JP4464170B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging device that controls an amplification gain value of a signal from an imaging device during flash imaging.

  In still image shooting by an imaging device such as a digital camera or a video camera, flash emission is automatically performed according to the brightness of the subject. Here, an example of an exposure control operation in a monitor mode other than flash photography will be described first.

  The amount of light incident from the photographing lens is limited by the diaphragm mechanism, and enters the image sensor. The signal photoelectrically converted by the image sensor is amplified by the AGC circuit, converted into a digital signal by the AD converter circuit, and further subjected to predetermined signal processing to be converted into a video signal. Then, luminance data is extracted from the video signal, and an exposure control calculation is performed based on the luminance data.

  If the calculated exposure is not appropriate, the settings of the aperture mechanism and electronic shutter are changed as appropriate, and the gain value in the AGC circuit is controlled. At this time, if the subject is dark, the gain value is set high. Then, a video signal under a high gain value is displayed on the monitor, and the photographer can shoot while checking the current exposure state.

  Next, the AGC operation and flash emission operation during flash photography will be described. When the photo trigger is pressed by the photographer, the mode shifts to the still image shooting mode. At this time, if the subject in the monitor mode is dark and the exposure state has a high gain in the AGC circuit, it is determined that flash photography is to be performed. In preparation for still image main photographing, first, the gain value of the AGC circuit is decreased to a first gain value (G1) smaller than the gain value (Gmon) in the monitor mode. Other exposure parameters such as aperture and electronic shutter setting values remain fixed from when the photo trigger is pressed until the end of still image shooting. Further, the photometric value at this time is stored as the first photometric value (Yold).

  In this way, the first light emission amount (Tpre) is calculated while the exposure state in which only the gain value is reduced, and a first light emission operation (hereinafter referred to as pre-light emission) by the light emitting unit is performed. The light emission amount at this time (first light emission amount: Tpre) is set according to the first photometric value (Yold) when the photo trigger 14 is pressed.

  When pre-emission is performed, the photometric value at this time is obtained as the second photometric value (Ypre). Using the second photometric value (Ypre), the first photometric value (Yold), and the predetermined target photometric value (Yref), a second light emission amount (Tmain) is calculated.

  Then, in the exposure state with the gain value set to the first gain value (G1), second light emission (hereinafter referred to as main light emission) is performed with the second light emission amount (Tmain). Photographing is performed, and photographed image data acquired at this time is recorded in a storage medium.

In such flash photography, there is one disclosed in Patent Document 1 as one of methods for appropriately setting the light emission amounts in pre-flash and main flash. This is to change the gain control method of the AGC circuit at the time of flash photography between pre-flash and main flash.
JP 2001-326852 A (paragraphs 0051-0062, FIG. 4 etc.)

  By the way, the light emission amount by the light emitting unit has a limit value (maximum light emission amount) according to the specification of the light emitting unit. For this reason, the second light emission amount (Tmain) calculated using the second photometric value (Ypre), the first photometric value (Yold), and the predetermined target photometric value (Yref) obtained at the time of pre-emission. However, if it exceeds the maximum amount of light emitted, for example, if the distance to the subject is far enough that the light emitted from the light emitting unit does not reach sufficiently, the brightness of the recorded image is captured in the monitor mode. It becomes darker than the brightness of the monitor image that the person has confirmed.

  Further, even the gain control method disclosed in Patent Document 1 does not take into account the situation where the brightness of the monitor image in the monitor mode is different from that of the captured recording image.

  Therefore, the present invention can avoid the occurrence of a situation in which, for example, the brightness of the monitor image and the captured recording image are greatly different by appropriately controlling the light emission amount and the AGC gain value during the main light emission. An object of the present invention is to provide a simple imaging device.

In order to achieve the above object, an imaging apparatus of the present invention is an imaging apparatus that performs main light emission after performing pre-light emission by a light emitting unit that emits light to a subject, and photoelectrically converts an image of the object. An imaging unit; an operation unit that receives an instruction to start a still image shooting operation; an amplifying unit that amplifies a signal from the imaging unit; a photometric unit that measures a subject based on an output from the imaging unit; and the photometric unit A light emission amount calculating means for calculating a light emission amount of the light emitting means based on a photometric result of the means; and a main light emission amount calculated by the light emission amount calculating means based on a photometric result when performing pre-flash. If the maximum light emission amount is larger than the maximum light emission amount, a light emission control means for causing the light emission means to perform main light emission at the maximum light emission amount, and a gain value of the amplification means for performing the main light emission of the light emission means at the maximum light emission amount That the gain calculation means, when the gain value calculated by the gain calculation means is greater than the gain value of the non-emission time which has been set before accepting the start instruction by the operation unit, the non-emission time of the gain value Setting means for setting a value equal to the gain value at the time of main light emission.

