JPH0514805A - Image pickup device - Google Patents

Abstract

PURPOSE:To offer an image pickup device which obtains a stable sensitivity state always irrespective of the illumination level of an object, and does not impair the stability of a picture. CONSTITUTION:The image pickup device is provided with a quantity of light detection circuit 12 to detect the intensity of illumination of the object at the time of image pickup and output a quantity of light signal L4, a sensitivity increase circuit 7 to input a video signal L1 and increase the sensitivity by using a prescribed adjusting quantity, and a sensitivity increase signal generation circuit 13 to activate the circuit 7 when the intensity of illumination is detected to be within a first illumination range on the basis of the signal L4, and it is constituted so as to shift and adjust the maximum gain of an AGC circuit 8 so that the adjusting quantity of the activated circuit 7 is reduced when the intensity of illumination transits to a second illumination range. The first illumination range is the illumination range in which the increase of the sensitivity is required, and the second illumination range is the illumination range in which picture quality is deteriorated on the contrary if the sensitivity is increased by the circuit 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device, and more particularly to an image pickup device having a function of adjusting sensitivity.

[0002]

2. Description of the Related Art An image pickup device has its own sensitivity at the time of image pickup, and this sensitivity is expressed by the minimum light input level required to secure a predetermined SN ratio for a video signal obtained by image pickup. ..

FIG. 4 is a schematic diagram showing the structure of an image pickup section of a conventional camera-integrated video tape recorder having a sensitivity adjusting function.

In the figure, an image pickup section of a video tape recorder with a built-in camera (hereinafter referred to as a VTR) makes reflected light from a subject incident and collects it, and forms an optical image of the subject on a predetermined image forming plane. As described above, an optical system 1 including a plurality of optical lenses, a diaphragm 2 for limiting the amount of incident light that has passed through the optical system 1, and a diaphragm 2 arranged on the image plane formed by the optical system 1 are converted into an image by photoelectric conversion. An image sensor 3 for deriving as a signal, a sampling circuit 4 for inputting an electrical signal output from the image sensor 3, sampling at a predetermined sampling period, and deriving while removing a noise component contained therein, It includes a clamp circuit 5 for receiving the output of the sampling circuit 4 and reproducing the DC component accordingly. Further, the image pickup unit includes an AGC (abbreviation of automatic gain control) circuit 8, a video signal processing circuit 9, a detection circuit 10, a mixing circuit 11, a light amount detection circuit 12, a sensitivity up signal generation circuit 13, and a sensitivity up switch SW1.

A diaphragm control circuit 6 is provided in association with the diaphragm 2 and receives the video signal L1 output from the clamp circuit 5,
The aperture ratio of the diaphragm 2 is adjusted according to the signal level.

The sensitivity increasing circuit 7 includes a video signal L1 output from the clamp circuit 5 and a sensitivity increasing signal generating circuit 13.
A sensitivity increase signal L6 (details will be described later) output by the input device is input, the amplitude of the video signal L1 given in response to the input level of the signal L6 is increased to perform sensitivity increase processing, and a video signal L2 is derived.

The light amount detection circuit 12 receives the video signal L1 output from the clamp circuit 5, detects the illuminance level of the object at the time of image pickup from the signal level, and outputs the high level or low level light amount detection signal L4. Derive.

The sensitivity up signal generation circuit 13 receives the switch signal L5 given by externally operating the sensitivity up switch SW1 connected to the preceding stage and the light amount detection signal L4 output from the light amount detection circuit 12, and detects the light amount. Only when the signal L4 is input at a high level, the applied switch signal L5 is derived to the output side and is output as the sensitivity up signal L6.

The AGC circuit 8 receives the applied video signal L2.
And adjust the gain accordingly to keep the optimum amplitude.
It is configured to derive the video signal L3. In detail,
The AGC amplification circuit 8a, the AGC amplification control circuit 8b, the maximum gain control circuit 8c, the gain error detection circuit 8d, and the reference voltage generation circuit 8e are included.

