Patent Publication Number: US-2005128314-A1

Title: Image-taking apparatus and image-taking system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to image-taking apparatuses and image-taking systems which are capable of sending video images over a network, such as a LAN or the Internet.  
      2. Description of Related Art  
      In recent years, network cameras have been proposed which send images that have been taken with a camera via a communications network such as a LAN or the Internet to a surveillance terminal unit, such network cameras being used as a replacement for cameras storing video images on such media as tape or film. Cameras used as this kind of network cameras may be placed on busy streets, at locations where they cannot be reached by people, and the image data taken there may be sent via the communications network and displayed on a liquid crystal panel of a surveillance terminal unit.  
      Moreover, network cameras have been proposed which allow such operations as panning, tilting or zooming of a remote camera by operating a. remote control provided at the surveillance terminal unit. With this kind of network camera, it is possible to take pictures of the object under surveillance from an angle and at a zoom ratio that suites the preferences of the operator, and it is possible to observe the taken images on the liquid crystal panel of the surveillance terminal unit.  
      With present network cameras, the capacity of the communication line tends to the bottleneck, and the resolution is restricted to CIF (352×288) when taking moving pictures at 30 frames per second.  
      In recent years, the number of pixels of CCDs serving as the image-pickup elements is on the rise, and video cameras using CCDs with high pixel densities are used to take moving pictures at NTSC level as well as to take still pictures with high resolutions of XGA level or higher, using the pixels of the CCD to the full extent.  
      Moreover, also with network cameras, it has become possible to take moving pictures at 30 frames per second at CIF level as well as to take still pictures or moving pictures with low frame rates of one or two frames per second with high resolutions at XGA (1024×768) level.  
      A network camera with which images can be taken while switching the resolution between still pictures and moving pictures is disclosed in Japanese Patent Application Laid Open No. 2001-189932A.  
      The network camera disclosed in this publication has a change ratio detecting means for judging whether a change ratio per predetermined time of moving picture data of an object that is taken is equal to or greater than a predetermined value, and switches between taking still pictures and taking moving pictures based on the judgment result of this change ratio detecting means.  
      However, in this configuration, the change of the filmed object is judged based on the change of the image data of the taken images, so that it is not possible to detect a change in the filmed object that is related to heat, sound, current leaks or the like, which do not appear in the taken image. Therefore, the range of events which can be monitored is narrow, and the camera is insufficient as a surveillance camera.  
     SUMMARY OF THE INVENTION  
      An image-taking apparatus according to one aspect of the present invention comprises an image-pickup element having a plurality of pixels; a control section selectively performing a first image-taking operation using the image-pickup element or a second image-taking operation at a higher pixel number or a lower frame rate than for the first image-taking operation; and a detecting section detecting a state of an image-taking object; wherein the control section performs the first image-taking operation when the state of the image-taking object detected by the detecting section is within a predetermined range, and performs the second image-taking operation when the state of the image-taking object detected by the detecting section is outside the predetermined range.  
      An image-taking apparatus according to another aspect of the present invention comprises an image-taking optical system; an image-pickup element having a plurality of pixels, the image-pickup element performing image-pickup through the image-taking optical system; a control section selectively performing a first image-taking operation using the image-pickup element or a second image-taking operation at a higher pixel number or a lower frame rate than for the first image-taking operation; and a detecting section detecting a state of the image-taking optical system; wherein the control section performs the first image-taking operation when the state of the image-taking optical system detected by the detecting section is within a predetermined range, and performs the second image-taking operation when the state of the image-taking optical system detected by the detecting section is outside the predetermined range.  
      These and further objects and features of the image-taking apparatus according to the present invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a functional block diagram of an image-taking system according to any of Embodiments 1 to 5.  
       FIG. 2  is a diagrammatic view of Embodiment 1.  
       FIG. 3  is a flowchart showing the control procedure of a surveillance camera unit according to Embodiment 1.  
       FIG. 4  is a diagrammatic view of Embodiment 2.  
       FIG. 5  is a flowchart showing the control procedure of a surveillance camera unit according to Embodiment 2.  
       FIG. 6  is a diagrammatic view of Embodiment 3.  
