JP2009177669A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device with the deeper objective depth of a shooting object and less image blur in case of a clear shooting object, by ensuring exposure controlling performance in controlling the exposure using the adjustment of an exposure time and a gain in addition to the adjustment of a diaphragm, and by using control of the diaphragm. <P>SOLUTION: The imaging device is equipped with: a diaphragm controlling means 1 for regulating an optical volume from the shooting object; an amplifying means 4 variable in gain for amplifying the output of an imaging element 3; an exposure-volume detecting means 7 for obtaining the exposure volume on the basis of the output of the imaging element 3; an exposure controlling means 6 for controlling the gain of the amplifying means 4 and the exposure time of the imaging element 3, using the exposure volume detected by the exposure-volume detecting means 7; and a diaphragm controlling means 8 for controlling the degree of the diaphragm in the diaphragm controlling means 1, based on the exposure volume, the exposure time, and the gain. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus such as an electronic still camera (digital camera), and more particularly to exposure control and improvement in depth of field of an imaging apparatus using a solid-state imaging device.

  Before the actual photographing, the digital camera captures an image, and exposure conditions are determined so that the level of the output signal corresponding to the luminance level of the captured image matches the target value. The exposure conditions are generally changed by adjusting the aperture, shutter speed (charge accumulation time), and gain.

  Further, as a conventional imaging apparatus, an apparatus that controls a diaphragm and a charge accumulation time with a common imaging control unit is known (for example, Patent Document 1).

JP 2000-354195 A (page 5-6, FIG. 1)

  However, in the SOC (System on Chip) type CMOS sensor that has been developed in recent years, in addition to the sensor, means for performing exposure control by gain and charge accumulation time are mounted in one integrated circuit chip. Since an external interface for aperture control is not provided, gain and charge accumulation time control and aperture control cannot be performed simultaneously (in combination).

  Further, when performing aperture control, it is necessary to newly add a function externally, and it is difficult to perform exposure control in the CMOS sensor and aperture control in a coordinated manner.

  In addition, if a bright lens with a small F value is used to achieve high sensitivity at low illuminance, the depth of field becomes shallow, and the high resolution performance of the high pixel sensor cannot be utilized, and short distance When shooting with a subject placed on the screen, there is a problem that the focus range is narrow and the image is easily blurred.

  The present invention has been made to solve the above-described problems, and ensures the performance of exposure control in which aperture adjustment is added to exposure control using adjustment of charge accumulation time (shutter speed) and gain. It is an object.

  It is another object of the present invention to provide an imaging device with less image blur by using aperture control to increase the depth of field when the subject is bright.

The imaging apparatus of the present invention
A diaphragm means for controlling the amount of light from the subject,
An image pickup device having a function of photoelectrically converting an optical signal whose light amount is controlled by the aperture means;
A gain variable amplifying means for amplifying the output of the image sensor;
An exposure amount detection means for integrating a signal proportional to the output of the image sensor for each predetermined photometry frame and obtaining an exposure amount;
Exposure control means for controlling the gain of the amplification means using the exposure amount detected by the exposure amount detection means;
A diaphragm control means for controlling a diaphragm amount of the diaphragm means based on the exposure amount and the gain.

  According to the present invention, the adjustment of the aperture is added to the image pickup apparatus including the exposure control unit using the adjustment of the gain and the adjustment of the exposure time, so that the exposure performance is improved without causing the adverse effect thereof. be able to.

  In addition, by controlling the aperture, when the subject is dark, the F value can be reduced to improve the sensitivity. On the other hand, when the subject is bright, the F value can be increased to increase the field of view. The depth can be increased, the depth of field can be increased, and the image blur can be reduced.

Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating the imaging apparatus according to the first embodiment. The illustrated imaging apparatus includes an aperture 1, a lens 2, an imaging unit 9, and an aperture control unit 8.
The imaging means 9 is composed of, for example, one integrated circuit chip, and includes an imaging element 3, an amplification means 4, an A / D conversion means 5, an exposure control means 6, and an exposure amount detection means 7. .

