacement, as long as they extend transversely thereto.

A common characteristic of all embodiments of the invention is that each of the light emitters 12 moves along a travel path which differs from the travel path of any other light emitter at most by lying in a different plane parallel thereto.

Preferably, one or several closely spaced rows of light emitters 12 are treated as a group, hereinafter referred to as an array and indicated in Fig. 1A by reference numeral 15. Preferably, each array 15 is mounted on a carrier 13, which in turn is mounted on one or more endless webs 20. Alternatively, the arrays 15 are mounted directly on an endless web 20.

Web 20 or each of webs 20 is driven for displacement in a direction indicated by one of arrows 16 by at least a pair of rollers 22. The rollers are driven in rotary motion by an electric motor (not shown) or any other suitable driving device.

In the illustrated embodiment, the webs 20 are arranged on a pair of rollers and define a pair of oppositely directed, generally flat surfaces 30. Alternatively, additional rollers may be provided in order to enable the webs to define more than two generally flat surfaces. The light emitters 12, whose paths around the loop are essentially similar to the paths of the webs, thus define corresponding generally flat surfaceg, herein termed viewing surfaces.

The above described apparatus is preferably enclosed within an enclosure 26, comprising at least one viewing window 28, through each of which a corresponding viewing surface is visible.

As will be explained hereinbelow, an image is generally formed on each viewing surface visible through a viewing window 28. Such an image is generally rectangular, having a width W and a height H. The values of H and W are determined electronically by the video signals and/or the control circuits. The maximum value of W is the horizontal extent of the plurality of light emitters, while the maximum value of H is slightly less than the height of the viewing surface. The dimensions of the viewing window are generally close to, but need not be identical with, W aqd H (as is also the case with conventional CRT displays).

Reference is now made to Fig. 2, which illustrates another embodiment of the present invention, wherein the viewing surface is not generally flat but rather is part of a cylindrical surface having a circular crosssection.

In the illustrated embodiment of Fig. 2, a multiplicity of light emitters 31 is disposed on the cylindrical surface of a drum 32 which is rotated about its cylindrical axis 34. The drum 32 and the multiplicity of light emitters 31 are enclosed within an enclosure 36 which comprises at least one viewing window- 38, past which the multiplicity of light emitters 31 moves in a direction indicated by an arrow 40.

Reference is now made to Fig. 3, which is a simplified 6 T_ block diagram illustration of the circuitry employed in a video display constructed and operative in accordance with a preferred embodiment of the present invention. Image information from a video source (not shown), such as a video recorder, is supplied to an image storage subsystem 50.

Image storage subsystem 50 supplies video signals corresponding to those received from the video source, though in a different format, to the light emitters 12, in synchronism with timing signals received from timing and control circuitry 52. Timing and control circuitry 52 is operative to generate timing signals in response to the sensed position of the light emitters on the display, as determined by position sensors 53. The timing signals govern the display cycle of each row of light emitters 12.

Suitable optical position sensors 53 are described in detail below with reference to Figs. 6A - 6D.

The image storage subsystem 50 is operative to store image information in a RAM 51, also termed herein the "image memory." The image storage subsystem 50 also periodically extracts image information from the image memory 51. The extracted image information is employed by the multiplicity of light emitters 12, each in its own current location, so as to generate a corresponding multiplicity of portions of an image display, which together form a display of the image as a whole.

Preferably, the dis play area is vertically divided into a multiplicity of rectangular image segments, which are illustrated in phantom in Fig. 1A and indicated by reference numerals 17, each of which corresponds to the area whose information content is stored in image memory 51 in a corresponding one of a plurality of memory segments 54.

The content of each memory segment 54 is transmitted along an appropriate transmission channel 55, which may be wireless or may communicate via a slip ring or other transmission medium, to a corresponding driver 56, which is operative to drive the light emitters 12 in an associated array 15. In an embodiment of the invention, wherein an array is mounted on a 7 support 13, the associated driver 56 is also mounted on the support 13.

Fig. 4A illustrates a preferred embodiment of an array driver 56. The array driver preferably comprises a shift register 57 having multiple taps, each being connected via a buffer register 58 to a digital-tocurrent converter 59. Each digital-to-current converter 59 drives a single light emitter 12.

Fig. 4B illustrates another preferred embodiment of an array driver 56. The array driver preferably comprises a shift register 60 having multiple taps, each being connected via a gate 61 to a digital-to-current converter 62. Each digital-to-current converter 62 drives a single light emitter 12.