       FIG. 7  is a flowchart showing the control procedure of a surveillance camera unit according to Embodiment 3.  
       FIG. 8  is a diagrammatic view of Embodiment 4.  
       FIG. 9  is a flowchart showing the control procedure of a surveillance camera unit according to Embodiment 4.  
       FIG. 10  is a diagrammatic View of Embodiment 5.  
       FIG. 11  is a flowchart showing the control procedure of a surveillance camera unit according to Embodiment 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  is a block diagram showing the configuration of a network camera system according to an embodiment of the present invention. This network camera system is made of a surveillance camera unit taking images of an object under surveillance, and a surveillance camera unit connected via a communication line to this surveillance camera unit.  
      First, the configuration of the surveillance camera unit is explained. Reference numeral  11  denotes a camera, having pan and tilt mechanisms which change the image-taking direction and a zoom mechanism which changes the image-taking zoom ratio (not shown in the drawings).  
      Moreover, an image-pickup element  11   a  (for example a CCD sensor or a CMOS sensor) which photoelectrically converts light reflected from an object and outputs it as electric signals is built into the camera  11 . In the present embodiment, it is preferable to use an image-pickup element with a high pixel number, in order to take high resolution images of the object under surveillance.  
      Here, if moving pictures are taken with the camera  11  at a high frame rate of 30 frames per second, then the image processing speed or the communication infrastructure may become a bottleneck, so that it is necessary to set the resolution of the taken images to CIF level (352×288).  
      Accordingly, in the present embodiment, when images are taken at a frame rate of 30 frames per second, then the resolution is set to CIF level, and when taking still pictures or when taking images at a low frame rate of one or two frames per second, then the pixels of the image-pickup element  11   a  are used in full, and image-taking with a resolution of at least XGA level (1024×768) is enabled.  
      Reference numeral  12  denotes an encoding section encoding the video images taken with the camera  11 , and reference numeral  13  denotes an image buffer section for buffering the video images encoded by the encoding section  12 .  
      Reference numeral  15  denotes a pixel number control section controlling the number of pixels read out from the image-pickup element  11   a . The number of pixels read out from the image-pickup element  11   a  is changed depending on whether image-taking is performed at low resolution and high frame rate or whether image-taking is performed at high resolution and low frame rate. Reference numeral  16  denotes a terminal control section controlling driving of the camera  11  in the pan direction, driving in the tilt direction, as well as controlling the zoom ratio.  
      Reference numeral  14  denotes a camera communication unit connected via a communication line to the surveillance terminal unit. Reference numeral  17  denotes a terminal parameter recording section, in which favorable parameters for the pan, tilt and zooming operation of the camera  11  in accordance with the detection region of various sensors  201  to  20   n  are recorded.  
      Reference numeral  18  denotes a sensor output judging section outputting a predetermined signal to the terminal control section  16  and the pixel number control section  15 , based on the signal output from the sensors  201  to  20   n . Details of the sensor output judging section  18  are explained further below. Reference numeral  21  denotes a surveillance object that is surveilled by the sensors  201  to  20   n.    
      The following is an explanation of the configuration of the surveillance terminal unit. Reference numeral  31  denotes a terminal communication unit that controls the communication with the surveillance camera unit. Reference numeral  32  denotes an image storage section recording image data sent from the camera communication unit  14  to the terminal communication unit  31 .  
      Reference numeral  33  denotes an image decoding section decoding image data stored in the image storage section  32  into images. Reference numeral  34  denotes a screen control section displaying the images decoded by the image decoding section  33  on a monitor  38 .  
      Reference numeral  35  denotes an image input control section, which is connected to the terminal communication unit  31  and which controls the pixel number control section  15  and the terminal control section  16  of the surveillance camera system via the communication line  30 . Reference numeral  36  denotes a memory control section controlling, the image storage section  32  and the image decoding section  33 , and reference numeral  37  denotes a screen output control section controlling the display state of the monitor  38 .  
      The following is an explanation of the operation of this surveillance camera system. When the sensors  201  to  20   n  detect that the state of the surveillance object  21  has changed, then this detection result is output to the sensor output judging section  18 , and it is judged whether the state of the surveillance object  21  is within a predetermined range. It should be noted that this predetermined range depends on the kind of the surveillance object  21  and the kind of the sensors  201  to  20   n . Specific examples are given in the following Embodiments 1 to 5.  
