JPS6171776A - Image pickup device - Google Patents

Abstract

PURPOSE:To improve the exposure accuracy with an image pickup device which performs the exposure control, etc. according to the luminance signal given from an image pickup element, by always changing the reference value of integration in response to the state of the image pickup device and therefore eliminating the fluctuation of the circuit conditions owing to the temperature change, etc. CONSTITUTION:The exposure time is decided by the information on the preliminary light leading and the aperture value. The picture information is read out of an image pickup element 4 in a field F4 next to the exposed field by a signal processing circuit 5. Then only the luminance signals are sampled out of the picture information, and the luminance signals equivalent to a screen are integrated by a luminance signal integration circuit 9. While the output of the circuit 9 is converted into digital signals via an A/D converter 12 at a time point t8 among those time points t7-t9. These digital signals are fetched by an arithmetic circuit 10. The circuit 10 checks in the field F4 whether the exposure value including the errors of a diaphragm 2 and a shutter 3 is proper or not. If some variance is detected, the diaphragm 2 is corrected between time points t10-t11 of the next field F5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an imaging device, and particularly to an imaging device that performs exposure control etc. based on a luminance signal from an image sensor.

[Prior art]

Conventionally, in this type of device, the luminance signal and its integral value change due to signal level fluctuations caused by temperature fluctuations of the image sensor, which adversely affects accuracy when performing exposure control etc. using this integral information. [Purpose] The present invention was made in view of the drawbacks of the conventional device, and it changes the reference value of the integral to always follow the state of the imaging device, thereby eliminating fluctuations in circuit conditions due to temperature fluctuations, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 0 (Embodiment) Aiming to provide an imaging device that improves cancellation exposure accuracy The content of the present invention will be described in detail below with reference to the attached circuit diagram. FIG. 1 is an electrical circuit diagram showing an embodiment of the present invention, in which 1 is an optical system for forming an optical image of a subject, 2 is an aperture, 2a is an aperture driver for driving the aperture 2, and 3 is an electric circuit diagram showing an embodiment of the present invention. 3a is a shutter driver for driving the shutter 3; 4 is an imaging device such as a COD as an imaging means, which converts an optical image into an electrical signal. 5 is a signal processing circuit, and 6 is a recording circuit.

7 is a clock circuit that generates various timing signals; 8
9 is a driver that drives the image sensor 4 based on the signal from the clock circuit, and 9 is an integrating means for extracting only the luminance signal corresponding to the subject luminance from the signal processing circuit 5 and integrating it for one screen. A brightness signal integrating circuit 10 is an arithmetic control circuit as a calculating means for controlling the entire imaging apparatus based on the timing signal from the clock circuit 7 and information from the brightness signal integrating circuit 9 and the like. Reference numeral 11 denotes a 12-fitted converter, which is a preliminary photometry circuit provided separately from the imaging means to measure the approximate brightness of the subject.

The above is a circuit diagram showing one embodiment of the present invention, and its operation will be explained below with reference to the timing diagram of FIG. 2.

FIG. 2 is a timing chart when one-frame photography is performed using the imaging apparatus of the present invention.

The figure (a) shows the vertical synchronization signal V generated by the clock circuit 7.
D, and each field separated by this is Fl, F2
．． F3. Name it... When a power switch (not shown) is turned on at time tl asynchronously with the vertical synchronization signal (FIG. 2(b)), the preliminary photometry circuit 11 measures an approximate value of the subject brightness and inputs it to the arithmetic control circuit 10. Next, at time t, a release (not shown) is performed (FIG. 2(b)), and from time t2 immediately thereafter, the arithmetic control circuit 10 causes the aperture driver 2a to adjust the aperture based on the preliminary photometry information. 2 to a predetermined aperture υ value. (Fig. 2 (C)) When the aperture is completed at time t and the aperture value settles to A1 in field F2, in the next field (F3), the arithmetic control circuit 1° operates the shutter driver based on the information of the preliminary photometry. 3a
The shutter 3 is driven via the shutter 3 to expose the image sensor 4 to light.

(Time t4 to ts in FIG. 2(d)) In this example, the shutter 3 has two blades d,
, d, and the blade d runs at time t4, and at time t5.
The exposure time (tst+) is increased by the movement of the blade d.
can be obtained.

