JPH03258084A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To prevent deterioration in the picture quality at a low illuminance by changing the speed of an electronic shutter to a slow speed when a level of an output signal of a solid-state image pickup element is lowered than a prescribed value at the outside of a control range of an automatic exposure means. CONSTITUTION:The illuminance of an object is taken on an X axis, let the lightness of points be A, B (A<B), and a detection output level from a detection circuit 6 is taken on a Y axis. When the lightness of the object at a point of time is lighter than that of the point B, the speed of an electronic shutter is set to 1/100sec and when the lightness of the object at a point of time is darker than that of the point A, the speed of the electronic shutter is set to 1/60sec. The speed of the electronic shutter changes from 1/60sec to 1/100sec at a block from the point A to the point B. Thus, flicker is automatically eliminated and a constant illuminance is obtained automatically at a low illuminance to automatically prevent the deterioration in the picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device, and particularly to a solid-state imaging device using a solid-state imaging element having an electronic shutter function.

[Summary of the invention]

The present invention provides a solid-state imaging device that includes automatic exposure means that automatically controls the amount of opening of the iris according to the illuminance of the subject and maintains a constant level of imaging output, and an electronic shutter within the control range of the automatic exposure means. When the speed is set to (1/100) second and the level of the output signal of the solid-state image sensor falls below a predetermined value outside the control range of the automatic exposure means, the electronic shutter speed is changed from (1/100) second to By providing a means for changing the speed to a slow speed, flicker can be automatically removed and image quality deterioration at low illuminance can be automatically prevented.

[Conventional technology]

NT equipped with a solid-state image sensor with electronic shutter function
I have an SC video camera.

When such an NTSC video camera is used to take pictures under the illumination of a discharge tube, for example, a fluorescent lamp, flickering occurs in the image in the area where the power frequency is 5.0 Hz.

The mechanism by which this flicker occurs is shown in FIG.

Figure 7A shows the electronic shutter speed of the video camera (1/
The period of exposure in the CCD when it is 60) seconds (60H
z), and FIG. 7B shows changes in the amount of light from a fluorescent lamp at a power supply frequency of 50 Hz.

As shown in the figure, since a fluorescent lamp is lit in both positive and negative directions, it flickers at 100 Hz, which is twice the power frequency of 50 Hz, whereas a CCD is exposed with an amount of incident light for an electronic shutter speed (1/60) second. Therefore, the integral value of the amount of incident light for (1/60) seconds varies every three fields, and a 20 Hz flicker occurs.

By the way, as shown in FIG. 7 CSD, it is generally known that flicker can be removed by setting the electronic shutter speed to (1/100) second.

FIG. 7C shows the charge sweep time TA and the exposure time TB when the electronic shutter speed is set to (1/100) seconds at a CCD exposure cycle of 60k. The change in the amount of light from a fluorescent lamp at a power supply frequency of 50 Hz is shown.

As shown in FIG. 7C, the field frequency 60) 1
If the first 6.7 ms of the 16.7 m period of z is the COD charge sweep time TA, and the remaining 10 m5 ((1/100) seconds) is the exposure time TB, the diagonal lines are added in the seventh diagram. The integrated value of the amount of incident light within the exposure time TB shown by is equal between each cycle of the field frequency of 60 Hz, and flicker is eliminated.

However, the electronic shutter speed is always (1/100
) seconds, the amount of exposure will be insufficient in low light conditions,
The S/N ratio deteriorated.

Therefore, it has been considered to remove flicker only when it occurs. Conventional techniques for removing flicker in this case include the following.

■When flicker occurs, the user can manually adjust the electronic shutter speed (1/100
) to be set in seconds.■Flicker is detected by an external sensor and the flicker is
Automatically adjusts the electronic shutter speed (1/1) when
00) What is set to seconds ■When flicker occurs, the output of the AGC amplifier changes periodically, so the gain of the AGC amplifier is changed so that the output of this AGC amplifier remains constant [Solved by the invention] [Problems to be Solved] The conventional flicker prevention measures described above have the following problems.

Regarding (2): Since the method is not automatic and must be operated by the user, it is difficult to ensure flicker removal.

Against (2): An external sensor is required, which complicates the hardware and reduces the degree of freedom in designing the exterior of the video camera. Moreover, it is not suitable for miniaturization and increases costs.

Regarding (2): The hardware for switching the gain of the AGC amplifier becomes complicated, the number of parts increases, and the cost increases.

Therefore, an object of the present invention is to provide a solid-state imaging device that can automatically remove flicker without complicating the hardware and can automatically prevent image quality deterioration at low illuminance.

