JPH0752926B2 - Storage time switching solid-state imaging device - Google Patents

Description

Description: INDUSTRIAL APPLICABILITY The storage time switching image pickup device of the present invention is used for a television camera, especially for a single-panel television camera, and the storage time mode is automatically switched so that anyone can use it easily. Suitable as a home camera that can

2. Description of the Related Art FIG. 9 shows a solid-state image pickup element used in a conventional image pickup apparatus. Figure 9 is a schematic diagram of an interline CCD.
Is a photodiode for converting an optical signal into an electric signal, 102 is a CCD for scanning in the vertical direction (hereinafter V-CCD), 103 is a CCD for scanning in the horizontal direction (hereinafter H-CCD), 104 is a photoelectrically converted charge Is a floating diffuser amplifier (hereinafter FDA) that converts to voltage. Photodiodes marked with ○ are read to the odd field V-CCD, and △
The marked photodiodes are even field V-CCDs.
, And are sequentially scanned in the vertical and horizontal directions.
For example, the signal of the photodiode 101-a is V-CCD
It is transferred from the position of 102a with the electrode of V ₁ , and is transferred in the vertical direction for each horizontal scanning. Set the V-CCD electrode to V _{1 to} V ₄
Then, the voltage waveforms of V _{1 to} V ₄ are shown in FIG. 10 (a). The signal charge is transferred to the electrode with a high applied voltage, and V ₁ to V ₄
Are sequentially transferred to the electrodes. H for horizontal scanning
Similarly for −CCD, voltage is sequentially applied to the electrodes from H ₁ to H ₄ . The voltage waveform is shown in FIG. 10 (c). In this way 1
When the scanning of the field is completed, the signal charge of the next field is read out to V-CCD. When the scanned field is an odd field marked with a circle, the next field is an even field marked with a triangle, and scanning is performed by applying the voltage shown in FIG. 10 (b). Therefore, the period for reading out the signal charges from the same photodiode is every two fields, and the accumulation time is 1/60 seconds when one field is 1/60 second.
30 seconds.

Problems to be Solved by the Invention In an image pickup apparatus in which a CCD is driven and scanned in this way, an image with less flicker can be obtained for image pickup when illuminated with flicker such as a fluorescent light, but a moving object such as There is a problem that an image obtained when a car or the like is imaged is out of focus.

As a second conventional example, as shown in FIG. 11, there is a method in which the reading method from the photodiode is changed so that the accumulation time is one field time. Reads simultaneously signal charges from the first ○ mark photodiodes 101a and 101b in the odd field to the electrodes of V ₃ of V-CCD. Figure 12 (a) shows the voltage waveform
Shown in. Scanning in the vertical direction is the same as in the first conventional example.
To sequentially transferred to V ₁ ~V ₄ per horizontal scan. In this way, signals are read out from all the photodiodes in the same field. In the next even field, the photodiode 10 marked with a triangle
Simultaneously the signal charge from 1b and 101c reads the electrode V ₃ of V-CCD. The voltage waveform is shown in FIG. 12 (b). By reading the signal from the photodiode in this way, the accumulation time is set to 1 field for 1/60 seconds, and there is an image in which blurring of an image when a moving object is imaged is improved. However, in this case, there is a problem in that an image picked up at the time of illumination with flicker such as a fluorescent lamp has a lot of flicker.

A third conventional example is disclosed, for example, in JP-A-57-178480. In this example, the driving method of the image sensor is switched to switch between the frame storage and the field storage shown in FIGS. 10 and 12, and a high resolution method for moving images and fluorescence in one imaging device. It is possible to switch between methods that are less affected by flicker due to lighting.

However, in this method, the way the pixel signals are mixed is different until the pixel signals are obtained as output signals from the image sensor. Therefore, there is a problem that it cannot be used in a single-plate color camera in which a mosaic color filter is attached to the image pickup element and color separation is performed by using the level difference of image signals.

