JP2764145B2 - Electronic still camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an electronic still camera that corrects an exposure value obtained by a photometry unit by pre-exposure to obtain an exposure value of main exposure.

[Conventional technology]

A conventional electronic still camera will be described with reference to FIG.

In the figure, 1 is an optical system that focuses a subject image on an image sensor, 2a is a stop that limits light flux from the subject, 2b is a driver that drives the stop, 3a is a mechanical shutter that limits an incident signal of subject light, 3d is a driver for driving the shutter, 4 is an image pickup device that separates a subject image into three primary colors and converts them into electric signals, 5 is a predetermined luminance signal Y based on R, G, and B primary color signals. It is a signal processing unit that derives a color difference signal (RY, BY).

In a conventional electronic still camera, the shutter release button is pressed, and the switch SW
When 1 (not shown) is pressed, photometry (so-called external photometry) is performed by the photometry unit 8 to obtain an exposure value EV.

When the switch SW2 (not shown) is pressed in the next stroke of the shutter button, the following series of operations is performed.

The aperture 2a and the shutter 3a are driven in accordance with the aperture value and the shutter speed obtained by the arithmetic control circuit 7b based on the previously obtained exposure value EV, and pre-exposure is performed. At this time, the R, G, and B signals obtained from the image sensor 4 are converted into a luminance signal Y by the signal processing unit 5 and integrated by the integration circuit 6 to obtain the previously obtained aperture value and shutter speed. Is obtained (correctly, an integral value proportional to the amount of incident light).

Then, in order to improve the accuracy of the exposure value EV previously obtained by the photometry unit 8, the arithmetic control circuit 7b corrects the exposure value EV by using the integral value obtained by the pre-exposure and proportional to the amount of incident light. Exposure value EV '
Again, the main exposure is performed, and the image signal is recorded.

[Problems to be solved by the invention]

However, in the above-described conventional example, an integral value proportional to the amount of incident light in the pre-exposure is obtained by integrating the luminance signal Y obtained from the signal processing unit 5. However, if there is a part having extremely high luminance in the screen. Even if the overall brightness level in the screen is low, the integral value increases depending on the portion, and it is determined that the incident light amount is larger than the predetermined light amount, and the exposure value in the main exposure is corrected to be small, or When a bright part such as the sky is included in the screen, the integral is increased by integrating that part, and the exposure value is corrected so that the correct exposure can be obtained in the bright part. Exposure was often under.

An integrating circuit using an operational amplifier as shown in FIG. 6 is used for the integrating circuit 6. However, the operational amplifier has an offset, which varies depending on each operational amplifier element. Had to be adjusted by volume or the like to make the offset zero.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an electronic still camera capable of obtaining an appropriate exposure value.

[Means for solving the problem]

In order to achieve the above object, in the present invention, an electronic still camera is configured as in the following (1) to (4).

(1) Pre-exposure is performed based on the exposure value obtained by the photometry unit, the luminance signal obtained by the pre-exposure is integrated by an integration circuit, and the exposure value is corrected by an arithmetic and control circuit based on the output of the integration circuit. An electronic still camera that obtains an exposure value of the main exposure, wherein the luminance signal is obtained from a signal read out after pre-exposure and after reading out signal charges accumulated in a partial area of the image sensor, and a signal An electronic still camera which inputs the high-level portion to the integration circuit via a circuit for compressing or clipping the high-level portion.

(2) The arithmetic control circuit stores the offset amount of the integrating circuit in advance, subtracts the offset amount from the output of the integrating circuit, corrects the exposure value based on the value, and obtains the exposure value of the main exposure. The electronic still camera according to (1).

(3) Pre-exposure is performed based on the exposure value obtained by the photometry unit, the luminance signal obtained by the pre-exposure is integrated by an integration circuit, and the exposure value is corrected based on the output of the integration circuit in an arithmetic control circuit. An electronic still camera that obtains an exposure value of the main exposure, wherein the integration circuit is reset during a first required period when a luminance signal obtained by the pre-exposure is input, and converts the luminance signal to a signal level. An electronic still camera that inputs to the integrator through a circuit that compresses or clips high parts of the image.

(4) The arithmetic control circuit stores the offset amount of the integration circuit in advance, subtracts the offset amount from the output of the integration circuit, corrects the exposure value based on the value, and obtains the exposure value of the main exposure. The electronic still camera according to (3).

[Action]

With the above configurations (1) to (4), proper exposure can be performed during the main exposure even if a part of the subject has an extremely high luminance, and a bright part such as the sky is part of the subject. In this case, proper exposure can be performed at the time of main exposure.
According to the configuration of (4), proper exposure can be performed at the time of main exposure regardless of the offset of the integration circuit.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

FIG. 1 is a block diagram of an electronic still camera according to a first embodiment of the present invention.

In FIG. 1, portions having the same reference numerals as those in FIG. 5 have the same configuration and operation as those in FIG. 5, and a description thereof will be omitted.

An operation control circuit 7a operates in the same manner as the operation control circuit 7b of the conventional example, and also generates a reset signal to the integration circuit 6 and a signal for partially clearing the image sensor 4 as described later. I do.

Reference numeral 9 denotes a KNEE circuit for compressing a high-level portion of the luminance signal, and reference numeral 10 denotes a reset signal for resetting the integration circuit 6. While this signal is low, the integration circuit 6 is reset and integration is not performed.

Next, the exposure control operation of this embodiment will be described with reference to FIGS.

In the electronic still camera shown in FIG. 1, the shutter release button is pressed, and the switch SW is switched at the first stroke.
When 1 (not shown) is pressed, photometry is performed by the photometry unit 8, and the arithmetic control circuit 7a determines the exposure value EV.

Then, when the switch SW2 (not shown) is pressed in the next stroke of the shutter release button, a series of operations described below are performed.

Clear unnecessary charge accumulated in the CCD (Charge Coupled Divice) 4 which is an image pickup device during the period from time t ₀ in Fig. 2 to t _1, the diaphragm is determined according to the exposure value EV previously obtained and shutter speed pre-exposure is carried out by (t ₃ from time t _2). Then, to eliminate the influence of certain areas of the top of the screen, in t ₅ from time t _4, the signal for the partial clear from the arithmetic control circuit 7a is issued CCD4, stored in the portion corresponding to the screen top of CCD4 Clear the charge
from t ₆ to start the reading of CCD4. At this time, it starts the operation of the integrating circuit 6 at time t ₆ by a reset signal 10 to High.

At this time, the luminance signal obtained by compressing the high level of the signal through the 9 KNEE circuits (characteristics of which are shown in FIG. 3 (a)) is integrated into the integrating circuit 6 to integrate the signal extremely into the screen. It is possible to reduce the influence when a high-luminance subject is included. It is needless to say that the same effect as when the KNEE circuit is used can be obtained even if a high level signal is clipped by using a CLIP circuit having characteristics shown in FIG. 6B instead of the KNEE circuit 9. No.

It starts integration operation from time t _6, the signal readout ends at time t _7, until resetting the integrator circuit 6 at time t _8, read level V is an integration output. Since this level is proportional to the amount of incident light at the time of the pre-exposure, the arithmetic control circuit 7a uses this value to determine whether the previously obtained exposure value EV is appropriate. To determine the exposure value EV '. (Pre-exposure is the actual aperture,
Since exposure is performed at the shutter speed, if the exposure value EV is appropriate, the level V becomes a constant value. Then, main exposure is performed at the aperture and shutter speed determined by the obtained exposure value EV ', and the image is recorded.

By the way, as described above, the integration circuit 6 has a configuration as shown in FIG. 6, but this has an offset and varies depending on each operational amplifier element. If an offset is present, an accurate integrated output cannot be obtained.To eliminate this, adjustment must usually be performed using a volume or the like.In this embodiment, instead, the offset amount of the operational amplifier element is measured in advance. The effect of the offset is eliminated by subtracting the stored offset amount from the integrated output obtained from the integration circuit 6 in the operation control circuit 7a. It is no longer necessary to correct the variation for each by adjusting the volume or the like.

In the electronic still camera of the present embodiment, as described above, when clearing the signal charge accumulated in the area corresponding to the upper portion of the screen of the image sensor CCD4 after the pre-exposure, the number of lines to be cleared is calculated by an arithmetic control circuit. It is better to write in 7a and make it possible to rewrite.

Next, a second embodiment of the present invention will be described. Its composition,
The operation is almost the same as that of the first embodiment described above, but differs from the first embodiment in the method of eliminating the influence of the high brightness area at the top of the screen during pre-exposure.

That is, in the first embodiment, in order to eliminate the influence of the upper part of the screen, the charges accumulated in the area corresponding to the upper part of the screen of the image sensor CCD4 are cleared prior to the reading, but in the present embodiment, FIG. as shown, reads the charge from usual CCD4 from time t _4, the in period (t ₄ ~t ₆₎ that reads an area of the top of the screen to reset the integrating circuit 6, the time
From t ₆ to the reset signal to High so as to start the integration operation. Even in this case, the same effect as in the first embodiment can be obtained. Note that the period (t _{4 to} t ₆ ) may be changeable.

〔The invention's effect〕

As described above, according to the inventions of the present application, an appropriate exposure value can be obtained even when there is a subject with extremely high brightness in the screen, and even when a bright portion such as the sky is included in the screen. An appropriate exposure value can be obtained, and a clear image can be obtained despite the use of an imaging device such as a CCD with a narrow exposure latitude.

Further, according to the second and fourth aspects of the present invention, an appropriate exposure value can be obtained despite the offset of the integration circuit, and the adjustment of the offset by the volume or the like becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a block diagram of the first embodiment, FIG. 2 is a timing chart showing the operation of the first embodiment, and FIG. 3 is a diagram showing characteristics of a circuit for compressing or clipping a high signal level portion. ) Is a characteristic diagram of the KNEE circuit, (b) is a characteristic diagram of the CLIP circuit, FIG. 4 is a timing chart showing the operation of the second embodiment, FIG. 5 is a block diagram of a conventional example, and FIG. It is a figure showing an example. 4 Image sensor 6 Integrator 7a Arithmetic control circuit 8 Photometer 9 KNEE circuit 10 Reset signal of integration circuit Y Luminance signal

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tsutomu Takayama 770 Shimonoge, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Inside the Tamagawa Works of Canon Inc. (56) References JP-A-61-69272 (JP, A) 203573 (JP, U)

Claims (4)

(57) [Claims] 1. A pre-exposure is performed based on an exposure value obtained by a photometry unit, a luminance signal obtained by the pre-exposure is integrated by an integration circuit, and an arithmetic control circuit calculates the exposure value based on an output of the integration circuit. An electronic still camera which obtains an exposure value of main exposure by correcting, wherein the luminance signal is obtained from a signal which is read after clearing signal charges accumulated in a partial area of the image sensor in advance after pre-exposure, An electronic still camera characterized in that a portion having a high signal level is input to the integration circuit via a circuit for compressing or clipping the portion. An arithmetic control circuit for storing the offset amount of the integrating circuit in advance, subtracting the offset amount from the output of the integrating circuit, correcting the exposure value based on the value, and obtaining the exposure value of the main exposure. The electronic still camera according to claim 1, wherein: 3. A pre-exposure based on an exposure value obtained by a photometry unit, a luminance signal obtained by the pre-exposure is integrated by an integration circuit, and an arithmetic control circuit calculates the exposure value based on an output of the integration circuit. An electronic still camera which obtains an exposure value of main exposure by correcting, wherein the integration circuit is reset during a first required period when a luminance signal obtained by pre-exposure is input, and An electronic still camera characterized in that a portion having a high signal level is input to the integration circuit via a circuit for compressing or clipping. 4. The arithmetic operation circuit stores the offset amount of the integration circuit in advance, subtracts the offset amount from the output of the integration circuit, corrects the exposure value based on the value, and obtains the exposure value of the main exposure. The electronic still camera according to claim 3, wherein: