JPH0834553B2 - Electronic still camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera, and more particularly to an electronic still camera that also uses a solid-state imaging device for photometric measurement of subject brightness.

[Conventional technology]

Recently, an electronic still camera for recording captured images on a still video floppy (hereinafter referred to as a video floppy) instead of the silver salt film has been provided. Such an electronic still camera captures an image signal using a solid-state imaging device, for example, an interline transfer CCD (hereinafter abbreviated as CCD). Regarding the exposure determination, it was general to use a light receiving element such as SPD, but recently, as described in, for example, JP-A-63-169180,
It is known that the exposure time is calculated by the electric charge output from the CCD.

[Problems to be Solved by the Invention]

By the way, as described in the above publication, when the exposure value is determined by the output charge from the CCD, the width of the brightness range that can be measured is, for example, about 8 EV while the SPD is about 21 EV. Since it is narrow, considering that the brightness distribution covers a range of about 5EV on a general subject screen, it is not uncommon for photometric errors to occur. In order to improve this, the applicant of the present invention has proposed an electronic still camera in which the photometric brightness range of the CCD is automatically changed and photometry is repeated a plurality of times to calculate an appropriate exposure value.

However, if the necessity of stroboscopic photography is determined after performing photometry multiple times in this way, in addition to the time required for photometry, preparation for using the strobe, for example, checking whether the charge amount of the capacitor is sufficient or not is checked. Therefore, there is a problem that the time required for the charging operation and the like, and the time from the pressing of the shutter button to the recording of the subject image on the video floppy, that is, a so-called time lag, becomes extremely large.

On the other hand, in order to determine the necessity of stroboscopic photography with one photometry without performing photometry multiple times, it is necessary to shift the photometric brightness range of the CCD to the low brightness side. In this case, there is a problem that it takes time for photometry for a general subject that does not require flash photography.

[Object of the Invention]

The present invention has been made to solve the above-described problems, and it is possible to accurately determine whether or not stroboscopic photography is necessary while performing photometry with a solid-state imaging device having a narrow photometry area, and general brightness It is an object of the present invention to provide an electronic still camera with a small time lag, which enables accurate photometry in a short period of time for subjects having a distribution.

[Means for solving the problem]

In order to achieve the above object, the electronic still camera of the present invention performs preliminary photometry in a predetermined photometric luminance range by a solid-state imaging device, and shifts the photometric luminance range based on the obtained preliminary photometric value. The main metering is performed with the main metering, and whether the flash photography is necessary or not is determined by whether the main metering value obtained by the main metering is biased toward the low brightness side by a predetermined brightness value or more than the preliminary metering value. is there.

[Action]

According to the above-described means, by performing the preliminary photometry, first, the photometric reference value is made to match the preset brightness value, so that the photometry is performed within the brightness range set as the preliminary photometry. Based on the preliminary photometric value which is the result of the photometry, the photometric range of the solid-state imaging device is corrected so as to be included in the range in which the subject brightness is distributed. Then, main metering is performed within this metering range, and whether or not stroboscopic photography is necessary is determined by whether or not the obtained main metering value is biased toward the lower brightness side by a predetermined brightness value or more than the preliminary metering value.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

〔Example〕

In FIG. 1 showing an optical system and a circuit block of an electronic still camera 1 of the present invention, an optical system of the electronic still camera 1 is composed of a taking lens 10 having two groups (lenses 10a, 10b) and a lens.
It is composed of an instantaneous aperture stop 11, an optical reduction pass filter (OLPF) 12, and a CCD 15, which are arranged between the lens 10a and the lens 10a.

The CCD 15 has C controlled by the overall control unit 16.
The CD drive circuit 17 is connected. Further, the CCD 15 outputs the read image signal to a predetermined sampling frequency (for example,
Preamplifier 2 which samples and holds and amplifies at 3.58MHz
0, a color separation circuit 21 for converting the signal from the preamplifier 20 into a primary color signal (RGB), and a γ correction circuit 22 for gamma-correcting each RGB color signal with γ = 0.45 are connected.

As shown in FIG. 2, the γ correction circuit 22 is a correction circuit for normalizing the gradation of the reproduced image in accordance with the light emission characteristics of the picture tube, and it corrects the image signal photoelectrically converted by the CCD 15. , It is designed to output a signal proportional to the 0.45th power. The photometric brightness range of the CCD15 for the input signal is E
_i about 8EV between to E _m, E _i are not 0 at the dark current or the like.

