JPH02149076A - electronic still camera - Google Patents

Abstract

PURPOSE:To obtain proper exposure at the time of main exposure even when an extremely high brightness part exists in a part of an object by inputting a brightness signal obtained by preexposure to an integrating circuit through a circuit for compressing or clipping a high signal level part. CONSTITUTION:Preexposure is executed at a stop or shutter speed determined in accordance with an obtained exposure value EV, a signal for partial clear is outputted from an operation control circuit 7a to a CCD 4, electric charge accumulated in a part corresponding to the upper part of the screen of the CCD 4 is cleared, and the reading of the CCD 4 is started. A brightness signal obtained by compressing the high level of a signal through a KNEE circuit 9 is inputted to the integrating circuit 6 to integrate the signal. Even when an object having extremely high brightness is included in a screen, its influence can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic still camera in which an exposure value obtained by a photometry section is corrected by pre-exposure to obtain an exposure value for main exposure.

[Conventional technology]

A conventional electronic still camera will be explained using FIG.

In the figure, 1 is an optical system that focuses the subject image on the image sensor, 2a is an aperture that limits the luminous flux from the subject, 2b is a driver that drives the aperture, and 3a is a mechanical device that limits the incident light from the subject. 3d is a driver for driving the shutter; 4 is an image sensor that separates the subject image into three primary colors and converts them into electrical signals; 5 is a predetermined luminance signal Y based on the three primary color signals of R2O and B; and color difference signal (R-Y.

This is a signal processing unit that derives B−Y).

In conventional electronic still cameras, when the shutter release button is pressed, the first stroke of the button releases the switch SW.
When I (not shown) is pressed, photometry (so-called external photometry) is performed by the photometry section 8, and an exposure value EV is obtained.

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

The aperture 2a and shutter 3a are driven according to the aperture value and shutter speed determined by the arithmetic control circuit 7b based on the previously obtained exposure value EV to perform pre-exposure. At this time, the signal processing unit 5 converts the R, G, and B signals obtained from the image sensor 4 into a luminance signal Y, and integrates it in the integrating circuit 6 to obtain the previously determined aperture value and shutter speed. The amount of incident light at (correctly, the integral value proportional to the amount of incident light) is determined.

In order to improve the accuracy of the exposure value EV previously obtained by the photometer 8, the arithmetic control circuit 7b corrects the exposure value EV using the integral value proportional to the amount of incident light obtained by pre-exposure. Then, main exposure is performed again using the exposure value EV' thus determined, and the image signal is recorded.

(Problem to be Solved by the Invention) However, in the above-mentioned conventional example, an integral value proportional to the amount of incident light in pre-exposure is obtained by integrating the luminance signal Y obtained from the signal processing section 5. If there is a part with extremely high brightness, the integral value will increase depending on that part, even if the overall brightness level in the screen is low.
If the amount of incident light is determined to be larger than the predetermined amount of light and the exposure value in the main exposure is corrected to be smaller, or if there is a bright part such as the sky in the screen, it may be necessary to integrate that part. , the integral value becomes large and the exposure value is corrected to obtain proper exposure in bright areas, which often results in the overall exposure being amplified.

In addition, the integrator circuit 6 uses an integrator circuit using an operational amplifier as shown in Fig. 6, but the operational amplifier has an offset, which varies depending on each operational amplifier element, so it is necessary to obtain an accurate h1 value. In this case, it was necessary to adjust the volume to bring the offset to zero.

The present invention has been made to solve such problems, and an object of the present invention is to provide an electronic still camera that can obtain appropriate exposure values.

(Means for Solving Problem 3t1) In order to achieve the above object, in the present invention, an electronic still camera is configured as shown in (1) to (4) below.

(1) Pre-exposure is performed using the exposure value determined by IJ by the FF4 optical section, the luminance signal obtained by the pre-exposure is integrated by an integrating circuit, and the above-mentioned exposure value is corrected in the arithmetic control circuit based on the output of the integrating circuit. In this electronic still camera, the luminance signal is input to the integrating circuit via a circuit that compresses or clips a portion with a high signal level.

