GB2522199A - Device and method for distributing image data, and multi-projection system - Google Patents

Abstract

A device and method for distributing image data obtained from a source device, 110, to a plurality of display devices, 101-104, of a multi-projection system. The device comprises a module for sending a first part of the image data, to a first display device of the plurality of display devices, the first part corresponding to a first sub-image to be displayed only by the first display device, and a module for transmitting a second part of the image data, to a set of display devices of the plurality of display devices, the second part corresponding to a second sub-image to be displayed by each device of the set of display devices. The module for sending the first part to the first display device sends the image data according to a point-to-point communication scheme and the module for transmitting the second part to the set of display devices sends the image data according to a broadcast communication scheme.

Description

Intellectual Property Office Application No. GB1400665.4 RTM Date:9 July 2014 The following terms are registered trade marks and should be read as such wherever they occur in this document: DisplayPort, HDMI, Wi-Fi Intellectual Property Office is an operating name of the Patent Office www.ipo.govuk DEVICE AND METHOD FOR DISTRIBUTING IMAGE DATA, AND MULTI-

PROJECTION SYSTEM

FIELD OF THE INVENTION

The present invention relates in general to video data transmission and in particular to video data transmission in multi-projection systems.

BACKGROUND OF THE INVENTION

Multi-projection systems (hereafter MP systems) are increasingly used, in particular in contexts where a very large display or projection area is required, for instance in a dome, a stadium or a concert hall, or for projection on buildings.

In practice, an MP system comprises an array of display devices, for instance of video projectors, that each projects or displays a part of an image on a screen.

MP systems exist wherein image data are distributed from a display device acting as a master device that receives the image data from the source device, to the remaining display devices of the MP system, which participate in displaying the image over a dedicated inter-display-devices network.

Usually, each of the individual display devices cover adjacent, partially overlapping zones of the total screen area in order to ensure a smooth transition between different projected image parts (sub-images) and provide tolerance against small displacements which may be introduced, for example, by vibrations or by thermal expansion.

To this end, a blending process is performed to generate adapted overlapping zones by duplicating pixels of the image, which will be displayed several times, and by adapting the intensity of the duplicated pixels in order to ensure a smooth transition between the different projected sub-images.

For instance, the width or height of such overlapping zones may be about % of the width or height of the area covered by a single display device.

These overlapping zones have to be synchronously displayed by several display devices, for example by two of them, or sometimes by four of them.

Thus, the corresponding display devices have to be each provided with a copy of the pixels to be displayed in common, in addition to their own image part to be displayed only by them.

However, the communication links to reach display devices have a limited bandwidth. Thus, there is a need to reduce the amount of pixels transmitted to the different display devices.

In addition, each display device has a limited number of network ports (or reception antennas) and a limited capacity for processing image data, for instance to cut it into several zones to be displayed by the display device itself or by others. For example, a given display device may support cutting an image into up to four zones.

Furthermore, timely synchronisation of image (or video frame) display between all display devices requires the buffering of image data by display devices. In particular, the higher the maximum routing latency from the master display device to the other display devices, the bigger the required buffer capacity.

This routing latency depends essentially on the number of intermediate relay nodes on the path from the source to the destination (hop count). Consequently, as the buffer memory capacity per display device is limited, the maximum hop count has to be kept below a predetermined value.

The routing latency that may vary for the different display devices is particularly undesirable in case of transmission of data that have to be displayed simultaneously by several display devices, like overlapping zones.

SUMMARY OF THE INVENTION

The present invention has been devised to address one or more of the foregoing concerns.

In this context, according to a first aspect of the invention, there is provided a device for distributing image data obtained from a source device, corresponding to at least part of an image, said image to be displayed by a plurality of display devices of a multi-projection system, the device comprising: -a module for sending a first part of said image data, to a first display device of the plurality of display devices, said first part corresponding to a first sub-image to be displayed only by said first display device, -a module for transmitting a second part of said image data, to a set of display devices of the plurality of display devices, said second part corresponding to a second sub-image to be displayed by each device of the set of display devices, wherein -the module for sending the first part to the first display device comprises communication means enabling sending of image data according to a point-to-point communication scheme, and the module for transmitting the second part to the display devices of the set, comprises communication means enabling transmission of image data according to a broadcast communication scheme.

Data duplication due to image data to be displayed simultaneously by several display devices, and transmission of the duplicated data to them, are limited.

This is achieved by using communication means enabling transmission of image data according to a broadcast communication scheme to transmit only one copy of the second part of image data, to a set of several display devices.

Consequently, the network bandwidth occupation due to the transmission of these duplicated data is reduced.

Furthermore, using communication means enabling transmission of image data according to a broadcast communication scheme means to simultaneously transmit image data to several display devices allows a better synchronization between the display devices of the multi-projection system.

In particular, using broadcasting to reach several display devices helps to reduce the hop count, thus also reducing the required buffer memory.

Optional features of the invention are further defined in the dependent appended claims.

In some embodiments, the communication means enabling sending of image data according to a point-to-point communication scheme may comprise wired communication means.

For example, the communication means enabling sending of image data according to a point-to-point communication scheme may comprise wireless communication means.

In some embodiments, the wireless communication means may comprise at least one directional antenna.

In some embodiments, the communication means enabling transmission of image data according to a broadcast communication scheme comprise wireless communication means.

For example, wireless communication means may comprise at least one omnidirectional antenna.

In some embodiments, the distributing device is one of the display devices of the plurality of display devices, relaying at least part of the image data obtained from the source device to other display devices of the multi-projection system.

For instance, the distribution of image data may be handled by display devices that have higher capacities for example to process image data and a sufficient number of output ports to send processed image data to other devices.

In some embodiments, the distributing device is the source device providing the image data to the multi-projection system.

In some embodiments, the image data correspond to video data to be displayed by video projectors as display devices.

According to a second aspect of the invention, there is provided a multi-projection system comprising a plurality of display devices for displaying parts of image corresponding to image data obtained from a source device, each display device comprising communication means enabling sending of image data according to a point-to-point communication scheme, and communication means enabling transmission of image data according to a broadcast communication scheme, said multi-projection system comprising at least one distributing device as aforementioned.

