JPS63167338A - Still video camera - Google Patents

Abstract

PURPOSE:To correct an exposure error including in an output from an image pickup means by controlling the gain of the output from the image pickup means based on an exposure error signal computed from a photometric integrating value and a voltage corresponding to a proper level of the image pickup means. CONSTITUTION:Light beams made incident through photographing lenses 1a, 1b when exposure control based upon a photometric value before exposure is started are made incident upon the image pickup means 7 such as a CCD and a part of the incident light beams are received by a photoelectric converter constituting a 2nd photometric means 8. A picture signal picked up by the means 7 and converted into an electric signal has an exposure error based upon the exposure control. On the other hand, a 2nd arithmetic means outputs an error signal corresponding to the exposure error based on an output signal from an integrating means 20 for integrating the output of the 2nd photometric means 8 and the voltage corresponding to the proper exposure level of the means 7. A gain control circuit 10 controls the gain so that the exposure error is removed from the picture signal in according with the error signal. Consequently, the output of the circuit 10 is recorded in a magnetic disk in a preferable state removing almost all the exposure error.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a still image having a photoelectric conversion type imaging means (such as a CCD) having a function of capturing a still image to be recorded on a magnetic disk and converting it into an electrical signal. Regarding video cameras.

2. Description of the Related Art A still video camera has been proposed in Japanese Patent Application Laid-open No. 194574/1983, in which exposure to a CCD is controlled based on photometric values before exposure, and gain control of an image signal of the CCD is controlled. However, this camera could not cope with sudden changes in subject brightness during the exposure period. Also, CC
A still video camera has been proposed in Japanese Patent Laid-Open No. 60-52635, which obtains proper exposure by photometering light equivalent to the light actually incident on D during the exposure period. According to this method, a proper exposure can be obtained even if the subject brightness suddenly changes, but the photographer may misunderstand that exposure control is performed based on the photometric value of the subject brightness before exposure. still,
When the subject brightness suddenly decreases, for example, the shutter speed becomes slower than the camera shake limit speed, causing camera shake or making it impossible to obtain the desired shutter effect.

Problems to be Solved by the Invention In general, in a lens-shutter camera that uses silver halide film, the exposure error of the shutter that also serves as an aperture is ±I.
It is normal for about Ev to occur.

Furthermore, an exposure error of about ±0.5 Ev may occur even in an eye reflex camera equipped with a focal plane shutter. Incidentally, in a still video camera, the exposure error must be suppressed within ±0.2 Ev because the imaging means such as a CCD and its signal processing system have a narrow Guinamin range.

Therefore, an object of the present invention is to enable a still video camera to record on a magnetic disk with an appropriate exposure error within ±0.2 EV, and to perform exposure control based on the photometric value before exposure. It's about doing.

Means for Solving the Problems The still video camera of the present invention solves the above problems.
a photographic lens, a first photometric means, a first calculating means for calculating exposure control data based on the photometric value of the first photometric means, and performing exposure control based on the exposure control data of the first calculating means. an exposure control means, a photoelectric conversion type imaging means for imaging a still image, a second photometry means for receiving and metering a part of the light incident on the imaging means, and gain control of the output of the I-layer imaging means. a gain control circuit for integrating the output of the second photometric means during the exposure control period; and an exposure error signal from the integrated voltage of the integrating means and the voltage corresponding to the appropriate exposure level of the imaging means. and a second calculation means for outputting the exposure error signal and supplying the exposure error signal to the gain control circuit as a gain control signal.

When exposure control based on the photometric value before the exposure is started, light entering through the photographic lens enters an imaging means such as a CCD, and a portion of the incident light is transferred to a photoelectric conversion element constituting the second photometry means. The light is received by the An exposure error based on the exposure control occurs in the image signal captured by the imaging means, converted into an electrical signal, and output.

On the other hand, the second calculation means outputs an error signal corresponding to the exposure error from the output signal of the integration means for integrating the output of the second photometry means and the voltage according to the appropriate exposure level of the imaging means. The gain control circuit performs gain control on the image signal according to the error signal so as to remove the exposure error. Therefore, the output of the gain control circuit is in a preferable state in which the exposure error caused by the exposure control described above is almost eliminated, and FIG. 1 shows an example of recording on the magnetic disk in this state. The configuration of the section is shown as a block circuit. Photography lens (la)
A lens shutter (2) serving as both an aperture and a shutter is arranged on the pupil plane (lb), and this lens shutter (2) is driven to open and close by a shutter drive mechanism (3). At the rear of the lens shutter (2), there is provided a light branching means (5) consisting of a half mirror fixedly arranged and tilted at a predetermined angle with respect to the optical axis (4). The light branching means (5) branches the incident light into a first direction (A) and a second direction (B), and the light guided in the first direction passes through an optical low-pass filter (6). CC
This leads to D(7). Further, the light guided in the second direction is received by a photometric means (8) consisting of a photoelectric conversion element.

A CCD (7) is used here as a photoelectric conversion type imaging means, and this C0D (7) is connected to a driver circuit (9).
Driven by. At that time, the photoelectrically converted two-dimensional image information signal is output as a temporal one-dimensional image information signal, and the gain control circuit (10) arranged in the next stage
given to.

The image signal whose gain has been controlled by the gain control circuit (10) is subjected to various processing in the signal processing circuit (11) to form a signal that conforms to the standards of still video cameras, and is stored on a magnetic disk in the next recording section (12). recorded in

The signal processing circuit (11) performs T correction, color separation, white balance, a matrix of color difference signals and luminance signals,
Performs signal processing such as modulation and synthesis. The output of the photometry means (8) is input to an exposure error calculation and strobe stop signal generation circuit (hereinafter referred to as "calculation/generation circuit") (13). This arithmetic/generating circuit (13) will be explained in detail later with reference to FIG. Light receiving element for photometry (to determine exposure value)
14) is installed in a separate location from the photographic lens,
The output is supplied to a photometric calculation circuit (15).

The system control circuit (16), which is the core of the control operation of the camera, exchanges signals with the arithmetic/generating circuit (13) and the photometry arithmetic circuit (15), as well as the shank-drive mechanism (3) and the driver. Circuit (9), recording section (
12) and the power supply circuit (17). In addition, the photometry switch (S+), the release switch (S2),
It is also connected to the switch (S3), etc. that indicates the completion of shutter closing, and these switches (s+) (sz) (
s3) information. The switch (S,) is turned on when shutter closing is completed, and turned off when shutter charging is completed. A synchro switch (SX) is connected to the strobe (18) and turns on when the shutter starts to close in conjunction with the shutter activation mechanism (3). When this synchro switch is turned on, the strobe (18)
) begins to emit light. The strobe (18) is stopped by a light emission stop signal from the calculation/generation circuit (13).

FIG. 2 shows a specific example of the arithmetic/generating circuit (13), in which an operational amplifier (19) is connected to the photometric means (8). A capacitor (20) for integrating and accumulating photometric current is connected between the output terminal and the negative input terminal (-) of this operational amplifier (19), and a switch is connected between both ends of this capacitor (20). The source and drain of the active field effect transistor (21) are coupled. The field effect transistor (21) has a gate connected to the system control circuit (16),
When a low level voltage is applied from the system control circuit (16), it turns on and shorts both ends of the capacitor (20), and when a high level voltage is applied, it turns off and charges (integrates) the capacitor (20). make it possible.

The positive input terminal (+) of the operational amplifier (19) has COD (corresponding to the film sensitivity value in the case of silver halide film).
7) A voltage (Vref) indicating the sensitivity value is also provided. The output voltage of the operational amplifier (19) is
It is applied to the negative input terminal (-) of an operational amplifier (23) in an error calculation section (22) via a resistor (24). On the other hand, a potentiometer (25) is connected between the positive input terminal (+) and the ground, and a variable resistor (26) is connected between the output terminal and the negative input terminal (-). Among the outputs of this error calculation section (22), CCD
The output during the period in which charge transfer is performed in (7) is a voltage corresponding to the appropriate exposure level and the operational amplifier (19).
) is adjusted by the variable resistor (26) and potentiometer (25) so as to generate an exposure error signal corresponding to the difference between the output voltage when the shutter is completely closed, and the error calculation unit (2
2) converts this exposure error signal into a gain control circuit (
10) as a gain control signal to remove the portion of the video signal from the CCD (7) based on the exposure error. A stop signal generating section (27) in the arithmetic/generating circuit (13)
) has a comparator (28), and a voltage (VO) corresponding to the appropriate exposure level is applied to the negative input terminal (-) of this comparator (28), and the positive input terminal (
+) is applied with the output voltage (V) of the operational amplifier (19) via a resistor (29). When the output voltage (v) of the operational amplifier (19) increases and exceeds the appropriate exposure voltage (vO), the output of the comparator (28) is inverted from low level to high level, and the high level is used as the light emission stop signal. The signal is supplied to the strobe (18) as a signal.

