JP2542087B2 - Photometric circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photometric circuit of a video camera device equipped with photometric means for photometrically measuring an image signal.

[Prior Art] In recent years, a video camera device such as an electronic endoscope device that obtains an image signal using a solid-state imaging device such as a CCD (charge coupled device) as an imaging unit has been put into practical use.

FIG. 14 is a configuration diagram of the electronic endoscope apparatus. The electronic endoscope apparatus 1 includes an electronic scope 2 formed in an elongated shape so that it can be inserted into, for example, a body cavity, and a universal cord (not shown) of the electronic scope 2. Main unit 3 to which is connected
And a monitor 4 for displaying a subject such as a body cavity part 5 by an output signal of the main body unit 3.

A light guide 6 for transmitting illumination light is inserted into the insertion portion of the electronic scope 2, and the illumination light supplied from the main body unit 3 to the incident end is transmitted to the emission end, and the body cavity portion 5 is transmitted from the emission end. It is designed to illuminate. The light reflected from the part 5 inside the body cavity is condensed by the objective lens 7, is incident on the image pickup element 8, and is photoelectrically converted into an image signal to reach the main body unit 3.

Further, the electronic scope 2 has a function of inserting the treatment tool 10 into the counter cavity through the channel 9. The treatment tool
There are a large number of 10 such as a treatment tool having a function of injecting a dyeing agent or an imaging agent, a treatment tool having a function of extracting a part of a tissue in a body cavity, and many of them use white Teflon and metal.

The main body unit 3 includes a light source section 20 for illuminating a subject,
The image signal processing unit 30 outputs a video signal to the monitor 4. The light source unit 20 includes a lamp 21, a diaphragm 22 for adjusting the amount of illumination light of the lamp 21, and a diaphragm control circuit 23 for generating a control signal for variably controlling the aperture ratio of the diaphragm 22,
It comprises a photometric circuit 24 that measures the illuminance of light incident on the image sensor 8 from an image signal and generates a signal to the diaphragm control circuit 23.
The image signal processing unit 30 includes an AGC circuit 31 that amplifies the image signal to an appropriate level, a photometric circuit 33 that measures the illuminance of illumination light incident on the image sensor 8 from the image signal and generates a signal to the AGC circuit 31, It comprises a signal processing circuit 32 for performing various kinds of signal processing and outputting it to the monitor 4.

The photometric circuits 24 and 33 are roughly classified into an average photometric circuit and a peak photometric circuit. The average photometry circuit is a circuit that detects the average value of the image signal level of the entire screen and generates a signal. When the average value of the image signal level is high, the aperture of the diaphragm 22 is narrowed to irradiate the body cavity portion 5 with the light. The amount of illumination light is reduced. The peak photometry circuit is a circuit that detects the maximum value of the image signal level and generates a signal. When the maximum value of the image signal level is high, the illumination light that irradiates the body cavity 5 with the aperture of the diaphragm 22 narrowed. The amount of light is reduced.

The AGC circuit is a circuit that amplifies a low image signal level that cannot be compensated by maximizing the aperture of the diaphragm 22 and maximizing the amount of illumination light to an appropriate level.

The electronic scope 2 is inserted into the body cavity, and the channel 9
The image shown in the example of FIG. 15 can be observed on the monitor 4 by inserting the treatment instrument 10 through the. FIG. 16 shows the image signal level in a time series of horizontal positions by paying attention to a certain horizontal scanning line AA 'in the image shown in FIG. The treatment tool 10 projects closer to the image pickup device 8 than the body cavity part 5, and since white Teflon or the like is used, it reflects illumination light with high efficiency, and as shown in FIG. Vs is much higher than the average value Va of the image signal level of the body cavity site 5. Therefore, the photometry circuits 24 and 33 have a high average value in the average photometry circuit and a high maximum value in the peak photometry circuit, so the signals generated by the photometry circuits 24 and 33 are not appropriate values, and the body cavity site The light amount for 5 decreases, and the amplification degree of the AGC circuit 31 also decreases.
Therefore, the image on the monitor 4 becomes dark as a whole.

Japanese Patent Application Laid-Open No. 62-10369 discloses, for example, a prior art for reducing the influence of the change in the level of the image signal in a specific portion of the captured image on the subject photographing.