The brightness range of the CCD15 that can be measured is wide compared to the contrast ratio of the television system of 30 (about 5 EV), so the knee part that compresses the high brightness side and the white clip part that cuts the higher brightness side are provided. , Video output. Generally, the dark part (black) of the video output image is 10IRE with the video signal.
("IRE" is a linear voltage output expressed as a percentage), and the bright part (white) is displayed as 100IRE in the video signal. Therefore, when using CCD15 as an AE sensor,
If you decide the exposure condition so that the video output will be 60 IRE,
The gradation of the reproduced image becomes normal.

A matrix circuit 23 for converting each gamma-corrected signal into a luminance signal and a color difference signal, and an encoder 25 for sending the luminance signal and the color difference signal to a recording unit 24 are sequentially connected to the γ correction circuit 22. There is.

A diaphragm drive circuit 26 controlled by the overall control unit 16 is connected to the diaphragm 11. In addition, the overall control unit 16 includes an AF distance measuring unit 27 for measuring the subject distance and an arc tube 28.
A flash drive circuit 29 for emitting light and a shutter button 30 are connected. Although not shown, the recording unit 24
Is composed of a magnetic head or the like for writing the image signal from the encoder 25 to the video floppy via the head amplifier.

Next, the operation of the electronic still camera 1 of the present invention configured as described above will be described. First, electronic still camera 1
When the video floppy is loaded into the and the power is turned on, the loaded video floppy starts to rotate and 60 seconds per second in about 30 ms.
Reach a steady number of rotations.

With the diaphragm 11 open, the photographing lens 10 is aimed at the subject and the shutter button 30 is half-pressed. The overall control unit 16 drives the AF distance measuring unit 27 to measure the subject distance according to the built-in program sequence as shown in the flowchart of FIG. 3, and drives the taking lens 10 according to the distance measuring data to adjust the focus. I do. Also, a command signal is sent to the strobe drive circuit 29 to start charging the main capacitor (not shown).

Next, when the shutter button 30 is fully pressed, a voltage is applied to the electrodes of the CCD 15 by the CCD drive circuit 17 according to the vertical synchronizing pulse, that is, so-called startup is performed. As a result, the CCD 15 enters a state in which it can photoelectrically convert incident object light and accumulate and transfer the obtained signal charge.

The photometric brightness range of the CCD 15 is determined only by the charge storage time because the diaphragm 11 is open. As for the charge accumulation time T ₀ during the preliminary photometry, the photometric reference value E ₀ of the preliminary photometry is, for example, 12 EV as shown in FIG. 4, and the standard subject brightness distribution B shown by the broken line is the latitude of the CCD 15 (about 8 EV). It is set to be included as much as possible.

The subject light that has passed through the shooting lens 10 is CC through the OLPF12.
When the first sweep pulse is incident on D15, the accumulated charge of CCD15 becomes zero, and at the same time, photoelectric conversion and charge accumulation of preliminary photometry are started. CCD1 after charge accumulation time t ₀
The charges accumulated in the photoelectric conversion unit 5 are read out by the sweep pulse and sent to the preamplifier 20.

The signal input to the preamplifier 20 is sampled and held at a predetermined sampling frequency and sent to the color separation circuit 21, where it is separated into R, G, and B color signals. Each of these color signals is gamma-corrected by the γ-correction circuit 22 and sent to the overall control unit 16. In this overall control unit 16, this R, G,
The brightness signal is detected from the B signal to calculate the preliminary photometric value E ₁ .

Subsequently, the overall control unit 16 shifts the charge accumulation time of the main photometry to t ₁ so that the photometric reference value of the main photometry becomes the preliminary photometry value E ₁ . The sweep pulse causes the accumulated charge in the CCD 15 to become zero, and at the same time, the main photometry is started. After the lapse of the charge accumulation time t _1, the charges accumulated in the CCD 15 are read out by the sweep pulse and sent to the preamplifier 20.

This signal charge is input to the overall control unit 16 via the color separation circuit 21 and the γ correction circuit 22. The overall control unit 16 calculates the main photometric value E ₂ based on this. It is calculated how much the main photometric value E ₂ is biased toward the low luminance side compared to the preliminary photometric value E ₁ , and when the width is equal to or more than a constant luminance value ε (for example, 1EV), flash photography is switched.