      If. the state of the surveillance object  21  is outside the predetermined range, then a predetermined instruction signal is output by the sensor output judging section  18  to the terminal control section  16  and the pixel number control section  15 , and the camera  11  is driven into a direction that is optimal for performing image-taking of the surveillance object  21 .  
      Here, optimum parameters regarding the driving direction of the camera  11  corresponding to the number of the sensors are stored in the terminal parameter storage section  17 . The terminal control section  16  reads out these parameters from the terminal parameter storage section  17  and drives the camera  11  accordingly. Thus, the camera  11  can be driven to the optimum position for image-taking of the surveillance object  21 .  
      Moreover, when the pixel number control section  15  has received the above-mentioned instruction signal, it increases the pixel number read out from the image-pickup element  11   a , and controls the camera  11  so as to allow image-taking at the CIF level. Thus, it is possible to take images of the surveillance object  21  at a high resolution when the state of the surveillance object  21  is outside the predetermined range.  
      The images taken with the camera  11  are encoded with the video encoding section  12  and buffered in the image buffer section  13 . The image data buffered in the image buffer section  13  is sent from the camera communication unit  14  via the communication line  30  (which may be a LAN, a WAN or the Internet, for example) to the terminal communication unit  31 , and stored in the image storage section  32 .  
      The image data stored in the image storage section  32  is decoded by the image decoding section  33  into images, and is displayed by the screen control section  34  on the monitor  38 .  
      Thus, an operator at the surveillance terminal unit can view the surveillance object  21  in detail on the monitor  38 , when the state of the surveillance object  21  has left the predetermined range. Moreover, by operating an operating panel (not shown in the drawings) as necessary, the operator can change the parameters of the pixel number control section  15  and the terminal control section  16  by driving the image input control section  35 . Thus, it is possible to take images in accordance with the operator&#39;s preferences.  
      Here, an action in which the operator operates the operation panel to set the zoom ratio of the camera  11  to the telephoto end indicates the operator&#39;s intention to obtain a more detailed image of the surveillance object  21 . Therefore, in the present embodiment, the pixel number control section  15  is driven and the image-taking mode of the camera  11  is switched to high-resolution image-taking, in accordance with the action of setting the camera  11  to the telephoto end.  
      Embodiment 1  
      Using  FIGS. 1 and 2 , the following is an explanation of Embodiment 1 of the present invention. This embodiment relates to a surveillance camera system with the purpose of detecting intruders, in which vibration sensors are attached to the doors and windows of a house and detect whether the doors and windows are open or closed. If an applied vibration level exceeds a predetermined value, high-resolution image-taking is performed.  FIG. 2  is a diagrammatic view showing how vibration sensors  41  to  4 n are attached to the door and windows of a house. The internal configuration of the surveillance camera unit and the surveillance terminal unit are not shown in  FIG. 2 , with the exception of the cameras.  
      If the vibration level detected with any of the vibration sensors  41  to  41 n is applied for more than a predetermined time or exceeds a predetermined level, then the sensor output judging section  18  judges that vibrations are applied because someone is trying to break into the house.  
      When the vibration sensor that has detected such a vibration is specified by the sensor output judging section  18 , then the parameters for panning, tilting and zooming the cameras  11  that are most suitable for taking the area of the sensor that has detected the vibration are read out by the terminal control section  16  from the terminal parameter recording section  17 , the pan and tilt position as well as the zoom ratio of the camera  11  are set in accordance with these parameters, and image-taking is performed at high resolution. The taken images are buffered in the image buffer section  13 , and sent to the surveillance terminal unit in accordance with the operator&#39;s requests.  
      With this configuration, since a detailed image of the intruder trying to break into the house can be obtained by taking high-resolution images, it is possible to obtain incriminatory evidentiary images. Moreover, by sequentially buffering the video images taken at high resolution in the image buffer section  13 , it is possible to confirm the temporal course of the events or incident.  
