JPH057335A - Electronic still camera - Google Patents

Abstract

PURPOSE:To realize photometry free from an error due to a smear phenomenon by providing a solid state image pickup element, a photometric means, a smear information detecting means and an exposure calculating means. CONSTITUTION:A variable gamma correction circuit 25 is set previously at gamma=1, and a variable gain amplifier 24 is set previously at gain suitable for the photometry. First of all, pre-scanning is executed for 1V period. All the accumulated charge of a photodiode is read in an effective period and smear information is detected by blank scanning 1H. A mean value calculation circuit 21 calculates the mean value Vsm per one time of a smear signal and holds it in a smear value memory 26 till the end of all photometric scanning. The photometric scanning is executed and the mean value Vmean per one picture element of a photometric area is obtained and the stored smear value Vsm is subtracted by a subtraction circuit 27 and the error of the information due to the smear is corrected. Charge accumulation time or a stop value is changed so that the value Vm after correction lies within the range of lower limit Vmin<=Vm<= upper limit Vmax. The optimum exposure is calculated on the basis of the obtained Vm and photometric operation is finished. Accordingly, the error of photometric information is never caused and the highly precise information can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera (also referred to as a still video camera), and more particularly to photometry thereof.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional electronic still camera. In the figure, 1 is a lens unit, 2 is a lens drive motor, 22 is a shutter, 3 is an aperture, and 4
Is a shutter / aperture drive circuit. Reference numeral 5 denotes a solid-state image sensor that converts an image into an electric signal, and has a function of resetting or reading the accumulated charge by designating an arbitrary row in the vertical direction according to an instruction from the system control circuit 9. Reference numeral 23 is a γ correction circuit. Reference numeral 6 denotes an A / D conversion circuit that performs analog-digital conversion on the output of the solid-state image sensor 5. Currently, most of the A / D conversion circuits that can be obtained at low cost have about 8-bit resolution. Therefore, the γ correction is performed by the γ correction circuit 23 and then the A / D conversion is performed to suppress the generation of quantization noise. A frame memory 7 stores the output of the A / D conversion circuit 6. A system control circuit 9 controls the entire system. An image pickup signal processing circuit 10 performs processing such as band limitation on the output of the memory 7. 11
Is a D / A conversion circuit for digital-to-analog converting the output of the imaging signal processing circuit 10. Reference numeral 12 is an FM modulation circuit that FM-modulates the output of the D / A conversion circuit 11. 13 is a REC (record) for current-amplifying the output of the FM modulation circuit 12.
It is an amplifier. Reference numeral 14 is a magnetic head, 15 is a magnetic sheet as a recording medium, 16 is a motor for rotating the magnetic sheet 15, and 17 is a motor servo circuit for stabilizing the rotation of the motor. Reference numeral 20 denotes a release switch. When the switch is turned on, a series of photographing operations is started. 21
Is an average value calculation circuit for calculating the average value of the signals of the A / D conversion circuit 6.

FIG. 5 is a conceptual diagram of an interline CCD as an example of a solid-state image pickup element that is often used. In the figure, reference numeral 102 denotes a photodiode that converts light into electric charges and accumulates the electric charges, and 103 denotes a vertical CCD that vertically transfers the accumulated electric charges transferred from the photodiode one by one in 1H (horizontal scanning period). V1 to V4 are transfer electrodes of the vertical CCD, and V1 also serves as a transfer gate for transferring the charges in the odd rows of the photodiodes to the vertical CCD. Also, V3
Are also transfer gates corresponding to the photodiodes in even rows. The vertical CCD is driven by four-phase transfer pulses. Reference numeral 104 denotes a horizontal CCD that horizontally transfers the charges transferred from the vertical CCD 103 one stage to 1H. H
Reference numerals 1 and H2 denote transfer electrodes of the horizontal CCD, which are driven by two-phase pulses. Reference numeral 105 denotes an output amplifier that converts charges into a voltage and outputs the voltage. Vout is an output terminal. Reference numeral 106 is a top drain for sweeping away unnecessary charges. Vs
ub is a substrate bias terminal.

FIG. 6 is an interline type CC shown in FIG.
It is a figure which shows the drive timing of D. In FIG. 6, the odd field vertical blanking period starts from time t1. At time t2, the transfer gate V1 is set to the high level to transfer the charges in the odd rows to the vertical CCD 103. Time t3
By applying drive pulses in four phases from V1 to V4, charges are shifted line by line in 1H to the horizontal CCD 104, and are transferred at high speed in the horizontal direction for reading. At time t5, the reading of the charges in the odd fields is completed, and the vertical blanking period of the even fields starts. Transfer gate V at time t6
By setting 3 to the high level, the charges in the even rows are transferred to the vertical CCD 103 and the reading is started from the time t7.
By applying a pulse of about 30 V to the substrate bias terminal Vsub, it is possible to sweep away the charges accumulated in the photodiode 102 until then in the substrate direction. This can be used to control the charge storage time. The time t4 in FIG. 6 is the horizontal blanking period, and as shown in the figure at the time t4, the substrate bias terminal Vs
When a pulse is applied to ub, the charge accumulation time of the photodiode 12 is from time t4 to t6.

