JP2008118442A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of performing imaging in a highly accurately focused state, and to provide an imaging method performed by the imaging apparatus. <P>SOLUTION: The imaging apparatus includes: a photographing lens 11 for transmitting subject light and forming an image by the action of a focus lens 22; a CCD 24 for generating an image signal which expresses colors of subject light imaged by transmitting the photographing lens 11 by the combination of a plurality of signal components corresponding to the plurality of prescribed colors, respectively, concerning the respective pixels so as to express an image composed of the plurality of pixels; a covariance calculation circuit 37 for calculating covariance using the two signal components concerning the plurality of pixels constituting the image; and an AF detecting circuit 38 for moving the focus lens 22 in a covariance increase direction along the optical axis of the photographing lens 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus that captures a subject image and an imaging method that is performed by such an imaging apparatus.

  2. Description of the Related Art Conventionally, imaging devices that receive subject light with a CCD imaging device (hereinafter referred to as a CCD) and image it have been widely used. Such an image pickup apparatus is provided with a focus lens in an optical system that forms an image of subject light, and has an autofocus function that automatically moves the focus lens to a focus position during image pickup. There are many things.

  In an imaging apparatus equipped with a CCD, subject light imaged by an optical system is received, and an image signal representing an image of the subject light is generated by imaging. Is called a subject image, and an image represented by an image signal obtained by imaging is referred to as a captured image in distinction from the subject image. An image signal representing a captured image is composed of pixel values representing the luminance of each pixel constituting the captured image. At this time, if the focus lens is away from the in-focus position and the subject image is blurred, the brightness of the subject image is generally uniformed, so the pixel values of many pixels in the captured image Is close to the average value, the dispersion of pixel values is reduced. On the other hand, when the focus lens is close to the in-focus position and a clear subject image is formed, various luminances are distributed in the subject image according to the subject, and the pixel value of the captured image is Dispersion increases. As described above, the dispersion of the pixel values in the captured image can be effectively used as a parameter for determining the focus state of the focus lens. Therefore, by moving the focus lens to a position where the dispersion becomes the maximum value, A technique for automatically moving the lens to the in-focus position has been proposed (for example, see Patent Document 1).

Here, random noise may be included in the image signal obtained by imaging, and the pixel value varies, resulting in a large variance even though it is not the in-focus position. As a result, the focus lens is moved from the in-focus position. There is a case where it is erroneously detected that it is in a focused state even though it is away. Therefore, a technique has been proposed in which the contribution of such random noise to the dispersion is calculated and the focus lens is moved based on the dispersion obtained by subtracting the calculated contribution (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 3-50513 JP 2003-501192 A

  By the way, the above-mentioned CCD has a small light receiving portion arranged two-dimensionally, and it is known that there are so-called point defects that are damaged from the time of manufacture in these light receiving portions. It has been. The presence of such a point defect is because the pixel value obtained by light reception at the point defect becomes an abnormal value that is significantly different from the pixel value obtained by light reception at other normal light receiving portions. This causes an increase and causes an erroneous focus state to be detected. Since the variation in pixel values caused by such point defects is different from the uniform variation caused by random noise, the technique disclosed in Patent Document 2 described above does not match the results caused by such point defects. It is difficult to prevent erroneous detection of the focus state.

  In view of the above circumstances, an object of the present invention is to provide an imaging device that can capture an image in a highly accurate in-focus state, and an imaging method executed by such an imaging device.

An imaging apparatus of the present invention that achieves the above object includes an optical system that allows subject light to pass through and forms an image by the action of one or more lenses,
Represents an image composed of a plurality of pixels in which the color of the subject light imaged through the optical system is represented by a combination of a plurality of signal components corresponding to each of a plurality of predetermined colors for each of the plurality of pixels. An imaging unit for generating an image signal;
A covariance calculating unit that calculates covariance using a predetermined two signal components of the plurality of signal components for a plurality of pixels constituting an image represented by an image signal generated by the imaging unit;
And a lens moving unit that moves the lens in a direction in which the covariance increases along the optical axis of the optical system.