The AGC amplifier circuit 8a amplifies the video signal L2 applied in parallel based on the signal level of the DC voltage signal applied from the AGC amplification control circuit 8b, and derives a gain-adjusted video signal L3. Gain error detection circuit 8
The video signal L3 output from the AGC amplifier circuit 8a is input and detected by d, and the reference voltage generation circuit 8e of this detection level is detected.
The error with respect to the signal level of the reference voltage signal given from is detected, is derived to the output side, and is given to the AGC amplification control circuit 8b. The maximum gain control circuit 8c controls the output of the AGC amplification control circuit 8b so that the gain adjustment amount in the AGC amplification circuit 8a does not exceed a predetermined maximum adjustment amount.
The maximum gain adjustment amount determined by the maximum gain control circuit 8c is uniquely determined by the voltage division level of the resistors R2 and R3.

The video signal processing circuit 9 is configured to receive the video signal L3, separate it into a luminance signal Y and a chroma signal C, and derive them. In detail, the front stage luminance system signal processing circuit 9a, the contour correction circuit 9b, and the contour correction amount control circuit 9
c, post-luminance signal processing circuit 9d, color signal processing circuit 9
e, a color system gain control circuit 9f, and a low luminance suppression signal generation circuit 9g.

The preceding stage luminance system signal processing circuit 9a inputs the supplied video signal L3 and performs signal processing on the luminance system signal such as carrier removal, gamma correction and knee correction in accordance therewith. The contour correction circuit 9b corrects the video signal given from the preceding stage luminance system signal processing circuit 9a connected to the preceding stage so as to emphasize the contour of the image based on the correction amount given from the contour correction amount control circuit 9c. Derive.

The post-luminance signal processing circuit 9d receives the two video signals output from the pre-luminance signal processing circuit 9a and the contour correction circuit 9b, and accordingly, white clip processing, pedestal correction processing, and synchronization with the input video signal. A luminance signal Y is derived by performing signal addition processing or the like.

The color system signal processing circuit 9e inputs the supplied video signal L3, extracts a color signal, performs gamma correction, white balance processing, matrix processing, color difference signal generation processing, etc., and generates a color difference signal. It is derived by performing carrier balance, encoding processing, burst addition processing, and the like.

The color system gain control circuit 9f adjusts the gain of the color signal supplied from the color system signal processing circuit 9e based on a low brightness suppression signal (details will be described later) L7 supplied from the low brightness suppression signal generation circuit 9g. Then, the chroma signal C is derived.

The low luminance suppression signal generation circuit 9g has a DC voltage signal E supplied from the detection circuit 10 connected to the preceding stage.
(Details will be described later) are input, and the low luminance suppression signal L7 corresponding to the input signal level is derived accordingly. Detection circuit 1
Reference numeral 0 includes a resistor R1 and a capacitor C1, and detects (integrates) the supplied video signal L3 to generate a DC voltage signal E.
Derive.

The mixing circuit 11 receives the luminance signal Y and the chroma signal C, mixes both signals in accordance with the luminance signal Y, and derives a composite video signal YC.

Next, the operation of the VTR image pickup section shown in FIG. 4 during image pickup will be described.

The incident light from the subject is imaged by the optical system 1 on a predetermined image plane. At this time, the angle of view and the amount of light of the incident light are controlled by the optical system 1 and the diaphragm 2 to be optimum. The image sensor 3 photoelectrically converts the subject image formed on the light receiving surface according to the light receiving level, and derives it as an electric signal. The sampling circuit 4 is
The sampling operation is performed so as to remove the noise component of the electric signal output by the image sensor 3. Sampling circuit 4
The signal output from the signal is reproduced by the clamp circuit 5 at the next stage, and the direct-current component is reproduced, and is further led to the aperture control circuit 6 and the sensitivity increasing circuit 7 as the video signal L1. Furthermore, the signal output from the sensitivity increasing circuit 7 is the AGC of the next stage.
The video signal L2 is supplied to the circuit 8.

The sensitivity increasing circuit 7 operates the AGC circuit 8 only when the sensitivity increasing signal L6 described later is at a high level.
The gain-up operation is performed so as to increase the signal level of the video signal L2 given to. Further, the aperture control circuit 6 is
The aperture ratio of the diaphragm 2 is feedback-controlled so that the signal level of the video signal L1 output from the clamp circuit 5 maintains a predetermined level.

