JPH02134986A - Image pickup device - Google Patents

Abstract

PURPOSE:To promptly and accurately execute photometry only with a solid-state image pickup element without using an exclusive photometry element by driving the solid-state image pickup element in a mnemonic characteristic mode when a charge is read out from the solid- state image pickup element for photometry and driving the solid-state image pickup element in an ordinary driving mode at image pickup time. CONSTITUTION:The title device is the image pickup device to control exposure by a photometry output read out from a solid-state image pickup element 4 before image pickup is executed, and a solid-state image pickup element driving means 15 has two types of driving modes, namely, the mnemonic characteristic driving mode to drive the solid-state image pickup element 4 so that the solid-state image pickup element 4 can have the mnemonic characteristic and the ordinary driving mode to ordinarily drive the solid-state image pickup element 4, drives the solid-state image pickup element 4 in the mnemonic characteristic mode when the charge is to be read out from the solid-state image pickup element 4 for photometry, and drives the solid-state image pickup element 4 in the ordinary driving mode at the image pickup time. Consequently, at photometry time, the dynamic range of the solid-state image pickup element 4 can be expanded. Thus, photometry can be executed promptly and accurately only with the solid-state image pickup element without using the exclusive photometry element.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an imaging device, and more particularly, to an imaging device capable of highly accurate exposure control.

(Background of the Invention) In cameras that use general photographic film, the latitude of the film is large, so deviations in exposure due to slight deviations in photometric values do not pose a problem. However, solid-state image sensors (C
In a still video camera that uses a CD (CD), the latitude of the CCD is small, so deviations in photometric values are a big problem.

Therefore, conventionally, prior to photographing, the following photometry was performed.

(2) Roughly photometering is performed using a dedicated photometering element, and a more accurate photometering value is obtained from the CCD light reception output after roughly adjusting the exposure based on this photometering value.

(2) Exposure multiple times using a CCD without changing exposure conditions, and finally obtain highly accurate photometric values from these signals.

(Problem to be Solved by the Invention) The method (2) described above requires a dedicated photometric element, photometric circuit, etc. Therefore, there was a drawback that the circuit configuration became complicated. Further, it is necessary to perform photometry at least twice, one using the photometric element and the other using the CCD, and it is time-consuming.

On the other hand, in method (2) above, a dedicated photometric element is not required, but since the dynamic range of the CCD is narrow, multiple exposures are required to approximate the appropriate exposure, and photometry takes time.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide an imaging device capable of quickly and accurately measuring light using only an image sensor, without using a dedicated photometric element. The aim is to realize this.

(Means for Solving the Problems) The present invention that solves the above problems includes a solid-state image sensor, a solid-state image sensor drive means that supplies a drive pulse to the solid-state image sensor, and a photometric output of the solid-state image sensor that controls exposure. and an exposure control means for controlling exposure based on a photometric output read from the solid-state image sensor prior to imaging, wherein the solid-state image sensor driving means has a knee characteristic for the solid-state image sensor. It has two types of drive modes: a knee characteristic drive mode in which the device is driven so that the image is captured, and a normal drive mode in which normal drive is performed. is characterized in that it is configured to be driven in a normal drive mode.

(Function) When reading charges from the solid-state image sensor for photometry, the solid-state image sensor is driven in knee characteristic mode, and during imaging, it is driven in normal drive mode.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an embodiment of the present invention.

In the figure, 1 is a lens system for focusing the image of the subject on the CCD, 2 is an iris (iris diaphragm) for limiting the amount of light passing through lens system 1, 3 is a shutter, and 4 is formed by lens system 1. Converts the optical image into an electrical signal (image data)
5 is an amplifier for amplifying the output of CCD 4, 6 is a process circuit for converting the output of CCD 4 into a video signal, and 7 is a converter for converting the video signal into a signal for recording on a video floppy. A recording circuit 8 is a video floppy on which images are recorded. 9 is CCD4
10 is a system control circuit that performs overall control of various parts in addition to exposure control, and 11 is an 830 circuit that generates a reference synchronization pulse. 12 is a normal drive waveform generation circuit that generates a drive signal for driving the CCD in a normal state based on the pulse generated by 5S011; 13 is a 5SG
A knee drive waveform generation circuit does not generate a drive signal for driving the CCD in a state that gives knee characteristics based on the pulses generated in II, and 14 is an output pulse of the normal drive waveform generation circuit and the knee drive waveform generation circuit. a switch that can be switched from the system control circuit 10 to switch the
15 is a CC based on the output pulse of either the normal drive waveform generation circuit or the knee drive waveform generation circuit.
This is a CCD drive circuit that generates a D drive pulse to drive the CCD 4.

The operation will be explained below using FIG. First, when performing photometry, the system control circuit 10 switches the switch 14 to the b side. Therefore, the CCD drive circuit 15 is driven by the pulse from the knee drive waveform generation circuit.
CD4 is driven to have knee characteristics.