According to a third aspect of the invention, there is provided a method of distributing image data obtained from a source device, corresponding to at least part of an image, said image to be displayed by a plurality of display devices of a multi-projection system, the method comprising the following steps: -sending a first part of said image data, to a first display device of the plurality of display devices, said first part corresponding to a first sub-image to be displayed only by said first display device, -transmitting a second part of said image data, to a set of display devices of the plurality of display devices, said second part corresponding to a second sub-image to be displayed by each device of the set of display devices, wherein -the first part is sent to the first display device using communication means enabling sending of image data according to a point-to-point communication scheme, and -the second part is transmitted to the display devices of the set, using communication means enabling transmission of image data according to a broadcast communication scheme.

In some embodiments, one of the display devices of the set of display devices corresponds to said first display device, and the second part comprising edge blending data corresponding to a portion of image which is adjacent to said first part.

In some embodiments, the second part to be transmitted is determined based on the network capacities and/or based on the capacities of the display devices of the set.

In some embodiments, the method further comprises a step of buffering parts of image data received at a display device, based on a timestamp received with said parts.

In some embodiments, the method further comprises a step of determining a route from said distributing device, to said first display device, over which said distributing device sends said first part of image data.

In some embodiments, the route may be determined so that the number of intermediaries to reach the first display device is minimized.

In some embodiments, the method further comprises the following steps: -identifying a relay among said plurality of the display devices and the source device, said relay comprising communication means enabling sending of image data according to a broadcast communication scheme, -determining a route from said distributing device, to said relay, over which said distributing device sends a third part of said image data to said relay, said third part corresponding to a third sub-image to be displayed by several display devices of the plurality of display devices.

In some embodiments, the route may be determined so that the number of intermediaries to reach the relay is minimized.

The multi-projection system and the aforementioned method have features and advantages similar to the distribution aforementioned device.

The invention also concerns a distributing device as hereinbefore described, with reference to, and as shown in, Figure 5 of the accompanying drawings, a multi-projection system as hereinbefore described, with reference to, and as shown in, Figures 1 to 4 or 7 of the accompanying drawings, and a method of distributing image data as hereinbefore described, with reference to, and as shown in, Figure 6 of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 schematically shows an overview of a multi-projection system according to embodiments, together with the resulting display screen layout; Figure 2 schematically shows a first example of distribution of image data for different screen zones to the display devices of Figure 1, according to embodiments; Figure 3 schematically shows a second example of distribution of image data which is a variant of Figure 2; Figure 4 schematically shows an example of distribution of image data in a multi-projection system comprising six display devices, according to embodiments; Figure 5 is a functional diagram illustrating a possible architecture of a device for distributing image data according to embodiments; Figure 6 schematically shows an example of steps of an algorithm for determining a routing scheme, in an MP system according to embodiments; Figure 7 schematically shows an overview of a multi-projection system according to particular embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention is related to a multi-projection system composed of multiple projectors (or display devices), generating adjacent, partially overlapping images on a projection screen, thus capable of forming a large image made of several sub-images in a seamless manner, and with a high image quality.

Figure 1 shows an example of a multi-projection (MP) system according to embodiments.

The MP system comprises a plurality of display devices, here four display devices 101, 102, 103 and 104, also marked by letters A, B, C, D. The invention is not limited thereto, and the description with reference to the present Figure can be easily adapted to MP systems with more display devices, for instance with six display devices as in Figure 4.

These display devices may be for instance video projectors.

The display devices 101 to 104 are interconnected by a network 100, which is preferably a high-speed network.

The representation of network 100 in Figure 1 is not limitative. In particular, the interconnection network 100 may be wired, wireless or hybrid, and may present different topologies, including topologies wherein the display devices are not all linked to each other.

For instance, in some embodiments, the network topology may be meshed.

In other words, the network may be composed of point-to-point links, where different display devices transmit data simultaneously to other display devices.

Point-to-point links may be wired links. For instance, they may be high definition video cables such as DisplayPort, HDMI, DVI or SDI.

In a variant, point-to-point links may be wireless. To that end, the display devices may be equipped with one or more antennas with highly directional characteristics, for instance operating in the 60 GHz band.

In some embodiments, the network topology may additionally comprise point-to-multipoint links, allowing a given display device to reach simultaneously several display devices.

In practice, these point-to-multipoint links may use antennas with omnidirectional characteristics in order to achieve multicasting, and preferably operating in the 60 GHz band.

Point-to-point links generally present a higher available bandwidth compared to point-to-multipoint links. However, contrary to point-to-point links, point-to-multipoint links allow several targets to be reached, possibly simultaneously depending on the distance between the emitting device and the targets. Both kinds of links may thus be advantageously used, in particular in a mesh network.

Each of the display devices 101 to 104 comprises a limited number (one or more) of input ports. The input port may be analogue (e.g. composite, S-video, VGA, etc.) ordigital (e.g. DVI, HDMI, DisplayPort, etc.).

A source device 110 may be connected to an input port of one of the display devices acting as a master, here the display device 101.

The source device 110 may be for example a digital video camera, a hard-disk or solid-state drive, a digital video recorder, a personal computer, a set-top box, a server, a video game console or the like.

Preferably, the source device 110 connects the input port of the display device 101 by means of an appropriate cable 111, e.g. an HDMI or DisplayPort connection cable. In a variant, a wireless connection is used.

In some embodiments, the source device 110 also comprises wireless means to perform point-to-multipoint communications with at least some of the display devices of the MP system, for instance here the display devices 101-104.

To that end, the source device 110 may comprise one or more omni-directional antennas, thus allowing broadcasting of image data in with a wide scanning range.

The functioning of the different aforementioned devices is now described.

The source device 110 is configured to generate data representing a source image to be displayed for example on a screen 120 by the display devices 101- 104 of the MP system, asafull image 130.

The source device 110 is also configured to send image data corresponding to the source image or part of it, to the master display device 101, using the aforementioned input port, and optionally to several display devices 101-104, for instance using point-to-multipoint links as aforementioned (e.g. omnidirectional antennas).

The present invention may be used in a context of transmission of video data. By way of non-limiting example, the source device 110 may be a video source that sends for instance a 4k2k (3840 x 2160) video stream at 60 frames per second.

The present invention may also be used to display picture-in-pictures on a megawall (see Figure 7). Other applications of the invention may be envisaged.

In preferred embodiments, the network 100 offers sufficient bandwidth and sufficiently low latency to cope with the transmission of compressed or uncompressed data streams with the desired resolution.

For instance, the network 100 may be configured so as to achieve the transmission of video data streams with a resolution of 4k2k and with a desired frame rate of 60 frames per second.

In the example of Figure 1, the image data originating from source device 111 is distributed by the master display device 101 over the network 100 to the other display devices 102, 103 and 104.

The display devices together display an aggregate, seamless image corresponding to the image 130 on the screen 120. An example of architecture of the display devices will be described below with reference to Figure 5.

In the example of Figure 1, the image to be projected or displayed by the MP system is composed of nine sub-images corresponding to the following screen zones: area a, area ab, area b, area ac, area abed, area bd, area c, area Cd, and area d.

Obviously, the number and shape of screen zones depends at least on the number of display devices of the MP system.

A variant with six display devices and fifteen screen zones (areas) is described below with reference to Figure 4. The description of the image comprising nine screen zones may be adapted rather easily to other configurations, since the projection by a bigger MP system relies on the same principles.

In practice, the display device A (101) displays area a of the image 130 and also areas ac, ab and abed. The display device B (102) displays area b of the image and also areas ab, bd, abed. The display device C (103) displays area e of the image and also areas ac, ed, abed. The display device D (104) displays area d of the image and also areas bd, cd, abed.

In other words, each of areas a, b, c and d of the image 130 is displayed only by only one display device, respectively display device A, B, C or D. The other areas form a vertical rectangle 131 occupying the full height of the rectangular area 130, and a horizontal rectangle 132 occupying the full width of the rectangular area 130, and are displayed simultaneously by several display devices. These areas correspond to edge blending zones of the image 130.

In particular, area ab is simultaneously displayed by both display device A and display device B, area ae is simultaneously displayed by both display device A and display device C, area bd is simultaneously displayed by both display device B and display device D, area ed is simultaneously displayed by both display device C and display device D, and area abed, located at the intersection of the vertical rectangle 131 and the horizontal rectangle 132, is simultaneously displayed by the four display devices A, B, C and D. The present invention is not limited to the representation of image 130 and overlapping zones 131-132 used in Figure 1.

In practice, the edge blending areas 131 and 132 should have a width or height corresponding to about 20 % of the width or height of the area covered by a single display device.

By way of non-limiting example, in an image of 3840 by 2160 pixels from a video stream to be projected within the display rectangle 130, when columns are numbered from left to right, the left border of the vertical edge blending area 131 may be for instance located at pixel column number 1706 of 3840 and the right border may be located at pixel column number 2133 of 3840. Correspondingly, when rows are numbered from top to bottom, the top border of the horizontal edge blending area 132 may be located at pixel row number 960 of 2160 and the bottom border may be located at pixel row number 1200 of 2160.

The present invention is not limited to an MP system comprising four display devices (see for instance Figure 4 which shows an example with six display devices).

In the general case there are a number m*n of display devices arranged in such a way that they display screen zones forming m vertical columns and n horizontal rows. Correspondingly, there are: -m*n image zones to be displayed each one by exactly one single respective display device, -(m1)*n image zones, each one located in one of the ni-i vertical edge blending zones, as well as m*(n1) image zones, each one located in one of the n-i horizontal edge blending zones, each one of the (mi)*n image zones to be displayed by exactly two respective adjacent display devices, each one of the m*(n1) image zones to be displayed by exactly two respective adjacent display devices and -(mi)*(n1) image zones, each one located at the intersection of a horizontal and a vertical edge blending zone, each one to be displayed by exactly four respective adjacent display devices.

This yields a total of (2mi)*(2n1) image zones to be cut, routed to the respective destination display devices and displayed.

According to preferred embodiments, image data corresponding to areas to be displayed by a single display device are transmitted through point-to-point communication links as aforementioned, and image zones (parts of the image) to be simultaneously displayed by four display devices, are sent through point-to-multipoint links as aforementioned.

Thus, each of the display devices 101-1 04 are configured to receive image data corresponding to parts of the source image, from the source device 110 and/or from the other display devices 101-104, either according to a point-to-point communication scheme, or according to a point-to-multipoint communication scheme.

In practice, a projective distortion generally appears which is different for each display device. Coordinates of the image zone 130 in the screen coordinate system may be transmitted to the display devices 101 to 104 and stored therein for the purpose of determining the geometric distortion correction parameters to apply to the received image data. Alternatively, homography matrices may be computed by the master display device 101 (or by the source device 110) and sent to the other display devices. Obviously, the matrix sent to a given display device is different from the matrix sent to another display device, due to their respective position.

Depending on their respective capacities, in terms of number of ports, processing capacities, memory availability, etc., one or more of the display devices 101-104 designated relay display devices, may duplicate and cut received image data, in order to route parts of it to other display devices, either using point-to-point communication links or point-to-multipoint communication links. More details are given about the routing process with reference to Figures 2, 3, and 4.

In addition, the display devices may be configured to perform other adjustments (photometric adjustments, colorimetric adjustments such as brightness, contrast, white balance etc.). In particular, these adjustments may be handled by the master device 101. Alternatively, these adjustments may be handled by the source device 110, or by a third party device (e.g. a calibration device including a calibration camera).

In some embodiments, the source device 110 and/or the master display device 101 is configured to determine and process the edge blending zones.

Alternatively, several display devices acting as relay display devices may also be configured to perform edge blending. As commonly known, edge blending consists in modifying the brightness of overlapping zones to be displayed by several display devices in such a manner as to obtain uniform brightness after superposition.

Figure 2 shows a first example of distribution of image data for different screen zones (including the edge blending zones) to the display devices of Figure 1, according to first embodiments.

In the example of Figure 2, the source device 110 sends a whole source image to the master display device 101, over link 111. The source image is here composed of nine pads to be displayed as areas a, ab, b, ac, abcd, bd, c, Cd, and d, of Figure 1.

In this example, the network 100 comprises: -four wired point-to-point links, namely link 201 from display device A (101) to B (102), link 202 from display device B (102) to display device 0 (104), link 203 from display device C (103) to display device 0 (104) and link 204 from display device A (101) to display device C (103), and -four omnidirectional antennas 211, 212, 213 and 214 attached to the respective display devices A, B, C and 0 (101, 102, 103 and 104).

The master display device A (101) is configured to cut the image data parts corresponding to the four screen zones a, ab, ac and abcd of each complete source image received from source 110, and also to display it.

In this example, the master display device A (101) is configured to apply a smooth reduction of luminance from left to right, top to bottom or both, within edge blending zones ab, ac and respectively abcd.

The master display device A (101) is also configured to cut a copy of the received image data into at least three pads, for instance: -a pad corresponding to areas ab, b, bd and d, -another part corresponding to areas ac, c and Cd, -still another part corresponding to area abcd.

The copy of image data corresponding to the four areas ab, b, bd and d, is sent to the display device B (102) over the point-to-point link 201 between the master display device A (101) and the display device B (102).

It should be noted that the sub-image composed of these four areas does not have a rectangular shape. In practice, in order to facilitate packetizing on the network link 201 and handling by the receiving display device B (102), these four areas are sent for example as two rectangular disjoint sub-images, for instance composed of pads ab and b and the other one composed of parts bd and d.

The copy of image data corresponding to the three areas ac, c and Cd, is sent to the display device C (103) over the point-to-point link 204 between the master display device A (101) and the display device C (103). In practice, these areas may also be sent as two rectangular parts as described above.

The copy of image data corresponding to area abcd is broadcast to the display devices B (102), C (103), and 0 (104), using the omnidirectional antenna 211 of the master display device A (101) and the respective reception antennas 212, 213, and 214 of the corresponding display devices B (102), C (103), and 0(104).

Using broadcasting allows image data to be provided to several display devices while sending only one copy of these image data.

It is to be noted that image data corresponding to area abcd are particularly adapted to broadcasting since they represent a relatively small part of the total image to be displayed, and also this area is to be displayed by all the display devices 101-104.

The display device B (102) is configured to merge and display image data corresponding to areas ab, b, and bd, received from display device A (101) over point-to-point link 201 and image data corresponding to area abed, received from display device A (101) using antenna 212.

The display device B (102) is also configured to cut a copy of the image data corresponding to areas bd and d, and to send itto the display device D (104) over the point-to-point link 202 between the display device B (102) and the display device D (104).

Similarly, the display device C (103) is configured to merge and display image data corresponding to areas ac, c, and Cd, received from display device A (101) over point-to-point link 204 and image data corresponding to area abed, received from display device A (101) using antenna 213.

The display device C (103) is also configured to cut a copy of the image data corresponding to area Cd and to send it to the display device D (104) over the point-to-point link 203 between the display device C (103) and the display device D (104).

Also, the display device D (104) is configured to merge and display image data corresponding to areas bd and d, received from display device B (102) over point-to-point link 202, image data corresponding to area cd received from display device C (103) over point-to-point link 203 and image data corresponding to area abed, received from display device A (101) using antenna 214.

Thus, in the example of Figure 2, display devices 101, 102 and 103 are relay devices since they perform cutting and routing of copies of image data to other display device(s). In contrast, display device 104 is not a relay device since it only receives and merges image data and displays it, without retransmitting any copy of data to another display device.

It can be noticed that thanks to broadcasting, image data corresponding to area abed do not need to be replicated twice on the network, to be received by each of the four display devices. Indeed, only one copy is broadcast, and reaches several display devices.

Furthermore, copies of image data corresponding to areas cd and bd are advantageously relayed to the display device D respectively by display device C and by display device B, which also have to display one of these areas.

Figure 3 shows a second example of image data distribution which is a variant of Figure 2.

In the example of Figure 3, the network 100 comprises an additional omnidirectional antenna 310 attached to the source device 110, able to communicate with the omnidirectional antennas 21 1-214 attached to the display devices 101-104 of Figure 2.

In the system implementation variant described in this Figure, the source device 110 is configured to cut image data parts for the display devices 101-104.

For example, the functional architecture of source device 110 may be similar to the one that will be described with reference to Figure 5, except that display device specific modules (e.g. adjustment unit 505, FIFO 506 and display unit 507) are not necessarily present.

In this second example, the source device 110 extracts the image data corresponding to the area abcd from the source image (here also composed of nine areas a, ab, b, ac, bd, c, cd, d, and abcd), which is broadcast over antenna 310, in order to be received over antennas 211-214 by the respective display devices 101-104.

Thus, no duplication/copy of image data is performed for the area abcd which is broadcast to the display devices once extracted from the source image by the source device 110.

Similarly to the first example, image data corresponding to the remaining areas a, ab, b, ac, bd, C, Cd and d are sent over link 111 to the display device A (101).

Consequently, a difference with the first example of Figure 2 is that the display device A (101) also receives image data over a point-to-multipoint link, in particular using antenna 211.

Furthermore, the display device A (101) is configured to merge image data corresponding to areas a, ab, ac received by the point-to-point link 111 and image data corresponding to the area abcd received over the point-to-multipoint link between antennas 310 and 211.

The following part of the process performed by the display devices 101-104 may be similar to what has been described above with reference to Figure 2.

Figure 4 shows an example of image data distribution in an MP system comprising six display devices A, B, C, D, E and F (101 to 106) for displaying an image covering a projection screen in two horizontal rows and three vertical columns.