This exposure time is determined according to the preliminary photometry information and the aperture value. Next field after exposure (F4)
Then, the signal processing circuit 5 reads image information from the image sensor 4, extracts only the luminance signal therein, and integrates the luminance signal for one screen in the luminance signal integration circuit 9. (Second
At time ts between time t and time 11 in FIG.
Incorporate into. (Fig. 2(f)) This causes the aperture 2. The arithmetic control circuit 10 evaluates whether the exposure amount including the error of the shutter 3 is appropriate within the field F4, and if there is a deviation, the exposure amount including the error of the shutter 3 is evaluated at time t1° to t11 of the next field F5.
to correct the aperture 2 from A1 to A2. (Figure 2 (
C)) Time t7. - When the aperture reaches the final value A2 to be corrected, the arithmetic control circuit 1
0 again drives the shutter 3 via the shutter driver 3a and exposes the image sensor 4 for a time (t, 3 to t12). This exposure time is determined by the aperture value A2 and the integral value of the luminance signal captured at time t6.

Furthermore, in the next field F7, the signal processing circuit 5 and the recording circuit 6 are activated to record the imaging information on the recording medium. (Period T2 in FIGS. 2(f) and (h)) Next, the luminance signal integration circuit 9 and its operation will be supplementarily explained with reference to FIGS. 2 and 3.

In FIG. 3, 100 is an operational amplifier, 101 is an integrating capacitor, 102 is a resistor, and 100 to 102 are an integrating circuit 10.
form 6. Reference numerals 103 and 104 are switching elements, and when the control terminals C and D are high, both ends are conductive.
When is low, both ends are non-conductive. 105 is a capacitor that holds the standard value of integration, and A and B are input/output terminals of the integrating circuit. 103, 105, etc. constitute a sample hold circuit as a reference level forming means. When the switch 104 becomes conductive, the integrating capacitor 101 is discharged,
The integration circuit is reset to a large swing, and integration is performed when the switch 104 is non-conductive. As will be described later, the switch 103 is turned on at a predetermined timing while the image sensor 4 is also outputting a signal, and the capacitor 105 is charged to a voltage corresponding to the reference level for integration.

At other times, switch 103 is non-conductive and capacitor 105 is held at the voltage at the reference level for integration. The above is the configuration of the luminance integrating circuit shown in FIG. 3, and its operation will be explained below with reference to FIG. 2 as well.

All terminals except field F4 are at high level,
The luminance signal integration circuit 9 is in a reset state except for performing an integration operation in field F4. (Fig. 2 (i)) Also, assuming that the image sensor 4 is a frame transfer type COD, the terminal C in Fig. 3 is at a high level for a moment (time t+oo) in the field F3 as shown in Fig. Assuming that, at time tlof1, the electric signal formed by the image sensor 4 in field F2 is read out and applied to terminal A in FIG. 2, and therefore, at time tlG. #@element output voltage corresponding to field F2 in switch 10
3 to capacitor 105 and then held at that value.

From FIG. 2(d), since the shutter 3 is closed in the field F2, what is sampled by the capacitor 105 at time t+oo is the output of the image sensor in the dark oscillation, and the output of the image sensor 4 immediately before shooting is sampled by the capacitor 105 at time t+oo. Contains information such as dark current and noise.

Next, time t1 immediately after time t+oo in field F3
01, the output of the luminance signal integration circuit 9 is taken into the arithmetic control circuit 10 via the A/D converter 12. At time t1°, the output of the image sensor 4 corresponding to the dark state is applied from the capacitor 105 to the non-inverting input of the operational amplifier 100, and as shown in FIG. 2(i), since the switch 104 is in the conducting state, the inverting input and output are The output BK of the luminance signal integrating circuit, which is short-circuited, receives the voltage of the non-inverting input as it is, and is once taken into the arithmetic control circuit 10 via the IV/D converter 12.

Next, in the field F4, the signal of the image sensor 4 exposed to the field F3 is integrated by the luminance signal integration circuit 9 as explained earlier, (Fig. 2<e)) From the time t when the fi minute is completed, At time t in field F4, the output of the luminance signal integration circuit 9 is again taken into the arithmetic control circuit 10 via the A/D converter 12t. (FIG. 2(f)) Then, by taking the difference between the value taken at time trot and the value taken at time t, it becomes the average value of the luminance signal for one screen. Based on this value, the aperture is corrected to A2 and a photograph is taken. The rest is already explained +lj
The explanation will be omitted since it is the same.

