Television – Special applications – Observation of or from a specific location
Reexamination Certificate
1997-10-21
2003-11-11
Le, Vu (Department: 2613)
Television
Special applications
Observation of or from a specific location
C348S014160, C348S014160, C348S159000, C348S211990, C348S143000, C455S003030
Reexamination Certificate
active
06646677
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image sensing control method and apparatus for remote-controlling an image sensing device such as a still camera, video camera, and the like, an image transmission control method, apparatus, and system for transmitting the sensed image, and a computer readable storage medium that stores a program for implementing the method.
A camera control system in which a plurality of cameras each having pan and tilt functions and a zoom function are set at the respective positions, and an operation device at the central position or an arbitrary position is connected to these cameras via a dedicated communication line to remote-control an arbitrary camera, is known. In such system, control signals (cables or signal lines) for transmitting camera control/status signals are required in addition to cables for transmitting video/audio signals. Also, a method of modulating these camera control/status signals and superposing them on video/audio signals is known. Theoretically speaking, however, such method is equivalent to a method of assigning separate communication channels to individual signals.
In such camera control system (a system that remote-controls cameras using the dedicated communication line), an apparatus for remote-controlling a camera is fixed in position, and becomes a bottleneck against easy system expansion.
For this reason, it is preferable to remote-control cameras on a network built by computers and the like. This is because both an apparatus for controlling a camera and an apparatus for remote-controlling a camera operate as members of a computer network (to be simply referred to as a network hereinafter), and users can freely remote-control these apparatuses from terminals (e.g., personal computers or the like) connected to the network.
On the other hand, a camera conference system that transmits audio signals onto the network in addition to images sensed by the cameras is receiving a lot of attention.
FIG. 1
schematically shows a general image communication system including the above-mentioned camera conference system.
FIG. 2
is a schematic block diagram showing the arrangement of the image communication system shown in
FIG. 1. A
communication terminal
100
serves as an image server for controlling, e.g., a video camera and transmitting the image sensed by the camera comprises a computer main body
101
, a keyboard
102
, a mouse
103
, a display
104
, and a video camera
105
, as shown in
FIG. 1. A
communication terminal
200
serving as an image client which receives image data from the communication terminal
100
and displays the received image comprises a computer main body
201
, a keyboard
202
, a mouse
203
, and a display
204
, as shown in FIG.
1
. The communication terminals
100
and
200
(client) are connected via a network
300
to be able to communicate with each other.
As shown in
FIG. 2
, the image sensed by the video camera
105
of the communication terminal
100
is converted into digital data by an image input unit
110
. The digital image data for one frame is packetized by a network transmitter/receiver
111
, and the obtained packet is output onto the network
300
. The packet output onto the network
300
is received by a network transmitter/receiver
211
of the client (communication terminal
200
). Upon reception of the packet, the client converts the received packet into data, and stores the data in an image buffer
210
. The client reads out the image data from the image buffer
210
at a predetermined timing, and displays the image on the display
204
.
By repeating the above operation, moving images captured by the communication terminal
105
via the video camera
105
can be displayed on the client side. The image data is stored in the image buffer
210
for the following reason.
A packet on the network has fluctuation (jitter) with respect to time for various reasons.
FIG. 3
shows this state. As shown in
FIG. 3
, even when the transmitter side of image data transmits the image data for one frame at a predetermined interval T, the receiver side does not always receive the image data at the predetermined interval T due to the influence of the jitter. For this reason, the reception interval may broaden, as indicated by A in
FIG. 3
, or may narrow, as indicated by B in FIG.
3
.
Hence, if the client displays the received data immediately without going through the image buffer
210
, the motion of images displayed on the display
204
may be too slow (the portion A) or too fast (the portion B). In order to prevent such irregular motion, image signals for a time that can absorb the jitter are normally buffered in the image buffer
210
, and the stored signals are read out at the same timing as that upon capture of the images in the image reproduction mode, thus removing the influence of the jitter.
However, this conventional system does not consider any case wherein the video camera
105
, the pan, tilt, zoom functions and the like of which can be externally controlled, is connected to the terminal
100
, and the position of the video camera
105
is controlled by a client on which an image is being displayed. This problem will be explained in detail below. In the conventional system, since the image data to be displayed are buffered by the receiving communication terminal
200
, the image acquisition time has a large difference from the image display time. For this reason, when the client on which an image is being displayed controls the pan, tilt, or zoom function of the video camera
105
while observing the displayed image, a certain lag time is produced from when the user controls a function of the video camera
105
until the image corresponding to the controlled function is displayed on the client side. Hence, the user controls the video camera
105
more than he or she wanted, and e.g., the field of view of the video camera
105
moves beyond the angle that the user intended.
A problem posed when the angle (including pan and tilt angles and zoom ratio) of the camera has changed will be explained below.
For example, as shown in
FIG. 4
, assume that a camera which points in a direction of an object A is panned to sense the image of an object B. In this case, since the transmission data volume is constant, images are captured at a predetermined frame rate and image data is kept transmitted to the client while the camera angle is being changed from the object A to the object B.
Such images transmitted during the change from the object A to the object B may be desirable in some respects, but are not so significant for the user who knows the positional relationship between the objects A and B. In fact, such user may feel that nonsense images are transmitted/received.
When the above-mentioned camera control communication terminal (camera control device) and client are built on the network, transmission of unwanted information is preferably precluded, since it influences the operability of other users on the network.
In particular, the “Internet” is receiving a lot of attention. When camera control devices and clients are built on such huge network, the above-mentioned problem comes into focus inevitably.
In the system that transmits images using digital transmission media such as the Internet, in general, the sensed digital image data is compressed by a compression technique, e.g., Motion JPEG, MPEG, or the like, and the compressed image data is transmitted. The compressed image data is expanded by a device (to be referred to as a viewer hereinafter), and thereafter, the expanded image is displayed on the display.
However, in such conventional system, it is a common practice not to perform compression processing upon transmission of images, or to permanently use a single compression scheme suitable for image contents or network characteristics (transmission rate or the like), if compression processing is done. For this reason, when an uncompressed image signal is transmitted from a network with a low transmission rate or when the frame rate drops since an imag
Noro Hideo
Oka Kiyoshi
Sasaki Akitomo
Suzuki Shigeo
Canon Kabushiki Kaisha
Le Vu
Morgan & Finnegan L.L.P.
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