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Description  |
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FIELD AND BACKGROUND OF THE INVENTION
The present invention relates in general to telecommunication equipment and
in particular to a new and useful system for conducting a videoconference
between a plurality of participants who are physically present at
different locations.
A comprehensive review of the prior art in this field is given in the
German publication Kommunikations-Endgerate Grundlagen, Verfahren,
Bausteine, Gerate, Systeme (Communication Terminals-Fundamentals, Methods,
Building Blocks, Systems) by Friedrich Ohmann, Springer publishing house,
Berlin, Heidelberg, New York, Tokyo 1983, chapter 7.5 "Bildkonferenz"
(Videoconference) pages 414-423. According to that source, what is
required of such conferences is that all subscribers
(interlocutors/participants) see and hear each other during the whole
time-simultaneously, and in the correct direction, and be able to show one
another written documents and objects. Besides the minimum technical
equipment necessary at every location for carrying out the conference, the
costs of terminals and their interconnections increase in an unjustifiable
proportion with the number of interconnected locations, if no particular
measures are taken, yet all of such measures have their advantages and
disadvantages.
To reduce these costs, particularly such as relate to the taking,
transmitting, and reproducing of pictures, measures such as parallel
processing and switching, and mixed forms developed therefrom, may be
provided. With the first mentioned measure, the number of needed terminals
and channels can be reduced, but always several conference participants
are required to be present together at the location. With the other means,
a single picture must always be transmitted to all of the interlocutors,
and while no full interconnection is required, nevertheless a continual
voice-controlled or manual switching is necessary, preferably by one of
the participants.
A solution, considered trivial, and requiring everyone of the participants
to be equipped with complete terminals, such that picture and sound from
one participant is transmitted individually to all other locations of the
conference and there reproduced with an individual loudspeaker and screen,
must certainly be rejected as unjustifiably expensive. That is why prior
art videoconferencing systems have been limited to arrangements where the
interlocutors are concentrated at two locations between which a
point-to-point communication for picture and sound in the two directions
is established (studio conference, committee room conference). Even in
systems designated "working place conference", the main communication, for
example through a public network, is established between two localities,
with the individual working places being in the same buildng or at the
same location, each equipped with a minimum of terminals and being
connected together within each of the localities through concentrators.
Prior art videoconferencing therefore has remained restricted to
conferences between two regional groups of participants.
SUMMARY OF THE INVENTION
The present invention is directed to a system for permitting a kind of
working place conference between participants at different, mutually
independent locations, and therefore, goes partly back to the already
mentioned solution, which is trivial in itself, of interconnecting the
individual locations by communication means in a manner such that all
video and sound signals of each of the locations can pass to all the other
locations. It must be ensured, as before, that all the participants can
see and hear each other continually and simultaneously and can show
written documents, objects, etc. However, the requirement mentioned above
that the participants look at one another in the correct direction applies
only to several participants present at the same location and is therefore
substantially irrelevant for individual participants using a terminal
exclusively.
The excessive costs which might have been expected with such a solution do
not materialize if the features of the present invention are provided.
Accordingly, an object of the present invention is to provide a
communication system for performing or holding videoconferences between a
plurality of participants who are present at different participant
locations, which comprises a participant terminal or subscriber station at
each location including a camera for producing a video source signal
corresponding to the scene at the participant location, a monitor or other
video sink means, i.e. video signal receiving and converting means, for
receiving a video signal to generate or reproduce a picture or image, a
microphone for generating audio source signals and a loudspeaker as audio
receiver or sink means, i.e. audio signal and receiving and converting
means, for receiving audio sink signals, i.e. transmitted audio source
signals, and converting such signals to sound, and control means which can
be manipulated to initiate communication with other participants and to
control the images displayed. A central station is connected to all of the
participant terminals and includes means for receiving source signals from
and transmitting sink or received signals to all the participant terminals
as well as storage units for storing in each case a large size picture and
at least one small coarse grained picture for each active participant
location or terminal, the central station having a programmed processor
for receiving control signals from the participant terminals to control
the display assembly and split screen of large and small or coarse
pictures at the participant terminals individually. The central or control
station also includes multiplexers for providing or outputting the video
signals to the various video monitors at the participant terminals. The
programmed processor includes a program read and write control for
assembling the large and coarse pictures. Connecting lines are connected
for switching between each participant terminal and the central station
with the control lines having sufficient bandwidth for video, audio and
control signal channels.
