JP2014137449A - Imaging device, control method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device, a control method and a program capable of correcting focal point detection deviation due to a light source and an object color.SOLUTION: An imaging device includes: a photographic lens 201; a focal point detection circuit 105; a photometric circuit 107 having a first photoelectric conversion part for photometrically measuring a specific wavelength region of a light flux which has transmitted through the photographic lens 201 and a second photoelectric conversion part for photometrically measuring a wavelength region different from the specific wavelength region; and a system controller 120. The system controller 120 corrects defocus amount on the basis of an R/W ratio as a ratio of the output of the first photoelectric conversion part to the output of the second photoelectric conversion part, the setting of a white balance and the chromatic aberration information of the photographic lens 201.

Description

  The present invention relates to an imaging apparatus that performs TTL (Through The Lenz) phase difference detection type autofocus (AF), and more particularly to an imaging apparatus having a colorimetric function used for light source detection, a control method, and a program. .

  Conventionally, in the TTL phase difference detection method, a pair of images formed by light passing through an imaging lens is photoelectrically converted by a focus detection light receiving element such as an image sensor, and imaged based on a deviation amount (phase difference) between the pair of images. The lens defocus amount (the amount by which the light receiving surface is displaced from the imaging surface in the optical axis direction) is obtained. Many of the focus detection light-receiving elements are constituted by PN junction photodiodes, and the sensitivity extends from the visible wavelength region to the near-infrared wavelength region. The reason is that light in the near-infrared wavelength region is used as auxiliary light irradiated to the subject when focus detection is performed on a dark subject.

  On the other hand, in general, an imaging lens is designed so that chromatic aberration is reduced in the visible wavelength range, but chromatic aberration is often not corrected well in the near-infrared light region. For this reason, when the subject is illuminated with sunlight, when illuminated with a light source with a low color temperature such as a tungsten lamp, and when illuminated with a light source with a high color temperature such as a fluorescent lamp, Since the relative ratio of near infrared light to visible light is different, the focus detection results are different. That is, even if the subject is the same distance, the focus detection result differs depending on the type of light source, and good focus control cannot be performed.

  In order to solve such a problem, it is necessary to detect (discriminate) the type of the light source and correct the focus detection result based on the detection result.

  As a technique for correcting the focus detection result from the detection result of the light source type, the following technique has been proposed (for example, see Patent Document 1). Japanese Patent Application Laid-Open No. 2004-228688 discloses that a light source type is specified according to a setting state of a white balance setting preset by a light source detection sensor and a camera, and focus correction is performed.

JP 2005-165186 A

  However, the technique described in Patent Document 1 identifies which light source at the time of shooting is a plurality of types of light sources from the white balance setting state and the output of the light source detection sensor. Accordingly, the focus detection result is corrected uniformly. For this reason, the shift in focus detection due to the subject color superimposed on the light source is not considered.

  An object of the present invention is to provide an imaging apparatus, a control method, and a program that can correct a focus detection shift due to a light source and a subject color.

  In order to achieve the above object, the present invention provides a focus detection unit that detects a defocus amount based on a light beam that has passed through a photographing lens, and a first photometric unit that measures a specific wavelength region of the light beam that has passed through the photographing lens. A second photometry unit that measures a wavelength range different from the specific wavelength range of the light beam that has passed through the photographing lens, a setting unit that sets a white balance, an output of the first photometry unit, and the second Correction means for correcting the defocus amount detected by the focus detection means based on the output ratio that is the ratio of the output of the photometry means, the white balance setting by the setting means, and the chromatic aberration information of the photographing lens And.

  According to the present invention, the defocus amount is corrected based on the output ratio of the first photometry means and the second photometry means, the white balance setting, and the chromatic aberration information of the photographing lens. Accordingly, it is possible to provide an imaging apparatus that can correct the focus detection deviation due to the light source and the subject color.

1 is a block diagram illustrating an electrical configuration of a camera system including a digital camera as an imaging apparatus according to a first embodiment of the present invention and an interchangeable photographing lens. It is a figure which shows an example of ranging and photometry arrangement | positioning of a digital camera, (a) is a figure which shows arrangement | positioning of the focus detection area within an imaging screen, (b) is arrangement | positioning of the photometry area | region within an imaging screen. FIG. 2C is a diagram in which the focus detection area and the photometry area are overlapped. It is a figure which shows an example of the longitudinal cross-section of the sensor in a photometry circuit. It is a figure which shows the spectral sensitivity characteristic of the sensor in a photometry circuit, and various light sources, (a) is a figure which shows the spectral sensitivity characteristic of a sensor independent, (b) is a figure which shows the spectral sensitivity characteristic of the whole measurement system. (C) is a figure which shows the spectral sensitivity characteristic of various light sources. It is a figure which shows the focus deviation | shift amount under various light sources. It is a figure which shows the relationship between the kind of light source, and the color temperature of a light source. It is a flowchart which shows a focus detection operation | movement. It is a flowchart which shows the detail of the ranging operation of FIG. It is a flowchart which shows the detail of the light source detection operation | movement of FIG. It is a flowchart which shows the detail of lens drive amount calculation of FIG. It is a flowchart which shows the light source detection operation | movement which concerns on the 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing an electrical configuration of a camera system including a digital camera as an imaging apparatus according to the first embodiment of the present invention and an interchangeable photographic lens.