  According to the imaging apparatus of the present invention, the lens is moved in the direction in which the covariance for the two signal components increases. Since the covariance basically becomes larger as the image of the subject light (subject image) becomes clearer, the lens moves closer to the in-focus position by being moved in this way. This covariance does not change even if the variation of only one of the two signal components increases, and increases when the variation of both signal components increases in the same way. Here, since the random noise included in the image signal has almost no correlation between the signal components constituting the image signal, the influence of the random noise can be avoided by using covariance. The influence of so-called point defects, which are light-receiving portions damaged from the time of manufacture, in a CCD image sensor in which minute light-receiving portions are two-dimensionally arranged is also as follows by using this covariance. Can be avoided. As a method for generating the image signal, there is a method in which a subject image is color-separated into, for example, RGB three colors, and each of the three CCDs receives each color of the subject image to generate an image signal. A combination of RGB three-color signal components for a pixel is generated by a set of three light receiving portions located at positions corresponding to each other among the three CCDs. There is also a method of receiving a subject image with a single CCD. In this method, a plurality of light receiving elements constituting the CCD are arranged adjacent to each other by three light receiving elements that generate signal components of three colors of RGB. Dividing into sets, a combination of RGB three-color signal components for one pixel is generated by the set of these three light receiving elements. In any method, the light receiving part that generates a signal component of one color for a certain pixel is physically different from the light receiving part that generates a signal component of another color, and both of these light receiving parts are point defects. The establishment is low. As a result, the fluctuation of the signal component due to the point defect has almost no correlation between the signal components. Therefore, the influence of this point defect can also be avoided by using the covariance. According to the imaging apparatus of the present invention, since the lens can be brought close to the in-focus position based on this covariance, imaging can be performed in a highly accurate in-focus state with almost no influence of random noise or point defects. Can do.

Here, in the imaging device of the present invention, “a sensitivity setting unit that sets sensitivity when the imaging device captures an image;
A dispersion calculating unit for calculating a dispersion using a predetermined signal component of the plurality of types of signal components for the plurality of pixels;
The lens moving unit moves the lens along the optical axis of the optical system in a direction in which the covariance increases, and the lens moves along the optical axis of the optical system. A second mode for moving in the direction in which the dispersion increases, and when the sensitivity set by the sensitivity setting unit exceeds a predetermined sensitivity, the lens is moved in the first mode, and the sensitivity setting unit The form of “characterized by moving the lens in the second mode when the acquired sensitivity is equal to or lower than the predetermined sensitivity” is a preferable form.

  Since the calculation for obtaining the covariance is an operation for two signal components, it takes time and effort compared to the calculation for obtaining a variance sufficient for the calculation for one signal component. According to the imaging apparatus of the above preferred form, since the noise level in the image signal is high and the detection of the in-focus state due to dispersion is likely to be difficult, the covariance is used only when imaging with high sensitivity. It is.

In the image pickup apparatus of the present invention, “the image pickup unit includes a replaceable image pickup device mounted with a memory in which the number of point defects of the image pickup device is stored, and the image signal using the image pickup device. Which generates
A point defect number acquisition unit that acquires the number of point defects stored in the memory, and a variance that calculates a variance using a predetermined signal component of the plurality of types of signal components for the plurality of pixels A calculation unit,
The lens moving unit moves the lens along the optical axis of the optical system in a direction in which the covariance increases, and the lens moves along the optical axis of the optical system. A second mode for moving in a direction in which the dispersion increases, and when the number of point defects acquired by the point defect number acquisition unit exceeds a predetermined number, the lens is moved in the first mode, A form in which the lens is moved in the second mode when the number of point defects acquired by the point defect number acquisition unit is a predetermined number or less is also a preferable mode.

  According to the imaging device of this preferred form, the mounted image sensor includes many point defects, and the covariance is used only when there is a high possibility that it is difficult to detect the focused state by dispersion. Is.

In the imaging apparatus of the present invention, “a temperature detection unit that directly or indirectly detects the temperature of the imaging unit;
A dispersion calculating unit for calculating a dispersion using a predetermined signal component of the plurality of types of signal components for the plurality of pixels;
The lens moving unit moves the lens along the optical axis of the optical system in a direction in which the covariance increases, and the lens moves along the optical axis of the optical system. A second mode for moving in the direction in which the dispersion increases, and when the temperature detected by the temperature detector exceeds a predetermined temperature, the lens is moved in the first mode, and the temperature detector A mode in which the lens is moved in the second mode when the detected temperature is equal to or lower than a predetermined temperature is also a preferable mode.

