JP2004287455A - Imaging apparatus and its focus display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform accurate focus display regardless of a subject during manual focus control. <P>SOLUTION: When focusing is performed by rotating a focus ring, the sign of the inclination of a focus signal is inverted when passing through a focusing position, so that a control microcomputer 8' stores the position of a focus lens 1, which is obtained when the sign is inverted. When a certain fixed range before and behind the stored position is set as a focusing range and the lens gets out of the range, a fact that it is front focus or rear focus is displayed in accordance with a direction where the lens gets out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image pickup apparatus such as a camera-integrated video tape recorder (hereinafter, referred to as a “camcorder”), and more particularly to a focus display during manual focus control.

  As an example of a focus control system in an imaging device such as a camcorder, there is one shown in FIG. In this figure, light from a subject (not shown) is condensed by a focus lens 1, adjusted to an appropriate light amount by an iris 2, and forms an image on a CCD image sensor 3. Then, the signal is converted into a video signal, subjected to noise removal and level adjustment in a sample / hold and AGC circuit 4, and then converted to a digital signal by an A / D converter 5. The video signal converted into the digital signal is subjected to camera signal processing such as Y / C separation and gamma correction in the camera signal processing unit 6. The output signal of the camera signal processing unit 6 is sent to a recording / reproducing circuit (not shown), and is subjected to a predetermined recording / reproducing process. The luminance signal separated in the camera signal processing unit 6 is sent to an autofocus (AF) detection unit 7.

  As shown in FIG. 5, the autofocus detector 7 includes a high-pass filter (or band-pass filter) 71 that passes a high-frequency component of the luminance signal, a rectifier circuit 72 that rectifies the output of the filter 71, and a rectifier circuit 72. A gate circuit 73 for extracting a luminance signal in the auto-focusing frame from the output, and a detection circuit for detecting a high-frequency component in the field by detecting an output of the gate circuit 73 to create a focus signal 74. As the detection circuit 74, an average value detection, a peak value detection, an intermediate detection method between them, and the like are used.

  FIG. 6 shows an example of the relationship between the level of the focus signal and the focus position created by the autofocus detector 7 shown in FIG. Thus, the level of the focus signal reaches a peak at the in-focus position.

  Returning to the description of FIG. The focus signal created by the autofocus detector 7 is sent to a control microcomputer (hereinafter, "microcomputer" is abbreviated to "microcomputer") 8.

  At the time of autofocus control, the control microcomputer 8 supplies a motor control signal for moving the focus lens 1 in a direction in which the level of the focus signal increases to the motor drive circuit 9. The motor drive circuit 9 rotates the motor 10 in a direction and a speed according to the motor control signal. That is, a closed loop is configured to move the focus lens 1 to a position where the peak of the level of the focus signal is detected. This autofocus control is called hill-climbing control because it detects the peak of the level of the focus signal.

  On the other hand, at the time of manual focus control, the rotation of the focus ring operated by the user is detected by the focus ring rotation detection unit 11, and the control microcomputer 8 supplies a control signal corresponding to the rotation state to the motor drive circuit 9. At this time, the control microcomputer 8 determines the focus state (front focus, rear focus, focus) based on the focus signal from the auto focus detection unit 7, and sends an instruction to the focus display unit 12.

  FIG. 7 shows the relationship between the inclination of the focus signal and the focus position. When the inclination is positive, the front is focused (state in front of the subject is in focus), and when the inclination is negative, the rear is focused (state in focus behind the subject), and the inclination is 0 at the in-focus position. It becomes.

  Then, the focus direction can be known by moving the focus lens minutely and detecting a change (inclination) of the focus signal. Further, when the level of the focus signal is at least a certain level and the inclination of the focus signal is small (below the focus determination level), it can be regarded as in focus. By displaying this, the user can perform highly accurate focusing even with a viewfinder having a low resolution.

  FIG. 8 shows an example of focus display. The user moves the focus ring in accordance with the display direction of the front focus and the rear focus, and can know the focus position by displaying a focus mark.

  Here, the definition of focusing in optics will be described. Light emitted from the subject converges again through the lens and forms an image. This image forming position is a position at which light emitted from one point of the subject converges again to one point. In a still camera, a film is placed at this position, and in an imaging device, an image pickup device such as a CCD is placed at this position to capture a subject image. Before and after this position, the light is not a point but a circle (referred to as a circle of confusion). As the position deviates from the image forming position, the circle of confusion increases and the image becomes blurred. However, if the size of the circle of confusion is smaller than the pixel of the image sensor, blur cannot be detected. In other words, it can be said that the image is not blurred in this range, that is, the image is in focus (focused).

  As described above, in optics, the case where the size of the circle of confusion is smaller than the pixel of the imaging device is defined as focusing, and this range is called a focusing range. The focusing range depends on the focal length of the lens, the F-number, etc., but does not depend on the shape of the subject, the spatial frequency, and the like.

JP-A-6-113184

  The shape of the focus signal differs depending on the shape of the subject, contrast, spatial frequency, and the like. For example, as shown in FIG. 9, the shape near the peak of the focus signal in the subject A is gentle, but the shape in the subject B is sharp. FIG. 10 shows the inclination of the focus signal for these subjects A and B.

  In the focus display, a range where the magnitude of the inclination of the focus signal is smaller than a certain level is determined to be in focus. However, the range is wide for the subject A and narrow for the subject B. As a result, the accuracy of focus determination is low for the subject A, and accurate focusing cannot be obtained. On the other hand, since the accuracy of the focus determination is too high for the subject B, it is not determined that the focus is in reality even in the focused state, and it is difficult to focus.

  The present invention has been made in view of such a problem, and performs accurate focus display regardless of a subject so that a user can easily perform smooth and accurate focusing regardless of a subject. It is an object of the present invention to provide an imaging device and a focus display method thereof.

  In order to achieve the above-described object, an image pickup apparatus according to the present invention includes a focus signal generating unit that generates a focus signal from a predetermined frequency component of an output signal of an image sensor, and a lens position detecting unit that detects a position of a focus lens A first storage unit that stores a position of the focus lens at a focal point detected from the focus signal; a second storage unit that stores a focus range of the focus lens; Based on the output, the position of the focus lens stored in the first storage means, the focusing range of the focus lens stored in the second storage means, and the current position of the focus lens. The apparatus includes a focus determination unit for performing a focus determination, and a display unit for displaying a result of the focus determination by the focus determination unit. Then, the focus determining means changes the focus determination level according to the position of the focus lens at the focus position and the current position information of the focus lens.

  In order to achieve the above-described object, a focus display method of an imaging apparatus according to the present invention stores a focus range of a focus lens and generates a focus signal from a predetermined frequency component of an output signal of an image sensor. When a focus point is detected from the focus signal, the focus lens movement position at the focus point is stored, and the focus signal, the stored focus lens movement position, and the focus lens movement position are stored in advance. Focus determination is performed based on the focus range of the focus lens and the current movement position of the focus lens, and the focus determination is based on the focus lens position at the focus position and the current focus lens position information. The focus determination level is changed accordingly, and the result of the focus determination is displayed.

As described above in detail, according to the imaging apparatus and the focus display method of the present invention,
The position of the focus lens at the focal point detected from the focus signal created from the predetermined frequency component of the output signal of the image sensor, the focusing range at the previously recorded focus lens position, and the current focus lens position , And the result is displayed, so that the user can easily perform smooth and accurate focusing regardless of the subject.

  Further, when the sign of the inclination of the focus signal is inverted, it is determined whether or not the difference between the current position of the focus lens and the position of the focus lens when the focus is detected from the focus signal is within the focus range. Detects and raises the focus determination level when it is within the focusing range, and lowers it when it is out of the focusing range, so that it is smooth and accurate without being affected by camera shake etc. A simple focusing can be easily performed.

Hereinafter, embodiments of the present invention, with reference to the drawings,
[1] Principle of focus determination [2] Imaging apparatus to which the present invention is applied (1) Configuration of imaging apparatus (2) Operation of imaging apparatus (3) Processing of control microcomputer (4) Control considering influence of camera shake and the like This will be described in detail in the order of processing by the microcomputer.

[1] Principle of Focus Determination First, the principle of focus determination in the present invention will be described. As shown in FIG. 7 or FIG. 10, when the user rotates the focus ring to perform focusing, the sign of the inclination of the focus signal is inverted at the moment when the user passes the focus position. Therefore, the position of the focus lens when the sign is inverted is stored, and a certain range before and after that is set as a focusing range. The certain range corresponds to the optical focusing range (depth of focus), and is calculated in advance from the F-number and the focal length of the focus lens and the size of the image sensor, and does not depend on the subject. Actually, this fixed range only needs to be approximately equal to the optical focusing range. In this way, it is possible to make an accurate focus determination while guaranteeing a certain accuracy regardless of the subject.

[2] Imaging apparatus to which the present invention is applied (1) Configuration of imaging apparatus FIG. 1 is a block diagram showing a configuration of an imaging apparatus to which the present invention is applied. Here, the same portions as those in FIG. 4 are denoted by the same reference numerals.

  An imaging apparatus to which the present invention is applied includes a focus lens 1 for condensing light from a subject (not shown), an iris 2 for adjusting the amount of light passing through the focus lens 1, and a A CCD imaging device 3 for converting an image into a video signal; a sample / hold and AGC circuit 4 for removing noise and adjusting a level of an output video signal of the CCD imaging device 3; and digitizing an output of the sample / hold and AGC circuit 4 A / D converter 5 and a camera signal processing unit 6 that performs signal processing such as Y / C separation and gamma correction on the digital output of the A / D converter 5.

  Further, the imaging apparatus to which the present invention is applied includes an auto-focus detection unit 7 that creates a focus signal for auto-focus control from the luminance signal separated in the camera signal processing unit 6 and sends the focus signal to a control microcomputer 8 ′ described later; A control microcomputer 8 'for controlling auto focus and manual focus (details will be described later), a motor drive circuit 9 for driving a motor 10 in response to a motor control signal sent from the control microcomputer 8', and a motor drive circuit 9 and a motor 10 for moving the focus lens 1.

  Further, the image pickup apparatus to which the present invention is applied includes a focus ring rotation detecting unit 11 which detects rotation of a focus ring (not shown) during manual focusing and sends the rotation to a control microcomputer 8 ', and a control ring 8' A focus display unit 12 that performs focus display in accordance with a received focus state display control signal, and a focus lens position detection unit 13 that detects the position of the focus lens 1 and sends the position to the control microcomputer 8 '. For example, when the motor 10 is a DC motor, the focus lens position detection unit 13 can be realized by integrating the rotation amount of the motor 10 with a rotary encoder. In this case, the position of the focus lens 1 may be directly observed with a potentiometer. When the motor 10 is a pulse motor (step motor), the control microcomputer 8 ′ integrates the rotation amount command value of the pulse motor to detect the rotation of the motor 10 or the position of the focus lens 1. This can be realized in the control microcomputer 8 'without using any element.

(2) Operation of Imaging Apparatus Next, the operation of the apparatus shown in FIG. 1 will be described. In FIG. 1, light from a subject (not shown) is condensed by a focus lens 1, adjusted to an appropriate light amount by an iris 2, and forms an image on a CCD image sensor 3. Then, the signal is converted into a video signal, subjected to noise removal and level adjustment in a sample / hold and AGC circuit 4, and then converted to a digital signal by an A / D converter 5. The video signal converted into the digital signal is subjected to camera signal processing such as Y / C separation and gamma correction in the camera signal processing unit 6. The output signal of the camera signal processing unit 6 is sent to a recording / reproducing circuit (not shown), and is subjected to a predetermined recording / reproducing process. The luminance signal separated in the camera signal processing unit 6 is sent to the auto focus detection unit 7.

  The auto-focus detector 7 creates a focus signal from the input luminance signal and sends it to the control microcomputer 8 '. The control microcomputer 8 'operates differently between the time of auto focus control and the time of manual focus control.

  At the time of autofocus control, the control microcomputer 8 ′ supplies a motor control signal for moving the focus lens 1 to the motor drive circuit 9 in a direction in which the level of the focus signal increases. The motor drive circuit 9 rotates the motor 10 in a direction and a speed according to the motor control signal. As a result, the position of the focus lens 1 is automatically controlled so that the level of the focus signal becomes a peak. Since the present invention relates to the operation at the time of manual focus control, the auto focus control will not be described further.

  At the time of manual focus control, when the user rotates the focus ring to perform focusing, the sign of the inclination of the focus signal is inverted when passing through the focus position. The position of the focus lens 1 when the sign is inverted based on the output is stored. Then, a certain range before and after the stored position is set as a focus range, and when it comes out of the range, a display control signal indicating that it is the front focus or the rear focus according to the direction in which it comes out is sent to the focus display unit 12. send. The focus display unit 12 displays the focus, the front focus, or the rear focus according to the display control signal. The user can keep the position of the focus lens 1 within the focusing range by rotating the focus ring while watching the display contents on the focus display section 12. The member operated by the user may be a lever or a switch instead of the focus ring, and the operation direction or the like may be detected.

(3) Processing of Control Microcomputer FIG. 2 is a flowchart showing an example of processing of the control microcomputer 8 'during manual focus control. As shown in the figure, the control microcomputer 8 'determines whether or not the sign of the inclination of the focus signal sent from the autofocus detector 7 in FIG. 1 has been inverted (step S1). If the focus lens is inverted, the position of the focus lens at that time is stored in an internal memory (not shown) (step S2), and the process proceeds to step S3. If it is not determined in step S1 that the sign has been inverted, the process directly proceeds to step S3.

  In step S3, the current position of the focus lens 1 is compared with the position of the focus lens 1 stored in the memory, and it is determined whether the difference is within a certain range. The value in the certain range is stored in a memory (ROM or the like) in the control microcomputer in advance. If it is within a certain range, it is determined that the image is in focus, and the focus display unit 12 outputs a display control signal for performing in-focus display (step S4). If it is not within a certain range, it is determined that the focus is not in focus, and the current focus lens 1 position is set to the front focus or the rear focus depending on whether the current focus lens 1 position is ahead or behind the focus lens position stored in the memory. A display control signal for performing display is output (step S5).

  Steps S1 to S5 are an infinite loop that repeats at the cycle of the vertical synchronization signal of the video signal obtained by imaging the subject.

(4) Processing by the control microcomputer in consideration of the influence of camera shake etc. When the focus signal has an ideal shape as shown in FIG. 6, accurate focusing judgment can be made only by the above-described method. In some cases, the sign of the inclination of the focus signal may be inverted at a position other than the in-focus position. Therefore, in the present invention, the control microcomputer 8 'further performs the processing as shown in FIG. 3, so that it is possible to make an in-focus determination that is accurate and strong against the influence of camera shake.

  3, steps S11, S12, and S13 are the same as steps S1, S2, and S3 in FIG. Steps 17 and 18 in FIG. 3 are the same as steps S4 and S5 in FIG. That is, the difference from FIG. 2 is that steps S14, S15, S16 are added. Note that all steps are in an infinite loop that repeats in the cycle of the vertical synchronization signal of the video signal, as in FIG. Hereinafter, steps S14, S15, and S16 will be described.

  In step S14, when the difference between the current position of the focus lens 1 in step S13 and the position of the focus lens 1 stored in the memory is within a certain range, the focus determination level described in FIG. This is the processing to be performed. Then, step S15 is a process of reducing the focus determination level when it is not within a certain range.

  The meaning of these two processes will be described. If the difference between the position of the focus lens 1 and the position of the focus lens 1 stored in the memory is within a certain range, it means that the camera is in the focusing range. Then, as is clear from FIG. 6 or FIG. 9, the inclination of the focus signal increases as the focus signal deviates from the in-focus position. That is, the absolute value of the gradient of the focus signal outside the focusing range is larger than the gradient of the focus signal within the focusing range. Therefore, when the sign of the focus signal is inverted outside the focusing range due to camera shake or the like, the change width of the inclination becomes large.

  Therefore, when the sign of the focus signal is inverted outside the focusing range, the focus determination level is reduced in step S15. On the other hand, when the sign of the focus signal is inverted within the focus range, the focus determination level is increased in step S14. Then, in the next step S16, it is determined whether or not the inclination of the focus signal is equal to or less than the focus determination level. Accordingly, when the sign of the inclination of the focus signal is inverted at a position outside the focusing range due to camera shake or the like, most subjects exceed the focus determination level and are not regarded as being in focus. On the other hand, when the sign of the inclination of the focus signal is reversed within the focusing range, the focus determination level is large within the focusing range, so that most subjects are determined to be in focus. Therefore, it is possible to eliminate erroneous focus determination and perform accurate focus determination with constant accuracy.