(2) In (1) above, the luminance signal obtained by pre-exposure is determined from the signal read out after pre-clearing the signal charge accumulated in a partial area of the image sensor after pre-exposure. do.

(3) In (1) above, it is assumed that the integrating circuit is reset during the initial required period when the luminance signal obtained by pre-exposure is input.

(4) In (1) to (3) above, the arithmetic control circuit:
It is assumed that the offset amount of the integrating circuit is stored in advance, the offset amount is subtracted from the output of the integrating circuit, and the exposure value is corrected using that value to obtain the exposure value for the main exposure.

[Function] With the configurations (1) to (4) above, even if there is an extremely bright part of the subject, proper exposure can be achieved during the main exposure. According to the configuration (4) above, proper exposure can be achieved during the main exposure even if there is a bright part of the subject such as the sky, and according to the configuration (4) above, the main exposure can be performed regardless of the offset of the integrating circuit. Proper exposure can be achieved.

(Example) Hereinafter, the present invention will be explained with reference to Examples.

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

In FIG. 1, parts with the same reference numerals as those in FIG. 5 have the same configuration and operation as in FIG. 5, and their explanations will be omitted here.

Reference numeral 7a denotes an arithmetic control circuit which operates in the same manner as the conventional arithmetic control circuit 7b.
A reset signal to the image sensor 4 and a signal for partially clearing the image sensor 4 are generated.

9 is a NEE circuit for compressing the high level portion of the luminance signal, and 10 is a reset signal for resetting the integrating circuit 6. While this signal is low, the integrating circuit 6 is reset and no integration is performed. .

Next, the exposure le I of this example? The Xl operation will be explained using FIGS. 1 and 2.

In the electronic still camera shown in Figure 1, when the shutter release button is pressed, the switch SW is
When I (not shown) is pressed, photometry is performed by the photometer 8, and the exposure value EV is determined by the arithmetic control circuit 7a.

Then, when the switch 5W2 (not shown) is pressed with the next stroke of the shutter release button, a series of operations described below are performed.

Time t in FIG. During the period from tl to tl, the image sensor CCD
ivice) 4, and pre-exposure is performed at the aperture and shutter speed (from time t2 to ts) determined according to the previously obtained exposure value EV.

Then, in order to eliminate the influence of a certain area of the screen improvement part, from time t4 to t5, a signal for partial clearing is sent from the arithmetic control circuit 7a to the CCD 4, and the signal is accumulated in the part of the CCD 4 corresponding to the screen improvement part. The charges are cleared and reading from the CCD 4 is started from time t6. At this time, the operation of the integrating circuit 6 is started by setting the reset signal 10 to High at time t6.

At this time, the luminance signal obtained by compressing the high level of the signal is input to the integrating circuit 6 through the NEE circuit (characteristics shown in FIG. 3(a)) in 9, and is integrated. It is possible to reduce the influence when a subject with high brightness is included in the image. Furthermore, in place of the NEE circuit 9, a CLI P circuit whose characteristics are shown in FIG. 6(b) can be used to clip the high level of the signal, and the same effect as when using the NEE circuit can be obtained. Needless to say.

The integration operation is started from time 0, and when the signal readout is finished at time t7, the level V, which is the integration output, is read before the integration circuit 6 is reset at time t8. Since this level is proportional to the amount of incident light during pre-exposure, using this value, the calculation Fr1l + control circuit 7a determines whether the previously determined exposure value EV is appropriate, and if it is not appropriate, an appropriate value is determined. Correction is performed to determine the exposure value EV'. (Pre-exposure is performed at the actual aperture and shutter speed, so if the exposure value EV is appropriate, the level V will be a constant value.) Then, the level V is determined by the exposure value EV' obtained here. Main exposure is performed at the aperture and shutter speed, and the image is recorded.

By the way, as mentioned above, the integration circuit 6 has a configuration as shown in FIG. 6, but this has an offset, which varies depending on each operational amplifier element. If there is an offset, it is not possible to obtain an accurate integral output, so in order to eliminate stiffness, it is usually necessary to make adjustments using a volume control, etc., but in this example, instead of that, the amount of offset of the operational amplifier element is measured in advance. is stored in the arithmetic control circuit 7a, and in the circuit 7a, the stored offset amount is subtracted from the integral output obtained from the subtraction circuit 6, thereby eliminating the influence of the offset.
This eliminates the need to correct variations between elements by adjusting the volume or the like.

In addition, in the electronic still camera of this embodiment, as described above, the screen on the image sensor CCD4 after pre-exposure is
When clearing the signal charges accumulated in the area corresponding to the F part, it is preferable to set the number of lines to be cleared in the arithmetic control circuit 7a and to have a configuration that allows rewriting.

Next, a second embodiment of the present invention will be described. Its configuration and operation are almost the same as those of the first embodiment described above, but differ 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 were cleared before reading, but in this embodiment, the charge accumulated in the area corresponding to the upper part of the screen was cleared before reading out. As shown in the figure, from time t4, CC
During the period (t4 to 70) when the charge is discharged from D4 and the upper area of the screen is read out, the integration circuit 6 is reset, and from time t6, the reset signal is set to High to start the integration operation. Make it. Even if you do this, the first
Effects similar to those of the embodiment can be obtained. Note that the period (t4 to t
Of course, o) may be changeable.

(Effects of the Invention) As explained above, according to each invention of the present application, an appropriate exposure value can be obtained even if there is an extremely bright subject within the screen. In the third invention, an appropriate exposure value can be obtained even when a bright part such as the sky is included in the screen, and a clear image can be obtained even though an image sensor such as a CCD with a narrow exposure latitude is used. can be obtained.

Further, according to the fourth invention of the present application, an appropriate exposure value can be obtained despite the offset of the integrating circuit, and offset adjustment using a volume or the like is not required.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the first embodiment, FIG. 2 is a timing chart showing the operation of the same embodiment, and FIG. 3 is a diagram showing the characteristics of a circuit that compresses or clips a portion with a high signal level. ) is the characteristic diagram of the NEE circuit, (b) is the CLIP
FIG. 4 is a timing chart showing the operation of the second embodiment, FIG. 5 is a block diagram of the conventional example, and FIG. 6 is a diagram showing an example of an integrating circuit. 4...Image sensor 6...Integrator circuit 7a...Arithmetic control circuit 8...Photometering section 9...KNEE circuit 10... ... Resetting the integration circuit No. 4X Y-...
...Professional 11 of Luminance Signal 1st Example. Figure 1

Claims (4)

[Claims] (1) Pre-exposure is performed using the exposure value obtained by the photometry section, the luminance signal obtained by the pre-exposure is integrated by an integrating circuit, and the arithmetic control circuit corrects the exposure value based on the output of the integrating circuit. What is claimed is: 1. An electronic still camera that obtains an exposure value for main exposure by using the luminance signal, and inputting the luminance signal to the integrating circuit via a circuit that compresses or clips a portion with a high signal level. (2) A claim characterized in that the luminance signal obtained by pre-exposure is obtained from a signal read out after clearing in advance signal charges accumulated in a partial area of the image sensor after pre-exposure. The electronic still camera according to item 1. (3) The electronic still camera according to claim 1, wherein the integrating circuit is reset during an initial required period when a luminance signal obtained by pre-exposure is input. (4) The arithmetic control circuit should store the offset amount of the integrating circuit in advance, subtract the offset amount from the output of the integrating circuit, and correct the exposure value using that value to obtain the exposure value for the main exposure. An electronic still camera according to any one of claims 1 to 3, characterized in that: