JP4240738B2 - Imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging device, and in particular, an imaging device such as a surveillance camera device in which an installation place is fixed, a time for continuous imaging at a time is as short as several minutes, and no diaphragm for adjusting the amount of light is provided. It relates to the device.
[0002]
[Prior art]
FIG. 7 is a block diagram showing a conventional imaging device (monitoring camera device). This image pickup apparatus includes an optical lens 1 that forms an image of a subject, and an image pickup device that stores light passing through the optical lens 1 in place of electric charges. The image of the subject is imaged from the electric charges accumulated in the image pickup device. An imaging circuit 2 that converts the signal into a signal and outputs it, a correlated double sampling circuit 6 that removes low-frequency noise from the video signal output from the imaging circuit 2, and a control pulse signal that outputs the charge accumulation time of the imaging device. The electronic shutter control circuit 3 to be adjusted and the video signal output from the imaging circuit 2 and from which the low frequency noise has been removed by the correlated double sampling circuit 6 are amplified and the amplification degree is adjusted in accordance with the video signal level after amplification. The automatic gain control circuit 4 and the video signal amplified by the automatic gain control circuit 4 are signal-processed and converted into a predetermined video signal format, and the amplitude of the video signal becomes an appropriate level. And a signal processing circuit 5 for controlling the electronic shutter control circuit 3 and the automatic gain control circuit 4 in. A CCD (Charge Coupled Device) is used as the imaging device, and the incident light is imaged on the light receiving surface of the CCD by the optical lens 1, and charges corresponding to the intensity of the incident light are accumulated inside the CCD for each pixel. A video signal at a level corresponding to the amount of accumulated charge is output from the imaging circuit 2.
[0003]
Here, since the amount of light incident on the CCD is proportional to the illuminance of the subject, for example, when the imaging device as described above is used outdoors, the subject illuminance is from 0.1 lux (illuminance under no illumination at night). The CCD is required to have a very wide dynamic range corresponding to a brightness change of about 1.5 million times, such as up to 150,000 lux (illuminance under daylight sunlight). However, the dynamic range that a normal CCD can follow is several hundred to several thousand times, and when a subject is imaged in a very bright scene such as under sunlight, the incident light is too strong and each pixel In some cases, the amount of charge accumulated in the battery exceeds the capacity. In this case, the amplitude of the video signal output from the imaging circuit 2 also reaches the upper limit, and when the video signal is displayed on a monitor or the like, the subject may be whitened and cannot be discriminated.
[0004]
On the other hand, there is an image pickup apparatus provided with a diaphragm for adjusting the amount of light incident on the CCD. However, the image pickup apparatus used as the monitoring camera apparatus as described above does not provide a diaphragm due to dimensional restrictions and cost. In many cases, in general, the amount of incident light is adjusted by providing a so-called electronic shutter function that prevents the accumulated charge from being saturated by sweeping away the excess charge accumulated in the CCD pixels. . That is, for captured images of bright scenes such as sunlight in the daytime, the charge accumulation time of the CCD is made shorter than usual to prevent saturation of the accumulated charge amount, and captured images of dark scenes such as overcast or nighttime In contrast, the charge accumulation time is set to a normal length so that sufficient charges can be accumulated.
[0005]
Incidentally, a control pulse signal (generally called a charge sweeping pulse or the like) for causing the image pickup circuit 2 to sweep away excess accumulated charges is a square pulse having a constant cycle as shown in FIG. As the illuminance of the subject becomes brighter than a predetermined level, a larger number is input. While the control pulse signal is being input, the image pickup circuit 2 sweeps out the charges accumulated in the CCD, thereby shortening the charge accumulation time. On the other hand, as shown in FIG. 9B, in a dark scene with low subject illuminance, the control pulse signal is not input to the imaging circuit 2, and the charge accumulation time corresponding to the video signal format (for example, one frame in the case of the NTSC system) Charge is accumulated in the CCD for the corresponding 1/30 second). The control pulse signal is output so that the signal processing circuit 5 sets the amplitude of the video signal to an appropriate level according to the brightness of the subject determined from the amplitude of the video signal.