In view of the above point, the present invention switches the storage time in the single-chip color camera between the frame cycle and the field cycle, eliminates the signal level change at the time of switching, and further determines whether the condition of the object being imaged, for example, the amount of light is sufficient. , The flicker is large or small, and the motion of the subject is large or small, the accumulation time is automatically switched, and the dynamic resolution according to the S / N of the reproduced image, the amount of flicker and the accumulation time is the best. It is an object of the present invention to provide a storage-time switching solid-state imaging device that can realize a single-plate color camera that performs control to achieve the above state.

Means for Solving the Problems In order to achieve the above object, the present invention provides a solid-state image sensor for converting an optical image into an electric signal, and a period of one cycle (hereinafter, accumulation) when the solid-state image sensor converts light into an electric signal. Storage time control circuit for switching the time), a narrowing control circuit for controlling the amount of light incident on the solid-state image sensor, a gain control circuit for varying the signal level of the solid-state image sensor, and a storage in the storage time control circuit. When the time is switched, the gain control circuit controls the increase / decrease of the output signal level of the image pickup device and the system control circuit for controlling the narrowing control circuit to keep the signal level constant. A flicker detection circuit that detects that the ratio is equal to or higher than a certain ratio, or a motion detection circuit that detects that the motion of the imaged subject is equal to or greater than a predetermined value, or the amount of illumination light is equal to or greater than a predetermined value. Switches the storage time based on one or more of the detection results of the three detection circuits of the level detection circuit for performing the following detection, and the system control circuit sets the storage time to one frame. Scan period (hereinafter frame accumulation mode) or 1 field scan period (hereinafter field accumulation mode)
When the frame storage mode is switched to the field storage mode, the gain of the gain control circuit is doubled after one field scanning period, and then the narrowing control circuit is controlled to double the amount of light. The gain of the gain control circuit is controlled so that the gain of the gain control circuit is gradually halved at the same time so that the output of the gain control circuit does not fluctuate in the signal level. When the condition for switching to the frame accumulation mode is reached, the squeezing control circuit is controlled to gradually close the squeezing until the amount of light becomes 1/2, and at the same time, the gain of the gain control circuit is gradually doubled. Control so that the signal level does not fluctuate at the output of the gain control circuit, and then the field accumulation mode is changed to the frame accumulation mode. Toggles, from the switching of the mode 1
After the field scanning period, the gain of the gain control circuit is halved.

The present invention detects the opening / closing ratio of the squeezing portion by the squeezing control circuit having the above-described configuration, changes the driving method of the image sensor in a state in which the squeezing is closed for a certain amount or more, and changes the signal charge during accumulation of one field at high speed. The drive mode is set by resetting by transfer to shorten the accumulation time, and a change in signal level caused by a change in the accumulation time is controlled by a gain control circuit and a narrowing control circuit. The flicker of the illumination light is determined by detecting the flicker state of the image pickup signal and the movement of the subject, and determining whether the flicker of the illumination light is a problem or the blur (dynamic resolution) due to the movement of the subject is a problem. When there is a problem, the accumulation time is lengthened (frame accumulation mode), and when the illuminance is high and the blur of the captured image due to the movement of the subject is a problem, the accumulation time is shortened (field accumulation mode). It is possible to solve the problems of flicker and blurring (dynamic resolution) of the captured image.

Practical Example FIG. 1 is a block diagram of a storage time switching solid-state image pickup device according to a first embodiment of the present invention. First
In the figure, 1 is a diaphragm for controlling the amount of incident light, 2 is an image sensor for converting an optical image into an electric signal, 3 is a gain control circuit for varying the signal level, and 4 is a process circuit for converting the image signal into a target signal format. Reference numeral 5 is a level detection circuit that detects the signal level of the image sensor, 6 is a squeezing control circuit that controls the squeezing opening and closing according to an input signal, and 8 is a system control circuit that determines the operating conditions of the imaging device according to the imaging conditions. is there.

The operation of the storage time switching solid-state imaging device of the present embodiment configured as described above will be described below.