The inventive solution substantially requires only a first and final
expenditure for the equipment of the central station for the
videoconference system. It is important that every participating location
needs, of course, a camera, a single monitor, and the usual
microphone-loudspeaker means, i.e. a minimum of terminal equipment, and
also the broad-band go and return channels needed in any case for any
videoconference. Another considerable advantage of the invention is that
no individual is needed for effecting the master control or composition of
the picture or split screen display. The control is effected from every
location individually, anytime as wanted and desired, without affecting
the other locations, within several predetermined patterns. This is a new
performance feature for videoconferencing. All the pictures under
individual control, with the information displayable in size and
arrangement on the local monitor, are produced by the central station of
the videoconference system and correspondingly transmitted as a full size
individual or mixed picture. The central station thus operates as an
intermediary or exchange between sources and sinks, i.e. transmitting and
receiving signal points, at the subscriber stations and, therefore, the
relatively expensive equipment for this mediation and processing for all
the connectable locations of individual video signals to image mixtures is
needed only in this station and only to an extent actually required for
the purpose. The same applies analogously to the far less expensive
processing and mediation in the audio section.
Particularly advantageous embodiments of the invention include respective
features which provide various advantages which will now be discussed.
If picture storage units and multiplexers are employed for video signals in
digital form, conventional networks can be used, as before, equipped for
transmitting analog signals. As far as the connecting lines are concerned
it should be possible to make sure that future requirements imposed on
quality will also easily be met, or at least not be difficult to meet.
Such requirements regard the transmission bandwidth of TV standard, e.g. 5
MHz, or future dgital HDTV (high definition television) instead of
PICTUREPHONE standard with presently 1 MHz; and audio channels of hi fi
quality, e.g. 10 KHz, instead of telephone quality bandwidth, usually 3
KHz. Since even in local networks advance systems with a broadband signal
transmission through optical fibers, i.e., multimode gradient fibers, have
already been provided, single mode systems must also be considered in both
the local and long distance regions.
Obvious limits are set on the number of participants in any conference, not
only videoconferences. This limit is from two to not more than about
twelve participants. According to the invention central stations can be
equipped with any number of picture storage units and multiplexers but at
least with a number needed for a single videoconference. With a sufficient
number, the equipment may then be interconnected in the central station to
groups for every one of the conferences, with a set of corresponding
control devices for each of these groups.
The problem of how to make the video signals coming from the individual
sources available in the central station, as both a complete or full
screen picture, or a split screen picture composed of a large picture and
at least one coarsened picture, i.e., reduced or small picture, can be
solved, as to the hardware, with picture storage units, for example,
having a storage capacity exceeding that of a large picture, i.e. a full
screen picture. That is, the large pictures and small pictures are stored
already in the way or size in which they are later to be available.
However, since in a mixed or split screen picture comprising a large
picture and a plurality of small ones, the large picture must be somewhat
smaller than the screen, i.e. particularly such that the marginal zones
must be suppressed vertically and/or horizontally, at one or both sides,
this can be done better in software terms while reading it out from a
picture storage, than in hardware terms. Picture storage units having a
capacity of only one complete or full screen picture are also possible in
which the complete picture, a large picture, and small pictures are read
out under a corresponding program control.
At every location, also the participant's own image can be displayed as a
complete or full screen picture or a mixture or split screen picture
arrangement on the individual monitors, since with the control freedom,
there is no difference between the transmitting and the receiving
location.
The size of a large picture and a coarsened picture, i.e., a small one,
should of course be only as small as needed, and, as large as possible.
Keeping the size of the complete, picture constant the size of the large
picture can freely be chosen at every location, as a function of the
number and size of the small pictures in the mixture, and conversely,
within the pattern or raster of split screen variants predetermined by the
central station.
For example, if at a location no display of split screen pictures of all
the participants is provided, i.e. where a more or less narrow selection
from the panel is preferred, or if only a few locations are interconnected
for a videoconference, the small pictures may remain relatively large.
Every location may be occupied by as minimal as a single participant, which
may even be the rule. With a plurality of participants at a location, they
will be seated adjacent each other. Then a control instruction may be
delivered to the central station to suppress in the picture received from
this location only the horizontal margins, and to make available small
pictures having a certain minimum width, for example, corresponding to
only half the width of the pick up field.
If no picture control instruction is received from a location, a picture is
delivered to this location corresponding to a standard program. This may
take into account control instructions from other locations, majority
decisions, etc. This also means that with a consent, a control keyboard as
a terminal equipment elements may be omitted at a location without any
functional disadvantage.
To produce small pictures, and thus reduce the number of picture elements
in the picture, a low pass filtering may be provided. Portraits, however,
furnish soft contours, so that with digital storage units, for example,
only the writing rate is to be varied relative to a large picture storage.
