JP3186083B2 - Exposure control device for video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure control device for a video camera.

[0002]

2. Description of the Related Art Conventionally, an exposure control device for a video camera has
As shown in the example in FIG. 4, the lens 1, the iris 3, the CCD image pickup device 5, the AGC amplifier 7, the signal processing circuit 9, the detection circuit 11, the comparator 13, the loop filter 15, and the exposure control reference value (reference level) setting circuit 17 Is configured.

When an object is photographed by the video camera, the image of the object is focused on the CCD image pickup device 5 through the lens 1 and the iris 3, and the image of the object is picked up via the CCD image pickup device 5. The signal is converted into a signal, and this image signal is output from the CCD image sensor 5 as an output signal. The output signal output from the CCD image pickup device 5 is input to the AGC amplifier 7, and the image signal level of the output signal is adjusted via the AGC amplifier 7, and the AGC
Output from the amplifier 7. The output signal output from the AGC amplifier 7 is input to a signal processing circuit 9, and a predetermined signal correction such as a gamma correction is performed via the signal processing circuit 9, and a signal processed by the signal processing circuit 9 is thus corrected. 9 (the signal output from the signal processing circuit 9 is referred to as a video output signal in the following description).

On the other hand, the output signal output from the AGC amplifier 7 is input to the detection circuit 11, and the image signal level of the image signal generated by the CCD image sensor 5 is detected. Output from the detection circuit 11. Then, the imaging signal level output from the detection circuit 11 is input to one input side of the comparator 13.

The other input side of the comparator 13 has an exposure control reference value (reference level) setting circuit 1
The exposure control reference value generated in step 7 is supplied. The comparator 13 compares the image signal level input from the detection circuit 11 with the exposure control reference value to generate a gain control signal. Is output from the comparator 13 and the AGC
It is supplied to the amplifier 7 as a gain control signal.

The output signal from the CCD image pickup device 5
The imaging signal level of the output signal input to the C amplifier 7 is adjusted via the AGC amplifier 7 based on the gain control signal, and output from the AGC amplifier 7.

When the adjustment is performed in this manner, the gain control signal output from the comparator 13 when the image signal level detected by the detection circuit 11 is determined to be smaller than the exposure control reference value (reference level). In this case, the gain control signal is used to control the gain of the AGC amplifier 7 to increase, and the comparator 13 determines that the imaging signal level is greater than the exposure control reference value (reference level) and outputs the signal. When the gain control signal is a gain control signal, the gain control signal is controlled so that the gain of the AGC amplifier 7 is decreased, and the level of the image signal of the output signal output from the comparator 13 is reduced to a predetermined level. AGC to be maintained in
This AGC amplifier 7 is controlled by the amplifier 7.
The signal is input to the signal processing circuit 9 and subjected to predetermined signal correction such as gamma correction via the signal processing circuit 9 as described above, and is output as a video output signal.

[0008]

However, in a conventional video camera exposure control apparatus having the structure shown in FIG.
Even when a scene in which the luminance level of the image incident from the subject gradually decreases, the AGC amplifier 7 remains at the maximum gain until the gain becomes maximum.
If the image signal level of the output signal output from the GC amplifier 7 is kept constant and the luminance level of the optical image incident from the subject on the CCD image sensor 5 is further reduced, the decrease may occur. Therefore, the level of the image signal of the output signal output from the AGC amplifier 7 is not maintained in a constant state and decreases, and the luminance of an image reproduced from the video output signal output from the signal processing circuit 9 changes unnaturally. I do.

The reason that the luminance of the reproduced image changes unnaturally is that in the conventional exposure control device of a video camera, a reference signal which is compared with a signal obtained by detecting an output of an AGC amplifier by a comparator. This is because the value is set to a fixed value and the gain of the AGC amplifier is controlled based on the control signal obtained as a result of the comparison. That is, when the brightness of the subject input to the exposure control device of the video camera is changed in a direction of increasing or decreasing, as described above, the imaging signal level of the output signal output from the AGC amplifier becomes a constant value. This AG to be kept in
It is controlled by a C amplifier. However, if the brightness of the subject is further reduced beyond the point at which the gain of the AGC amplifier is maximized, the gain control of the AGC amplifier is out of the possible range, and the output signal of the AGC amplifier is The imaging signal level is reduced in accordance with the decrease in luminance. Therefore, in a video in which a video output signal is captured by a video camera having the conventional exposure control device and the subject whose brightness is being reduced is reproduced, the reduced brightness indicates that the actual brightness of the subject is reduced. Scenes that are far apart from the state of 、, for example, a scene that captures a state that gradually changes from a dusk state to a darker state, changes from a continuous daytime scene to a suddenly darker scene, playing as an unnatural image Is done.

It is an object of the present invention to change the image pickup signal level in accordance with the change in the brightness level of the subject, particularly when the brightness level of the subject to be shot is changed from a high level to a low state. An object of the present invention is to provide an exposure control device for a video camera capable of obtaining an imaging signal in a state.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems and the like, and to achieve the above-mentioned object, a first aspect of the present invention is described.
Exposure control device of the video camera described above, an image pickup device means that a subject is imaged on an imaging screen through a lens unit and an iris unit, and an output signal of an imaging signal level according to a change in the luminance level of the subject, AGC to which this output signal is supplied and the image signal level of the output signal is controlled
Means for detecting an output signal of the AGC means and detecting an image signal level of an output signal generated by the image sensor means; an exposure control reference value setting means for generating an exposure control reference value; An exposure controller for a video camera, comprising: a comparator for comparing a level of an image signal detected by the detector with an exposure control reference value generated by the exposure control reference value setting unit to generate a gain control signal. A luminance level calculating means for generating a signal corresponding to a change in the luminance level of the subject based on the gain control signal; and a modulation coefficient generating in accordance with the change in the luminance level generated by the luminance level calculating means. Modulation coefficient generation means, and a modulation means for modulating the exposure control reference value of the exposure control reference value setting means according to the modulation coefficient generated by the modulation coefficient generation means, Gain control amount of the opening and / or AGC amplifier of the iris on the basis of a gain control signal obtained from the comparison means, characterized in that a control amount calculation means control signal is generated to be controlled for. According to a second aspect of the present invention, there is provided an exposure control device for a video camera, wherein a subject is imaged on an imaging screen through a lens unit and an iris unit, and an output signal of an imaging signal level corresponding to a change in luminance level of the subject is output. Imaging device means,
AGC means for supplying the output signal and controlling the image signal level of the output signal, and detecting means for detecting the output signal of the AGC means and detecting the image signal level of the output signal generated by the image sensor means Exposure control reference value setting means for generating an exposure control reference value, and gain control by comparing the image signal level detected by the detection means with the exposure control reference value generated by the exposure control reference value setting means. An exposure control device for a video camera having a comparison means for generating a signal, wherein an opening of an iris and / or a gain control amount of an AGC amplifier are controlled based on the gain control signal obtained from the comparison means. A control amount calculating means for generating a control signal; and a signal corresponding to a change in the luminance level of the subject is generated from the control signal obtained from the control amount calculating means. Luminance level calculating means, modulation coefficient generating means for generating a modulation coefficient from a signal corresponding to a change in the luminance level of the subject generated by the luminance level calculating means, and modulation generated by the modulation coefficient generating means. Modulation means for modulating the exposure control reference value of the exposure control reference value setting means according to the coefficient is provided.

[0012]

According to the exposure control apparatus for a video camera of the present invention, the change in the luminance level of the object to be photographed, which is input to the exposure control apparatus for the video camera, is compared with the exposure control reference value. The exposure control reference value is modulated based on the obtained result.

According to a second aspect of the present invention, a change in the luminance level of the object to be photographed, which is input to the exposure control device of the video camera, is compared with an exposure control reference value. Based on the result obtained, the opening of the iris and / or the gain of the AGC amplifier are controlled, and the exposure control reference value is modulated according to the control.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of an exposure control apparatus for a video camera according to the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram showing a main part of an example of an embodiment of an exposure control device for a video camera according to the present invention. In FIG. 1, the same parts as those in FIG. I do. The exposure control device of this video camera includes a lens 1, a control amount calculation circuit 2, an iris 3, a luminance level calculation circuit 4, a CCD image pickup device 5, a ROM 6, an AGC amplifier 7,
Multiplier 8, signal processing circuit 9, D / A converter 10, detection circuit 11, iris drive circuit 12, comparator 1
3, an A / D converter 14, a loop filter 15, and an exposure control reference value (reference level) setting circuit 17.

A CCD image pickup device 5 via an AGC amplifier 7
The output signal of the CCD image pickup device 5 whose output signal has been gain-adjusted and converted into a digital signal via the A / D converter 14 is input to the detection circuit 11.
, The image signal level of the output signal output from the AGC amplifier 7 is detected, and a detection signal corresponding to the detection is output from the detection circuit 11 and input to one input side of the comparator 13. . The exposure control reference value generated and output by the exposure control reference value (reference level) setting circuit 17 and the modulation coefficient K are input to the multiplier 8, and a signal obtained by multiplying the exposure control reference value by the modulation coefficient K is output. It is generated and input to one input side of the comparator 13. Then, by multiplying the exposure control reference value by the modulation coefficient K, the signal obtained by modulating the exposure control reference value signal with the modulation coefficient K and the detection signal are compared by the comparator 13, and according to the comparison result, The generated gain control signal is output from the comparator 13. The gain control signal is input to the control amount calculation circuit 2 via the loop filter 15, and the opening amount of the iris 3 and the gain of the AGC amplifier 7 are respectively controlled via the control amount calculation circuit 2 in accordance with the gain control signal. Desired.

An output signal of the control amount calculating circuit 2 which is a signal representing the opening degree of the iris 3 and the gain of the AGC amplifier 7 is input to a luminance level calculating circuit 4 and is transmitted through the luminance level calculating circuit 4. The luminance level of the subject is obtained based on the output signal, and an output signal corresponding to the luminance level of the subject is output from the luminance level calculation circuit 4.

An output signal corresponding to the luminance level of the subject is input to the ROM 6. On the other hand, the ROM 6 stores the luminance level and the modulation coefficient K as shown in FIG.
Therefore, an output signal corresponding to the luminance level of the subject is converted into a modulation coefficient K according to the correlation via the ROM 6 and output. That is, as shown in FIG. 2, when the luminance level on the object side is 100 (lux) or more, 1 is output from the ROM 6 as the modulation coefficient K, and the luminance level on the object side falls to 100 (lux) or less. Accordingly, the value of the modulation coefficient K gradually decreases, and when the luminance level on the object side is 5 (lux), 0.5 is output from the ROM 6 as the output modulation coefficient K. A modulation coefficient K having a value changed in correlation with the change in the luminance level is input to one side of the input of the multiplier 8.

On the other hand, the other input of the multiplier 8 receives an exposure control reference value from an exposure control reference value (reference level) setting circuit 17, and multiplies the exposure control reference value by the modulation coefficient K. Is generated via the multiplier 8 and input to the comparator 7. Therefore, the signal input from the multiplier 8 to the comparator 7 is a signal whose value is changed in accordance with the value of the modulation coefficient K being changed between 1 and 0.5, that is, the luminance level of the subject. Is an exposure control reference value modulated so that the value is changed in accordance with the change.

The value of the modulation coefficient K is appropriately set so as to obtain a more natural image as an exposure control device of a video camera.

The output signal of the control amount calculation circuit 2 is input to the iris drive circuit 12 and also to the AGC amplifier 7 via the D / A converter 10.

Therefore, as shown in FIG. 1, the brightness level of the subject changes due to the loop formed by the comparator 13 → the loop filter 15 → the control amount calculation circuit 2 → the brightness level calculation circuit 4 → the ROM 6 → the multiplier 8 → the comparator 13. The gain control signal obtained by comparing the exposure control reference value modulated so as to be changed in accordance with the operation and the imaging signal level detected by the output signal of the AGC amplifier 7 via the detection circuit 11 is obtained. As described above, the input amount is input to the control amount calculation circuit 2 via the loop filter 15, and the opening amount of the iris 3 is obtained through the control amount calculation circuit 2, and the obtained opening amount of the iris 3 is obtained. Is input to the iris drive circuit 12, whereby the opening of the iris 3 is controlled. At the same time, the gain level of the AGC amplifier 7 is obtained through the control amount calculation circuit 2, and the obtained gain level of the AGC amplifier 7 is input to the AGC amplifier 7, whereby the gain level of the AGC amplifier 7 is controlled. Is done.

In the example shown in FIG. 1, the control amount calculation circuit 2, the luminance level calculation circuit 4, the ROM 6, the multiplier 8, the signal processing circuit 9, the detection circuit 11, the comparator 1
3, loop filter 15, exposure control reference value setting circuit 17
Are digital signal processing, whereas CC
Since each of the D image pickup element 5 and the AGC amplifier 7 has been subjected to analog signal processing, a D / A converter 10 is inserted between the signal output side of the control amount calculation circuit 2 and the AGC amplifier 7, and the AGC amplifier 7 Are connected to the signal input side of the signal processing circuit 9 and the signal input side of the detection circuit 11 via the A / D converter 14, respectively.

Further, according to the example shown in FIG. 1, as shown in FIG.
When the value is larger than x, the value of the modulation coefficient K becomes 1, and the exposure control device of the video camera operates in a state where the constant value exposure control reference signal generated by the exposure control reference value setting circuit 17 is input to the comparator 13. Operate.

On the other hand, the luminance level of this subject is 100 lu
When it is made to decrease in the direction below x,
With this decrease, the value of the modulation coefficient K is decreased in a direction below 1 and when the luminance level of the subject is reduced to 5 lux, the value of the modulation coefficient K is reduced to 0.
It is reduced to 5. Therefore, in this state, the value of the exposure control reference signal input to the comparator 13 is reduced to half the value when the luminance level of the subject is as large as 100 lux or more.

Therefore, as shown in FIG. 4, the horizontal axis represents the change in the luminance level of the subject in lux units, and the vertical axis represents the output level (peak) value of the video output signal. In response to this change in the luminance level, the output level of the video output signal changes along the broken line m in the conventional example shown in FIG. On the other hand, in the example of the embodiment according to the present invention shown in FIG. 1, the output level of the video output signal obtained according to the output of the AGC amplifier 7 changes along the solid line M. That is, the characteristic difference between the change characteristic of the output level of the video output signal indicated by the broken line m and the change characteristic of the output level of the video output signal indicated by the solid line M indicates the difference between the change in the luminance level of the subject. This results in a difference in the ability to follow the level change of the video output signal. Therefore, according to the example of the embodiment of the present invention shown in FIG. 1, the change in the luminance of the image obtained by reproducing the video output signal output from the signal processing circuit 9 is the same as that indicated by the broken line m in FIG. The problem with the conventional video camera exposure control apparatus, that is, an unnatural change that does not follow the change in luminance of the video camera, is solved.

Next, the "lowest" and "recommended" shown in FIG.
A description will be given of the points indicated as. Note that FIG. 3 illustrates an example in which a color bar screen is photographed as the subject, and thus the description will be made using illuminance instead of luminance. The “minimum” refers to the minimum subject illuminance (the minimum subject illuminance that can be photographed with a video camera), and the “recommended” refers to the recommended subject illuminance when photographing with a video camera. And FIG.
In the exposure control device of this video camera shown in
Generally, when the illuminance of the subject is sufficiently bright, FIG.
Is set such that the video output signal level (peak) is always 100 [IRE] on the side brighter than (100 [lux]) on the horizontal axis.

Also, in the example shown in FIG. 1, as shown in FIG. 3, the level of this video output signal has a peak value of 1
The iris 3 is set to the open state and the gain of the AGC amplifier 7 is set to the maximum state at the lowest subject illuminance having a peak value 50 [IRE] which is half of 00 [IRE].

That is, in the example shown in FIG. 1, as shown in FIG. 3, the video output signal level has a value of 100 [IR
E] is the recommended subject illuminance,
The subject illuminance value (50 [l]) which is half (about 50 [IRE]) of the video output signal level at the recommended subject illuminance
ux]) is the minimum subject illuminance.

Further, as shown by the solid line M in FIG. 3, the change in the video output signal level in the example shown in FIG. When the signal is input to the exposure control device, as described above, the value of the modulation coefficient K is set to be 1, so that the change in the video output signal output level in the conventional example shown in FIG. Similarly, a video output signal output that changes is output from the exposure control device of the video camera. Therefore, in an illuminance region equal to or higher than the recommended subject illuminance, exposure control equivalent to the exposure control of the conventional video camera is performed, and there is no unnatural feeling in photographing.

On the other hand, in the example shown in FIG. 1, when the subject illuminance changes between the recommended subject illuminance and the minimum subject illuminance, the modulation coefficient K is set to 1 as shown in FIG.
In response to a change between .about.0.5, the video output signal level is changed in the state represented by the solid line M shown in FIG. Therefore, in the range of the change in the illuminance, the unnatural feeling felt when reproducing the image signal photographed in the exposure control of the conventional video camera can be eliminated.

In this case, when a gamma circuit is provided in the signal processing circuit 9, in a linear region of the gamma curve, the video output signal level changes substantially in proportion to the change of the modulation coefficient K.

Next, in the luminance level calculation circuit 4,
As an example of a method of obtaining the luminance level, the shutter speed is fixed at a value of 1/60 [second] and the minimum subject illuminance is set to a value of 5
[Lux] will be described as an example. The output level A of the detection circuit 11 is the brightness (luminance level) of the subject.
L, the gain of the iris 3 is I, the gain of the AGC amplifier 7 is G, the gain of the electronic shutter is S,
Where a is the photoelectric conversion efficiency of

[0034]

A = L × I × G × S × a

From equation (1), (0.5 × exposure control reference value) = 5 [lux] × Imax × Gmax × S × (1 /
60) × a (provided that the minimum subject illuminance is 5 [l
ux], K = 0.5 from FIG. 2 and Imax,
Gmax is the maximum value of I and G, respectively.) Since the photoelectric conversion efficiency a is determined from this relational expression, a
Is substituted to obtain the luminance level L.

As described above, according to the example shown in FIG. 1, the modulation coefficient K is set for the luminance signal level detected by the luminance level calculation circuit 4, and the modulation coefficient K is set.
Modulates the exposure control reference value (reference level).

Therefore, since the gain control of the iris 3 and the AGC amplifier 7 can be properly performed, natural exposure control can be performed according to the change in the luminance level of the subject.

Further, according to the example shown in FIG. 1, since the modulation coefficient K is stored in the ROM 6,
By exchanging the ROM 6, the modulation coefficient K can be easily changed. Therefore, in accordance with the exposure control characteristics required for the exposure control device of the video camera,
It becomes easy to set the correlation of the modulation coefficient K with the change in the brightness level.

In addition, since the brightness level L is obtained from the above equation 1, it is possible to perform a more natural exposure control in accordance with a change in the brightness level of the subject photographed by the video camera.

[0040]

According to the exposure control apparatus for a video camera according to the present invention, the change in the luminance level of the subject input to the exposure control apparatus for the video camera is compared with the result obtained by comparing the exposure control reference value. By performing the modulation of the exposure control reference value, a video output signal whose level is appropriately changed with respect to a change in the luminance level of the subject to be photographed is obtained as an output of the exposure control device of the video camera.

According to the exposure control apparatus for a video camera of the present invention, the result obtained by comparing the change in the luminance level of the object to be photographed with the exposure control reference value, which is input to the exposure control apparatus for the video camera, is obtained. The exposure control reference value is modulated in accordance with the control in which the opening of the iris and / or the gain of the AGC amplifier are controlled based on the control. The changed video output signal is obtained as the output of the exposure control device of the video camera.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of an exposure control device for a video camera according to the present invention.

FIG. 2 is a correlation diagram showing a correlation between a luminance level and a modulation coefficient of the exposure control device.

FIG. 3 is a correlation diagram showing a correlation between a luminance level of the exposure control device and a video output signal output level.

FIG. 4 is a configuration diagram of a conventional video camera exposure control device.

[Explanation of symbols]

2 ... Control amount calculation circuit, 3 ... Iris, 4 ...
Brightness level calculation circuit, 5, CCD image pickup devices 5, 6,
... ROM, 7 ... AGC amplifier, 8 ... Multiplier,
11 detection circuit, 12 iris drive circuit, 1
3 Comparator 17 Exposure control reference value (reference level) setting circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-60378 (JP, A) JP-A-62-272771 (JP, A) JP-A-1-231576 (JP, A) JP-A 63-272 131279 (JP, A) JP-A-1-120969 (JP, A) JP-A 1-212083 (JP, A) JP-A-61-157917 (JP, A) JP-A 1-212084 (JP, A) JP-A-64-44430 (JP, A) JP-A-59-65305 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/222-5/257

Claims (3)

(57) [Claims] 1. An image pickup device means for forming an image of an object on an imaging screen through a lens unit and an iris unit, and outputting an output signal of an image signal level corresponding to a change in the luminance level of the object, and supplying the output signal. An AGC means for controlling an image signal level of the output signal; a detection means for detecting an output signal of the AGC means and detecting an image signal level of the output signal generated by the image sensor means; An exposure control reference value setting means for generating a value, and a gain control signal is generated by comparing the imaging signal level detected by the detection means with the exposure control reference value generated by the exposure control reference value setting means. An exposure control device for a video camera, comprising: a luminance level at which a signal corresponding to a change in the luminance level of the subject is generated based on the gain control signal. Calculation means; a modulation coefficient generation means for generating a modulation coefficient in accordance with the change in the luminance level generated by the luminance level calculation means; and the exposure in accordance with the modulation coefficient generated by the modulation coefficient generation means. A modulation means for modulating the exposure control reference value of the control reference value setting means; and an opening of the iris and / or a gain control amount of an AGC amplifier are controlled based on the gain control signal obtained from the comparison means. An exposure control device for a video camera, comprising: a control amount calculating means for generating a control signal. 2. An imaging element means for forming an image of an object on an imaging screen through a lens unit and an iris unit, and outputting an output signal of an imaging signal level corresponding to a change in the luminance level of the object, and supplying the output signal. An AGC means for controlling an image signal level of the output signal; a detection means for detecting an output signal of the AGC means and detecting an image signal level of the output signal generated by the image sensor means; An exposure control reference value setting means for generating a value, and a gain control signal is generated by comparing the image signal level detected by the detection means with the exposure control reference value generated by the exposure control reference value setting means. An exposure control device for a video camera having a comparing means, wherein the iris opening and / or AGC angle is controlled based on the gain control signal obtained from the comparing means. Control amount calculating means for generating a control signal for controlling the gain control amount of the control signal; and a luminance level for generating a signal corresponding to a change in the luminance level of the subject from the control signal obtained from the control amount calculating means. Calculation means, a modulation coefficient generation means for generating a modulation coefficient from a signal corresponding to a change in the luminance level of the subject generated by the luminance level calculation means, and a modulation coefficient generated by the modulation coefficient generation means. And a modulating means for modulating the exposure control reference value of the exposure control reference value setting means accordingly. 3. The exposure control device for a video camera according to claim 1, wherein the iris opening, AGC
An exposure control device for a video camera, wherein the luminance level is detected based on a gain control amount of an amplifier and an electronic shutter speed.