JP2007053482A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of accurately detecting a focal position independently of a change in the transfer efficiency or the like. <P>SOLUTION: A transfer efficiency detecting unit 70 is a unit for detecting the transfer efficiency of a CCD 36. A camera sensitivity detecting unit 72 acquires sensitivity (ISO) information of the CCD 36 established at photographing. A light source color temperature detection unit 74 acquires color temperature information of a light source calculated by a CPU 10. A drive frequency detection unit 76 acquires a drive pulse frequency (drive frequency of the CCD 36) outputted from a TG 48. An enclosure temperature detection unit 78 detects the temperature of an enclosure of a camera 10. A focus peak detection unit 80 detects a focus peak position by the CPU 10. A focus peak correction unit 82 corrects the focus peak position (detected value). The focus peak detection unit 80 outputs the corrected focus peak position to the CPU 10. The CPU 10 carries out focus control on the basis of the corrected focus peak position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that captures an image of a subject using an imaging element.

Conventionally, an imaging device (electronic camera, digital camera) using an imaging element using photoelectric conversion such as a CCD (Charge Coupled Device) has been developed. When imaging is performed by an imaging apparatus using a CCD, signal charges are accumulated in each pixel of the CCD according to the exposure time. The signal charge accumulated in each pixel is transferred from the vertical transfer path to the horizontal transfer path and output to the image processing circuit. The signal charges accumulated in each pixel are sequentially transferred through potential wells formed in each transfer element of each transfer path. At this time, since the signal charge remains without being completely transferred to the next transfer element, the signal charge remaining in the transfer element and a signal charge of a different color by the next transfer are mixed to cause color mixing. On the other hand, for example, Patent Document 1 discloses a signal correction device for a distance measuring CCD that corrects distortion of an image signal due to a transfer error and eliminates a distance measurement failure. Further, in Patent Document 2, the total of the vertical transfer remaining amount of each image sensor arranged in the TDI stage direction is obtained in advance from the vertical transfer efficiency of the TDI image sensor, and the output of the TDI image sensor when the sample is imaged by the TDI image sensor. An image processing method for subtracting the sum of the remaining vertical transfer amounts obtained in advance and performing image processing using the subtracted output is disclosed.
JP 7-146139 A JP 2004-295709 A

  By the way, as described above, when the transfer efficiency of the image sensor decreases and pixel mixing (color mixing) occurs at an analog level, for example, when G and R color mixing, a low pass filter (LPF) is applied. The state becomes similar to the state, and the frequency characteristics of the image signal change. For this reason, there is a problem in that the focus position cannot be accurately detected because the peak position of the focus evaluation value for detecting the focus position is shifted or the peak value is lowered. Also, color mixing is likely to occur depending on the color temperature of the light source under the shooting conditions, which may affect the focus.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an imaging apparatus capable of accurately detecting the in-focus position regardless of a change in transfer efficiency or the like.

  In order to achieve the above object, an imaging apparatus according to claim 1 drives an imaging optical system that forms an image, an imaging element that acquires an image formed by the imaging optical system, and the imaging optical system. Driving means; focus evaluation value detection means for detecting a focus evaluation value indicating a degree of focus of the image; detection means for detecting parameters of the image sensor including at least transfer efficiency of the image sensor; A focus peak position correction unit that corrects a position of the imaging optical system at which the focus evaluation value reaches a peak based on the parameters of the imaging element, and the focus evaluation value reaches a peak when the imaging optical system is driven. And a focus determination means for determining the position of the imaging optical system as a focus position.

  According to the imaging apparatus of the first aspect, it is possible to correct the focus peak position shift caused by the mixing of pixels due to the change in the parameters of the imaging element, and therefore it is possible to accurately detect the in-focus position. Note that the imaging element may be driven instead of the imaging optical system at the time of focus detection.

  According to a second aspect of the present invention, there is provided an imaging apparatus according to the first aspect, wherein the acquired image is divided into a plurality of divided areas and color information acquisition means for acquiring color information of each divided area; And a light source information acquisition unit configured to acquire light source information under a photographing condition based on the information, and the focus peak position correction unit corrects the focus peak position based on the acquired light source information.

  According to the imaging device of the second aspect, it is possible to correct the focus peak position shift caused by the mixing of the pixels in accordance with the light source information (color temperature of the light source). be able to.

  An imaging apparatus according to a third aspect includes an imaging optical system that forms an image, an imaging element that acquires an image formed by the imaging optical system, a driving unit that drives the imaging optical system, Based on focus evaluation value detection means for detecting a focus evaluation value indicating the degree of focus, detection means for detecting parameters of the image sensor including at least the transfer efficiency of the image sensor, and based on the detected parameters of the image sensor The focus determination threshold value correction means serving as a reference for determining the focus and the position of the imaging optical system where the focus evaluation value is larger than the focus determination threshold value when the imaging optical system is driven Focus determining means for determining the in-focus position as a focus position.

  According to the imaging device of the third aspect, when the focus evaluation value of the focus peak position decreases due to the mixing of pixels, the focus position is determined by lowering the focus determination threshold according to the parameters of the image sensor. It can be detected reliably.

  According to a fourth aspect of the present invention, there is provided an imaging apparatus according to the third aspect, wherein the acquired image is divided into a plurality of divided areas to obtain color information of each divided area, and the acquired color information is included in the acquired color information. And a light source information acquisition unit configured to acquire light source information under a shooting condition based on the information, wherein the focus determination threshold value correction unit corrects the focus determination threshold value based on the acquired light source information. And

  According to the imaging device according to claim 4, when the focus evaluation value of the focus peak position is lowered due to the mixing of pixels, the focus determination threshold value is lowered according to the light source information (color temperature of the light source), The in-focus position can be reliably detected.

  An imaging apparatus according to claim 5, an imaging optical system that forms an image, an imaging device that acquires an image formed by the imaging optical system and outputs an image signal indicating the image, and the imaging optical system Drive means for driving, a detection filter for passing or blocking a specific frequency component of the image signal, detection means for detecting parameters of the image sensor including at least transfer efficiency of the image sensor, and the detected A filter selection unit that selects the detection filter based on the parameters of the image sensor, and a focus that detects a focus evaluation value indicating a degree of focus of the image from an image signal input through the detection filter When the evaluation value detection means and the imaging optical system are driven, the position of the imaging optical system at which the focus evaluation value reaches a peak is determined as the in-focus position. Characterized in that it comprises a focus determination unit that.

  According to the imaging device of the fifth aspect, when the frequency characteristic of the image signal changes due to pixel mixing, the in-focus position is accurately detected by selecting the detection filter according to the parameters of the imaging device. can do.

  According to a sixth aspect of the present invention, there is provided an image pickup apparatus according to the fifth aspect, wherein the acquired image is divided into a plurality of divided areas and color information acquiring means for acquiring color information of each divided area; And a light source information acquisition unit configured to acquire light source information under imaging conditions based on the acquired light source information. The filter selection unit selects a detection filter based on the acquired light source information.

  According to the imaging device of the sixth aspect, when the frequency characteristic of the image signal changes due to the mixing of pixels, the focus position is selected by selecting the detection filter according to the light source information (color temperature of the light source). Can be accurately detected.

  According to a seventh aspect of the present invention, in the first to sixth aspects, the imaging device parameter includes at least one of sensitivity, driving frequency, and temperature of the imaging device. The seventh aspect limits the parameters of the image pickup device according to the first to sixth aspects.

  According to the present invention, the focus peak position, the focus peak determination threshold, and the light source information (for example, the color temperature of the light source) or the image sensor parameters (transfer efficiency, sensitivity, drive frequency or temperature of the image sensor) By selecting a filter for detection applied to the image signal, the in-focus position can be accurately detected.

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

  FIG. 1 is a block diagram showing the main configuration of the imaging apparatus according to the first embodiment of the present invention. An imaging apparatus 1 (denoted as camera 1 in the following description) shown in FIG. 1 is a digital camera having functions for recording and reproducing still images and moving images. The operation of the entire camera 1 is a central processing unit (CPU). 10 for overall control. The CPU 10 functions as a control means for controlling the camera system according to a predetermined program, and performs various calculations such as automatic exposure (AE) calculation, automatic focus adjustment (AF) calculation, and white balance (WB) adjustment calculation. Functions as a means. The power supply circuit 12 supplies power to each block of the camera system.

  A ROM (Read Only Memory) 16 and an EEPROM (Electronically Erasable and Programmable Read Only Memory) 18 are connected to the CPU 10 via a bus 14. The ROM 16 stores programs executed by the CPU 10, various data necessary for control, and the like, and the EEPROM 18 stores CCD pixel defect information, various constants / information related to camera operation, and the like.

  A memory (SDRAM, Synchronous Dynamic Random Access Memory) 20 is used as a program development area and a calculation work area for the CPU 10, and is also used as a temporary storage area for image data and audio data. A video random access memory (VRAM) 22 is a temporary storage memory dedicated to image data, and includes an A area 22A and a B area 22B. The memory 20 and the VRAM 22 can be shared.

  The camera 1 is provided with an operation switch group 24 such as a mode selection switch, a shooting button, a menu / OK key, a cross key, and a cancel key. Signals from these various operation switches are input to the CPU 10, and the CPU 10 controls each circuit of the camera 1 based on the input signals. For example, lens drive control, shooting operation control, image processing control, and image data recording / reproduction. Control and display control of the image display device (liquid crystal monitor) 26 are performed.

  The mode selection switch is an operation means for switching between the shooting mode and the playback mode. The shooting button is an operation button for inputting an instruction to start shooting, and includes a two-stroke switch having an S1 switch that is turned on when half-pressed and an S2 switch that is turned on when fully pressed. The menu / OK key is an operation having both a function as a menu button for instructing to display a menu on the screen of the image display device 26 and a function as an OK button for instructing confirmation and execution of selection contents. Key. The cross key is an operation unit for inputting instructions in four directions, up, down, left, and right, and functions as a button (cursor moving operation means) for selecting an item from the menu screen or instructing selection of various setting items from each menu. To do. The up / down key of the cross key functions as a zoom switch at the time of shooting or a playback zoom switch at the time of playback, and the left / right key functions as a frame advance (forward / reverse feed) button in the playback mode. The cancel key is used to delete a desired target such as a selection item, cancel an instruction content, or return to the previous operation state.

  The image display device 26 is composed of a liquid crystal monitor capable of color display. An image display device 26 (referred to as a liquid crystal monitor 26 in the following description) can be used as an electronic viewfinder for checking the angle of view at the time of shooting, and is used as means for reproducing and displaying recorded images. The liquid crystal monitor 26 is also used as a user interface display screen, and displays information such as menu information, selection items, and setting contents as necessary. Instead of the liquid crystal monitor, other types of display devices such as organic EL (electro-luminescence) can be used.

  The camera 1 has a media socket (media mounting portion) 28, and a recording medium 30 can be mounted on the media socket 28. The form of the recording medium 30 is not particularly limited, and various media such as a semiconductor memory card represented by xD-PictureCard (trademark) and smart media (trademark), a portable small hard disk, a magnetic disk, an optical disk, and a magneto-optical disk can be used. Can be used. The media controller 32 performs necessary signal conversion in order to transfer input / output signals suitable for the recording medium 30 mounted in the media socket 28.

