JP2000155351A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device capable of extending the range enabling accurate object illuminance calculation, performing an appropriate flashing in the case of still image photographing by use of a flash device and obtaining a satisfactory still image by temporarily increasing sensitivity when the illuminance is low. SOLUTION: In the case of photographing a still image by using a flash device 110 under the low illuminance, as a means for temporarily increasing the sensitivity of an image pickup system, in order to increase the sensitivity more than the maximum sensitivity at a normal exposure control time, the gain of an automatic gain control(AGC) circuit 105 is increased up to the maximum gain for the AGC circuit 105 exceeding the maximum gain at the normal exposure control time, or a shutter speed is made low, then, the accumulation time of the image pickup element 104 is maintained >=1/60 sec, besides, the object illuminance measuring extent is enlarged by using the two means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus capable of photographing a still image using a flash light emitting device. The present invention relates to an imaging device having an exposure control unit that enables more accurate calculation of subject illuminance, which is determined based on the current subject illuminance.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to a block diagram showing an example of a basic configuration of an imaging apparatus shown in FIG.

[0003] Light incident from a lens 102 is
After that, the image is formed on the image sensor 104, photoelectrically converted by the image sensor 104, and stored as a video signal.

[0004] The time accumulated in the image sensor 104 (hereinafter referred to as "
The shutter speed is determined by a pulse output from a timing signal generator (TG) 108 based on time data transmitted from the camera control unit 107.

[0005] The video signal stored and output by the image sensor 104 is amplified by the AGC circuit 105 and processed by the camera signal processing unit 106.

The camera signal processing unit 106 has an integration circuit for integrating the luminance component (Y signal) of the video signal. The camera control unit 107 controls the aperture 103 based on the level of the integrated luminance component. , The shutter speed of the image sensor 104, and the gain of the AGC circuit 105 to control exposure.

Here, the maximum value of the AGC gain in the normal exposure control is determined in order to secure the S / N of the video signal to some extent.
Exposure control is performed with the gain set lower than the limit gain controllable by the AGC circuit 105.

Next, at the time of photographing a still image, the flash light emitting device 110
Is mounted, and in the case of a low illuminance subject in which an appropriate exposure cannot be obtained unless the gain of the AGC circuit 105 is increased, the video signal generated by increasing the gain of the AGC circuit 105 In order to avoid a decrease in S / N, the auxiliary lighting by the flash light emitting device 110 is used to reduce the AG.
Shooting is performed with the gain of the C circuit 105 lowered.

In the image pickup apparatus having such a configuration, at the time of photographing a still image using the flash light emitting device 110, the light emission amount of the preliminary light emission for determining the light emission amount of the flash light emitting device 110 during the main light emission is determined by the exposure control. The illuminance of the subject is calculated from the state, and is determined based on the calculation result.

The calculation of the illuminance of the subject is performed in the following procedure.

That is, the camera control unit 107 previously sets the aperture to full (F1.0) and sets the shutter speed to 1 /
For 60 seconds, when the AGC circuit 105 is at 0 dB, luminance information that allows the subject to be properly exposed is stored. In order to measure the illuminance of the object, the aperture amount from the open state, the change amount of the shutter speed from 1/60 second, the AGC circuit 105
By calculating the amount of change in gain from 0 dB, the amount of change in subject photometric value from an appropriate value, and the like.

Here, I is the aperture amount from the opening of the aperture, S
The following formula is established, where is the change amount of the shutter speed from 1/60 second, A is the gain change amount of the AGC circuit 105 from 0 dB, and Y is the change amount of the subject photometric value from the proper exposure.

Subject illuminance = reference illuminance + I + SA + Y As an example, the aperture is F1.4 and the shutter speed is 1 /
When the AGC circuit 105 is 0 dB and the exposure is appropriate for 120 seconds, the aperture is increased by one step from F1.0, so that I = 1 and the shutter speed is increased by one step from 1/60 second. Therefore, S = 1, and the AGC circuit 105 has 0 dB
A = 0, and Y = 0 because the exposure is proper.
Thus, subject illuminance = reference illuminance + 1 + 1-0 + 0 = reference illuminance + 2.

Here, assuming that the reference subject illuminance is 8.0 EV, the subject illuminance = 8 + 2 = 10 EV in the above example.

Based on the subject illuminance information calculated as described above, the camera control unit 107 sets the amount of preliminary light emission of the flash light emitting device so as to irradiate the subject with an appropriate amount of light.

[0016]

However, in the above-mentioned conventional example, at low illuminance where sufficient luminance cannot be obtained even if the sensitivity is raised to the limit in normal exposure control, the subject photometric value Since the value of Y cannot be obtained correctly, the subject illuminance cannot be correctly calculated, the subject illuminance is determined to be 0, and the subject may be preliminarily illuminated with an excessive light emission amount.

As a result, it becomes impossible to calculate the light emission amount at the time of the main light emission in which the luminance of the subject becomes appropriate, and it is sometimes impossible to obtain a good still image photographing result with the appropriate luminance.

The present invention has been made in view of the above situation, and extends the range in which correct subject illuminance can be calculated by temporarily increasing the sensitivity at low illuminance. It is an object of the present invention to provide an imaging device that emits light appropriately in image capturing and can obtain a good still image.

[0019]

The present invention can solve the above-mentioned problems by providing the following constitution.

(1) In the case of photographing a still image using a flash light emitting device under low illuminance, if it is not possible to measure the illuminance of the subject for determining the amount of light emission of the preliminary flash, the sensitivity of the imaging system is temporarily determined. An image pickup apparatus for increasing a sensitivity beyond a maximum sensitivity in a normal exposure control, thereby extending a subject illuminance measurable range.

(2) As means for increasing the sensitivity of the image pickup system, means for increasing the gain of the automatic gain control (AGC) circuit beyond the maximum gain during normal exposure control to the maximum gain in the AGC circuit is used. The imaging device according to the above (1), wherein:

(3) The image pickup apparatus according to the above item (1), wherein the means for increasing the sensitivity of the image pickup system is a means for lowering the shutter speed and holding the accumulation time of the image pickup element for 1/60 second or more. apparatus.

(4) As means for increasing the sensitivity of the imaging system, means for increasing the gain of an automatic gain control (AGC) circuit beyond the maximum gain during normal exposure control to the maximum gain in the AGC circuit, and a shutter (2) The imaging apparatus according to the above (1), wherein two means are used to reduce the speed and maintain the accumulation time of the image sensor for 1/60 second or more.

[0024]

Embodiments of the present invention will be described below.

FIG. 1 is a block diagram showing an example of the basic configuration of an image pickup apparatus, FIG. 2 is a flowchart of the operation in the first embodiment, FIG. 3 is a timing chart of the operation in the first embodiment, and FIG. FIG. 5 is a timing chart of the operation in the second embodiment.

First, an example of the basic configuration of the imaging apparatus will be described.
The symbols which have not been explained yet will be explained here, since they have been roughly described above with reference to FIG.

Reference numeral 108 denotes an image sensor timing signal generator (TG: timing generator), which connects the camera controller 107 to the image sensor 104 in the lens unit 101, and an aperture control circuit 109 is operated by a command from the camera controller 107. An aperture value of the aperture 103 in the lens unit 101 is controlled, and a shooting button 111 is provided in cooperation with the camera control unit 107.

(First Embodiment) Regarding the first embodiment,
The operation will be described below with reference to FIGS. 1 and 3 based on the operation flowchart of FIG.

The camera control unit 107 has a shooting button 111
The photographing trigger signal generated by pressing is monitored, and if the photographing trigger signal is not generated, the normal exposure control is maintained (S201). When the photographing button 111 is pressed and the photographing trigger signal is generated, The value of Y, which is the photometric value of the subject, is confirmed, and it is determined whether the subject illuminance can be calculated (S202). When it is determined that the subject illuminance can be calculated, the subject illuminance calculation is started (S204) (FIG. 3).
[1] period). When it is determined that the subject illuminance cannot be calculated, the value of Y, which is the subject photometric value, cannot be sufficiently obtained when the gain of the AGC circuit 105 is the maximum value of the normal exposure control (here, 12 dB). Because AG
The gain of the C circuit 105 is controlled to a limit value (here, 18 dB) (S203), and the sensitivity can be increased to extend the subject illuminance measurable range by one step. Is measured ([2] in FIG. 3).
Period). Based on the obtained subject photometric value and the data of the aperture, shutter speed, and AGC gain, the same subject illuminance calculation as in the conventional example is performed (S204). However, AG
When the gain of the C circuit 105 is controlled to the limit value, even if the subject photometric value Y is not sufficiently obtained, the sensitivity cannot be further increased.

In preparation for the preliminary light emission, the gain of the AGC circuit 105 is controlled to 0 dB (S205).

After confirming that the gain of the AGC circuit 105 has become 0 dB, the light emission amount of the preliminary light emission is determined based on the pre-calculated subject illuminance (S206), and the flash light emitting device 110 is determined based on the light emission amount. Is made to emit preliminary light (S20
7) (Period [3] in FIG. 3).

The photometric value of the subject at the time of preliminary light emission is measured, and the light emission amount at the time of main light emission is calculated (S208) ([4] in FIG. 3).
Period). The flash light emitting device 110 is caused to emit light based on the light emission amount at the time of the main light emission determined by calculation, and a still image is captured (S209). When the still image shooting is completed, the process returns to the normal exposure control (S210).

