JPS63250979A - Still video camera - Google Patents

Abstract

PURPOSE:To use the shutter and the diaphragm of low precision by synchronizing a signal showing an exposure quantity with a horizontal blanking pulse, comparing it with a reference signal and adjusting the gain of an amplifier circuit while an image pickup element is at least exposed. CONSTITUTION:If a switch S2 is turned on, a shutter control circuit 11 once closes the shutter 22 and it is opened by a time corresponding to a shutter speed which has been decided by the decided value of a lens opening. Thus, exposure for the image pickup element 24 is executed and data (charge) showing an object picture is temporarily stored in the image pickup element 24. A comparator 30 compares a signal component which has been synchronized with the horizontal blanking pulse HBL among the output signals C of the amplifier circuit 27 during an exposure time zone and a prescribed reference voltage given from a reference voltage generation circuit 31. The gain of the amplifier circuit 27 is adjusted to an almost appropriate size. A video signal outputted from the amplifier circuit 27 is settled in the range of a nearly constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention Although the exposure amount is determined by the shutter speed and the aperture value, it may not necessarily be set appropriately and errors may occur. An amplification circuit that can control the gain is used as an amplification circuit for amplifying the output video signal of the image sensor. The exposure amount is measured, a signal representing the exposure amount is given to the above amplifier circuit in synchronization with the blanking pulse, and the output signal component of the amplifier circuit in synchronization with the blanking pulse is compared with a predetermined reference level. The gain of the amplifier circuit is feedback-controlled so that the level of the output signal component remains constant.

BACKGROUND OF THE INVENTION This invention utilizes an electronic camera (such as a CCD) to photograph a subject.
) and records the output video signal on, for example, a magnetic disk.

In still video cameras, the video signal output from the image sensor has a defined level range (dynamic range) in order to obtain a signal with a good S/N ratio, and its error tolerance is small. .

On the other hand, the level of the image (source signal) is determined by the amount of exposure to the image sensor, and the amount of exposure is determined by the shutter speed of the Nyatta and the aperture value of the aperture.For this reason, the shutter and aperture are required to be highly accurate. Conventional shutter-equipped still video cameras use special shutters and apertures that are manufactured with high precision, and are inevitably expensive.

Relatively inexpensive aperture and dual-purpose shutter (so-called program shutter) like those used in conventional electronic cameras
At present, the exposure accuracy was not very high and it could not be used for still video cameras.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a still video camera that can also use a shutter or aperture with low precision.

The still video camera according to the present invention includes an amplifier circuit whose gain can be controlled to amplify an output video signal of an image sensor, and a photometric element, and an exposure measurement circuit that outputs a signal representing the amount of exposure to the image sensor.

a synchronization circuit that provides a signal representing the exposure amount to the amplifier circuit in synchronization with the horizontal blanking pulse; and a reference signal that outputs the output of the amplifier circuit and represents a predetermined value in synchronization with the horizontal blanking pulse. By comparison, a signal for adjusting the gain of the amplifier circuit at least during exposure of the image sensor so that the amplified level of the signal synchronized with the horizontal blanking pulse becomes a predetermined partial level. It is characterized by comprising means for outputting.

Preferably, the synchronization circuit includes a gate circuit that extracts a signal component synchronized with the blanking pulse of the signal representing the exposure amount, and a mixing circuit that mixes the output of the gate circuit and the output signal of the image sensor. It consists of

A signal representing the amount of exposure to the image sensor is detected during the exposure time period, and this signal is applied to the amplification circuit in synchronization with the horizontal blanking pulse, where it is amplified. The difference between the component of the output of the amplifier circuit that is synchronized with the horizontal blanking pulse and a predetermined reference signal is detected, and based on this difference, the component of the output of the amplifier circuit that is synchronized with the horizontal blanking pulse is detected. The gain (amplification factor) of the amplification circuit is feedback-controlled so that the component of the amplification circuit has a substantially constant value.