  The camera 1 also includes an external connection interface (I / F) unit 34 as communication means for connecting to a personal computer or other external devices. The camera 1 can exchange data with the external device by connecting the camera 1 and the external device using a USB cable (not shown). Of course, the communication method is not limited to USB, and IEEE1394, Bluetooth, and other communication methods may be applied.

  Next, the shooting function of the camera 1 will be described. When the shooting mode is selected by the mode selection switch, power is supplied to the imaging unit including the color CCD solid-state imaging device 36 (hereinafter referred to as CCD 36), and the camera is ready for shooting.

  The lens unit 38 is an optical unit that includes a photographic lens 44 including a focus lens 40 and a zoom lens 42 and a mechanical shutter 46 that also serves as an aperture. Focusing of the photographic lens 44 is performed by moving the focus lens 40 by the focus motor 40A, and zooming is performed by moving the zoom lens 42 by the zoom motor 42A. The focus motor 40A and the zoom motor 42A are driven and controlled by the focus motor driver 40B and the zoom motor driver 42B, respectively. The CPU 10 controls the focus motor driver 40B and the zoom motor driver 42B by outputting control signals.

  The diaphragm 46 is a so-called turret-type diaphragm, and changes the diaphragm value (F value) by rotating a turret plate in which diaphragm holes of F2.8 to F8 are formed. The diaphragm 46 is driven by an iris motor 46A. The iris motor 46A is driven and controlled by an iris motor driver 46B. The CPU 10 controls the iris motor driver 46B by outputting a control signal.

  The light that has passed through the lens unit 38 forms an image on the light receiving surface of the CCD 36. A large number of photodiodes (light receiving elements) are two-dimensionally arranged on the light receiving surface of the CCD 36, and red (R), green (G), and blue (B) primary color filters corresponding to each photodiode. They are arranged in a predetermined arrangement structure (Bayer, G stripe, etc.). The CCD 36 has an electronic shutter function for controlling the charge accumulation time (shutter speed) of each photodiode. The CPU 10 controls the charge accumulation time in the CCD 36 via a timing generator (TG) 48.

  The subject image formed on the light receiving surface of the CCD 36 is converted into signal charges of an amount corresponding to the amount of incident light by each photodiode of the CCD 36. The signal charge accumulated in each photodiode is sequentially read out as a voltage signal (image signal) corresponding to the signal charge based on a drive pulse given from the TG 48 in accordance with a command from the CPU 10.

  The signal output from the CCD 36 is sent to an analog processing unit (CDS / AMP) 50, where the R, G, B signals for each pixel are sampled and held (correlated double sampling processing), amplified, and then A / It is added to the D converter 52. The dot sequential R, G, B signals converted into digital signals by the A / D converter 52 are stored in the memory 20 via the image input controller 54.

  The image signal processing circuit 56 processes the R, G, and B signals stored in the memory 20 in accordance with instructions from the CPU 10. That is, the image signal processing circuit 56 includes a synchronization circuit (a processing circuit that converts a color signal into a simultaneous expression by interpolating a spatial shift of the color signal associated with the color filter array of the single CCD), a white balance correction circuit, It functions as an image processing means including a gamma correction circuit, a contour correction circuit, a luminance / color difference signal generation circuit, etc., and performs predetermined signal processing using the memory 20 in accordance with commands from the CPU 10.

  The RGB image data input to the image signal processing circuit 56 is converted into a luminance signal (Y signal) and a color difference signal (Cr, Cb signal) by the image signal processing circuit 56, and predetermined processing such as gamma correction is performed. Applied. The image data processed by the image signal processing circuit 56 is stored in the VRAM 22.

  When the captured image is output to the liquid crystal monitor 26, the image data is read from the VRAM 22 and sent to the video encoder 58 via the bus 14. The video encoder 58 converts the input image data into a predetermined display signal (for example, an NTSC color composite image signal) and outputs the converted signal to the liquid crystal monitor 26.

  With the image signal output from the CCD 36, image data representing an image for one frame is rewritten alternately in the A area 22A and the B area 22B of the VRAM 22. Of the A area 22A and B area 22B of the VRAM 22, the written image data is read from an area other than the area where the image data is rewritten. In this way, the image data in the VRAM 22 is periodically rewritten, and an image signal generated from the image data is supplied to the liquid crystal monitor 26, whereby the image being captured is displayed on the liquid crystal monitor 26 in real time. . The photographer can check the shooting angle of view from the video (through movie image) displayed on the liquid crystal monitor 26.

  When the shooting button is pressed halfway and S1 is turned on, the camera 1 starts AE and AF processing. That is, the image signal output from the CCD 36 is input to the AF detection circuit 60 and the AE / AWB detection circuit 62 via the image input controller 54 after A / D conversion.

  The AE / AWB detection circuit 62 includes a circuit that divides one screen into a plurality of areas (for example, 8 × 8 or 16 × 16) and integrates RGB signals for each divided area, and provides the integrated value to the CPU 10. . The CPU 10 detects the brightness of the subject (subject brightness, AE brightness value) based on the integrated value obtained from the AE / AWB detection circuit 62, and calculates an exposure value (shooting EV value) suitable for shooting. According to the obtained exposure value and a predetermined program diagram, the aperture value and the shutter speed are determined, and the CPU 10 controls the electronic shutter and iris of the CCD 36 according to this to obtain an appropriate exposure amount.

  The AE / AWB detection circuit 62 calculates an average integrated value for each color of the RGB signals for each divided area during automatic white balance adjustment, and provides the calculation result to the CPU 10. The CPU 10 obtains an integrated value of R, an integrated value of B, and an integrated value of G, obtains a ratio of R / G and B / G for each divided area, and calculates R / G and R / G of the values of B / G. The light source type is determined based on the distribution in the color space of the G, B / G axis coordinates, and the gain value (white balance correction value) for the R, G, B signals of the white balance adjustment circuit according to the determined light source type. To correct the signal of each color channel.

  For example, contrast AF that moves the focus lens 40 so that the high-frequency component of the G signal of the image signal is maximized is applied to the AF control in the camera 1. That is, the AF detection circuit 60 cuts out a signal in a focus target area set in advance in a high-pass filter that passes only a high-frequency component of the G signal, an absolute value processing unit, and a screen (for example, the center of the screen). An area extraction unit and an integration unit that integrates absolute value data in the AF area are configured.

  The integrated value data obtained by the AF detection circuit 60 is notified to the CPU 10. The CPU 10 calculates focus evaluation values (focus evaluation values) at a plurality of AF detection points while moving the focus lens 40 by controlling the focus motor driver 40B. Then, the position (focus peak position) of the focus lens 40 at which the focus evaluation value is maximized is detected by a focus peak detector 80 described later. The CPU 10 determines the focus peak position detected by the focus peak detection unit 80 as the focus position. Then, the CPU 10 controls the focus motor driver 40B so as to move the focus lens 40 to the obtained in-focus position. Note that the calculation of the focus evaluation value is not limited to the mode using the G signal, and a luminance signal (Y signal) may be used.

  The shooting button is pressed halfway, AE / AF processing is performed when S1 is turned on, the shooting button is fully pressed, and the shooting operation for recording starts when S2 is turned on. The image data acquired in response to S2 ON is converted into a luminance / color difference signal (Y / C signal) in the image signal processing circuit 56, subjected to predetermined processing such as gamma correction, and then stored in the memory 20. The

  The Y / C signal stored in the memory 20 is compressed according to a predetermined format by the compression / decompression circuit 64 and then recorded on the recording medium 30 via the media controller 32. For example, a still image is recorded in JPEG (Joint Photographic Experts Group) format.

  When the playback mode is selected by the mode selection switch, the compressed data of the last image file (last recorded file) recorded on the recording medium 30 is read. When the file related to the last recording is a still image file, the read image compressed data is decompressed into an uncompressed YC signal via the compression / decompression circuit 64, and then via the image signal processing circuit 56 and the video encoder 58. Are converted into display signals and then output to the liquid crystal monitor 26. As a result, the image content of the file is displayed on the screen of the liquid crystal monitor 26.

  During single-frame playback of still images (including playback of the first frame of a movie), the file to be played can be switched (forward / reverse frame advance) by operating the right or left key of the four-way controller. it can. The image file at the frame-advanced position is read from the recording medium 30, and still images and moving images are reproduced and displayed on the liquid crystal monitor 26 in the same manner as described above.

  When an external display such as a personal computer or a television is connected to the camera 1 via the video input / output terminal 66 in the playback mode, the image data recorded on the recording medium 30 is output by the video output circuit 68. It is processed and displayed on this external display.

  The camera 1 of the present embodiment includes a transfer efficiency detection unit 70, a camera sensitivity detection unit 72, a light source color temperature detection unit 74, a drive frequency detection unit 76, a casing temperature detection unit 78, a focus peak detection unit 80, and a focus peak correction unit. 82 is further provided.

  The transfer efficiency detection unit 70 is a device that detects the transfer efficiency of the CCD 36. Here, a method for calculating the transfer efficiency will be described with reference to FIG. FIG. 2 is a diagram schematically showing a charge transfer path in the CCD 36. As shown in FIG. 2, the CCD 36 forms an image of light that has entered through the photographing lens 30, and an effective pixel area that is used for capturing an image and an invalid area around the effective pixel area that is not used for capturing an image. Are divided into various optical black (OB) regions.

  When a subject (for example, a monochrome chart) is imaged by the camera 10, charges are accumulated in each pixel of the CCD 36. This charge is vertically transferred through the horizontal transfer path 92 after one pixel in the vertical direction is vertically transferred through the vertical transfer path 90. This charge is converted into a voltage by the charge-voltage converter 94 and output to the analog signal processing circuit 42. By repeating this for the number of pixels in the vertical direction, the charges of all the pixels of the CCD 36 are read out.

  The transfer efficiency detection unit 70 acquires the voltage value of one pixel 96B on the OB area side in the boundary area where the effective pixel area changes to the OB area. The voltage value of one pixel 96B on the OB region side corresponds to the amount of charge left during transfer of one pixel 96A on the effective pixel region side. The transfer efficiency detector 70 calculates the transfer efficiency of the CCD 36 based on the voltage values of the pixels 96A and 96B.

  In the present embodiment, the transfer efficiency is not calculated by the transfer efficiency detection unit 70, but the transfer efficiency value is stored in the memory 20 or the like in advance, and the transfer efficiency detection unit 70 acquires the transfer efficiency value. Also good. For example, the memory 20 may store the transfer efficiency for each elapsed time after the power is turned on.

  Returning to the description of FIG. The camera sensitivity detector 72 acquires sensitivity (ISO) information of the CCD 36 set at the time of imaging. The light source color temperature detection unit 74 acquires the color temperature information of the light source calculated by the CPU 10. The drive frequency detector 76 acquires the frequency of the drive pulse output from the TG 48 (drive frequency of the CCD 36). The casing temperature detection unit 78 detects the temperature of the casing of the camera 10. In this embodiment, instead of the temperature of the housing of the camera 10, the temperature of a block that processes the analog signal including the CCD 36, the analog processing unit 50, and the A / D converter 52 may be detected. .