Thereby, even when the main light emission is not performed with an appropriate light emission amount, it is possible to avoid the photographed image from being significantly different from the brightness intended by the photographer.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an imaging apparatus that is an embodiment of the present invention. Here, the image pickup apparatus shown in FIG. 1 shows a typical configuration of various image pickup apparatuses such as a digital camera integrated with a photographing lens, a single-lens reflex digital camera, and a video camera capable of taking a still image.
In FIG. 1, reference numeral 1 denotes a photographing lens that forms a subject image, and reference numeral 2 denotes a diaphragm mechanism that controls the amount of light that passes through the photographing lens 1. An aperture motor 3 drives the aperture mechanism 2, and an aperture drive circuit 4 drives the aperture motor 3. An aperture detector 5 detects the state of the aperture mechanism 2.

  Reference numeral 6 denotes an image sensor made up of a CCD sensor, a CMOS sensor, or the like that photoelectrically converts incident light. Reference numeral 7 denotes an image sensor driving circuit that reads out a signal photoelectrically converted by the image sensor 6 and controls a so-called electronic shutter function for controlling the accumulation time of the signal. Reference numeral 8 denotes a CDS circuit that samples a signal photoelectrically converted by the image sensor 6, and 9 denotes an AGC circuit that electrically amplifies the signal sampled by the CDS circuit 8.

Reference numeral 10 denotes an A / D converter that converts an analog signal output from the AGC circuit 9 into a digital signal. 11 performs processing such as gamma correction, color separation, and color difference matrix on the digital signal from the A / D converter 10 , and further adds a synchronizing signal to the signal to generate a video signal such as a standard television signal. A signal processing circuit. Reference numeral 12 denotes a field memory for storing image data processed by the signal processing circuit 11, and 20 denotes a recording medium such as a semiconductor memory, a magnetic disk, or an optical disk for recording still image data read from the field memory 12. .

  Reference numeral 13 denotes a microcomputer as control means for issuing a processing command to the signal processing circuit 11, the image sensor driving circuit 7, and the aperture driving circuit 4. A photo trigger (switch) 14 is operated by a photographer when taking a still image.

  A monitor 21 projects image data (video) sequentially read from the field memory 12.

  In the microcomputer 13, reference numeral 15 denotes a photometric unit that calculates a photometric value from the video signal, and reference numeral 16 denotes an aperture driving circuit 4 and an image sensor driving circuit for setting appropriate exposure control parameters based on the photometric result of the photometric unit 15. 7 and an exposure changing unit that outputs a command for controlling the AGC circuit 9. Reference numeral 17 denotes a photometric value memory for storing the first photometric value used for calculating the second light emission amount during flash photography. A light emission amount calculation unit 18 calculates a second light emission amount based on the first photometric value and the second photometric value during flash photography. The second light emission amount and the first and second photometric values will be described later. Reference numeral 22 denotes a gain calculation unit for calculating a second gain value to be described later.

  A light emitting unit 19 illuminates the subject.

  In the imaging apparatus configured as described above, an exposure control operation in a monitor mode other than during flash photography will be described first.

First, the amount of light incident from the photographing lens 1 is limited by the diaphragm mechanism 2 and enters the image sensor 6. The signal photoelectrically converted by the image sensor 6 is converted into a digital signal by the A / D converter 10 through the CDS circuit 8 and the AGC circuit 9. The digital signal is subjected to the signal processing described above in the signal processing circuit 11 and converted into a video signal.

  Luminance data corresponding to the exposure control area in the video signal is transmitted to the photometry unit 15 in the microcomputer 13. The photometry unit 15 performs an exposure control calculation based on the luminance data extracted from the video signal. In accordance with the calculation result, the exposure changing unit 16 sets the exposure control parameters such as the aperture setting value, the charge accumulation time in the electronic shutter, and the gain value in the AGC circuit 9 appropriately. A control command is output to the image sensor driving circuit 7 and the AGC circuit 9.

  At this time, if the brightness of the subject is dark, the gain value in the AGC circuit 9 is increased. The captured image with the gain value increased is displayed on the monitor 21. Thereby, the photographer can confirm the current exposure state.

  Next, the AGC operation and flash emission operation during flash photography will be described. When the photo trigger 14 is pressed by the photographer, the mode shifts to the still image shooting mode. When shifting to the still image shooting mode, the microcomputer 13 determines whether or not the subject in the monitor mode described above is dark and the gain value of the AGC circuit 9 is set higher than a predetermined value, and the gain value exceeds the predetermined value. If it is high, set the flash shooting mode.

  In the flash shooting mode, as a preparatory operation for still image main shooting, first, the exposure changing unit 16 controls the AGC circuit 9, and the first gain value is smaller than the gain value (third gain value: Gmon) in the monitor mode. Decrease to gain value (G1). Other exposure control parameters such as the aperture setting value and the charge accumulation time at the electronic shutter are fixed from when the photo trigger 14 is pressed until the end of still image shooting. At this time, the photometric value obtained by the photometric unit 15 is stored in the photometric value memory 17 as the first photometric value (Yold).