[0006]
[Problems to be solved by the invention]
In the case of an imaging device that requires a very wide dynamic range, such as a surveillance camera device used outdoors as described above, there is a limit to the dynamic range in which an appropriate image can be obtained due to the ability of an imaging element such as a CCD. Arise. In particular, in the case of a surveillance camera device, there is often a problem in a dark scene where the subject illumination is low. That is, when it is determined that the subject illuminance is low based on the amplitude of the video signal, the signal processing circuit 5 does not output the control pulse signal to the electronic shutter control circuit 3 and the gain for the automatic gain control circuit 4 However, due to the sensitivity of the CCD and the gain limit of the automatic gain control circuit 4, it may be difficult to capture an object in a dark scene.
[0007]
Therefore, as shown in FIG. 10, it is conceivable to provide an amplification circuit 7 for amplifying the video signal between the correlated double sampling circuit 6 and the automatic gain control circuit 4 to compensate for the gain limit of the automatic gain control circuit 4. When a video signal is amplified, noise components included in the video signal are also amplified, and in a relatively bright scene with high subject illuminance, the S / N ratio decreases and noise becomes conspicuous. It is desirable that the video signal is amplified only by the amplifying circuit 7 and not in a bright scene.
[0008]
By the way, when the gain of the amplifier circuit 7 is adjusted by the control signal output from the automatic gain control circuit 4 as in the image pickup apparatus described in Japanese Patent Publication No. 28072828, the electronic shutter control circuit 3, the automatic gain control circuit. 4 and the signal processing circuit 5 are formed as a one-chip semiconductor device (integrated circuit), an output terminal for taking out the control signal to the outside is required, resulting in a problem of increased cost. In addition, recently, it is rare that the control signal is extracted from a single-chip semiconductor device.
[0009]
The present invention has been made in view of the above circumstances, and an object of the present invention is to appropriately output a video signal according to the brightness of a subject to be imaged with a simple configuration without reducing the S / N ratio. An object of the present invention is to provide an imaging apparatus capable of providing a level.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the invention of claim 1 includes an optical lens that forms an image of a subject, and an imaging element that accumulates light passing through the optical lens in place of electric charges, and is stored in the imaging element. An image pickup circuit that converts an image of a subject into a video signal from the generated charge and outputs the image signal, an electronic shutter control circuit that outputs a control pulse signal to adjust the charge accumulation time of the image pickup device, and a video signal output from the image pickup circuit An automatic gain control circuit that amplifies and adjusts the amplification degree according to the level of the video signal after amplification, and the video signal amplified by the automatic gain control circuit is signal-processed and converted into a predetermined video signal format, and the video signal A signal processing circuit for controlling the electronic shutter control circuit and the automatic gain control circuit so that the amplitude becomes an appropriate level, and a control pulse signal output from the electronic shutter control circuit And brightness determination circuit for determining the brightness of the subject on the basis of the number of pulsesA switching amplifier circuit provided in a preceding stage of the automatic gain control circuit and capable of switching between a process of amplifying the video signal and a process of not amplifying the video signal so that the video signal is at an appropriate level according to the determination result in the brightness determination circuit;The video signal is set to an appropriate level according to the discrimination result in the brightness discrimination circuit.In addition, the process in the switching amplifier circuit is fixed to one according to the determination result in the brightness determination circuit in a predetermined time after the start of imaging.Since the control pulse signal output from the electronic shutter control circuit changes according to the brightness of the subject, the brightness determination circuit does not provide a separate brightness detection element. The brightness of the object can be determined by counting the number of pulses of the control pulse signal. Then, according to the determination result, for example, when the illuminance of the subject is low, the video signal is set to an appropriate level by turning on the illumination load, etc., so that the image is captured with a simple configuration without reducing the S / N ratio. The video signal can be set to an appropriate level in accordance with the brightness of the subject.When the subject illuminance is low, the switching amplifier circuit performs processing to amplify the video signal so that the video signal becomes an appropriate level. When the subject illuminance is high, the switching amplifier circuit performs processing that does not amplify the video signal. As a result, the S / N ratio does not decrease due to excessive amplification. As a result, the video signal is set to an appropriate level according to the brightness of the subject to be imaged without reducing the S / N ratio and with a simple configuration. can do. Further, immediately after the start of imaging, the control of the electronic shutter control circuit and the automatic gain control circuit by the signal processing circuit is not stable, and the determination of the brightness of the subject in the brightness determination circuit is not accurate, so that the processing of the switching amplifier circuit is not performed. Switching may be frequently performed and the image may be disturbed. However, depending on the determination result of the brightness determination circuit at a predetermined time when the control of the electronic shutter control circuit and the automatic gain control circuit is stabilized, the process of the switching amplifier circuit is performed. By fixing to, image disturbance (hunting phenomenon) due to frequent switching of the amplification degree can be prevented.