(Second Embodiment) A second embodiment will be described.
The operation will be described below with reference to FIGS. 1 and 5 based on the operation flowchart of FIG.

In S401 and S402, the above-described S20
1, the description is omitted because it is the same as S202.
Step 02 corresponds to the period [1] in FIG.

When the shutter speed of the image sensor 104 is the maximum value of the normal exposure control (here, 1/60 second), the value of Y, which is the photometric value of the subject, cannot be obtained sufficiently. Is controlled to the limit value (here, 1/15 second) and accumulation is performed (S40).
3) (Period [2] in FIG. 5). This raises the sensitivity,
The subject illuminance measurable range can be extended by two steps.

When the accumulation of 1/15 second in the image sensor 104 is completed, the shutter speed control of the image sensor 104 is returned to 1/60 second (S404), and the photometric value of the subject obtained by the 1/15 second accumulation is measured. I do.

Further, based on the obtained subject photometric value and the data of the aperture, shutter speed, and AGC gain, the subject illuminance is calculated in the same manner as in the conventional example (S40).
5). However, when the shutter speed is controlled to 1/15 second, the sensitivity cannot be further increased even if the value of the subject photometric value Y is not sufficiently obtained, so that the subject illuminance is treated as 0 (FIG. 5). [3] period).

When the shutter speed of the image sensor 104 is 1
/ 60 seconds, and based on the subject illuminance calculated in advance, the light emission amount at the time of preliminary light emission is determined (S40).
6) Then, the flash light emitting device 110 is caused to perform preliminary light emission based on the light emission amount (S407) (period [4] in FIG. 5).

The photometric value of the subject at the time of preliminary light emission is measured, and the light emission amount at the time of main light emission is calculated (S408) ([5] in FIG. 5).
Period).

The flash light emitting device 110 is caused to emit light based on the light emission amount at the time of the main light emission determined by the calculation, and a still image is shot (S409) (period [6] in FIG. 5).

After the completion of the still image shooting, the process returns to the normal exposure control (S410).

The flash light emitting device may be of a built-in type or an external type with respect to the image pickup device.

[0043]

As described above, according to the present invention,
By temporarily increasing the sensitivity at low illuminance, the range in which the correct illuminance of the subject can be calculated is expanded, and appropriate light emission can be performed in still image shooting using a flash light emitting device, and a good still image can be obtained. Take effect.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a basic configuration example of an imaging apparatus.

FIG. 2 is a flowchart of an operation in the first embodiment.

FIG. 3 is a timing chart of an operation in the first embodiment.

FIG. 4 is a flowchart of an operation in the second embodiment.

FIG. 5 is a timing chart of the operation in the second embodiment.

[Explanation of symbols]

Reference Signs List 101 lens unit 102 lens 103 aperture 104 image sensor 105 AGC circuit 106 camera signal processing unit 107 camera control unit 108 image sensor timing signal generator (TG: timing generator) 109 aperture control circuit 110 flash light emitting device 111 shooting button

Continued on the front page F term (reference) 2H002 CD07 CD13 DB02 HA02 HA03 JA07 JA08 2H053 AA01 AD12 AD23 BA00 BA85 DA03 5C022 AA13 AB04 AB12 AB15 AB18 AB20 AC31 AC32 AC41 AC54 AC56 AC69 5C024 AA05 BA01 CA13 CA17 DA04 EA02 EA04 FA01 HA10 HA10

Claims (4)

[Claims] 1. When photographing a still image using a flash light emitting device under low illuminance, if it is impossible to measure the illuminance of a subject to determine the amount of light emission of preliminary flash, the sensitivity of the imaging system is temporarily reduced. As an increasing means, an imaging device is characterized in that an object illuminance measurable range is extended by increasing the sensitivity beyond a maximum sensitivity at the time of normal exposure control. 2. As means for increasing the sensitivity of the imaging system,
2. The image pickup apparatus according to claim 1, wherein a means for increasing a gain of the automatic gain control (AGC) circuit beyond a maximum gain in the normal exposure control to a maximum gain in the AGC circuit is used. 3. As means for increasing the sensitivity of the imaging system,
2. The image pickup apparatus according to claim 1, wherein a means for lowering a shutter speed and holding an accumulation time of the image pickup element for 1/60 second or more is used. 4. As means for increasing the sensitivity of the imaging system,
Means for increasing the gain of the automatic gain control (AGC) circuit beyond the maximum gain in the normal exposure control to the maximum gain in the AGC circuit, reducing the shutter speed, and increasing the accumulation time of the image sensor to 1/60 second or more 2. The imaging apparatus according to claim 1, wherein two means of holding are used.