  The aperture 1 controls its aperture value F according to the aperture control signal from the aperture control means 8. The larger the aperture value F, the smaller the degree of aperture opening. By controlling the aperture value F, the amount of light from the subject to be imaged on the image sensor 3 through the lens 2 can be adjusted, and thereby the brightness of the image can be controlled.

  Also, by controlling the aperture value F, the depth of field can also be controlled. When the aperture value F is minimized (maximum open state), the image becomes brighter but the depth of field is the shallowest. When the aperture value F is maximized (open degree is minimized), the field is reduced. While the depth is deepest, the image is darkest.

  The lens 2 forms an image of light from the subject on the image sensor 3 and has a focus adjustment function for adjusting the focus. In addition, one having a zoom function can be used.

  The image sensor 3 is composed of an area-type solid-state image sensor such as a CCD sensor or a CMOS sensor. The light condensed through the lens 2 is photoelectrically converted by a photodiode constituting the pixel, and an imaging output in the form of a voltage value is taken out. Further, the image sensor 3 controls the charge accumulation time in the photodiode in accordance with an instruction from the exposure control means 6. This charge accumulation time may be referred to as “exposure time” or may be expressed as “electronic shutter speed”. The shutter speed is proportional to the reciprocal of the charge accumulation time or exposure time, and an increase in charge accumulation time or exposure time means the same as a decrease in shutter speed.

  The amplifying unit 4 amplifies an analog image pickup signal from the image pickup device 3 and its gain (amplification factor) is variable. The gain in the amplification unit 4 is adjusted by a gain control signal from the exposure control unit 6.

  The A / D conversion means 5 digitally converts the analog imaging signal from the amplification means 4. The digital imaging signal YL from the A / D conversion unit 5 is taken out from the imaging unit 9 as an output signal.

The digital image pickup signal YL of the A / D conversion means 5 is also sent to the exposure amount detection means 7, and a signal level corresponding to the luminance level of the image is measured.
As this signal level, the average value of the signal values of all the pixels on the entire screen may be obtained, the signal level for each predetermined measurement frame (for example, the average value for each measurement frame) is obtained, and the signal for each measurement frame is obtained. A weighted average of levels may be obtained, or a signal level of only a preselected measurement frame may be used. Further, a histogram of signal values may be created for each measurement frame, and the signal level of the entire screen may be obtained based on the signal level of the measurement frame selected or extracted based on the distribution of signal values. Below, the case where the signal level for every measurement frame is calculated | required is demonstrated. Since such a signal level corresponds to the exposure amount or the exposure amount, detection of the signal level as described above is also referred to as “exposure amount detection” or “exposure amount detection”.

  When obtaining the exposure amount for each measurement frame and obtaining the exposure amount for the entire screen based on the exposure amount, the exposure amount detection means 7 outputs the digital imaging signal YL (for each pixel) output from the A / D conversion means 5. Is obtained for each measurement frame, and the integrated value is divided by the number of pixels subject to the integration to obtain the exposure amount in the measurement frame.

  The photometric frame is determined in advance at the design stage, for example, to perform automatic exposure control of the system. When the imaging surface of the imaging device 3 has a size of 640 pixels in the horizontal direction and 480 in the vertical direction, the horizontal direction 20 A rectangular area composed of pixels and 20 pixels in the vertical direction is defined as each frame. In this case, the imaging surface of the imaging device 3 is divided into 32 horizontal frames and 24 vertical frames.

The exposure amount detection means 7 may output the exposure amount in each frame obtained in this way, and calculates the average (simple moving average or weighted moving average) of the exposure amount of each frame over a predetermined number of frames in the past. You may output as exposure amount.
The exposure control unit 6 adjusts the gain G, shutter speed SS, and aperture F so that the exposure amount EX obtained by the exposure amount detection unit 7 converges to a predetermined target value TG, for example, an average luminance level APL (Average Picture Level). Control.

  With reference to FIG. 2, a general exposure control method (conventional method) is shown. The horizontal axis indicates the brightness L of the subject, and the vertical axis indicates the gain G (solid line), the shutter speed SS (chain line), and the aperture F (dashed line).

