Image pickup apparatus

To obtain a high-quality image, there is provided an image pickup apparatus having a plurality of pixels including a photoelectric conversion unit for converting an optical signal from an object into an electrical signal and a read unit for reading out the signal from the photoelectric conversion unit, a difference circuit for performing difference processing on a noise component contained in the signal read by the read unit, a detection circuit for detecting image pickup conditions, and a correction circuit for performing correction of execution of difference processing in accordance with an output from the detection circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pickup apparatus with an array of a plurality of pixels each having a photoelectric conversion function, and an image pickup system using the solid-state image pickup apparatus.

2. Related Background Art

Solid-state image pickup elements are roughly classified into charge transfer type elements such as a CCD, and XY address type elements such as a MOS image pickup device.

Using this solid-state image pickup element as a sensor provides not only many merits but also demerits. One of the demerits is image deterioration called as “smear” generated when a bright object image is picked up.

In the CCD, part of object light leaks as photo-leak to a vertical transfer register adjacent to a photodiode, and is observed as a white noise band on the image in the vertical direction of the bright object image. This phenomenon occurs with a light quantity corresponding to about 60 dB to about 100 dB of light amount with which the photodiode saturates.

In the MOS image pickup device, as shown inFIG. 1, the pixel is generally made up of a photodiode1, an amplification MOS transistor2for amplifying and outputting a signal from the photodiode, a transfer MOS transistor3for transferring the signal from the photodiode1to the amplification MOS transistor2, a reset MOS transistor for supplying a reset potential to the gate region of the amplification MOS transistor, and a selection MOS transistor5for selectively outputting a signal from the amplification MOS transistor2. It has been understood that the smear can be avoided substantially when the gate electrode region of the amplification MOS transistor is reset before the signal from the photodiode1is transferred to the amplification MOS transistor2. For example, the transfer time from the photodiode to the amplification MOS transistor is several μs, while an exposure time is 16 or 17 ms for a movie camera such as a video camera. The light quantity difference is about 100 dB, and the gate electrode region of the amplification MOS transistor is shielded from light. In this situation, it has been understood that smear is considered not to occur.

However, the present inventors have conducted image pickup experiments to find the following problems.

There is a conventional solid-state image pickup apparatus having a difference means for subtracting a noise component in order to remove a noise component contained in a signal photoelectrically converted and output by a photoelectric conversion means such as a photodiode.

An example of the solid-state image pickup apparatus having the difference means is shown inFIG. 2.FIG. 3is a timing chart showing the operation timing of the solid-state image pickup apparatus inFIG. 2.

A pixel6has the same structure as that of the pixel shown inFIG. 1. A reset signal vn obtained when the input of an amplification MOS transistor is reset, is stored in a memory CN7during a period t1, and a signal vs generated by photoelectric conversion by a photoelectric conversion means is transferred to the input of the amplification MOS transistor during a period t2. At the same time, a signal VS output from the amplification MOS transistor is stored in a memory CS8. The signal VS stored in the memory CS8contains the signal (vs) generated by photoelectric conversion and the reset signal (vn).

The reset signal vn stored in the memory CN7and the signal VS (=vs+vn) stored in the memory CS8are read out to a differential amplifier9. The differential amplifier calculates difference VS−vn, and outputs a signal vs free from any noise component, from which signal vs the reset signal as a noise component is removed.

The input of the amplification MOS transistor should be reset during the period t1, but a photo-leak noise signal v1is added to the reset signal which is a noise component, owing to photo-leak of very strong light (VN=vn+v1). Hence, an output signal from the differential amplifier is VS−VN=vs−v1. If v1saturates, the output signal vs−v1becomes 0, and the image becomes darkened regardless of a bright object.

FIG. 4is a conceptual view showing this phenomenon. The abscissa represents the incident light quantity on the photoelectric conversion means, and the ordinate represents the level of a signal generated in the photoelectric conversion means.