  For example, it is known that a point defect in an image sensor such as a CCD becomes apparent as the ambient temperature increases, and a spot-like scratch or the like is likely to appear in a captured image. According to this preferable form of the imaging apparatus, the temperature of the imaging device is high, and as a result, spot-like scratches or the like are likely to appear in the captured image, and it is difficult to detect the in-focus state because the dispersion is affected by the scratches. It is efficient because covariance is used only when there is a high probability that

An imaging method of the present invention that achieves the above object is an imaging method executed by an imaging device that captures an image of subject light.
A plurality of signals corresponding to a plurality of predetermined colors for each of a plurality of pixels, and the colors of the subject light formed through an optical system that passes through the subject light and forms an image by the action of one or more lenses. An imaging process for generating an image signal representing an image composed of a plurality of pixels expressed by a combination of components;
A covariance calculation process for calculating covariance using a predetermined two signal components of the plurality of signal components for a plurality of pixels constituting an image represented by the image signal generated in the imaging process;
And a lens moving process for moving the lens in the direction in which the covariance increases along the optical axis of the optical system.

  According to these imaging methods of the present invention, it is possible to take an image in a highly accurate in-focus state.

  Note that the imaging method of the present invention is only shown here in its basic form, but this is merely for avoiding duplication, and the imaging method of the present invention is not limited to the basic form described above but has been described above. The form corresponding to the preferable form of an imaging device is included.

  As described above, according to the present invention, it is possible to capture an image in a highly accurate in-focus state.

  Hereinafter, first to fourth embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an external perspective view common to the digital cameras according to the first to fourth embodiments of the present invention.

  A zoom lens barrel 12 having an imaging lens 11 including a focus lens therein is provided at the center of the front surface of the digital camera shown in FIG. In addition, a flash light emitting device 13 that emits a flash in synchronization with imaging and an optical viewfinder objective window 14 are provided at the upper front of the digital camera. A slide-type power switch 15 is provided on the left side of the front surface of the digital camera. Further, a release button 16 is provided on the upper surface of the digital camera.

  The first embodiment of the present invention will be described below.

  FIG. 2 is a block diagram showing a circuit configuration of the digital camera according to the first embodiment of the present invention.

  In the digital camera 1 shown in FIG. 2, the zoom lens 21 and the focus lens 22 that constitute the imaging lens 11, the iris 23 whose aperture diameter can be adjusted in multiple stages, and the zoom lens 21 and the focus lens 22 are used. A CCD image sensor (hereinafter referred to as a CCD) 24 that receives the formed subject image and generates an analog signal is provided. Here, the CCD 24 has a minute light receiving portion arranged two-dimensionally. Three light receiving portions adjacent to each other correspond to one pixel, and each of the three light receiving portions is not shown. Each of R (red), G (green), and B (blue) subject light transmitted through the filter is received. Then, in each light receiving portion that receives light of each RGB color, an analog signal component of each color is generated, and an analog signal that expresses the color of each pixel by a combination of RGB three color signal components is generated.

  In addition, the digital camera 1 is provided with a reading circuit 25 that controls light reception by the CCD 24, reading of an image signal, and the like. The readout circuit 25 includes a timing generator that controls the light reception timing of the CCD 24 and the readout timing of the image signal, an amplification circuit that amplifies the analog signal read from the CCD 24 in accordance with the sensitivity of the digital camera 1, and the amplified circuit. And an A / D conversion circuit for converting the analog signal into a digital image signal. The digital camera 1 also includes an image input controller 26 that transmits a digital image signal from the readout circuit 25 to the bus line 50, and the digital image signal input via the bus line 50 as luminance (Y). An image signal processing circuit 27 for converting into a YC signal represented by color (C) is provided.

  Further, the digital camera 1 includes a compression processing circuit 28 that compresses the YC signal input via the bus line 50, and an NTSC (National TV Standards Committee) signal that converts the YC signal input via the bus line 50. A video encoder 29 is provided for converting into a video. The NTSC signal output from the video encoder 29 is supplied to a liquid crystal display (hereinafter referred to as LCD) 30 and an image is displayed on the LCD 30.

  The digital camera 1 includes a CPU 31 that controls the entire digital camera 1, a motor driver 32 that drives the zoom lens 21, a motor driver 33 that drives the iris 23, and a motor driver 34 that drives the focus lens 22. A release button 16 shown in FIG. 1 is also provided.

