JPH0439831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an imaging device capable of controlling the sensitivity of an imaging means.

(Prior Art) When photographing using a conventional imaging device, the sensitivity of existing imaging elements is not sufficient for objects with low brightness. As a means to overcome this problem, the sensitivity of the image sensor is apparently increased by using artificial illumination or by electrically increasing the gain of the signal processing system. To explain in detail the latter case, that is, increasing the sensitivity of the image sensor electrically, for example, some conventional video cameras are equipped with an ALC circuit that automatically controls the aperture according to the output of the image sensor. In such a camera, when the aperture reaches its maximum aperture and the average value of the output level of the imaging means is lower than an appropriate value, the gain is automatically increased.

However, in such a device in which the gain is automatically increased, the S/N ratio of the image signal may suddenly change in the middle, regardless of the operator's intention. That is, when the gain is increased, the internal noise of the image sensor is also amplified, resulting in a sudden drop in image quality.

However, operators often do not notice this. This is because it is difficult to discern changes in S/N using an EVF (electronic viewfinder).

(Purpose) The present invention has been made in view of the above-mentioned problems of conventional devices, and it is an object of the present invention to reliably inform the photographer whether or not the current shooting is in a state where the sensitivity is increased, thereby preventing the camera from inadvertently increasing the sensitivity. The purpose is to prevent failures in shooting.

(Example) The content will be described in detail below based on an example of the present invention.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 1 is an optical system for forming a subject image, 2 is an aperture, 3 is a shutter, and 4 is an image sensor as an imaging means such as a CCD image pickup tube. , 5 is a process processing circuit.
6 is a gain control circuit as a sensitivity control means, and 7 is a recording section.

Reference numeral 8 denotes an arithmetic control circuit which calculates photographing conditions from the output states of the photometry circuit 12, shutter speed setting circuit 13, aperture setting circuit 14, mode selection circuit 15, integration circuit 17, etc.

Here, the integrating circuit 17 is for integrating the video signal passed through the gain control circuit 6.

The calculation control circuit includes an aperture drive circuit 9 for driving the aperture 2 based on the calculated photographing conditions, a shutter drive circuit 10 for driving the shutter, a clock driver 11 for driving the image sensor,
It controls the gain control circuit 6, the oscillator 19, the switch circuit 21, and also controls the gate circuit 23.
Exposure information, etc. is displayed on the input terminal.

Note that 19 is an oscillator for making the display device 24 blink. 20 is a frequency divider, 21 is a switch circuit, 22 is a NAND gate, and 23 is a gate circuit. Further, 18 is a resistor for forming a high level potential. Further, DLY is a display section as a display means.

Next, the operation of the arithmetic control circuit 8 of this embodiment will be explained based on the flowcharts shown in FIGS. 2a, b, and c.

In FIG. 2a, when a power source (not shown) is turned on, a program in the arithmetic and control circuit starts (step (1)), and the setting mode of the mode selection circuit 15 is read. (Step (2)) Then, it is determined in Step (3) whether or not the aperture priority mode is selected, and if so, Step (4) is performed.
Proceed to the aperture priority mode subroutine.

If it is determined in step (3) that the mode is not the aperture priority mode, then in step (5) it is determined whether the mode is the shutter priority mode. If it is not the shutter priority mode, proceed to step (6) and proceed to the manual mode subroutine.

Also, in the case of shutter priority mode, the step
Proceed to (7). In this embodiment, the case of the shutter priority mode will be explained.

The flowchart from FIG. 2b onwards is a flowchart of the shutter priority mode _.
(Step (8)).

Here, _TV corresponds to the time value in the APEX method. Next, in step (9), the photometric value B _V from the photometric circuit 12 is read. Here, B _V corresponds to the brightness value in the APEX method.

Further, the photometry circuit 12 detects, for example, a part of the light flux behind the aperture 2 using SPC or the like. Next, in step (10), A _V =B _V -T _V is calculated. Here, _AV corresponds to the aperture value in the APEX method.

Further, in step (11), it is determined whether the aperture value A _V is greater than or equal to the aperture value A _Vp when the lens is in the open state. If this is not the case, that is, if the aperture value is smaller than in the open aperture state, the aperture aperture value is decreased by one step in step (12). In other words, the aperture is narrowed down by one stop. Further, in step (13), the gain of the gain control circuit 6 is doubled.

Along with this, in step (14), the outputs (X ₁ , X ₂ ) of the arithmetic control circuit 8 are set to (1, 0), thereby causing the aperture display value on the display device 24 to blink.

That is, the outputs (X ₁ , X ₂ ) are normally (0, 0), and in this state, the oscillation of the oscillator 19 is stopped, and the switch 21 is connected to the a side. Therefore, at this time, the output of the NAND gate 22 becomes high level, and the input signal of the gate circuit 23 is outputted as an output signal.

Further, various calculation results of the calculation control circuit are input as input signals to the gate circuit 23, and therefore, these are normally displayed as they are on the display device 24.

However, when X ₁ =1 in step (14), the oscillator 19 starts oscillating, and the gate circuit 23 is closed in accordance with the divided frequency ₂ of this oscillation signal, so that the displayed value on the display device blinks.

Note that since the shutter priority mode is selected here, the aperture value is displayed as the displayed value.

Now, in step (15) after this step (14), it is determined whether the aperture value A _V is smaller than the aperture value A _Vp when the lens is open, and if not, the aperture value A _V = A _Vp is set. (Step (16)).

If A _V ≧ A _Vp in step (11) or (15), or if A _V = A _Vp is set in step (16), proceed to the next step (17).