The configuration of the image sensor 1 and the mosaic filter are shown in FIG.
It shows in (b). The image pickup device 1 is a conventionally used interline CCD, 11 is a photodiode, 12 is a V-CCD for transferring and scanning a signal charge in a vertical direction, 13
Is an H-CC that performs scanning by transferring signal charges in the horizontal direction
D and 14 are floating diffusion amplifiers (FDA) that convert signal charges into voltages and output them, and FIG. 2B is a mosaic filter attached to the front surface of this image sensor. W is a color filter that transmits all colors, G is a green color, Y _e is a yellow color, and C _y is a cyan color. The color filter 15a is placed on the photodiode 11a, and the color filter 15b is placed on the photodiode 11b. Similarly, the photodiode of the image sensor corresponds to each mosaic color filter.

Drive pulses applied to the image sensor are shown in FIG. The upper part of the figure shows the positional relationship of the pulses in the frame storage mode, and the lower part shows the positional relationship of the pulses in the field storage mode. The V pulses 28 and 30 drive the V-CCD 12,
The H pulses 29 and 31 drive the H-CCD 13. twenty four~
The pulses other than the 26 V high-speed transfer pulse are shown in FIG.
It is the same as that shown in (c). The operation of the image sensor in each accumulation mode is as follows. First, in the frame accumulation mode, the photodiode signal is the read pulse 21
Are read alternately for each field. In FIG. 2 (a), the photodiodes 11a and 11c marked with a circle are read in odd fields, and the photodiodes 11b marked with a triangle are read.
Read from 11d etc. into an even field. This is a conventionally used signal reading mode, and a single-chip color camera (imaging device) is formed by using a mosaic color filter capable of color separation in this mode. Pixel signals of W, G, C _y , and Y _e are read in each field, and the process circuit of 4 performs color separation as in the following equation.

R indicates a red signal, B indicates a blue signal, and Y indicates a luminance signal. The process circuit 4 performs white balance, gamma correction, matrix processing, etc. on these signals, converts them into NTSC signals, and outputs them.

V is within blanking in field accumulation mode
Add high-speed transfer pulses 24-26. If the 21 read pulse is in the odd field, the read pulse 24 reads the signal from the even field photodiode. If the 21 read pulses are in the even field, the 24 read pulses are read from the odd field. After reading, a pulse 25 for high speed transfer is applied to the V-CCD 12. Normal V transfer is approximately 15.8KHz once in 1H scanning period, but high speed transfer pulse is 200KHz
The frequency is set to about 1 MHz so that the vertical scanning is completed within the V blanking. Horizontal scanning is not performed during high-speed transfer, all electrodes of H-CCD13 are set to high potential, and FDA
The charges transferred from the unit 14 are read out.

In this way, by reading the charges from the photodiodes separately from the signal reading, it is possible to perform frame reading with only a short storage time. That is, reading of the field accumulation frame can be realized. By using this readout method, the pixel signal readout relationship does not change even if the storage time is switched, so it is possible to switch the storage time of the image sensor in a single-chip color camera that performs color separation based on the signal level difference for each pixel. Becomes

Next, control of the signal level when switching between the field storage mode and the frame storage mode will be described.

FIG. 4 shows the amount of light, opening / closing of the aperture, the signal level of the image pickup device, the gain of the gain control circuit, and the output signal level of the image pickup apparatus. The horizontal axis is time. quantity increases before and after t _1, the control value of the iris in t ₁ is closed to the reference level 1. At this point, the system control circuit 8 controls the drive circuit 7 to switch the storage mode of the image sensor from the frame storage mode to the field storage mode. Therefore, the signal level of the image sensor is reduced to 1/2 at the time of switching. The system control circuit 8 controls the gain control circuit 3 to control the gain from 1 to 2 at t ₁₀ after the mode switching 1 field scanning period. Thus, the gain control circuit is gradually opened after controlling the accumulation mode and the gain control circuit, and the gain of the gain control circuit is gradually decreased from 2 to 1 (time period from t _{1 to} t ₂ ) in this way, with the signal level kept constant. By lowering the gain of 1 to 1, the switching from the frame accumulation mode to the field accumulation mode is completed. Next, switching from the field storage mode to the frame storage mode will be described. Down light quantity before and after the time t _3, the control of the aperture is opened up to the reference level 2. At this time, the system control circuit 8 controls the squeeze and the gain control circuit to gradually close the squeeze and raise the gain to 2. At this time, control is performed so that the signal level after gain control is constant. The gain of the gain control circuit became 2 t ₄
At the point of time, the field accumulation mode is switched to the frame accumulation mode, and after one field scanning time, at t ₂₀ , the gain of the gain control circuit is returned to 2 to 1. In this way, it becomes possible to switch the storage mode without changing the output signal level of the image pickup apparatus.