  In addition, the digital camera 1 includes a timer 36 for measuring various times, a digital image signal composed of RGB three color signal components, and an R color signal component and a G color signal component. A covariance calculation circuit 37 that calculates covariance, which will be described later, an AF detection circuit 38 that moves the focus lens 22 to the in-focus position by detecting a focus state based on the calculated covariance, and a digital image signal. AE & AWB detection circuit 39 that detects the exposure amount (hereinafter referred to as EV value) and white balance based on the brightness of the subject image based on the exposure value, and exposure control that performs exposure control based on the EV value detected by the AE & AWB detection circuit 39 Circuit 40, a memory (SDRAM) for temporarily storing various control programs and digital image signals used for controlling the digital camera 1 1, an image signal after being compressed by the compression processing circuit 28 media controller 42 for recording on the recording medium 100 is a portable recording medium are provided.

  Further, the digital camera 1 has an imaging mode for performing imaging in response to pressing of the release button 16 and a playback mode for reading the captured image recorded on the recording medium 100 from the recording medium 100 and displaying it on the LCD 30. A switch group 43 composed of various switches for switching and instructing the extension of the zoom lens 21, the power switch 15 shown in FIG. 1, and a power source that is controlled by turning on / off the power switch 15 and supplies power to each unit A circuit 44, a battery 45 as a power source for supplying power to the power supply circuit 44, and the flash light emitting device 13 also shown in FIG.

  Here, the imaging lens 11 corresponds to an example of an optical system according to the present invention, and the focus lens 22 corresponds to an example of a lens according to the present invention. Further, the combination of the CCD 24 and the readout circuit 25 corresponds to an example of an imaging unit according to the present invention. Further, the covariance calculation circuit 37 corresponds to an example of a covariance calculation unit according to the present invention, and the combination of the AF detection circuit 38 and the motor driver 34 for driving the focus lens 22 is a lens according to the present invention. This corresponds to an example of a moving unit.

  Next, a general imaging sequence of the digital camera 1 will be described.

  FIG. 3 is a flowchart showing an imaging sequence executed by the digital camera 1 shown in FIG.

  The process shown in the flowchart shown in FIG. 3 corresponds to an embodiment of the imaging method of the present invention.

  When the power is turned on, the process shown in the flowchart shown in FIG. 3 starts. First, the zoom lens barrel 12 shown in FIG. 1 is extended and the LCD 30 is turned on, and a through image that is a moving image for display is displayed on the LCD 30. It is displayed (step S101). Thereafter, the state is in a standby state until the release button 16 is half-pressed (step S102). When the release button 16 is half-pressed (Yes determination in step S102), first, focus control for moving the focus lens 22 to the in-focus position is performed. It is executed (step S110). This focus control (step S110) will be described in detail later.

  When the focus control (step S110) ends, the display on the LCD 30 is temporarily fixed to the image in a state where the focus lens 22 is in the in-focus position, and the exposure that is the brightness of the subject image is based on the image. The amount (EV value) is detected, and based on the detected EV value, the shutter time when the CCD 24 captures the subject image at the time of actual imaging, the aperture value indicating the aperture diameter of the iris 23, and the like are determined. Exposure control is executed in the exposure control circuit 40 such that the shutter time, aperture value, etc. are set to the determined values (step S103). In the process of step S103, it is also determined whether or not the flash can be emitted during actual imaging.

  When these processes are completed, the through image is displayed again on the LCD 30, and this time, a standby state is entered until the release button 16 is fully pressed (step S104). When the release button 16 is fully pressed (Yes determination in step S104), all pixels are read out under conditions such as the shutter speed, the aperture value, and the in-focus position set when the shutter button is pressed halfway. It is generated (step S105). Here, the process of step S105 corresponds to an example of an imaging process according to the present invention.

  Thereafter, an image represented by the image signal generated in the process of step S105 is displayed on the LCD 30, and the image signal is recorded on the recording medium 100 (step S106), and the imaging sequence represented by this flowchart is completed. After this process is completed, the through image is displayed again on the LCD 30 and the next imaging is possible.

  Next, details of the focus control (step S110) shown in FIG. 3 will be described.

  FIG. 4 is a flowchart showing the flow of focus control.

  When the process starts, first, the position of the focus lens 22 is adjusted to a predetermined initial position (step S111). Here, in the digital camera 1 of the present embodiment, the focus lens 22 can be moved stepwise from the initial position to the limit position. In the following, the position of the focus lens 22 at the arbitrary stage “k” is represented by “F (k)”, the stage corresponding to the initial position is represented by “A”, and the stage corresponding to the limit position is represented by “B”.