When, for example, a bright object (the sun, a light source, or the like) exists in an object to be picked up, the corresponding portion becomes a darkened image depending on image pickup conditions, resulting in low image quality.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image pickup apparatus capable of obtaining high image quality regardless of image pickup conditions.

To achieve the above object, according to aspect of the present invention, there is provided an image pickup apparatus comprising a plurality of pixels including photoelectric conversion means for converting an optical signal from an object into an electrical signal and read means for reading out the signal from the photoelectric conversion means, difference means for performing difference processing on a noise component contained in the signal read by the read means, detection means for detecting an image pickup condition, and correction means for performing correction of execution of difference processing in accordance with an output from the detection means.

According to another aspect of the present invention, there is provided an image pickup apparatus comprising a plurality of pixels including photoelectric conversion means for converting an optical signal from an object into an electrical signal and read means for reading out the signal from the photoelectric conversion means, difference means for performing difference processing on a noise component contained in the signal read by the read means, detection means for detecting an image pickup condition, and correction means for controlling the difference means in accordance with an output from the detection means.

In addition, according to still another aspect of the present invention, is provided an image pickup apparatus comprising a pixel including photoelectric conversion means for converting an optical signal from an object into an electrical signal and read means for reading out the signal from the photoelectric conversion means, difference means for performing difference operation on a noise component contained in the signal read by the read means, detection means for detecting a signal level of noise generated in the pixel, and correction means for correcting the signal read by the read means in accordance with the detection means.

Other objects and features of the present invention will be apparent from the following description in conjunction with an output of the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the present invention will be described.FIG. 5shows a solid-state image pickup apparatus100according to the first embodiment.

InFIG. 5, a plurality of pixels6shown inFIG. 1are arranged horizontally and vertically in an image pickup area10. As shown inFIG. 1, each pixel is made up of a photodiode1serving as a photoelectric conversion means, an amplification MOS transistor2serving as a read means for amplifying and outputting a signal from the photodiode, a transfer MOS transistor3serving as a transfer means for transferring the signal from the photodiode1to the amplification MOS transistor2, a reset MOS transistor serving as a reset means for supplying a reset potential to the input of the amplification MOS transistor, and a selection MOS transistor5serving as a selection means for selectively outputting a signal from the amplification MOS transistor2. A vertical shift register11sequentially outputs signals from pixels on horizontal lines in units of lines. An S memory8accumulates a signal VS as a sum of a photoelectrically conversion signal generated in the photodiode1and output from the amplification MOS transistor2in the pixel and a reset signal vn which is a noise component. An N memory7accumulates a signal VN as a sum of the reset signal vn which is a noise signal, and a photo-leak noise signal v1. A horizontal shift register12outputs signals accumulated in the S memory8and N memory7in units of lines. An amplifier13amplifies the signals VS and VN respectively output from the S memory8and N memory7. A differential amplifier9serves as a difference means for performing difference operation on the signals VS and VN in order to subtract the noise component from the signal VS output from the amplifier13. A level detection circuit14serves as a detection means for detecting image pickup conditions including the object conditions of an object to be picked up. A switch15serves as a correction means for performing correction of (selectively switching between execution/non-execution of difference operation) execution of difference processing in accordance with an output from the level detection circuit14. When the switch15is opened in accordance with an output from the level detection circuit, the differential amplifier does not receive any signal VN, and receives the signal VS not subjected to difference processing. An A/D conversion circuit16converts an analog signal output from the differential amplifier into a digital signal. A timing generator17controls the timings of the image pickup area10and A/D conversion circuit16.

The operations of the level detection circuit14and switch15will be described in detail.

FIG. 6is a graph in which the abscissa represents the incident light quantity on the photodiode1, and the ordinate represents the level of a signal generated in the photodiode. The signal vs generated in the photodiode saturates at a light quantity B, and the photo-leak noise v1gradually reaches a high signal level around a light quantity C. When difference processing is done at the light quantity C or more, the image becomes dark.

