CN1940699A - Camera having automatic lens system - Google Patents

Abstract

A camera having: a contrast detector that continuously detects contrast data of an object image formed on a light-receiving surface of an image sensor, and a focus detector that detects a focus condition based on the contrast data. The camera also has a focuser that focuses on a subject by driving a photographing optical system. When the object is out of focus, the focuser drives the camera optics, moving the imaging surface forward and backward. Then, the focus detector detects standard contrast data corresponding to the position before moving the imaging surface, forward contrast data corresponding to the forward position, and backward contrast data corresponding to the backward position. The focuser moves the imaging surface in a direction of increasing contrast data obtained from standard contrast data, forward contrast data, and backward contrast data.

Description

Camera with auto focus system

technical field

The invention relates to a camera with an autofocus system. In particular, the invention relates to a camera with an autofocus system using a contrast detection method.

Background technique

In digital cameras such as compact digital cameras, an autofocus system utilizing a contrast detection method is incorporated in the camera as an automatic control device. In this contrast detection method, autofocus is performed by continuously detecting contrast data based on image pixel signals read from an image sensor. When the peak or maximum contrast data is detected, in other words, when the high spatial high frequency component in the object image becomes a maximum, it is determined that the object is in focus and the focusing lens is driven to focus. Users can confirm the focus through the LCD monitor on the rear surface of the camera.

In general, the focus position is detected by a gradient method (so-called "hill climbing method") that searches for an apex in a distribution curve of a high-frequency portion. The contrast data is continuously detected, while the focus lens is continuously driven, and when the contrast data has a peak value, it is determined that the object is in a focused state.

When the object image is changed from a clear object image to a blurred object image due to misalignment of the object focus, the focus position is searched, and the imaging surface is moved to the front and rear directions of the optical axis at the same time. Likewise, the focusing lens returns to the initial position and is driven continuously until the focusing position is found. These drives of the focusing lens make it difficult to shorten the time required for focusing.

Contents of the invention

It is an object of the present invention to provide a camera capable of precise and rapid focusing.

The camera according to the invention has a contrast detector and a focus detector. The contrast detector continuously detects contrast data of an object image formed on the light receiving surface of the image sensor. A focus detector detects focus based on the contrast data. The camera also has a focuser that focuses on an object by driving a photographic optical system.

In the present invention, when the object is out of focus, the focuser drives the photographing optical system, thereby moving the imaging surface forward and backward to the final focus position corresponding to the light receiving surface. The imaging surface is moved to a forward position close to the photographing optical system and to a rearward position away from the photographing optical system. Then, the focus detector detects standard contrast data corresponding to a position before moving the imaging surface, forward contrast data corresponding to a forward position, and backward contrast data corresponding to a backward position. The focuser moves the imaging surface in a direction of increasing contrast, where contrast data is obtained from standard contrast data, forward contrast data, and backward contrast data.

Preferably, the focuser moves the imaging surface forwards and backwards when the object changes from in-focus to out-of-focus. Also, preferably, the focuser moves the imaging surface forward and backward when the contrast of the object image is low. In this case, when the forward and backward contrast data are smaller than the standard contrast data, and the difference between the standard contrast data and the forward and backward contrast data is within an allowable range, the focus detector determines that it is in focus. For example, the focuser moves the imaging surface so that the position corresponding to the standard contrast data, the forward position and the backward position are arranged at substantially constant intervals.

Description of drawings

The present invention will be better understood by the following description of the preferred embodiment with reference to the accompanying drawings, in which:

1 is a rear view of a digital camera according to an embodiment of the present invention;

Figure 2 is a block diagram of a digital camera;

Fig. 3 is the flowchart of the automatic focusing method that is carried out by system control circuit;

Figure 4 is a dot plot representing contrast data and contrast difference data;

5A and 5B are views showing three adjacent contrast data.

Detailed ways

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a rear view of a digital camera according to an embodiment of the present invention.

The digital camera 10 has an LCD monitor 30 on a rear surface 10B, and a viewfinder 22 above the LCD monitor 30 . In addition, there are a series of buttons on the rear surface 10B. Here, a zoom-in button 12 ; a cross-shaped button composed of an up button 16U, a down button 16D, a right button 16R, and a left button 16L; an OK button 18 ; and a mode button 19 are provided. The mode button 19 operates to switch between a photo mode, a video mode and a playback mode.

There is a main button 11 and a release button 13 on the upper surface 10U. The camera 10 is turned on by pressing the main button 11 and the object image is recorded by operating the release button 13 . A photographing optical system is installed in a lens barrel (not shown in the drawings) located on the front surface of the camera 10 .

FIG. 2 is a block diagram of the digital camera 10 according to the present embodiment.

A system control circuit 50 including a CPU, ROM, and RAM controls the camera 10, and the main switch 11A, the zoom switch 12A, the release half-press switch 13A, the release full-press switch 13B, the selection switch 16A, the entry switch 18A, and the mode switch 19A are connected with The system control circuit 50 is connected. In the ROM, programs for controlling the operation of the camera 10 are stored.

When the photographing mode is selected, signal processing for displaying a movie image or a video image on the LCD monitor 30 is performed. An object image is formed on the light receiving surface of the CCD 40 by light passing through the photographing optical system, and image pixel signals corresponding to the object image are generated in the CCD 40. The CCD 40 is driven by the CCD driver 52 so that image pixel signals are continuously read from the CCD 40 at constant intervals. Here, image pixel signals are read from the CCD 40 at intervals of 1/30 or 1/60 second. The image pixel signal is amplified in the amplifier 42 and converted from an analog signal to a digital signal in the A/D converter 44 .

In the signal processor 46, various kinds of processing such as white balance and gamma correction processing are performed on the digital image. The processed image signal is temporarily stored in a frame memory (not shown in the drawing), and supplied to the LCD driver 47 . The LCD driver drives the LCD monitor 30 based on the image signal, so that video images are displayed on the LCD monitor 30 . Furthermore, a luminance signal is continuously generated from the image signal in the signal processor 46 , and the luminance signal is supplied to the system control circuit 50 . In the system control circuit 50, contrast data is continuously generated from the luminance signal.

When the release button 13 is half-pressed, the release half-press switch 13A is turned on. Autofocus is thereby performed, and the brightness of the subject is detected. The focusing lens 15A included in the photographing optical system 15 is driven along the optical axis so that the imaging surface coincides with the light receiving surface of the CCD 40. Here, autofocus using a contrast detection method is employed. The focus lens 15A is driven by a lens driver 64 including a stepping motor (not shown in the figure). The exposure controller 58 controls the position of the focus lens 15A based on a control signal from the system control circuit 50 . The system control circuit 50 detects the position of the focus lens 15A.

When the release button 13 is fully pressed, the release full-press switch 13B is turned on, so that the shutter 28 is opened for a specified time interval. Shutter 28 is controlled by exposure controller 58 . A frame-worth of image-pixel signal (one frame-worth of image-pixel signal) is read from the CCD 40, and is processed in various ways in the amplifier 42, the A/D converter 44 and the signal processor 46. Then, the image data is compressed in the recording circuit 62 , and the compressed image data is stored in the memory card 60 .

When the playback mode is selected, the compressed data is read from the memory card 60 and decompressed. The decompressed image data is supplied to the LCD driver 47 , and the LCD driver 47 drives the LCD monitor 30 so that the recorded subject image is displayed on the LCD monitor 30 . When the video image recording mode is selected, a series of image pixel signals read from the CCD 40 for several seconds are subjected to image processing, and video image data is compressed and recorded on the memory card 60.

FIG. 3 is a flow chart of the autofocus method executed by the system control circuit 50 .

In step S101 , the focus lens 15A is set to an initial position, and then driven to move the imaging surface along the optical axis E continuously. The position of the imaging surface along the optical axis varies with the distance from the camera to the object being photographed. The initial position of the focusing lens 15A focuses on an object close to the camera 10, and the focusing lens 15A is continuously driven so that the imaging surface moves toward a direction in which an object at a certain distance from the camera or an object at infinity is focused. By changing the focal length and moving the position of the imaging surface, the object image is clearly or sharply formed on the imaging surface. The amount of movement of the imaging surface along the optical axis E depends on the amount of rotation of a stepping motor included in the lens driver 64 .

In step S102, contrast data is obtained. The contrast data representing the high-frequency portion in the image data is continuously generated from the image pixel signal of one frame at intervals of 1/30 or 1/60 second. The contrast signal is obtained by calculating a brightness difference, which is a difference between a maximum brightness level and a minimum brightness level in a frame of image pixel signals. Note that, for low-pass filter processing, here the contrast signal is obtained by calculating the average value of the currently obtained contrast signal and the previously obtained contrast signal.

In step S103, contrast difference data is calculated. The contrast difference data represents the difference between the currently detected contrast data and the previously detected contrast data stored in the RAM. Then, in step S104, it is determined whether the previously detected contrast data is the peak value or the highest data in a series of detected contrast data.

Fig. 4 is a dot plot showing contrast data and contrast difference data.

In FIG. 4 , contrast data "D0" to "D6" and contrast difference data "T1" to "T6" are plotted along the direction in which the imaging surface moves. As the imaging surface moves, the contrast data gradually increases. Then, when the imaging surface moves to a position near the focus position, in other words, to the position of the light-receiving surface of the CCD 40, the contrast data sharply increases. Contrast decreases dramatically as the imaging surface moves beyond the focus position. On the other hand, as the contrast data increases, the contrast difference data gradually increases, and when the imaging surface approaches the focus position (the position of the light receiving surface of the CCD 40), the contrast difference data increases sharply. Then, the contrast difference data decreases sharply as the imaging surface moves beyond the focus position. Generally, the contrast difference data becomes a value close to zero or a negative value (in FIG. 4 , a negative value) when the imaging surface goes beyond the focus position. In step S104 shown in FIG. 3 , it is determined whether the current or last contrast data is lower than the previous (previous) or latest (latest) contrast data, and it is determined whether the calculated contrast difference data exceeds a specified value. decline. Here, it is determined whether the decreasing difference "ΔD" between the currently calculated contrast data and the previous calculated contrast data exceeds a predetermined standard difference " T0 ".

When it is determined that the current contrast data is not lower than the previous contrast data, or the difference "ΔD" does not exceed the predetermined standard difference "T0" (ie, when it is determined that the previous contrast data is not the peak or highest data), the process returns to step S102. On the other hand, when it is determined that the previous contrast data is peak data, the process goes to step S105. In FIG. 4, the contrast data "D6" is lower than the contrast data "D5" detected last time. In this case, the difference "ΔD" between the currently calculated contrast difference data "T6" and the previously calculated contrast data "T5" exceeds the standard difference "T0". The standard difference “ T0 ” is defined according to the focal length of the photographing optical system 15 .

In step S105, a quadratic approximation curve "PM" is calculated from a series of detected contrast data, and maximum peak contrast data "DT", which is the maximum value in the curve "PM", is obtained from the curve "PM". The position "FP" of the imaging surface (hereinafter, referred to as "focus position") is then calculated, which corresponds to the maximum contrast data "DT". In step S106 , the focus lens 15A is driven to return the imaging surface to the focus position "FP", which coincides with the light receiving surface of the CCD 40 . Thus, a reliably focused image is displayed on the LCD monitor 30 .

In step S107, the contrast data is recently acquired. Then, in step S108, it is determined whether the object is maintained in the focused state. Here, it is determined whether the difference between the contrast data obtained most recently and the contrast data detected last time is within a predetermined allowable range. When the difference is within the allowable range, it is determined that the contrast data obtained most recently is approximately the same as the contrast data detected last time (ie, the focus condition is maintained); then the process goes to step S107. When the focus condition is maintained, steps S107 to S108 are repeatedly performed. On the other hand, when it is determined that the difference exceeds the allowable range (ie, when the object is out of focus), the process goes to step S109. An in-focus condition may become an out-of-focus condition due to rotation or change of the object being photographed, object motion or camera 10 motion.

In step S109, it is determined whether the detected contrast data has a relatively low value; that is, whether the object image has a low contrast, that is, the range of variation of the image is small. Here, it is determined whether the maximum data among a series of detected contrast data is equal to or lower than a specified value. When it is determined that the contrast data is not low-contrast data, the process goes to step S110, where the focus lens 15A is driven to the initial position. Then, perform steps S102-S106 to focus on the object. On the other hand, when it is determined that the contrast data is low-contrast data, the process goes to step S111.

In step S111, the focusing lens 15A is driven forward and backward so that the imaging surface moves toward a direction in which an object close to the camera is focused (hereinafter, referred to as “forward direction”), and then further toward an object far from the camera is focused. direction (hereinafter referred to as "backward direction"). The imaging surface is moved forward to the specified position and moved backward to the specified position. These two positions (hereinafter, respectively referred to as "forward position" and "rearward position") are separated from the position determined in step S106 by a common interval. When the focus lens 15A is driven, contrast data is detected at a forward position (hereinafter, referred to as “forward contrast data”), and contrast data is detected at a backward position (hereinafter, referred to as “backward contrast data”). ). In step S112, based on the forward and backward contrast data and the contrast data obtained in step S107 (hereinafter, referred to as "standard contrast data"), it is determined whether the focus condition is maintained substantially in the low contrast condition. Standard contrast data is detected at a position prior to moving the imaging surface.

Fig. 5A is a view showing three adjacent contrast data. Contrast data P1 represents standard contrast data obtained before moving the focus lens 15A, and contrast data P2 and P3 represent forward contrast data and backward contrast data, respectively. The forward and backward contrast data P2 and P3 are lower than the standard contrast data P1, and the difference between the standard contrast data P1 and the forward and backward contrast data P2 and P3 is small. In this case, the in-focus condition is substantially maintained. In step S112, it is determined whether the forward and backward contrast data are smaller than the standard contrast data, and whether the rate of decline of the standard contrast data is equal to or less than 2%. When it is determined that the focus condition is substantially maintained, the process returns to step S107.

On the other hand, when it is determined that the in-focus condition is not maintained, the process goes to step S113. In step S113, the moving direction of the imaging surface is determined based on the standard contrast data and the forward and backward contrast data. The moving direction is a forward direction approaching the photographing optical system 15, or a backward direction away from the photographing optical system 15, and the direction in which the contrast data increases is determined as the moving direction. Then, the focus lens 15A is driven according to the determined moving direction.

Fig. 5B is a view showing other three adjacent contrast data. Contrast data P1' represents standard contrast data, and contrast data P2' and P3' represent backward contrast data and forward contrast data, respectively. As shown in FIG. 5B, the forward contrast data P2' is lower than the standard contrast data P1', and the backward contrast data P3' is higher than the standard contrast data P1'. In this case, since the imaging surface is in a forward position with respect to the light receiving surface of the CCD 40 , the imaging surface moves in a rearward direction away from the photographing optical axis system 15 . In step S113, the focusing lens 15A is driven such that the imaging surface coincides with the light receiving surface of the CCD 40. After step S113 is executed, the process returns to step S102.

In this way, in this embodiment, the focusing lens 15 is driven, the imaging surface of the CCD 40 is continuously moved from the initial position, and contrast difference data is calculated. Then, it is determined whether the object is in focus based on the drop of the contrast data and the drop amount of the contrast difference data. When it is determined that the object has been in focus, the focus position is calculated by approximation, and the focus lens 15A is driven so that the imaging position is located at the calculated focus position; that is, the light-receiving surface position of the CCD 40. Since the focus is detected by the latest contrast data obtained after the imaging surface has passed the focus position, autofocus can be performed quickly.

In addition, when the contrast of the object image is low, the moving direction of the imaging surface is determined by three contrast data adjacent to each other. This enables fast autofocus even when the object image has low contrast.

When the contrast of the object image is low, the focus can be determined after the contrast data is continuously reduced. Contrast data can be detected by other data than luminance difference data.

Alternatively, whether or not the imaging surface has crossed the focus position can be determined by the amount of drop of the contrast difference data. Alternatively, the direction of movement of the imaging surface can be determined even when the contrast of the object image is not low. The imaging surface can be moved first to a rearward position and then to a forward position.

Finally, those skilled in the art can understand that the above description is a description of a preferred embodiment of the device, and that various changes and modifications can be made to the present invention without departing from the spirit and scope of the present invention.

Claims (8)

1, a kind of camera comprises:

The Contrast Detection device, it detects the contrast-data of the image that forms continuously on the optical receiving surface of imageing sensor;

Focused detector, it detects the focusing situation based on contrast-data; With

Focalizer, it focuses on object by driving camera optical system, when the object focus alignment, described focalizer drives described camera optical system, thereby forward and move backward on the optical receiving surface with imaging surface, described focused detector detects and the mobile imaging surface corresponding standard contrast data in position before, with the corresponding contrast-data forward of forward facing position, with with the corresponding contrast-data backward in position backward, described focalizer is to the direction mobile imaging surface of contrast-data increase, wherein this contrast-data is from the standard contrast data, forward contrast-data and obtaining in the contrast-data backward.

2, camera as claimed in claim 1, wherein, when object became focus alignment with respect to the focusing situation, described focalizer is the mobile imaging surface forward and backward.

3, camera as claimed in claim 1, wherein, when the contrast of image was low, described focalizer is the mobile imaging surface forward and backward.

4, camera as claimed in claim 3, wherein, when contrast-data forward and backward is lower than the standard contrast data, and standard contrast data the and when difference between the contrast-data was in the permissible range forward and backward, described focused detector determined to be in the focusing situation.

5, camera as claimed in claim 1, wherein, described focalizer mobile imaging surface makes and the corresponding position of standard contrast data, forward facing position and backward positional alignment on the interval of constant.

6, be used to focus on the equipment of object, comprise:

Focused detector, its contrast-data based on continuous detecting detects the focusing situation; With

Focalizer, it focuses on object by driving camera optical system, when the object focus alignment, described focalizer drives described camera optical system, thereby forward and move backward to optical receiving surface with imaging surface, described focused detector detects and the mobile imaging surface corresponding standard contrast data in position before, with the corresponding contrast-data forward of forward facing position, with with the corresponding contrast-data backward in position backward, described focalizer is to the direction mobile imaging surface of contrast-data increase, wherein this contrast-data is from the standard contrast data, forward contrast-data and obtaining in the contrast-data backward.

7, a kind of computer program comprises:

Focused detector, its contrast-data based on continuous detecting detects the focusing situation; With

Focalizer, it focuses on object by driving camera optical system, when the object focus alignment, described focalizer drives described camera optical system, thereby forward and move backward to optical receiving surface with imaging surface, described focused detector detects and the mobile imaging surface corresponding standard contrast data in position before, with the corresponding contrast-data forward of forward facing position, with corresponding in the back contrast-data with position backward, described focalizer is to the direction mobile imaging surface of contrast-data increase, wherein this contrast-data is from the standard contrast data, forward contrast-data and obtaining in the contrast-data backward.

8, a kind of method that is used to focus on object comprises:

Contrast-data based on continuous detecting detects the focusing situation;

When the object focus alignment, drive described camera optical system, thereby make imaging surface forward and move backward to optical receiving surface;

Detect with the mobile imaging surface before the corresponding standard contrast data in position, with the corresponding contrast-data forward of forward facing position and with the corresponding contrast-data backward in position backward; With

To the direction mobile imaging surface that contrast-data increases, wherein this contrast-data is from the standard contrast data, forward contrast-data and obtaining in the contrast-data backward.

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