As explained above, if the reference voltage for luminance signal integration is set to the output of the image sensor 4 when the shutter is closed, the temperature characteristics (dark current, noise) of the image sensor will be lower than when the reference voltage is set to a certain value. etc.), and characteristic fluctuations such as temperature drift of the offset of the signal processing circuit 5 and the luminance signal integration circuit 9 can be canceled, thereby reducing errors caused by these in subject luminance measurement and improving the accuracy of exposure control. I can give it to you.

(Second Embodiment) In the first embodiment, an example has been described in which the image sensor 4 is darkened by the shutter 3, but the image sensor 4 may be darkened by the diaphragm 2. In this case, the embodiments of the present invention can be applied to, for example, an imaging device that can take both still images and moving images, but does not use a shutter when shooting moving images. In other words, if the luminance signal integration circuit is standardized with the aperture fully closed before shooting starts, the image sensor 4. The fluctuation factors of the signal processing circuit 5.4 and the variable signal integration circuit 9 can be removed.

(Third Embodiment) In cases where it is not possible to darken the aperture or shutter due to the system or sequence, if the standard of luminance signal integration is taken while COD transmission is stopped, changes in the characteristics of the image sensor 4 itself can be avoided. Even if it cannot be removed, the amplifier and other peripheral circuits in the image sensor 4 and the signal processing circuit 5. The fluctuation factors of the brightness signal integration circuit 9 can be removed, and the brightness of the subject can be measured accordingly! '[The image quality increases, and exposure accuracy can be improved.

(Fourth Embodiment) Further, as shown in FIG. 4(a), when a part 14 (shaded area in the figure) of the image sensing screen 13 of the image sensor 4 is illuminated, this is shown in FIG. 4(b). This is an initial part of time TOB within one horizontal scanning period Th. As shown in Figure 4(b,), T0
Since the input to the luminance signal integration circuit 9 corresponds to the dark level of the image sensor 4 at time tx within n, this time t
By inputting the reference value of the integrating circuit 9 to x into the arithmetic control circuit 10, characteristic fluctuations from the image sensor 4 to the luminance signal integrating circuit 9 can be canceled.

(Fifth Embodiment) This dark area is usually called an optical black area and is often provided in advance within the image sensor.
Since it is used as the reference level of the circuit, this clamp level may be used as the reference for integration. In this way, the same effect can be obtained with a simpler configuration than that of the fourth embodiment (sixth embodiment).In the above embodiment, time t, is transmitted through the integrating circuit. The arithmetic control circuit 10 is used to obtain the difference between the dark image signal at time t1 and the imaging integral signal at time t8.
It is also possible to provide a hold circuit that holds the signal at 1 and use a differential amplifier that obtains the difference between the output of this hold circuit and the output of the integrating circuit.

(Effects) As explained above, according to the present invention, it is possible to reduce signal level fluctuations caused by temperature fluctuations in the imaging element or peripheral circuits, and it is possible to perform controls such as exposure control with high precision. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of the lfi image device of the present invention, FIG. 2 is an operation timing chart thereof, FIG. 3 is a diagram showing an example configuration of an integrating circuit, and FIG. 4 is a diagram explaining a fourth embodiment of the present invention. It is. 4... Imaging element as an imaging means, 106... Integrating circuit as an integrating means, 107...
Sample and hold circuit as a reference level forming means. Figure 4 (a) (b) (b2)

Claims (4)

[Claims] (1) an imaging means for converting an optical image into an electrical signal; an integrating means for integrating the output of the imaging means; a reference level forming means for forming an integrated reference level signal of the integrating means using a predetermined output of the imaging means; An imaging device having: (2) Claim (1) characterized in that the reference level forming means forms a reference level signal based on an electrical signal formed by the imaging means when no light is incident on the imaging means. The imaging device described. (3) The imaging apparatus according to claim (1), wherein the reference level forming means forms a reference level signal based on a signal of an optically black portion of the imaging means. (4) The imaging device according to claim (1), wherein the reference level forming means forms the reference level signal based on the output signal of the imaging means in a state where the driving of the imaging means is stopped. .