JPH0137072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an imaging device that converts a subject image into an electrical signal using an imaging device such as an imaging tube or a CCD.

[Description of prior art]

Conventionally, in an imaging device using an imaging device such as an image pickup tube or a CCD, the dynamic range of the imaging device is narrow, and the output level of the imaging device changes significantly even with a slight exposure deviation. Therefore, in order to electrically correct this, an automatic gain control circuit (hereinafter referred to as AGC) using a negative feedback loop is used to transmit the signal to the signal processing and recording circuit regardless of the magnitude of the output from the image sensor. The level of was always kept almost constant. However, such an apparatus has the disadvantage that it cannot cope with cases where the photometry conditions before photography and the exposure conditions during photography are completely different, such as in flash photography.

Therefore, in Japanese Patent Application No. 57-208920, the present applicant proposed an imaging device capable of eliminating such drawbacks.

That is, in the above-mentioned image pickup apparatus, the conventional drawbacks are solved by controlling the gain of the image pickup signal to be a predetermined constant gain when taking an image using a flash device such as a flash.

〔the purpose〕

An object of the present invention is to improve the above-mentioned imaging device and provide an imaging device having a wider dynamic range.

〔Example〕

The contents of the present invention will be explained in detail below with reference to the attached drawings. FIG. 1 is a block diagram of an electrical system showing one embodiment of the present invention.
is an image sensor as an imaging means such as a CCD, an X-Y address type MOS image sensor, or an image pickup tube, and converts a subject image into an electrical signal. The output is transmitted to an automatic gain control (AGC) circuit 3 via a signal processing circuit 2, and the output of the AGC circuit 3 is further guided to a recording circuit 4. A gain control terminal 3a of the AGC circuit 3 is connected to a terminal 5d of a switch circuit 5 as a switching means. The switch circuits 5 and 6 have terminals 5 and 6 when their control terminals 5a and 6a are at high level.
b-5d and 6c-6d are conductive, and control terminals 5a,
When 6a is at low level, terminals 5c-5d, 6
b-6d conducts. Terminal 5a of switch circuit 5
is connected to the charging completion terminal B1 of the flash generation circuit B, the terminal 5b is connected to the terminal 6d of the switch circuit 6, and the terminal 5c is connected to the AGC through the inverting amplifier 16.
Connected to the output end of circuit 3. A control terminal 6a of the switch circuit 6 is connected to a connection point 7a between the resistor 7 and the analog gate 10, a terminal 6b is connected to the reference voltage source 8, and a terminal 6c is connected to the output terminal of the sample and hold circuit 9.

The sample and hold circuit 9 samples the input voltage when the control terminal 9a is at a high level, and holds the previous sample value when the control terminal 9a is at a low level. The control terminal 9a is connected to the timing pulse generator 13, and the input terminal is connected to the reciprocal circuit 12.
connected to the output terminal of analog switch 10
is 10a when the control terminal 10c is at high level.
-10b is in a conductive state, and is in a non-conductive state when it is at a low level, and the pulse _Y1 output from the timing pulse generator 13 is supplied to the control terminal 10c.

The output terminals of the vertical synchronizing signal forming circuit 14 and the release switch 15 are both connected to the timing pulse generator 13. Timing pulse generator 13
The output terminal is the synchro terminal B of the flash generation circuit B.
2. Connected to the recording control terminal 4a of the recording circuit 4, etc.

A portion A surrounded by a broken line is a photometry circuit as a detection means for detecting reflected light from a flash, and includes a comparator 101, a reference voltage source 102, and an integrating capacitor 1.
03, consists of a light receiving element 104. This photometry circuit A
is housed in the casing C of the flash generator B,
The housing C is detachably attached to the imaging device 16.

A connection point A1 between the light receiving element 104 and the integrating capacitor 103 in the photometric circuit A is connected to the inputs of the window comparator 11 and the reciprocal circuit 12.

Note that the terminal B1 becomes high level after the charging level of the main capacitor (not shown) in the flash generation circuit B exceeds a predetermined level and charging is completed.

Further, this main capacitor is used to store energy for causing a flash light source (not shown) in the flash light generation circuit B to emit light.

Also, window comparator 11, reciprocal circuit 1
2. The sample and hold circuit 9, the analog switch 10, the switch circuit 6, etc. form a correction means according to the present invention.

One embodiment of the present invention has the above-described configuration, and its operation will be described below with reference to FIG. 2 as well.

First, when the power switch (not shown) of the imaging device is turned on, the terminal B1 is at a low level, and the control terminal 5a of the switch circuit 5 is at a low level, so that the switch circuit 5 is electrically connected between terminals 5c and 5d. Therefore, the output of the AGC circuit 3 is fed back to the gain control terminal 3a of the AGC circuit 3 via the inverting amplifier 16, and the gain of the output of the CCD 1 is controlled to be constant.

Next, turn on the power switch (not shown) in the flash generation circuit.
When turned ON, the main capacitor in the flash generation circuit begins to charge. When the charging energy of this main capacitor becomes sufficient for flashlight emission, a display (not shown) indicates the completion of charging and the terminal B1 becomes high level. Therefore, in the switch circuit 5, conduction occurs between 5b and 5d.

When the release switch 15 is turned on after the charging of the main capacitor is completed, a release signal _X1 is generated as shown in FIG. Generate a synchronization signal from the output terminal _Y0 at an appropriate timing.
(Fig. 2c) However, if the image pickup device is an image pickup tube or an X-Y address type image sensor, this synchronization signal is generated within the vertical blanking period after release. The synchronization signal from _Y0 is input to the input terminal B2 of the flash generation circuit, causing the flash light source to emit light. The reflected light from the object caused by the flash irradiation is photoelectrically converted by the light receiving element 104, and the integral capacitor 103 is charged with the electrical signal. The charging voltage of the integrating capacitor gradually increases according to the amount of reflected light, and when it becomes higher than the voltage of the reference voltage source 102, the output of the comparator 101 changes from low level to high level, which causes the flash generation circuit B to
is input. This causes the flash light source in the flash light generation circuit B to stop emitting light.