For example, if the exposure is insufficient, the level of the signal representing the exposure aperture is relatively low, so the gain of the amplifier circuit is increased; if the exposure is overexposure, the gain is spontaneously reduced.

In this way, according to the present invention, even if there is an exposure error due to inappropriate speed or aperture value, the level fluctuation of the video signal based on this error is compensated for in the video signal amplification circuit. Therefore, it is also possible to use a shutter that is relatively inexpensive, although it does not necessarily have high precision like the conventionally used aperture shutter.

Further, since the signal representing the exposure amount is feedback-controlled through the amplifier circuit in order to adjust the gain of the amplifier circuit, the control system is stabilized and the influence of circuit drift can be eliminated. Further, since the signal representing the exposure amount is sampled in synchronization with the horizontal blanking pulse and no video signal exists during this blanking period, there is no risk of adversely affecting the video signal.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows part of the electrical configuration of a still video camera.

The overall operation of the still video camera is controlled by the control device 10.
supervised by. This control device 10 is.

The device imaging optical system, which is composed of a CPU, memory, interface, etc., includes an imaging lens system 21. for forming a subject image. and an aperture shutter (so-called program shutter) 22. A half mirror (beam splitter) 23 is provided in a part of the optical path of this optical system to split and extract a part of the incident light, and the split light is sent to a photodiode (photometric element 16).
). The output signal of this photodiode 16 is input to the shutter control circuit 11. In response to a command from the control device 10, the shutter control circuit 11 measures the incident light illuminance from the light reception signal input from the photodiode 16, and adjusts the shutter speed and The aperture value is determined and the aperture/shutter 22 is controlled.

A solid-state image sensor 24 such as a CCD is arranged on the focal plane of the imaging optical system. The synchronization signal generation circuit 13 is horizontal,
A vertical synchronizing signal 5YNC is generated and applied to the imaging cable drive circuit 12 and the control device 10. The synchronization signal generation circuit 13 is also

A horizontal blanking pulse HBL synchronized with the synchronizing signal 5YNC is generated every horizontal scanning period (IH) (see FIG. 3). The image data of the subject imaged on the imaging surface of the imaging cable 24 is read out periodically in accordance with the synchronization signal provided by the drive circuit 12, and is read out periodically by the preamplifier circuit 25. Mixing circuit 26
．． Variable gain amplifier circuit (gain controllable amplifier circuit) 27
The process matrix circuit 28 is manually powered through the process matrix circuit 28.

Since color photography is generally performed, the imaging probe 24 has an imaging surface for the three primary colors, R (red), G (green), and B (blue), and video signals of the three colors are read out. Only one video signal is shown in FIG. 1 for simplicity.

In the case of color photography, the process matrix circuit 28 creates a luminance signal Y and two color difference signals RY and BY based on input three-color video signals. These signals are then input to a recording signal processing circuit (not shown). This processing circuit includes a line sequentialization circuit, a pre-emphasis circuit, an F
M modulation circuit.

It includes a synthesis circuit and the like, and an FM-modulated composite video signal is output from this processing circuit and applied to the magnetic head. This composite video signal is then written on a predetermined track of the magnetic disk that rotates once.

The shutter release button 15 is of a two-stage stroke type, in which the first stage of depression releases switch S1, and the second stage of further depression of the button 15 causes switch S2.
are respectively turned on.

The output signal of the photodiode 16 is further transmitted to the integrator circuit 1.
4, where it is integrated during exposure to measure the exposure amount. The integrated output of the integrating circuit 14 is applied to the above mixing circuit 2B via the gate circuit 17. The gate circuit 17 allows this integral output to pass only when the horizontal blanking pulse HBL is input.