When the brightness L is equal to or less than a second predetermined value (a value close to the maximum value in the brightness range) La2, which will be described later, the diaphragm F is maintained at the minimum value Fmin (maximum open state).
When the brightness L is the minimum value La0 (of the range in which normal imaging is performed), the shutter speed SS is set to the minimum value (minimum value within the allowable range, for example, the same speed as the frame rate) SSmin, and the gain Let G be the maximum value Gmax. In other words, when the aperture F is the minimum value, the shutter speed SS is the minimum value SSmin, and the gain G is the maximum value Gmax, the brightness L at which the exposure amount EX matches the target value TG is the minimum value La0.

In a range where the brightness L is greater than the minimum value La0 and is equal to or less than the first predetermined value (level located at the center of the range where normal imaging is performed) La1, the shutter speed SS is fixed to the maximum value SSmin and the gain G is bright. The exposure amount EX is adjusted by gradually decreasing the length L.
When the brightness L is the first predetermined value La1, the gain G is the minimum value Gmin. In other words, when the aperture F is set to the minimum value Fmin, the shutter speed SS is set to the minimum value SSmin, and the gain G is set to the minimum value Gmin, the brightness L at which the exposure amount EX matches the target value TG is the first predetermined value. La1.

  Note that the minimum value Gmin of the gain G is determined from the saturation signal level of the image sensor 3. That is, the output value of each pixel varies under strong illumination, and the output value of the analog imaging signal with respect to the incident light amount of the imaging device 3 is set to a linear region before the knee region in order to prevent saturation unevenness. Is set.

In an area where the brightness L is greater than the first predetermined value La1 and is equal to or less than the second predetermined value (a value close to the maximum value of the range in which normal imaging is performed) La2, the gain G is fixed to the minimum value Gmin, and the shutter speed The exposure amount EX is adjusted by gradually increasing the SS with the brightness L.
When the brightness L is the second predetermined value La2, the shutter speed SS is the maximum value SSmax. In other words, when the aperture F is set to the minimum value Fmin, the gain G is set to the minimum value Gmin, and the shutter speed SS is set to the maximum value SSmax, the brightness L at which the exposure amount EX matches the target value TG is the second predetermined value. La2.

  In a region where the brightness L is greater than the second predetermined value La2, the gain G is fixed to the minimum value Gmin, the shutter speed SS is fixed to the maximum value SSmax, and the aperture F is increased with the brightness L (lowering the open value). ) To adjust the exposure amount EX.

  In the above method, in the region below the second predetermined value La2, the diaphragm F maintains the minimum value Fmin (open state), so that imaging is performed with a shallow depth of field, which may be undesirable. . The present invention aims to solve this problem.

  The aperture control unit 8 receives information indicating the set value of the gain G and information indicating the set value of the shutter speed SS from the exposure control unit 6, and receives the exposure amount EX from the exposure amount detection unit 7.

  Hereinafter, exposure control according to this embodiment will be described with reference to FIG. 3, the same reference numerals as those in FIG. 2 indicate the same or corresponding values. In FIG. 3, the horizontal axis indicates the brightness L of the subject, and the vertical axis indicates the gain G (solid line), the shutter speed SS (chain line), and the aperture F (dashed line).

  In a range where the brightness L is less than or equal to the minimum value La0 (in the range where normal imaging is performed), the aperture F is set to the minimum value Fmin (maximum open state), and the shutter speed SS is set to the minimum value (minimum value within the allowable range, For example, SSmin and the gain G are set to the maximum value Gmax. In other words, when the aperture F is the minimum value, the shutter speed SS is the minimum value SSmin, and the gain G is the maximum value Gmax, the brightness L at which the exposure amount EX matches the target value TG is the minimum value La0.

  In a range where the brightness L is greater than the minimum value La0 and equal to or less than a first predetermined value (level located at the center of the range where normal imaging is performed) La1, the shutter speed SS is fixed to the minimum value SSmin, and the brightness L is The exposure amount EX is adjusted by gradually decreasing the gain G and gradually increasing the aperture F as the size increases.