FIG. 7 is a diagram showing an operation sequence of the conventional electronic still camera shown in FIG. When the release switch 20 is turned on at time T0, the shutter 22 is opened and a series of photographing sequences is started. From time T0 to T1
In the meantime, scanning is performed M times, that is, photometric scanning while changing the charge accumulation time at a certain aperture value, and the optimal aperture value Av and the optimal shutter speed Tv are calculated from the average output value of the solid-state image sensor 5. In more detail, the photometry operation will be described. First, the diaphragm 3 is opened, the scanning is performed K times while changing the charge accumulation time, and at the same time, the average value calculation circuit 21 calculates the average value for each output scan of the solid-state image sensor 5. The charge storage time is set to the maximum value (for example, 1/30 seconds) in the first scan and is changed to ½ of the previous scan in each scan. The average value calculation circuit 21 is a shutter speed and an aperture value at which the system control circuit 9 obtains an appropriate exposure amount (also referred to as an optimum exposure amount) from an output average value within a range of a certain value. Tv and Av can be calculated. If the average value is too large, it is considered that most of the area of the solid-state image sensor 5 is saturated. If the average value is too small, the S / N is too bad and the calculation error when obtaining the appropriate exposure amount becomes too large. Therefore, scanning is performed while changing the charge accumulation time until the average value of the image falls within the appropriate range. ..
If the optimum exposure amount is not obtained even with the minimum charge accumulation time, the diaphragm 3 is narrowed down by one step and scanning is performed M times while changing the charge accumulation time again. This operation is repeated until the optimum exposure amount is obtained. The aperture is set to Av between T1 and T2, and a reset pulse is applied to Vsub of the solid-state image sensor 5 at T2 to sweep all the accumulated charges to the substrate and start the main exposure. At time T3, the shutter 22 is closed and the main exposure is finished.
Next, from time T4 to T5, the signal read scanning is performed and the processed signal is recorded on the magnetic sheet 15.

[0006]

Conventionally, as shown in FIG. 7, in the photometric scanning, the solid-state image pickup device 5 is left open without closing the shutter 22 each time the scanning is performed in order to shorten the time. The electronic shutter operation controls the charge storage time. However, in the conventional example,
When there is a high-luminance subject with a short charge accumulation time, a phenomenon called smear occurs and the photometric accuracy deteriorates.
FIG. 8 is a diagram for explaining the smear phenomenon. In the interline CCD, vertical transfer is performed one stage at 1H.
At locations where an image of a high-brightness subject is projected, exposure charges are generated in the vertical transfer path due to the influence of obliquely incident light or the like. Since this charge is transferred and output one stage at 1H, it becomes a vertical band-shaped false signal. When actually recording an image, smear does not occur because the signal of the solid-state image sensor 5 is read with the shutter 22 closed to prevent the smear phenomenon. Therefore, if the optimum exposure amount is obtained from the signal including the smear signal during photometry, the exposure amount may be insufficient during the main exposure depending on the amount of smear.

The present invention has been made in order to solve such a problem, and an object thereof is to provide an electronic still camera capable of photometry without an error due to a smear phenomenon.

[0008]

According to the present invention, in order to achieve the above object, an electronic still camera is constructed as described in (1) below.

(1) Solid-state imaging device, photometric means for driving the solid-state imaging device to obtain photometric information, smear information detecting means for driving the solid-state imaging device to detect smear information, and output of the photometric means. An electronic still camera comprising: an exposure amount calculation unit that calculates a required exposure amount based on the output of the smear information detection unit.

[0010]

With the configuration (1), the photometric information and the smear information are obtained, and the required exposure amount is calculated based on the photometric information and the smear information.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples.
FIG. 1 shows an "electronic still camera" which is a first embodiment of the present invention.
It is a block diagram of. In the figure, blocks denoted by the same numbers as in FIG. 4 have the same function, except that the variable gain amplifier 24 for switching the gain for the output of the solid-state imaging device 5 and the output of the variable gain amplifier 24 are different. Variable γ correction circuit 25 configured to turn on / off the γ correction by means of, a smear value memory 26 for storing the average value of the smear component from the scan before the photometry, the smear value is subtracted from the average value of the data of the photometry area during the photometry scan Is a subtraction circuit 27 for

FIG. 2 is a timing chart showing the photometric operation of this embodiment, and FIG. 3 is a flow chart showing the photometric operation of this embodiment. Referring to FIGS. 2 and 3 below,
The operation of this embodiment will be described.

First, γ is set to 1 in the variable γ correction circuit 25.
(See step S1). Variable gain amplifier 2
4 is set to a gain suitable for photometry.

Before the photometric scanning for obtaining the actual photometric data, the pre-photometric scanning is performed for 1V period (S2). The smear signal (information) is obtained by performing a blank scan for 1H after reading out all the charges accumulated in the photodiode 102 in the effective period.
Is detected. The average value Vsm per pixel of the smear signal is calculated by the average value calculation circuit 21 (S3) and stored in the smear value memory 26 (S4), and the value is held until all photometric scanning is completed. Next, photometric scanning is performed to obtain photometric data (S5, photometric scanning 1). After obtaining the average value Vmean per pixel in the photometric area (S6), the previously stored smear value Vsm is subtracted from the data average value Vmean in the photometric area by the subtraction circuit 27 (S6).
By 7), the data error due to smear is corrected.

The corrected value Vm is a predetermined upper limit value Vma.
If x is within the range of the lower limit value Vmin (S8 YE
S), and the optimum exposure amount is calculated based on this value Vm (S
9) End the photometric operation. When the Vm is not within the range between the upper limit value Vmax and the lower limit value Vmin (S8 NO),
Change the charge accumulation time or aperture value (S10) Step S
Returning to step 5, the photometric scanning (photometric scanning 2) is repeated again. When Vmin ≦ Vm ≦ Vmax is obtained by repeating such photometric scanning (photometric scanning 1, 2, ...), the optimum exposure amount is calculated based on the Vm value and the photometric operation is completed. Although omitted in the flow chart, when Vmin ≦ Vm ≦ Vmax is not satisfied due to the repetition of the above-described photometric scanning, the photometric operation is ended outside the photometric range.

The aperture value Av and the shutter speed Tv are determined based on the calculated optimum exposure amount, and the main exposure is performed. At the time of main exposure, the γ value of the variable γ correction circuit 25 is set to 0.45.

In the above-described first embodiment, in the pre-photometric scanning, after all the accumulated charges are read during the effective period, the blank scan is performed to detect the smear information, but the reading of the accumulated charges is prohibited. You may make it detect smear information. This example will be described as a second embodiment of the present invention.

The configuration of this embodiment has a system control circuit 9,
The configuration is the same as that of the first embodiment except the average value calculation circuit 21. As shown in FIGS. 9 and 10, the vertical CCD of the solid-state imaging device 5
The pre-photometric scanning is performed for 2V period without setting the transfer electrodes V1 and V3 of (1) to the high level (without applying the read pulse from the photodiode 102 to the vertical CCD 103). As a result, only the smear signal is output during the second V, that is, the effective period of the pre-photometric scan 2, in a state in which the reading of the accumulated charge is prohibited. That is, during the period of pre-photometric scanning 1 and pre-photometric scanning 2,
A smear signal which is a charge generated in the vertical CCD is output.

In this embodiment, signals in the same image range are averaged during pre-photometric scanning and during photometric scanning, and the average value of smear signals can be calculated by the same method as during photometric scanning. ..

Further, the reading of the accumulated charge may be prohibited by another method to detect the smear information. This example will be described as a third embodiment of the present invention.

The configuration of this embodiment is the same as that of the second embodiment except the system control circuit 9. As shown in FIG. 11, the vertical C from the photodiode 102 at times t2 and t6.
Immediately before the charge is read out to the CD 103, the substrate bias terminal Vs
Reading is prohibited by applying a reset pulse to ub and sweeping away all the accumulated charges toward the substrate.

In each of the above embodiments, the smear information is detected by the pre-photometric scanning, and the smear information is stored in the memory to calculate the optimum exposure amount. However, the present invention is not limited to this. Alternatively, it is also possible to carry out a method in which the photometric information is held in the memory, the smear information is detected by the post-photometric scanning, and the optimum exposure amount is calculated based on the photometric information and the smear information.

Although the term "optimal exposure amount" is used in the description of the conventional example and the example, this "optimal" condition varies uniquely depending on the photographing purpose, lighting conditions, subjectivity of the photographer, etc. It is not decided. Therefore, in order to avoid doubt, the term “required exposure amount” is used in the claims to correspond to the optimum exposure amount.

[0024]

As described above, according to the present invention, an extremely high photometric data can be obtained because an error of the photometric data due to smear does not occur when obtaining the photometric data in the TTL by using the solid-state image pickup device used for imaging. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is a timing chart showing the photometric operation of the first embodiment.

FIG. 3 is a flowchart showing a photometric operation of the first embodiment.

FIG. 4 is a block diagram of a conventional example.

FIG. 5 is a conceptual diagram of an interline CCD.

FIG. 6 is a diagram showing an example of driving tones of an interline CCD.

FIG. 7 is a diagram showing an operation sequence of a conventional example.

FIG. 8 is an explanatory diagram of the smear phenomenon.

FIG. 9 is a timing chart showing the photometric operation of the second embodiment.

FIG. 10 is a diagram showing the drive timing of the interline CCD in the photometric operation of the second embodiment.

FIG. 11 is a diagram showing the drive timing of the interline CCD in the photometric operation of the third embodiment.

[Explanation of symbols]

 5 Solid-state image sensor 9 System control circuit

Claims (1)

Claim: What is claimed is: 1. A solid-state image sensor, a photometric unit that drives the solid-state image sensor to obtain photometric information, a smear information detection unit that drives the solid-state image sensor, and detects smear information. An electronic still camera comprising: an exposure amount calculation unit that calculates a required exposure amount based on the output of the photometric unit and the output of the smear information detection unit.