Therefore, in the mixing circuit 26, a pulse-like signal representing an integral output synchronized with the horizontal blanking pulse and an output signal A of the preamplifier circuit 25 (when no reading from the imaging probe 24 is being performed) are combined. is a zero level signal)
The signal B is mixed with the signal B and is applied to the amplifier circuit 27. The output signal C of the amplifier circuit 27 is input to the process matrix circuit 28 as described above, and is also applied to one input terminal of the comparison circuit 30 via the gate circuit 29. This gate circuit 29 is also controlled by the horizontal blanking pulse HBL. Output signal C of amplifier circuit 27
Of these, the signal component synchronized with the horizontal blanking pulse HBL is sent to the reference voltage generation circuit 31 in the comparator circuit 30.
is compared with a predetermined reference voltage given by The output of this comparison circuit 30 is held in a holding circuit 32 for each comparison until the next comparison operation.

It is used to adjust the gain of the amplification circuit 27 described above. The reference voltage provided by the generation circuit 31 corresponds to an appropriate exposure level for the image sensor 24.

The control device 10 not only controls writing of the combined video signal onto the magnetic disk, but also controls the shutter and the like, as will be described later.
In response to input signals from the switches Sl and S2 of the release button 15, the shutter control circuit 11 measures illuminance, the timing of the operation of the diaphragm/shutter 22, the operation timing of the drive circuit 12, the reset of the integration circuit 14, etc. control.

Next, the overall operation of the imaging process will be explained with reference to FIG.

The diaphragm/diaphragm handle 22 is normally in a fully open state.

Shutter release button 15 is pressed and switch S
1 is turned on, the shutter control circuit 11 measures the illuminance of the incident light based on the light reception signal of the photodiode I6, and determines the shutter speed and aperture value according to this illuminance as described above. Also.

Unnecessary charges from the imaging probe 24 are discharged.

This continues until the shutter 22 is once closed and then opened again.

Next, when the switch S2 is turned on, the shutter control circuit 1
1, the shutter 22 is once closed, and then the shutter 22 is opened for a time corresponding to the determined aperture value and the determined shutter speed.

As a result, the image pickup element 24 is exposed to light, and data (charge) representing the subject image is temporarily stored in the second image pickup element 24. Prior to this exposure, the integration circuit 14 is reset (for example, in synchronization with the input signal of switch S2) and integrates the input signal from the first diode 1G during the exposure. When the exposure is completed, the shutter 22 is closed. Therefore, the integrating circuit 14 holds the voltage value integrated during the exposure time.

This represents the amount of exposure.

As will be described in detail later, the gain of the amplifier circuit 27 is adjusted to an approximately appropriate level during this exposure time period.

After the exposure is completed and the shutter 22 is closed, the video data stored in the image sensor 24 is read out by the exposure, and in synchronization with this, the processed video signal is also written to the magnetic disk. . The video signal read out from the imaging probe 24 is processed through the amplifier circuit 27.
Since the gain of the amplifier circuit 27 sent to the matrix circuit 28 has already been adjusted, the video signal output from the amplifier circuit 27 falls within a substantially constant level range.

FIG. 3 shows how the gain of the amplifier circuit 27 is adjusted. The output signal A of the preamplifier circuit 25 is held at a zero level until reading from the image sensor 24 is started. The output of the integrating circuit 14 gradually increases during the exposure time period (from this signal, only the component synchronized with the horizontal blanking pulse HB L is extracted in the data 1 circuit 17, and is amplified via the mixing circuit 26. input to circuit 27;

The component of the cutting edge signal C of the amplifier circuit 27 which is equal to 1 and 1 with the horizontal blanking pulse HBL passes through the gate circuit 29 and is compared with the reference voltage in the comparator circuit 30, and the gain of the amplifier circuit 27 is adjusted so that the difference becomes small. be adjusted. As described above, since the output signal of the integrating circuit 14 tends to increase, the gain of the amplifier circuit 27 is adjusted to decrease, and its output C also decreases.

When the exposure period ends, the output signal of the integrating circuit 14 becomes a constant value, so the gain of the amplifier circuit 27 also settles down to a certain constant value.

