JPH03231581A - Level adjustment device for image pickup signal - Google Patents

Abstract

PURPOSE:To adjust automatically an image pickup signal level to be constant by providing a shutter control means or the like controlling an electronic shutter so as to extend a charge storage period longer as a level of an image pickup signal is smaller. CONSTITUTION:The device is provided with an image pickup element (CCD image sensor) 3 having an electronic shutter function, a level detection means 6 detecting a level of an image pickup signal outputted from the CCD image sensor 3, and a shutter control means controlling the electronic shutter so as to extend more a charge storage period as a level of the image pickup signal detected by the level detection means 6 gets smaller. Then the iris priority mode in which an opening of the iris 2 is adjusted automatically and the shutter priority mode in which the shutter speed is adjusted automatically are selected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a level adjustment device that adjusts an ill image signal level to a constant value.

[Prior Art] FIG. 3 is a diagram showing the configuration of an example of a conventional video camera.

In the figure, image light from a subject (not shown) passes through an imaging lens 1 and an iris 2 to an imaging device, such as a CC.
It is supplied to the D image sensor 3.

This CCD image sensor 3 is assumed to have an electron shutter function for adjusting the charge accumulation period Te. For example, an OFD (overflow drain) is used as is well known in the art. In other words, by supplying the sweep pulse, the signal charge accumulated in the light receiving section (photodiode) can be caused to flow to the OFD. Therefore, by controlling the supply period of the sweep pulse, the charge accumulation period T
This is to control e.

Timing pulses such as a read start pulse, a transfer pulse, and a sweep pulse required by the CCD image sensor 3 are supplied from a timing generator 4. The timing generator 4 is supplied with a 3-bit shutter control signal Ssh indicating a shutter performance selected from, for example, 1760 seconds, 1/125 seconds, 1/250 seconds and 11500 seconds.

When the shutter speed is 1760 seconds, the timing generator 4 does not supply the sweep pulse to the CCD image sensor 3, and the readout start pulse (shown in FIG. 4B, and FIG. 4A shows the vertical synchronization pulse 0). The charge accumulation period Te until supply is 16.6 m5ec (1/60
seconds) (as shown in Figure C).

Also, 1/125 second, 1/250 second and 17500
When the shutter speed is seconds, a sweep pulse is supplied from the timing generator 4 to the CCD image sensor 3 for the corresponding period, and the charge accumulation period Te until the readout start pulse is supplied is 8 m5 ec.
(1/125 seconds), 4ms ec (1/250 seconds), and 2m5ec (11500 seconds) (Figure D-F
(illustrated).

The output signal of the CCD image sensor 3 is supplied to a sample hold circuit 5 formed of a CDS circuit (correlated double sampling circuit) in order to reduce reset noise, for example. The imaging signal output from this sample hold circuit 5 is supplied to a level detector 6 that constitutes an iris controller, and the detection signal is supplied to an iris driver 7.

The opening of the iris 2 is controlled by this driver 7. As a result, the large amount of light directed to the CCD image sensor 3 is automatically adjusted, and the level of the output signal of the CCD image sensor 3, that is, the imaging signal, is kept constant.

Further, the image signal outputted from the sample hold circuit 5 is level-controlled by the AGC circuit 8, and then the signal processing circuit (
(not shown) to form, for example, an NTSC video signal.

[Problems to be Solved by the Invention] In the example shown in FIG. 3, when photographing a dark subject with the iris 2 open, it is impossible to keep the level of the output signal of the CCD image sensor 3 constant using the iris controller. becomes.

Conventionally, an electronic viewfinder (not shown in Figure 3)
When observing the image capture screen and finding that the brightness is insufficient, the shutter speed is manually changed to a slower one.

Since such manual switching of the shutter speed requires a predetermined amount of time, it cannot immediately respond to the brightness of the subject. Therefore, there is a drawback that the brightness of the imaging screen is insufficient during the period until the switching is completed.

In addition, there are only four types of shutter speeds that can be switched, making it impossible to finely adjust the brightness of the imaging screen.
There was a drawback that image disturbances such as overexposure occurred on the imaging screen when switching.

SUMMARY OF THE INVENTION Accordingly, the present invention provides an imaging signal level adjustment device that eliminates the above-mentioned drawbacks.

[i! Means for Solving the Problem] The present invention provides an image sensor having an electronic shutter function for adjusting a charge accumulation period, a level detection means for detecting the level of an image signal output from the image sensor, and the level detection means. and shutter control means for controlling the electronic shutter so that the charge accumulation period becomes longer as the level of the image pickup signal detected by the sensor becomes smaller.