  When the position F (k) of the focus lens 22 is adjusted to the initial position F (A), RGB image signals in that state are first acquired (step S112). The processing in step S112 also corresponds to an example of an imaging process according to the present invention.

  When the image signal is acquired, the covariance for the R color signal component and the G color signal component is calculated for the image signal, as will be described below, and the calculated covariance is calculated. The distribution is temporarily stored in the memory 41 shown in FIG. 2 (step S113). The processing in step S113 corresponds to an example of a covariance calculation process according to the present invention.

  Here, before describing the covariance, the dispersion that has been conventionally used as a parameter for focus control will be described.

  For example, it is assumed that the dispersion of the R color signal component for the area of L × M = n pixels in the central portion of the image represented by the image signal among the RGB three color signal components is used for focus control.

  The R signal component corresponding to an arbitrary pixel in the area is R (i, j), the average value of the R signal component for all the pixels in the area is Rav, and the variance for the R signal component is distributed. Assuming Sr, this variance is expressed by the following equation.

  As shown in the equation (1), this variance is obtained by calculating the average of the square of the difference between the signal component and the average value for the R color. Accordingly, when the focus lens 22 is shifted from the in-focus position and the subject image is blurred and the luminance is generally uniform, the pixel values of many pixels in the captured image are close to the average value, and thus dispersion is achieved. Get smaller. On the other hand, when the focus lens is close to the in-focus position and a clear subject image is formed, various pixel values are distributed in the captured image according to the brightness of the subject image, resulting in a large variance. . In focus control based on dispersion, a position where such dispersion becomes the maximum value is detected as a focus position. However, when a lot of noise is generated in the image signal, the number of pixels whose signal components are greatly deviated from the average value is large, and as a result, the variance increases. Further, when a point defect occurs in the light receiving portion that generates the R color signal component, the signal component greatly deviates from the average value in the pixel corresponding to the point defect, and the number of such point defects increases. And dispersion will also increase. Such an increase in dispersion due to noise or point defects occurs regardless of the position of the focus lens 22, and therefore there is a high possibility of causing a problem of erroneous detection of the in-focus position.

  For this reason, in the present embodiment, as described below, a covariance having the property of being hardly affected by noise and point defects, that is, strong resistance to noise and point defects is used as a parameter for focus control.

  In the present embodiment, the covariance Srg for the R color signal component and the G color signal component is obtained for an area of L × M = n pixels in the center portion of the image represented by the image signal. Here, R (i, j) is an R color signal component corresponding to an arbitrary pixel in the area, Rav is an average value of R signal components for all the pixels in the area, and an arbitrary pixel in the area. G (i, j) corresponding to G, the average value of R signal components for all pixels in the area is Gav, and the covariance between the R signal component and the G signal component Is Srg, this covariance is expressed by the following equation.

  Hereinafter, the property that the covariance represented by the equation (2) is less susceptible to noise and point defects, that is, resistance, will be described in detail.

  As shown in the equation (2), the covariance is obtained by calculating the average of the multiplication results of the difference between each signal component and the average value for each of the R color and the G color. Here, the multiplication result for each pixel has a large value when both the R color difference and the G color difference are large, and the covariance also has a large value when there are many such multiplication results. Conversely, when one of the two differences is small, the multiplication result is small and the covariance is also a small value. That is, the covariance is large when the signal components are correlated with each other and deviate from the average value. One signal component deviates from the average value, but the other signal component is close to the average value. When the values are uncorrelated with each other, such as a value, the value is small.

  Here, most of the noise contained in the signal components of each of the RGB three colors in the image signal occurs uncorrelated between the signal components of the three RGB colors. Therefore, the deviation from the average value due to noise in each signal component is often uncorrelated with each other, and the increase in covariance due to such noise is small. That is, the covariance is hardly affected by noise and can be said to have strong resistance to noise.

  Next, the resistance to covariance point defects will be described with reference to FIG.

  FIG. 5 is a diagram schematically showing the effects of dispersion and covariance from point defects.

  In FIG. 5, pixels are assumed to be one-dimensionally arranged in order to simplify the description.