That is, from step (17) onwards, in the sequence for imaging, it is first determined in step (18) whether or not a release switch (not shown) has been turned on, and if it has been turned on, the process proceeds to the next step (19). In step (19), the aperture drive circuit 9 is driven by the output of the arithmetic control circuit 8, and the aperture 2 is stopped down to the aperture value _AV .

Then, in step (20), the integral output of the integrating circuit 17 is input. This allows the diaphragm to change to the aperture value.
Actual aperture photometry using the image sensor 4 is performed with the aperture stopped down to A _V.

Next, in step (21), the aperture value is reset using this actual aperture photometry result _B'V and _the set value TV of the shutter time setting circuit 13. That is, the recalculated aperture value is determined as A′ _V =B′ _V −T _V.

Furthermore, find the aperture error △A _V =A′ _V −A _V.

Next, in step (22), this △A _V is converted into A _V
is added to control the aperture aperture value to be A′ _V.

Next, in step (23), it is determined whether this corrected aperture aperture value _A'V is smaller than the lens aperture value A _Vp , and if it is, the process proceeds to step (24) where the gain of the gain control circuit has already been increased by one level. Determine whether or not the minute is up. If the gain has not been increased yet, the gain is doubled in step (25), and in conjunction with this, the aperture aperture value _A'V at this time is made to blink in the same manner as in step (14) (step (26)).

Furthermore, in step (27), the aperture value is increased by one step (equivalent to narrowing down the diaphragm by one step).Step (28) is performed to determine whether this aperture value A′ _V is smaller than A _Vp .
Determine by

If A' _V ≧A _Vp , exposure control is possible within the range of the larger aperture value A _Vp of the lens, so the process proceeds to step (31).

In step (24), it is determined that the gain up has already been performed, or in step (28), A′ _V <
If it is determined that it is A _Vp , it is determined that proper exposure control is impossible, and the blinking cycle of the displayed value is changed in step (29).

That is, the output (X ₁ , X ₂ ) of the arithmetic control circuit 8 is (1,
1), the switch 21 is connected to the b side, and a signal of frequency ₁ is input to the input of the NAND gate 22. Therefore, the blinking cycle of the displayed value on the display device 24 becomes faster.

Thereafter, in step (30), the aperture value of the diaphragm is set to A' _V =A _Vp , and then the process proceeds to step (31).

Note that even if it is determined in step (23) that A' _V ≧A _Vp , appropriate exposure control is possible, so the process proceeds to step (31).

In step (31), the aperture value of the diaphragm is corrected so that it becomes this A′ _V.

Thereafter, in step (32), the shutter is operated to open for a predetermined time to perform exposure, and in step (33), the image formed by this exposure is read out and processed in the process circuit 5.
Gain control circuit 6 having a predetermined gain
It is recorded in the recording section 7 via the.

After that, if the power is on, the process returns to step (1) and performs the same control.

As described above, according to this embodiment, even if the sensitivity of the imaging device unexpectedly changes due to exposure conditions or the like, the operator can accurately grasp this change, thereby making it possible to prevent the failure of performing unintentional imaging.

For example, instead of increasing the apparent sensitivity by increasing the gain and performing imaging, it is possible to perform imaging with priority on image quality, such as changing the illumination condition and performing imaging.

Further, in performing such a display, since the display on the display device blinks to indicate that the gain-up state is present, there is no need to increase the number of display elements, and the display can be performed with a simple configuration. Furthermore, if the exposure cannot be optimized even after the gain is increased, the blinking cycle is changed, which has the effect of simplifying the structure of the display device.

The oscillation (blinking) period may be changed by changing the amount of increase in sensitivity of the image sensor according to the amount of underexposure (for example, increasing by one step or increasing by two steps).

Also, in this example, we explained the aperture priority mode, but the same applies to the shutter priority mode, program mode, etc. At that time, the displayed aperture value (or shutter speed value) changes in the same way as above. Of course, it is also possible to increase the sensitivity (stepwise) and issue an underexposure warning.

Further, in this embodiment, a gain control circuit is used as an example of the sensitivity control means, but the present invention is not limited to this. For example, the gain control circuit may be used to change the bias of the target electrode of the image pickup tube. Including everything else that can adjust the gain of the image sensor.

Further, in the embodiment, the operating state of the sensitivity control means is displayed by the blinking period, but for example, the sensitivity value may be displayed numerically, or the change in sensitivity may be made to correspond to the change in color of another display.

(Effects) As explained above, according to the present invention, since the present invention includes a display means for displaying the state of automatic sensitivity change of the imaging device, it is possible to prevent the formation of an undesired image with degraded image quality. I can do things.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of an imaging apparatus according to the present invention, and FIGS. 2a to 2c are flowcharts showing the operation of the imaging apparatus according to the invention. 6...gain control circuit as sensitivity control means, DLY...display section as display means.

Claims (1)

[Scope of Claims] 1. An imaging means for photoelectrically converting imaging light from a subject; an exposure amount control means for setting the amount of light incident on the imaging means according to the brightness of the subject; and the above-mentioned imaging means. a sensitivity control means for variably setting the sensitivity of the sensor; a display means for displaying the sensitivity state set by the sensitivity control means; and the sensitivity control means and the display means are controlled in conjunction with the exposure amount control means. and a control means, the control means displays the state of increased sensitivity of the sensitivity control means, and displays the above in a different display mode if a signal at an appropriate level is not obtained even in the state of increased sensitivity. An imaging device characterized by displaying information on a means. 2. The imaging device according to claim 1, wherein the display means varies the light emitting cycle of a single display means according to a sensitivity setting state by the sensitivity control means.