Fig. 4C illustrates yet another preferred embodiment of an array driver 56. The array driver preferably comprises a shift register 63 having multiple taps, each being connected via a buffer register 64 to a corresponding gate 65 and thence to a digital-to-current converter 66. Each digital-to-current converter 66 drives a single light emitter 12.

Fig. 5A is a simplified illustration of a portion of a video signal transmission channel 55 employed in the embodiment of Fig. 3 in accordance with a preferred embodiment of the present invention. The video signal transmission channel may include a serial encoder 70 which receives an output from a meiRory segment 54 of memory 51 and provides an output to an LED driver 72. The LED driver drives an LED 74 which illuminates a photodetector 76, such as a photodiode, which may be attached to the back of a support 13 or to the back of a web 20 (Figs. 1A and 1B).

It is noted that the LEDs 74 of various transmi sion channels have somewhat overlapping impingement areas. Typically, therefore, the LEDs 74 are arranged in an alternating manner in at least two different planes (not shown), whereas the photodetectors 76 are mounted in all of the at least two planes. Each transmission channel is thereby served by a unique LED/photodetector pair, each pair comprising an individual one of LEDs 74 and an individual one of photodetectors 76.

8 T_ Fig. 5B is a simplified illustration of the moving circuit elements of the video signal transmission channel partially shown in Fig. 5A. This illustration indicates that the output signal from photodetector 76 is amplified by an amplifier 78 and supplied to a detector circuit 79, such as a Schmitt trigger. The detector circuit 79 converts the amplified signal to a standard binary signal, which is supplied to a decoder 81. The output of decoder 81, comprising digital values representing the respective brightness of successive light emitters along a row or along several rows in an array, is typically supplied to a shift register 57 (Fig. 4A).

According to an alternative embodiment of the present invention, at any instant there is no more than a single row within the display area defined by the viewing window. The image storage 50 is replaced by a digitizer and a buffer memory of at most a few scan lines. This embodiment is particularly suitable for real time display of a moving image represented by incoming video signals, such as a standard broadcast signal.

Typically, the number of arrays disposed on the endless loop is three and each array comprises three closely spaced rows of light emitters, one row for each primary color. Each sweep of an array down the display area corresponds to a single video "field."

- Operation of the embodiment illustrated in Figs. 1A-1B, 3, 4A-4C, and 5A-5B will now be described. Operation of the embodiment of Fig. 2 is similar, with appropriate modifications.

In the event that there are several active viewing surfaces (e.g., two in the embodiment illustrated in Figs. 1A-1B), the following description applies to each of these viewing surf,aces.

Their operation is essentially simultaneous.

In the present embodiment, it is assumed that each array 15 comprises a single row of light emitters. In this case, for a color display, every three successive arrays 15 contain emitters of the three primary colors in an alternating pattern. It is appreciated that an array may consist of more than one row, e.g., a triad of rows of the three primary colors, or a plurality 9 1q.

of such triads which are mutually displaced, as discussed in more detail hereinbelow.

The display area is divided vertically into n image segments 17. Preferably n should be equal to, or just greater than, the number of arrays that appear within the display area at any instant. The image memory 51 is likewise divided into n memory segments 54 and there are correspondingly n transmission channels 55. Each transmission channel operates to transmit signals from one corresponding memory segment 54 to a corresponding image segment 17. The LED's 74 are vertically disposed so as to illuminate the paths of the photodetectors 76 while the arrays with which they are associated travel within their corresponding image segments.

Whenever an array enters the top of an image segment, data for the first raster line of that segment is acquired from the corresponding segment in the image memory 51 and delivered to the corresponding transmission channel 55, where it is encoded by serial encoder 70 (Fig. 5A) and transmitted via LED driver 72 and LED 74 to photodetector 76 associated with that array.

The signal from the photodetector 76 (Fig. 5B) is amplified by amplifier 78, binarized by detector 79, decoded by decoder 81, and fed to shiftregister 57 (Fig. 4A). After shift register 57 is filled with the data of the entire raster line, the data is transferred to the buffer register 58. The outputs of the buffer register 58 are applied to digital-to-current converters 59, which feed appropriate currents to the corresponding display LEDs in the array. The LEDs emit light accordingly, each LED thus causing one pixel of the image to be displayed.

