JP2003015024A - Digital still camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital still camera capable of realizing autofocusing photography with simple constitution even when the light quantity of a subject is insufficient. SOLUTION: This camera is provided with an imaging device 3 having sensitivity to near infrared light and visible light, an infrared cut means 2, a switching means 7 for switching the cut means 2 to a position where light made incident on the imaging device 3 passes through or a position where it does not pass through and an autofocusing means. The autofocusing means switches the cut means 2 to the position where the light made incident on the imaging device 3 does not pass through by using the switching means 7 at the autofocusing time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital still camera, and more particularly to a digital still camera capable of performing autofocus photography with a simple structure even when the light quantity of a subject is insufficient.

[0002]

2. Description of the Related Art When shooting with a digital still camera,
Auto-focusing is performed by generating images of a subject at a plurality of lens positions, analyzing the plurality of images, and setting the lens positions where the images with the highest focusing ratio are generated.

The analysis of a plurality of images as described above is performed by Fourier-transforming the obtained image signal.
When the obtained image signal is Fourier transformed, high frequency components increase at the boundary between the bright portion and the dark portion. Therefore, as a result of the analysis by the Fourier transform, it is possible to determine that the image having the largest high frequency component has the clearer contour, that is, the image having the higher focusing rate.

However, when the subject is photographed in a dark condition such as at night, the amount of light on the subject is insufficient, so the difference in brightness between the contours of the subject decreases, and the high frequency component of the Fourier transformed value does not increase. Since the outline will not be clear,
The focusing rate decreases.

Further, in order to enable autofocus photography even when the light quantity of the subject is insufficient, infrared rays are radiated toward the subject, and the infrared rays reflected from the subject are received by a light receiving sensor, and the distance from the subject is detected. There is also a method of adjusting the lens position by measuring

However, in order to perform such auto-focus photographing, it is necessary to provide an infrared ray emitting source for irradiating a subject and a sensor for receiving reflected light of the infrared ray and measuring a distance, which increases cost. In addition to this, there is a possibility that the device may become complicated.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a digital still camera capable of autofocus photography with a simple structure even when the light quantity of a subject is insufficient.

Other objects of the present invention will become apparent from the following description of the present specification.

[0009]

According to a first aspect of the present invention, an image sensor having sensitivity to near infrared light and visible light, infrared cut means, and the infrared cut means are incident on the image sensor. The switching means for switching to a position where the light passes or a position where the light does not pass, and an auto-focusing means. It is a digital still camera characterized by switching to a position where it does not pass.

According to a second aspect of the present invention, there is provided external light judging means for judging the quantity of external light, and the autofocus means is such that the external light judging means does not have a shortage of light quantity during autofocusing. If it is determined, the switching unit switches the infrared cut unit to a position where the light incident on the image sensor passes, and if it is determined that the amount of light is insufficient, the switching unit switches 2. The digital still camera according to claim 1, wherein the infrared cut means is switched to a position through which light incident on the image pickup element passes.

According to a third aspect of the present invention, there is provided a digital still camera according to the first aspect, wherein the digital still camera has an infrared light emitting means and the infrared light emitting means irradiates an object with infrared light during autofocusing. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

FIG. 1 is a functional block diagram showing one state of the digital still camera of the present invention, FIG. 2 is a functional block diagram showing another state of the digital still camera of the present invention, and FIG. 3 is signal processing. It is a functional block diagram of a part.

A processing flow until an image signal is obtained by the digital still camera of the present invention will be described with reference to FIGS. 1 to 3.

In the figure, the subject image formed by the cooperation of the plurality of image pickup lenses 1 is finally formed on the light receiving surface of the image pickup device 3. At this time, the imaging lens 1
A diaphragm (not shown) or the like is driven by a control unit (not shown) to adjust the lens position and the diaphragm ratio suitable for imaging. The image pickup device 2 photoelectrically converts the subject image formed on the light receiving surface into a charge amount, and outputs an analog image signal by a transfer pulse from an image pickup device driving means (not shown). The output analog signal is subjected to CDS (correlated double sampling) processing in the pre-processing means 40 to reduce noise, and the gain is adjusted. Then, after being converted into a digital image signal by the A / D conversion means 41, luminance processing and color processing are performed in the image signal generation unit 42 to perform digital processing (eg, luminance signal (Y) and color difference signal (Cr, Cb)) and is output to the frame memory 43 which is a temporary storage means for temporarily storing at least one frame of digital video signal.

The digital video signal stored in the frame memory 43 has been subjected to thinning processing and the like, and is input to a video memory (hereinafter referred to as VRAM) 44 (not shown). A signal based on the digital video signal input to the VRAM 44 is sequentially read and displayed on the liquid crystal display unit 45 which is a display unit. That is, the subject image formed by the taking lens 1 is photoelectrically converted into an image signal by the image pickup element 2, and images based on this image signal are sequentially displayed on the liquid crystal display means 45.

The operator looks at the image displayed on the liquid crystal display means 45 to determine whether or not to take a picture, and if the picture is taken, a release button (not shown) is pressed,
The digital video signal stored in the frame memory 43 is transferred to the image storage memory 46 which is a recording unit,
Remember. This image storage memory 46 is, for example, SR
Not only AM, DRAM, EEPROM and the like, but also a removable recording medium such as a PC card may be used.

Although the digital video signal stored in the frame memory 43 is transferred to the image storage memory 46 by pressing the release button in the above example, the liquid crystal display means 45 displays an image. In this case, the number of pixels imaged by the image sensor 3 is reduced (reduced) to improve the processing speed, and the release button is pressed. After performing the processing of (1), the image may be transferred to the image storage memory 46. The data stored in the image storage memory 46 may be data obtained by compressing a digital video signal.

The digital still camera of the present invention is
When the release button is pressed halfway during image pickup, automatic focus adjustment is performed by the camera control unit 6 which is the autofocus means of the present invention (hereinafter, also referred to as autofocus).

In the present invention, the autofocus means to adjust the focus of an image pickup object by the automatic control of the camera. By performing such autofocus,
A user using the digital still camera of the present invention can obtain a so-called in-focus image without having to adjust the image by himself.

As the image pickup device 3, an image pickup device having sensitivity to near infrared light and visible light can be used.

The image pickup device 3 is provided with an infrared cutting means which is switchable between a position (see FIG. 1) and a position (see FIG. 2) through which the incident light passes by the switching means 7 so as to be close to each other. There is.

The infrared cut means is a means capable of blocking the near-infrared light, and for example, an infrared cut filter which blocks light having a wavelength in the above range can be used, but is not particularly limited.

The switching means 7 has a position (see FIG. 1) through which the light incident on the image pickup device 3 passes through the infrared cut means and a position (see FIG. 1) where the light does not pass through the infrared cut means according to a command from the camera control section 6 which is the autofocus means of the present invention. (See FIG. 2), and examples thereof include means for driving the infrared cut filter by a motor.

The image pickup device 3 can be made to function as an image pickup device having sensitivity only to visible light or an image pickup device having sensitivity to near infrared light and visible light by the infrared cut means 2. That is, the image pickup device 3 is cut by the switching means 7 to a position where the light incident on the infrared cutting means 2 passes, whereby the infrared light is cut, and a signal of only visible light is generated. The infrared light is not cut by being switched to a position where the light incident on the infrared cut unit 2 does not pass, and the infrared light is incident to generate signals of visible light and near infrared light.

The switching means 7 causes the infrared light to enter the image sensor 3 by switching the infrared cut means 2 to a position where the light incident on the image sensor 3 does not pass through when the auto focus is performed by the auto focus means. .

FIG. 4 is a diagram showing an example of a processing flow when performing autofocus by the autofocus means.
The flow of autofocus of the present invention will be described in detail below with reference to FIG.

First, when the release button is half-pressed prior to photographing, a program as shown in FIG. 4 is activated by the autofocus means, and the switching means 7 causes the infrared ray cutting means 2 to move from the position shown in FIG. The position is switched to the position shown in (S1).

By the processing of S1, infrared light and visible light are made incident on the image pickup device 3, and an image signal is obtained by picking up a subject image with near infrared light and visible light (S
2) The signal processing unit 4 performs a Fourier transform on the obtained image signal (S3).

The Fourier-transformed data are compared in S2 to determine whether or not the high frequency component peak has been detected (S4). If it is determined that the high frequency component peak has not been detected, the lens position is moved. (S5), S2 and S
The process of 3 is repeated.