  When the brightness L is the first predetermined value La1, the gain G is the minimum value Gmin, and the diaphragm F is a value Fm1 that is slightly larger than the minimum value Fmin. In other words, when the shutter speed SS is the minimum value SSmin, the gain G is the minimum value Gmin, and the aperture F is the value Fm1, the brightness L at which the exposure amount EX matches the target value TG is the first predetermined value La1. It is. The first predetermined value La1 in FIG. 3 is somewhat larger than the first predetermined value La1 in FIG.

  In a region where the brightness L is greater than the first predetermined value La1 and is equal to or less than the second predetermined value (a value close to the maximum value of the range in which normal imaging is performed) La2, the shutter speed SS is fixed to the minimum value SSmin, and the gain The exposure amount EX is adjusted by fixing G to the minimum value Gmin and gradually increasing the aperture F together with the brightness L.

  When the brightness L is the second predetermined value La2, the diaphragm F has a maximum value Fmax (not a completely closed state but a minimum open state within a range adjustable by the diaphragm control). In other words, when the shutter speed SS is set to the minimum value SSmin, the gain G is set to the minimum value Gmin, and the aperture F is set to the maximum value Fmax, the brightness L at which the exposure amount EX matches the target value TG is a second predetermined value. La2. The second predetermined value La2 in FIG. 3 is not necessarily the same as the second predetermined value La2 in FIG.

  In a range where the brightness L is greater than the second predetermined value La2 and is equal to or smaller than the third predetermined value La3 (a value closer to the second predetermined value La2 than the maximum value in the normal imaging range), the gain G is minimized. The value is fixed to Gmin, the aperture F is fixed to the maximum value Fmax, and the shutter speed SS is increased together with the brightness L.

  When the brightness L is the third predetermined value La3, the gain G is the minimum value Gmin, the aperture F is the maximum value Fmax, and the shutter speed SS is the maximum value SSmax. In other words, when the gain G is set to the minimum value Gmin, the aperture F is set to the maximum value Fmax, and the shutter speed SS is set to the maximum value SSmax, the brightness L at which the exposure amount EX matches the target value TG is the third predetermined value. La3.

  In a region where the brightness L is greater than the third predetermined value La3, the gain G is fixed to the maximum value Gmin, the diaphragm F is fixed to the maximum value Fmax, and the shutter speed SS is fixed to the maximum value SSmax.

  Specifically, the control for adjusting the gain G, the shutter speed SS, and the aperture F as shown in FIG. 3 according to the brightness L is performed by comparing the first exposure amount EX with the target value TG. Depending on the result, the gain G, the shutter speed SS, and the aperture F are changed by a predetermined value or an integral multiple thereof (in steps). This change is performed for each frame. The width of one step for change is predetermined.

  In this case, the range of change in one step may be changed according to the range of the brightness L, and the change may be made according to the difference between the exposure amount EX and the target value TG. You may make it change the width | variety.

  Hereinafter, the procedure of exposure control performed by adjusting the gain G, the shutter speed SS, and the aperture F according to the difference between the exposure amount EX and the target value TG will be described with reference to the flowchart of FIG.

  In steps S1 and S2 in FIG. 4, a new exposure amount is calculated once in one frame period, and in steps S3, S4, S6, S8, S10, S13, S14, and S16 in the next frame period. , S18, S20, and steps S7, S9, S11, S17, S19, or S21 are performed in the next frame period.

  In step S1, the exposure amount EX is detected by the exposure amount detection means 7. In this case, the exposure amount EX may be output by taking the average (simple average or weighted average) of the past several frames.

In step S2, the brightness L is obtained from the exposure amount EX, the gain G, the shutter speed SS, and the aperture F, for example, by the following equation (1).
L = K × EX × SS × (1 / G) × F ² (1)
Here, K is a constant.

Step S3 and subsequent steps show a comparison between the exposure amount EX of the exposure control means 6 and the target value TG and a control value change process based on the comparison result.
Step S3 determines whether the exposure amount EX is larger than the target value TG, and step S13 determines whether the exposure amount EX is smaller than the target value TG.

  When it is determined in step S3 that the exposure amount EX is larger than the target value TG (YES in S3), the processes in steps S4 to S11 are performed as described in detail below. In steps S4 to S11, control is performed to reduce the exposure amount EX. That is, any one of a decrease in gain G, an increase in shutter speed SS, an increase in aperture value F, or a combination thereof is performed.

  When it is determined in step S13 that the exposure amount EX is smaller than the target value TG (YES in S13), the processes in steps S14 to S21 are performed as described in detail below. In steps S14 to S21, control is performed to increase the exposure amount EX. That is, one of the increase of the gain G, the decrease of the shutter speed SS, the decrease of the aperture value F, or a combination thereof is performed.

  When the exposure amount EX is equal to the target value TG (NO in step S3 and NO in step 13), the current control value is maintained. That is, the control value is not changed and the process returns to step S1.

In steps S4, S6, S8, S10, S14, S16, S18, and S20, it is determined in which range the brightness L obtained in step S2 is.
If L ≦ La0, YES is obtained in steps S4 and S14.
If La0 <L ≦ La1, YES is obtained in steps S6 and S16.
If La1 <L ≦ La2, YES is obtained in steps S8 and S18.
If La2 <L ≦ La3, YES is obtained in steps S10 and S20.

  If YES in steps S4 and S14, that is, if the exposure amount EX is greater than the target value TG and the brightness L is less than or equal to the minimum value La0, the gain G is the maximum value Gmax, the shutter speed SS is the minimum value SSmin, The diaphragm F has a minimum value Fmin (open state), and this state is maintained. That is, the process returns to step S1 without changing the exposure control value.

Steps S7 and S17 are performed when La0 <L ≦ La1.
In this brightness region, the shutter speed SS is fixed, and the gain G and the aperture F are changed according to the brightness L.
The process of step S7 is performed when the exposure amount EX is larger than the target value TG. In this case, the aperture F is increased from the current value by a predetermined width ΔF1 (more closed). At the same time, the gain G is reduced from the current value by a predetermined width ΔG1.

In this case, the feedback rate with respect to the gain G is further increased.
That is, with the aperture F and the exposure time S fixed, the change in gain G for changing the exposure amount EX by a predetermined change width (one unit amount) EXu is fixed, and the exposure amount S is fixed with Gu, gain G, and exposure time S fixed. When the change of the diaphragm F for changing EX by the above-mentioned 1 unit amount EXu is Fu,
ΔG1 and ΔF1 are determined so that ΔG1 / Gu> ΔF1 / Fu.
Thereby, the response speed of gain control can be increased. In other words, the time constant for gain control can be effectively made shorter than the time constant for aperture control.

  The process of step S17 is performed when the exposure amount EX is smaller than the target value TG. In this case, the aperture F is reduced from the current value by a predetermined width ΔF1 (more open). At the same time, the gain G is increased from the current value by a predetermined width ΔG1.

Steps S9 and S19 are performed when La1 <L ≦ La2.
In this brightness region, the shutter speed SS is fixed to the minimum value SSmin, the gain G is also fixed to the minimum value Gmin, and the aperture F is changed according to the brightness L.

  The process of step S9 is performed when the exposure amount EX is larger than the target value TG. In this case, the diaphragm F is increased from the current value by a predetermined width ΔF2 (more closed). The predetermined width ΔF2 is set to a value larger than the predetermined width ΔF1.

Also in this case, the feedback rate for the gain G is increased.
That is, with the aperture F and the exposure time S fixed, the change in gain G for changing the exposure amount EX by a predetermined change width (one unit amount) EXu is fixed, and the exposure amount S is fixed with Gu, gain G, and exposure time S fixed. When the change of the diaphragm F for changing EX by the above-mentioned 1 unit amount EXu is Fu,
ΔG2 and ΔF2 are determined so that ΔG2 / Gu> ΔF2 / Fu.
Thereby, the response speed of gain control can be increased. In other words, the time constant for gain control can be effectively made shorter than the time constant for aperture control.

  The process of step S19 is performed when the exposure amount EX is smaller than the target value TG. In this case, the diaphragm F is decreased from the current value by a predetermined width ΔF2 (more open).

In this brightness region, the gain G is the minimum value Gmin, and an image with less noise is obtained.
In this area of brightness, the contrast of the subject (difference between light and dark) is large (the image is sharp), and depending on the performance of the lens, blurring of the image may be noticeable, but the aperture is increased (the degree of opening) Can be made deeper and the blur of the image can be eliminated. Further, exposure control is performed by controlling the aperture F, and the gain G is fixed, so that the S / N is kept constant, and an image with less noise is obtained.

Steps S11 and S21 are performed when La2 <L ≦ La3.
In this brightness region, the gain G is fixed to the minimum value Gmin, the diaphragm F is fixed to the maximum value Fmax, and the shutter speed SS is changed according to the brightness L.
The process of step S11 is performed when the exposure amount EX is larger than the target value TG. In this case, the shutter speed SS is increased by a predetermined width ΔSS3.
The process of step S21 is performed when the exposure amount EX is smaller than the target value TG. In this case, the shutter speed SS is reduced by a predetermined width ΔSS3).

If NO in steps S10 and S20, that is, if La3 <L, the gain G is fixed to the minimum value Gmin, the shutter speed SS is also fixed to the maximum value SSmax, and the aperture F is also fixed to the maximum value. is there. That is, the process returns to step S1 without changing the exposure control value.
With the processing described above, the imaging apparatus capable of controlling the exposure according to the first embodiment can be realized.

Among the above, the process of step S1 is performed by the exposure amount detection means 7, and the process of step S2 is performed by the exposure control means 6.
Steps S3, S4, S6, S8, S10, S13, S14, S16, S18, and S20 are performed in parallel by both the exposure control means 6 and the aperture control means 8.
Of the processes in steps S7, S9, S11, S17, S19, and S21, the shutter speed SS and the gain G are controlled by the exposure control means 6, and the aperture F is controlled by the aperture control means 8.
The data representing the exposure amount EX detected by the exposure amount detection means 7, the data representing the shutter speed SS and the gain G generated by the exposure control means 6, and the data representing the brightness L are, for example, those of the imaging means 9. The aperture control means 8 is transmitted to the aperture control means 8 through an existing terminal for inputting / outputting serial data, and the aperture control means 8 controls the aperture F based on these pieces of information.

By using the exposure amount EX from the exposure amount detection unit 7 for the exposure control unit 6 and the aperture control unit 8, the aperture control can be performed asynchronously with the shutter speed control and the gain control, and the exposure can be controlled.
Further, by using the aperture control together, an imaging device with less blurring of the image can be realized by increasing the depth of field.
Furthermore, aperture control can be realized by adding the minimum necessary components such as an existing FPGA (Field Programmable Gate Array) and CPU, and a system can be configured at low cost.

  In the above embodiment, the exposure control means 6 and the aperture control means 8 perform control using the exposure amount EX supplied from the exposure amount detection means 7, but the exposure control means 6 and the aperture control means 8 are used. Alternatively, different information may be supplied as the exposure amount EX. For example, first information (first exposure amount) EXa is supplied to the exposure control means 6, and second information (second exposure amount) EXb is supplied to the aperture control means 8.

  In this case, the detection time for calculating these may be different for the first exposure amount EXa and the second exposure amount EXb. For example, the detection time for obtaining the second exposure amount EXb is set longer than the detection time for obtaining the information EXa representing the first exposure amount. For example, a value for each frame may be used as the first exposure amount EXa, and an average value over a plurality of frames may be used as the second exposure amount EXb. Instead, an average value over p frames may be used as the first exposure amount EXa, and an average value over q frames (q> p) frames may be used as the second exposure amount EXb. The exposure control unit 6 controls the gain G and the shutter speed SS so that the first exposure amount EXa matches the target value TG, and the aperture control unit 8 sets the second exposure amount EXb to the target value TG (exposure control). The aperture is controlled so as to coincide with the same target value TG) used in the means 6.

  As a result, the response speed of the aperture control can be slowed down, and the time constant of the aperture control can be effectively made longer than the time constant of the gain and exposure time control. In addition, the exposure can be adjusted earlier than the stop F (with a short delay time) by the gain G and the shutter speed SS.

  In the above example, the change widths ΔF1, ΔG1, ΔF2, and ΔSS3 of the control value are constant, but the control value (target value) corresponding to the obtained brightness L and the current control value (current value). It is good also as a value proportional to the difference with). Further, the ratio of the change width of the control value to the current control value may be constant.

Embodiment 2. FIG.
In the above embodiment, the shutter speed SS is changed in the process when L> La2, that is, in steps S11 and S21. However, the shutter speed SS is kept fixed, and only the gain G and aperture F are changed. The exposure may be controlled. The characteristics in this case are shown in FIG. At brightness La2 or higher, the difference is that the exposure is controlled by changing the aperture F and the shutter speed SS is not changed.
In addition, exposure control can be realized even in a specification in which the aperture F is completely closed.

Embodiment 3 FIG.
FIG. 6 is a diagram illustrating the characteristics of exposure control according to the third embodiment. The threshold values Lb4 and Lb41 are provided between the threshold value Lb0 corresponding to the brightness threshold value La0 and the threshold value Lb1 corresponding to the threshold value La1 in the first embodiment, and the threshold value Lb15 is provided between the brightness threshold value Lb1 and the threshold value La2. The shutter speed SS is fixed to a first value SSa (for example, equal to the minimum value SSmin) in a range equal to or less than Lb4, and is increased stepwise by Lb4. In a range from Lb4 to Lb41, a second value SSb ( Fixed to a first value SSa), increased stepwise at Lb1, and fixed to a third value SSc (greater than a second value SSb) in a range from Lb1 to La2, from La2 to La3 In the range, the brightness is increased with the brightness L, and is fixed to a fourth value SSd (for example, equal to the maximum value SSmax) in the range larger than La3.

  On the other hand, the diaphragm F has a first value Fa (for example, equal to the minimum value Fmin) below Lb0, and has a first inclination angle (gradient) with respect to the brightness L in the range from Lb0 to Lb04. It increases from the first value Fa to the second value Fb, and in the range from Lb04 to Lb4, the second inclination angle (gradient) with respect to the brightness L (greater than the first inclination angle) and the second From the value Fb to the third value Fc, and in the range from Lb4 to Lb41, the third value with respect to the brightness L at a third inclination angle (gradient) (substantially equal to the first inclination angle). From Fc to the fourth value Fd, in a range from Lb41 to Lb1, the fourth inclination angle (gradient) with respect to the brightness L (approximately equal to the second inclination angle) from the fourth value Fd. It increases to the fifth value Fe, and in the range from Lb1 to Lb15, the brightness L Is increased from the fifth value Fe to the sixth value Ff at a tilt angle (gradient) of (same as the first tilt angle), and in the range from Lb15 to La2, the sixth tilt with respect to the brightness L An angle (gradient) (greater than the first tilt angle and smaller than the second tilt angle) increases from the sixth value Ff to the seventh value Fg (eg, equal to the maximum value Fmax), and in a range greater than La2 The seventh value Fg is fixed.

On the other hand, the gain G is maintained at the first value Ga (for example, equal to the maximum value Gmax) in the range up to Lb0, and in the range from Lb0 to Lb04, the gain G increases from the first value Ga to the second value as L increases. The value is gradually decreased to the value Gb, maintained from the second value Gb to Lb04 to Lb4, and increased from the second value Gb to the third value Gc in a stepwise manner at Lb4, and the increase of L from Lb4 to Lb41. The third value Gc is gradually decreased from the third value Gc to the fourth value Gd, the fourth value Gd is maintained from Lb41 to Lb1, and is increased stepwise from the fourth value Gd to the fifth value Ge at Lb1. , Lb1 to Lb15 are gradually decreased from the fifth value Ge to the sixth value Gf as L increases, and are maintained at the sixth value Gf above Lb15.
The second, fourth, and sixth values Gb, Gd, and Gf are, for example, equal to the minimum value Gmin.