       FIG. 3  is a flowchart showing the control procedure of the surveillance camera unit of the present embodiment. The procedure shown in the following flowchart is mainly executed by the terminal control section  16  and the pixel number control section  15 .  
      When the vibration sensors  41  to  4   n  do not detect a vibration, moving pictures are taken at the ordinary low resolution (at a high frame rate of 30 frames per second) (Step  21 ).  
      When at least one of the vibration sensors  41  to  4   n  detects that a vibration is applied to one of the windows of the house, for example, then a signal is output from this vibration sensor. Based on this output signal, the sensor output judging section  18  judges whether the level of the detected vibrations or the time for which the vibrations carry on is above a predetermined value (Step  22 ). If it is not above a predetermined value, then image-taking with a low resolution is continued. In that case, the image-taking mode is not changed.  
      On the other hand, if the vibration level or the time for which the vibrations carry on is above a predetermined value, then the procedure advances to Step  23 , and the vibration sensor that has detected the vibrations is specified. Then, at Step  24 , the pan and tilt positions and the zoom ratio suitable for image-taking of the specified vibration sensor are read out from the terminal parameter recording section  17 .  
      Then, at Step  25 , the camera  11  is driven in the pan direction and the tilt direction in accordance with the values of the parameters read out from the terminal parameter recording section  17 , and the zoom ratio is changed by moving a zoom lens (not shown in the drawings) built into the lens barrel of the camera  11 .  
      When the image-taking conditions have been adjusted by these camera operations, high-resolution image-taking is performed using the camera  11 . It should be noted that the resolution can be changed by controlling the number of pixels read out from the image-pickup element  11   a  as described above with the pixel number control section  15 .  
      At Step  27 , the images taken at high resolution are buffered as image data in the image buffer section  13 . For how much time image data is buffered depends on the capacity of the image buffer section  13 .  
      At Step  28 , it is judged whether a request to send the images taken at high resolution has been issued by a surveillance terminal unit on the network. If there was a send request, then the image data of the images taken at high resolution is sent via the communication line  30  to the surveillance terminal unit.  
      With the above-described configuration, it is possible to alleviate the traffic on the network, because high-resolution images are sent only if there was a send request for them.  
      Even if there is no send request, high-resolution image-taking is continued, and the high-resolution images are buffered in the image buffer section  13 , so that it is possible to provide them in the event of further requests for the sending of high-resolution images from the surveillance terminal unit.  
      At Step  30 , it is detected whether a signal has been entered which instructs the surveillance camera unit to stop high-resolution image-taking and revert to ordinary image-taking. If a signal instructing the surveillance camera unit to stop high-resolution image-taking and revert to ordinary image-taking has been entered from the surveillance terminal unit, then the procedure returns to Step  21 , and the image-taking mode is switched to ordinary image-taking at low resolution and high frame rate.  
      Embodiment 2  
      Referring to  FIGS. 1 and 4 , the following is an explanation of Embodiment 2 of the present invention.  
      In Embodiment 2, a plurality of microphones  51  to  5 n (detecting means) are placed in a street, and high-resolution image-taking is performed if a sound level exceeds a predetermined value.  FIG. 4  is a diagrammatic view showing how a plurality of cameras are arranged on a street, such as a busy main street, and images of the street are taken. The microphones  51  to  5 n have directionality, and the sound from a plurality of directions can be picked up using the plurality of microphones.  
      The sensor output judging section  18  judges whether the sound level of the sound that is picked up with the microphones  51  to  5   n  exceeds a predetermined value. If the sound level exceeds a predetermined value, then the sensor output judging section  18  judges from which direction the sound comes. It is possible to specify the direction of the sound if there are at least two directional microphones. When the direction of the sound is specified, the cameras  11  are driven to positions corresponding to this specified direction, and high-resolution image-taking can be performed while pointing the image-taking lens into the direction from which the sound is emitted. The taken images are recorded in the image buffer section  13 .  
      Thus, by taking the location from which sound of at least a predetermined sound level is emitted at a high resolution, it is possible to examine the cause of the sound (for example a traffic accident or other incident) in detail. Also, the images taken at high resolution are successively buffered in the image buffer section  13 , so that by reading out and confirming the buffered images, it is possible to accurately assess the course of the accident or incident.  
       FIG. 5  is a flowchart showing the control procedure of the surveillance camera unit of the present embodiment. The following flowchart is executed mainly by the structural elements of the surveillance camera unit in  FIG. 1 .  
      At Step  51 , image-taking is performed at the ordinary low resolution and at a high frame rate of 30 frames per second. The sensor output judging section  18  judges whether the sound level of the sound that is picked up by the microphones  51  to  5   n  exceeds a predetermined value, and if it does exceed a predetermined value, then the procedure advances to Step  52 , whereas if it does not exceed a predetermined value, then low-resolution image-taking is continued, and there is no particular change of the image-taking mode.  
      At Step  53 , the direction of the sound emitted at more than a predetermined value is specified by the sensor output judging section  18 . At Step  54 , the cameras  11   a  to  11   n  are driven towards the direction of the sound specified at Step  53 , and at Step  55 , high-resolution image-taking is performed. As in Embodiment 1, high-resolution image-taking is performed by driving the pixel number control section  15  and increasing the number of pixels read out from the image-pickup element  11   a.    
      At Step  56 , the images taken at high resolution are buffered as image data in the image buffer section  13 . For how much time image data is buffered depends on the capacity of the image buffer section  13 . At Step  57 , it is judged whether a request to send the images taken at high resolution has been issued by the surveillance terminal unit on the network.  
      If there was a send request for the images taken at high resolution, then, at Step  58 , the images taken at high resolution are sent to the surveillance terminal unit. With the above-described configuration, it is possible to alleviate the traffic on the network, because high-resolution images are sent only if there was a send request for them.  
      Even if there is no send request from the surveillance terminal unit, high-resolution image-taking is continued, and the high-resolution images are buffered in the image buffer section  13 , so that it is possible to provide them in the event of further requests for the sending of high-resolution images from the surveillance terminal unit.  
      At Step  59 , it is judged whether a signal has been entered which instructs the surveillance camera unit to stop high-resolution image-taking and revert to ordinary image-taking.  
      If a signal instructing the surveillance camera unit to revert to ordinary image-taking has been entered from the surveillance terminal unit, then the procedure returns to Step  51 , and the image-taking mode is switched to ordinary image-taking at low resolution and high frame rate.  
      Embodiment 3  
      Referring to  FIGS. 1 and 6 , the following is an explanation of Embodiment 3. Embodiment 3 relates to an image-taking apparatus for the purpose of monitoring the speed of vehicles, in which a speed sensor detecting the speed of vehicles is disposed beside a roadway. If the speed of a vehicle exceeds a predetermined speed, then high-resolution video images are automatically taken, which is useful to identify the vehicle holder.  FIG. 6  is a diagrammatic view showing how the speed sensor for detecting vehicle speed is arranged beside the roadway and how it detects the speed of vehicles driving by.  
      When the sensor output Judging section  18  judges that the speed of a vehicle detected by the speed sensor  71  exceeds a predetermined speed, then the cameras  11   a  to  11   n  automatically take high-resolution video images of the vehicle driving at excessive speed. The taken video images are buffered as video data in the image buffer section  13 .  
      Thus, by taking high-resolution images of vehicles driving at excessive speed, it is possible to obtain detailed image data showing, for example, the number plate of the vehicle or the face of the driver, so that it is easy to identify the offending vehicle or the offending driver. Moreover, the video images taken at high resolution are successively buffered in the image buffer section  13 , so that it is possible to later confirm the course of an accident or incident.  
       FIG. 7  is a flowchart showing the control procedure of the surveillance camera unit of the present embodiment. The procedure of the following flowchart is executed by the structural elements of the surveillance camera unit in  FIG. 1 .  
      At Step  71 , image-taking is performed at the ordinary low resolution and at a high frame rate of 30 frames per second. At Step  72 , the sensor output judging section  18  judges whether the speed of the vehicle detected with the speed sensor  71  exceeds a predetermined speed. If the speed exceeds the predetermined speed, then the procedure advances to Step  73 , and images of the speeding vehicle are taken at high resolution.  