[Means to solve the problem]

This invention includes automatic exposure means that automatically controls the opening amount of the iris according to the illuminance of the subject and maintains a constant level of imaging output, and an electronic shutter speed that is controlled by (1/1) within the control range of the automatic exposure means. 100) seconds, and if the level of the output signal of the solid-state image sensor falls below the predetermined value outside the control range of the automatic exposure means, the electronic shutter speed is set to (1/10) seconds.
0) seconds to a slow speed.

[Function] The automatic exposure means automatically controls the opening amount of the iris according to the illuminance of the subject and operates to maintain a constant level of imaging output, so the electronic shutter speed is within the control range of the automatic exposure means. is (1/100) second.

Further, if the level of the output signal of the solid-state image sensor exceeds a predetermined value even outside the control range of the automatic exposure means, the electronic shutter speed is set to (1/100) second.

However, when the level of the output signal of the solid-state image sensor falls below a predetermined value outside the control range of the automatic exposure means, that is, when the illuminance is low, the electronic shutter speed is changed from (1/100) second to a slower speed.

This allows flicker to be automatically removed and
When the illuminance is low, a constant illuminance can be automatically obtained and image quality deterioration can be automatically prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

In the configuration shown in FIG. 1, an optical image from a lens system 1 is transmitted via an iris 2 to a CCD having a color filter (not shown).
A is photoelectrically converted to form an imager output.

This image output is supplied from the CCD 3 via a preamplifier 4 to an AGC circuit 5 and a detection circuit 6. Incidentally, the above-mentioned iris 2 is driven by an iris motor 7 and its opening amount is controlled.

The AGC circuit 5 amplifies the imager output from the CCD 3 to a predetermined level, and supplies the amplified imager output via a terminal 8 to a next-stage signal processing circuit (not shown).

In the detection circuit 6, the image output power from the CCD 3 is integrated to form a DC signal S6. This signal S
6 is supplied to a microprocessor 9.

A signal 310 representing the opening amount of the iris 2 is sent from the position detection sensor 10 that detects the opening amount of the iris 2 to the amplifier 11.
The signal is supplied to the microprocessor 9 via the microprocessor 9. Note that this position detection sensor 10 uses, for example, a Hall element.

The microprocessor 9 is a computer for electronic shutter control, and the above-mentioned signals S6 and SIO are converted to 8 by an A/D converter (not shown) in the microprocessor 9.
It is converted into bit digital signals D6 and Dlo.

The microprocessor 9 determines an electronic shutter speed based on the above-mentioned digital signal D6, and forms a serial data control signal DC91 that defines this electronic shutter speed. This control signal DC91 is then supplied to the driver circuit 13 via the bus 12.

Furthermore, the microprocessor 9 determines the opening amount of the iris 2 based on the above-mentioned digital signal DIO, and receives a serial data control signal D that defines the opening amount of the iris 2.
Form C92. This control signal DC92 is then supplied to the driver circuit 14 via the bus 12.

The driver circuit 13 drives and controls the CCD 3 at a specified electronic shutter speed based on the above-mentioned control signal DC91.

The driver circuit 14 drives and controls the iris motor 7 of the iris 2 based on the above-mentioned control signal DC92.

The operation will be explained below.

As shown in Figure 2, the illuminance of the subject, that is, the brightness, is plotted on the horizontal axis, and the brightness of the points formed are A and B (A<B).
shall be. Furthermore, the detection output level from the detection circuit 6 is plotted on the vertical axis.

If the brightness of the subject is brighter than point B, set the electronic shutter speed to (1/100) second, and if the brightness of the subject is darker than point A, set the electronic shutter speed to (1/100) second. Set to (1/60) seconds.

In this section from point A to point B, the electronic shutter speed can vary from (1/60) second to (1/100) second.

In the detection output level shown in FIG. 2, the solid line L1 indicates the change in the detection output level when the electronic shutter speed is variable.
The broken line L2 shows the change in the detection output level when the electronic shutter speed is fixed at (1760) seconds (conventional),
Then, the - dotted chain line L3 indicates the electronic shutter speed (1/10
It shows the change in the detection output level when fixed to 0) seconds. In the figure, the area to the right (direction of arrow X) from the detection output level LDBOO point is the iris control range where the amount of incident light is controlled by the iris 2 under the condition that the shutter speed is (1/100) seconds. , and the detection output level LDX
To the right of the XO point (arrow X direction), the shutter speed is (1
This is the iris control range in which the amount of incident light is controlled by the iris 2 under the condition of /60) seconds. In the iris control range, the detection output level is kept constant. The detection output level in the iris control range is for iris control.

In addition, to the left of the detection output level LDBOO point mentioned above (in the direction of arrow IX), in order to compensate for the decrease in illuminance, the iris 2 is in the range where it is fully open under the condition of the shutter speed (1/100) second. In addition, the detection output level LDXXO is set to the left (in the direction of arrow IX) to compensate for the decrease in illuminance.
This is the range in which the iris 2 is fully opened under the condition of a shutter speed of (1/60) seconds. In this range, the amount of incident light is controlled not by the iris 2 but by the CCD 3.