[Problems to be Solved by the Invention] In the above-mentioned prior art example, the effect is obtained only when a subject having a higher brightness than the central portion of the screen is present in the peripheral portion of the screen of the photographing screen, and an electronic endoscope apparatus is taken as an example. Therefore, it is not effective for a subject having high brightness from the peripheral portion of the screen to the central portion of the screen due to the treatment tool or the like.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a photometric circuit in which a subject having a higher luminance than the average luminance of the photographing screen does not affect the entire photographing screen.

[Means and Action for Solving the Problem] Photometric integration means for outputting a photometric signal proportional to the light amount of the illumination light source by integrating the input image signal of the present invention over the entire screen, and the input image signal within the horizontal period. Input image signal analyzing means for integrating with a time constant in response to the fluctuation of the input image signal and outputting an input image integrated signal, and signal level detection for detecting a signal output period in the input image signal equal to or higher than the signal level of the input image integrated signal. Means and control means for controlling the signal level of the photometric signal output from the photometric integration means according to the output signal of the detection means.

With this configuration, the input image signal is higher than a predetermined value,
In addition, when the duration has a predetermined period, the input image signal is excluded from the subject of photometry.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 relate to the first embodiment of the present invention.
The figure shows the configuration of the photometric circuit, and FIG. 2 is an explanatory diagram showing the operation of the photometric circuit.

The photometric circuit 50 shown in FIG. 1 is the configuration of the photometric circuit of a video camera device such as an electronic endoscope, and includes an integrator 51, a bias power source 53, and an addition for adding the output of the integrator 51 and the bias power source 53. Device 52, a comparator 54 that compares the image signal with the output of the adder 52, a switch 55 that turns the image signal on and off by the output of the comparator 54, and a metering device that integrates the image signal through the switch 55 And an integrator 56.

In FIG. 1, the image signal is supplied from an input end of the photometric circuit 50 to a photometric integrator 56 via a switch 55, integrated by the photometric integrator 56 with a predetermined time constant, and the AGC circuit and aperture control. It is designed to be output as a control signal for circuits and the like.

The image signal is also applied to the input terminals of the integrator 51 and the comparator 54.

The image signal having a period td in which the signal level of the image signal shown by the solid line in FIG. 2 (a) input to the integrator 51 is remarkably high is integrated by a time constant longer than the period td, and the adder 52 Is added to the potential Vb of the bias power source 53 set to the minimum value of the image signal level, etc., and the signal level of the image signal becomes an averaged signal level as shown by the broken line in FIG. Add to one input end of 54. Further, the image signal shown by the solid line in FIG. 2 (a) having a portion where the signal level of the same image signal as that of the input end of the integrator 51 is extremely high is applied to the other input end of the comparator 54. Comparator 54
The output signal of is normally "L" as shown in FIG. 4 (b), and becomes "H" only during the period td during which the image signal level becomes extremely high. The switch 55 is on when the output signal of the comparator 54 is “L” and off when it is “H”.

Therefore, in the period td when the signal level of the image signal is significantly high, the image signal is not added to the photometric integrator 56 and is excluded from the photometric target.

By appropriately selecting the time constant of the integrator and the potential Vb of the bias power source using this photometric circuit, for example, in an electronic endoscope, an image signal of a high-luminance subject such as a treatment instrument is applied to the photometric integrator. Instead, the phenomenon that the entire photographed image becomes dark due to the decrease in the amplification factor of the AGC circuit and the aperture of the aperture controlled by the aperture control circuit disappears, and the observation of the subject becomes easy.

3 and 4 relate to a second embodiment of the present invention,
The figure shows the configuration of the photometric circuit, and FIG. 4 is an explanatory diagram showing the operation of the photometric circuit.

The photometering circuit 60 shown in FIG. 3 has the same structure as that of the first embodiment, and includes an integrator 51 and an integrator 51 based on an image signal.
A subtractor 62 for subtracting the output signal of 51, a reference power supply 63, a comparator 54 for comparing the output signal of the subtractor 62 with the reference power supply 63, and an image signal on / off by the output of the comparator 54. Switch 55 and a photometric integrator 56 that integrates the image signal passed through the switch 55.

In this embodiment, the image signal is supplied from the input end of the photometric circuit 60 to the photometric integrator 56 via the switch 55, integrated by the photometric integrator 56 with a predetermined time constant, and the AGC circuit and the aperture control circuit. And the like are output as control signals.

The image signal is also applied to the input terminals of the integrator 51 and the subtractor 62.

The image signal having a period td in which the signal level of the image signal shown by the solid line in FIG. 4 (a) input to the integrator 51 is remarkably high is integrated by a time constant longer than the period td. The signal level indicated by the broken line in (a) is subtracted from the image signal level by the subtractor 62, and the averaged signal level having a portion where the signal level of the image signal is extremely high as shown in FIG. 4 (b). And is applied to one input terminal of the comparator 54. The reference potential Vref of the reference power supply 63 is applied to the other input terminal of the comparator 54. The output signal of the comparator 54 is normally "L" as shown in FIG.
The signal level applied from 62 is the reference potential Vref of the reference power source 63.
It becomes "H" only during the period when it exceeds. Switch 55 is a comparator
When the output signal of 54 is "L", it is on, and when it is "H", it is off.

Therefore, in the period td when the signal level of the image signal is significantly high, the image signal is not added to the photometric integrator 56 and is excluded from the photometric target.

Therefore, also in this embodiment, the same effect as that of the first embodiment can be obtained by appropriately selecting the specific number of integrators and the reference potential Vref of the reference power source.

FIG. 5 and FIG. 6 relate to the third embodiment of the present invention.
The figure shows the configuration of the photometric circuit, and FIG. 6 is an explanatory diagram showing the operation of the photometric circuit.

The photometric circuit 70 shown in FIG. 5 has the same photometric circuit configuration as that of the first embodiment.
A subtractor 62 for subtracting the output signal of 51, a reference power supply 63, a clip circuit 74 for extracting the output signal of the subtractor 62 above the potential of the reference power supply 63, and an output signal of the clip circuit 74 from an image signal. It is composed of a subtractor 77 for subtracting and a photometric integrator 56 for integrating the output signal of the subtractor 77.

In FIG. 5, the image signal is applied from the input end of the photometric circuit 70 to the input ends of the integrator 51, the subtractor 62 and the subtractor 77.

An image signal having a period td in which the signal level of the image signal shown by the solid line in FIG. 4 (a) input to the integrator 51 is remarkably high is integrated by a time constant longer than the period td. The signal level indicated by the broken line in a) becomes the subtractor
At 62, it is subtracted from the image signal level, and as shown in FIG. 6 (a), it becomes an averaged signal level having a portion where the signal level of the image signal is extremely high, and it is added to the clipping circuit 74, and FIG. Clip potential of the reference power source 63 as shown in (b)
The potential portion above Vref becomes the extracted analog signal, which is subtracted from the image signal level by the subtractor 77 as shown in FIG. 6 (c), and then added to the photometric integrator 56, and then by the photometric integrator 56. It is integrated with a predetermined time constant and output as a control signal for the AGC circuit and aperture control circuit.

In this embodiment, the time constant of the integrator and the reference power source 63
By appropriately selecting the clipping potential Vref of, the image signal level similar to the other periods can be added to the photometric integrator 51 even in the period td when the signal level of the image signal is significantly increased. Continues the integration operation.

7 to 12 relate to a fourth embodiment of the present invention,
FIG. 7 is a block diagram showing a configuration of an electronic endoscope apparatus using an external television camera for an endoscope, FIG. 8 is an explanatory view of an endoscope display screen, and FIG. 9 is a case of FIG. FIG. 10 is a waveform diagram showing an image signal, FIG. 10 is a block diagram showing the configuration of the electronic endoscope apparatus, FIG. 11 is an explanatory diagram showing control of the photometric circuit, and FIG. 12 is a configuration diagram of the photometric circuit.

An electronic endoscope apparatus using an external television camera for an endoscope (hereinafter referred to as a TV camera) is, as shown in FIG.
An endoscope 11 using an image guide described later, a TV camera 12 detachably connected to the endoscope 11, and the endoscope
11 and the main body unit 13 to which the TV camera 12 is connected.

The endoscope 11 is composed of, for example, an elongated insertion portion that can be inserted into a body cavity, and a large-diameter operation portion that is connected to the rear end of the insertion portion. A ride guide 14 that transmits illumination light is inserted into the insertion portion of the endoscope 11, and the illumination light supplied from the main body unit 13 to the incident end is transmitted to the emission end, and the body cavity portion is transmitted from the emission end. It is designed to irradiate toward 5. The body cavity part 5 illuminated by this illumination light is imaged by the objective lens 15 on the incident end of the image guide 16, is guided through the image guide 16, and the eyepiece of the eyepiece provided at the rear end of the operation part. It is designed to be observed by the naked eye with the eyepiece lens 17. The above-mentioned TV / TV camera 12 is detachably connected to this eyepiece.

In this TV camera 12, a lens 18 is provided at a position facing the eyepiece lens 17 of the endoscope 11, and an image pickup device 19 such as a CCD is provided at the rear end of the lens 18. The image of the facing inner portion 5 is formed on the image pickup surface of the image pickup device 19 by the lens 18. Further, a signal line is connected to the image pickup element 19, and the signal line is detachably connected to the main body unit 13.

The main body unit 13 includes a light source unit 20 for illuminating a subject.
And an image signal processing unit 30 for outputting a video signal to the monitor 4. The light source unit 20 includes a lamp 21, a diaphragm 22 that adjusts the amount of illumination light of the lamp 21, and a diaphragm control circuit that generates a control signal for variably controlling the aperture ratio of the diaphragm 22.
23, and a photometric circuit 25 that measures the illuminance of the light incident on the image sensor 19 from the image signal and generates a signal to the aperture control circuit 23.The image signal processing unit 30 sets the image signal to an appropriate level. AGC circuit 31 for amplifying the
The illuminance of the illumination light incident on 9 is measured, and a photometric circuit 34 that generates a signal to the AGC circuit and various signal processing are performed on the monitor 4.
And a signal processing circuit 32 for outputting to.

When the TV camera 12 is connected to the eyepiece of the endoscope 11 and the endoscope 11 is inserted into the body cavity, the image shown in the example of FIG. FIG. 9 is a time-series illustration of the image signal level and the output level of the integrator 51 in the above-described embodiment, paying attention to a certain horizontal scanning line BB 'of the image shown in FIG. As shown in FIG. 8, the image displayed on the monitor 4 has a high brightness, for example, a substantially circular shape having the same shape as the end surface of the image guide 16 with the center of the screen as the center. Therefore, the image signal level sharply increases at the center of the horizontal position as shown by the solid line in FIG. 9, so that the output level of the integrator 51 becomes flat as shown by the broken line in FIG. I will end up. As a result, the image signal is not added to the photometric integrator 56,
The brightness of the central part of the screen rises, resulting in overexposure.

Therefore, in the present embodiment, in order to avoid the above-mentioned state, the regulation means for regulating the operation of the input control means for limiting the input of the photometric circuit is provided.

The control means for controlling this regulating means will be described using the electronic endoscope apparatus shown in FIG.

To the main body unit 80 of the electronic endoscope apparatus, for example, a slender electronic scope 81 that can be inserted into a body cavity or a TV camera 86 that can be connected to the eyepiece of the endoscope 11 is detachably connected. It is supposed to be done. Further, the endoscope 11 can also be detachably connected.

A light guide 6 for transmitting illumination light is inserted into the insertion portion of the electronic scope 81, and the illumination light supplied from the main body unit 80 to the incident end is transmitted to the emission end, and the body cavity portion 5 is transmitted from the emission end. It is designed to illuminate. The light reflected from the part 5 inside the body cavity is condensed by the objective lens 7 and is incident on the image pickup device 8, and is photoelectrically converted into an image signal to reach the main body unit 80. Further, the electronic scope 81 is provided with a discriminating circuit 82 for controlling a photometric circuit described later.

The TV camera 86 is the above-mentioned TV camera 12 provided with a discrimination circuit 87 for controlling a photometry circuit described later.

The main body unit 80 is a light guide for the endoscope 11.
14 or a light source section 20 for supplying illumination light to the light guide 6 of the electronic scope 81, and an image signal processing section 30 for outputting a video signal to the monitor 4. The light source unit 20 is a lamp
21 and a diaphragm 22 for adjusting the amount of illumination light of this lamp 21.
And a diaphragm control circuit 23 for generating a control signal for variably controlling the aperture ratio of the diaphragm 22, and an image sensor 8 of the electronic scope 81 or an image sensor of the TV camera 86 from an image signal.
The illuminance of the light incident on 19 is composed of a photometric circuit 26 for generating a signal to the aperture control circuit 23, and the image signal processing section 30 is an AGC circuit 31 for amplifying the image signal to an appropriate level.
And a photometric circuit 35 that measures the illuminance of illumination light incident on the image pickup device 8 of the electronic scope 81 or the image pickup device 19 of the TV camera 86 from the image signal, and generates a signal to the AGC circuit,
A signal processing circuit 32 for performing various kinds of signal processing and outputting to the monitor 4. In addition, the photometric circuit 26,35
A discriminating circuit 82 provided in the electronic scope 81 or a discriminating circuit 87 provided in the TV camera 86 is connected to this.

The main body unit 80 is provided with terminals 83 and 84 between it and the electronic scope 81 or the TV camera 86, for example, as shown in FIGS. The terminal 83 is connected to the photometric circuits 26 and 35, and the terminal 84 is connected to a power source.

In the discrimination circuit 82, as shown in FIG. 11A, for example, the terminals 83 and 84 are electrically connected to each other in the electronic scope 81.

For example, as shown in FIG. 11B, the discrimination circuit 87 is in an open state in which the terminals 83 and 84 are not connected in the TV camera 86.

The specifics of the photometric circuits 26 and 35 are, for example, a photometric circuit 90 shown in FIG. The same operation as that of the above-described embodiment is designated by the same reference numeral and its description is omitted.

The photometric circuit 90 includes an integrator 51, an adder 52, a bias power source 53, a comparator 54, a switch 55, and this switch.
A switch 91 for restricting the control of 55 by the comparator 54, a photometric integrator 56, and a pull-down resistor 97 described later.

A control end for turning on / off the switch 91 is connected to the above-mentioned terminal 83 and is grounded via the resistor 97.

In the switch 91, power is supplied to the terminal 83 and the resistance 97
Current flows through the resistor 97, a voltage is generated in this resistor 97, and the control end is "H".
Is turned on. That is, as described above, by connecting the electronic scope 81 to the main body unit 80, the photometric circuit 90 performs the same operation as in the first embodiment.

Further, the switch 91 is off when power is not supplied to the terminal 83 and the control end is “L”. That is, as described above, when the TV camera 86 is connected to the main body unit 80, the output signal of the comparator 54 is not applied to the switch 56, the switch 55 is always on, and the photometric integrator 56 continuously integrates. Take action.

That is, in this embodiment, the effect when the low-luminance portion of the screen needs to be observed is the same as that of the first to third embodiments, and when the high-luminance portion of the screen needs to be observed. Also in this case, there is an effect that an appropriate photometric operation can be performed, and observation of the low brightness portion or the high brightness portion can be easily switched.

FIG. 13 is a block diagram of a photometric circuit according to the fifth embodiment of the present invention. It should be noted that the same reference numerals are used for the same functions as those in the above-described embodiment, and the description thereof will be omitted.

The photometric circuit 100 of this embodiment includes an integrator 51 and an adder 52.
A bias power source 53, a comparator 54, a switch 55, a switch 91, a photometric integrator 56, a resistor 97, and an AND circuit 103 for controlling the switch 91.

The first input end of the AND circuit 103 of the photometric circuit 100 is connected to the terminal 83 and is also grounded via the resistor 97. The second input terminal of the AND circuit 103 has a peak metering / average metering discriminating circuit (hereinafter referred to as peak
An output terminal of an average determination circuit 102) is connected.

A momentary switch (hereinafter referred to as a switch) 101 provided on, for example, an exterior surface of the main body unit 80 is connected to an input end of the peak / average determining circuit 102. When the switch 101 is pressed, the output signal at the output end is alternately changed to "L" and "H" in the peak / average determining circuit 102, which is "L" for peak metering and "L" for average metering. H ". Whether or not the photometry is performed with the peak value or the average value is displayed by, for example, a display unit provided in the main body unit 80 (not shown).

A control terminal for turning on / off the switch 91 is grounded to an output terminal of the AND circuit 103.

The output terminal of the AND circuit 103 is supplied with power to the terminal 83 connected to the first input terminal, a current flows through the resistor 97, a voltage is generated in the resistor 97, and the first input terminal becomes “H”. , And a peak / average discrimination circuit 102 connected to the second input terminal
It becomes "H" when the output signal of becomes "H". Therefore, the switch 91 is turned on when the output terminal of the AND circuit 103 connected to the control terminal becomes “H”. That is, as described above, the electronic scope 81 is connected to the main body unit 80, and the average photometry is selected, so that the photometry circuit 90 performs the same operation as in the first embodiment.

The output terminal of the AND circuit 103 is not supplied with power to the terminal 83 connected to the first input terminal, and the first input terminal is “L” or the peak terminal connected to the second input terminal. When the output signal of the average determination circuit 102 is "L", it becomes "L". Therefore, the switch 91 is off because the output end of the AND circuit 103 connected to the control end is “L”.
That is, as described above, when the TV camera 86 is connected to the main unit 80 or the peak metering is selected, the comparator 54
Is not applied to the switch 56, the switch 55 is always turned on, and the photometric integrator 56 continuously performs the integrating operation.

In the present embodiment, the peak / average discrimination circuit 102
May be provided in the photometric circuit 100.

The output terminal of the peak / average determination circuit 102 may be directly connected to the control terminal of the switch 91 so that peak metering and average metering can be switched even when the TV camera 86 is connected.

That is, in the present embodiment, even in the main body unit 80 to which the electronic scope is connected, when it is necessary to observe the high-luminance portion of the screen, it is possible to easily switch the observation of the low-luminance portion or the high-luminance portion. There is.

When the present invention is used in a photometric circuit of an electronic endoscope apparatus to which an electronic scope is connected, the period td during which the image signal level of the treatment tool is significantly high is 1 to 1 in the NTSC television system.
2 μs, and a good effect was obtained when the time constant of the integrator 51 was set to about 160 μs.

In order to obtain the same effect as that of the above-described embodiment regardless of the size of the subject having high brightness, the integrator 51 of this photometric circuit is used.
Means for varying the time constant of may be provided.

Further, the switch 91 and the configuration related to the switch 91 described in the fourth or fifth embodiment are used for controlling the switch 55 in the second embodiment, and the clipping circuit of the subtractor 77 in the third embodiment. It may be used to control the input end connected to 74.

Furthermore, although the above-described embodiment has been described using the electronic endoscope apparatus, it may be applied to other video camera apparatuses.

[Effects of the Invention] As described above, according to the present invention, it is possible to easily remove the influence of a subject having a higher brightness than the average brightness of the shooting screen on the entire shooting screen, and obtain a shooting screen suitable for the situation. The effect is that you can.

[Brief description of drawings]

1 and 2 relate to the first embodiment of the present invention. FIG. 1 is a block diagram of a photometric circuit, FIG. 2 is an explanatory diagram showing the operation of the photometric circuit, and FIGS. According to a second embodiment of the invention,
FIG. 3 is a block diagram of the photometric circuit, FIG. 4 is an explanatory diagram showing the operation of the photometric circuit, FIGS. 5 and 6 relate to the third embodiment of the present invention, and FIG. 5 is a block diagram of the photometric circuit. , FIG. 6 is an explanatory diagram showing the operation of the photometric circuit, and FIGS. 7 to 12 are the fourth diagram of the present invention.
FIG. 7 is a block diagram showing a configuration of an electronic endoscope apparatus using an external television camera for an endoscope according to an embodiment, and FIG.
FIG. 9 is an explanatory view of an endoscope display screen, FIG. 9 is a waveform diagram showing an image signal in the case of FIG. 8, FIG. 10 is a block diagram showing a configuration of an electronic endoscope apparatus, and FIG. 11 is a photometric circuit. 12 is a block diagram showing the configuration of a photometric circuit according to the fifth embodiment of the present invention, FIG. 14 is a block diagram showing a conventional example, FIG. [FIG. 16] is an explanatory view showing the appearance of the treatment tool on the endoscope display screen, and FIG. 16 is a waveform diagram showing an image signal in the case of FIG. 50 …… photometering circuit, 51 …… integrator 53 …… bias power supply, 54 …… comparator 55 …… switch, 56 …… photometering integrator

Claims (1)

(57) [Claims] 1. A photometric integrating means for outputting a photometric signal proportional to the light quantity of an illumination light source by integrating the input image signal over the entire screen, and the input image signal responding to variations within its horizontal period. An input image signal analyzing means for integrating with a time constant to output an input image integrated signal; a signal level detecting means for detecting a signal output period in the input image signal equal to or higher than a signal level of the input image integrated signal; A photometric circuit comprising: control means for controlling the signal level of the photometric signal output from the photometric integration means in accordance with the output signal of the means.