Obviously, the present invention is not limited to MP systems comprising four (Figure 1) or six display devices. The elements having the same references as those of Figure 1 or 2 have been described above. In particular, display devices 105 and 106 may be similar to display devices 101-1 04 that have been described above.

Point-to-point links 401-406 may present the same characteristics as links 101-104.

Antennas 411-416 may be similar to omnidirectional antennas 111-114.

In this example, the source device 110 sends a whole soulce image to the master display device 101, over link 111. The source image is here composed of fifteen parts corresponding to the following screen zones: area a, area ab, area b, area ac, area abed, area bd, area e, area cd, area d, area ce, area edef, area df, area e, area of, and area f.

In practice, the display device A (101) displays area a of the image 130 and also areas ac, ab and abed. The display device B (102) displays area b of the image and also areas ab, bd, and abed. The display device C (103) displays area e of the image and also areas ac, cd, and abed. The display device D (104) displays area d of the image and also areas bd, Cd, abed, cdef, and df. The display device F (105) displays area e of the image and also areas Ce, ef, and cdef. The display device F (106) displays area f of the image and also areas of, df and edef.

Thus, each of areas a, b, C, d, e and f of the image 130 is displayed only by one display device, respectively display device A, B, C, D, E or F. On the screen, areas ae, abed and bd form a first vertical rectangle and areas Ce, edef, and df form a second vertical rectangle, both rectangles occupying the full height of the rectangular area 130. Areas ab, abed, ed, edef and of form a horizontal rectangle occupying the full width of the rectangular area 130. The first and second vertical rectangles and the horizontal rectangle are displayed simultaneously by several display devices. These areas correspond to edge blending zones of the image 130.

In particular, area ab is simultaneously displayed by both display device A and display device B, area ae is simultaneously displayed by both display device A and display device C, area bd is simultaneously displayed by both display device B and display device D, area ed is simultaneously displayed by both display device C and display device D, area ee is simultaneously displayed by both display device C and display device F, area ef is simultaneously displayed by both display device F and display device F, area df is simultaneously displayed by both display device D and display device F, area abed, is simultaneously displayed by the four display devices A, B, C and D, and area edef, is simultaneously displayed by the four display devices C, D, E and F. Consequently, a huge amount of duplicated image data is to be provided over the network. To that end, in this example, a network is considered comprising the following features: -six point-to-point links (e.g. using cables), namely link 401 from display device A (101) to B (102), link 402 from display device B (102) to display device D (104), link 403 from display device C (103) to display device D (104) and link 404 from display device A (101) to display device C (103), link 405 from display device C (103) to display device E (105) and link 406 from display device 0 (104) to display device C (106), and -six omnidirectional antennas 411, 412, 413, 414, 415 and 416 attached to the respective display devices A, B, C, 0, E and F (101, 102, 103, 104, 105, and 106).

In this example, the whole image is transmitted from the source device 110 to display device A (101) through link 111.

In a variant (similar to Figure 3), the source device 110 may comprise one (or more) omnidirectional antenna and may broadcast some of the image data using it, to be received by several of the display devices 101-106 (using their own antennas 411-416). This variant allows even more duplicated data to be reduced.

In order to reduce the overload of point-to-point links even more and to bypass the problem of a limited number of input/output ports, several display devices acting as relay devices may use broadcasting to route certain image data to other display devices.

Preferably, image data corresponding to areas to be displayed simultaneously by several (two, four, or more) display devices are broadcast to these display devices instead of being sent through point-to-point links. In doing so, further copies of the same image data are avoided.

In the example of Figure 4, display device A (101) is configured to cut the image data parts corresponding to the four screen zones a, ab, ac and abcd of each complete source image received from source 110, and to display it.

Display device A (101) is also configured to split a copy of received image data in at least three parts, for instance: -a part corresponding to areas ab, b, bd, d, df, and f -another part corresponding to areas ac, c, cd, Ce, cdef, e, and ef -again another part corresponding to area abed.

Next, the copy of image data corresponding to areas ab, b, bd, d, df, and f is sent to the display device B (102) over the point-to-point link 401 between the display device A (101) and the display device B (102).

The copy of image data corresponding to areas ac, c, cd, ce, cdef, e, and ef is sent to the display device C (103) over the point-to-point link 404 between the display device A (101) and the display device C (103).

The copy of image data corresponding to area abed is broadcast to display devices B (102), C (103), and D (104), using the omnidirectional antenna 411 of display device A (101) and the respective reception antennas 412, 413, and 414 of the corresponding display devices B (102), C (103), and D (104). Thus, only one copy is needed to reach the display devices B, C, D. Display device B (102) is configured to merge and display image data corresponding to areas ab, b, and bd, received from display device A (101) over point-to-point link 401 and image data corresponding to area abed, received from display device A (101) using antenna 412.

Similarly, display device C (103) is configured to merge and display image data corresponding to areas ac, C, ce, cdef and ed, received from display device A (101) over point-to-point link 404 and image data corresponding to area abed, received from display device A (101) using antenna 413.

In this example, display device C (103) is also configured to split a copy of received image data (corresponding to areas ac, c, cd, Ge, cdef, e, and efl into at least three parts, for instance: -a part corresponding to areas ce and e -another part corresponding to area cd -still another part corresponding to areas cdef and ef.

Next, the copy of image data corresponding to areas ce and e is sent to the display device E (105) over the point-to-point link 405 between the display device C (103) and the display device E (105).

The copy of image data corresponding to area cd is sent to the display device D (104) over the point-to-point link 403 between the display device C (103) and the display device D (104).

The copy of image data corresponding to areas cdef and ef is broadcast to display devices 0 (104), E (105), and F (106), using the omnidirectional antenna 413 of display device C (103) and the respective reception antennas 414, 415, and 416 of the corresponding display devices D (104), E (105), and F (106).

Because display device 0(104) is not concerned by area ef (i.e. area ef will not be displayed by this display device), image data corresponding to area ef is discarded prior to merging areas to be displayed.

In particular, display device 0 (104) is configured to merge and display image data corresponding to areas bd, d, and df, received from display device B (102) over point-to-point link 402, image data corresponding to area Cd received from display device C (103) over point-to-point link 403, image data corresponding to area abed, received from display device A (101) using antenna 414, and also image data corresponding to area cdef, received from display device C (103) using antenna 414.

Display device E (105) is configured to merge and display image data corresponding to areas Ce, and e, received from display device C (103) over point-to-point link 405 and image data corresponding to areas ef and cdef, received from display device C (103) using antenna 415.

Similarly, display device F (106) is configured to merge and display image data corresponding to areas df, and f, received from display device 0 (104) over point-to-point link 406 and image data corresponding to areas ef and cdef, received from display device C (103) using antenna 416.

Interferences may occur between the radio transmission channels of display devices A and C. To avoid such a phenomenon, channel sharing I multiplexing methods like TDMA or EDMA may be used.

The sharing is facilitated by the fact that image data transmitted on both channels represent only a small percentage of the bandwidth requirement for transmitting the total image data (i.e. corresponding to the full source image).

Figure 5 is a functional diagram illustrating a possible architecture of a device for distributing image data according to embodiments, for instance one of the display devices 101 to 106 of Figures 1-4.

This functional diagram essentially shows flows of image data and control data. The system boundary 500 (thick dashed line) delimits the internal units of the display device from the outside world.

The display device comprises a limited number (one or more) of input ports.

The input port 501 may be analogue (e.g. composite, S-video, VGA, etc.) or digital (e.g. DVI, H DM1, DisplayPort, etc.). It may be capable of receiving image data for instance from the source device 110, through point-to-point link 111 of Figures 1-4.

Image data originating from input 501 are handled by an input interface 502. The input interface 502 is configured to provide a control unit 509 with information on the available image data (e.g. resolution, colour depth, chroma subsampling, frame rate etc.), and also to be configured by the control unit 509 on the basis of that information.

The image stream is then optionally handled by an optional downscaling unit 503. In accordance with instructions from the control unit 509, the downscaling unit 503 applies initial downscaling in case of significant mismatch between the resolution of the input image data and the available display resolution, taking into account the size of the display window 130 where the image is to be finally displayed.

Next, the input image data are handled by a cut and merge unit 504, and the cut and merge unit 504 may also handle other image data incoming from other display devices, through an inter-display-devices network interface unit 508, either by means of point-to-point links 513 or by means of broadcasting link(s) 511.

In practice, the broadcasting link 511, which is part of the inter-display-device network (network 100 of Figure 1), may be a wireless link communicating through an antenna with omnidirectional characteristics. The high-speed point-to-point links 511, also part of the network, may consist for instance of at least one but preferably several directional antennas operating in the 60 GHz range, wired Ethernet ports, HDMI inputs and outputs or a combination thereof. In a particular embodiment, smart antennas configurable on the fly to act either as omnidirectional or as directional antennas (with selectable direction) may alternatively play the role of links 511 or 513.

For instance, the cut and merge unit 504 of display device B of Figure 2 may receive areas ab, b, bd, d over the point-to-point link 513 (link 201 in Figure 2) with display device A and area abed over the broadcasting link 511 (antenna 212 in Figure 2), through the network interface 508.

The cut and merge unit 504 is also configured to split a copy of the received image data into several parts corresponding to one or more screen zones (e.g. ab, b, bd, d), according to configuration instructions on the cut positions given by control unit 509.

Furthermore, Image data corresponding to screen zones to be displayed by the currently described display device (e.g. ab, b, bd, and abed to be displayed by display device B) are then merged in the cut and merge unit 504 and transmitted to a processing unit 505.

In practice, the processing unit 505 is configured to perform geometric and photometric adjustments upon configuration by the control unit 509. For instance, a smooth reduction of luminance from left to right, top to bottom or both is applied within edge blending zones (e.g. ab, bd respectively abcd). Also, the processing unit 505 may also apply geometric distortion correction and scaling so that the areas displayed by the display device exactly fit a part of the total image area 130, without going over the limits of the image zone 130. Following the application of these adjustments, the processed image data are transmitted to a FIFO unit 506.

The FIFO 506 acts as a buffer. In other words, it is configured to store a predetermined number of frames in order to delay their display and compensate for transmission delays or latencies varying with the network hop count.

In practice, the synchronisation is also controlled by the control unit 509, so that the image data to display is transmitted to a display unit 507 in a timely manner.

Thanks to the FIFO unit 506, all the display devices of the MP system will start displaying their respective parts of a same image frame, virtually at the same time.

Time synchronisation between the different display devices is also achieved thanks to the exchange of local time data (timestamps) through the control unit 509 of the other display devices of the network through interface 508, and the control unit 509 of the currently described display device.

The display unit 507 then controls the light valve (typically an LCD, LC0S or DLP unit) of the display device.

Moreover, the cut and merge unit 504 is configured to merge other image data corresponding to screen zones to be routed to one or more other display devices (e.g. bd and d to be transmitted from display device B to display device D on Figure 2). The merge data are then sent through the network interface 508 using either point-to-point link 513 (e.g. link 202 between display device B and display device D) or broadcasting link 511 (see for instance Figure 4, antenna 413 of display device C used for the transmission of merge data corresponding to areas cdef and ef to display devices D, E and F).

The control unit 509 is the central functional block and is configured to implement embodiments. It may for instance comprise a CPU with dedicated RAM working memory, executing instructions, representing the algorithms described above and below, stored as firmware in a ROM memory; furthermore communicating through a suitable bus or internal control links with other control blocks of other display devices.

A control interface 510 may manage the communication with a user of the display device, through a control link 512. The control link 512 may comprise an infrared input from the remote control interface 510. Alternatively, the user input interface 510 may comprise a button panel. In both cases, output may be presented to the user through on-screen pop-up menus. Other possible user interfaces may comprise a terminal or a dedicated control application running for instance on a PC or a smartphone, in which case the control link 512 may be for instance a USB link, an RS- 232 link or a TCP/IP connection over Ethernet or Wi-Fi.

The invention also relates to embodiments wherein the source device 110 also plays the role of a distributing device, in that it comprises modules/units described above with reference to display devices 101-106. Generally, the source device does not include FIFO unit 506 or display unit 507 which are specific to the architecture of display devices.

Thanks to these modules, the source device may perform a differentiated distribution of image data (i.e. cutting source image data and sending a part of it through a point-to-point link and another part of it though a broadcasting link), according to embodiments, as described for instance with reference to Figure 3.

Figure 6 shows an example of steps of an algorithm for determining configuration information, also called routing scheme, in an MP system as described above.

In practice, this algorithm may be executed by the control unit 509 of the display device to which the source device 110 is attached, typically the master display device 101.

Required input information available to each of the other display devices (e.g. display devices 102, 103, 104, and possibly 105 and 106) is transmitted to the master display device 101 over network 100. Output data resulting from the algorithm (i.e. configuration information) are distributed by master display device 101 to the other display devices through this network.

The process starts at step 600. Various kinds of information need to be gathered in order to determine configuration information.

At step 601, all display devices of the MP system are identified. Their cut capacity and their merge capacity are obtained. In particular, the cut capacity corresponds to the maximum number of image data parts the display device is able to extract from the received frames, including the data part to be displayed directly by the display device in question. The merge capacity corresponds to the maximum number of image data parts obtained over different paths that the display device is able to consolidate.

At step 602, the number m of vertical display device columns, the number n of horizontal display device rows (see above the description of Figure 1) are determined. Also, the pixel coordinates of the borders of all edge blending zones in the coordinate system of the image to be displayed, are obtained.

The sizes in pixels and consequently in bits, of all (2m1)*(2n1) image data parts corresponding to the screen zones are determined, based on the aforementioned coordinates. Finally, knowing the frame rate and possible network overhead (packet headers, check sums, error correction coding...), the network bandwidth requirement for each image data part is determined.

At step 603, a list of all wired and wireless links in the inter-display-devices network 100 is obtained, together with the characteristics (point-to-point or broadcasting type; which destination can be reached) and the capacity in Gbitls of each link. The way to address each display device on network 100 is also determined.

A loop 604 is executed for all edge-blending zones that need to be displayed by four display devices. It comprises sub-steps 605 and 606 which are executed until a route has been found for all the edge blending zones to be displayed by four displays.

At sub-step 605, a relay display device capable of reaching simultaneously the four destination display devices in question through broadcasting is identified.

Alternatively, this relay display device is part of the four destination display devices and only reaches the remaining destination display devices through broadcasting.

In both cases, the relay display device identified extracts the edge-blending zone in question for local display. In this sub-step the bandwidth required to transmit the image data in question must fit within the network bandwidth available for broadcasting. If the source device 110 has broadcasting and cutting capacities as described with reference to Figure 3, it also constitutes a candidate for being a relay.

At sub-step 606, a route/path of point-to-point links from the source device to the relay display device identified at sub-step 605 is determined if the relay is not the source device 110 itself. In practice, enough bandwidth must be available on this path to transmit the image data. For instance, the path may be determined so that the hop count to reach the relay is minimal.

Once a route has been determined for all the edge blending zones to be displayed by four display devices, another loop 607 is executed for all edge-blending zones that need to be displayed by two display devices. This comprises sub-steps 608 and 609 which are executed until a route has been defined for all the edge blending zones to be displayed by two display devices.

At sub-step 608, a route of point-to-point links from the source device 110 having one of the destination display device as terminal node and the other one as intermediate node, is identified. To that end, the bandwidth requirements, as well as the cut/merge capacities of the involved display devices are taken into account. The routes already identified during the loop 604 are also considered in the current identification of the route of point-to-point links.

If no suitable route has been found at sub-step 608, a broadcasting relay display device capable of reaching the two destination display devices in question, and a route of point-to-point links from source device 110 to said relay are determined.

Again, bandwidth requirements and cut/merge capacities are taken into account in this route determination.

For instance, display device C (103) in Figure 4 may be identified as a broadcasting relay for image data corresponding to both screen zones cdef and ef, which cover a rectangular screen area and hence may be transmitted as a single sub-stream, the cutting of which may be deferred to the respective destination display devices.

Once a route has been determined for all the edge blending zones to be displayed by two display devices, another loop 610 is executed for all screen zones to be displayed by only one display device (e.g. areas a, b, c, d, and e, f). It comprises a sub-step 611 that is executed for each area to be displayed by only one display device.

At sub-step 611, a route from the source device 110 to a given display device is determined, taking into account the bandwidth requirements and the display device's cut/merge capacities.

After loop 610 the algorithm stops at step 612.

Figure 7 shows an example of a MP system, according to particular embodiments, as a variant of the MP system of Figure 1.

Similarly to the MP system of Figure 1, the MP system comprises a plurality of display devices, here two display devices 701 and 702, also marked by letters A and B. These display devices may be projectors, for instance video projectors.

Display device 701 is connected to a source device 110 similar to the source device of Figure 1, by means of a point-to-point link 721. For instance, link 721 is a wired link. It may also be a wireless link using for example directional antennas attached to the source device 110 and the display device 701.

In this example, display device 702 is also connected to the source device 110, by means of a point-to-point link 722. For example, link 722 is a wired link. It may also be a wireless link using for example directional antennas attached to the source device 110 and the display device 702.

The source device 110, and the display devices 701 and 702, may also comprise a communication means with wide-range characteristics, thus adapted to perform broadcasting communications. To that end, one or more omnidirectional antenna(s) 710 similar to antenna 310 of Figure 3, may be attached to the source device 110, and one or more omnidirectional antenna(s) may be attached to the display devices 701 (antenna 711) and 702 (antenna 712).

The antennas 711 and 712 may be similar to antennas 211 and 212 on Figure 3.

In some embodiments, smart antennas configurable on the fly both as directional (with chosen direction) or wide-area antennas may be used to establish both point-to-point links 721 and 722, and broadcasting links.