When the reading of data from the image sensor 24 is started, the output video signal of the image sensor 24 is multiplied by the pulse signal given from the gate circuit 29 in the mixing circuit 26 and input to the amplifier circuit 27 . Since the output of the gate circuit 29 is synchronized with the horizontal blanking pulse HBL, it appears during a period in which no video signal component exists, so that the video signal component is not affected by any adverse effects such as distortion. The output signal C of the amplifier circuit 27 is subjected to the above-described processing in the process matrix circuit 28, and at this time, the horizontal blanking pulse H
The component C1 synchronized with BL is removed using a horizontal blanking pulse HBL input to this circuit 28.

Since the component synchronized with the horizontal blanking pulse HBL in the output signal C is still input to the comparison circuit 30, the feedback control of the gain of the amplifier circuit 27 is still continued.

In the case of a configuration in which only three color video signals are output from the image sensor 24, the mixing circuit 26. Amplification circuit 27. A feedback control circuit including a comparison circuit 30 may be provided for each of these three video signals, or only three amplifier circuits 27 may be provided, and the gains of these amplifier circuits 27 may be adjusted by the output of one comparison circuit 3o. It can also be controlled. Generally, a variable gain amplifier circuit for color balance adjustment is provided for these video signals. The above amplifier circuit 27 can also be used as a variable gain amplifier circuit for color balance adjustment.

In the above embodiment, the cane of the amplifier circuit 27 is adjusted in an analog manner, but it may also be controlled digitally. The amplification circuit 27 is set so that the tin of the magnification scale can be selected. For example, this may be accomplished by selecting an element (such as a resistor) that determines the gain using a switch. The output representing the comparison result of the comparison circuit 30 is taken into the control device 10, and the control device 10 selects one of the plurality of types of gains described above according to the comparison result.

FIG. 4 shows the relationship between the characteristics of the imaging probe 24 and the luminance signal Y output from the process matrix circuit 28.

The level of the output video signal of the image sensor 24 has a range (operating range) that is approximately proportional to the amount of incident light, and when the amount of incident light exceeds this range, the output signal is saturated. Image sensor 24
The range used is set to about 173 of this operating range. Then, when a signal having a level within this range of use is amplified by an amplifier circuit and then given to the professional smart matrix circuit 28, a white peak signal is output from the process matrix circuit 28. An f1g degree signal Y that falls within the level range is obtained.

If the deviation value or image speed is inappropriate and the amount of light incident on the image sensor 24 is too large, a larger video signal is output from the image sensor 24 as shown by the broken line. If this video signal is amplified by an amplifier circuit with the same cane, the signal input to the process matrix circuit 28 will have a higher level. Since this circuit 28 works to clip the signal with a level exceeding the white peak, the portion of the level exceeding the white peak will represent the same brightness.

In this way, the luminance component of the video signal is distorted.

According to the present invention, when a video signal with a higher level is output from the image sensor 24, the gain of the amplifier circuit 27 is reduced as described above, and the amplified video signal is transferred to the process/7 trix circuit. It is designed to fit within the clip level of 28.

As a result, only the distortion of the luminance signal is eliminated. Also.

When the level of the video signal output from the video element 24 is low due to insufficient exposure, the gain of the amplifier circuit 27 is increased, and the peak of the video signal is amplified to the same level as the clip level.

A luminance signal Y similar to that obtained when proper exposure is performed is obtained. After such a video signal is recorded on a magnetic disk, when it is reproduced, a reproduced signal that causes the screen to become dark will not be obtained, and an image with appropriate brightness will be obtained.

FIG. 5 shows a modification. Photo diode 16
C) is only used to measure total exposure. Another photo diode 18 is provided on the outside of the camera, and the output signal of this photo diode 18 is input to the shutter control circuit 11, and the shutter speed and aperture chain are determined based on the output signal of this photo diode 18. be done. In this example, as shown in FIG.
There is no need to open the shutter 22 to determine the aperture value. The other J14 components are the same as shown in FIG.