The AGC circuit 8 receives the supplied video signal L2.
The automatic gain control is performed to keep the amplitude of the optimum. AG
The C amplifier circuit 8a is supplied with the video signal L in response to the DC voltage level supplied from the AGC amplification control circuit 8b.
2 is amplified and derived as a video signal L3. Video signal L3
Is supplied to the video signal processing circuit 9 in the next stage. The video signal L3 is also given to the gain error detection circuit 8d. The gain error detection circuit 8d compares the DC voltage level obtained by smoothing and detecting the video signal L3 with the level of the reference voltage provided from the reference voltage generation circuit 8e, and amplifies the comparison result to obtain a DC voltage. It is given to the AGC amplification control circuit 8b. The AGC amplification control circuit 8b increases the amplification rate of the video signal L3 when the amplitude of the video signal L3 decreases, and when the amplitude of the video signal L3 increases, the amplification rate of the AGC amplification control circuit 8b increases. Control to be reduced.
In addition, the AGC amplification control circuit 8b includes a gain error detection circuit 8
While the level of the DC voltage given from d maintains the predetermined range, that is, while the signal level of the gain-adjusted video signal L3 output from the AGC amplifier circuit 8a maintains the predetermined range, the amplification operation of the AGC amplification circuit 8a is performed. Control to make it continuous. This continuous amplification operation is performed by the maximum gain control circuit 8
The AGC amplification control circuit 8 is limited so that the amplification factor of the AGC amplification circuit 8a does not exceed a certain maximum value.
Control the operation of b. This is because, if the amplification factor of the AGC amplifier circuit 8a is increased without limit, the SN ratio of the video signal L3 output by adjusting the gain of the AGC amplifier circuit 8a deteriorates,
This is because there is a risk of reaching a video signal level that is practically unbearable. The maximum value of the amplification factor of the AGC amplifier circuit 8a is uniquely determined by applying the bias voltage determined by the resistors R2 and R3 to the maximum gain control circuit 8c.

The video signal L3 output from the AGC circuit 8 is
Further, it is given to the preceding luminance system signal processing circuit 9a, and also given to the color system signal processing circuit 9e and the detection circuit 10. The pre-stage brightness system signal processing circuit 9a performs processing such as carrier removal, gamma correction, and knee correction on the video signal L3, and then supplies it to the contour correction circuit 9b and the post-stage brightness system signal processing circuit 9d. The video signal output from the preceding luminance system signal processing circuit 9a is subjected to the contour correction by the contour correction circuit 9b using the DC voltage signal provided from the contour correction amount control circuit 9c, and then is output to the subsequent luminance system signal processing circuit 9d. Given. The post-luminance signal processing circuit 9d converts the output signal from the pre-luminance signal processing circuit 9a into the contour correction circuit 9
The contour-corrected signal given from b is used for contour correction, and after signal processing such as white clipping, pedestal correction, and synchronization signal addition, it is derived as a luminance signal Y and given to the mixing circuit 11.

The video signal L3 output by the AGC circuit 8 is
In addition, the color system signal processing circuit 9e performs color separation processing, gamma correction, white balance, matrix, and color difference signal generation processing.
After being subjected to encoding processing, burst addition, etc., they are given to the color system gain control circuit 9f.

The color system gain control circuit 9f controls the gain of the applied video signal using the low brightness suppression signal L7 supplied from the low brightness suppression signal generation circuit 9g, and outputs it as the chroma signal C to the mixing circuit 11. To do.

The detection circuit 10 receives the supplied video signal L3.
Is subjected to smoothing detection and is applied to the low luminance suppression signal generation circuit 9g as a DC voltage signal E. The low luminance suppression signal generation circuit 9g
The DC voltage signal E is input, the low luminance suppression signal L7 is derived in accordance with the DC voltage signal E, and the low luminance suppression signal L7 is simultaneously given to the contour correction control circuit 9c and the color system gain control circuit 9f. The mixing circuit 11 inputs the given luminance signal Y and chroma signal C and performs mixing processing accordingly to derive a composite video signal YC. Composite video signal YC
Is applied to a recording processing circuit or the like in the subsequent stage (not shown) or the like to be sequentially recorded on the recording medium.

The low luminance suppression signal L7 is the composite video signal YC obtained when the illuminance of the subject at the time of image pickup is low.
It acts so as to prevent the S / N ratio of 1 from deteriorating. That is, in general, when the subject is in low illuminance, S of the video signal is
It is known that the N ratio deteriorates. For example, when the illuminance is low, the signal level of the DC voltage signal E output from the detection circuit 10 becomes low, so that the low-luminance suppression signal L7 lowers the contour correction amount of the contour correction circuit 9b via the contour correction amount control circuit 9c. , The noise component of the luminance signal system is reduced. In parallel with this, the color system gain control circuit 9f is also supplied with the low luminance suppression signal L7 at the time of low illuminance, so that the gain adjustment amount is reduced and the derived chroma signal C is obtained.
The noise component contained in is also reduced. Therefore, it is possible to prevent the SN ratio of the video signal from deteriorating when the illuminance is low.

FIG. 5 is a characteristic diagram of the video signal L1 with respect to the illuminance of the subject at the time of image pickup. In FIG. 5, the horizontal axis represents the magnitude of the illuminance e, and the vertical axis represents the signal level of the video signal L1.

Next, the output operation of the sensitivity up signal generation circuit 13 shown in FIG. 4 for the sensitivity up signal L6 during image pickup will be described with reference to FIGS.

In FIG. 5, during the high illuminance period when the illuminance e is (e ≧ e8), the aperture control can control the aperture 2 by the aperture circuit 6 of FIG. 4 to keep the signal level of the video signal L1 constant. Area. However, the illuminance e is (e
In the low illuminance period within the range of <e8), the diaphragm 2 has already been set to a sufficiently open state by the control of the diaphragm control circuit 6 in order to obtain a sufficient light amount, and thus the video signal L1 is , Is derived at a low level proportional to the illuminance e of the subject. In this way, the diaphragm 2 is fully open,
Further, in a range of the illuminance e that requires further increase in sensitivity, particularly in the case of (e <e2), the light amount detection circuit 12 sets the level of the light amount detection signal L4 to high, and conversely, the subject illuminance e becomes (e> During the period of e2), the light amount detection signal L4 operates so as to be level low. That is, in the light amount detection signal L4, the illuminance e of the subject at the time of imaging is (e <e
When it is within the range of 2), the level high is maintained, and (e>
When it is within the range of e2), it is derived while maintaining the level low. The sensitivity up switch SW1 is an on / off switch that is externally operated according to the user's desire, and derives a switch signal L5 that causes the level to be high when the sensitivity is turned on and the level to be low when the sensitivity is turned off. Therefore, the sensitivity up signal generation circuit 13 inputs the switch signal L5 obtained by the external operation of the sensitivity up switch SW1 together with the above-described light amount detection signal L4, and the light amount detection signal L4 has a high level, that is, the illuminance e of the subject is ( e
Only in the case of <e2), the switch signal L5 is derived to the output side and is supplied to the sensitivity increasing circuit 7 as the sensitivity increasing signal L6 to activate the sensitivity increasing operation.

As described above, the sensitivity increasing circuit 7 operates based on the sensitivity increasing signal L6 when the light amount detection signal L4 is detected.
Is a period during which the sensitivity up switch SW1 is externally operated and the switch signal L5 is set at a high level. The sensitivity increasing signal L6 for activating the sensitivity increasing circuit 7 is once set to the level high, and thereafter the light amount detection signal L4 is changed to the level low (that is, the illuminance increases and (e> e in FIG. 5).
Even in the state of (2) transition to the illuminance range), the signal level (level high) is output so as to be maintained. This is because if the subject illuminance e changes every moment as the imaging conditions change, and the unstable operation is performed such that the sensitivity up circuit 7 is frequently activated or disabled, This is to prevent the video signal obtained by the VTR from becoming unstable due to the time constant of the AGC circuit 8 connected to the next stage and causing the display screen to become unnatural and difficult to see.

FIG. 6 is a diagram showing an example of the characteristics of the video signal L2 with respect to the illuminance of the subject at the time of image pickup. The vertical axis represents the signal level of the video signal L2, and the horizontal axis represents the illuminance e. In FIG. 6, the solid line is the characteristic curve of the video signal L2 obtained in the increased sensitivity state, and the alternate long and short dash line is the characteristic curve of the image signal L2 obtained in the non-sensitized state.

FIG. 7 is a diagram showing an example of characteristics of the AGC circuit 8 shown in FIG. 4, in which the vertical axis represents the signal level of the video signal L3 and the horizontal axis represents the signal level of the video signal L2. Is taken. The slope of the straight line AB in FIG. 7 is uniquely determined by the bias resistors R2 and R3 in FIG.

FIG. 8 is a diagram showing an example of the characteristic of the video signal L3 with respect to the illuminance of the subject at the time of conventional image pickup, in which the vertical axis represents the signal level of the video signal L3 and the horizontal axis represents the illuminance e. Be done. In FIG. 8, the dotted line is the characteristic curve of the video signal L3 obtained without increasing the sensitivity, and the solid line is the characteristic curve of the video signal L3 obtained with the increased sensitivity. The characteristic curves in FIG. 8 are all shown in FIG. 6 and FIG.
The characteristic of the video signal L3 with respect to the illuminance e of the subject is obtained from the characteristic curve shown in FIG.

By the way, when the illuminance of the subject at the time of image pickup is low, deterioration of the SN ratio of the obtained video signal is prevented by the action of the low luminance suppression signal L7 as described above. However, the prevention of the SN ratio deterioration by this method is inadequate when the sensitivity increasing circuit 7 is activated and is in the sensitivity increasing state, and therefore the deterioration of the SN ratio cannot be avoided. That is, the video signal L input to the sensitivity up circuit 7
1 always includes a noise component including a random high-frequency signal having no correlation with the amount of incident light at a constant level (this noise component is mainly generated due to the circuit characteristics of the image sensor 3). On the other hand, the video signal L1 is a signal depending on the light reception level of the image sensor 3. Therefore, when the illuminance e of the subject is decreasing, the signal level of the video signal L1 also decreases as the illuminance decreases. SN of video signal L1
The ratio has deteriorated. Therefore, when the video signal L1 whose SN ratio is deteriorated is input to the sensitivity increasing circuit 7 and the sensitivity is increased accordingly, further deterioration of the SN ratio is expected, and therefore the SN using the low luminance suppression signal L7 described above is expected. There was a problem that the ratio recovery ability was insufficient.

[0035]

As described above, conventionally, when the illuminance of the subject at the time of image pickup is low, the sensitivity increasing circuit 7 is activated to increase the sensitivity. Illuminance e that is especially desired to increase sensitivity
Is a low illuminance range of (e <e2) as described in FIG. 5, and in the illuminance range of (e2 <e <e8), sensitivity is intentionally increased until the SN ratio of the obtained video signal is deteriorated. The illuminance level does not need to be set. The sensitivity up circuit 7
As described above, since the sensitivity increasing operation is switched ON / OFF in response to the sensitivity increasing signal L6, the sensitivity increasing signal L6 that is at the high level in the illuminance range of (e2 <e <e8) described above. Is forcibly set to level low, the sensitivity increasing operation in the sensitivity increasing circuit 7 is stopped, and the SN ratio of the video signal is sufficiently restored by the low luminance suppression signal L7. By doing so, it is possible to control the sensitivity increasing circuit 7 so as not to operate in the illuminance region where it is not necessary to increase the sensitivity even if the SN ratio of the video signal is deteriorated. However, when there is a sudden change in the light amount, the level of the video signal L2 also changes abruptly, and the time constant of the AGC circuit 8 acts to cause the video signal to fluctuate unstablely, resulting in an unnatural display screen. Therefore, the above measures cannot be a fundamental solution. Therefore, once the sensitivity increase circuit 7 is activated within the illuminance range where the subject illuminance is (e <e2), (e2 ≦
In the case of e), the sensitivity increasing circuit 7 cannot be automatically disabled to stop the sensitivity increasing operation. Therefore, when the illuminance e is in the range of (e2 <e <e8), there is a problem that the image signal becomes unnecessarily increased in sensitivity, the image quality becomes unstable, and the display screen is very difficult to see.

Therefore, it is an object of the present invention to prevent the stability of the screen obtained by increasing the sensitivity from being impaired in the illuminance range of an object in which the sensitivity is not required to be improved, and always provide a high quality screen. It is to provide an imaging device that does.