  As described above, the focus peak detection unit 80 detects the lens position (focus peak position) at which the focus evaluation value calculated for each position of the focus lens 40 by the CPU 10 is maximized. The focus peak correction unit 82 corrects the focus peak position (detection value). The focus peak detector 80 outputs the corrected focus peak position to the CPU 10. The CPU 10 performs focus control based on the corrected focus peak position.

  FIG. 3 is a graph illustrating a change in focus evaluation value with respect to transfer efficiency. In FIG. 3, the horizontal axis is the position of the focus lens 40 (focus position), and the vertical axis is the focus evaluation value.

  In general, the peak of the R signal with a long wavelength tends to appear on the infinity side, and the peak of the B signal with a short wavelength tends to appear on the close side. Further, as described above, the focus evaluation value is calculated from the G signal. For example, if the relationship of the signal amount in the image signal input from the CCD 36 is R <B, the G signal is strongly influenced by the B signal due to pixel mixing. For this reason, as shown in FIG. 3A, the peak position of the focus evaluation value calculated from the G signal shifts to the near side as the transfer efficiency of the CCD 36 decreases. The focus peak position (detection value) detected by the focus peak detection unit 80 is a focus peak position that is shifted due to a decrease in transfer efficiency of the CCD 36 or the like. In this embodiment, the shift amount of the focus evaluation value accompanying the decrease in the transfer efficiency of the CCD 36 is measured in advance by experiments. Then, a correction value (focus peak position correction value 1) for correcting the shift amount of the focus peak position is calculated based on the measured shift amount of the focus evaluation value. The camera 1 stores the relationship between the transfer efficiency of the CCD 36 and the focus peak position correction value 1 in a table of the memory 20 (correction value table 1). The focus peak correction unit 82 acquires the focus peak position correction value 1 from the correction value table 1 in accordance with the detected transfer efficiency of the CCD 36. The focus peak correction unit 82 adds the focus peak position correction value 1 to the detection value of the focus peak position and corrects it. Further, the memory 20 stores correction value tables 2 to 5 in which correction values (focus peak position correction values 2 to 5 respectively) for the sensitivity of the CCD 36, the driving frequency, the color temperature of the light source, and the housing temperature are stored. Yes. The focus peak correction unit 82 acquires the focus peak position correction values 2 to 5 according to the detected sensitivity of the CCD 36, the drive frequency, the color temperature of the light source, and the housing temperature, and the following equation (1-1) is obtained. As shown, correction is made by adding to the detected value of the focus peak position. As a result, as shown in FIG. 3B, the focus peak position is corrected so as to coincide with the focus peak position when the transfer efficiency is 100%.

(Corrected focus peak position) = (detected value of focus peak position) + (focus peak position correction value 1) + (focus peak position correction value 2) + (focus peak position correction value 3) + (focus peak position correction) Value 4) + (Focus peak position correction value 5) (1-1)
Next, the flow of focus peak position correction processing will be described with reference to the flowchart of FIG. FIG. 4 is a flowchart showing the flow of processing for correcting the focus peak position.

  First, the transfer efficiency, camera sensitivity, drive frequency, and light source color of the CCD 36 are determined by the transfer efficiency detector 70, camera sensitivity detector 72, drive frequency detector 76, light source color temperature detector 74, and housing temperature detector 78. The temperature and the housing temperature are acquired (step S10). Next, focus peak position correction values 1 to 5 for correcting the focus peak position are acquired based on the transfer efficiency, camera sensitivity, drive frequency, light source color temperature, and housing temperature detected in step S10. (Step S12 to Step S20). Then, as shown in the above equation (1-1), the focus peak position is corrected by adding the focus peak position correction values 1 to 5 to the detection value of the focus peak position (step S22).

  According to the present embodiment, it is possible to correct the shift of the peak position of the focus evaluation value due to pixel mixing caused by changes in the transfer efficiency and sensitivity of the CCD 36, the driving frequency, the color temperature of the light source, and the temperature of the housing. The in-focus position can be accurately detected.

  In the present embodiment, the focus peak position correction values 1 to 5 are added to the focus peak position detection value. However, the present invention is not limited to this. For example, the following formula (1- As shown in 2), correction coefficients for correcting the focus peak position corresponding to the transfer efficiency and sensitivity of the CCD 36, the drive frequency, the color temperature of the light source, and the temperature of the housing (focus peak position correction coefficients 1 to 5 respectively) are set. The detection value of the focus peak position may be multiplied. As described above, any of addition, subtraction, multiplication, and division may be used as a calculation method for correcting the focus peak position.

(Corrected focus peak position) = (detected value of focus peak position) × (focus peak position correction coefficient 1) × (focus peak position correction coefficient 2) × (focus peak position correction coefficient 3) × (focus peak position correction) Coefficient 4) × (focus peak position correction coefficient 5) (1-2)
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram showing the main configuration of an imaging apparatus according to the second embodiment of the present invention. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, the imaging apparatus (camera) 1 of this embodiment further includes a focus peak determination threshold value correction unit 84. In the present embodiment, the focus peak detection unit 80 determines that the focus peak position is a focus peak position when the focus evaluation value is larger than a predetermined focus peak determination threshold value, and outputs the focus peak position to the CPU 10. The CPU 10 performs focus control based on the focus peak position thus detected. The focus peak determination threshold correction unit 84 corrects the focus peak determination threshold according to the transfer efficiency of the CCD 36 and the like.

  FIG. 6 is a graph illustrating changes in focus evaluation values with respect to transfer efficiency. In FIG. 6, the horizontal axis represents the position of the focus lens 40 (focus position), and the vertical axis represents the focus evaluation value. Also, the broken line in the figure is the focus peak determination threshold value.

  When the transfer efficiency of the CCD 36 is lowered, pixel mixing occurs at an analog level (for example, G and R are mixed), so that the state is the same as when LPF is applied, and the focus evaluation value decreases. In the example shown in FIG. 6A, when the transfer efficiency of the CCD 36 is 98% and 96%, the focus evaluation value at the focus peak position is smaller than the focus peak determination threshold value. For this reason, the focus peak detection unit 80 cannot detect the focus peak position (focus position).

  In this embodiment, the amount of decrease in the focus evaluation value that accompanies the decrease in the transfer efficiency of the CCD 36 is measured in advance by experiments. Then, a focus peak determination threshold value is set according to the amount of decrease in the measured focus evaluation value. The camera 1 stores the relationship between the transfer efficiency of the CCD 36 and the focus peak determination threshold correction value 1 for correcting the focus peak determination threshold in a table (threshold correction table 1) of the memory 20. . As shown in FIG. 6B, the focus peak determination threshold is lowered according to the transfer efficiency of the CCD 36. Thereby, even when the transfer efficiency of the CCD 36 is lowered, the focus peak can be detected even if the focus evaluation value is lowered by lowering the focus peak determination threshold value.

  The memory 20 also includes a threshold correction table 2 in which correction values for the sensitivity of the CCD 36, the drive frequency, the color temperature of the light source, and the casing temperature (focus peak determination threshold correction values 2 to 5, respectively) are stored. 5 is stored. The focus peak determination threshold value correction unit 84 acquires focus peak position correction values 2 to 5 in accordance with the detected sensitivity, drive frequency, light source color temperature, and housing temperature of the CCD 36, and the following equation (2) As shown in -1), correction is made by adding to the detected value of the focus peak position. As a result, the focus peak determination threshold value is corrected, and the focus detection can be accurately performed regardless of the transfer efficiency and sensitivity of the CCD 36.

(Corrected focus peak determination threshold value) = (focus peak determination threshold value (default value)) + (focus peak determination threshold correction value 1) + (focus peak determination threshold correction value 2) + ( Focus peak determination threshold correction value 3) + (focus peak determination threshold correction value 4) + (focus peak determination threshold correction value 5) (2-1)
Next, the flow of the focus peak determination threshold correction process will be described with reference to the flowchart of FIG. FIG. 7 is a flowchart showing a flow of processing for correcting the focus peak determination threshold value.

  First, the transfer efficiency, camera sensitivity, drive frequency, and light source color of the CCD 36 are determined by the transfer efficiency detector 70, camera sensitivity detector 72, drive frequency detector 76, light source color temperature detector 74, and housing temperature detector 78. The temperature and the housing temperature are acquired (step S30). Next, from the focus peak determination threshold correction value 1 for correcting the focus peak position based on the transfer efficiency, camera sensitivity, drive frequency, light source color temperature, and housing temperature detected in step S30. 5 is acquired (from step S32 to step S40). Then, as shown in the above equation (2-1), the focus peak position is corrected by adding the focus peak determination threshold correction values 1 to 5 to the focus peak determination threshold (default value) (step S1). S42).

  According to this embodiment, when the focus evaluation value decreases due to pixel mixing caused by changes in the transfer efficiency and sensitivity of the CCD 36, the drive frequency, the color temperature of the light source, and the temperature of the housing, the focus peak determination threshold value is set. By correcting, the in-focus position can be accurately detected.

  In the present embodiment, the focus peak position correction values 1 to 5 are added to the focus peak determination threshold value (default value). However, the present invention is not limited to this, and for example, the following As shown in Expression (2-2), correction coefficients for correcting the focus peak determination threshold corresponding to the transfer efficiency and sensitivity of the CCD 36, the drive frequency, the color temperature of the light source, and the temperature of the housing (each of the focus peaks). The focus threshold determination threshold (default value) may be multiplied by the determination threshold correction coefficient 1 to 5). Thus, any of addition, subtraction, multiplication and division may be used as a calculation method when correcting the focus peak determination threshold value.

(Corrected focus peak determination threshold) = (focus peak determination threshold (default value)) × (focus peak determination threshold correction coefficient 1) × (focus peak determination threshold correction coefficient 2) × ( Focus peak determination threshold correction coefficient 3) × (focus peak determination threshold correction coefficient 4) × (focus peak determination threshold correction coefficient 5) (2-2)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 8 is a block diagram showing the main configuration of an imaging apparatus according to the third embodiment of the present invention. In the following description, the same components as those in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 8, the imaging apparatus (camera) 1 of this embodiment further includes a detection filter control unit 86. The detection filter control unit 86 passes or blocks only a specific frequency component of the image signal output from the CCD 36 based on the transfer efficiency of the CCD 36 detected in the above (band pass filter, BPF). A set of detection filters including a plurality of types (for example, 3 to 5 types) is selected (a process for selecting a set of detection filters will be described later). The detection filter control unit 86 selects the first detection filter from the selected set of detection filters and applies it to the image signal input from the CCD 36. The CPU 10 applies a first detection filter to the image signal input from the CCD 36 and calculates a focus evaluation value from the obtained image signal. The focus peak detection unit 80 detects the focus peak position from the focus evaluation value calculated for each position of the focus lens 40 by the CPU 10. If the focus peak position is not detected, the detection filter control unit 86 newly selects a second detection filter that passes or blocks other frequency components. Then, the focus peak detection unit 80 detects the focus peak position based on the focus evaluation value calculated from the image signal input through the newly selected detection filter. The CPU 10 controls each block and repeats the selection of the detection filter and the detection of the focus peak position until the focus peak position is detected.

  Next, a procedure for selecting a set of detection filters will be described. In general, when mixing of pixels occurs due to a decrease in transfer efficiency of the CCD 36, as shown in FIG. 9, the same effect as when a low-pass filter (FIG. 9B) is applied to the image signal is produced. A low frequency component is extracted from the output image signal, and the frequency characteristic changes (FIG. 9C). When a detection filter A (FIG. 10B) for extracting a high frequency component is applied to this image signal (FIG. 10A), the focus evaluation value becomes small as shown in FIG. 10C. Therefore, the detection of the focus peak position is performed by selecting the detection filter B (FIG. 11B) for extracting the low frequency component and increasing the focus evaluation value calculated as shown in FIG. 11C. Can be easily.

  Further, the focus peak position may be shifted depending on the frequency component due to the change in the frequency characteristics of the image signal as described above. FIG. 12 is a graph showing a shift in the focus peak value for each frequency component due to a decrease in the transfer efficiency of the CCD 36. FIG. 13 is a graph showing the focus peak position when the detection filter is appropriately selected.

  In the example shown in FIG. 12A, when the transfer efficiency of the CCD 36 is 98%, the focus evaluation value at the focus peak position falls below the focus peak determination threshold value (broken line in the figure), and the focus peak position cannot be detected. . Then, as described above, the detection filter control unit 86 selects another detection filter and detects the focus peak position again. However, as shown in FIG. 12B, the focus peak position shifts depending on the frequency component due to the change in the frequency characteristic of the image signal. For this reason, the focus peak position cannot be accurately detected depending on how the detection filter is selected.

  Therefore, in the present embodiment, changes in the frequency characteristics of the image signal accompanying changes in the transfer efficiency and sensitivity of the CCD 36, the driving frequency, the color temperature of the light source, and the housing temperature are measured in advance by experiments. A set of detection filters is selected so that the focus peak position does not deviate for each condition of the transfer efficiency, sensitivity, drive frequency, light source color temperature, and housing temperature of the CCD 36. For example, in the example shown in FIG. 13A, as in FIG. 12A, when the transfer efficiency of the CCD 36 is 98%, the focus evaluation value at the focus peak position is the focus peak determination threshold value (broken line in the figure). ) And the focus peak position cannot be detected. Therefore, as shown in FIG. 13B, when the transfer efficiency of the CCD 36 is 98%, the detection filter control unit 86 selects the detection filter 2 ′ in which the focus peak position does not shift or the shift is small. Thus, the focus peak position is accurately detected.

  The relationship between the conditions such as the transfer efficiency of the CCD 36 and the detection filter set is stored in the memory 20 as a parameter (detection filter selection coefficient) for selecting the detection filter set. In the following description, parameters for the transfer efficiency, sensitivity, drive frequency, light source color temperature, and housing temperature of the CCD 36 are described as detection filter selection coefficients 1 to 5, respectively. The detection filter control unit 86 acquires detection filter selection coefficients 1 to 5 according to the detected transfer efficiency, sensitivity, drive frequency, color temperature of the light source, and housing temperature of the CCD 36, and the following equation (3) As shown in -1), a filter selection coefficient for detection is calculated. Then, a set of detection filters is selected based on the calculated detection filter selection coefficient.

(Detection filter selection coefficient) = (detection filter selection coefficient 1) × (detection filter selection coefficient 2) × (detection filter selection coefficient 3) × (detection filter selection coefficient 4) × (detection filter selection coefficient) 5) ... (3-1)
Next, processing for detecting the focus peak position in the camera 1 of the present embodiment will be described with reference to FIG. FIG. 14 is a flowchart showing a flow of processing for detecting the focus peak position. First, the transfer efficiency of the CCD 36 is detected, a filter selection coefficient for detection is calculated, and a set of detection filters is selected (step S50). Then, the detection filter control unit 86 selects the first detection filter (step S52), and applies it to the image signal input from the CCD 36. Both the image signal input from the CCD 36 and the image signal subjected to the first detection filter are stored in the memory 20. Then, focus evaluation values are calculated at a plurality of AF points from the image signal subjected to the first detection filter (step S54). Next, the focus peak position is searched from the focus evaluation value calculated in step S54 (step S56), and when the focus peak position is detected (Yes in step S58), the process ends. On the other hand, if the focus peak position has not been detected (No in step S58), the process returns to step S52, the second detection filter is newly selected from the set of detection filters, and steps S52 to S58 are performed. The process is repeated.

  Next, processing for selecting a detection filter will be described with reference to FIG. FIG. 15 is a flowchart showing a flow of processing for selecting a set of detection filters in step S50. First, the transfer efficiency, camera sensitivity, drive frequency, and light source color of the CCD 36 are determined by the transfer efficiency detector 70, camera sensitivity detector 72, drive frequency detector 76, light source color temperature detector 74, and housing temperature detector 78. The temperature and the housing temperature are acquired (step S500). Next, detection filter selection coefficients 1 to 5 are acquired based on the transfer efficiency, camera sensitivity, drive frequency, color temperature of the light source, and housing temperature detected in step S500 (steps S502 to S510). ). Then, as shown in the above equation (3-1), a detection filter selection coefficient is calculated, and a set of detection filters is selected (step S512).

  According to this embodiment, when the frequency characteristic of the focus evaluation value changes due to pixel mixing caused by changes in the transfer efficiency and sensitivity of the CCD 36, the drive frequency, the color temperature of the light source, and the temperature of the housing, the detection filter is added. By selecting appropriately, the in-focus position can be accurately detected.

  In this embodiment, any of addition, subtraction, multiplication and division may be used as the calculation method when calculating the detection filter selection coefficient. For example, addition may be used as shown in the following equation (3-2). Good.

  (Detection filter selection coefficient) = (detection filter selection coefficient 1) + (detection filter selection coefficient 2) + (detection filter selection coefficient 3) + (detection filter selection coefficient 4) + (detection filter selection coefficient) 5) ... (3-2)

1 is a block diagram showing the main configuration of an imaging apparatus according to a first embodiment of the present invention. The figure which shows typically the transfer route of the electric charge in CCD36 Graph showing changes in focus evaluation value with respect to transfer efficiency Flow chart showing the flow of focus peak position correction processing The block diagram which shows the main structures of the imaging device which concerns on the 2nd Embodiment of this invention. Graph showing changes in focus evaluation value with respect to transfer efficiency Flow chart showing the flow of focus peak determination threshold correction processing The block diagram which shows the main structures of the imaging device which concerns on the 3rd Embodiment of this invention. The figure which shows typically the change of the frequency characteristic of the image signal by the mixture of the pixel Graph showing image signal obtained by applying filter for detection Graph showing image signal obtained by applying filter for detection The graph which shows the shift | offset | difference of the focus peak value for every frequency component by the fall of the transfer efficiency of CCD36 Graph showing focus peak position when filter for detection is properly selected Flow chart showing the flow of processing for detecting the focus peak position The flowchart which shows the flow of the process which selects the set of the filter for a detection of step S50.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Imaging device (camera), 10 ... Central processing unit (CPU), 12 ... Power supply circuit, 14 ... Bus, 16 ... ROM, 18 ... EEPROM, 20 ... Memory (SDRAM), 22 ... VRAM, 24 ... Operation switch group , 26 ... Image display device (liquid crystal monitor), 28 ... Media socket, 30 ... Recording medium, 32 ... Media controller, 34 ... External connection interface (I / F) section, 36 ... CCD, 38 ... Lens unit, 40 ... Focus Lens: 42 ... Zoom lens, 44 ... Shooting lens, 46 ... Aperture / mechanical shutter, 48 ... Timing generator (TG), 50 ... Analog processing unit (CDS / AMP), 52 ... A / D converter, 54 ... Image input Controller 56... Image signal processing circuit 58. Video encoder 60. AF detection circuit 62 A / AWB detection circuit, 64 ... compression / decompression circuit, 66 ... video input / output terminal, 68 ... video output circuit, 70 ... transfer efficiency detection unit, 72 ... camera sensitivity detection unit, 74 ... light source color temperature detection unit, 76 ... drive frequency Detecting unit, 78 ... Case temperature detecting unit, 80 ... Focus peak detecting unit, 82 ... Focus peak correcting unit, 84 ... Focus peak determination threshold correcting unit, 86 ... Detection filter control unit, 90 ... Vertical transfer path, 92 ... Horizontal transfer path, 94 ... Charge-to-voltage converter, 96A ... one pixel on the effective pixel region side of the boundary changing from the effective pixel region to the OB region, 96B ... on the OB region side of the boundary changing from the effective pixel region to the OB region 1 pixel

Claims (7)

An imaging optical system that forms an image;
An image sensor for acquiring an image formed by the imaging optical system;
Driving means for driving the imaging optical system;
Focus evaluation value detection means for detecting a focus evaluation value indicating the degree of focus of the image;
Detecting means for detecting parameters of the image sensor including at least transfer efficiency of the image sensor;
Focus peak position correcting means for correcting the position of the imaging optical system at which the focus evaluation value reaches a peak, based on the detected parameters of the imaging element;
Focus determination means for determining, when the imaging optical system is driven, a position of the imaging optical system at which the focus evaluation value reaches a peak as a focus position;
An imaging apparatus comprising: Color information acquisition means for dividing the acquired image into a plurality of divided areas and acquiring color information of each divided area;
Further comprising light source information acquisition means for acquiring light source information under shooting conditions based on the acquired color information,
The imaging apparatus according to claim 1, wherein the focus peak position correcting unit corrects a focus peak position based on the acquired light source information. An imaging optical system that forms an image;
An image sensor for acquiring an image formed by the imaging optical system;
Driving means for driving the imaging optical system;
Focus evaluation value detection means for detecting a focus evaluation value indicating the degree of focus of the image;
Detecting means for detecting parameters of the image sensor including at least transfer efficiency of the image sensor;
A focus determination threshold value correction means serving as a reference for determining the focus based on the detected parameters of the image sensor;
Focus determination means for determining, when the imaging optical system is driven, a position of the imaging optical system at which the focus evaluation value is larger than the focus determination threshold value as a focus position;
An imaging apparatus comprising: Color information acquisition means for dividing the acquired image into a plurality of divided areas and acquiring color information of each divided area;
Further comprising light source information acquisition means for acquiring light source information under shooting conditions based on the acquired color information,
The imaging apparatus according to claim 3, wherein the focus determination threshold value correcting unit corrects a focus determination threshold value based on the acquired light source information. An imaging optical system that forms an image;
An image sensor that acquires an image formed by the imaging optical system and outputs an image signal indicating the image;
Driving means for driving the imaging optical system;
A detection filter that passes or blocks a specific frequency component of the image signal;
Detecting means for detecting parameters of the image sensor including at least transfer efficiency of the image sensor;
Filter selection means for selecting the detection filter based on the detected parameter of the image sensor;
Focus evaluation value detection means for detecting a focus evaluation value indicating the degree of focus of the image from the image signal input through the detection filter;
Focus determination means for determining, when the imaging optical system is driven, a position of the imaging optical system at which the focus evaluation value reaches a peak as a focus position;
An imaging apparatus comprising: Color information acquisition means for dividing the acquired image into a plurality of divided areas and acquiring color information of each divided area;
Further comprising light source information acquisition means for acquiring light source information under shooting conditions based on the acquired color information,
The imaging apparatus according to claim 5, wherein the filter selection unit selects a detection filter based on the acquired light source information.   The imaging device according to claim 1, wherein the parameter of the imaging device includes at least one of sensitivity, driving frequency, and temperature of the imaging device.

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