After a period of time considered sufficient for the flash light source to emit light (for example, several milliseconds), a positive pulse having a length up to the next field is generated from the terminal _Y1 of the timing pulse generator 13. (Fig. 2d) In addition to the pulse _Y1 , a sampling pulse _Y2 having a very short rising pulse width is generated.
(Fig. 2 e) By doing this, if the illumination by the flash light source is appropriate and the photoelectric conversion integral value of the reflected light from the subject is approximately equal to the voltage of the reference voltage source 102, in other words, appropriate dimming is possible. is tested, the output of the window comparator 11 is at a low level, and while this signal _Y1 is at a high level, it is guided to ground via the analog switch 10 and the resistor 7. Therefore, the connection point 7a becomes low level, and the switch circuit 6 becomes conductive between the terminals 6b and 6d. Yotsute AGC
A constant voltage from a reference voltage source 8 is input to the gain control terminal 3a of the circuit 3, and the AGC circuit 3 operates in a predetermined fixed gain mode.

On the other hand, if the light intensity of the flash is insufficient for the subject distance and reflectance, or if the light intensity control by the flash generation circuit is not successful, the photoelectric conversion integral value of the reflected light from the subject may be lower than that of the reference voltage source 102. When the voltage is significantly different from the voltage, the output of the window comparator 11 becomes high level, and while the pulse _Y1 is at high level, it is led to the ground via the analog switch 10 and the resistor 7, and the control terminal of the switch circuit 6 is connected to the ground. 6a becomes high level. Therefore, the switch circuit 6 is electrically connected between the terminals 6c and 6d. As a result, the output of the sample hold 9 is input to the gain control terminal 3a of the AGC circuit 3. A voltage proportional to the reciprocal of the charging voltage of the integrating capacitor 103 immediately after the completion of flash emission is held at the output of the sample and hold circuit.

Therefore, when the amount of reflected light from the object is excessive, that is, when it is much higher than the level of the charging voltage source 102 of the integrating capacitor 103, the output voltage of the sample and hold circuit is low and the gain of the AGC circuit 3 is reduced. Conversely, if the amount of reflected light from the subject is small,
The gain of AGC circuit 3 increases. Therefore, even if the amount of reflected light from the flash illumination is significantly different from the requirement of the image sensor, the AGC circuit operates to electrically correct this.

The signal whose gain has been adjusted in the gain control circuit as described above is sent from the timing pulse generator 13 to the second
The recording circuit 4 records the timing pulse _Y3 shown in Figure f.
recorded by supplying the

In the embodiment shown in the first figure, the photometric circuit A is provided within the housing of the flash generation circuit B, but when performing TTL light control or the like, this circuit A may be provided within the imaging device.

Further, in this embodiment, flash light (e.g., strobe light, flash bulb light) is considered as the illumination light, but the present invention is applicable to any case where at least one frame of a subject image signal is formed and recorded immediately after the start of illumination. Of course, it is possible to do so, and in that case, the illumination light only needs to have a high rise speed, and there is no problem even if it is a flash of light that remains on for a while after being emitted.

〔effect〕

As described above, the imaging device of the present invention includes an imaging means that converts a subject image into an electrical signal, an automatic gain control circuit that automatically controls the gain of the electrical signal, and a gain control circuit that automatically controls the gain of the electrical signal to a predetermined value during flash photography. and a correction means for correcting the gain according to the amount of reflected light from the flash, so that when a subject is momentarily illuminated and a subject image obtained thereby is captured, the responsiveness of the automatic gain control circuit is improved. This has the effect of easily correcting exposure errors and the like during flash photography.

That is, when controlling the amount of light emitted by a light control circuit during flash photography, it is necessary to stop the light emission immediately after the flash light is emitted for a very close subject or a subject with a high reflectance. However, depending on the response characteristics of the dimming circuit, it may be difficult to do this accurately, resulting in exposure errors. Even in such a case, according to the present invention, an appropriate signal level can be obtained. Therefore, a wide dynamic range can be obtained.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of an imaging apparatus according to the present invention, and FIG. 2 is an operation timing diagram thereof. 1; An imaging device such as a CCD as an imaging means;
2; Signal processing circuit, 3; Automatic gain control (AGC)
Circuit, 4; Recording circuit, 5; Switch circuit as switching means, 6; Switch circuit, 8, 102; Reference voltage source, 9; Sample and hold circuit, 10; Analog switch, 11; Window comparator,
12; reciprocal circuit, 13; timing pulse generator, 14; vertical synchronization signal forming circuit, 15; release switch, 16; inverting amplifier, A; photometric circuit,
101; Comparator, 103; Integrating capacitor, 104; Light receiving element, B; Flash generation circuit, C;
Flash generation circuit housing, 16; imaging device.

Claims (1)

[Scope of Claims] 1. Imaging means for converting a subject image into an electrical signal, gain control means for variably controlling the gain of the electrical signal of the imaging means, separate from the imaging means for detecting the amount of light from the subject. a light amount detection means, a control signal forming means for setting the signal gain in the gain control means to a predetermined value when recording a still image using flash illumination, and a control signal forming means for detecting the light amount from the subject by the detection means, An imaging device comprising: correction means for correcting the signal gain in the gain control means to a value other than the predetermined value.