To prevent this phenomenon, the level detection circuit14detects at least whether the signal vs generated in the photodiode saturates or the photo-leak noise signal v1reaches a predetermined level or more, and when the circuit14detects this, the switch15is opened to stop difference processing. A signal not subjected to difference processing contains a noise component, and is processed as a saturation signal (compressed by Knee processing).

The signal detected as a saturation signal is set to be a signal at given level VA or more which is slightly smaller than a signal level at which the signal completely saturates.

In the first embodiment, the level detection circuit detects whether the signal VS output from the S memory8is at signal level VA or more, thereby detecting saturation of the photodiode, or detects whether the signal VN output from the N memory7is at signal level VB or more, thereby detecting that the photo-leak noise signal v1is a predetermined level or more.

When the level detection circuit14detects that the signal VS is at signal level VA or more, or the signal VN is at signal level VB or more, difference processing is not executed, thereby obtaining an image free from being darkened.

The first embodiment has exemplified the level detection circuit14as a detection means. However, the detection means suffices to detect image pickup conditions, and may be located not at the output stage of the amplifier13but, e.g., within the pixel.

The first embodiment has exemplified the switch15for stopping difference processing as a correction means. However, the correction means suffices to perform correction of execution of difference processing in accordance with an output from the detection means, and may be located in, e.g., the image pickup area10. The correction means may stop transfer of an input or output to or from the N memory7, or stop transfer of a noise signal from the pixel6.

All the building elements of the solid-state image pickup apparatus100may be formed on a single semiconductor substrate by the CMOS process or the like. Alternatively, e.g., the A/D conversion circuit16and timing generator may be formed on different semiconductor substrates.

The pixels of the solid-state image pickup apparatus in the first embodiment may be area sensors arranged two-dimensionally, or line sensors arranged one-dimensionally.

The second embodiment of the present invention will be described.FIG. 7is a block diagram showing part of a solid-state image pickup apparatus100according to the second embodiment. The input stage of an amplifier13, which is not illustrated inFIG. 7, is the same as that described in the first embodiment.

A memory18accumulates a signal from an A/D conversion circuit16. A conversion circuit19serving as a correction means performs correction of execution of difference processing (converts a signal having undergone difference processing into a signal of a predetermined signal level) in accordance with an output of a level detection circuit14serving as a detection means. The level detection circuit serving as a detection means detects image pickup conditions including the object conditions of an object to be picked up by the same method as in the first embodiment.

In the second embodiment, unlike the first embodiment, a differential amplifier9serving as a difference means executes difference processing (VS−VN) even when a signal VS is detected by the level detection circuit to be at signal level VA or more or even when a signal VN is detected to be at signal level VB or more. Further, the processed signal is converted into a digital signal by the A/D conversion circuit16, and stored in the memory18. In reading out a signal from the memory18, when the signal VS is detected by the level detection circuit to be at signal level VA or more or when the signal VN is detected to be at signal level VB or more, the conversion circuit19converts the signal into a signal of a predetermined level (e.g., signal level VA). Alternatively, a digital signal from the A/D conversion circuit16may be converted into saturation data upon reception of a saturation detection signal from the level detection circuit14.

In other words, when the level detection circuit14detects that the signal VS is at signal level VA or more, or the signal VN is at signal level VB or more, the conversion circuit19is operated to obtain an image free from being dardened.

The second embodiment has exemplified the level detection circuit14as a detection means. However, the detection means suffices to detect image pickup conditions, and may be located not at the output stage of the amplifier13but, e.g., within the pixel.

The second embodiment has exemplified as a correction means an arrangement of converting a signal read out from the memory into a signal of a predetermined level. However, the correction means suffices to perform correction of execution of difference processing in accordance with an output of the detection means, and may be located in, e.g., the image pickup area10.

All the building elements of the solid-state image pickup apparatus100may be formed on a single semiconductor substrate by the CMOS process or the like. Alternatively, e.g., the A/D conversion circuit16and timing generator may be formed on different semiconductor substrates.

The pixels of the solid-state image pickup apparatus in the second embodiment may be area sensors arranged two-dimensionally, or line sensors arranged one-dimensionally.

