JP2003309773A - Device and method for image pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for image pickup by which an image free from mixing of noise accompanying a variation in substrate bias voltage can be obtained though the luminance of a subject is low. <P>SOLUTION: The image pickup device is provided with: a luminance calculation means for obtaining subject luminance from the image pickup signal of an imaging device; and an electric charge accumulation period control means for controlling the electric charge accumulation period of the imaging device at multiple temporal intervals of a vertical transferring period by prohibiting the electric charge discharging of the imaging device by an electric charge discharging pulse when the obtained subject luminance is lower than a prescribed value. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to exposure control of an image pickup device.

[0002]

2. Description of the Related Art In an image pickup apparatus using a CCD having a vertical overflow structure as an image pickup element, Japanese Patent Application Laid-Open No. 11-8802 discloses a technique for controlling the exposure amount of the image pickup element.
A so-called electronic shutter described in Japanese Patent Laid-Open No. 6-62323 is known.

In this technique, by applying a voltage to the substrate bias, the charges accumulated in the photoelectric conversion unit are discharged to the substrate side to start accumulating new charges, and from that time, the charges accumulated in the photoelectric conversion unit are started. The exposure amount is controlled by controlling the time until the data is read to the vertical transfer unit.

[0004]

However, when performing the above electronic shutter operation, since a high voltage continuous pulse (hereinafter referred to as "charge discharging pulse") is applied as the substrate bias voltage, the substrate bias causes voltage fluctuation. Sometimes it happened.

FIG. 9 is a diagram showing a timing chart when a voltage fluctuation occurs. A read pulse is applied to the vertical transfer clock at a specific point in the vertical synchronization period, and the charge accumulated in the photoelectric conversion unit is read to the vertical transfer path by the read pulse and sequentially transferred by the subsequent vertical CCD transfer pulse.

On the other hand, a charge discharging pulse is applied to the substrate bias to discharge the charges accumulated in the photoelectric conversion section. Since this charge discharge pulse has a high voltage, it causes a slight voltage fluctuation in the substrate bias between the time of pulse generation and the time of pulse stop.

Therefore, when the charge reading operation from the image pickup device is executed when the substrate bias voltage fluctuates due to the electronic shutter operation, there is a problem that noise due to the substrate bias is superimposed on the read signal. This problem is particularly noticeable when the output of the image sensor is amplified and read because the subject has low brightness.

FIG. 10 shows an image in which this noise is generated. Horizontal stripes (upper and lower steps) are generated in the image due to the mixing of noise accompanying the fluctuation of the substrate bias voltage.

The present invention has been made in view of the above circumstances, and an image pickup apparatus and an image pickup method capable of obtaining an image in which noise is not mixed due to fluctuations in the substrate bias voltage even when the subject has low luminance. The purpose is to provide.

[0010]

SUMMARY OF THE INVENTION To solve the above-mentioned problems, the present invention provides a brightness calculating means for obtaining a subject brightness from an image pickup signal of an image pickup device, and an electric charge when the obtained subject brightness is lower than a predetermined value. An image pickup apparatus comprising: a charge accumulation time control unit that prohibits charge discharge of the image sensor by a discharge pulse and controls the charge accumulation time of the image sensor at a time interval that is an integral multiple of the vertical transfer period.

According to the present invention, in the image pickup device according to the above-mentioned invention, when the charge storage time is controlled at a time interval that is an integral multiple of the vertical transfer period, the amplification degree or aperture value of the output signal of the image pickup device. The image pickup apparatus is provided with an exposure control unit that controls the amount of accumulated charge.

Further, according to the present invention, the subject brightness is obtained from the image pickup signal of the image pickup device, and when the obtained subject brightness is lower than a predetermined value, the charge discharging of the image pickup device by the charge discharging pulse is prohibited, and the vertical transfer period is stopped. Is an imaging method for controlling the charge accumulation time of the image sensor at time intervals that are an integral multiple of.

According to the present invention, in the image pickup method according to the above-mentioned invention, when the charge accumulation time is controlled at a time interval which is an integral multiple of the vertical transfer period, the amplification degree or aperture value of the output signal of the image pickup device. Is an imaging method for controlling the amount of accumulated charge.

[0014]

1 is a block diagram showing the structure of an image pickup apparatus to which the present invention is applied.

The present image pickup apparatus includes a lens group including a zoom lens 111 and a focus lens 112, a diaphragm mechanism 113 for controlling exposure, a CCD image pickup element 16 for converting a subject image into an electric signal, and signals from the CCD image pickup element 16. An image pickup circuit 2 for converting into a digital signal, an AE processing section 3, an AF processing section 4, an image processing circuit 5, which is connected to the signal bus 100 and performs various processing on the digitalized image pickup signal.
A nonvolatile memory 6, a built-in memory 7, a compression / expansion unit 8, a removable memory 9, and an LCD driver 10 are provided.