      As in Embodiment 1, high-resolution image-taking is performed by driving the pixel number control section  15  and increasing the number of pixels read out from the image-pickup element  11   a . If no speeding vehicle is detected, then the ordinary low-resolution image-taking is continued and there is no particular change in the image-taking mode.  
      At Step  74 , the images of the vehicle taken at high resolution are buffered as image data in the image buffer section  13 . For how much time image data is buffered depends on the capacity of the image buffer section  13 .  
      At Step  75 , it is judged whether a request to send the video images taken at high resolution has been issued by the surveillance terminal unit on the network. At Step  75 , if there was a send request from the surveillance terminal unit for the video images taken at high resolution, then the video images taken at high resolution are sent to the surveillance terminal unit at Step  76 .  
      With the above-described configuration, it is possible to alleviate the traffic on the network, because high-resolution images are sent only if there was a send request for them. Even if there is no send request from the surveillance terminal unit, high-resolution image-taking is continued, and the high-resolution images are buffered in the image buffer section  13 , so that it is possible to provide them in the event of further requests for the sending of high-resolution images from the surveillance terminal unit.  
      At Step  77 , it is detected whether a signal has been entered which instructs the surveillance camera unit to stop high-resolution image-taking and revert to ordinary image-taking. If a signal instructing the surveillance camera unit to revert to ordinary image-taking has been entered, then the procedure returns to Step  71 , and the image-taking mode is switched to ordinary image-taking at low resolution and high frame rate.  
      In the present embodiment, the sensor output judging section  18  judges whether the speed of vehicles exceeds a predetermined speed, but it is also possible to let the sensor output judging section  18  judge whether the speed of vehicles is below a predetermined speed and thus monitor the traffic for traffic jams.  
      It is also possible to arrange cameras and speed sensors along a carry path of containers on a conveyor, and let the sensor output judging section  18  judge whether the carry speed of the containers is below a predetermined value. Thus, when the carry speed is slow, it is possible to take high-resolution images of the containers, and to accurately monitor for jamming of the containers.  
      Embodiment 4  
      Referring to  FIGS. 1 and 8 , the following is an explanation of Embodiment 4 of the present invention. This Embodiment 4 relates to an image-taking apparatus for the purpose of preventing fires, in which temperature sensors are placed at locations that are prone to catch on fire, such as a kitchen or the like, and high-resolution image-taking is performed if the detected temperature reaches at least a predetermined value.  
       FIG. 8  is a diagrammatic view showing the arrangement of a plurality of temperature sensors  91  to  9   n  at locations within a kitchen that tend to be the cause for fires, as well as the arrangement of cameras  11   a  to  11   n  for taking these locations. If the sensor output judging section  18  judges that at least one of the temperatures detected by the temperature sensors  91  to  9   n  exceeds a predetermined temperature, then the cameras  11   a  to  11   n  point their image-taking lenses toward the temperature sensor which has detected the heightened temperature, and high-resolution video images are automatically obtained.  
      The pan and tilt direction of the image-taking lenses as well as the zoom ratio are set by reading out parameters correlating the positions at which the temperature sensors  91  to  9   n  are arranged and the driving directions of the image-taking lenses from the terminal parameter recording section  17 .  
      By automatically obtaining high-resolution video images of high-temperature locations, it is possible to specify locations at which a fire has not yet occurred but which are at a heightened temperature, and to observe these locations closely, so that it is possible to prevent fires before they occur.  
       FIG. 9  is a flowchart showing the control procedure of the surveillance camera unit of the present embodiment. The procedure of the following flowchart is executed by the structural elements of the surveillance camera unit in  FIG. 1 .  
      At Step  91 , image-taking is performed at the ordinary low resolution and at a high frame rate of 30 frames per second. At Step  92 , the sensor output judging section  18  judges whether the temperature detected by the temperature sensors  91  to  9   n  exceeds a predetermined temperature. If there is an excessive temperature, then the procedure advances to Step  93 , and it is specified which of the temperature sensors  11   a  to  11   n  has detected the heightened temperature.  
      If there is no particular location at which a heightened temperature is detected, then the ordinary low-resolution image-taking is continued and there is no particular change in the image-taking mode.  