FIG. 8is a view showing the section of the pixel. The pixel is completely shielded from light in order to prevent any photo-leak.

InFIG. 8, a photodiode (corresponding toFIG. 1) is constituted by a region20serving as an n-type semiconductor region, and a region21serving as a p-type semiconductor region. A region23serving as an n-type semiconductor region corresponds to the input of the amplification MOS transistor. A gate electrode24transfers signals from the regions20and21constituting the photodiode to the region23. Photo-shield films25,26, and27are made of aluminum, and a black member28prevents any photo-leak together with the photo-shield films25,26, and27.

However, in the solid-state image pickup apparatus according to the first and second embodiment, the pixel can be shielded from light by a simple process. That is, the black member28is unnecessary, and the photo-shield film27can also be eliminated by efficiently using the photo-shield film26. By eliminating the black member and photo-shield film27, the distance between the photodiode and the microlens can be shortened to increase the focusing efficiency by the microlens.

The third embodiment of the present invention will be described.

FIG. 9is a block diagram showing an application of the solid-state image pickup apparatus in the first or second embodiment to a video camera serving as an image pickup system.

A photographing lens201comprises a focus lens201A for adjusting the focus, a zoom lens201B for performing zoom operation, and an imaging lens201C.

An iris202is arranged after the photographing lens201. A solid-state image pickup apparatus100described in the first or second embodiment photoelectrically converts an object image formed on the image pickup plane into an electrical image pickup signal. A process circuit205performs predetermined processing such as gamma correction, color separation, or blanking processing on a video signal output from the image pickup apparatus100, and outputs a luminance signal Y and chrominance signals C. The chrominance signals C output from the process circuit205are subjected to white balance correction and color balance correction by a chrominance signal correction circuit221, and output as color difference signals R-Y and B-Y. The luminance signal Y output from the process circuit205, and the color difference signals R−Y and B−Y output from the chrominance signal correction circuit221are modulated by an encoder circuit (ENC circuit)224, and output as a standard television signal. The standard television signal is supplied to a video recorder or a monitor EVF such as an electronic view finder (neither is shown).

An iris control circuit206controls an iris driving circuit207based on a video signal supplied from a the solid-state image pickup apparatus100and automatically controls an ig meter208in order to control the aperture value of the iris202so as to keep the level of the video signal at a predetermined level.

Bandpass filters (BPFs)213and214have different band limitations for extracting high-frequency components necessary for focus detection from the video signal output from the solid-state image pickup apparatus100. Signals output from the first bandpass filter (BPF1)213and second bandpass filter (BPF2)214are gated by a gate circuit215and a focus gate frame signal. The peak values of these signals are detected by a peak detection circuit216, and then the signals are held and input to a logic control circuit217. These signals are called a focus voltage, and the focus is adjusted based on the focus voltage. A focus encoder218detects the moving position of the focus lens201A, a zoom encoder219detects the focal length of the zoom lens201B, and an iris encoder220detects the aperture value of the iris202. The detection values of the encoders are supplied to the logic control circuit217for controlling the system.

The logic control circuit217detects the focus with respect to an object to be picked up, and adjusts the focus on the basis of a video signal corresponding to a set focus detection area. That is, the logic control circuit217receives peak value information of high-frequency components supplied from the bandpass filters213and214. To drive the focus lens201A to a position at which the peak values of the high-frequency components maximize, the logic control circuit217supplies to the focus driving circuit209a control signal for the rotational direction, rotational speed, and rotation/stop of a focus motor210, thereby controlling the focus motor210.

In the third embodiment, the solid-state image pickup apparatus100and the remaining building elements such as the process circuit205and logic control circuit may be formed on different semiconductor substrates, or may be formed on a single semiconductor substrate by the CMOS process or the like.

The fourth embodiment of the present invention will be described.

FIG. 10is a block diagram showing an application of the solid-state image pickup apparatus in the first or second embodiment to a still camera serving as an image pickup system.

InFIG. 10, a barrier301serves as both a lens protector and main switch. A lens302forms an optical image of an object on a solid-state image pickup apparatus100. An iris303changes the quantity of light having passed through the lens302. The solid-state image pickup apparatus100described in the first or second embodiment receives the object image formed by the lens302as an image signal. A signal processing unit307performs various correction processes on image data output from the solid-state image pickup apparatus100, and compresses data. A timing generation unit308outputs various timing signals to the solid-state image pickup apparatus100and signal processing unit307. A system control and operation unit309performs various operations, and controls the whole video camera. A memory unit310temporarily stores image data. An I/F unit311records and reads data on and from a recording medium. A removable recording medium312such as a semiconductor memory records and reads image data. An I/F unit313communicates with an external computer or the like.

The operation of the still video camera having this arrangement in photographing will be explained.

When the barrier301is opened, the main power, the power of the control system, and the power of the image pickup system are sequentially turned on.

To control the exposure amount, the system control and operation unit309sets the iris303to a full-aperture state, and a signal output from the solid-state image pickup apparatus100is input to the signal processing unit307. Operation for exposure is done by the system control and operation unit309using the processed data. The system control and operation unit309determines the brightness from the results of photometry, and controls the iris in accordance with the result of the determination.

The system control and operation unit309extracts an high-frequency component from a signal output from the solid-state image pickup apparatus100, and calculates the distance to the object. Then, the lens is driven to determine whether the camera is in focus or out of focus, and if the camera is determined to be out of focus, the lens is driven again to measure the distance. After the camera is confirmed to be in focus, actual exposure starts.

Upon completion of exposure, an image signal output from the solid-state image pickup apparatus100is written in the memory unit by the system control and operation unit309via the signal processing unit307.

The data accumulated in the memory unit310is recorded on the removable recording medium312such as a semiconductor memory via the recording medium control I/F unit311under the control of the system control and operation unit309.

Alternatively, the data may be directly input to a computer or the like via the external I/F unit313to process the image.

The fifth embodiment of the present invention will be described.

FIGS. 11 and 12are views showing an application of the solid-state image pickup apparatus in the first or second embodiment to a sheet feed type original image recording apparatus serving as an image pickup system.

FIG. 11is a schematic view showing an original image read apparatus for reading an original image.

A contact type image sensor (to be referred to as “CIS” hereinafter)401is constituted with a solid-state image pickup apparatus100described in the first embodiment, SELFOC lens403, LED array404, and contact glass405.

Feeding rollers406are arranged before and after the CIS401, and used to place an original. A contact sheet407is used to bring the original into contact with the CIS401. A control circuit410processes a signal from the CIS401.

An original detection lever408detects insertion of an original. When an original is inserted, the original detection lever408inclines to change an output of an original sensor409. This detection state is transferred to a CPU515in the control circuit410, and the CPU515determines insertion of the original to drive the driving motor (not shown) of the original feeding rollers406. Accordingly, the feeding rollers406start feeding the original, and the original is read.

FIG. 12is a block diagram showing an electrical arrangement to explain the control circuit410inFIG. 11in detail. The circuit operation will be explained with reference toFIG. 12.

InFIG. 12, the image sensor401(CIS401inFIG. 11) is integrally constituted with the LEDs404of R, G, and B colors serving as a light source. While an original is fed onto the contact glass405of the CIS401, an LED control (drive) circuit503switches between and turns on the LEDs404of R, G, and B colors in units of lines to read a color image line-sequentially for the R, G, and B colors.

A shading RAM506stores shading correction data by reading a calibration sheet in advance. A shading correction circuit507performs shading correction of a read image signal on the basis of the data in the shading RAM506. A peak detection circuit508detects the peak value of read image data for each line, and is used to detect the leading end of an original.

A gamma conversion circuit509performs gamma conversion of image data read in accordance with a gamma curve set in advance by the host computer.