As described above, according to the present embodiment, the system control circuit simultaneously controls the drive mode, the gain control circuit, and the squeezing control circuit of the image pickup device, so that the frame accumulation in the single-chip color camera using one image pickup device is performed. It is possible to switch between the mode and the field storage mode, and it is possible to eliminate the fluctuation of the signal level at the time of switching the mode.

FIG. 5 is a block diagram of a storage time switching solid-state imaging device showing a second embodiment of the present invention. In the figure, 1 is a diaphragm for controlling the amount of light incident on the image pickup device, 2 is an image pickup device for converting an optical image into an electric signal, 3 is a gain control circuit for changing the gain of a circuit system, and 5 is a level detection for detecting a signal level. The circuit, 7 is a drive circuit for operating the image pickup device 2, and the above is the same as the configuration of FIG. The difference from the configuration of FIG. 1 is that the narrowing control circuit 30 operates independently and is not controlled by the system control circuit 31, and the system control circuit 31 drives the drive circuit 7 to switch the accumulation mode of the image sensor.
That is, the gain control circuit 3 is controlled.

The operation of the storage time switching solid-state image pickup device of the second embodiment configured as described above will be described below.

The drive mode of the image sensor 2 is the same as that of the first embodiment,
There are frame accumulation mode and field accumulation mode. In the field accumulation mode, the signal charges in one field are reset by high-speed transfer during V-blanking, and the charges in the remaining fields are read out in the same manner as in normal frame accumulation. The frame accumulation mode is a normal mode without high-speed transfer within V blanking. The control at the time of switching between these two modes is shown in FIG.

The amount of light increases before and after time t ₁ , and the element output reaches the reference level 1 at time t ₁ . At time t ₁ , the frame storage mode is switched to the field storage mode. At this time, the image sensor 1
Output becomes 1/2, the gain of the gain control circuit is doubled at t ₁₀ after one field scanning period. The output of the image sensor increases as the amount of light increases, and the gain of the gain control circuit is lowered accordingly. Next, switching from the field storage mode to the frame storage mode will be described. Before and after the time t ₄ , the light amount decreases and the level of the output of the image pickup device becomes the reference level 2 at the time t ₄ . At time t ₄ , the field storage mode is switched to the frame storage mode. At this time, since the output level of the image pickup element is doubled, the gain of the gain control circuit is reduced to 1/2 at t ₂₀ after one field scanning period and the output level of the signal is fixed as an image pickup apparatus to switch the accumulation mode. .

As described above, according to the present embodiment, it is possible to perform mode switching of the image sensor without changing the output signal level, without controlling the squeezing circuit from the system control circuit.

In the first and second embodiments described above, the storage mode is switched depending on the state of the light amount of the illumination. Next, a third embodiment will be described in which the storage mode is switched depending on the size of the flicker of the illumination light and the size of the motion of the subject.

FIG. 7 is a block diagram of a storage time switching solid-state imaging device showing a third embodiment of the present invention. In the figure, 1 to 7 are the same as the configuration of the first embodiment (FIG. 1), and a description thereof will be omitted. The configuration different from that of FIG. 1 is a flicker detection circuit 40, a motion detection circuit 41, and a system control circuit 42.
The decision to switch the accumulation time is made not only by the illuminance but also by the flicker state and the image movement state. Since the control of the squeezing control circuit 6, the gain control circuit 3 and the drive circuit 7 at the time of switching the accumulation time is the same as that of the first embodiment, the description thereof will be omitted.

The operation of the flicker detection circuit and the motion detection circuit and the method of determining the accumulation time switching will be described below. FIG. 8 (a) is a block diagram of the flicker detection circuit, and 40a is a bandpass filter (hereinafter BPF) 40b is a level detection circuit. In a discharge tube such as a fluorescent lamp, if the power supply is 50Hz, the flicker of 20Hz or 10Hz will be included in the image pickup signal depending on the relationship with the field accumulation time of 1/60 seconds. Therefore, the BPF 40a separates frequency components of 20 Hz and 10 Hz from the image pickup signal, and the level detection circuit 40b determines the magnitude of the separated components.

FIG. 8 (b) is a block diagram of the motion detection circuit.
Is a memory for delaying a signal in one field or one frame period, and 41b is a motion detection circuit for calculating a motion amount by obtaining a difference between picked-up images from two image signals at different times.

Next, the decision of switching the storage mode is made according to the flow chart shown in FIG.

The system control circuit 42 makes the above determination to switch the accumulation time. By performing such control, the flicker is reduced as the frame accumulation mode under the illumination where the flicker becomes large, and when the motion of the imaged subject is large, it is switched to the field accumulation mode with high dynamic resolution.
Furthermore, when the amount of illumination light is low, it is possible to automatically determine the conditions for obtaining a high-quality image, such as switching to the frame accumulation mode with a good S / N ratio of the signal, and it is possible to capture a high-quality image and However, it is possible to realize a user-friendly video camera (imaging device) that can be used.

In the present embodiment, the single-chip camera using the WGC _y Y _e complementary color filter has been described, but it is possible to use all the other color filters used for frame accumulation even in the Bayer method using the RGB primary color filters. Needless to say.

Although the present embodiment has been described by taking a single-plate color camera using one image pickup device as an example, it goes without saying that it can be applied to a multi-plate camera.

Further, the determination of the storage mode switching need not be limited to the present embodiment, and it is needless to say that the determination may be made based on the combination of the three conditions of the illumination light amount, the flicker, and the movement of the captured image, which have a strong required degree. Further, the method of judging these three conditions is not limited to the present embodiment, and it is natural that the judgment is changed according to the purpose, and it is naturally possible to judge by adding other conditions.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to switch the accumulation time even in a single plate color camera. Also, since there is no change in the signal level at the time of switching, it is possible to arbitrarily switch during image capturing, for example, automatic switching of the storage time using changes in the amount of light is also possible, and it is possible to use frame storage mode for illumination under fluorescent light. It is possible to realize an image pickup device capable of reducing the influence of flicker and setting the field storage mode in a bright outdoor place to pick up an image with high dynamic resolution (less blur), and its practical effect is large.

[Brief description of drawings]

FIG. 1 is a block diagram of a storage time switching solid-state imaging device according to an embodiment of the present invention, FIG. 2 (a) is a schematic diagram showing the structure of an image sensor, and FIG. 2 (b) is a schematic diagram showing the structure of a color filter. FIG. 3 is a time chart showing the drive timing of the image pickup device, FIG. 4 is a waveform chart showing the operation relationship of each block,
FIG. 5 is a block diagram of a storage time switching image pickup apparatus according to the second embodiment of the present invention, FIG. 6 is a waveform diagram showing an operation relation of each block of the second embodiment, and FIG. 3 is a block diagram of a storage time switching solid-state imaging device according to the third embodiment;
FIG. 8 (a) is a circuit diagram of the flicker detection circuit, and FIG. 8 (b).
Is a configuration diagram of a motion detection circuit, FIG. 7C is a flowchart showing a procedure for determining whether to switch the storage mode, and FIGS. 10 (a) to (c) and FIG. 12 (a),
(B) is a waveform diagram showing a drive pulse of a conventional image sensor. 1 ... Squeezing, 2 ... Imaging element, 3 ... Gain control circuit,
4 ... Process circuit, 5 ... Level detection circuit, 6,30 ...
Squeezing control circuit, 7 ... drive circuit, 8,31, 42 ... system control circuit, 40 ... flicker detection circuit, 41 ... motion detection circuit, 40a ... bandpass filter, 40b ... level determination circuit, 41a ...... Memory, 41b …… Variation amount calculation circuit, 11 ……
Photodiode, 12 ... Vertical CCD, 13 ... Horizontal CCD, 14 ...
Floating diffusion amplifier, 15 ... Mosaic color filter, 20 ... Vertical transfer pulse, 21,24 ... Readout pulse, 22 ... Horizontal blanking part, 23 ... Horizontal transfer pulse, 25 ... Vertical high-speed transfer pulse, 26 ... Vertical blanking section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-37777 (JP, A) JP-A-60-18069 (JP, A) JP-A-57-4672 (JP, A) Actual development Sho-60- 50568 (JP, U)

Claims (4)

[Claims] 1. A solid-state image sensor for converting an optical image into an electric signal, and a storage time control circuit for switching one cycle time (hereinafter referred to as storage time) when the solid-state image sensor converts light into an electric signal.
A squeeze control circuit that controls the amount of light incident on the solid-state image sensor, a gain control circuit that changes the signal level of the solid-state image sensor, and an increase in the output signal level of the image sensor when switching the accumulation time in the accumulation time control circuit. A decrease is the gain control circuit and a system control circuit that controls the squeezing control circuit to keep the signal level constant. The accumulation time control circuit detects flicker of illumination light at a certain rate or more. One of the detection results of the three detection circuits, that is, a circuit, a motion detection circuit that detects the movement of the imaged subject is equal to or more than a predetermined value, or a level detection circuit that detects the illumination light amount is equal to or more than a predetermined value. The accumulation time is switched based on one or more results, and the system control circuit changes the accumulation time to one frame scanning period (hereinafter referred to as frame accumulation period). Product mode) or 1
When the field scanning period (hereinafter referred to as the field accumulation mode) is controlled and the frame accumulation mode is switched to the field accumulation mode, the gain of the gain control circuit is doubled after one field scanning period, and then the squeezing control circuit is controlled. Control is performed so that the aperture is gradually opened until the amount of light doubles, and at the same time, the gain of the gain control circuit is controlled to be gradually halved so that there is no fluctuation in the signal level at the output of the gain control circuit. In addition, when the condition for switching from the field accumulation mode to the frame accumulation mode is satisfied, the squeezing control circuit is controlled to gradually close the squeezing until the light amount becomes 1/2, and at the same time, the gain control is performed. The gain of the circuit is controlled to be gradually doubled so that the output of the gain control circuit does not change in signal level. From the field storage mode to the frame storage mode, and the gain of the gain control circuit is halved one field scanning period after the switching of this mode. 2. The system control circuit switches to the frame storage mode when the flicker detection circuit detects a predetermined amount or more of flicker, and switches to the field storage mode in other cases. A storage time switching solid-state imaging device according to the above item. 3. The system control circuit, when the flicker detection circuit detects a flicker of a predetermined amount or more, or when the flicker is a predetermined amount or less and the level detection circuit determines that the illumination light amount is a predetermined amount or less, a frame accumulation mode. 2. The storage time switching solid-state image pickup device according to claim 1, wherein the solid-state imaging device is switched to the field accumulation mode in other cases. 4. The system control circuit, when the flicker detection circuit detects a flicker of a predetermined amount or more, or when the flicker is a predetermined amount or less and the motion detection circuit detects a motion of a predetermined value or less, and the level. When the detection circuit determines that the illumination light amount is less than or equal to a predetermined amount, it switches to the frame accumulation mode,
The storage time switching solid-state imaging device according to claim 1, wherein the field storage mode is switched in other cases.