Written documents and objects etc. are usually always displayed as large
or full pictures and if in such an instance a document is displayed in
small size, with not quite distinct characters, even such a quality is
satisfactory if it is capable of stirring interest in seeing a large, more
distinct picture.
The individually selectable distribution in a split screen picture should
be based on a structure pattern predetermined by a standard program of the
central unit. For example, with five participants, one at each location,
the participant at a given location might appear in a large picture, the
other four in a vertical row of four small pictures at the right side of
the screen. First the raster of the mixed or split screen picture is
transmitted and each of the participants may now individually make changes
in the raster.
The audio channels may be switched in parallel with the switching of the
video signals, and in any case this is done also in the central station.
Quite generally, conferences are kept to a speaking discipline, so that
usually a single participant will be heard at any one time. Because of the
large freedom permitted with the picture control, it may happen in the
case of a parallel switching of audio and video channels, that only a
large picture of a participant will appear at one location while another
participant throws in an important comment which then will not be heard at
that location. It is therefore advisable to transmit the audio signals of
all the other sources as a summation signal to every sink or receiving
point. In terminals with a two-channel sound reproduction, it is
advantageous in addition to reproduce the speech signals belonging to the
small pictures at the right-hand or left-hand side of a monitor,
corresponding to the right or left audio channel, and the speech signals
belonging to a large picture and to participants who are not in the
picture at the same time, from the middle portion of the monitor.
A sound control with individually controllable sound mixers, i.e.
controllable intermediate amplifiers or preamplifiers in the central
station for every audio signal coming from a source, and suitable sound
control equipment at the individual locations, make it possible to
simulate the so-called "cocktail party effect".
That is, should one of the participants wish to concentrate acoustically on
a certain other participant whose audio signal is too drowned out by the
summation signal, he or she may increase through the audio control the
level of the respective audio signal in the central station, and even
decrease at the same time the other levels.
For this purpose, and also to permit an individual picture control, the
participants may be aided with a useful expedient consisting of
distinguishing marks which are permanently or temporarily mixed into the
pictures and comprise figure or letter combinations, or pictorial
characters, etc., and permit a quick and clear identification of a picture
with the source and the corresponding button of the keyboard. These
measures however, do not contribute to the sought directional accuracy in
looking at and receiving the sound from the other participants.
Other embodiments of the invention are particularly advantageous from the
viewpoint of communication technology. They may readily be employed in
radial or star type networks, one of the most usual structures of public
communication systems. To successfully conduct or perform a video
conference, the central station therefore is of course to be located in
the proximity of most of the participating locations. Locations which are
far or very far away therefrom may be supplied at least through a common
return channel, to save channel capacity and cost for long transmission,
such as through intercontinential connections. In such an instance, of
course, only individual control wishes of a single one of such remote
locations can be taken into account. Changes in the control, however, may
be agreed in the acoustical way, i.e. via the audio transmission.
The various features of novelty which characterize the invention are
pointed out with particularity in the claims annexed to and forming a part
of this disclosure. For a better understanding of the invention, its
operating advantages and specific objects attained by its uses, reference
is made to the accompanying drawings and descriptive matter in which a
preferred embodiment of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
Details of the invention are diagrammatically shown in the drawings in
which:
FIG. 1 is an overall diagram of a videoconference communication system;
FIG. 1a is a 12 participant station system corresponding to FIG. 1.
FIG. 2 is a simplified block diagram of the equipment for mixing, switching
and transmitting video signals in the central station;
FIG. 3 is a simplified block diagram of the equipment for mixing,
switching, and transmitting audio signals in the central station;
FIG. 4 illustrates the size proportion between a complete or full screen
picture and three variants of large pictures;
FIGS. 5 to 7 show three variants of small pictures;
FIGS. 8 to 11 show variants of mixed or split screen pictures, composed of
large and small pictures; and
FIG. 12 shows a control desk unit with elements for selecting and
controlling the sound and picture reproduction.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates the concept of a system for videoconferencing according
to the invention. Considering its performance, the system comes closest to
those which are known under the designation of "working place
videoconference". Such systems can conduct a videoconference between
plural participants who are each at their own work place at spaced
locations from each other.
At each of the selected connectable subscriber stations or terminal
locations 25, five such locations or stations 25-A to 25-E being shown in
FIG. 1, equipment is needed (see location 25-A where details are
indicated) having a terminal connecting unit 35 for the following pieces
of equipment 26 to 30:
sinks or receiving and converting means 27, 29 for video and audio signals
42, 40 (namely a monitor 27 and loudspeaker 29);
sources 26, 28 of video and audio signals 41, 39 (namely a camera 26 and
microphone 28);
controller unit 30 (FIG. 12), comprising a dialling device 31, a video
control selector 32 and an audio control selector 33, provided for
establishing communication or entering control instructions.