FIG. 6 shows yet another example. Here, the photodiode 16 is arranged so as to receive the reflected light from the imaging surface of the imaging element 24, and the half mirror 23 becomes unnecessary. The other parts are the same as those shown in FIG.

If a solid-state image pickup device having a non-mechanical shutter function is used, the shutter 22 and the shutter control circuit 11 are not necessary. Such an image sensor is composed of a light-receiving area that is exposed to light and a temporary storage area that is shielded from light, and can be realized by a frame transfer (FT) type CCD in which a transfer electrode is arranged between these areas.

The CC of this FT method is compared with the opening/closing operation of
The operation of D is explained as follows.

First, a high-speed clock pulse is applied to the transfer electrode, and the charges of all pixels in the light receiving area are immediately transferred to the temporary storage area (first transfer). This first transfer corresponds to the shirt opening.

As a result, the light receiving area starts accumulating optical signals.

The signal charges in the temporary storage area are discharged to the outside via the output terminal. After the time corresponding to the shutter speed has elapsed, a high-speed clock pulse is applied to the transfer electrode again, and the signal charge accumulated in the light receiving area is transferred to the temporary accumulation area (
second transfer). This second transfer corresponds to shutter release.

Integrating circuit 14 is reset during the first transfer and integrates the output signal of photodiode 16 from this time to the time of the second transfer. A gate circuit is provided between the photo diode 16 and the integrating circuit 14, and after the second transfer, the gate circuit is closed to prevent the output signal of the photo diode 16 from inputting to the integrating circuit 14. Therefore, after the second transfer, the output signal of the integrating circuit 14 is kept at a constant value. During the exposure window from the first transfer to the second transfer.

As described above, the output signal of the integrating circuit 14 is used to adjust the gain of the amplifier circuit 27. After this.

The signal charges transferred to the temporary storage region are read out by the second transfer described above.

A similar operation is possible using an interline transfer (ILT) type CCD.

The present invention is also applicable to still video cameras that use the above-mentioned special image pickup device that can perform operations substantially equivalent to opening and closing a shutter.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, and Fig. 1 shows an embodiment of the present invention.
3 is a time chart showing the overall operation, FIG. 3 is a time chart 1 showing the gain adjustment operation, and FIG. 4 is a graph showing the characteristics of the image sensor and the luminance signal. FIGS. 5 and 6 are block diagrams showing modified examples. ”0...control device. 13.Synchronization signal generation circuit. 14...Integrator circuit. 16...Photo transistor. 17, 29...Gate circuit. 24--Image sensor. 2G...Mixed circuit. 2I...Variable gain amplifier circuit. 30... Comparison circuit. 31...Reference voltage generation circuit. Patent applicant: Fuji Photo Film Co., Ltd. Agent
Patent attorney Asamichi Kajiang (1 other person) Figure 5 Figure 6

Claims (2)

[Claims] (1) A gain controllable amplifier circuit that amplifies the output video signal of the image sensor, an exposure measurement circuit that includes a photometric element and outputs a signal representing the amount of exposure to the image sensor, and that is synchronized with the horizontal blanking pulse. and a synchronization circuit that supplies a signal representing the exposure amount to the amplifier circuit, and compares the output of the amplifier circuit with a reference signal representing a predetermined value in synchronization with the horizontal blanking pulse, and performs the horizontal blanking. - means for outputting a signal for adjusting the gain of the amplifier circuit at least during exposure of the image sensor so that the amplified level of the signal synchronized with the pulse becomes a predetermined constant level; ·Video camera. (2) The synchronization circuit includes a gate circuit that extracts a signal component synchronized with the blanking pulse of the signal representing the exposure amount, and a mixing circuit that mixes the output of the gate circuit and the output signal of the image sensor. A still video camera according to claim (1), comprising: