JP2005308769A - Automatic focusing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing device capable of quickly performing focusing operation when high image quality is not especially expected in a machine loaded with a high pixel CCD. <P>SOLUTION: The automatic focusing device is provided with a function for changing the moving quantity of a focusing lens for each sampling when sampling a focus evaluation value in accordance with a compression ratio set by a recording image compression ratio setting means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging device including an autofocus device.

In recent years, user needs for digital cameras have been diversified. For example, in response to the need to record with high image quality, a high pixel CCD is mounted.
JP 06-217180 A

  In a high-pixel CCD-equipped machine, the number of sheets that can be recorded on a recording medium of the same capacity decreases as the number of recording pixels increases. In particular, when high image quality is not required and it is desired to shoot as much as possible, the number of recording pixels is set to a small value or the compression rate of the recorded image is set to a high value. However, when a captured image is recorded with high compression, the image quality is degraded.

  In addition, there is a need to shorten the release time lag, but high-precision CCD control with a small pixel size requires high-precision AF control, and the focus evaluation value is sampled while the focus lens is driven. In the autofocus device for detecting the image, it is necessary to reduce the sampling interval, but at the same time, there arises a problem that the focusing operation time becomes long.

  For this reason, in particular, when recording with high compression for reducing the image size without requiring high image quality, the high-pixel CCD-equipped machine is conspicuous only in terms of a long focusing operation time.

  An object of the present invention is to provide an autofocus device capable of performing a focusing operation in a short time in the case where high image quality is not expected as described above.

To achieve the foregoing object, the autofocus device of claim 1 comprises:
A focus lens that adjusts the focus of the subject image, an image sensor that converts the subject image formed by the focus lens into an electrical signal, and an A / D that converts the electrical signal into a digital image signal by A / D conversion Conversion means; focus evaluation means for outputting a focus evaluation value from a high-frequency component of the subject from the digital image signal; and sampling for sampling the focus evaluation value obtained by the focus evaluation means while moving the position of the focus lens Means, a recorded image compression ratio setting means for setting a compression ratio when recording an image, a focus position detection means for detecting a focus position based on a sampling result of the focus evaluation value of the sampling means, and the focus Focus lens driving means for driving the focus lens at the in-focus position detected by the position detection means
The amount of movement of the focus lens for each sampling when sampling the focus evaluation value is changed according to the compression rate set in the recording image compression rate setting means.

  According to the automatic focusing apparatus of the first aspect, since the moving amount of the focus lens at the time of sampling the focus evaluation value is changed according to the recording image compression rate setting, for example, it is set to high compression and high image quality is not expected. In this case, the focusing operation can be performed in a short time by setting the sampling interval for the focus evaluation value to be large.

  As described above, according to the automatic focusing apparatus of the first aspect, the amount of movement of the focus lens at the time of sampling the focus evaluation value is changed according to the recording image compression rate setting. When it is considered that the image quality is not expected, the focusing operation can be performed in a short time by setting the sampling interval of the focus evaluation value large.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an automatic focusing apparatus to which an embodiment of the present invention is applied.

  Reference numeral 101 denotes a fixed lens, 102 denotes a diaphragm and shutter for controlling the amount of light, 103 denotes a motor for moving the diaphragm and the shutter, 104 denotes a mechanical system driving circuit for driving the motor 103 to move the diaphragm and the shutter 102, and 105 denotes an image pickup device described later. A focus lens 106 for focusing on the photo lens, a photo interrupter 106 for detecting the reset position of the focus lens 105, a motor 107 for driving the focus lens 105, and a focus lens driving circuit 108 for driving the focus lens 105 by driving the motor 107. , 109 is an image sensor as a light receiving means or photoelectric conversion means for converting the reflected light from the subject into an electrical signal, 110 is a timing signal generating circuit for generating a timing signal necessary for operating the image sensor 109, and 111 is an image sensor. Output of element 109 System control for controlling the system such as a CDS circuit for removing noise and a pre-processing circuit having a non-linear amplifier circuit to be performed before A / D conversion, 112 an A / D converter, 113 an image processing unit, and 114 a photographing sequence CPU, 115 is a buffer memory, 116 is a memory controller that controls memory read / write and DRAM refresh operations, 117 is an interface for connection to a recording medium to be described later, 118 is a recording medium such as a memory card or hard disk, 119 Indicates an operation assist display and camera status display, an operation display section for displaying a shooting screen and a distance measurement area at the time of shooting, 120 an operation section for operating the camera from the outside, and 121 an electrically rewritable A non-volatile memory (EEPROM) 122 is a main switch for powering on the system. H and 123 are switches for performing shooting standby operations such as AF and AE (hereinafter referred to as SW1), 124 is a shooting switch for performing shooting after operation of SW1 (hereinafter referred to as SW2), and 125 is for setting a shooting mode. A mode switch 126 is a flash.

  The focus lens drive circuit 108 moves the focus lens 105 in the optical axis direction by the motor 107 in accordance with a control signal supplied from the system control CPU 114. The 115 buffer memory is used as a high-speed buffer as temporary image storage means, or a working memory for image compression / decompression.

  The image processing unit 113 divides the digital image data input from the A / D converter 112 into color differences and luminance signals, and performs various processing, correction, and image compression / decompression data processing.

  The system control CPU 114 controls the imaging operation, automatic exposure (AE) operation, and the like in addition to the AF operation control.

  The operation unit 120 includes members for externally performing function selection and various settings, for example, a menu switch for performing various settings such as settings during image reproduction, sensitivity settings during shooting, and the number of pixels recorded during image recording. And function keys to set the compression rate, etc.

  The operation of the embodiment of the present invention will be described in detail below with reference to FIG. FIG. 2 is a flowchart showing the operation of the autofocus device to which the embodiment of the present invention is applied.

  First, the state of the main switch 122 is detected in step S201, and if it is ON, the process proceeds to step S202. Here, the function of the main switch 122 is to turn on the system. In step S202, the remaining capacity of the recording medium 118 for recording an image is checked. If the remaining capacity is 0, the process proceeds to step S203, and if not, the process proceeds to step S204. In step S203, a warning is given that the remaining capacity of the recording medium 118 for recording an image is 0, and the process returns to step S201. The warning may be displayed on the operation display unit 119, a warning sound may be emitted from a sound output unit (not shown), or both may be performed. In step S204, the focus lens 105 is reset according to the flowchart of FIG. In step S205, the state of the switch SW1 is checked. If it is ON, the process proceeds to step S207, and if not, the process proceeds to step S206. Here, the function of SW1 is to perform a shooting standby operation such as AF or AE. In step S206, the state of the main switch 122 is checked. If it is ON, the process proceeds to step S204, and if not, the process proceeds to step S201.

  In step S207, an AF operation is performed according to the flowchart of FIG. In step S208, the state of SW2 is checked. If ON, the process proceeds to step S210, and if not, the process proceeds to step S209. Here, the function of SW2 is to perform photographing after operation of SW1. In step S209, the state of SW1 is checked. If ON, the process returns to step S208. Otherwise, the process returns to step S204. In step S210, a photographing operation is performed according to the flowchart of FIG. In step S211, the remaining capacity of the recording medium 118 for recording an image is checked. If the remaining capacity is 0, the process proceeds to step S203, and if not, the process proceeds to step S212. In step S212, the state of SW2 is checked, and if not ON, the process proceeds to step S209.

  Hereinafter, the reset operation of the focus lens 105 in S204 in the flowchart of FIG. 2 will be described with reference to the flowchart of FIG. FIG. 3 is a flowchart of the subroutine of the reset operation (S204) of the focus lens 105 in the flowchart of FIG.

  In this description, the relationship between the position of the photointerrupter 106 and the output is shown in FIG. 4, and when the focus lens 105 is on the infinite end side with respect to the photointerrupter output switching position, the output of the photointerrupter 106 is “Lo”. When it is on the near end side, it is assumed to be “Hi”.

  First, in step S301, the output state of the photo interrupter 106 is checked. If “Lo”, the process proceeds to step S302; otherwise, the process proceeds to step S303. In step S302, the focus lens 105 is determined to be on the infinite end side with respect to the photointerrupter output switching position based on the output of the photo interrupter 106 in step S301, so the focus lens 105 is moved one step toward the closest end side. In step S303, the output state of the photo interrupter 106 is checked. If “Hi”, the process proceeds to step S304, and if not, the corresponding process is terminated. In step S304, since it is determined that the focus lens 105 is on the near end side with respect to the photo interrupter output switching position based on the output of the photo interrupter 106 in step S303, the focus lens 105 is moved to the infinite end side by one step.

  The operation when the focus lens 105 is reset in this way will be described. First, when the position of the focus lens 105 when the main switch 122 is turned on is on the infinite end side with respect to the photointerrupter output switching position, the output of the photointerrupter 106 is “Lo”, so step S301 in FIG. In step S302, the focus lens 105 is moved step by step toward the closest end until the output of the photo interrupter 106 becomes “Hi”. Since the output of the photo interrupter 106 is switched to “Hi” when the photo interrupter output switching position in FIG. 4 is exceeded, this time is infinite until the output of the photo interrupter 106 becomes “Lo” according to steps S303 and S304 in FIG. It is moved step by step to the end side. Thus, the focus lens 105 finally stops at the reset position in FIG. When the position of the focus lens 105 when the main switch 122 is turned on is close to the photo interrupter output switching position, the focus lens 105 is moved only to the infinite end side and the output of the photo interrupter 106 is output. Stop when “Lo” becomes “Lo”. Thus, as in the case where the position of the focus lens 105 when the main switch 123 is turned on is on the infinite end side with respect to the photointerrupter output switching position, the focus lens 105 finally becomes the reset position in FIG. Stop on.

  Hereinafter, the AF operation subroutine of step S207 in the flowchart of FIG. 2 will be described with reference to the flowchart of FIG. The AF operation is performed by detecting a peak of a high frequency component (focus evaluation value) of a signal obtained from the image sensor 109. FIG. 5 is a flowchart of the subroutine of the AF operation (step S207) in the flowchart of FIG.

  First, in step S501, the focus lens 105 is set in the AF operation. Specifically, settings such as a scan start position, a scan end position, and a lens movement amount of the focus lens 105 at the time of sampling are performed. The amount of lens movement of the focus lens 105 at the time of sampling is set according to the flowchart of FIG. In step S502, the focus lens 105 is moved to the scan start position. Here, it is assumed that the scan start position is set to an infinite end in the distance measurement range. In step S503, the focus evaluation value and the position of the focus lens 105 are stored. When the stepping motor is used as the focus lens driving motor 107, the position of the focus lens 105 is detected as a relative position from the reset position detected by the reset position detection photo interrupter 106. In step S504, it is checked whether or not the lens position is at the end position. If it is the end position, the process proceeds to step S506, and if not, the process proceeds to step S505. Here, the scan end position is set to the closest end in the distance measurement range. In step S505, the focus lens 105 is driven in the closest direction by the amount of movement set in step S501. In step S506, the maximum focus evaluation value stored in step S503 is obtained, and the position of the focus lens 105 at that time is extracted. In step S507, the focus lens 105 is moved to a position where the focus evaluation value shows the maximum value.

  The subroutine for setting the lens position movement amount in step S501 in the flowchart of FIG. 5 will be described below with reference to the flowchart of FIG. FIG. 6 is a flowchart of the subroutine for lens position movement amount setting (step S501) in the flowchart of FIG.

  First, in step S601, it is checked whether the recording image compression rate setting is low compression. If low compression is set, the process proceeds to step S602, and if not, the process proceeds to step S603. In step S602, the lens position movement amount of the focus lens 105 is set to 3step. In step S603, it is checked whether or not the recording image compression rate setting is medium compression. If medium compression is set, the process proceeds to step S604, and if not, the process proceeds to step S605. In step S604, the lens position movement amount of the focus lens 105 is set to 5 steps. In step S605, it is checked whether the recording image compression rate is set to high compression. If high compression is set, the process proceeds to step S606. If not, the process ends. In step S606, the lens position movement amount of the focus lens 105 is set to 7step.