  As described above, the third embodiment performs the same operation as the first embodiment except that the shutter speed is changed stepwise in accordance with the brightness Lb4, La1, and Lb5, and has the same effect.

  Since the shutter speed can be controlled to change stepwise, the aperture control can be changed gradually. In addition, by controlling the shutter speed stepwise, the depth of field can be gradually increased, so that a sudden change in the depth of field can be prevented.

Embodiment 4 FIG.
FIG. 7 shows a block diagram of exposure control according to the fourth embodiment. The integration means used for aperture control is not obtained from the imaging means 9, but is integrated for each photometric frame with an IC in which the output of the A / D conversion means is provided externally such as an FPGA (field programmable gate array). The difference is that an additional exposure amount detection means (second exposure amount detection means) 10 for obtaining the exposure amount EXb is provided. In FIG. 7, the exposure amount output from the exposure amount detection means 7 is represented by the symbol EXa for distinction.

  A system that controls the aperture, gain, and shutter speed even when the exposure amount information EXa output from the exposure amount detection means 7 in the imaging means 9 cannot be used by the aperture control means 8 by being provided outside. Can be built.

  The description of the modified example described for the first embodiment also applies to the second embodiment, the third embodiment, and the fourth embodiment.

It is a block diagram which shows the structure of the exposure control of Embodiment 1 of this invention. It is a figure which shows an example of the characteristic of the conventional exposure control. 6 is an example of exposure control characteristics according to the first embodiment. 6 is a flowchart of exposure control according to the first embodiment. It is a figure which shows an example of the characteristic of the exposure control of Embodiment 2 of this invention. It is an example of the characteristic of exposure control of Embodiment 3 of this invention. It is a block diagram which shows the structure of the exposure control of Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Diaphragm, 2 Lens, 3 Imaging means, 4 Amplification means, 5 A / D conversion means, 6 Exposure control means, 7 Exposure amount detection means, 8 Aperture control means, 9 Imaging means, 10 2nd exposure amount detection means

Claims (6)

Aperture means for controlling the amount of light from the subject by changing the aperture amount;
An image pickup device having a function of photoelectrically converting an optical signal whose light amount is controlled by the aperture means;
A gain variable amplifying means for amplifying the output of the image sensor;
An exposure amount detection means for integrating a signal proportional to the output of the image sensor for each predetermined photometry frame and obtaining an exposure amount;
Exposure control means for controlling the gain of the amplification means using the exposure amount detected by the exposure amount detection means;
An imaging apparatus comprising: the exposure amount; and an aperture control unit that controls an aperture amount of the aperture unit based on the gain. The image sensor further has an electronic shutter function for controlling the exposure time of the photoelectrically converted signal,
The exposure control means also controls the exposure time of the image sensor using the exposure amount detected by the exposure amount detection means,
The imaging apparatus according to claim 1, wherein the aperture control unit controls the aperture amount of the aperture unit based on the exposure amount, the exposure time, and the gain. A feedback time constant in aperture control by the aperture control means,
The imaging apparatus according to claim 1, wherein the imaging apparatus is set to be longer than a feedback time constant in gain control by the amplification means. A feedback time constant in aperture control by the aperture control means,
The imaging apparatus according to claim 2, wherein the imaging apparatus is set to be longer than a feedback time constant in gain control by the amplifying unit and a feedback time constant in exposure time control by the imaging element.   The imaging apparatus according to claim 1, wherein an exposure time of the imaging element is fixed, and the gain and the aperture amount are controlled according to the exposure amount.   The imaging apparatus according to claim 2, wherein the exposure time of the imaging element is changed stepwise with respect to an increase in brightness.

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