JPH0834556B2 - 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 that records a captured image 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]

However, the width of the brightness range that can be measured by CCD is, for example, S
The PD is about 21EV, while it is narrow at about 8EV. Therefore, considering that the brightness distribution covers a range of about 5 EV on a general subject screen,
There are some errors in photometry. In other words, there is no problem if the brightness range of about 5 EV on the subject screen is included in the measurable brightness range of about 8 EV of the CCD,
If the brightness range of the subject screen is out of the brightness range that can be measured by CCD, the problem arises that accurate metering cannot be performed.

In order to improve such a problem, the applicant of the present invention has proposed an electronic still camera in which photometric reference values are automatically changed and photometry is repeated a plurality of times to calculate an appropriate exposure value. However, since charging check and charging operation take time during stroboscopic photography, there is a problem that the time from pressing the shutter button until the subject image is recorded on the video floppy, so-called time lag, becomes extremely large.

[Object of the Invention]

The present invention has been made to solve the above-mentioned problems, and while performing photometry with a solid-state imaging device having a narrow photometry area, it is possible to always take a picture with proper exposure, and there is little time lag during stroboscopic imaging. An object is to provide an electronic still camera.

[Means for solving the problem]

In order to achieve the above object, the electronic still camera of the present invention performs preliminary photometry with a solid-state imaging device within a predetermined photometric brightness range, and if the obtained photometric value is lower than a predetermined reference value, flash photography is performed. When the value is higher than the reference value, the main metering is performed by shifting the measurable range based on the preliminary metering value.

[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. If the photometric result is lower than a predetermined reference value, the flash photography is switched. When the result of the preliminary photometry is higher than the predetermined reference value, the photometry reference value is made to match the preliminary photometry value based on the result of the photometry, and the photometry range of the solid-state imaging device is the range where the subject brightness is distributed. Is modified to include.

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 according to the present invention, an optical system of the electronic still camera 1 includes an imaging lens 10 having two groups (lenses 10a and 10b) and a lens.
It is composed of an instantaneous aperture type aperture stop 11 in which 10a is placed between lenses 10b, an optical low pass filter (OLPF) 12, and a CCD 15.

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. In addition, since the CCD15 has a wide photometric brightness range compared to the TV contrast ratio of 30 times (about 5 EV), the knee part that compresses the high brightness side and the white clip part that cuts the higher brightness side are higher. Is provided for video output. When the CCD 15 is used as an AE sensor, if the exposure conditions are determined so that the video output is 60 IRE, the gradation of the reproduced image will be 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 chromaticity signal to a recording unit 24 are sequentially connected to the γ correction circuit 22. ing.

A diaphragm drive circuit 26 controlled by the overall control unit 16 is connected to the diaphragm 11. The overall control unit 16 also 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 program sequence contained therein, as shown in the flowchart of FIG. 3, and drives the imaging lens 10 according to the distance measuring data to adjust the focus. I do. 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 in accordance with the vertical synchronizing pulse, 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 subject light that has passed through the imaging lens 10 is CC through the OLPF12.
When the first sweep pulse is incident on D15, the charge stored in the CCD 15 becomes zero, and at the same time, photoelectric conversion for preliminary photometry and charge storage are started. Metering reference value E ₀ during this preliminary metering
Is set to the low brightness side, for example, 9 EV to determine whether or not stroboscopic photography is necessary. As shown in FIG. 4, the measurable brightness range is about 5 EV to 13 EV.

The charge accumulated in the photoelectric conversion unit of the CCD 15 is read out by the sweep pulse after the charge accumulation time t ₀ has elapsed and is 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. The overall control unit 16 detects the luminance signal from the R, G, B signals and calculates the preliminary photometric value E ₁ .

This preliminary photometric value E ₁ is about 7 EV when the subject has the luminance distribution A as shown by the solid line. When comparing the preliminary photometry value E ₁ with the photometry reference value E ₀ , the overall control unit 16 determines that the flash photography is performed because “E ₁ <E ₀ ”, and the main capacitor of the flash drive circuit 29 (see FIG. (Not shown) is fully charged.

If it is not sufficient, a command signal is sent to the strobe drive circuit 29 to charge the main capacitor, and the aperture value A _v1 and shutter speed T _v1 for strobe photography are set. When the charging is completed, the diaphragm 11 is narrowed down to the diaphragm value A _v1 and the sweep-out pulse reduces the accumulated charge of the CCD 15 to zero, and at the same time, 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 priang 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.

When the subject has the brightness distribution B as shown by the broken line, the preliminary photometric value E ₁ is about 11.4 EV and “E ₁ > E ₀ ”.
Therefore, it is judged that the auxiliary light by the strobe is not necessary, and the non-stroboscopic photographing is switched to the main metering. The charge accumulation time of the main metering is shifted to "t ₀ + α" so that the reference metering value of the main metering becomes the preliminary metering 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 ₀ + α”, the charges accumulated in the CCD 15 are read out by the sweep pulse and sent to the preamplifier 20. This signal charge is transferred to the color separation circuit 21, γ
It is input to the overall control unit 16 via the correction circuit 22. The overall control unit 16 calculates the main photometric value E ₂ based on this, and the absolute value | E ₂ −E ₁ | of the difference between the main photometric value E ₂ and the preliminary photometric value E ₁ is a constant value ε (for example, It is determined whether it is smaller than 1EV).

If │E ₂ -E ₁ │ <ε, it can be determined that the brightness distribution area of the subject is covered by the CCD15 launch range during the main metering, so the main metering value E ₂ is the proper metering value of the subject. It is a reliable value. Therefore, this main photometric value E ₂
The aperture value A _v2 and the shutter speed T _v2 are set based on Subsequently, the overall control unit 16 sends a signal to the diaphragm drive circuit 16 to narrow down the diaphragm 11 to the diaphragm value A _v2 .

When the diaphragm 11 is narrowed down, the charge of the CCD 15 is made zero by the sweep pulse synchronized with the next vertical synchronizing pulse,
Exposure is started. When the set shutter speed T _v2 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 following description is the same as that at the time of stroboscopic photography, and is therefore omitted.

If | E ₂ -E ₁ | <ε is not true, the main photometric value E ₂ is a low-reliability value, so photometry is repeated until | E ₂ -E ₁ | <ε is satisfied. Further, the brightness signal for photometry input to the overall control unit 16 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 in a predetermined photometric brightness range,
If the obtained photometric value is lower than the predetermined reference value, it switches to flash photography, and if it is higher than the reference value, the metering range is shifted based on the preliminary photometric value, and then the main photometry is performed. Thus, it is possible to provide an electronic still camera that can always perform shooting with proper exposure while performing photometry with a solid-state imaging device having a narrow photometry area and that has a small time lag during flash photography.

[Brief description of 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 the brightness range in which preliminary metering and main metering are possible. 1 …… Electronic still camera 15 …… CCD 16 …… General control unit 29 …… Strobe drive circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 5/335 Q

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. If the obtained preliminary photometric value is lower than a predetermined reference value, flash photography is switched to, and if it is higher than the reference value, new charge accumulation is performed by shifting the photometric brightness range based on the preliminary photometric value. An electronic still camera characterized in that after the time is set, the main photometry is performed at this charge accumulation time.