JPH0726874B2 - Electronic still camera - Google Patents

Description

The present invention relates to an electronic still camera. More specifically, the present invention relates to an electronic still camera that also uses a solid-state imaging device for photometry 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 determination of exposure, it was general to use a light receiving element such as SPD, but recently, as described in, for example, JP-A-63-169180, CC
It is known that the exposure time is calculated by the output charge from D. According to this method, since it is possible to perform photometry with the same image information as that of the photographic screen, it is possible to accurately calculate the exposure value, and it is not necessary to separately provide a photometric system, which is advantageous in that it can contribute to downsizing and cost reduction. .

[Problems to be Solved by the Invention]

However, the width of the brightness range that can be measured by CCD is, for example, SPD.
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, it is not uncommon for photometric errors to occur. In other words, there is no problem when the brightness range of about 5EV on the subject screen is included in the photometric brightness range of about 8EV of the CCD, but the brightness range of the subject screen is outside the brightness range that can be measured by the CCD. If so, there is a problem that accurate photometry cannot be performed.

[Object of the Invention]

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electronic still camera that can always take a picture with proper exposure while performing photometry with a solid-state imaging device having a narrow photometry area. To do.

[Means for Solving the Problems]

In order to achieve the above object, the electronic still camera of the present invention performs preliminary photometry with a solid-state imaging device to measure the subject brightness, and automatically shifts the brightness center value set during photometry based on this photometric value. Then, the main photometry is performed after shifting the photometric range.

[Action]

According to the above-mentioned means, by preliminary photometry, first, by making the photometric center value coincide with the preset brightness value,
Photometry is performed within the brightness range in which photometry is set as preliminary photometry. Based on this photometric result, the photometric center value is made to match the preliminary photometric value, and the photometric range of the solid-state imaging device is corrected to be included in the range in which the subject brightness is distributed.

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)
It is composed of an instantaneous aperture diaphragm 11, an optical low-pass filter (OLPF) 12, and a CCD 15 arranged between the lens 10a and the lens 10b.

CCD 15 is controlled by the overall control unit 16.
The drive circuit 17 is connected. Further, the CCD 15 reads the read image signal at a predetermined sampling frequency (for example, 3.
Pre-amplifier 20 which samples and holds and amplifies at 58MHz),
A color separation circuit 21 for converting a 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 to E a _m at about 8 EV, 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 CCD15 is used as AE sensor, video output is 6
If the exposure condition is determined to be 0IRE, the gradation of the reproduced image becomes normal.

The gamma correction circuit 22 includes a matrix circuit 23 for converting each gamma-corrected signal into a luminance signal and a color difference signal, and an encoder for sending the luminance signal and the color difference signal to the recording unit 24.
25 are connected in sequence.

A diaphragm drive circuit 26 controlled by the overall control unit 16 is connected to the diaphragm 11. The overall control unit 16 is also connected to an AF distance measuring unit 28 for measuring the subject distance, a flash drive circuit 29, and a shutter button 30. In addition,
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 a video floppy via a head amplifier.

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

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 28 to measure the subject distance according to the program sequence contained therein, 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. Next, when the shutter button 30 is fully pressed, the CCD drive circuit 17 activates the CCD 15 in accordance with the vertical synchronizing pulse.

The subject light that has passed through the taking lens 10 passes through the OLPF12 and CCD1
As shown in the timing chart of FIG. 4, the first sweep pulse P ₁ causes the charge stored in the CCD 15 to become zero, and at the same time, photoelectric conversion for preliminary photometry and charge storage are started. The brightness range that can be measured by CCD15 is determined by the aperture and the charge storage time, but during this preliminary photometry, the aperture of the taking lens 10 is open, so the only brightness range that can be measured by preliminary photometry is the CCD15 charge storage time. Depends on. The charge storage time t _O during this preliminary metering is 60% when the video output is 60 when a standard subject with an average brightness of 12 EV is metered.
Predetermined to be IRE.

The charge accumulated in the photoelectric conversion part of CCD15 is the charge accumulation time t
After the passage of _O , it is read by the sweep pulse P ₂ 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 RG 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 RG and B signals to calculate a photometric value, compares the photometric value with 12EV which is the preset luminance value at the time of preliminary photometry, and compares the shift amount shown in FIG. Calculate about 2.5 EV from the figure to the negative side. This calculation is performed during the blanking period after reading, and after the elapse of the time t _A (about 500 μs) required for this, the sweep pulse P
_{By 3} , the charge accumulated in the CCD 15 becomes zero and at the same time the main photometry is started.

Based on the shift amount, the charge accumulation time is shifted to “t _O + α” so that the photometric value becomes the connection luminance value at the time of main photometry, and the charge accumulated in the CCD 15 is time “t _O + α”. Is read out by the sweep pulse P ₄ after the passage of, and is sent to the preamplifier 20. This signal charge is transferred to the color separation circuit 21,
It is input to the overall control unit 16 via the γ correction circuit 22. The overall control unit 16 calculates the main photometric value based on this, and calculates the exposure value T based on the main photometric value (the time required for this is about 500 μs, which is indicated by symbol t _B in FIG. 4). Of course, the sign of α is a positive value if the subject brightness value is lower than 12EV, and a negative value if it is high.

Subsequently, the overall control unit 16 sets an appropriate aperture value f _r and shutter speed S _T corresponding to the exposure value T and sends a signal to the aperture drive circuit 26 to narrow down the aperture 11 to the aperture value f _T. At the same time when the diaphragm 11 is narrowed down, the sweep pulse P ₅ causes CCD 15
Is zeroed, and exposure is started. When the set shutter speed S _T has elapsed, the charge accumulated in the photosensitive portion of the CCD 15 is read by the sweep pulse P ₆ 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,
It is sent to the recording unit 24 via the encoder 25. The image signal read from the CCD 15 is instantly recorded on the video floppy by the recording unit 24, and at the next moment, the aperture 11
Is returned to the open state.

Note that, for example, when the brightness information is separately obtained from the central portion and the peripheral portion, and when the main subject in the central portion is larger than the peripheral luminance, it is determined that the backlight is backlit even if the overall luminance value is bright, and the strobe light is emitted. You may In addition, the overall control unit 16
The brightness signal for photometry input to may be taken from the encoder 25.

〔The invention's effect〕

As described above, according to the electronic still camera of the present invention, by performing the preliminary photometry and the main photometry, the photometric brightness range of the solid-state imaging device is automatically shifted according to the brightness level of the subject. Therefore, it is possible to provide an electronic still camera that can always take a picture with proper exposure while performing photometry with a solid-state imaging device having a narrow photometry area.

[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 timing chart of the main part of this embodiment. FIG. 5 is a schematic diagram showing a brightness range in which preliminary metering and main metering are possible. 1 ... Electronic still camera 11 ... Aperture, 15 ... CCD 16 ... General control unit, 22 ... γ correction 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. An electronic still camera characterized in that after a new charge accumulation time is set based on the obtained photometric value, the main photometry is performed at this charge accumulation time.