As shown in FIG. 3, the electronic shutter speed of the CCD 3 is (1/10
0) seconds, and from point B to point A is (1/100)
It is variable between seconds and (1/60) seconds, and point A
to the direction of arrow IX is fixed at (1/60) seconds.

As is clear from FIGS. 2 and 3, when the electronic shutter speed is always set to (1/100) second, the amount of light is lower than when the electronic shutter speed is set to (1/60) second. That is, the detection output level decreases by about 6 dB, resulting in deterioration of image quality at low illuminance.

Therefore, in order to prevent this, the illuminance of the subject should be adjusted to point A-B.
When the illuminance of the subject decreases within the section of
The electronic shutter speed is gradually lowered so that the illuminance of the subject does not become lower than the detection output level LDB. The lowering timing depends on the loop time constant, but it is approximately 2 to 6 V (I V = 16
．． 6113). This electronic shutter speed is continuously varied so that the image quality does not become unnatural.

Also, when the illuminance of the subject increases within the section between points A and B, the illuminance of the subject is compared with the detection output level LDA to the point in the middle of the figure, and the illuminance of the subject is made to prevent it from becoming higher than the detection output level LDA. Increase the electronic shutter speed step by step. The timing to raise it depends on the loop time constant, but it is approximately 2~
It is about 6V (IV=16°611s). In addition, in this embodiment, the detection output level of points A and B is LDA5LD.
B are made equal.

In the figure, point XX is the point where the control loop of iris 2 at the electronic shutter speed (1/60) seconds is broken;
From point XX in the direction of arrow X, the amount of incident light is controlled by the iris 2, and from point XX in the direction of arrow IX, the amount of incident light is controlled by the CCD 3.

When the illuminance of the object is higher than the illuminance corresponding to point XX, the control loop of the iris 2 maintains the detection output level as a substantially constant reference value.

In this way, the conventional minimum object illuminance level LD
While maintaining M, flicker can be removed by setting the electronic shutter speed to (1/100) second under illumination comparable to a fluorescent lamp.

Setting the electronic shutter speed and making the electronic shutter speed variable can be done without using an external sensor or changing the gain of the AGC amplifier, and therefore without setting up a new complicated circuit configuration. This can be realized as an extension of the system.

Next, the processing within the microprocessor 9 will be explained according to the flowchart shown in FIG.

In step 101, the data of the digital signal DIO supplied from the position detection sensor 10 and subjected to A/D conversion is confirmed, and the process proceeds to step 102.

In step 102, it is determined whether the iris 2 is fully open or not based on the data of the digital signal DIO described above. If it is determined that the iris 2 is not fully open, it is determined that the illuminance of the subject is high, and the process moves to step 105. Further, if it is determined that the iris 2 is fully open, the process moves to step 103.

In step 103, the data of the digital signal D6 supplied from the detection circuit 6 and subjected to AID conversion is li! If approved, the process proceeds to step 104.

In step 104, the data of the digital signal D6 described above is compared with the reference detection output levels LDA and LDB,
Digital signal D6 has detection output level LDA, LDB
When the value is larger than , the process proceeds to step 105, and when it is smaller, the process proceeds to step 111. In actual judgment, since the signal S6, which is the source of the digital data described above, contains jitter, a slight dead zone is set.

In step 105, the current electronic shutter speed is checked.

In step 105, the electronic shutter speed is set to (1/1.0
0) It is determined whether or not it is set to seconds. young 1
/100) seconds, the process advances to step 107 and returns to the start.

In addition, if the time is less than (1/100) seconds, step 10
At step 8, a control signal DC91 is output to the driver circuit 13 to increase the electronic shutter speed by one step according to the electronic shutter speed table shown in FIG. still,
In the electronic shutter speed table described above, the arrow UP represents increasing the electronic shutter speed, and the arrow DWN represents decreasing the electronic shutter speed.

When the above-mentioned control signal DC91 is sent, the result of the control is fed back from the detection circuit 6 as a detection output level, but when considering hunting prevention, the feedback time is 2 to several volts (1v=16.611s). Therefore, the process is temporarily stopped in step 109. After that, the process advances to step 110 and returns to the start.

This tying is shown in FIG.

In FIG. 5, if a command COI to increase the electronic shutter speed is issued at the beginning of the first Vl, the accumulated charge will be swept out in the next step (2), and the charge will be reduced to several volts, for example. 6v, the control operation by the microprocessor 9 is stopped. After that, the control operation shown in the flowchart of FIG. 4 is performed.