On the other hand, if it is determined in S4 that the peak of the high-frequency component can be detected, the lens position is adjusted to the position where the image signal having the peak of the high-frequency component of the Fourier transformed value is obtained (S6), and the switching is performed in S1. As shown in FIG. 1, the infrared cut means is switched to a position where the light incident on the image pickup device 3 passes through (S7), whereby autofocus processing is performed.

Further, in FIGS. 1 and 2, it is preferable to provide an external light judging means for judging the brightness of external light.
The outside light determining means is preferably provided in the signal processing unit 4.

The outside light determining means is such that the light quantity of visible light is not less than a predetermined value with respect to the image signal generated by the image pickup device 3 provided at the position where the light incident on the infrared cutting means by the switching means 7 passes. Determine if there is.

The predetermined value of the light quantity can be freely set, but for example, when photographing in the automatic strobe light emission mode,
It is possible to set the brightness of the subject so dark that the flash fires.

When such external light judging means is provided, the autofocus means switches the infrared cutting means by the switching means 7 when the external light judging means judges that the light quantity is not more than the predetermined value. Process. When it is determined that the light amount is equal to or larger than the predetermined value, the process of S1 for switching the infrared cut unit by the switching unit 7 is not performed.

FIG. 5 is a diagram showing a processing flow when performing autofocus of the autofocus means in the case where the external light judging means is provided. The autofocus in the case where the external light judging means is provided by using FIG. The processing flow of will be described.

When the release button is pressed halfway down, the autofocus program shown in FIG. 5 is activated to pre-capture the subject image (S10). The light quantity of the image signal obtained in S10 is judged by the outside light judging means (S11), and S11
It is determined whether or not the light amount determined in step S4 is equal to or greater than the predetermined value (S12). If it is determined that the amount of light is not greater than the predetermined value, the switching unit switches the infrared cut unit (S13).

After that, S14 to S19 in FIG.
The processing flow of is similar to the processing flow of S2 to S7 of FIG. 4, and therefore its description is omitted.

By doing so, the infrared cut means is switched by the switching means when the amount of visible light is insufficient, so that autofocus photography can be performed when the amount of light is insufficient.

Further, it is preferable to provide infrared light emitting means for emitting infrared light to the subject.

The infrared light emitting means emits at least light having the wavelength of the near infrared light, for example, an infrared LED.
Etc. can be used. The infrared light emitting means emits infrared light when pre-imaging is performed by the auto focus means.

Light emission by the infrared light emitting means is performed when pre-imaging is performed by the process of S2 of FIG. 4 or the process of S14 of FIG.
Emit infrared rays toward the subject.

By doing so, the amount of light is further increased, so that the difference in light and darkness of the subject becomes severe, and more accurate autofocus can be performed.

[0044]

As described above, according to the present invention, it is possible to provide a digital still camera capable of performing autofocus photography with a simple configuration even when the light amount of a subject is insufficient.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a state of a digital still camera of the present invention.

FIG. 2 is a functional block diagram showing another state of the digital still camera of the present invention.

FIG. 3 is a functional block diagram of a signal processing unit.

FIG. 4 is a diagram showing an example of a processing flow when autofocus is performed by an autofocus unit.

FIG. 5 is a diagram showing a processing flow when performing auto-focusing of the auto-focusing means in the case where the external light judging means is provided.

[Explanation of symbols]

1: Imaging lens 2: Infrared cutting means 3: Image sensor 4: Signal processing unit 40: Preprocessing means 41: A / D conversion means 42: Image data generator 43: Frame memory 44: VRAM 45: Liquid crystal display means 46: Image storage memory 6: Camera control unit 7: Switching means

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Claims (3)

[Claims] 1. An imaging device having sensitivity to near-infrared light and visible light, infrared cutting means, and switching for switching the infrared cutting means to a position where light incident on the imaging device passes or does not pass. Means and an autofocus means, wherein the autofocus means switches the infrared cut means to a position where light incident on the image sensor does not pass by the switching means during autofocus. . 2. An external light determining means for determining the amount of external light, wherein the autofocus means determines that the amount of external light is not insufficient during autofocus. When the switching unit switches the infrared cut unit to a position where the light incident on the image sensor passes, and when it is determined that the light amount is insufficient, the switching unit images the infrared cut unit. The switching is performed to a position where light incident on the element passes through.
The described digital still camera. 3. The digital still camera according to claim 1, further comprising infrared light emitting means, wherein the infrared light emitting means irradiates the subject with infrared light during autofocusing.