Once the data from the shift register 57 has, been transferred to the buffer register, data for the next raster line is brought from the same segment of memory and transmitted to the shift register 57 in the manner described above. It is noted that this transmission takes place while the data for the previous scan line is being held in the buffer register, and the LEDs keep emitting light accordingly. Generally, the LEDs emit light continuously, modulated by the data in the buffer register which generally changes from line to line.

In this embodiment, the emission of light corresponding to a pixel continues while the LED moves the distance to the next raster line position. There is, therefore, a visual smear effect, blending vertically adjacent pixels and thus reducing the apparent vertical image sharpness. In an improved embodiment, illustrated in Fig. 4B, this effect is avoided by replacing the buffer register 58 with a parallel array of gates 61.

Once the shift register 60 is full, the gates 61 are opened by a short pulse, to transfer the outputs of the shift register 60 directly to the digital-to-current converters 62. A very high current is supplied by each converter, to ensure that the resultant time-integrated brightness remains sufficiently high.

For example, assuming linear operation, if the pulse length is one fifth of the pulse period, and if in the first embodiment a continuous current of 10 mA is required by a LED to effect a certain brightness level, then the pulsed current amplitude in the improved embodiment will be 50 mA to achieve the same apparent brightness.

In this last described embodiment, the total instanta neous current drain during the pulse may be too high forthe current supply circuit. Therefore, in a further preferred embod iment, illustrated in Fig. 4C, a buffer register 64 is utilized as in the first embodiment, but its outputs are fed to an array of gates 65. Pulses are applied to successive gates 65 in a time staggered manner, so that the last pulse occurs just before the data for the next scan line is to be transferred from the shift register 63 to the buffer register 64. 1 This process is repeated line after line until the array enters the next segment. At that time the array begins to receive data from the corresponding next segment of memory 51, through the corresponding next transmission channel. It is noted that the switch to the new segment has no effect on the operation of the array, except that an alternate photodetector 76 is activated to receive the data from the LED 74 of the new trans- 11 mission channel. This effect occurs because, as explained above, the LEDs of adjacent channels are horizontally displaced in order to avoid overlapping illumination.

When the array reaches the bottom of the display area, all the data in its registers are set to a null value, thereby extinguishing all the display LEDs.

The process described above applies to each array 15 within the display area. Thus there are as many simultaneous data transmissions as there are arrays within the display area. It is noted that in general the number of segments, n, is chosen to be just greater than the maximum number of arrays 15 within the display area at any time. This choice ensures that there is at most one array within any display segment.

In an alternative embodiment, the memory 51 is not segmented, as shown, but rather holds the data for the whole display in a single buffer; it has as many read access ports as the maximal number of arrays within a display area. This is also the number of transmission channels.

When an array enters the top of the display area, it is assigned one port in the memory and, initially, the top transmission channel. When the next array enters the top of the display area, this array is assigned another port, as well as the top transmission channel. The previous array is then assigned the next successive transmission channel. The process occurs for all arrays within the display area and the data from the ports are commutated among the transmission channels accordingly.

The transmission channels as described above are physically separate channels, each with its own optical path. In an alternative embodiment, several or all transmission channels, are combined into a single physical channel, by any of the multiplexing methods known in the electronic communication art, such as, in particular, Time Division Multiplexing (TDM). In this embodiment the optical arrangement shown in Fig. 5A may be modified so that each LED illuminates several photodetectors 76 at any one time. Alternatively, identical signals may be fed to several LEDs.

12 T_ In yet another alternative embodiment, the optical path is replaced by another physical medium such as radio waves. In this case, the LEDs 74 are replaced by a radio transmitter and the photodetectors 76 are replaced by radio receivers.

Another possible medium is an electrical conductive path. Such a path may, for example, include slip contacts between a stationary flexible tongue and a conductive track on the inner surface of one of the webs 20 (Figs 1A and 1B).

Power to the moving circuits and to the LEDs is preferably transmitted by means of sliding contacts, preferably followed by noise-suppressing filters. The sliding contacts may be implemented as slip contacts between a stationary flexible tongue and conductive tracks on the inner surface of one of the webs 20 (Figs. 1A and 1B). Alternatively, they may be implemented as slip rings mounted in a coaxial fashion on one of the rollers 22, followed by rolling contacts between coplanar conductive tracks on the surfaces of the roller and of one of the webs. Another possible way of supplying power to the moving assembly is alternatingcurrent magnetic coupling or radio-frequency power coupling, followed by rectifiers and filters.

In order for the displayed image pixels to appear in their correct vertical locations, the timing of the data transfer into the buffer registers 58 (Fig. 4A), or, in the improved embodiments, the timing of the gating pulses, must be exactly controlled. This timing is affected by two variables, namely the speed of motion of the arrays along their path, and of the webs to which they are attached, and the relative position of each array along that path.

The first variable is preferably sensed by means of a grating attached to a web, while the second variable is sensed by a marking on each array, as described below, with reference to Figs. 6A-6D.

Fig. 6A illustrates a strip 80 of flexible material, which is attached to a portion of the inner surface of web 20 (Figs. 1A and 1B). On strip 80 is marked a grating, comprising alternating black and white, but otherwise identical, short 13 T rectangular areas.

Fig. 6B shows schematically a side view of the strip 80 and of a segment of the web 20, as well as an optical position sensor 82, to be explained hereunder. It will be noted that the position sensor 82 is stationary, whereas the grating strip moves together with the web and the arrays.

The position sensor 82 preferably comprises an infrared light source 84, illuminating a slit aperture 86, a lens 88, which focuses the slit onto the strip 80, and a number of photodetectors 90, such as photo-diodes. The photodetectors 90 receive light reflected from the grating on the strip 80.

The signals from the photodetectors 90 of position sensor 82 are amplified and combined by an edge detection circuit (not shown), which performs differentiation and thresholding, to detect the time at which each grating edge passes the corresponding slit image. The resultant binary signal, also termed herein the "grating signal", is fed to the timing and control circuit 52 (Fig. 3).

According to one embodiment, the boundaries between the rectangular areas in the grating indicate relative raster line positions in the image. The edge information carried by the grating signal is then converted by the timing and control circuit 52 into a timing signal, also termed herein the "gating signal," for gating out the image data for a new scan line from the shift register 57 (Figs. 4A and 4B) or the buffer resister 64 (Fig. 4C).

According to an alternative embodiment, the gating signals are generated from clock pulses. These pulses are synchronized to the grating signal by a phase-lock loop circuit,.

It is appreciated that there may also exist other means for sensing the speed of the web, instead of the grating and optical position sensor described above, such as a combination of a magnetic strip and reading head, or an angular encoder attached to one of the rollers 22 (Figs. IA1B) or to the axis of the drum 32 (Fig. 2).

Fig. 6C illustrates schematically the back side of the 14 portion of web 20 near a typical array 15, or in an alternative embodiment, of a typical support 13 (Fig. 1A). The circles in this illustration indicate the positions, on the front side, of light emitters 12 in one row of the array. Also shown is a short horizontal line 92 that is marked on the back side of the web 20 or the support 13 at a known distance d from the centerline of the row of light emitters. The line 92 may be a black line on a white background or vice-versa. It is appreciated that the line 92 need not be marked at the end of the array, as shown, but could be marked at any convenient location along its length.

Fig. 6D shows schematically a side view of a crosssection of the web portion, or the support, of Fig. 6C. Also shown in Fig. 6D is an optical position sensor 94, similar to position sensor 82 of Fig. 6B, with the slit imaged onto the back surface of the web or support in the path of line 92 (which, in Fig. 6D, is shown in a position, relative to the position sensor 94, such that the marked line 92 is about to be sensed). The edge detection circuit in this case is designed to detect both edges of the line and to determine the median position between them.

The position sensor 94 is deployed at the top of the display area, so that it senses the exact position of each array as it is about to enter the display area. Upon each such sensing it.- sends a suitable signal to the timing and control circuit 52 (Fig. 3). In response, the timing and control circuit 52 initiates the transmission of image data to that array, as described hereinabove, and adjusts the exact timing of all subsequent gating signals to the driver of that array. The effect of such timing adjustment is that the vertical position of the image pixels produced by all the arrays for any one raster line is constant, regardless of the actual position of each array within the loop path. It is appreciated that other means for sensing the position of an array

may be provided, such as a magnetic proximity switch, or an optical alignment sensing device.

The gating signal is fed to each array, either as a.

special code over the current data transmission channel, or via a separate transmission channel, which may be similar to the data transmission channel.

As mentioned above, an array 15 may include more than one row of light emitters. In one such embodiment there are three rows, one for each of the three primary colors. In another embodiment the number of light emitters that can physically fit into a single row is less than the desired number of pixels along the width of the array. In this embodiment successive light emitters are placed in two or more rows in an alternating and mutually staggered manner.

A third embodiment, illustrated in Fig. 7A, is a combination of the first two. In this example, each array contains three pairs of rows, each pair comprising light emitters in one of the primary colors. The two rows of each pair are mutually staggered. Thus, when the array moves vertically, as it does along the loop in a direction indicated by the arrow 18, the traces of the light emitters interleave, as represented in the illustration by the vertical lines above the array, effectively halving the distances between adjacent traces.

In an alternative approach, rows on successive arrays along the loop are mutually staggered. Fig. 7B, which illustrates one example, shows two successive arrays, in horizontal alignment. Each array contains a triad of rows, each row comprising light emitters of one primary color. The triads in the two arrays are mutually staggered. The resultant traces, again, interleave, as represented by the vertical lines in the illustration.

The apparatus described hereinabove may be modified in several ways to implement the above embodiments.

First, the image storage subsystem 50 and the data extraction algorithm are structured so as to feed to each array image data corresponding to the raster line to be generated by all its rows for its position at the next gating pulse. These raster lines typically are not mutually adjacent.

Second, the image data for all the rows in an array is 16 encoded so as to be sent simultaneously over the corresponding transmission channel.

Third, the data for each array may be fed to a single shift register and then, in parallel, to the several rows. Alternatively, the received data may be separated by rows and fed in parallel to several corresponding shift-registers.

Fourth, depending on whether or not the vertical distances between the rows in an array are integral multiples of the distance between successive scan lines, the gating signal may either be common to all rows, or otherwise, each row may be fed its own properly timed gating signal.

In yet another alternative embodiment, not each array 15 of light emitters 12 need extend the full image width W, but may, for example extend over one half or one third of W. In such a case, several arrays, mutually vertically displaced, cooperate as a group, in effect, to extend the full width W. Fig. 8 illustrates an example where two pairs of vertically displaced halfwidth arrays constitute two successive groups.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow:

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Claims (14)

C L A I M S

1.

Video display apparatus comprising: a multiplicity of light emitters, each moving in an endless planar loop, each of the multiplicity of light emitters being arranged so that the endless planar loops defined thereby differ, at most, in that they lie in different mutually parallel planes; and apparatus for governing the light output of each of the light emitters in accordance with information contained in at least one video signal, thereby to provide a visible image corresponding to the information contained in the at least one video signal.

2.

Video display apparatus comprising: at least one array of light emitters, each array comprising at least one row of light emitters extending in a first direction; displacement apparatus for displacing the at least one array of light emitters in a second direction perpendicular to the first direction; and a modulating unit for modulating the light output of each of the light emitters in accordance with information con-talned in at least one video signal, thereby to provide at least one visible image corresponding to the information contained in the at least one video signal.

3. Apparatus according to either of the precedingclaims and wherein said light emitters comprise light sources. 1

4. Apparatus according to either of the preceding claims 1 and 2 and wherein said each of said light emitters comprises a light modulator operative to modulate light f rom a separate source in response to an electrical signal.

5.

Apparatus according to claim 2 and wherein said dis- 18 placement apparatus is operative to displace the at least one array along an endless loop.

6. Apparatus according to claim 1 and wherein said multi plicity of light emitters are arranged as at least onearray comprising at least one row which is transverse to said endless planar loops.

7. Apparatus according to claim 5 and wherein the loop is displaced so that each array is displaced along an endless loop.

8. Apparatus according to any of claims 5 - 7 and wherein said endless loop is configured to define at least one generally flat surface.

9. Apparatus according to claim 8 and wherein said endless loop defines a pair of generally flat, oppositely facing sur- faces.

10. Apparatus according to any of claims 5 - 7 and wherein said endless loop is configured to define a cylindrical surface of circular cross-section.

Apparatus according to any of claims 1, 2 and 5 - 7 and comprising means for storing, processing and transmitting each of said at least one video signals, said means comprising, for each individual video signal, a plurality of transmission channels, each transmission channel transmitting to one of the at least one arrays of light emitters as it traverses a display,area portion corresponding to the individual video signal.

12. Apparatus according to claim 11 wherein each of said plurality of transmission channels comprises optical transmission means.

13. Apparatus according to any of claims 1, 2 and 5 - 7 and 19 also comprising a position sensor operative to sense the position of each array of light emitters.

14. Apparatus according to claim 13 wherein said position sensor comprises an optical position sensor.

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