In an original way, the hereby described MP system is configured to display an image on a screen 750 (e.g. a megawall) composed of several sub-screens 751 and 752, here located adjacently.

In some embodiments (not shown), the sub-screens may not be located adjacently.

Such screen may be useful to display an image that comprises for instance pop-up windows over a background, or so called picture-in-picture.

In this example, the MF system is configured to display two sub-images a and b on the screen 750. In particular, sub-image a is displayed in the background of the sub-screen 751, and sub-image b is displayed in the background of the sub-screen 752. In addition, a third sub-image c is displayed in a small window located in the foreground of sub-screen 751 and also in the foreground of sub-screen 752.

In some embodiments, sub-images a, b and c may be for instance from a video stream.

According to embodiments, the source device 110 may distribute image data corresponding to sub-images a, b and c as follows: -image data corresponding to sub-image a are sent to display device 701 through the point-to-point link 721, -image data corresponding to sub-image b are sent to display device 702 through the point-to-point link 722, -image data corresponding to sub-image c are broadcast to both display devices 701 and 702 using antenna 710 and received respectively by antennas 711 and 712.

Thus, in accordance with the principle of preferred embodiments, image data corresponding to a sub-image to be displayed simultaneously by several display devices are transmitted over a broadcasting link while image data corresponding to a sub-image to be displayed by only one display device is sent over a regular point-to-point link.

Variants of this configuration that are not represented in this Figure may comprise more than two display devices.

For instance, similarly to what has been described with reference to Figures 2 and 4, broadcasting of image data corresponding to sub-image c (to be displayed by several of these display devices) may be performed by one or several of the display devices rather than by (or in addition to) source device 110 in such a case.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims. In particular different features from different embodiments may be interchanged, where appropriate.

Claims (20)

1. CLAI MS1. A device for distributing image data obtained from a source device, corresponding to at least part of an image, said image to be displayed by a plurality of display devices of a multi-projection system, the device comprising: -a module for sending a first part of said image data, to a first display device of the plurality of display devices, said first part corresponding to a first sub-image to be displayed only by said first display device, -a module for transmitting a second part of said image data, to a set of display devices of the plurality of display devices, said second part corresponding to a second sub-image to be displayed by each device of the set of display devices, wherein -the module for sending the first part to the first display device comprises communication means enabling sending of image data according to a point-to-point communication scheme, and -the module for transmitting the second part to the display devices of the set, comprises communication means enabling transmission of image data according to a broadcast communication scheme.
2. 2. The distributing device according to claim 1, wherein said communication means enabling sending of image data according to a point-to-point communication scheme comprise wired communication means.
3. 3. The distributing device according to claim 1, wherein said communication means enabling sending of image data according to a point-to-point communication scheme comprise wireless communication means.
4. 4. The distributing device according to claim 3, wherein said wireless communication means comprise at least one directional antenna.
5. 5. The distributing device according to claim 1, wherein said communication means enabling transmission of image data according to a broadcast communication scheme comprise wireless communication means.
6. 6. The distributing device according to claim 5, wherein said wireless communication means comprise at least one omnidirectional antenna.
7. 7. The distributing device according to any one of claims 1 to 6, wherein said distributing device is one of the display devices of the plurality of display devices, relaying at least part of the image data obtained from the source device to other display devices of the multi-projection system.
8. 8. The distributing device according to any one of claims 1 to 6, wherein said distributing device is the source device providing the image data to the multi-projection system.
9. 9. The distributing device according to any one of claims 1 to 8, wherein said image data correspond to video data to be displayed by video projectors as display devices.
10. 10. A multi-projection system comprising a plurality of display devices for displaying parts of image corresponding to image data obtained from a source device, each display device comprising communication means enabling sending of image data according to a point-to-point communication scheme, and communication means enabling transmission of image data according to a broadcast communication scheme said multi-projection system comprising at least one distributing device according to any one of claims ito 8.
11. 11. A method of distributing image data obtained from a source device, corresponding to at least part of an image, said image to be displayed by a plurality of display devices of a multi-projection system, the method comprising the following steps: -sending a first part of said image data, to a first display device of the plurality of display devices, said first part corresponding to a first sub-image to be displayed only by said first display device, -transmitting a second part of said image data, to a set of display devices of the plurality of display devices, said second part corresponding to a second sub-image to be displayed by each device of the set of display devices, wherein: -the first part is sent to the first display device using communication means enabling sending of image data according to a point-to-point communication scheme, and -the second part is transmitted to the display devices of the set, using communication means enabling transmission of image data according to a broadcast communication scheme.
12. 12. The method according to claim 11, wherein said second part to be transmifted is determined based on the network capacities and/or based on the capacities of the display devices of the set.
13. 13. The method according to any one of claims 11 to 12, further comprising a step of buffering parts of image data received at a display device, based on time data received with said parts.
14. 14. The method according to any one of claims 11 to 13, further comprising a step of determining a route from said distributing device, to said first display device, over which said distributing device sends said first part of image data.
15. 15.The method according to claim 14, wherein the route is determined so that the number of intermediaries to reach the first display device is minimized.
16. 16. The method according to any one of claims 11 to 15, further comprising the following steps: -identifying a relay among said plurality of the display devices and the source device, said relay comprising communication means enabling sending of image data according to a broadcast communication scheme, -determining a route from said distributing device, to said relay, over which said distributing device sends a third part of said image data to said relay, said third part corresponding to a third sub-image to be displayed by several display devices of the plurality of display devices.
17. 17. The method according to claim 16, wherein the route is determined so that the number of intermediaries to reach the relay is minimized.
18. 18.A distributing device as hereinbefore described, with reference to, and as shown in, Figure 5 of the accompanying drawings.
19. 19. A multi-projection system as hereinbefore described, with reference to, and as shown in, Figures 1 to 4 or 7 of the accompanying drawings.
20. 20. A method of distributing image data as hereinbefore described, with reference to, and as shown in, Figure 6 of the accompanying drawings.