Next, the operation of the embodiment shown in FIGS. 1 and 2 will be explained in FIGS. 3 to 5.
This will be explained with reference to the figures.

In FIG. 3, (a) shows the operation of the power supply circuit (17), which is activated when it is at a high level and inoperative when it is at a low level. (b) similarly shows the operation of the photometric calculation circuit (15). (c) shows a release pulse generated when the release switch (S2) is turned on.

(d) shows the operation of the shutter (2), and the joint axis represents the opening area of the shutter. (e) shows the strobe light, (f) shows the operation of the shutter closing switch (S, ), and the high level shows on and the low level shows off. (
(g) shows the charge transfer operation in CCD (7),
(to) is the power on, (tl) is the release switch (
S2) is turned on, (t2) is when the lens shutter (2) starts to open, (t,) is when the shutter starts to close, (t4) is when the strobe stops emitting light, (t,) is when the shutter is completely closed, (
t, ) represent completion of recording and power off, respectively.

First, the operation when the strobe is not used will be explained.

to=t,: shutter phase provided on the outer surface of the camera (
When the switch (not shown) is pressed halfway, the photometry switch (Sl) turns on, and in response, the system control circuit (16
) outputs a signal that activates the power supply circuit (17),
Power is supplied to each part within the camera [to]. The system control circuit (16) also includes a photometry calculation circuit (15).
) is also commanded to start operation.

As a result, a current corresponding to the amount of light received by the photometric light receiving element (14) is processed and calculated by the photometric calculation circuit (15) to determine an exposure value. This exposure value data is given to the system control circuit (16). Regarding the CCD, idle transfer (charge transfer only in the transfer section) for removing smear is performed under the control of the driver circuit (9).

t1-L: Next, the shutter chain is fully pressed and the release switch (S2) is turned on [tl], while the shunter drive mechanism (3) is activated based on the exposure data recorded in the system control circuit (16). It works and the shutter begins to open. Along with this, exposure begins. The CCD stops transferring when the release switch is turned on [t,].
Accumulates photoelectric charge from the time the shutter begins to open. The shutter (2) starts to close at 0.3) based on the exposure data, and closes completely at [t5]. During exposure, the photographic lens (1
The incident light on a) passes through the shutter (2) and is split into two directions by the light branching means (5). One of the lights passes through the low-pass filter (6) as mentioned above to the CCD.
(7) is reached and the CCD is caused to take an image. The light from the other direction is received by the photometric means (8), and an output current (i) is generated according to the intensity of the light. The release switch (
S2) turns on (tl), the system control circuit (16) sends a signal to the field effect transistor (21) to turn off the transistor (21) [Figure 4 (a)]
is supplied, and the short circuit of the capacitor (20) is released.

As a result, the capacitor (20) and the operational amplifier (19) start integrating the output current (i) of the photometric means (8), and the output voltage (V) of the operational amplifier (19) is calculated by the following equation. obtain.

1.

-751·dt+νref Here, cs + -dt is the accumulated voltage of the capacitor (20), and Vref is the sensitivity value voltage of the CCD mentioned above. This voltage ■ is (t
It increases from zE and reaches a constant value when the shutter is completely closed [mu 5].

t5-tb: When shutter (2) is completely closed, CC
D (7) starts the transfer and sends the accumulated photocharges as an image signal to the gain control circuit (10).