      At Step  94 , the parameters for panning, tilting and zooming that are most suitable for taking the area that is the cause of the temperature detected by the temperature sensor (i.e. the vicinity of that temperature sensor) is read out from the terminal parameter recording section  17 . Then, the procedure advances to Step  95 , and the cameras  11   a  to  11   n  are driven to the optimum image-taking position in accordance with the parameters read out from the terminal parameter recording section  17 .  
      At Step  96 , images are taken at high resolution with the cameras  11   a  to  11   n  which have been driven to the optimum image-taking positions. The high-resolution image-taking is performed by driving the pixel number control section  15  as described above and increasing the number of pixels read out from the image-pickup element  11   a.    
      At Step  97 , the video image data taken at high resolution is buffered as image data in the image buffer section  13 . For how much time image data is buffered depends on the capacity of the image buffer section  13 .  
      At Step  98 , it is judged whether a request to send the video images taken at high resolution has been issued by the surveillance terminal unit on the network.  
      If there was such a send request, then, at Step  99 , the video images taken at high resolution are sent to the surveillance terminal unit. With the above-described configuration, it is possible to alleviate the traffic on the network, because high-resolution video images are sent only if there was a send request for them.  
      Even if there is no send request from the surveillance terminal unit, high-resolution image-taking is continued, and the high-resolution images are buffered in the image buffer section  13 , so that it is possible to provide them in the event of further requests for the sending of high-resolution images from the surveillance terminal unit.  
      At Step  100 , it is detected whether a stop signal instructing the surveillance camera unit to stop high-resolution image-taking has been entered. If a signal instructing the surveillance camera unit to stop high-resolution image-taking and to revert to ordinary image-taking has been entered from the surveillance terminal unit, then the procedure returns to Step  91 , and the image-taking mode is switched to ordinary image-taking at low resolution and high frame rate.  
      Embodiment 5  
      Referring to  FIGS. 1, 10  and  11 , the following is an explanation of Embodiment 5 of the present invention. This embodiment relates to an image-taking apparatus for the purpose of crime prevention and taking evidentiary video images, in which a switch is provided at the door of an office or the like to detect when the door is opened or closed. When it is detected with this switch that the door is opened, high-resolution video images are taken automatically.  
       FIG. 10  is a diagrammatic view showing how an office door is provided with a switch detecting when the door is opened or closed as well as the arrangement of a camera  11  taking images of the area around the door. The camera  11  is arranged at a position where it is possible to take images of the face of an intruder opening the door and trying to enter the office. It should be noted that the intruder may be aware of the fact that the camera  11  is set up, which may also serve as a deterrent to crime. Moreover, high-resolution images can serve as evidence in the case that a burglary or the like has been committed.  
       FIG. 11  is a flowchart showing the control procedure of the surveillance camera unit of the present embodiment. The procedure of the following flowchart is executed by the structural elements of the surveillance camera unit in  FIG. 1 .  
      At Step  1101 , image-taking is performed at the ordinary low resolution and at a high frame rate of 30 frames per second. At Step  1102 , the sensor output judging section  18  judges, based on a possible displacement of the door detected by the switch  1000 , whether the door is open or closed.  
      If it is judged that the door has been opened, then it is judged that an intruder has entered the office, and the procedure advances to Step  1103 .  
      At Step  1103 , the surveillance camera unit is driven and high-resolution video images of the intruder&#39;s face are automatically taken. As described above, the high-resolution image-taking is performed by driving the pixel number control section  15  so that the number of pixels read out from the image-pickup element  11   a  is high.  
      At Step  1104 , the video images of the intruder&#39;s face taken at high resolution are buffered in the image buffer section  13 . The high-resolution video images buffered in the image buffer section  13  are sent to the surveillance terminal unit only when there is a send request from the surveillance terminal unit. With this configuration, it is possible to alleviate the traffic on the network and to protect the privacy of individuals.  
      When the high-resolution image-taking has finished, the procedure returns to Step  1101 , and the image-taking mode switches again to low resolution and high frame rate.  
      While preferred embodiment(s) have been described, it is to be understood that modification and variation of the present invention may be made without departing from the scope of the following claims.  
      “This application claims priority from Japanese Patent Application No. 2003-412604 filed on Dec. 10, 2003, which is hereby incorporated by reference herein.”