  In FIG. 1, the camera system of this embodiment includes a digital camera 100 that is a single-lens reflex camera, a photographing lens unit 200, and a strobe device 300. The digital camera 100 (imaging device) includes a pentaprism 101, a quick return mirror 102, a sub mirror 103, an AF sensor unit 104, a focus detection circuit 105, a photometry circuit 107, a system controller 120, and the like. The photographing lens unit 200 includes a photographing lens 201, a diaphragm 202, and the like. It should be noted that the description of the configuration of FIG. 1 that is not directly related to the gist of the present invention is simplified or omitted.

  A photographic lens unit 200 is detachably attached to the digital camera 100 via a mount mechanism (not shown). The electrical contact group 210 of the mount unit transmits a control signal, a status signal, a data signal, and the like between the digital camera 100 and the photographing lens unit 200. The contact group 210 also has a function of supplying currents of various voltages and a function of transmitting a signal to the system controller 120 when the photographing lens unit 200 is connected. Thereby, communication is performed between the digital camera 100 and the photographing lens unit 200, and the photographing lens 201 and the diaphragm 202 in the photographing lens unit can be driven.

  The contact group 210 may be configured to transmit not only electrical communication but also optical communication, voice communication, and the like. In the present embodiment, the lens included in the photographic lens unit 200 is shown as a single photographic lens 201 for the sake of convenience. However, as is well known, it is actually composed of a larger number of lenses.

  At the time of photographing with a digital camera, the photographing light flux from the subject image is guided to the quick return mirror 102 that can be driven in the direction of the arrow through the photographing lens 201 and the diaphragm 202. The central portion of the quick return mirror 102 is a half mirror, and a part of the light beam is transmitted when the quick return mirror 102 is lowered. The transmitted light beam is reflected downward by the sub mirror 103 attached to the quick return mirror 102.

  The AF sensor unit 104 includes a field lens, a reflection mirror, a secondary imaging lens, a diaphragm, a line sensor (not shown) including a plurality of CCDs, and the like arranged in the vicinity of the imaging surface. Operates with the phase difference detection method. The focus detection circuit 105 controls the AF sensor unit 104 based on a control signal from the system controller 120, and performs focus detection by a known phase difference detection method. The focus detection circuit 105 detects the defocus amount based on the light beam that has passed through the photographing lens 201. The AF sensor unit 104, the focus detection circuit 105, the image data controller 115, and the system controller 120 constitute a focus detection unit.

  On the other hand, the photographing light beam reflected by the quick return mirror 102 reaches the eyes of the photographer via the pentaprism 101 and the eyepiece 106. The photometric circuit 107 includes a sensor that measures the luminance of the subject. The sensor in the photometry circuit 107 is disposed in the vicinity of the eyepiece lens 106, and the sensor output is supplied to the system controller 120 through the photometry circuit 107.

  When the quick return mirror 102 is raised, the light beam from the photographing lens 201 reaches the image sensor 112 typified by a CMOS or the like via the focal plane shutter 108 and the filter 109 which are mechanical shutters.

  The filter 109 has a function of cutting infrared rays and guiding only visible light to the image sensor 112 and a function as an optical low-pass filter. The focal plane shutter 108 has a front curtain and a rear curtain, and controls transmission / blocking of a light beam from the photographing lens 201. When the quick return mirror 102 is up, the sub mirror 103 is folded.

  The system controller 120 is composed of a CPU that controls the entire digital camera, appropriately controls the operation of each unit described later, and executes processing shown in flowcharts of FIGS. 7 to 11 described later based on the control program. The system controller 120 is connected to a lens control circuit 204 and an aperture control circuit 206 of the photographing lens unit 200 via a lens control microcomputer (hereinafter referred to as a microcomputer) 207. The lens control circuit 204 controls the lens driving mechanism 203 that moves the photographing lens 201 in the optical axis direction and performs focusing. A diaphragm control circuit 206 controls a diaphragm driving mechanism 205 that drives the diaphragm 202.

  Also connected to the system controller 120 is a shutter charge / mirror drive mechanism 110 that controls up / down driving of the quick return mirror 102 and shutter charge of the focal plane shutter 108. The system controller 120 is connected to a shutter control circuit 111 that controls the travel of the front curtain and the rear curtain of the focal plane shutter 108. Further, the system controller 120 is connected to an EEPROM 122 that stores parameters that need to be adjusted for controlling the digital camera, camera ID information that enables individual identification of the digital camera, AF correction data, automatic exposure correction values, and the like. ing.

  The lens control microcomputer 207 also includes a lens storage unit that stores information unique to the lens (for example, information such as focal length, wide aperture, and lens ID assigned to each lens) and information received from the system controller 120.

  Further, the system controller 120 controls the lens driving mechanism 203 via the lens control microcomputer 207 to form a subject image on the image sensor 112. Further, the system controller 120 controls the aperture driving mechanism 205 based on the set Av (Aperture Value) value, and further outputs a control signal to the shutter control circuit 111 based on the set Tv (Time Value) value. To control exposure.

  The front curtain and the rear curtain of the focal plane shutter 108 are configured by a spring as a driving source and require a spring charge for the next operation after the shutter travels. The shutter charge / mirror drive mechanism 110 controls spring charge and raises / lowers the quick return mirror 102.