  Thus, in the exposure setting state in which only the gain value is decreased, the light emission amount calculation unit 18 calculates the first light emission amount (Tpre: the unit is μS, and the other light emission amounts are the same). The microcomputer 13 causes the light emitting unit 19 to perform a pre-light emission operation (first light emission operation) with the first light emission amount (Tpre).

  As the first light emission amount (Tpre), the light emission amount read from the data table according to the first photometric value (Yold) obtained when the photo trigger 14 is pressed is used.

  Photometry is performed by the photometry unit 15 using the video signal when the pre-flash operation is performed, and a second photometry value (Ypre) is obtained as a photometry result. The light emission calculation unit 18 uses the second photometry value (Ypre), the first photometry value (Yold), and the target photometry value (Yref) automatically set in advance by the photographer or by the microcomputer 13. The second light emission amount (Tmain) is calculated using Equation 1.

Tmain = [(Yref−Yold) / (Ypre−Yold)] × Tpre
... (Formula 1)
Next, the gain calculation unit 22 performs the third light emission which is the limit value (maximum light emission amount) of the light emission amount based on the second light emission amount (Tmain) calculated by (Equation 1) and the specifications of the light emitting unit 19. The amount (Tmax) is compared (Formula 2).

Tmain> Tmax (Expression 2)
Here, the third light emission amount (Tmax) may be determined in advance, or may be calculated according to the state of charge of a light emitting capacitor (not shown).

  When it is determined that the second light emission amount (Tmain) is larger than the third light emission amount (Tmax) (Equation 2), for example, the distance to the subject is far enough that the light emitted from the light emitting unit 19 does not reach sufficiently. In such a case, the gain calculation unit 22 calculates the second gain value using Equation 3.

G2 = [20 log (Tmain / Tmax)] × k + G1 (k is a coefficient)
... (Formula 3)
FIG. 2 shows the relationship between the second gain value (G2) calculated by Expression 3 and the second light emission amount (Tmain). Conventionally, even when the second light emission amount (Tmain) is larger than the third light emission amount (Tmax), the second gain value (G2) is equal to the first gain value (G1) set during the pre-light emission. It was the same. On the other hand, in this embodiment, when the second light emission amount (Tmain) is equal to or less than the third light emission amount (Tmax), the second gain value (G2) is the same as the first gain value (G1). The same, but when the second light emission amount (Tmain) is larger than the third light emission amount (Tmax), it depends on the ratio between the second light emission amount (Tmain) and the third light emission amount (Tmax). Thus, the second gain value (G2) is set larger than the first gain value (G1).

  However, when the second gain value (G2) is larger than the gain value (Gmon) in the monitor mode (Equation 4), the second gain value (G2) is changed to the gain value (Gmon) in the monitor mode. Set (Equation 5). Thereby, it is possible to prevent the photographer from feeling uncomfortable because the captured image is brighter than the monitor image in the monitor mode or the S / N is deteriorated.

G2> Gmon (Formula 4)
G2 = Gmon (Formula 5)
The exposure changing unit 16 controls the AGC circuit 9 in synchronization with the main light emission operation of the light emitting unit 19, and the gain calculating unit 22 determines the first gain value (G1) that has been set so far. It is increased to the second gain value (G2) (Gmon when Expression 4 is satisfied). Further, a third light emission amount (Tmax) is set as the light emission amount of the main light emission operation. Then, the actual photographing operation is performed, and the image data taken into the field memory 12 from the video signal generated by the image processing circuit 11 at that time is recorded in the storage medium 20.

  With the above operation, it is possible to avoid that the brightness of the monitor image in the monitor mode becomes much darker than that of the captured recording image, and it is possible to prevent the photographer from feeling uncomfortable.

  Next, a still image shooting control program that operates on the microcomputer 13 shown in FIG. 1 will be described with reference to the flowchart of FIG.

  In step S1, the microcomputer 13 determines whether or not the photo trigger 14 has been pressed. If the photo trigger 14 has been pressed (turned on), the process proceeds to step S2. If not, the process waits until the photo trigger 14 is pressed.

  In step S2, the gain value of the AGC circuit 9 is lowered from the gain value (Gmon) in the monitor mode to the first gain value (G1), and the first photometric value (Yold) at this time is further stored in the photometric value memory 17. Store, and proceed to step S3.

  In step S3, the first light emission amount (Tpre) is calculated to perform pre-light emission. At this time, photometry is also performed to obtain a second photometric value (Ypre). Then, the process proceeds to step S4.