FIG. 2 is a characteristic diagram showing charge accumulation characteristics when knee-driving a CCD. In the example shown in this figure, the knee characteristic is obtained by changing the level of the overflow control gate (OF CG) (from V1 to V2) during exposure to change the maximum accumulated charge amount.

FIG. 3 shows the knee characteristics at this time. As shown in this figure, there is a knee point where the light amount is ■.
The dynamic range of the amount of incident light is expanded.

Further, FIG. 4 is a characteristic diagram showing another example for obtaining knee characteristics. In this method, the maximum accumulated charge amount of the light receiving section is not changed, but the charges of a certain level or more in the light receiving section are read out and discarded at a certain timing. As a result, the charges accumulated in each pixel become as shown in FIG. Therefore, knee characteristics similar to those shown in FIG. 3 can be obtained.

Because of this knee characteristic, ordinary CCD (γ-1)
The dynamic range is considerably wider than that of .

Therefore, no matter what the brightness of the subject is, it will never be too dark or too bright. Therefore, a photometric value can be obtained from the photometric circuit 9 through one exposure.

Incidentally, the output of the CCD at this time uses a multi-division photometry method in which the finder screen is divided into a plurality of areas and photometered as shown in FIG. In the example shown in this figure, the entire screen is 9
It is divided into several photometry areas. Of these nine photometry areas, the center area is used for photometry of the main subject, and the outer eight areas are used for photometry of the background. 2 to CCD
If a device with 0 to 400,000 pixels is used, each photometry area will integrate signals for tens of thousands of pixels. Therefore, the influence of fixed pattern noise that occurs during knee characteristic driving is eliminated.

Based on the photometric value obtained from the exposure output of the CCD, the system control circuit 10 adjusts the aperture value of the iris 2 so that proper exposure is achieved when the CCD is driven in a normal state. And the system control circuit 10
, switch the switch 14 to the a side. For this reason,
The CCD drive circuit 15 drives the CCD 4 in a normal state (γ=1) using pulses from the normal drive waveform generation circuit 12. During this imaging, the iris 2 is adjusted to provide proper exposure, so even if the CCD 4 is driven in a normal state, the subject will not be too dark or too bright. Therefore, there is no need to perform knee driving, and there is no possibility that fixed pattern noise will occur.

Then, the output of the CCD 4 is transferred to the process circuit 6. Recording circuit 7
The signal is converted into a recording signal and recorded on the video floppy 8. If you want to continue this recording, repeat the above operation.

In the above description, the knee drive is performed during photometry and the normal drive is performed during photography, but the following application examples are also possible. That is, during photometry, two drives are performed to widen the dynamic range of the amount of incident light. When photographing, shallow knee driving is performed to slightly widen the dynamic range of the amount of incident light. In this way, since the knee drive is shallow during photographing, fixed pattern noise caused by variations in the maximum accumulated charge amount is hardly noticeable. In this case, two types of dual drive waveform generation circuits may be provided.

When photographing, the CCD may be driven with Vl in FIG. 2 or 4 close to V2.

(Effects of the Invention) As explained in detail above, in the present invention, the image sensor is driven in the knee characteristic mode when reading the charge from the image sensor for photometry, and is driven in the normal drive mode during imaging. . Therefore, during photometry, the dynamic range of the image sensor is widened. As a result, it is possible to realize an imaging device that can quickly and accurately perform photometry using only the image sensor without using a dedicated photometering element.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a characteristic diagram showing charge accumulation characteristics for obtaining knee characteristics, Fig. 3 is a characteristic diagram of knee characteristics, and Fig. 4 is a characteristic diagram showing charge accumulation characteristics for obtaining knee characteristics. A characteristic diagram showing another example of the charge accumulation characteristic for obtaining the knee characteristic, and FIG. 5 is an explanatory diagram illustrating the state of photometry during multi-division photometry. 1... Lens system 2... Iris 3...
Shutter 4...CCD5...Amplifier
6... Process circuit 7... Recording circuit
8... Video floppy 9... Photometry circuit 10... System control circuit 11... 5SG 12... Normal drive waveform generation circuit 13... Knee drive waveform generation circuit

Claims (1)

[Scope of Claims] A solid-state image sensor, a solid-state image sensor driving means for supplying a drive pulse to the solid-state image sensor, and an exposure control means for determining exposure based on a photometric output of the solid-state image sensor, and prior to image capturing. An imaging device that controls exposure based on a photometric output read from the solid-state image sensor, wherein the solid-state image sensor driving means operates in a knee characteristic drive mode in which the solid-state image sensor is driven so as to have a knee characteristic, and in a normal mode. It has two types of drive modes, a normal drive mode for driving, and is configured to drive in the knee characteristic mode when reading charges from the solid-state image sensor for photometry, and drive in the normal drive mode during imaging. Characteristic imaging device.