  Hereinafter, the subroutine of the photographing operation in step S210 in the flowchart of FIG. 2 will be described with reference to the flowchart of FIG. FIG. 7 is a flowchart of the subroutine of the photographing operation (step S210) in the flowchart of FIG.

  First, in step S701, the subject brightness is measured. In step S702, the image sensor 109 is exposed in accordance with the subject brightness measured in step S701. The image formed on the surface of the image sensor is photoelectrically converted into an analog signal. In step S703, the output noise of the image sensor 109 is removed or nonlinear processing is performed by the pre-processing circuit 111, and the A / D converter 112 is processed. Convert analog signals to digital signals. In step S 704, the output signal from the A / D converter 112 is subjected to image processing such as white balance adjustment, image format conversion into a JPEG format, and the like by the image processing unit 113, and the buffer memory 115 via the memory controller 116. Temporarily store. In a format that can be compressed such as the JPEG format in image format conversion, the image is compressed at a set compression rate. In step S705, the data in the buffer memory 115 is transferred to the recording medium 118 such as a memory card attached to the camera via the memory controller 116 and the recording medium interface 117 and recorded.

  The flow chart for setting the lens position movement amount described above is an example in which the compression rate is low compression, medium compression, and high compression, but the compression rate setting is not limited to three. Further, the lens movement amount in each compression rate setting is not limited to 3 step (low compression setting), 5 step (medium compression setting), and 7 step (high compression setting) described above.

  By controlling the autofocus device as described above, the autofocus device using this embodiment changes the focus lens movement amount during sampling of the focus evaluation value according to the recording image compression rate setting. For example, when high compression is set and it is considered that high image quality is not expected, since the scan range needs to be sampled a small number of times, the AF operation time can be shortened.

It is a block diagram which shows the structure of the autofocus camera to which this invention is applied. It is a flowchart figure showing operation | movement of the autofocus camera to which this invention is applied. FIG. 3 is a flowchart illustrating a reset operation of the focus lens in FIG. 2. It is a figure showing the relationship between the position of a photo interrupter, and an output. FIG. 3 is a flowchart of an AF operation subroutine in FIG. 2. It is a flowchart figure of the subroutine of the lens position movement amount setting in FIG. FIG. 3 is a flowchart of a shooting operation subroutine in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Fixed lens 102 Aperture and shutter 103 Motor 104 Mechanical system drive circuit 105 Focus lens 106 Photo interrupter 107 Motor 108 Focus lens drive circuit 109 Image sensor 110 Timing signal generation circuit 111 Pre-processing circuit 112 A / D converter 113 Image processing part 114 Format converter, CPU for system control
115 Buffer Memory 116 Memory Controller 117 Interface 118 Recording Medium 119 Operation Display Unit 120 Operation Unit 121 EEPROM
122 Main switch 123 Switch (SW1)
124 Shooting switch (SW2)
125 Mode switch 126 Flash

Claims (1)

A focus lens that adjusts the focus of the subject image, an image sensor that converts the subject image formed by the focus lens into an electrical signal, and an A / D that converts the electrical signal into a digital image signal by A / D conversion Conversion means; focus evaluation means for outputting a focus evaluation value from a high-frequency component of the subject from the digital image signal; and sampling for sampling the focus evaluation value obtained by the focus evaluation means while moving the position of the focus lens Means, a recorded image compression ratio setting means for setting a compression ratio when recording an image, a focus position detection means for detecting a focus position based on a sampling result of the focus evaluation value of the sampling means, and the focus Focus lens driving means for driving the focus lens at the in-focus position detected by the position detection means
An automatic focusing apparatus, wherein a moving amount of the focus lens at each sampling when sampling the focus evaluation value is changed according to a compression rate set in the recording image compression rate setting means.

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