JP2879569B2 - Imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, particularly to an auto iris (automatic aperture) system for a video camera or the like.

[Prior Art] In a conventional auto iris system of a video camera of this type, a case where an aperture (iris aperture) changes from an open aperture to a small aperture or vice versa according to the brightness of a subject is changed. The circuit configuration was designed so that the same gain could be obtained for both.

[Problems to be solved by the invention]

However, in such a conventional method, for example, when the subject changes from dark to strong light, that is, in an auto iris system, the apparent auto iris when the aperture 2 changes from open to a small aperture state. Conversely, the loop gain is higher when the subject changes from strong light to darkness, that is, in the auto iris system, than the apparent auto iris loop gain when the aperture 2 changes from the small aperture to the open state, The operation response speed when the former diaphragm 2 changes from the open state to the small aperture is different from the operation response speed when the latter diaphragm 2 changes from the small aperture to the open state.

For this reason, when the aperture becomes smaller from the former,
If the gain of the circuit is determined so as to suppress hunting of the iris operation, on the contrary, the response speed when changing from the small aperture to the open state becomes extremely slow, which may result in an unnatural auto iris operation. There was a point.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional example described above, and it is an object of the present invention to realize an auto iris system of this kind that can obtain an iris operation with an optimum response speed in any of the change directions of the aperture. It is an object.

[Means for solving the problem]

For this reason, in the present invention, this kind of imaging device is
Imaging means, aperture means for adjusting the amount of incident light to the imaging means in response to an aperture control signal formed based on the output of the imaging means, and a diaphragm opening of the aperture means from a predetermined small aperture side to the open side Gain control means for correcting the gain of the aperture control signal when opening toward the aperture to be greater than the gain of the aperture control signal when closing from the open side to the predetermined small aperture side. Is to achieve.

[Action]

With the configuration of the auto iris system as described above,
In the image pickup apparatus according to the present invention, a substantially optimum response speed of the aperture operation can be obtained even for various changes in brightness of the subject.

〔Example〕

FIG. 1 is a block diagram showing a configuration of an embodiment of a video camera having an auto iris circuit according to the present invention.

(Configuration / Operation) A light image from a subject is formed on the image sensor 3 via the optical lens 1 and the aperture 2. In accordance with this image formation state, an image pickup signal is supplied from the image pickup device 3 to the sample / hold (S / H) circuit 4, where the image pickup signal is sampled and holed. The imaging signal output from the S / H circuit 4 is supplied to a signal processing circuit 5, where a luminance signal Y and a chrominance signal C are extracted as a video signal. It is output from the camera unit in the form of a signal or the like.

On the other hand, the image pickup signal output from the S / H circuit 4 is clamped by the clamp circuit 7 and used as an aperture control signal for controlling the aperture 2 to obtain an appropriate exposure according to the screen luminance state. That is, the clamped image pickup signal is extracted by the gate circuit 8 only from the photometric portion of the screen, and is supplied to the integrating circuit 12. In the integrating circuit 12, the imaging signal is integrated into a signal close to a DC signal, smoothed, and supplied to a non-linear amplifier circuit 10 as a response speed optimizing control unit according to the present invention via an amplifier circuit 11. In the case where the aperture is changed from the wide aperture to the small aperture, and conversely, in the case where the aperture is changed from the small aperture to the open, a signal corrected so as to have an appropriate response speed is generated. The aperture mechanism 2a is controlled.

FIG. 2 shows a specific circuit example of the nonlinear amplifier circuit 10 of the present invention, and FIG. 3 shows a linear amplifier circuit diagram corresponding to this part of the conventional example in comparison. According to the present invention, when the Schottky or diode or other semiconductor element D1 and the resistor R2 are connected in series and connected in parallel between both ends of the resistor R1 in FIG. The input integration signal (point A) from the inverting terminal (B
When the voltage drops below (point), the semiconductor element D1 becomes conductive,
The gain of the inverting amplifier OP is amplified. FIG. 4 shows gain characteristic diagrams (output level / input level ratio) 14 and 13 of the conventional inverting amplifier and the nonlinear inverting amplifier 13 of the present invention, respectively. In other words, the operation of the diaphragm 2 is controlled via the iris drive circuit 9 shown in FIG. 1 by forming the amplifier gain not into the linear characteristic 14 shown in FIG. It is possible to make the response speed substantially appropriate.