  An image data controller 115 is connected to the system controller 120. The image data controller 115 is configured by a DSP (digital signal processor), and executes control of the image sensor 112, correction and processing of image data input from the image sensor 112, based on instructions from the system controller 120. The item of image data correction / processing includes auto white balance (a function for correcting a portion of maximum brightness in a captured image to a predetermined color (white)). In the auto white balance, the correction amount can be changed by a command from the system controller 120.

  The image data controller 115 divides the image signal into regions, supplies a value obtained by integrating each Bayer pixel in each region to the system controller 120, and evaluates the integrated signal by the system controller 120 to perform photometry.

  A timing pulse generation circuit 114, an A / D converter 113, a DRAM 121, a D / A converter 116, an image compression circuit 119, and a contrast detection circuit 140 are connected to the image data controller 115. The timing pulse generation circuit 114 outputs a pulse signal necessary for driving the image sensor 112.

  The A / D converter 113 receives the timing pulse generated by the timing pulse generation circuit 114 together with the image sensor 112, and converts an analog signal corresponding to the subject image output from the image sensor 112 into a digital signal. The DRAM 121 temporarily stores image data (digital data) before processing or data conversion into a predetermined format.

  An image data recording medium 401 is connected to the image compression circuit 119. The image compression circuit 119 uses a hard disk, a flash memory, a floppy (registered trademark) disk, or the like, and performs compression or conversion (for example, JPEG) on image data stored in the DRAM 121. The converted image data is stored in the image data recording medium 401.

  In addition, an image display circuit 118 is connected to the D / A converter 116 via an encoder circuit 117. The image display circuit 118 is a circuit that displays image data picked up by the image sensor 112 and is generally composed of a color liquid crystal display element.

  The image data controller 115 converts the image data on the DRAM 121 into an analog signal by the D / A converter 116 and outputs the analog signal to the encoder circuit 117. The encoder circuit 117 converts the output of the D / A converter 116 into a video signal (for example, an NTSC signal) necessary for driving the image display circuit 118.

  The image data controller 115 passes a filter having a predetermined frequency characteristic on the corrected image data, and evaluates the contrast in a predetermined direction of an image signal obtained by performing a predetermined gamma process. The result is supplied to the system controller 120. The system controller 120 communicates with the lens control circuit 204, adjusts the focal position, and adjusts the focal position so that the contrast evaluation value is higher than a predetermined level.

  The system controller 120 is connected to an operation display circuit 123, a shooting mode selection button 130, a main electronic dial 131, a decision switch (hereinafter referred to as SW) 132, a distance measuring point selection button 133, and an AF mode selection button 134. Further, the system controller 120 is connected with a photometry mode selection button 135, release SW 1 and 136, release SW 2 and 137, and finder mode selection SW 138.

  The operation display circuit 123 causes the external liquid crystal display device 124 and the internal liquid crystal display device 125 to display information about the operation mode of the digital camera, exposure information (shutter time, aperture value, etc.), and the like. The shooting mode selection button 130 is operated when the user sets a mode to cause the digital camera to execute a desired operation. The distance measuring point selection button 133 is operated when a focus detection position to be used is selected from a plurality of focus detection positions of the AF sensor unit 104. The release SWs 1 and 136 are operated when shooting preparation operations such as photometry and distance measurement are started. The release SWs 2 and 137 are operated when the imaging operation is started.

  The finder mode selection SW 138 is operated when switching between an optical finder mode in which a light beam passing through the eyepiece lens 106 can be confirmed and a live view display mode in which an elephant signal received by the image sensor 112 is sequentially displayed on the image display circuit 118. To do.

  Further, the strobe device 300 is detachably attached to the digital camera 100 via a mount mechanism (not shown). The electrical contact group 310 of the mount unit has a light emitting terminal for controlling the light emission timing, and transmits a control signal, a status signal, a data signal, etc. between the digital camera 100 and the strobe device 300, and also has a signal transmission function. Have. The strobe device 300 includes a Xe (xenon) tube 301, a reflective shade 302, a light emission control circuit 303, a charging circuit 304, a power source 305, and a strobe control microcomputer 306.

  FIG. 2 is a diagram illustrating an example of distance measurement and photometry arrangement of the digital camera, FIG. 2A is a diagram illustrating the arrangement of focus detection areas in the imaging screen, and FIG. 2B is an imaging screen. FIG. 2C is a diagram showing the arrangement of the photometric areas in the figure, and FIG. 2C is a diagram in which the focus detection areas and the photometric areas are superimposed.

  In FIG. 2A, reference numeral 251 denotes an imaging screen. Reference numeral 252 denotes a plurality (21 in this embodiment) of focus detection areas. In FIG. 2A, numbers from A1 to A21 are given to the 21 focus detection areas. The number and arrangement of the focus detection areas are not limited to those shown in the drawing.

  In FIG. 2B, the arrangement of the photometric areas in the imaging screen 251 is shown. Reference numeral 253 denotes a plurality of photometric areas (63 in this embodiment). In FIG. 2B, the numbers Bmn (m = 0, 1, 2,... 6, n = 0, 1, 2,... 8 m: column number, n: row number) are assigned to 63 photometric areas. It is attached. The number and arrangement of the photometry areas are not limited to those shown in the drawing.

  In FIG. 2C, 21 focus detection areas 252 and 21 photometry areas 253 are arranged so as to overlap (coincide) with each other in a substantially circular area (first area) including the center of the imaging screen 251. ing. Forty-two photometric areas 253 are arranged in the central area and the peripheral area (second area). It should be noted that the focus detection area 252 and the photometry area 253 do not have to have a perfect coincidence as shown in the central area in the figure, and it is sufficient that at least a part of them overlap.

  FIG. 3 is a diagram illustrating an example of a longitudinal sectional structure of a sensor in the photometric circuit.

  In FIG. 3, a vertical cross-sectional structure of the B00 pixel is shown as an example of the structure of the sensor in the photometric circuit 107. Pixels other than the B00 pixel also have the same structure. Reference numeral 301 denotes a p-type semiconductor substrate (hereinafter referred to as a p substrate). Reference numerals 302 and 302 denote p-type regions (hereinafter referred to as cn regions) formed to electrically connect to the p substrate 301 and to separate adjacent pixels. Electrodes are drawn from the cn regions 302 and 304, and pixel separation is performed electrically by connecting the p substrate 301 to GND (ground).

  Reference numeral 304 denotes an n-type epitaxial layer (hereinafter nEpi) formed on the p substrate 301. 305 is a p-type well (hereinafter referred to as p-well) formed inside nEpi304. Reference numeral 306 denotes an n-type region (hereinafter referred to as an n region) formed inside the p-well 305.

  Reference numeral 307 denotes a photocurrent Ir_00 that flows through the PN junction of the second photoelectric conversion unit (photodiode) configured by nEpi 304 and p-well 305. Ir_00 means the photocurrent Iw from the B00 pixel. The second photoelectric conversion unit has a spectral sensitivity peak from the red region to the infrared light region.

  Reference numeral 308 denotes a photocurrent Iw_00 that flows through the PN junction of the first photoelectric conversion unit (photodiode) configured by the p-well 305 and the n region 306. Iw_00 means the photocurrent Iw from the B00 pixel. The first photoelectric conversion unit has a spectral sensitivity peak in the visible light region.

  Thus, the first photoelectric conversion unit and the second photoelectric conversion unit have different spectral sensitivity characteristics, and the direction in which the light from the photographing lens 201 enters (the thickness of the sensor in the photometric circuit 107 ( It has vertical structures that overlap each other in the depth (direction). In other words, the first photoelectric conversion unit and the second photoelectric conversion unit are formed on the same semiconductor substrate and overlapped in the thickness direction of the semiconductor substrate.

  Note that the sensor structure shown in FIG. 3 is an example, and in the embodiment of the present invention, light from the photographing lens 201 is incident on the first and second photoelectric conversion units having different spectral sensitivity characteristics. What is necessary is just to have the vertical structure which at least one part mutually overlaps in a direction. That is, the first photoelectric conversion unit and the second photoelectric conversion unit may be slightly shifted in the light incident plane direction. The number of photoelectric conversion units having different spectral sensitivity characteristics is not limited to two.

  The photocurrents Iw_00 and Ir_00 are logarithmically compressed by an electric circuit in the photometry circuit 107 and converted into voltages Vw_00 (first output or first signal) and Vr_00 (second output or second signal), It is output to the system controller 120. Vw_00 and Vr_00 mean output voltages Vw and Vr corresponding to the photocurrents Iw and Ir from the B00 pixel, respectively.

  4A and 4B are diagrams showing spectral sensitivity characteristics of the sensor and various light sources in the photometry circuit. FIG. 4A is a diagram showing the spectral sensitivity characteristics of the sensor alone, and FIG. FIG. 4C is a diagram showing the spectral sensitivity characteristics of the system, and FIG. 4C is a diagram showing the spectral sensitivity characteristics of various light sources.

  In FIG. 4A, 401 indicates the spectral sensitivity of an IR cut filter that is disposed in the AF sensor unit 104 and cuts unnecessary infrared light. The infrared cut wavelength is set to a wavelength slightly longer than 700 nm, and is configured to transmit a near infrared wavelength used for auxiliary light. Reference numeral 402 denotes a spectral sensitivity characteristic of a first photoelectric conversion unit configured by a PN junction of the p-well 305 and the n region 306 and outputting a photocurrent Iw_00 among the sensors in the photometry circuit 107 of FIG. The first photoelectric conversion unit has a peak sensitivity (main sensitivity) with respect to a wavelength near 500 nm.

  Note that the peak sensitivity wavelength of the first photoelectric conversion unit is not limited to around 500 nm, and may be slightly shorter or longer. However, since the spectral sensitivity characteristic of human eyes, so-called specific visual sensitivity, has a peak at 555 nm in the bright field, it is desirable that the peak sensitivity wavelength is near 555 nm.

  Reference numeral 403 denotes a spectral sensitivity characteristic of a second photoelectric conversion unit that is configured by a PN junction of nEpi 304 and p-well 305 and outputs a photocurrent Ir_00 among the sensors in the photometry circuit 107 of FIG. The second photoelectric conversion unit has a peak sensitivity (main sensitivity) with respect to a wavelength near 750 nm.

  Note that the peak sensitivity wavelength of the second photoelectric conversion unit is not limited to around 750 nm, and may be slightly shorter or longer. However, it is desirable to have sufficient sensitivity near the wavelength of the auxiliary light used at the time of focus detection.

  The first photoelectric conversion unit corresponds to a first photometric unit that measures a specific wavelength range of the light beam that has passed through the photographing lens 201, and the second photoelectric conversion unit has the specific wavelength of the light beam that has passed through the photographing lens 201. This corresponds to a second photometry means for photometry in a wavelength range different from the range.