That is, when the subject brightness distribution A shown by the solid line in FIG. 4 is “E ₁ −E ₂ > ε”, the brightness is extremely low as compared with the standard subject brightness distribution B, and thus natural light is obtained. Switching from photography to strobe photography, the overall control unit 16 confirms whether or not the main capacitor of the strobe drive circuit 29 is sufficiently charged.

If not enough, a command signal is sent to the strobe drive circuit 29 to continue charging the main capacitor. Along with the completion of charging, the aperture value for flash photography A _v1 and shutter speed T _v1 are set, and the aperture value 11 is reduced to the aperture value A _v1 .
At the same time that the charge accumulated in the CCD 15 is made zero by the sweep pulse, a command signal is sent to the strobe drive circuit 29 to cause the arc tube 28 to emit light. When the shutter speed T _v1 elapses, the charge accumulated in the photosensitive portion of the CCD 15 is read by the sweep pulse and transferred to the preamplifier 20.

The image signal input to the preamplifier 20 is processed by the color separation circuit 21 and the γ correction circuit 22 as in the case of photometry, and then input to the matrix circuit 23 to be converted into a luminance signal and a color difference signal, and is passed through the encoder 25. And is sent to the recording unit 24. The image signal read from the CCD 15 is instantly recorded on the video floppy by the recording unit 24, and the aperture 11 is returned to the open state at the next moment.

If "E ₁ -E ₂ >ε" is not satisfied, it can be determined that the subject brightness is extremely high (eg, 17EV), or the subject's brightness distribution area is sufficiently covered by the CCD15 latitude during the main metering. It is determined that the auxiliary light is unnecessary and the mode is switched to non-flash photography.

Note that, for example, a brightness of 17 EV or more means an aperture of F100, which is ISO100.
Since the shutter speed is 1/1000 seconds or more, it is a very special shooting that is close to the brightness of a light emitter such as the sun, and such a special case is not taken into consideration.

In non-flash photography, the aperture value A _v2 and the shutter speed T _v2 are set based on the main photometric value E ₂ . Subsequently, the overall control unit 16 sends a signal to the diaphragm drive circuit 16 to transmit the diaphragm 11
To the aperture value A _v2 . When the diaphragm 11 is narrowed down, the sweep pulse synchronized with the next vertical sync pulse causes CC
The electric charge of D15 is made zero and exposure is started. When the set shutter speed T _v2 elapses, the charge accumulated in the photosensitive section of the CCD15 is read by the sweep pulse,
Transferred to the preamplifier 20. The following description is the same as that at the time of stroboscopic photography, and is therefore omitted.

In the embodiment described above, in order to reduce the consumption of the amount of electricity, the start of photometry is set after the shutter button is fully pressed, but it is possible to perform preliminary photometry or main photometry by pressing the shutter button halfway. Good.

The brightness signal for photometry input to the overall control unit 16 is
It may be taken from the encoder 25.

〔The invention's effect〕

As described above, according to the electronic still camera of the present invention, preliminary photometry is performed by the solid-state imaging device within a predetermined photometric luminance range, and the photometric luminance range is shifted based on the obtained photometric value. Since the main metering is performed by using this function, the necessity of stroboscopic shooting is determined based on the photometric value obtained by this main metering. It is possible to provide an electronic still camera that can perform accurate determination and that can accurately perform photometry for a subject having a general luminance distribution in a short time with a small time lag.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the structure of an embodiment of the present invention. FIG. 2 is a reference diagram showing a state in which the image signal is gamma-corrected. FIG. 3 is a flow chart showing the main part of the sequence program of this embodiment. FIG. 4 is a schematic diagram showing an example of the subject brightness distribution and the photometric brightness range of the preliminary photometry and the main photometry. 1 …… Electronic still camera 15 …… CCD 16 …… General control unit 29 …… Strobe drive circuit.

Claims (1)

[Claims] 1. An electronic still camera, which is disposed on an image plane and which converts an optical image into an electric signal and outputs the signal, and which also serves as a photometer for subject brightness, performs preliminary photometry at a predetermined charge accumulation time. Based on the obtained preliminary metering value, a new charge accumulation time is set by shifting the measurable luminance range, main metering is performed at this charge accumulation time, and the obtained main metering value is more than the preliminary metering value. An electronic still camera, characterized in that whether or not stroboscopic photography is necessary is determined depending on whether or not the brightness value is biased to a low brightness side or more.