A buffer RAM510temporarily stores image data in order to match the timings of actual read operation and communication with the host computer. A packing/buffer RAM control circuit511performs packing processing corresponding to an image output mode (binary, 4-bit multilevel, 8-bit multilevel, or 24-bit multilevel) set in advance by the host computer, then writes the data in the buffer RAM510, and reads out image data from the buffer RAM510to an interface circuit512.

The interface circuit512receives a control signal from an external apparatus such as a personal computer serving as the host apparatus of the image read apparatus according to the fifth embodiment, and outputs an image signal to the external apparatus.

A CPU515is implemented by, e.g., a microcomputer, has a ROM515A storing processing sequences and a work RAM515B, and controls the respective units in accordance with a procedure stored in the ROM515A.

An oscillator516is, e.g., a quartz oscillator, and a timing signal generation circuit514divides the frequency of an output of the oscillator516in accordance with the settings of the CPU515to generate various timing signals serving as the reference of the operation. An external apparatus513is connected to the control circuit via the interface circuit512. An example of the external apparatus is a personal computer.

In the fifth embodiment, the solid-state image pickup apparatus100and control circuit410may be formed on different semiconductor substrates, or may be formed on a single semiconductor substrate by the CMOS process or the like.

The sixth embodiment of the present invention will be described.

FIGS. 13 and 14are views showing an application of the solid-state image pickup apparatus described in the first or second embodiment to an original image read apparatus serving as an image pickup system having a communication function and the like.

FIG. 13is a block diagram showing the arrangement of the image processing unit of the image read apparatus. InFIG. 13, a reader unit601reads an original image (not shown), and outputs image data corresponding to the original image to a printer unit602and image I/O control unit603. The printer unit602records an image corresponding to image data from the reader unit601and image I/O control unit603on a recording sheet.

The image I/O control unit603is connected to the reader unit601, and comprised of a facsimile unit604, file unit605, computer interface unit607, formatter unit608, image memory unit609, and core unit610. The facsimile unit604transfers to the core unit610image data obtained by decompressing compressed image data received via a telephone line613, and transmits via the telephone line613compressed image data obtained by compressing image data transferred from the core unit610. The facsimile unit604is connected to a hard disk612to allow temporarily storing the received compressed image data.

The file unit605is connected to the photo-magnetic disk drive unit606. The file unit605compresses image data transferred from the core unit610, and stores the image data together with a keyword for retrieving it in a photo-magnetic disk arranged in the photo-magnetic disk drive unit606. The file unit605retrieves the compressed image data stored in the photo-magnetic disk based on a keyword transferred via the core unit610. The file unit605reads and decompresses the retrieved compressed image data, and transfers the decompressed image data to the core unit610.

The computer interface unit607is an interface between a personal computer or work station (PC/WS)611and the core unit610.

The formatter unit608develops code data representing an image transferred from the PC/WS611into image data recordable by the printer unit602. The image memory unit609temporarily stores data transferred from the PC/WS611.

The core unit610controls the data flow between the reader unit601, facsimile unit604, file unit605, computer interface unit607, formatter unit608, and image memory unit609.

FIG. 14is a sectional view showing the structures of the reader unit601and printer unit602inFIG. 13.

InFIG. 14, an original feeding device701of the reader unit601feeds the pages of an original (not shown) one by one from the last page to a platen glass702, and discharges the original to the platen glass702after original read operation. When the original is fed to the platen glass702, a lamp703is turned on, and a scanner unit704starts moving, thereby exposing and scanning the original.

Light reflected by the exposed/scanned original is guided to a solid-state image pickup apparatus100in the first or second embodiment by mirrors705,706, and707and lens708. The scanned original image is read by the solid-state image pickup apparatus100. Image data output from the solid-state image pickup apparatus100is subjected to processing such as shading correction, and transferred to the printer unit602or core unit610.

Laser drivers821of the printer unit602drive corresponding laser beam-emitting units801to cause the laser beam-emitting units801to emit laser beams corresponding to the image data output from the reader unit601.

The laser beams irradiate different positions on a photosensitive drum802to form a latent image corresponding to these laser beams on the photosensitive drum802.

A developing mix adheres to the latent image portion of the photosensitive drum802by a developing device803.

At a timing synchronized with the start of laser beam irradiation, a recording sheet is fed from either of cassettes804and805and conveyed to a transfer unit806, and the developing mix adhered to the photosensitive drum802is transferred onto the recording sheet. The recording sheet to which the developing mix was transferred is conveyed to a fixing unit807, and the developing mix is fixed to the recording sheet by the heat and pressure of the fixing unit807.

The recording sheet having passed through the fixing unit807is discharged by discharge rollers808. A sorter820sorts discharged recording sheets in corresponding bins to sort them. When the sorter820is not set, the rotational direction of the discharge rollers808is reversed after a recording sheet is conveyed to the discharge rollers808, and the recording sheet is guided to a refeeding path810by a flapper809.

When multiple recording is not set, a recording sheet is guided to the refeeding path810by the flapper809so as not to convey the recording sheet to the discharge rollers808. The recording sheet guided to the refeeding path810is fed to the transfer unit806at the above-described timing.

The seventh embodiment of the present invention will be described below.

FIG. 15is a block diagram showing a camera control system serving as an image pickup system having, e.g., the video camera in the third embodiment using the solid-state image pickup apparatus in the first or second embodiment.

The seventh embodiment is not limited to the video camera in the third embodiment, and may be applied to the still camera in the fourth embodiment.

FIG. 15is a block diagram showing the schematic arrangement of the camera control system.

A network910transmits digital video data and digital camera control information (including status information), and is connected to n video transmission terminals912(912-1to912-n).

Each video transmission terminal912(912-1to912-n) is connected to a camera916(916-1to916-n) via a camera control device914(914-1to914-n). The camera control device914(914-1to914-n) controls the pan, tilt, zoom, focus, and iris of the connected video camera916(916-1to916-n) in accordance with control signals from the video transmission terminal912and video camera916(916-1to916-n).

The video camera916(916-1to916-n) receives power from the camera control device914(914-1to914-n), and the camera control device914(914-1to914-n) controls the power-on/off operation of the video camera916(916-1to916-n) in accordance with an external control signal.

The network910is connected to video reception terminals918(918-1to918-m) for receiving and displaying video information transmitted from the video transmission terminals912(912-1to912-n) to the network910. Each video reception terminal918(918-1to918-m) is connected to a monitor920(920-1to920-m) formed with a bitmap display or CRT.

This network910need not be a wire network, and may be a radio network using a radio LAN or the like. In this case, the video reception terminal918can be integrated with the monitor920to constitute a portable video reception terminal device.

The video transmission terminal912(912-1to912-n) compresses an output video signal from the connected camera916(916-1to916-n) by a predetermined compression scheme such as H.261, and transmits the compressed data to a requesting video reception terminal918or all the video reception terminals918via the network910.

The video reception terminal918can control power-on/off operation with various parameters (photographing azimuth, photographing magnification, focus, and iris) of an arbitrary camera916via the network910, video transmission terminal912, and camera control device914.

The video transmission terminal912can serve as a video reception terminal by connecting a monitor and arranging a video decompression device for decompressing compressed video data. The video reception terminal918can serve as a video transmission terminal by connecting the camera control device914and video camera916and arranging a video compression device. These terminals comprise ROMs for storing software necessary for video transmission or video reception.

With the above arrangement, the video transmission terminal912transmits a video signal to the video reception terminal918at a remote place via the network910, and receives a camera control signal transmitted from the video reception terminal918to control the pan and tilt of the camera916.

The video reception terminal918transmits a camera control signal to the video transmission terminal912. The video transmission terminal912having received the camera control signal controls the camera916in accordance with the contents of the camera control signal, and sends back the current state of the camera916.

The video reception terminal918receives video data transmitted from the video transmission terminal912, performs predetermined processing, and displays in real time the photographed image on the display screen of the monitor920.

As has been described above, according to the first to seventh embodiments, a high-quality image can be obtained regardless of the conditions of an object to be picked up.