(Other Embodiments) Next, FIG. 5 corresponding to FIG. 1 of the second embodiment of the present invention is shown in FIG. 5, and is the same as (corresponding to) FIG. 1 of the first embodiment.
The components are denoted by the same reference numerals.

In this embodiment, instead of the nonlinear amplifier circuit 10 of the first embodiment shown in FIG.
The microcomputer 19 (hereinafter, abbreviated as "microcomputer") outputs a predetermined correction signal using an aperture value (opening) detecting means (for example, the Hall element 15).

That is, similarly to the first embodiment, the imaging signal output from the imaging device 3 is smoothed by the integration circuit 12 and
Is output through The output signal is converted by an A / D circuit 21 from an analog value to a digital value and input to the microcomputer 19.

On the other hand, the opening degree state of the diaphragm 2 is detected by the Hall element 15 and input to the analog / digital (A / D) circuit 17 via the amplifier circuit 16. Here, the analog value is converted into a digital value and input to the microcomputer 19. Further, the reference voltage V _ref also converts an analog value into a digital value by the A / D circuit 20 and inputs the digital value to the microcomputer 19 to perform predetermined correction.

The operation of the microcomputer 19 will be described with reference to the sequence flowchart of FIG.

First, in steps S1 and S2, the digital value Y of the imaging signal output from the A / D circuit 21 and the digital value Ref of the reference voltage _Vref output from the A / D circuit 20 are taken. Find the difference signal between the value Y and Ref,
And Similarly, in step S4, the digital value H of the Hall element voltage output from the A / D circuit 17 is fetched.

Next, in step S5, the digital When comparing the ipecac I H _before before H and one H _before <H selects the gain table B which will be described later in step S6, H _before
If ≧ H, the gain table A is selected in step S7. These gain tables A and B are shown in Table 1. The output value of the Hall element, that is, a predetermined correction value according to the aperture value is stored in advance, and the correction value of the gain table is stored in the memory. The drive data _Dr is output in step S8 by multiplying the difference signal Y by Y. At this time, the correction value of the gain table A or B is determined so that the response speed from the opening to the small aperture and the response speed from the opening of the small aperture to the opening are substantially appropriate.

In Table 1, the gain table A is a gain table when responding to the opening from the small aperture, and the gain table B is a gain table when responding to the small aperture from the opening. In order to eliminate the operation hunting due to the small aperture and to achieve the optimum response speed, the gain is reduced by lowering the gain in the small aperture area of the gain table B than in the small aperture area of the gain table A.

In this embodiment shown in Table 1, the F value is divided into eight steps, but it is also possible to divide the F value into any appropriate steps to determine the gain and correct the gain.

Then the output signal D _r corrected by above step S9
5, the digital value is converted into an analog value by the D / A circuit 18 in FIG.

As described above, since the optimum response speed can be corrected, it is possible to sufficiently absorb variations in the IG meter and the like.

〔The invention's effect〕

As described above, according to the present invention, it is possible to optimize the response speed of the aperture operation in the auto iris system of an imaging device such as a video camera with a simple circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a video camera according to the present invention, FIG. 2 is a specific example of the nonlinear amplifier circuit of FIG. 1, FIG. 3 is an example of a conventional linear amplifier circuit, FIG. Is
FIG. 3 is a comparison diagram of each gain characteristic of the circuit, FIG. 5 is a block diagram of a circuit configuration of another embodiment, and FIG. 6 is an operation sequence flowchart of the microcomputer of FIG. DESCRIPTION OF SYMBOLS 1 ... Optical lens 2 ... Aperture 2a ... Aperture mechanism 3 ... Imaging element 9 ... Iris drive circuit 10 ... Nonlinear amplifier circuit (response speed optimization control means) D1 ... Semiconductor element (response speed optimization) Control means) 12 Integrator circuit (smoothing means) 13 Input / output characteristics of nonlinear amplifier circuit 14 Input / output characteristics of conventional linear amplifier circuit 15 Hall element (response speed optimizing means) 19 Microcomputer (response speed optimization means)

Claims (1)

(57) [Claims] 1. An image pickup means, an aperture means for adjusting an amount of incident light on the image pickup means in response to an aperture control signal formed based on an output of the image pickup means, and a predetermined small aperture for an aperture opening of the aperture means. Gain correction means for correcting the gain of the aperture control signal when opening from the side toward the open side to be greater than the gain of the aperture control signal when closing from the open side to the predetermined small aperture side. Imaging device.