Charge can be swept out only during the period when a high voltage is applied to the substrate of the CCD 3 within the horizontal blanking period.

For example, 262 different timings can be set for the 100-pulse width WPO in correspondence with the electronic shutter speed.

Step 111 is reached when the iris 2 is fully open and the detection output level of the illuminance of the object is smaller than the reference detection output levels L'DA and LDB, and it is determined that the illuminance is low under this condition. In step 112,
The current electronic shutter speed is checked.

In step 112, the electronic shutter speed is (1/60)
It is determined whether the time is set to seconds. young 176
If it is set to 0) seconds, the process advances to step 113 and returns to the start.

If it is not set to (1/60) second, that is, if it exceeds (1/60) second, in step 114, the electronic shutter speed is increased by one step according to the electronic shutter speed table shown in FIG. Driver circuit 13 to lower
A control signal DC91 is output.

When the above-mentioned control signal DC91 is sent, the result of the control is fed back from the detection circuit 6 as a detection output level, but considering the prevention of hunting, the feedback time is 2 to several V (IV = 16.6 m5). Therefore, the process is temporarily stopped in step 115. Thereafter, the process advances to step 116 and returns to the start.

According to this embodiment, within the control range of the iris 2,
Since the electronic shutter speed is always set at (1/100) second, flicker can be automatically removed without using an external sensor or changing the gain of the AGC amplifier.

In addition, at low illumination times when the detection output level of the subject is outside the control range of the iris 2 and is lower than the reference detection output level LDAXLDB, the electronic shutter speed is set to (1/ 60) seconds to (
Since it is variable within 1/100) seconds, image quality deterioration can be automatically prevented.

Further, since no external sensor is used and the circuit configuration is not complicated, the degree of freedom in exterior design is increased, the set can be made smaller, and cost increases can be prevented.

Further, since the gain of the AGC amplifier is not changed and the circuit configuration is not complicated, an increase in cost can be prevented.

Furthermore, it is possible to improve the dynamic resolution for general subjects and to prevent blurring of images due to excessive aperture of the iris 2 outdoors. It should be noted that improvement in dynamic resolution particularly refers to improvement in resolution when a slow-moving subject is recorded and reproduced as a still image.

In this embodiment, the reference detection output level LDA.

Although the LDBs are set at the same level, the LDBs are not limited to this, and it is also possible to set them to different levels.

[Effects of the Invention] According to the solid-state imaging device according to the present invention, within the control range of the automatic exposure means that automatically controls the opening amount of the iris according to the illuminance of the subject to maintain a constant level of imaging output. The electronic shutter speed is set to (1/100) seconds, and if the level of the output signal of the solid-state image sensor falls below a predetermined value outside the control range of the automatic exposure means, the electronic shutter speed is set to (1/100) seconds.
Since the speed is changed from 1/100) second to a slower speed,
Flicker can be automatically removed without using an external sensor or changing the gain of the AGC amplifier, and since the electronic shutter speed is variable at low illuminance, it is possible to automatically obtain a constant illuminance. This has the effect of automatically preventing image quality deterioration.

Furthermore, since no external sensor is used and the circuit configuration is not complicated, the degree of freedom in exterior design is increased, the set can be made smaller, and cost increases can be prevented.

Further, since the gain of the AGC amplifier is not changed and the circuit configuration is not complicated, there is an effect that an increase in cost can be prevented.

Further, according to the embodiment, compared to the conventional method, it is possible to improve the dynamic resolution for general subjects and to prevent blurring of images due to excessive aperture of the iris outdoors.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the relationship between the illuminance level of the subject and the detection output level at each electronic shutter speed, and Fig. 3 is a diagram showing the relationship between the illuminance level of the subject and the detection output level at each electronic shutter speed. FIG. 4 is a flowchart explaining the processing in the microprocessor; FIG. 5 is a diagram showing the timing of the electronic shutter speed control signal and charge sweep from the CCD; FIG. 6 is a diagram showing the relationship between electronic shutter speeds; A diagram showing an electronic shutter speed table and FIG. 7 are diagrams each illustrating a mechanism for generating flicker. Explanation of main symbols in the drawings 2: Near iris, 3: CCD, 6: Detection circuit,
7: Iris motor, 9: Microprocessor, 1
0: Position detection sensor, 13.14: Driver circuit, LDA, LDB: Detection output level.

Claims (1)

[Scope of Claims] Automatic exposure means that automatically controls the opening amount of the iris according to the illuminance of the subject and maintains a constant level of imaging output, and an electronic shutter speed within the control range of the automatic exposure means. (1/100) seconds, and when the level of the output signal of the solid-state image sensor falls below a predetermined value outside the control range of the automatic exposure means, the electronic shutter speed is set to (1/100) seconds.
00) seconds to a slow speed.