  In addition, the first photoelectric conversion unit includes a light receiving unit (first light receiving unit) that absorbs light from the PN junction formed in the semiconductor substrate of FIG. 3 and has main sensitivity in the visible light region. The light receiving unit (first light receiving unit) corresponds to the boundary between the p-well 305 and the n region 306. Further, the second photoelectric conversion unit has a wavelength region different from that of the first photoelectric conversion unit from a PN junction formed at a depth different from that of the first photoelectric conversion unit in the semiconductor substrate of FIG. And a light receiving portion (second light receiving means) having main sensitivity in the infrared light region. The light receiving unit (second light receiving unit) corresponds to the boundary between nEpi 304 and p-well 305.

  In FIG. 4B, reference numeral 404 denotes a spectrum when the spectral sensitivity characteristic 402 of the first photoelectric conversion unit (305, 306) shown in FIG. 4A is combined with the spectral transmittance characteristic of the IR cut filter 401. The sensitivity characteristic is shown.

  Reference numeral 405 denotes a spectral sensitivity characteristic when the spectral sensitivity characteristic 403 of the second photoelectric conversion unit (304, 305) shown in FIG. 4A is combined with the spectral transmittance characteristic of the IR cut filter 401. Due to the IR cut filter, the spectral sensitivity characteristic has a peak sensitivity in the vicinity of 700 nm which is the wavelength of the auxiliary light.

  In FIG. 4C, there are three types of light sources for illuminating the subject, such as daylight, fluorescent lamps, tungsten lamps (incandescent lamps, etc.). Reference numerals 406 to 408 denote spectral sensitivities of daylight, fluorescent light, and tungsten lamp, respectively. Daylight includes a wide range of infrared components from 400 nm to more than 700 nm. The fluorescent lamp includes a visible light component from 400 nm to 700 nm, and hardly includes an infrared component beyond that. In addition, the tungsten lamp has a characteristic that the ratio of the contained component decreases as the wavelength becomes shorter with the vicinity of 800 nm as the apex.

  FIG. 5 is a diagram showing the amount of focus deviation under various light sources.

5A and 5B, the sensors in the case where various subjects are measured under various light sources having the spectral sensitivity characteristics shown in FIG. 4C using the sensors in the photometric circuit 107 having spectral sensitivity characteristics such as 404 and 405. And the relationship between the output of the photographic lens and the defocus amount of the photographing lens. The horizontal axis represents the R / W ratio (output ratio of the first photometric means and the second photometric means) which is the ratio of Vr and Vw output from the sensor, and the vertical axis represents the amount of focus deviation of the taking lens at that time Represents. The 0 position on the horizontal axis is plotted based on the R / W ratio during the adjustment process of the focus detection system.
In the adjustment process of the focus detection system, adjustment is performed using an achromatic chart using a light source having spectral sensitivity characteristics equivalent to daylight. Accordingly, when the R / W ratio is large, it can be regarded as a subject with a lot of red components, and when the R / W ratio is small, it can be regarded as a subject with many blue components. The amount of focus deviation on the vertical axis is adjusted so as to be just in focus on the achromatic chart under the adjustment light source.

  Reference numeral 501 denotes a fluorescent lamp, 502 denotes daylight, and 503 denotes a light source detection R / W and a defocus amount result under a tungsten lamp. In daylight photography having the same spectral sensitivity as the adjustment light source of the focus detection system, R / W = 0 for an achromatic subject, and a just-focus image is obtained with a focus shift amount of almost zero. For subjects with a lot of red component, focus is on the front (the surface in focus is in front of the subject), and for subjects with a lot of blue component, the focus is on the back (with the surface in focus behind the subject) A focus detection result is obtained.

  The relationship between the amount of focus deviation under daylight and R / W is linear, and the amount of focus deviation can be corrected using R / W. Assuming that the amount of focus deviation is ΔZd, the equation (1) is obtained. Here, α below and β and γ described later are inclinations of correction straight lines obtained by linear interpolation of the light source detection results.

ΔZd = α × (R / W) (1)
When the photographing light source is a fluorescent lamp, the focus shift amount is indicated by 501. Since the fluorescent lamp does not contain near-infrared light of 700 nm or more with respect to daylight, the graph is shifted to the rear pin as a whole, and the inclination is reduced.

  Similar to the shooting under daylight, the relationship between the focus shift amount under the fluorescent lamp and the R / W is linear, and the focus shift amount can be corrected using the R / W. Assuming that the amount of focus deviation is ΔZf, the equation (2) is obtained.

ΔZf = β × (R / W) + b (2)
When the photographing light source is tungsten, the focus shift amount is indicated by 503. Since tungsten light is a light source whose color temperature is lower than that of daylight, the ratio of the red component is high in spectral sensitivity characteristics, the graph is shifted to the front pin as a whole, and R / W is increased. That is, the result is that there are many red components.

  Similar to the shooting under daylight, the relationship between the focus shift amount of tungsten light and R / W is linear, and the focus shift amount can be corrected using R / W. When the amount of focus deviation is ΔZt, the equation (3) is obtained.

ΔZt = γ × (R / W) + c (3)
However, the amount of focus deviation differs between daylight, fluorescent lamp, and tungsten light for the same R / W ratio. For this reason, in the case of performing a good defocus amount correction under any light source, in addition to the R / W ratio, it is determined whether or not shooting is performed under daylight, fluorescent light, and tungsten light. It is necessary to make an appropriate correction under the light source.

  FIG. 6 is a diagram showing the relationship between the type of light source and the color temperature of the light source.

  In FIG. 6, the light source has a different color temperature (K) according to the type of the light source (sunlight, shade, cloudy, incandescent light bulb, white fluorescent light). In a digital camera, the balance of the reflected light from the subject differs depending on the color temperature of the light source that illuminates the subject, so the color of the subject cannot be faithfully reproduced without correction. Therefore, correction called white balance is performed so that white is reproduced under any light source.

  Usually, a function called auto white balance, which automatically determines and corrects the type of light source, is mounted on a digital camera. However, when the subject does not include white, there is a case where the light source cannot be easily determined. For this reason, digital cameras are generally equipped with a preset white balance function in which the user selects the type of light source from a menu and a manual white balance function in which the color temperature of the light source can be directly specified.

  Although omitted in the detailed description of FIG. 1, the digital camera of this embodiment can also set preset and manual white balance in addition to auto white balance. That is, in this embodiment, an arbitrary mode is selected from an auto mode in which white balance data is automatically extracted from a captured image, and a manual setting mode in which white balance is set by designating the type of light source or the color temperature of the light source. Can be selected. Auto and manual white balance settings are made by the system controller 120.

  FIG. 7 is a flowchart showing the focus detection operation.

  7, first, when an AF operation request is issued by operating the AF mode selection button 134 by the user of the digital camera, the system controller 120 starts executing the AF operation program (step S700). Next, the system controller 120 communicates with the photographic lens unit 200 to shoot the focal length, open aperture value, minimum aperture value, lens drive sensitivity information, chromatic aberration information (chromatic aberration amount), and the like necessary for distance measurement and photometry. Information on the lens 201 is acquired (step S701). Next, the system controller 120 executes a ranging operation subroutine (step S702).

  Next, the system controller 120 determines whether or not the distance measurement operation is impossible (step S703). If distance measurement is impossible, the system controller 120 ends the AF operation. If distance measurement is not impossible, the system controller 120 executes a subroutine for light source detection operation (step S704). Next, the system controller 120 calculates the lens driving pulse number LP (lens driving amount) based on the distance measurement result and the light source detection result (step S705), and drives the photographing lens 201 by the calculated lens driving pulse number LP (step S705). Step S706).

  Next, the system controller 120 checks whether or not it is in focus (step S707). If not in focus, the system controller 120 returns to step S702 and performs the AF operation again. If it is in focus, the system controller 120 ends the AF operation. The above is the overall movement of the AF operation.

  FIG. 8 is a flowchart (subroutine) showing details of the distance measuring operation of FIG.

  In FIG. 8, first, the system controller 120 starts a distance measuring operation (focus detection) (step S801). Next, the system controller 120 starts an accumulation operation of a focus detection sensor (not shown) that accumulates signal charges in the photodiode based on the incident light (step S802). The system controller 120 monitors the terminal of the focus detection sensor and checks the accumulation operation end signal that is output when the output of the photodiode reaches a predetermined voltage, thereby determining whether or not the accumulation operation has been completed (step S803). ).

  If the accumulation operation has been completed, the system controller 120 stores the accumulation time in the EEPROM 122 (step S804), and proceeds to step S807. If the accumulation operation has not been completed, the system controller 120 checks the time of a timer (not shown) that starts timing simultaneously with the start of the accumulation operation, and determines whether or not a predetermined time has elapsed (step S805). ).

  If the predetermined time has not elapsed, the process returns to step S803 to determine again whether or not the accumulation operation has been completed. If the predetermined time has elapsed, the system controller 120 forcibly ends the accumulation operation of the focus detection sensor by transmitting a signal to the focus detection sensor (step S806).

  Next, when the accumulation operation of the focus detection sensor is terminated by an AGC (Auto Gain Control) circuit or the forced accumulation by the system controller 120 is terminated, the system controller 120 performs the next reading operation. An image signal is read from the AF sensor unit 104 (step S807). Next, the system controller 120 uses the adjustment data stored in the EEPROM 122, the accumulation time, etc., to correct the read image signal (step S808).

  Next, the system controller 120 calculates the signal amount of the photodiode of the focus detection sensor and the difference between the maximum value and the minimum value of the image signal based on the accumulation time stored in the EEPROM 122 and the corrected image signal output. Further, a primary determination is made as to whether distance measurement is possible based on the calculated signal amount and contrast value (step S809).

  If distance measurement is not possible, the distance measurement is NG (step S813), and this subroutine is terminated. If distance measurement is possible, the system controller 120 performs a known correlation calculation from the image signal output to detect the defocus amount and the defocus direction (whether the front pin is the rear pin) (step S810). The defocus amount is corrected based on the R / W ratio, the white balance setting, and chromatic aberration information (chromatic aberration amount) of the photographing lens 201. The correction will be described later.

  Next, the system controller 120 determines reliability from the distance measurement data obtained in step S810 and the degree of coincidence between the images of the two fields of view (step S811). If it is determined that there is reliability, the system controller 120 calculates the defocus amount Z based on the obtained correlation calculation result and lens information obtained in step S810 (step S812), and ends this subroutine. If it is determined that there is no reliability, it is determined as ranging NG (step S813), and this subroutine is terminated.

  FIG. 9 is a flowchart (subroutine) showing details of the light source detection operation of FIG. In order to simplify the description, the setting of the light source type and the color temperature is limited to three types (sunlight, incandescent bulb, white fluorescent lamp, 5000K or more, 3000K or less, 3000K or more and 4000K or less).