Further, the present image pickup apparatus has a main CPU 1 for overall control of each section, an input section 12 including various operation switches, an LCD 17 for displaying an operation state and a mode state, and a drive control for a lens. Zoom control unit 101, focus control unit 102, motors 121 and 12
2. A diaphragm control unit 103 for controlling the diaphragm 113, a motor 123, and a TG circuit 1 for controlling the CCD 15.
4, a CCD driver 15, a speaker 13 for outputting an alarm, and a power supply unit 11.

In the present image pickup apparatus, the main CPU 1 centrally performs all the control, and particularly the exposure control and CC
It is responsible for a series of processing related to image reading and signal reading by driving control of the D image sensor 16.

Next, the operation of the image pickup apparatus will be described.
The input unit 12 is provided with various operation switches such as a zoom lever, a release switch, and a power switch.
Here, when the photographer operates the release SW and pushes it in one step, AE and AF operations are performed.

In the AE operation, the image signal from the image pickup circuit 2 is taken into the AE processing section 3. The AE processing unit 3 calculates an AE evaluation value obtained by integrating image signals in a predetermined area, and transmits the AE evaluation value to the main CPU 1.

In the main CPU 1, the AE evaluation value is compared with an internal reference value, and when it is determined that the brightness of the subject is low, for example, the amplification factor of the image pickup circuit 2 is increased through the TG circuit 14, or the aperture is stopped. Aperture 1 via control unit 103
Instructions such as opening 13. In this way, appropriate exposure control is executed.

Next, the AF operation is performed. The image signal from the image pickup circuit 2 is input to the AF processing unit 4, and the AF processing unit 4
Then, the high frequency component is extracted from the image signal by the filtering process. Then, the AF evaluation value or the contrast value obtained by integrating the high frequency components is calculated, and the calculated value is transmitted to the main CPU 1. The main CPU 1 controls the focus controller 102 to drive the motor 122 so that the AF evaluation value becomes maximum. Focusing control is executed in this manner.

When the release SW is pushed in two steps, a normal photographing operation is started. The image of the subject is formed on the image sensor 16 via the zoom lens 111, the focus lens 112, and the diaphragm 113. Then, the image sensor 1
The image pickup signal generated in 6 is input to the image pickup circuit 2 and is input to the CDS.
After being subjected to processing such as (correlated double sampling) and signal amplification, it is converted into a digital signal and output to the signal bus 100.

The signal bus 100 has an AE processing unit 3,
The AF processing unit 4, the image processing circuit 5, the non-volatile memory 6, the built-in memory 7, the compression / expansion unit 8, the removable memory 9, the LCD driver 10, and the like are connected.

The image data from the image pickup circuit 2 is temporarily buffered in the built-in memory 7 and then processed in the image processing circuit 5 such as Y / C and color matrix. Then, the image is compressed in the compression / expansion unit 8 and stored in the removable memory 9. On the other hand, the image data from the image pickup circuit 2 is input to the LCD driver 10 as a video signal and displayed on the LCD 17 as a through image.

When the photographer performs an image reproducing operation, the image data stored in the removable memory 9 is read out, and the compression / expansion unit 8 performs expansion processing.
The image is converted into an image of a required size by the image processing circuit 5, and the LCD is displayed.
It is input to the driver 10 and displayed on the LCD 17.

The nonvolatile memory 6 stores various programs or set values for performing the above-described processes.

FIG. 2 is a diagram showing the configuration of the CCD image pickup device 16 and the drive circuit. The CCD image pickup device 16 is composed of photosensors 22, a vertical transfer path 23, a horizontal transfer path 24, and an output amplifier 25 which are arranged in a matrix in the image pickup area.

The vertical transfer path 23 is a register which is provided corresponding to the vertical column of each photosensor 22 and which reads the accumulated charge from each photosensor 22 and transfers it in the vertical direction. The horizontal transfer path 24 is a register that transfers the charges transferred from the vertical transfer path 23 in the horizontal direction. Then, the output amplifier 25 converts the charges transferred from the horizontal transfer path 24 into a voltage and amplifies it.

The CCD driver 15 discharges the vertical transfer pulses φV1 to φV4 for driving the vertical transfer path 23, the horizontal transfer pulses φH1 and φH2 for driving the horizontal transfer path 24, and the charge accumulated in the photosensor 22. A pulse φSUB is generated. The pulse output operation of the CCD driver 15 is controlled by the TG circuit 14.

FIG. 3 is a program diagram showing an exposure control method according to the present invention, and FIG. 4 is a flow chart showing a schematic exposure control procedure. The exposure control method according to the present invention will be described below with reference to FIGS.

When the image pickup apparatus is displaying a through image (S1), the AE evaluation value is obtained from the image signal (S).
2) Calculate the subject brightness Bv based on the value (S)
3). Then, the exposure control method is selected according to the value of the subject brightness Bv.

The exposure calculation uses the apex calculation represented by the equation (1). Ev = Av + Tv = Sv + Bv (1) where Ev: exposure, Av: aperture, Tv: shutter speed,
Sv: When the amplification subject brightness Bv is 3 or more, the amplification Sv is set to 5 (ISO = 100) and the aperture Av is set to 3 (Fno = 2.8) according to the program diagram. Then, the shutter speed Tv
Is calculated from the apex operation of equation (2) (S5). Tv = Sv + Bv-Av (2) Then, the exposure is set using these values (S1).
0).

FIG. 5 is a time chart showing the exposure control operation. When the image pickup apparatus is displaying a through image, as shown in FIG. 5, a read pulse is output in synchronization with the interval of the vertical synchronizing signal, and the above-described exposure calculation and exposure setting are repeatedly executed in sequence. Has been done. Here, the interval of the vertical synchronizing signal is called a frame period.

In FIG. 5, the charges accumulated in the exposure time shown in the exposure in the first frame period are read in the second frame period, and the AE evaluation value is calculated based on this value, and the above-mentioned method is used. By this, an appropriate exposure time is calculated. Then, the resulting proper exposure value is set in the third frame period and reflected in the exposure time indicated by the exposure in the fourth frame period.

In FIG. 4, when the subject brightness Bv is 0 or more and less than 3, according to the program diagram, the shutter speed T
v = 5 (shutter speed = 1/30) and the aperture Av is 3 (F
no = 2.8). Then, the amplification degree Sv is calculated by the equation (3).
It is obtained by the apex operation of (S6). Sv = Tv + Av-Bv (3) Then, the exposure is set using these values (S1).
0).

FIG. 6 is a time chart showing the operation of exposure control. In this figure, the read pulse is output in synchronization with the interval of the vertical synchronizing signal, but unlike FIG. 5, the charge discharging pulse is not output. This is because the shutter speed is matched with the cycle of the vertical synchronizing signal, so that the discharging operation is unnecessary. Therefore, in this operation, since the charge discharging pulse is not output, the through image without noise can be obtained without changing the substrate bias voltage.

In FIG. 6, the charges accumulated in the exposure time shown in the exposure in the first frame period are read out in the second frame period, and the AE evaluation value is calculated based on this value, and the above-mentioned method is used. Exposure time is 1/30
Is calculated. The proper exposure value obtained as a result is set in the third frame period and is set to stop the output of the charge discharging pulse, and is reflected in the exposure time indicated by the exposure in the fourth frame period.

In FIG. 4, when the subject brightness Bv is -1 or more and less than 0, the shutter speed Tv = 4 (shutter speed = 1/15) and the aperture Av is 3 according to the program diagram.
(Fno = 2.8). Then, the amplification degree Sv is obtained by the apex operation of the equation (3) (S7). And
The exposure is set using these values (S10).

FIG. 7 is a time chart showing the operation of exposure control. In this figure, the read pulse is output in synchronization with a cycle twice the interval of the vertical synchronizing signal, and unlike FIG. 5, the charge discharging pulse is not output. This is because the discharge operation is unnecessary by making the shutter speed coincide with the cycle of twice the vertical synchronizing signal. Therefore, in this operation, since the charge discharging pulse is not output, the through image without noise can be obtained without changing the substrate bias voltage.

In FIG. 7, the charge accumulated during the exposure time shown in the exposure in the first and second frame periods is read out in the third frame period, and A is calculated based on this value.
E The evaluation value is calculated and the exposure time is reduced to 1 /
The calculation of 15 is performed. The proper exposure value obtained as a result is set in the fourth frame period and is set to stop the output of the charge discharging pulse, and is reflected in the exposure time indicated by the exposure in the fifth and sixth frame periods. .

In FIG. 4, when the subject brightness Bv is not less than −2 and less than −1, the shutter speed Tv = 3 (shutter speed = 1 / 7.5) and the aperture Av is 3 (Fno = Fno = according to the program diagram). 2.8). Then, the amplification degree Sv is obtained by the apex operation of the equation (3) (S8). And
The exposure is set using these values (S10).

FIG. 8 is a time chart showing the operation of exposure control. In this figure, the read pulse is output in synchronization with a cycle four times the interval of the vertical synchronizing signal, and unlike FIG. 5, the charge discharging pulse is not output. This is because the shutter speed is made to coincide with the cycle of four times the vertical synchronizing signal, so that the discharging operation is not required. Therefore, in this operation, since the charge discharging pulse is not output, the through image without noise can be obtained without changing the substrate bias voltage.

In FIG. 8, the charges accumulated during the exposure time shown in the exposure in the first to fourth frame periods are read out in the fifth frame period, and A is calculated based on this value.
E The evaluation value is calculated and the exposure time is reduced to 1 /
The calculation of 7.5 is performed. The proper exposure value obtained as a result is set in the eighth frame period and is set to stop the output of the charge discharging pulse, and is reflected in the exposure time in the subsequent frame periods.

In FIG. 4, when the subject brightness Bv is not less than -3 and less than -2, the shutter speed Tv = 2 (shutter speed = 1 / 3.75) and the aperture Av is set according to the program diagram.
Is 3 (Fno = 2.8). Then, the amplification degree Sv is obtained by the apex operation of the equation (3) (S9). Then, the exposure is set using these values (S10).

Also in this exposure control operation, similarly to the above-mentioned operation, the read pulse is output in synchronization with the cycle of eight times the interval of the vertical synchronizing signal, and unlike FIG. 5, the charge discharging pulse is not output. Therefore, in this operation, since the charge discharging pulse is not output, the through image without noise can be obtained without changing the substrate bias voltage.

In this embodiment, the subject brightness Bv is 3
However, the present invention is not limited to this mode, and the charge ejection pulse may be suppressed when the subject brightness Bv is less than a value other than 3. good. Further, the values of the shutter speed Tv and the aperture Av at that time may be appropriately selected.

Further, in the present embodiment, the read pulse is output in synchronization with a cycle that is an even multiple of the interval of the vertical synchronizing signal, but the present invention is not limited to this form.
The read pulse may be output in synchronization with a cycle that is an integral multiple of the interval of the vertical sync signal.

Further, in the exposure control according to the program diagram, the amplification degree Sv is changed and controlled, but the diaphragm Av may be controlled.

Although the through image noise reduction method has been described in the present embodiment, the present invention is not limited to this embodiment, and a person skilled in the art can easily configure it to be applied to the main exposure. Can be implemented in

Each function according to the present invention has a main CPU.
It may be realized by incorporating it as a program in 1 or may be configured by using hardware.

Since the embodiments include inventions at various stages, various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the problem described in the section of the problem to be solved by the invention can be solved, and the effect described in the section of the effect of the invention can be solved. When the above is obtained, a configuration in which this constituent element is deleted can be extracted as an invention.

[0052]

As described above, according to the present invention, it is possible to obtain an image in which noise is not mixed with the variation of the substrate bias voltage even if the subject has low luminance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image pickup apparatus to which the present invention is applied.

FIG. 2 is a diagram showing a configuration of a CCD image sensor and a drive circuit.

FIG. 3 is a program diagram showing an exposure control method according to the present invention.

FIG. 4 is a flowchart showing a schematic exposure control procedure.

FIG. 5 is a time chart showing the operation of exposure control.

FIG. 6 is a time chart showing the operation of exposure control.

FIG. 7 is a time chart showing the operation of exposure control.

FIG. 8 is a time chart showing the operation of exposure control.

FIG. 9 is a diagram showing a timing chart when a voltage change occurs.

FIG. 10 is a diagram showing an image in which noise is generated.

[Explanation of symbols]

1 ... Main CPU 2 ... Imaging circuit 3 ... AE processing unit 14 ... TG circuit 15 ... CCD driver 16 ... CCD image sensor 113 ... Aperture 22 ... Photo sensor 23 ... Vertical transfer path 24 ... Horizontal transfer path 25 ... Output amplifier

Claims (4)

[Claims] 1. An image pickup apparatus for controlling a charge accumulation amount of an image pickup device by changing an interval between a charge discharging pulse and a charge read pulse applied to the image pickup device, wherein object brightness is obtained from an image pickup signal of the image pickup device. Luminance calculation means, and when the obtained subject luminance is lower than a predetermined value, charge discharge of the image pickup device by the charge discharge pulse is prohibited, and the image pickup device of the image pickup device is timed at an integer multiple of a vertical transfer period. An image pickup apparatus comprising: a charge storage time control unit that controls a charge storage time. 2. The exposure control means for controlling the charge storage amount by the amplification degree or aperture value of the output signal of the image pickup device when the charge storage time is controlled at a time interval which is an integral multiple of the vertical transfer period. The image pickup apparatus according to claim 1, further comprising: 3. An image pickup method of controlling an amount of accumulated charge of the image pickup device by changing an interval between a charge discharging pulse and a charge read pulse applied to the image pickup device, wherein object brightness is obtained from an image pickup signal of the image pickup device. If the obtained subject brightness is lower than a predetermined value, the charge discharge of the image sensor by the charge discharge pulse is prohibited, and the charge accumulation time of the image sensor is set to an integer multiple of the vertical transfer period. An image pickup method characterized by controlling. 4. When the charge storage time is controlled at a time interval that is an integral multiple of the vertical transfer period, the charge storage amount is controlled by the amplification degree or aperture value of the output signal of the image sensor. The imaging method according to claim 3.