The equipment may comprise to a very large extent conventional,
commercially available means. Two or more channel stereophonic devices
should be provided for the audio signals (picking up or recording,
transmission, reproduction).
From such a location 25, one or several participants can hold a
videoconference with participants at other, very remote and mutually
independent locations 25, through connecting lines 36 and a
videoconference central station 1.
Connecting lines 36 must be provided for a go channel 38 and a return
channel 37. The go channel as well as the return channel require
transmission capacities for a video broadband channel, an audio medium
band channel, and a signal narrow band channel (not shown in FIG. 1).
An audio channel may also be dimensioned for a two-channel or multichannel
sterophony. The signalling channel is needed initially for dialling or
building up the communication and later, i.e. after the conference
circuitry is established, occasionally for control instructions.
The equipment outside the videoconference central or control station 1 thus
does not comprise more than that of a TV-standard picture-telephone
station. This already is a substantial advantage of the invention since it
makes any such picture-telephone station suitable for videoconferencing.
The videoconference central station 1 includes all equipment necessary for
distributing and mixing the incoming source signals to form the outgoing
signals transmitted to the receiving means, i.e. the sink signals, but
only to the extent of satisfying the traffic needs of the videoconference.
This equipment is assigned to the participating locations 25 always for
the duration of a video conference and it substantially comprises large
picture storages 5 and small picture storages 6 as well as multiplexers
(MUX) 7 for the outgoing video sink or reception signals. For outgoing
audio sink or reception signals 40, sound mixers 8 are provided. The large
picture storages 5, small picture storages 6, multiplexers (MUX) 7, and
sound mixers 8, needed for a certain connection are selectable in a number
corresponding to the number of participating locations 25, and are
interconnected to respective groups and associated with a video control 2
and an audio control 3.
The structure and function of a videoconference central station 1 as far as
video signals are concerned, may be learned from FIG. 2 where the control
equipment in the central station 1 which is necessary for one
participating location 25, is shown. The video source signals 41 coming
from a camera 26 are supplied to an analog-to-digital converter 9
wherefrom they pass, through an intermediate or first-in-first-out buffer
storage (FiFo) 10, if provided, to a large picture storage 5. Through a
detecting and selecting synchronization separator 12, for example, the
synchronizing information is retrieved from the incoming video signal 41,
for a write control 13. Parallel to large picture storage 5 a coarsened or
small picture, i.e. one whose number of picture elements is
two-dimensionally reduced (width and height), is produced for example by
low-pass filtering through low-pass filter (2-d-low-pass) 11, followed by
subsampling effected by a corresponding setting of write control 13, and
supplied to a small picture storage 6.
In a video control processor 16, a standard program is stored according to
which mixed or split screen pictures of the individual large pictures
46(u), 46(v), 46(w) (FIG. 4) and/or small picture 47(x), 47(y), 47(z),
(FIGS. 5 to 7), are combined to the size of a full or complete screen
picture 45 (FIG. 8). By means of control signals which are received from
the individual participating terminal stations or locations 25-A, 25-B,
25-C, 25-D, 25-E (up to 12 such stations) and include individual station
split screen video controlling instructions, the video signals 42 for a
complete or full screen picture 45, consisting of signals of large
pictures 46 and small pictures 47 are directed, in accordance with the
transmission clock frequency (cycle clock), by an addressing program
processor 15 and a read control 14 and, if provided also by a write
control 13, to multiplexers (MUX) 17, 18 and therefrom, through a
digital-to-analog converter 19, as an individually composed monitor video
signal 42 to the respective connecting line 36.
As to audio signals, the structure and function of the videoconference
central station may be learned from FIG. 3. The audio signal 39 coming
from a microphone 28 (FIG. 1) is amplified by a preamplifier 20 and passes
through level adjustors or gain controls 21 to summation amplifier 22 for
the left-hand channel and an identical amplifier 23 for the right-hand
channel. Each participating subscriber station 25 receives its individual
pair of output signals 40-L and 40-R for the left-hand and right-hand
audio sink or receiver (such as loudspeakers 29-L and 29-R (FIG. 1)). The
amplification and damping settings of the individual adjustors or gain
controls 24 may be effected by means of an audio control program per
programmed audio control processor 24. Particularly advantageous is
blocking of the participant's own sound, to eliminate acoustic feedback.
For the audio control, which also may be effected according to a standard
program applying to all the participating subscriber stations or locations
25, i.e. with or without overriding or control, the video conference
central or control station 1 includes the sound mixer 8 and audio control
3 already mentioned in connection with FIG. 1. A cocktail party effect can
be simulated in a simple way by setting the respective level adjustors 21,
i.e. such that the audio signal 39 of the participant whose voice is to be
emphasized is correspondingly amplified and those of the other
participants are damped or attenuated.
FIG. 4 shows a monitor screen in true proportions according to the
conventional TV standard. A complete or full screen picture 45 has a width
of 4/5 d and a height of 3/5 d, with d being the diagonal 48 of the
complete picture screen. Picture sizes which show a face while omitting
horizontal or vertical, or horizontal and vertical, margins may be
considered a large picture 46(u), 46(v), 46(w).
One of the variants of a large picture, 46(u), for example, is reduced only
in its width and thus is a square of the dimensions 3/5 d and 3/5 d with d
still being the diagonal 48 of the complete or full screen picture 45.
Another large picture 46(v) having the width and height dimensions 4/5 d
and 2/5 d is useful if a plurality of participants is to be shown which
are all at the same terminal or location, since in such an instance only
the horizontal margins are omitted. Still another large picture 46(w)
having the width and height dimensions 3/5 d and 2/5 d has all the margins
omitted.
FIGS. 5, 6 and 7 show three different sizes of small pictures 47(x), 47(y),
47(z). All of these have the same height of 1/5 d, which permits the use
of the marginal zones of all the large picture sizes 469(u), 46(v) and
46(w), shown in FIG. 4. The dimensions 1/5 d, 4/15 d and 2/5 d are
provided as useful widths of small pictures 47(x), 47(y), and 47(z),
respectively. Which of the small picture sizes to produce in central
station 1 depends particularly on the provided maximum number of pictures
of a split-screen combination to be shown. Stated another way, the
particular large and small picture dimensions to be provided by the
central station 1 depends on the maximum number of pictures which are to
be displayed on a given split-screen. If a greater number of large and
small picture sizes or dimensions is programmed or provided which are not
all absolutely necessary, the number of possible combinations, i.e. the
degree of freedom for selecting possible combinations forming one full
screen picture, is correspondingly enlarged as well.
FIGS. 8, 9 and 10 show a selection of some examples of split-screen
combinations of large pictures 46(u), 46(v) and 46(w) and small pictures
47(x), 47(y), and 47(z).
FIG. 11 shows the raster for a maximum of 12 small pictures 47(x) and, in
broken lines, for a corresponding maximum of 9 small pictures 47(y). In
each of the small picture areas, for example in one of the upper corners
an identifying mark 49 for the respective participant at a respective
subscriber station or terminal 25 may be reproduced, which is delivered by
a special signal generator 4 which is in the central station 1 (see FIG.
1a).
FIG. 12 is a diagrammatical perspective view of a controller unit 30 at a
participant location or subscriber station 25, for carrying actuating
elements needed by a participant to produce individual control
instructions. More specifically, controller unit 30 comprises front panel
controls 31, 32, 33 and a display unit 34 for individual control
instructions.
The selection or dialling, audio control or video control instructions as
the case may be, are entered respectively, by means of for example a
conventional dialling keyboard 31 and switches 32 and audio control
selector potentiometers 33. The instructions are transmitted through the
terminal connecting unit 35 (see FIG. 1) to the central station 1. The
participants receive check-back information on the status of the selector
or dialling keyboard 31, the audio control 33, the video control 32, the
terminal connecting unit 35, the central station 1, etc. through an
optical indicator or display 34, such as signal lamps, alphanumeric
display, etc.
Accordingly, the invention comprises a communication system for conducting
or performing a videoconference between a plurality of participants who
are located, optionally yet preferably as single participants, at a
plurality of participant locations, i.e. at a plurality of participating
subscriber stations, comprising;
a participant terminal or subscriber station 25 at each connectable
participant location, each having video signal source means 26 for
generating a video source signal 41 constituting the recording of the
screen at the participant location, i.e. at the participant's terminal,
video signal sink means for receiving and converting means 27 for
receiving a video sink signal 42 to produce a complete or full screen
picture 45, and selector means including a video control selector 32 for
generating control signals 43 for controlling scene images or picture
compositions, especially from other participating subcriber stations or
locations used to make up the complete or split screen picture;
a central station 1 for receiving video source or originating signals 41
and control signals 43 from each participating subscriber station or
terminal 25 and for outputting video sink or reception signals 42 to each
such participating subscriber station or terminal, said central station 1
includng video storage means 5, 6 for storing received video source
signals 41 from each such participating | | |