[0037]

An image pickup apparatus according to the present invention is an image pickup apparatus which adjusts the sensitivity of image pickup in accordance with the illuminance of an object at the time of image pickup, and more specifically, a detection for detecting the illuminance of the object at the time of image pickup. Means, sensitivity adjustment means for inputting a video signal obtained by image pickup, increasing the gain according to a predetermined adjustment amount, and increasing the sensitivity of the image pickup device, and detecting the illuminance of the subject by the detection means. In response to the detection of being within the first illuminance range, the activating means for activating the sensitivity adjusting means and the detecting means have detected that the illuminance of the subject is within the second illuminance range. In response to this, the adjustment amount reducing means for reducing the adjustment amount is provided, the first range is an illuminance range in which an increase in sensitivity is required, and the second range is the sensitivity adjustment means. Image quality deteriorates due to rising Configured to be that illuminance range.

[0038]

The image pickup apparatus according to the present invention is configured as described above, and the activating means activates the sensitivity adjusting means in response to the illuminance of the subject reaching the first illuminance range during image pickup. , Increase the sensitivity. After that, when the illuminance of the subject is within the second illuminance range, the adjustment amount reducing means acts to reduce the adjustment amount by the sensitivity adjusting means. Therefore, since the sensitivity is increased as described above, if the second illuminance range that deteriorates the image quality is rather brought about, the sensitivity adjusting means is still in the activated state, but the sensitivity is increased. Since the adjustment amount for is reduced, the obtained image signal is not subjected to sensitivity increase processing to an unnecessary level, and the image quality can be maintained in a good state.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic view showing the arrangement of an image pickup section of a camera-integrated video tape recorder having a sensitivity adjusting function according to an embodiment of the present invention.

The image pickup unit according to one embodiment of the present invention shown in FIG. 1 is compared with the conventional image pickup unit shown in FIG. 4 described above. The difference in structure is that the image pickup unit shown in FIG.
New transistors Q1 and Q2, resistors R4 and R
5 and the capacitor C2. The other circuits and their functions except these are similar to those shown in FIG. 4 of the related art, and detailed description thereof will be omitted.

The transistors Q1 and Q2 are digital transistors. The light amount detection signal L4 is input to the base side of the transistor Q1, the collector side thereof is connected to the base side of the transistor Q2, and the sensitivity is increased via the resistor R4. It is connected to the signal L6. When the transistor Q2 is in the off state, the maximum gain control circuit 8c has a maximum gain adjustment amount determined by the voltage division ratio of the resistors R2 and R3. On the contrary, when the transistor Q2 is in the ON state, the maximum gain adjustment amount of the maximum gain control circuit 8c is reduced by the voltage division ratio of the resistors R2, R3 and R5. When the sensitivity up signal generation circuit 13 outputs the sensitivity up signal L6 at a high level based on the light amount detection signal L4 and the switch signal L5, the imaging condition changes and the illuminance increases, and the illuminance e of the subject becomes (e2 When the illuminance level of <e) is reached, the light amount detection circuit 12 accordingly changes the light amount detection signal L4 to level low and derives it, and accordingly the digital transistor Q1 is turned off. At this time, since the collector side of the transistor Q1 is connected to the sensitivity up signal L6 by the resistor R4, the level becomes high. Since the signal on the collector side of the transistor Q1 is connected to the base side of the digital transistor Q2, the transistor Q2 is accordingly turned on, which causes the maximum gain control circuit 8c to change its voltage division ratio of the resistors R2, R3 and R5. The bias is shifted so that the maximum gain adjustment amount of the AGC circuit 8 is reduced.

FIG. 2 is a schematic diagram showing characteristics of the AGC circuit 8 according to one embodiment of the present invention. FIG. 3 is a diagram showing an example of the characteristic of the video signal L3 with respect to the illuminance of the subject at the time of image pickup according to the embodiment of the present invention.

In FIG. 2, the vertical axis represents the signal level of the video signal L3, and the horizontal axis represents the signal level of the video signal L2. In FIG. 2, the solid line is a characteristic curve obtained when the maximum gain of the AGC circuit 8 is the same as the conventional one (the transistor Q2 is in the off state), and is the same as that shown in FIG. Further, in FIG. 2, the chain double-dashed line is a characteristic curve obtained when the maximum gain of the AGC circuit 8 is lowered by the voltage division ratio of the resistors R2, R3 and R5 (transistor Q2 is in the ON state) according to this embodiment. .. As can be seen from FIG.
When the maximum gain of the GC circuit 8 is lowered, the gain adjustment of the AGC circuit 8 acts gently with respect to the increase of the signal level of the video signal L2, and the signal level of the video signal L3 derived from the AGC circuit 8 is lowered. It can be seen that does not rise extremely as shown by the solid line in the figure, but rises with a gentle slope. The characteristic curve shown by the chain double-dashed line in FIG. 2 and the characteristic curve shown by the solid line in FIG.
Based on the characteristic curve of the video signal L2 in the C circuit 8), the characteristic of the video signal L3 output from the AGC circuit 8 shown in FIG. 1 is as shown in FIG.