  In FIG. 9, when a light source detection operation request is issued, the system controller 120 executes a light source detection operation program and starts a light source detection operation (step S900). Next, the system controller 120 acquires the output voltage Vw corresponding to the photocurrent Iw flowing through the PN junction of the first photoelectric conversion unit that constitutes the sensor in the photometry circuit 107 (step S901). Further, the system controller 120 acquires an output voltage Vr corresponding to the photocurrent Ir flowing through the PN junction of the second photoelectric conversion unit that constitutes the sensor in the photometric circuit 107 (step S902).

  Next, the system controller 120 calculates an R / W ratio that is a ratio between the acquired output voltage Vw and the output voltage Vr (step S903). Next, the system controller 120 checks whether or not the white balance (WB) setting is auto (step S904).

  If the white balance setting is auto, the process proceeds to step S911 described later. If the white balance setting is not automatic, the system controller 120 determines whether the light source type / color temperature is set to 5000 K or more in the preset setting with sunlight or manual setting (step S905). If the light source type / color temperature is set to 5000K or higher in the preset setting with sunlight or manual setting, the process proceeds to step S908. Otherwise, the process proceeds to step S906.

  Next, the system controller 120 determines whether or not the light source type / color temperature is set to an incandescent bulb (tungsten lamp) by preset setting or 3000K or less by manual setting (step S906). If the light source type / color temperature is set to an incandescent bulb (tungsten lamp) by preset setting or 3000K or less by manual setting, the process proceeds to step S909, and if not, the process proceeds to step S907.

  Next, the system controller 120 determines whether or not the light source type / color temperature is set to a white fluorescent lamp as a preset setting or from 3000K to 4000K as a manual setting (step S907). If the light source type / color temperature is set to white fluorescent lamp in the preset setting or 3000 K to 4000 K in the manual setting, the process proceeds to step S910.

  In step S908, step S909, step S910, and step S911, the calculation of the defocus amount for correcting the focus detection result is executed according to the R / W calculation result and the white balance setting, and the result is used as a variable. It is stored in the EEPROM 122 as ΔZ.

  In step S908, ΔZd is obtained using the above equation (1), ΔZt is obtained using the above equation (3) in step S909, and ΔZdf is obtained using the above equation (2) in step S910. Yes. The inclinations α, β, γ and intercepts b, c of the correction straight line obtained by linear interpolation of the light source detection result are the chromatic aberration information acquired from the photographing lens 201 and the design value or experiment of the R / W of the subject color under various light sources. Each is determined based on the value. Since a specific method is well-known, description is abbreviate | omitted.

  If the white balance setting is set to auto in step S904, the digital single lens reflex camera takes white balance from an image taken when taking an image using an optical viewfinder. Therefore, the result of white balance cannot be known in advance. In such a case, the correction amount may be set to a small amount so that a certain amount of effect can be obtained under any light source. For example, ΔZa is obtained using equation (4), and the result is stored in the DRAM 121 as a variable ΔZ (step S911).

ΔZa = δ × (R / W) + d (4)
Here, moderate correction is possible by setting β <δ <α, d <b, and the like. Further, the present invention is not limited to the above-described coefficient setting, and it is conceivable to perform correction similar to daylight with high photographing frequency. Thus, the calculation of the variable ΔZ is completed, and this subroutine is terminated.

  FIG. 10 is a flowchart (subroutine) showing details of the lens driving amount calculation of FIG.

  In FIG. 10, when the AF operation and the light source detection operation are completed, a final lens drive amount calculation subroutine is executed (step S1000). First, the system controller 120 subtracts the defocus correction amount ΔZ detected from the light source detection result from the defocus amount Z detected based on the light beam transmitted through the photographing lens 201 by the focus detection circuit 105. Further, the final defocus amount obtained by subtraction is newly stored in the variable Z (step S1001). The variable Z is a defocus amount calculated in consideration of the type of light source and subject color.

  That is, the R / W ratio (output ratio of the first photometry means and the second photometry means) which is the ratio of the output voltage Vr and the output voltage Vw output from the sensor in the photometry circuit 107, the white balance setting, The defocus amount is corrected based on the chromatic aberration amount of the photographing lens 201. In this case, a defocus correction amount is calculated by a linear interpolation method based on the R / W ratio and chromatic aberration information of the photographing lens 201, and the defocus amount is corrected according to the defocus correction amount. The system controller 120 corresponds to setting means for setting white balance and correction means for correcting the defocus amount.

  Next, the system controller 120 calculates the lens driving pulse number LP for driving the photographing lens 201 using the lens driving sensitivity information B included in the photographing lens 201 and the corrected defocus amount Z (step S1002). This process ends.

  As described above, according to the present embodiment, when the light source and the color temperature are designated in the white balance setting or manually, the slope and intercept of the correction line by the linear interpolation method of the light source detection result are changed. As a result, it is possible to obtain an appropriate correction amount for focus detection under various light sources, thereby improving the focus accuracy.

  That is, the R / W ratio, which is the ratio of the output voltage Vr of the first photoelectric conversion unit and the output voltage Vw of the second photoelectric conversion unit constituting the sensor in the photometry circuit 107, white balance setting, and photographing The defocus amount is corrected based on the chromatic aberration information of the lens 201. Accordingly, it is possible to provide an imaging apparatus that can correct the focus detection deviation due to the light source and the subject color.

[Second Embodiment]
The second embodiment of the present invention is different from the first embodiment in the point described in FIG. 11 described later. Since the other elements of this embodiment are the same as the corresponding ones of the first embodiment (FIG. 1), description thereof is omitted.

  Even when the digital camera uses the optical viewfinder with the white balance setting set to auto, for example, when continuous shooting is performed, the following correction is possible. From the white balance result obtained after the first frame shooting, the result of auto white balance is reflected from the second frame, and the slopes α, β, γ and intercepts b, c of the correction line by the linear interpolation of the light source detection result are appropriately selected. It is possible to correct the focus detection deviation using.

  The following digital cameras have also been commercialized. In the live view mode that is becoming popular as a digital single lens reflex function, when the user designates the start of AF operation, the quick return mirror 102 is once returned to the photographing standby position. Further, after focus detection is performed by the AF sensor unit 104, the quick return mirror 102 is retracted again to perform live view shooting. In this case, even if auto white balance is set, the inclination α, β, γ and intercept b of the correction line by the linear interpolation method of the light source detection result using the white balance result obtained in advance by live view shooting. , C can be used to correct the focus detection deviation.

  FIG. 11 is a flowchart showing the light source detection operation according to the present embodiment.

  11 is different from FIG. 9 in that step S913, step S914, and step S915 are added, and only the added portion will be described so as not to overlap with the description of FIG. In step S913, the system controller 120 checks whether or not white balance data exists. If no white balance data exists, the process proceeds to step S911, and a correction amount is set so that a certain effect can be obtained under any light source. If the white balance data exists, the system controller 120 determines whether the color temperature of the light source is 5000K or higher (step S914).

  If the color temperature of the light source is equal to or higher than 5000K, the process proceeds to step S908 to execute correction when the photographing light source is daylight. If the color temperature of the light source is not 5000K or higher, the system controller 120 determines whether the color temperature of the light source is 3000K or lower (step S915). When the color temperature of the light source is 3000 K or less, the process proceeds to step S909, and the system controller 120 performs correction when the imaging light source is equivalent to an incandescent bulb (tungsten). If the color temperature of the light source is not 3000K or less, the process proceeds to step S910, and the system controller 120 performs correction when the imaging light source is equivalent to a white fluorescent lamp.

  As described above, according to the present embodiment, even when the white balance setting is set to auto, correction calculation of the defocus amount ΔZ can be appropriately executed in continuous shooting, live view shooting, or the like. Accordingly, it is possible to provide an imaging apparatus that can correct the focus detection deviation due to the light source and the subject color.

[Other Embodiments]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed. The computer-readable program of the present invention operates on a digital camera (imaging device) and realizes the functions of the above-described embodiments.

104 AF sensor unit 105 Focus detection circuit 107 Photometry circuit 120 System controller 201 Shooting lens

Claims (7)

Focus detection means for detecting a defocus amount based on a light beam transmitted through the photographing lens;
A first photometric means for measuring a specific wavelength range of a light beam transmitted through the photographing lens;
A second photometric means for measuring a wavelength range different from the specific wavelength range of the light beam transmitted through the photographing lens;
A setting means for setting the white balance;
The focus detection means based on the output ratio which is the ratio of the output of the first photometry means and the output of the second photometry means, the white balance setting by the setting means, and the chromatic aberration information of the photographing lens Correction means for correcting the defocus amount detected by
An imaging apparatus comprising:   The correction means calculates a defocus correction amount using a linear interpolation method based on the output ratio of the first photometry means and the second photometry means and chromatic aberration information of the photographing lens. The imaging apparatus according to claim 1, wherein the defocus amount is corrected according to the defocus correction amount.   The setting means includes an auto mode for automatically extracting white balance data from a photographed image, and a manual setting mode for setting a white balance by designating a type of light source or a color temperature of the light source. The imaging device according to claim 1.   The correction means, when the type of light source or the color temperature of the light source is designated by the setting means, selects the slope and intercept of the correction straight line by the linear interpolation method according to the type of the designated light source or the color temperature of the light source. The imaging apparatus according to claim 2, wherein the imaging apparatus is an imaging apparatus. The first photometric means and the second photometric means are formed on the same semiconductor substrate and at least partially overlapped in the thickness direction of the semiconductor substrate,
The first photometric means includes first light receiving means that absorbs light from a PN junction formed in the semiconductor substrate and has main sensitivity in the visible light region,
The second photometric means absorbs light in a wavelength region different from that of the first photometric means from a PN junction formed at a depth different from that of the first photometric means in the semiconductor substrate. The imaging apparatus according to claim 1, further comprising a second light receiving unit having a main sensitivity in an infrared light region. A method for controlling an imaging apparatus,
A focus detection step of detecting a defocus amount based on a light beam transmitted through the photographing lens;
A first photometric step for measuring a specific wavelength range of a light beam transmitted through the photographing lens;
A second photometric step of measuring a wavelength range different from the specific wavelength range of the light beam transmitted through the photographing lens;
A setting process for setting white balance;
The focus detection step based on the output ratio which is the ratio of the output of the first photometry step and the output of the second photometry step, the white balance setting by the setting step, and the chromatic aberration information of the photographing lens A correction step of correcting the defocus amount detected by
A control method characterized by comprising:   A computer-readable program for causing a computer to execute the control method according to claim 6.

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