[0013]
  Claim2Claims1According to the invention, there is provided a video muting circuit for prohibiting the output of the video signal from the signal processing circuit to the outside only until the processing in the switching amplifier circuit is fixed to either one, and the switching amplification Until the processing of the circuit is fixed to either one, the video disturbance is not output to an external device such as a monitor device, so that the quality can be improved.
[0014]
  Claim3Claims1In the invention, the processing of the switching amplifier circuit within a predetermined time after the start of imaging is fixed to the amplification processing of the video signal, and the brightness of the subject to which the control pulse signal is output from the electronic shutter control circuit is relatively The brightness of the subject that can switch the process of the switching amplifier circuit according to the determination result of the brightness determination circuit can also be lowered, and the process of amplifying the video signal to the switching amplifier circuit in a darker scene is performed. Can be made.
[0016]
  Claim4Claims 1 to3In any one of the inventions, at least an electronic shutter control circuit, an automatic gain control circuit, and a signal processing circuit are formed as a one-chip semiconductor device, which can be reduced in size and cost, and is controlled by a brightness determination circuit. Since the brightness of the subject is determined based on the pulse signal, it is not necessary to separately provide a signal output terminal for determining the brightness of the subject in the semiconductor device, and the configuration can be simplified.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
  Before describing an embodiment of the present invention, a reference example having the same basic configuration as the present invention will be described.
  (Reference example1)
  Figure 1 shows a bookReference exampleThe basic configuration is the same as that of the conventional example shown in FIG. Therefore, the same components are denoted by the same reference numerals, and the description thereof is omitted.Reference exampleOnly the structure which becomes the characteristic of will be described.
[0018]
  BookReference example1 includes a brightness determination circuit 8 that determines the brightness of the subject based on the number of pulses of the control pulse signal output from the electronic shutter control circuit 3 as shown in FIG. It is characterized in that the video signal is set to an appropriate level according to the above.
[0019]
That is, the number of pulses of the control pulse signal output from the electronic shutter control circuit is small or zero when the subject illuminance is high, and increases as the subject illuminance decreases. The number of pulses is counted, and the brightness of the subject is determined from the counted value. That is, the brightness of the subject can be determined based on the number of pulses of the control pulse signal without separately providing an element for detecting brightness such as a phototransistor.
[0020]
  And booksReference exampleIn this case, when the brightness of the subject determined from the number of pulses of the control pulse signal is below a predetermined threshold, the illumination load control signal is output from the brightness determination circuit 8 to turn on the illumination load 9, and the illumination load The video signal is set to an appropriate level by illuminating with 9 to increase the illuminance of the subject.
[0021]
  Book as aboveReference exampleIs provided with a brightness discriminating circuit 8 for discriminating the brightness of the subject based on the number of pulses of the control pulse signal output from the electronic shutter control circuit 3, and the video signal is output according to the discrimination result in the brightness discriminating circuit 8. Since the level is appropriate, it is possible to determine the brightness of the subject without providing a separate element or the like for brightness detection, and the illumination load 9 is turned on when the subject illuminance is low according to the determination result. Thus, since the video signal is set to an appropriate level, the video signal can be set to an appropriate level according to the brightness of the subject to be imaged with a simple configuration without reducing the S / N ratio.
[0022]
By the way, when the electronic shutter control circuit 3, the automatic gain control circuit 4, and the signal processing circuit 5 are formed as a one-chip semiconductor device (for example, a digital signal processor) 10, it is possible to reduce the size and cost of the imaging apparatus and to increase brightness. Since the brightness determination circuit 8 determines the brightness of the subject based on the control pulse signal, there is no need to separately provide a signal output terminal for determining the brightness of the subject in the semiconductor device 10, and the configuration can be simplified. There is.
[0023]
  (Reference example2)
  Figure 2 shows a bookReference exampleFIG. 7 is a block diagram of the conventional example shown in FIG.Reference example1 and the basic configuration are common. Therefore, the same components are denoted by the same reference numerals, and the description thereof is omitted.Reference exampleOnly the structure which becomes the characteristic of will be described.
[0024]
  BookReference exampleThe switching amplifying circuit 11 that switches between a process of amplifying the video signal and a process of not amplifying the video signal so that the video signal is at an appropriate level according to the discrimination result in the brightness discrimination circuit 8 is provided before the automatic gain control circuit 4. There is a feature in the point provided in.
[0025]
The switching amplifier circuit 11 includes an amplifier 11a for amplifying a video signal and a switch 11b for switching and connecting a common terminal connected to the output terminal of the correlated double sampling circuit 6 to the input terminal and the output terminal of the amplifier 11a. . Further, the switch 11b is switched to the input end side of the amplifier 11a by the brightness discrimination circuit 8 when the brightness of the subject determined from the number of pulses of the control pulse signal is below a predetermined threshold, and exceeds the above threshold. If it is, it is switched to the output end side of the amplifier 11a.
[0026]
Thus, when the illuminance of the subject is low, the switching amplifier circuit 11 amplifies the video signal by the amplifier 11a so that the video signal becomes an appropriate level. When the illuminance of the subject is high, the switching amplifier circuit 11 sets the amplifier 11a. The video signal is output without being amplified. Therefore, the video signal is amplified only in a dark scene with low subject illuminance, and the S / N ratio does not decrease due to excessive amplification in a bright scene with high subject illuminance. Accordingly, the video signal can be set to an appropriate level.
[0027]
  (Embodiment1)
  by the wayReference example2, the presence / absence of amplification processing by the switching amplifier circuit 11 is switched according to the determination result of the brightness determination circuit 8. For example, the determination of the brightness determination circuit 8 is performed when the subject moves within the imaging range of the CCD. Since the result may change, the video signal output from the signal processing circuit 5 when the discrimination result of the brightness discrimination circuit 8 changes every time the subject moves and the presence or absence of the amplification process by the switching amplifier circuit 11 is switched. Is displayed on a monitor device or the like, the video becomes very unsightly.
[0028]
For example, when the brightness determination circuit 8 determines that the subject is dark, the video signal amplification processing is performed and the amplitude of the video signal output from the switching amplification circuit 11 increases instantaneously. When it is determined that the subject is bright from the amplitude of the video signal, a control pulse signal and a control signal are output to the electronic shutter control circuit 3 and the automatic gain control circuit 4 to reduce the amplitude of the video signal. However, since a time lag occurs between these controls and the actual amplitude change of the video signal, the screen of the monitor device or the like becomes darker after being brightened for a moment. If the brightness determination circuit 8 determines that the subject is bright, the switch 11b is switched to the output end side of the amplifier 11a and the amplification process of the video signal is not performed. Although the amplitude decreases instantaneously, if the signal processing circuit 5 determines that the subject is dark from the amplitude of the video signal, the control pulse signal and the control signal are output to the electronic shutter control circuit 3 and the automatic gain control circuit 4 to output the video. Control that increases the amplitude of the signal works. However, in this case as well, a time lag occurs between the above control and the actual change in the amplitude of the video signal. Therefore, in a monitor device or the like, the screen becomes darker and then gradually brightens. As described above, when the switching amplification circuit 11 switches the presence / absence of the amplification process of the video signal, the video is instantaneously disturbed on the screen of the monitor device or the like. Furthermore, when the brightness of the subject is in the vicinity of the threshold value of the brightness determination circuit 8, a phenomenon (hunting phenomenon) in which switching of presence / absence of amplification processing frequently occurs is caused.
[0029]
  Therefore, in the present embodiment, the operation described below is performed to prevent the occurrence of the hunting phenomenon. The configuration of this embodiment is as follows:Reference example2 and the illustration and description are omitted.
[0030]
As shown in the flowchart of FIG. 3, a predetermined time (control stabilization waiting time) until the control operation of the electronic shutter control circuit 3 and the automatic gain control circuit 4 is stabilized after power is supplied to the imaging circuit 2 and imaging is started. ) Is counted (S1), and the brightness determination circuit 8 counts the number of pulses of the control pulse signal output from the electronic shutter control circuit 3 when the control stabilization waiting time elapses to determine the brightness of the subject. (S2, S3) If the brightness of the determined subject is below a predetermined threshold value, the switch 11b is switched to the input end side of the amplifier 11a by the brightness determination circuit 8, and the video signal is amplified by the switching amplifier circuit 11. (S4) If the threshold value is exceeded, the switch 11b is switched to the output end side of the amplifier 11a and the amplification process of the video signal by the switching amplifier circuit 11 is performed. No I (S5). As a result, it is possible to prevent image disturbance (hunting phenomenon) due to frequent switching of the amplification degree as described above.
[0031]
In the present embodiment, after the above processing, while the power is supplied to the imaging circuit 2, the brightness determination circuit 8 does not switch the switch 11b even if the brightness of the subject changes. In other words, there is a possibility that the brightness of the subject changes with the location and time of imaging. However, the imaging device of this embodiment is a surveillance camera device, the installation location and the imaging location are fixed, and one imaging time is required. Since it is short, there is almost no problem even if the switch 11b is not switched as described above.
[0032]
Thus, in the present embodiment, the processing in the switching amplifier circuit 11 is fixed to one according to the determination result in the brightness determination circuit 8 for a predetermined time after the start of imaging, so that the signal processing circuit 5 immediately after the start of imaging. Since the control of the electronic shutter control circuit 3 and the automatic gain control circuit 4 due to the above is not stable and the brightness determination of the subject in the brightness determination circuit 5 is not accurate, the process of the switching amplifier circuit 11 is frequently switched. The image may be distorted, but switching is performed according to the determination result of the brightness determination circuit 8 at a predetermined time (when the control stabilization wait time elapses) when the control of the electronic shutter control circuit 3 and the automatic gain control circuit 4 is stabilized. By fixing the processing of the amplifier circuit 11 to one side, it is possible to prevent image disturbance (hunting phenomenon) caused by frequent switching of the amplification degree.
[0033]
  (Embodiment2)
  FIG. 4 shows a block diagram of the present embodiment. The conventional example shown in FIG.Reference example2 and the basic configuration are common. Therefore, the same components are denoted by the same reference numerals, description thereof is omitted, and only the components that are characteristic of this embodiment will be described.
[0034]
  Embodiment described above1In this case, the amplifying process by the switching amplifier circuit 11 can be performed only when the subject is dark by preventing the hunting phenomenon, but the switching is performed according to the determination result of the brightness determination circuit 8 when the control stabilization waiting time elapses. When the switch 11b of the amplifier circuit 11 is switched, the screen of the monitor device or the like may be disturbed.
[0035]
Therefore, in order to prevent such disturbance of the screen, in the present embodiment, the video signal from the signal processing circuit 5 to the outside (the monitor device or the like) is only until the processing in the switching amplifier circuit 11 is fixed to either one. The video muting circuit 12 for prohibiting the output of the image is provided, and this is a feature of this embodiment.
[0036]
The video muting circuit 12 has a conventionally well-known configuration, and the video signal output from the signal processing circuit 5 for the predetermined time from when the control stabilization waiting time elapses until the switching processing of the switching amplifier circuit 11 is completed. Instead of outputting to a monitor device or the like, a predetermined video signal (for example, a video signal for displaying a black or blue screen) is output instead.
[0037]
Thus, the present embodiment includes the video muting circuit 12 that prohibits the output of the video signal from the signal processing circuit 5 to the outside only until the processing in the switching amplifier circuit 11 is fixed to either one. Therefore, video disturbance is not output to an external device such as a monitor device until the process of the switching amplifier circuit 11 is fixed to either one, and the quality can be improved.
[0038]
  (Embodiment3)
  By the way, the embodiment1, The number of pulses of the control pulse signal output from the electronic shutter control circuit 3 after the elapse of the control stabilization waiting time is counted to determine the brightness of the subject. When it is determined that the subject is dark, the switching amplifier circuit 11 The switch 11b is switched to the input end side of the amplifier 11a to amplify the video signal. In this case, the minimum value of the brightness discrimination level in the brightness discrimination circuit 8 is 0 or 1 in the number of control pulse signals. The value is near one boundary. However, the number of output pulses of the control pulse signal varies depending on the presence or absence of amplification processing in the switching amplifier circuit 11. That is, when the switch 11b is switched to the output end side of the amplifier 11a and the switching amplifier circuit 11 is not performing amplification processing, for example, the brightness determination circuit 8 has a minimum determination level under ambient illuminance of about 100 lux. However, when the switch 11b is switched to the input end side of the amplifier 11a and the switching amplifier circuit 11 performs the amplification process, the minimum value of the determination level of the brightness determination circuit 8 is a level lower than 100 lux. Become. That is, when amplification processing is performed by the switching amplifier circuit 11, the signal processing circuit 5 determines that the subject is bright because the video signal is amplified by the switching amplifier circuit 11 even when the imaging scene is dark. The electronic shutter control circuit 3 and the automatic gain control circuit 4 are controlled so as to reduce the amplitude of the video signal. As a result, the number of control pulse signals output from the electronic shutter control circuit 3 increases.
[0039]
  Thus, in the present embodiment, the brightness of the subject that can switch the processing of the switching amplifier circuit 11 according to the determination result of the brightness determination circuit 8 is lowered by performing the operation described below. ing. The configuration of this embodiment is as follows:Reference example2 and the illustration and description are omitted.
[0040]
As shown in the flowchart of FIG. 5, when power is supplied to the imaging circuit 2 and imaging is started, the switching amplifier circuit 11 always switches the switch 11b to the input end side of the amplifier 11a to amplify the video signal. (S1). Then, as described in the third embodiment, the control stabilization waiting time until the control operations of the electronic shutter control circuit 3 and the automatic gain control circuit 4 are stabilized is counted (S2), and when this control stabilization waiting time elapses. The brightness determination circuit 8 counts the number of control pulse signals output from the electronic shutter control circuit 3 to determine the brightness of the subject (S3, S4), and the determined brightness of the subject reaches a predetermined threshold value. If it is lower, the switch 11b is kept as it is, and the video signal is amplified by the switching amplifier circuit 11 (S5). If it exceeds the threshold value, the switch 11b is switched to the output end side of the amplifier 11a to switch and amplify. The amplification process of the video signal by the circuit 11 is not performed (S6). That is, since the video signal is always amplified by the switching amplifier circuit 11 when the control stabilization waiting time elapses, the discrimination level of the brightness discrimination circuit 8 is compared with the case where the video signal is not amplified by the switching amplifier circuit 11. The minimum value of can be lowered.
[0041]
Thus, in this embodiment, the processing of the switching amplifier circuit 11 within a predetermined time after the start of imaging is fixed to the amplification processing of the video signal, so that the brightness of the subject to which the control pulse signal is output from the electronic shutter control circuit 3 Is relatively low, and the brightness of the subject to which the process of the switching amplifier circuit 11 can be switched according to the determination result of the brightness determination circuit 8 can also be decreased. As a result, it is possible to cause the switching amplifier circuit 11 to perform processing for amplifying the video signal in a darker scene.
[0042]
  (Embodiment4)
  By the way, the embodiment1, The number of pulses of the control pulse signal output from the electronic shutter control circuit 3 after the elapse of the control stabilization waiting time is counted to determine the brightness of the subject. When it is determined that the subject is dark, the switching amplifier circuit 11 The switch 11b is switched to the input end side of the amplifier 11a to amplify the video signal. After that, while the power is supplied to the imaging circuit 2, the brightness determination circuit 8 is switched even if the brightness of the subject changes. 11b is not switched. That is, since the imaging apparatus of the present embodiment is a monitoring camera apparatus and the imaging time for one time is short, the predetermined timing after the start of imaging is assumed on the assumption that the brightness of the subject is unlikely to change during imaging. Thus, the presence or absence of amplification processing of the switching amplifier circuit 11 is switched. However, there is little possibility that the brightness will change due to the movement of the subject.
[0043]
  Therefore, in the present embodiment, the operation described below is performed to prevent the occurrence of the hunting phenomenon while following the actual brightness of the subject. The configuration of this embodiment is as follows:Reference example2 and the illustration and description are omitted.
[0044]
As shown in the flowchart of FIG. 6, after the power is supplied to the imaging circuit 2 and imaging is started, the control stabilization waiting time until the control operation of the electronic shutter control circuit 3 and the automatic gain control circuit 4 is stabilized is counted. (S1) When the control stabilization waiting time elapses, the brightness determination circuit 8 counts the number of control pulse signals output from the electronic shutter control circuit 3 to determine the brightness of the subject (S2, S3). If the brightness of the determined subject is below a predetermined threshold value, the brightness determination circuit 8 switches the switch 11b to the input end side of the amplifier 11a and amplifies the video signal by the switching amplifier circuit 11 (S4). If the threshold value is exceeded, the switch 11b is switched to the output end side of the amplifier 11a and the amplification process of the video signal by the switching amplifier circuit 11 is not performed (S ). The operation of the present embodiment is different from that of the third embodiment in that the control stabilization waiting time is counted again after switching the presence or absence of amplification processing by the switching amplifier circuit 11 (S1), and the above operation is repeated. As a result, the brightness discrimination circuit 8 discriminates the brightness of the subject at a relatively long time interval (for example, several tens of seconds) which is not shorter than the control stabilization waiting time, and the presence / absence of amplification processing in the switching amplifier circuit 11 is switched. Therefore, although some video disturbance occurs at the time of switching, it is possible to prevent the hunting phenomenon caused by frequent switching of the amplification degree while following the actual brightness of the subject.
[0045]
【The invention's effect】
  The invention of claim 1 includes an optical lens that forms an image of a subject, and an image sensor that accumulates light passing through the optical lens in place of electric charges, and images the subject image from the electric charges accumulated in the image sensor. An image pickup circuit that converts the signal into an output signal, an electronic shutter control circuit that outputs a control pulse signal to adjust the charge accumulation time of the image pickup device, an image signal output from the image pickup circuit, and an amplified image signal An automatic gain control circuit that adjusts the amplification degree according to the level, and the video signal amplified by the automatic gain control circuit is signal-processed and converted into a predetermined video signal format, and the amplitude of the video signal becomes an appropriate level. A signal processing circuit for controlling the electronic shutter control circuit and the automatic gain control circuit, and a subject based on the number of control pulse signals output from the electronic shutter control circuit. And brightness determination circuit for determining the brightnessA switching amplifier circuit provided in a preceding stage of the automatic gain control circuit and capable of switching between a process of amplifying the video signal and a process of not amplifying the video signal so that the video signal is at an appropriate level according to the determination result in the brightness determination circuit;The video signal is set to an appropriate level according to the discrimination result in the brightness discrimination circuit.In addition, the process in the switching amplifier circuit is fixed to one according to the determination result in the brightness determination circuit in a predetermined time after the start of imaging.Therefore, since the control pulse signal output from the electronic shutter control circuit changes according to the brightness of the subject, the brightness determination circuit does not provide a separate brightness detection element. By counting the number of pulses, the brightness of the subject can be determined, and according to the determination result, for example, when the subject illuminance is low, the illumination signal is turned on to turn the video signal to an appropriate level. Therefore, there is an effect that the video signal can be set to an appropriate level according to the brightness of the subject to be imaged with a simple configuration without reducing the S / N ratio.When the subject illuminance is low, the switching amplifier circuit amplifies the video signal so that the video signal is at an appropriate level. When the subject illuminance is high, the switching amplifier circuit performs processing that does not amplify the video signal. As a result, the S / N ratio does not decrease due to excessive amplification. As a result, the video signal is set to an appropriate level according to the brightness of the subject to be imaged without reducing the S / N ratio and with a simple configuration. There is an effect that can be done. Further, immediately after the start of imaging, the control of the electronic shutter control circuit and the automatic gain control circuit by the signal processing circuit is not stable, and the determination of the brightness of the subject in the brightness determination circuit is not accurate, so that the processing of the switching amplifier circuit is not performed. Switching may be frequently performed and the image may be disturbed. However, depending on the determination result of the brightness determination circuit at a predetermined time when the control of the electronic shutter control circuit and the automatic gain control circuit is stabilized, the process of the switching amplifier circuit is performed. By fixing to, there is an effect that image disturbance (hunting phenomenon) caused by frequent switching of the amplification degree can be prevented.
[0048]
  Claim2Claims1In the present invention, since the video muting circuit for prohibiting the output of the video signal from the signal processing circuit to the outside is provided only until the processing in the switching amplifier circuit is fixed to either one, the processing of the switching amplifier circuit Video is not output to an external device such as a monitor device until the image is fixed to either one, and the quality can be improved.
[0049]
  Claim3Claims1In this invention, since the processing of the switching amplifier circuit within a predetermined time after the start of imaging is fixed to the amplification processing of the video signal, the brightness of the subject to which the control pulse signal is output from the electronic shutter control circuit becomes relatively low. The brightness of the subject that can switch the process of the switching amplifier circuit according to the determination result of the brightness determination circuit can also be lowered, and the switching amplifier circuit can perform the process of amplifying the video signal in a darker scene. There is an effect that can be done.
[0051]
  Claim4Claims 1 to3In any of the inventions, at least the electronic shutter control circuit, the automatic gain control circuit, and the signal processing circuit are formed as a one-chip semiconductor device, so that the size and cost can be reduced, and the brightness discrimination circuit uses the control pulse signal. Since the brightness of the subject is determined, it is not necessary to separately provide a signal output terminal for determining the brightness of the subject in the semiconductor device, and the configuration can be simplified.
[Brief description of the drawings]
[Figure 1]Reference example of the present invention1 is a block diagram showing 1. FIG.
[Figure 2]Reference example of the present invention2 is a block diagram showing 2. FIG.
FIG. 31It is a flowchart for operation | movement description.
FIG. 4 Embodiment2FIG.
FIG. 5 is an embodiment.3It is a flowchart for operation | movement description.
FIG. 6 is an embodiment.4It is a flowchart for operation | movement description.
FIG. 7 is a block diagram showing a conventional example.
FIG. 8 is a waveform diagram for explaining the operation of the above.
FIG. 9 is a waveform diagram for explaining the operation of the above.
FIG. 10 is a block diagram showing another conventional example.
[Explanation of symbols]
1 Optical lens
2 Imaging circuit
3 Electronic shutter control circuit
4 Automatic gain control circuit
5 Signal processing circuit
6 Correlated double sampling circuit
7 Amplifier circuit
8 Brightness discrimination circuit
9 Lighting load

Claims (4)

An optical lens that forms an image of a subject and an image sensor that stores light passing through the optical lens in place of electric charges are stored, and the subject image is converted into a video signal from the electric charges accumulated in the image sensor and output. An imaging circuit, an electronic shutter control circuit that adjusts the charge accumulation time of the imaging device by outputting a control pulse signal, and amplifies the video signal output from the imaging circuit and increases the amplification degree according to the level of the amplified video signal An automatic gain control circuit to be adjusted, a video signal amplified by the automatic gain control circuit, signal-processed and converted into a predetermined video signal format, and an electronic shutter control circuit and automatic so that the amplitude of the video signal becomes an appropriate level Discriminating the brightness of the subject based on the signal processing circuit for controlling the gain control circuit and the number of pulses of the control pulse signal output from the electronic shutter control circuit And that of the determination circuit, provided before the automatic gain control circuit, the processing and the switching which is not amplified and the process of amplifying the video signal so that the video signal may have an appropriate level in accordance with the determination result in the brightness determination circuit A switching amplifier circuit, the video signal is set to an appropriate level according to the determination result of the brightness determination circuit, and the switching amplifier circuit according to the determination result of the brightness determination circuit at a predetermined time after the start of imaging. An imaging apparatus characterized by fixing the process in one side . 2. The imaging according to claim 1, further comprising a video muting circuit that prohibits the output of the video signal from the signal processing circuit to the outside only until the processing in the switching amplifier circuit is fixed to either one. apparatus. Imaging device according to claim 1, wherein the fixing process of the switching換増width circuit within a predetermined time after the start of imaging the amplification process of the video signal. At least an electronic shutter control circuit, the image pickup apparatus according to any one of claims 1 to 3, characterized in that the formation of the automatic gain control circuit and a signal processing circuit as one-chip semiconductor device.

Images