[Function] In the above configuration, the level detection signal is controlled to become smaller and the charge accumulation period becomes longer as the imaging signal level becomes smaller, so that the level of the imaging signal is increased. In other words, the imaging signal level is automatically adjusted to a constant value.

Further, since the charge accumulation period is continuously varied according to the level of the imaging signal, it is precisely adjusted so that the imaging signal level becomes a constant value.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In this example, it is possible to select between an iris priority mode in which the iris opening is automatically adjusted and a shutter priority mode in which the shutter speed is automatically adjusted.

In the figure, the control signal Ssh supplied to the timing generator 4 is as follows in the iris priority mode.
The signal is similar to the example in FIG. 3, but in the shutter priority mode, it is a 3-bit signal indicating a shutter speed of, for example, 1/1000 seconds.

Here, when the control signal Ssh indicates a shutter speed of 1/1000 seconds, the timing generator 4 outputs the following:
The sweep pulse is set so that there is a non-output period of lm5ec (1/1000 seconds) before the readout start pulse (shown in FIG. 2B, and FIG. 2A shows the vertical periodic pulse VD) is supplied to the CCD image sensor 3. is output (G in the same figure)
(illustrated).

The sweep pulse output from the timing generator 4 is +l! of the changeover switch 11! It is supplied to the L side fixed terminal of the changeover switch 12.

The H side fixed terminal of the changeover switch 12 is grounded, and its output signal is supplied to all fixed terminals of the changeover switch 11.

The changeover switch 11 is set to i in the iris priority mode.
(Connected to [, and connected to the S side in shutter priority mode.The output signal of this switch
It is supplied to the sweep pulse input terminal of the D image sensor 3.

Further, the output signal of the level detector 6 is supplied to the fixed terminal on the i side of the changeover switch 13, and the output signal of the changeover switch 13 is
The fixed terminal on the side is grounded. This changeover switch 13 is
In the iris priority mode, it is connected to 1g4, and in the shutter priority mode, it is connected to the S side. The output signal of this changeover switch 11 is supplied to the iris driver 7.

Further, the output signal of the level detector 6 is supplied to the inverting input terminal of the DC amplifier 14 and amplified. Volume 15 is for adjusting the offset voltage. In this case, the level of the output signal Vo from the amplifier 14 is determined by the level detector 6.
When the level of the output signal of the level detector 6 becomes high, it becomes low, and when the level of the output signal of the level detector 6 becomes low, it becomes high.

The gain and offset of this DC amplifier 14 are such that its output signal 0 is within a certain range, for example, 1.5v to 4v
2nd v! JD (as shown in the figure).

The output signal vO of this amplifier 14 is supplied to a comparator 16. The sawtooth signal generator 17 is supplied with a vertical periodic pulse VD from the timing generator 4, and this generator 17 outputs a vertically periodic sawtooth signal 5AW (shown in E of the figure). This sawtooth wave signal SAW is kept at a constant level during a period corresponding to the non-output period of the sweep pulse of the timing generator 4 when the control signal Ssh indicates a shunter speed of 1/1000 seconds, and during this period, the sawtooth signal SAW is kept at a constant level. After the elapse of time, the level is sequentially lowered, and then returned to a constant level during a period corresponding to the next non-output period. This sawtooth signal SAW is within a certain range, for example, 1.5v to 3.5v, considering the range of the output signal vO of the amplifier 14 mentioned above.
It is formed to vary within v.

The sawtooth signal SAW output from the generator 17 is supplied to the comparator 16 as a comparison reference signal. From the comparator 16, the output signal Vo is the sawtooth signal SA.
When it is larger than W, the signal SCM becomes high level rHJ, and in the opposite state, the signal SCM becomes low level "L". The output signal SCM of this comparator 16 is supplied as a control signal to the changeover switch 12, and this changeover switch 12 is connected to H (lIl) when the signal SCM is at a high level "H", and on the other hand, when the signal SCM is at a low level "L". Sometimes it is connected to the L side.

This example is configured as described above, and the operation will be explained below.

In the case of the iris priority mode, the changeover switches 11 and 13 are each connected to the L side, resulting in a configuration similar to that of the example in FIG. 3. Therefore, since the operation in this case is similar to the example shown in FIG. 3, the explanation thereof will be omitted.

Next, in the case of the shutter priority mode, the changeover switches 11 and 13 are each connected to 5flN.

The input side of the iris driver 7 is at ground potential, and the iris 2 is fixed in an open state. In other words, the iris 2 no longer adjusts the large amount of light to the CCD image sensor 3.

Further, since the sweep pulse outputted from the timing generator 4 is supplied to the CCD image sensor 3 via the changeover switches 12 and 11, the CCD image sensor 3
The charge accumulation period is controlled according to the level of the imaging signal, and the level of the imaging signal is adjusted to a constant value.

For example, when the imaging signal output from the sample and hold circuit 5 is as shown in FIG. 2C, and the output signal Vo of the amplifier 14 is as shown in FIG.
The output signal SCM becomes as shown in FIG. F, and the sweep pulse outputted from the changeover switch 12 and supplied to the CCD image sensor 3 becomes as shown in FIG. H.

From this state, when the subject becomes brighter and the level of the imaging signal output from the sample and hold circuit 5 increases, the level of the output signal Vo of the amplifier 14 decreases, and therefore the low level "L" of the output signal SCM of the comparator 1st ” period becomes longer and the selector switch 12 is set to C.
The supply period of the sweep pulse supplied to the CD image sensor 3 becomes longer, the charge accumulation period Te becomes shorter, and the level of the imaging signal is made smaller.

On the other hand, when the subject becomes dark and the level of the imaging signal output from the sample-and-hold circuit 5 becomes low, the level of the output signal Vo of the amplifier 14 increases, and therefore the low level "L" of the output signal SCM of the comparator 16 increases.
'' is shortened, the supply period of the sweep pulse supplied to the CCD image sensor 3 from the changeover switch 12 is shortened, the charge accumulation period Te is lengthened, and the level of the imaging signal is increased.

Therefore, the supply period of the sweep pulse supplied to the CCD image sensor 3, that is, the charge accumulation period Te, is controlled according to the level of the imaging signal, so that the level of the imaging signal is adjusted to a constant value.

2, according to this example, in addition to the iris priority mode in which the iris 2 controls the amount of light incident on the CCD image sensor 3 so that the level of the imaging signal becomes a constant value, A shutter priority mode can be selected in which the charge accumulation period Te is controlled so that the level of the imaging signal is adjusted to a constant value. When the shutter priority mode is selected, even if the subject is dark such that the iris 2 is open, the level of the imaging signal is automatically adjusted to a constant value by controlling the charge accumulation period Te.

Therefore, it is possible to immediately respond to the brightness of the subject, and unlike conventional methods in which the shutter speed is manually switched, the brightness of the imaging screen does not become insufficient until the switching is completed. Furthermore, since the charge accumulation period Te is continuously controlled, the level of the image pickup signal can be controlled to a constant value with higher accuracy than in the conventional method in which the shutter speed is switched stepwise.

In the above embodiment, the supply of the sweep pulse output from the timing generator 4 to the CCD image sensor 3 is restricted by the changeover switch 12, but depending on the level of the imaging signal, For example, the output period of the sweep pulse from the timing generator 4 may be controlled based on the output signal SCM of the comparator 16.

[Effects of the Invention] As explained above, according to the present invention, the charge accumulation period of the image sensor is controlled according to the imaging signal level, and the imaging signal level is automatically adjusted to a constant value. Even when photographing a dark subject where the iris is fully open, the imaging signal level can be adjusted to a constant value by immediately responding to the brightness of the subject. This eliminates the possibility that the brightness of the imaging screen becomes insufficient during the period until the switching is completed. Furthermore, since the charge accumulation period is controlled continuously, it is possible to control the level of the imaging signal to a constant value with higher precision than in the conventional method in which the shutter speed is changed stepwise.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram for explaining its operation, Fig. 3 is a block diagram of a conventional example, and Fig. 4 is a block diagram showing an embodiment of the present invention.
The figure is a diagram for explaining the operation.・Imaging lens, iris, CCD image sensor, timing generator, sample hold circuit, level detector, iris driver, AGC circuit, changeover switch, DC amplifier, comparator, sawtooth signal generator

Claims (1)

[Claims] (1) An image sensor having an electronic shutter function to adjust the charge accumulation period, a level detection means for detecting the level of the image signal output from the image sensor, and a level of the image signal detected by the level detection means. and shutter control means for controlling the electronic shutter so that the charge accumulation period becomes longer as the value becomes smaller.