  In step S4, the second light emission amount (Yold) is stored using the first photometric value (Yold) stored in step S2, the second photometric value (Ypre) at the time of pre-emission, and the target photometric value (Yref). Tmain) is calculated (formula 1), and the process proceeds to step S5.

  In step 5, it is determined whether or not the second light emission amount (Tmain) calculated in step S <b> 4 is larger than a third light emission amount (Tmax) that is the limit light emission amount of the light emitting unit 19. When the second light emission amount (Tmain) is larger than the third light emission amount (Tmax), the process proceeds to step S6. Otherwise, the process proceeds to step S9.

  In Step S6, the second gain value (G2) is calculated by Expression 3, Expression 4 and Expression 5, and the process proceeds to Step S7.

  In step S7, the gain value (first gain value G1) of the AGC circuit 9 is increased to the second gain value (G2) calculated in step S6, and the process proceeds to step S8.

  In step S8, the main light emission is performed by the light emitting unit 19 with the third light emission amount (Tmax), and the main photographing is performed. Then, an image (still image) photographed by the actual photographing is recorded in the storage medium 20, and the present flow ends.

  On the other hand, if it is determined in step S5 that the second light emission amount (Tmain) is not greater than (or less than) the third light emission amount (Tmax) and the process proceeds to step S9, the second light emission amount (Tmain) is determined. ) Causes the light emitting unit 19 to perform main light emission and performs main photographing. Then, an image (still image) photographed by the actual photographing is recorded in the storage medium 20, and the present flow ends.

  As described above, the imaging control described in the present embodiment can be realized by a hardware configuration or by a computer program.

1 is a block diagram illustrating a configuration of an imaging apparatus that is an embodiment of the present invention. The graph which shows the 2nd gain of an Example, and the relationship between emitted light amount. The flowchart which shows the still image shooting program of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting lens 2 Aperture mechanism 3 Aperture motor 4 Aperture drive circuit 5 Aperture detector 6 Image sensor 7 Image sensor drive circuit 8 CDS circuit 9 AGC circuit 10 A / D converter 11 Signal processing circuit 12 Field memory 13 Microcomputer 14 Photo trigger DESCRIPTION OF SYMBOLS 15 Photometry part 16 Exposure change part 17 Photometric value memory 18 Light emission amount calculation part 19 Light emission unit 20 Recording medium 21 Monitor 22 Gain calculation part

Claims (4)

An imaging device that performs main light emission after performing pre-light emission by a light emitting unit that emits light to a subject,
An imaging means for photoelectrically converting an object image;
Operation means for accepting an instruction to start a still image shooting operation;
Amplifying means for amplifying a signal from the imaging means;
Photometric means for measuring the subject based on the output from the imaging means;
A light emission amount calculating means for calculating a light emission amount of the light emitting means based on a photometric result of the light measuring means;
Light emission control for causing the light emitting means to perform main light emission at the maximum light emission amount when the main light emission amount calculated by the light emission amount calculating means based on the photometric result when pre-light emission is performed is larger than the maximum light emission quantity of the light emitting means Means,
Gain calculating means for calculating a gain value of the amplifying means when the light emitting means is caused to perform main light emission at the maximum light emission amount;
If the gain value calculated by the gain calculation means is greater than the gain value of the non-emission time which has been set before accepting the start instruction by the operation unit, the light emission value equal to the gain value during the non-emission An image pickup apparatus comprising: setting means for setting a gain value at the time. Exposure control means for controlling the aperture value and the charge accumulation time based on the photometric result of the photometric means,
The imaging apparatus according to claim 1, wherein the exposure control unit makes the aperture value and the charge accumulation time during main light emission equal to the aperture value and the charge accumulation time during pre-emission.   The imaging apparatus according to claim 1, wherein the maximum light emission amount changes in accordance with a charging state of a light emitting capacitor for causing the light emitting unit to emit light. An image pickup unit that photoelectrically converts an image of a subject, an operation unit that receives an instruction to start a still image shooting operation, an amplification unit that amplifies a signal from the image pickup unit, and a photometric measurement of the subject based on an output from the image pickup unit A method for controlling an imaging apparatus that performs main light emission after performing pre-light emission by a light-emitting means that emits light to a subject.
A light emission amount calculating step of calculating a light emission amount of the light emitting unit based on a photometric result of the photometric unit;
Light emission control for causing the light emitting means to perform main light emission at the maximum light emission amount when the main light emission amount calculated in the light emission amount calculating step is larger than the maximum light emission amount of the light emitting means based on the photometric result when pre-light emission is performed Steps,
A gain calculating step of calculating a gain value of the amplifying means when the light emitting means is caused to perform main light emission at the maximum light emission amount;
If the gain value calculated by the gain calculation step is greater than the gain value of the non-emission time which has been set before accepting the start instruction by the operation unit, the light emission value equal to the gain value during the non-emission And a setting step for setting the gain value at the time.