On the other hand, the output of the error calculation unit (22) is used during the period t, to t, when the shank (2) is completely closed, and the output voltage V at this time is assumed to be V. The error calculation unit (22) calculates V, >V, where v2 is the voltage corresponding to the appropriate exposure level.

When , there is overexposure and the output of the CCD (7) is large, so an exposure error signal is output that lowers the gain of the gain control circuit (16). Conversely, when V<V, there is underexposure and the output of the CCD (7) is small, so an exposure error signal is output that increases the gain of the gain control circuit (16). Gain control circuit (1
6), the gain control signal (
The gain is changed according to the exposure error signal) to correct the exposure error in the video signal. In this way, the corrected image signal passes through the signal processing circuit (11) and the recording section (12).
) is recorded on a magnetic disk. When recording is completed, the power supply circuit (17) is turned off [t6].

FIG. 5(a) shows the relationship between the gain of the gain control circuit (10) and the output voltage (vl) of the operational amplifier (19), and FIG. 5(b) shows the gain after correction by the exposure error signal. The relationship between the output of the control circuit (16) and the output voltage (vl) of the operational amplifier (19) is shown.

Next, to explain the operation when using a strobe, the synchro switch (SX) is turned on in conjunction with the shutter drive mechanism (3) starting to close the shutter.
, ], the strobe (18) starts emitting light. The strobe light is emitted from the stop signal generator (27) by the light emission stop signal [
FIG. 4(C)] is applied to the strobe (18), thereby turning it off [t4]. At this time, the error calculation section (2
2) and the gain control circuit (10) operate in the same way as when the strobe is not used, so the output of the gain control circuit (10) becomes a desired signal with exposure errors corrected. As mentioned earlier, the light emission stop signal is generated when the output voltage (V) of the operational amplifier (19) increases, and the appropriate exposure signal is applied to the negative input terminal (-) of the comparator (28). Output when the voltage (Vo) is exceeded.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible. For example, a CCD as a single layer imaging means.
MOSIC may be used instead of 0. Further, the present invention is not limited to a camera with a lens shank set, but can also be applied to a focal plane shutter set-eye reflex camera. Furthermore, in the above embodiment, a part of the light that should be incident on the CCD is split by a half mirror, and the light is received by a light receiving section separate from the CCD, thereby outputting a light emission stop signal. However, a light-receiving element is installed between each pixel in a part of the most image area (for example, the center part) of the CCD, and when the amount of light received by this light-receiving element reaches a value corresponding to the health after proper exposure, a light emission stop signal is generated. You can do it like this.

Effects of the Invention According to the present invention, the equivalent amount of light incident on the actual imaging means that has passed through the lens shank is photometered and calculated from the photometric integral value and the voltage corresponding to the appropriate level of the imaging means. Since the output of the imaging means is gain-controlled by the exposure error signal, the exposure error included in the output of the imaging means is corrected, and this is particularly effective for still video cameras that employ a single type lens shack. be.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram of a still video camera embodying the present invention, Fig. 2 is a circuit diagram of its main parts, Figs. 3 and 4 are signal waveform diagrams of each part, and Fig. 5 is a block circuit diagram of a still video camera implementing the present invention. FIG. 3 is a diagram showing the effect of exposure error correction. (la) (lb)...Taking lens, (2)...Lens shutter, (7)...CCD (imaging means),
(8)...Second photometric means, (10)...Gain control circuit, (20)...Capacitor (integrating means)
, (22)...error calculation section, (Vref)...C
CD sensitivity value voltage.

Claims (1)

[Claims] (1) A photographic lens, a first photometry means, a first calculation means for calculating exposure control data based on the photometry value of the first photometry means, and an exposure control based on the exposure control data of the first calculation means. a photoelectric conversion type imaging means for imaging a still image; a second photometry means for receiving and metering a part of the light incident on the imaging means; and gain control for the output of the imaging means. an integrating means for integrating the output of the second photometric means during the exposure control period, and outputting an error signal from an integrated voltage of the integrating means and a voltage corresponding to an appropriate exposure level of the imaging means. and second calculation means for supplying the error signal to the gain control circuit as a gain control signal.