1 is a block diagram illustrating a configuration of an imaging device to which the present invention has been applied. 6 is a flowchart illustrating an example of an operation of a control microcomputer at the time of manual focus control in an imaging device to which the present invention has been applied. 9 is a flowchart illustrating another example of the operation of the control microcomputer at the time of manual focus control in the imaging device to which the present invention has been applied. FIG. 11 is a block diagram illustrating a configuration of a focus control system in a conventional imaging device. FIG. 5 is a block diagram illustrating a configuration of an autofocus detection unit in the focus control system of FIG. 4. FIG. 4 is a diagram illustrating an example of a relationship between a focus signal level and a focus position. FIG. 4 is a diagram illustrating an example of a relationship between a focus signal inclination and a focus position. FIG. 4 is a diagram illustrating an example of focus display. FIG. 3 is a diagram illustrating a relationship between the level of a focus signal of subjects A and B and a focus position. FIG. 10 is a diagram illustrating the relationship between the inclination of focus signals of subjects A and B in FIG. 9 and the focus position.

Explanation of reference numerals

1 focus lens, 7 auto focus detector, 8, 8 'control microcomputer, 10 motor, 12 focus display, 13 focus lens position detector

Claims (10)

Focus signal creating means for creating a focus signal from a predetermined frequency component of the output signal of the image sensor,
Lens position detecting means for detecting the position of the focus lens;
First storage means for storing a position of the focus lens at a focal point detected from the focus signal;
Second storage means for storing a focus range of the focus lens;
The output of the focus signal generating means, the position of the focus lens stored in the first storage means, the focus range of the focus lens stored in the second storage means, and the current focus lens Focus determination means for performing focus determination based on the position;
Display means for displaying the result of the focus determination by the focus determination means,
The imaging apparatus according to claim 1, wherein the focus determination unit changes a focus determination level according to a position of the focus lens at a focus position and current position information of the focus lens. The first storage unit stores a position of a focus lens when a focal point is detected from the focus signal,
The in-focus determining unit detects whether a difference between the current position of the focus lens and the position of the focus lens stored in the first storage unit is within the in-focus range. 2. The image pickup apparatus according to claim 1, wherein it is determined that the object is in focus when. The focusing determination means determines whether the moving position of the focus lens is located before or after the focal point,
The display means performs a display indicating whether the state of the movement position of the focus lens is a focus state, a front focus state, or a rear focus state, according to a result of the determination by the focus determination means. The imaging device according to claim 1.   The imaging apparatus according to claim 1, wherein the focus range of the focus lens is a depth of focus of the focus lens. When the sign of the inclination of the focus signal is inverted,
Detecting whether a difference between the current position of the focus lens and the position of the focus lens stored in the first storage means is within the focusing range,
If the focus is within the focus range, the focus determination level is increased,
The imaging apparatus according to claim 1, wherein the focus determination level is reduced when the focus is out of the focus range. Memorize the focus range of the focus lens,
Create a focus signal from a predetermined frequency component of the output signal of the image sensor,
When the focal point is detected from the focus signal, the moving position of the focus lens at the focal point is stored,
Based on the focus signal, the stored movement position of the focus lens, the focus range of the focus lens stored in advance, and the current movement position of the focus lens, perform focus determination,
The focus determination changes the focus determination level according to the position of the focus lens at the focus position and the current focus lens position information,
A focus display method for an imaging device, wherein a result of the focus determination is displayed.   It detects whether the difference between the current position of the focus lens and the position of the focus lens when the in-focus point is detected from the focus signal is within the in-focus range, and when it is within the in-focus range, 7. The method according to claim 6, wherein the focus is determined. Judge whether the moving position of the focus lens is located before or after the focal point,
7. The image pickup apparatus according to claim 6, wherein a display indicating whether the state of the moving position of the focus lens is a focused state, a front focus state, or a rear focus state is performed according to a result of the focus determination. Focus display method.   7. The method according to claim 6, wherein the focus range of the focus lens is a depth of focus of the focus lens. When the sign of the inclination of the focus signal is inverted, it is detected whether or not the difference between the current position of the focus lens and the position of the focus lens when the focus is detected from the focus signal is within the focus range. 7. The imaging method according to claim 6, wherein the focus determination level is increased when the focus is within the focus range, and the focus determination level is decreased when the focus is out of the focus range. How to display the focus of the device.

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