The capacitor C2 shown in FIG. 1 has a maximum gain control circuit 8 when the transistor Q2 is turned on.
The characteristic curve of the video signal L3 is C− as shown by the solid line in FIG. 3 because it acts so as to have a time constant that moderates the operation of shifting the bias in c.
The characteristic curve is indicated by D-E-F. If the capacitor C2 is not connected, the video signal L3 becomes the characteristic curve of C-D-G-E-F shown in FIG. 3, and the signal level of the video signal L3 suddenly changes at the illuminance e2 of the subject,
That is, it can be seen that the maximum gain in the AGC circuit 8 suddenly changes. This sudden change in the maximum gain causes deterioration of image quality, so it is important to provide the capacitor C2 and shift the bias of the maximum gain control circuit 8c while having a time constant.

As the characteristic curve shown by the solid line in FIG.
The illuminance e of the subject for which sensitivity enhancement is not particularly required is (e
In the range of 2 <e <e8), the sensitivity increase signal L6
As a result, even if the sensitivity up circuit 7 is once activated and set to the sensitivity up state, the maximum gain adjustment amount in the AGC circuit 8 is immediately reduced, so that even if the sensitivity up circuit 7 is in the sensitivity up state. The sensitivity of the imaging unit is reduced. Therefore, regardless of the subject illuminance, it is possible to stably maintain a good image quality.

[0047]

As described above, according to the present invention, the activating means activates the sensitivity adjusting means in response to the illuminance of the object reaching the first illuminance range, and temporarily raises the sensitivity. After that, when the subject illuminance transitions to the second illuminance range,
The adjustment amount reducing means acts to reduce the adjustment amount by the sensitivity adjusting means. Therefore, in the second illuminance range where the image quality is rather deteriorated due to the sensitivity increase, the adjustment amount for sensitivity increase is reduced and the video signal becomes stable accordingly, so that during imaging. In the above, there is an effect that it is possible to maintain stable image quality in which the sensitivity is well adjusted regardless of the illuminance of the subject.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an image pickup unit of a camera-integrated video tape recorder having a sensitivity adjusting function according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing characteristics of an AGC circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of characteristics of a video signal with respect to illuminance of a subject at the time of image capturing according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of an image pickup section of a camera-integrated video tape recorder having a conventional sensitivity adjustment function.

FIG. 5 is a characteristic diagram of a video signal with respect to the illuminance of a subject during image capturing.

FIG. 6 is a diagram showing an example of characteristics of a video signal with respect to illuminance of a subject at the time of image capturing.

7 is a diagram showing an example of characteristics of the AGC circuit shown in FIG.

FIG. 8 is a diagram showing an example of characteristics of a video signal with respect to the illuminance of a subject during conventional imaging.

[Explanation of symbols]

 7 Sensitivity up circuit 8 AGC circuit 12 Light intensity detection circuit 13 Sensitivity up signal generation circuit Q1 and Q2 Transistors R2, R3 and R5 Resistor C2 Capacitors L1, L2 and L3 Video signal L4 Light intensity detection signal L5 Switch signal L6 Sensitivity up signal Each In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

Claim: What is claimed is: 1. An image pickup apparatus for adjusting the sensitivity of image pickup according to the illuminance of an object at the time of image pickup, and a detection means for detecting the illuminance of the object at the time of image pickup, which is obtained by image pickup. When a video signal is input and a gain is increased in accordance with a predetermined adjustment amount to increase the sensitivity of the image pickup apparatus, the detection unit detects the illuminance of the subject within a first illuminance range. Activating means for activating the sensitivity adjusting means in response to being detected, and the adjusting means in response to detecting by the detecting means that the illuminance of the subject is within a second illuminance range. The first range is an illuminance range in which it is necessary to increase the sensitivity, and the second range is image quality because the sensitivity is increased by the sensitivity adjusting unit. It is the illuminance range that deteriorates, Imaging device.