  Part (a) of FIG. 5 captures a certain subject image when point defects of the R light receiving portion are locally concentrated in two locations in a one-dimensional pixel array. The graph G1 which shows the signal component of each color at the time is described. In this graph G1, the horizontal axis indicates one-dimensional coordinates, and the vertical axis indicates the level of the signal component. In the example of part (a) of FIG. 5, a point defect that lowers the signal level occurs in the R light receiving portion and the G light receiving portion in the left local portion C1 in the drawing, and the right local portion C2 Has a point defect that raises the signal level in the R light receiving portion. Further, more point defects with respect to the light receiving portion of R color occur in the left local portion C1 than in the right local portion C2, and the fluctuation of the signal component is larger in the left local portion C1. Further, in the local portion C1 on the left side, point defects mainly occur in the R light receiving portion, and few point defects occur in the G light receiving portion. As a result, in the left local portion C1, the signal component varies more in the R color than in the G color.

  Part (b) of FIG. 5 is a graph G2 showing a change between dispersion and covariance in the minute area Ar1 when the one-dimensional minute area Ar1 shown in part (a) is moved in the arrow D direction. Are listed. In the flat part where the signal component does not change with respect to the coordinates in the graph G1 of the part (a), as shown in the graph G2 of the part (b), since the signal component is equal to the average value in the minute area Ar1, the variance is also covariance. Both become “0”. In addition, in the intermediate part C3 of the graph G1 of the part (a), the signal components of the respective colors change downward, and in the intermediate part C3, the signal components take various values with respect to the average value. A peak P2 occurs in the dispersion, and a peak P1 also occurs in the covariance.

  Here, in the local part C1 on the left side of the graph G1 of the part (a), the signal component of the R color and the signal component of the G color are fluctuated due to the point defect, so as shown in the graph G2 of the part (b), Both dispersion and covariance have peaks. However, since the covariance is affected by the small variation in the G color signal component, the covariance peak P3 is smaller than the dispersion peak P4 determined only by the variation in the R color signal component. Become. Furthermore, in the local portion C1 on the right side of the graph G1 of part (a), only the R color signal component varies due to point defects, and therefore, as shown in the graph G2 of part (b), a peak P5 occurs for dispersion. However, the covariance remains “0”.

  The variance or covariance used for focus control needs to represent the overall focus level of the main part of the subject image, and is thus obtained for the wide area Ar2 as shown in part (b) of FIG.

  Conventionally, focus control using dispersion, which is often performed, is such that the height of the peak P2 based on the subject image included in the dispersion in such a wide area Ar2 is the degree of focusing by the position of the focus lens 22 It is based on increasing / decreasing according to. That is, the height of the peak P2 based on the subject image is low when the focus lens 22 is out of the focus position and the image is unclear, and increases as the focus lens 22 approaches the focus position and the image becomes clear. The focus lens 22 is moved in the direction in which the dispersion increases, and the focus lens 22 is adjusted to a position where the dispersion becomes the maximum value, so that the in-focus position is detected. However, the dispersion in the wide area Ar2 also includes peaks P4 and P5 due to point defects as shown in part (b). Since the heights of these peaks P4 and P5 depend only on the number of point defects, they remain substantially constant regardless of the position of the focus lens 22. As a result, the dispersion in the wide area Ar2 shows a large value even though the focus lens 22 is not in the in-focus position, which is one of the causes of erroneous detection of the in-focus position when using the dispersion. It has become one.

  On the other hand, in the present embodiment, in the covariance in the wide area Ar2 used for focus control, as shown in Part (b), the number of peaks due to point defects included in the covariance is The number of such peaks is less, and the height of the peaks is lower than the height of the peaks in the dispersion. For this reason, the size of the covariance in the wide area Ar2 depends only on the peak P1 based on the subject image, and the in-focus position can be accurately detected. Thus, it can be said that covariance is hardly affected by point defects and has strong resistance to point defects.

  FIG. 6 is a diagram schematically showing the influence of the relationship between the position of the focus lens 22 and each of dispersion and covariance from noise and point defects.

  FIG. 6 shows how the line L1 representing the covariance in the wide area Ar2 and the line L2 representing the dispersion with respect to the position of the focus lens 22 change as random noise and point defects increase. It is shown. First, for random noise, the variance increases as the noise increases, but the covariance that is resistant to noise is almost unchanged. Also, for point defects, the dispersion greatly increases with increasing point defects and the peak at the in-focus position is considerably buried, whereas the covariance having resistance to point defects is almost It is invariant and a clear peak appears at the in-focus position.

  As described above, the covariance has strong resistance to noise and point defects, and in this embodiment, this covariance is used for focus control.

  Hereinafter, returning to FIG. 4, the description of the processing after step S112 in the flowchart of FIG. 4 will be continued.

  In step S113, the covariance when the position F (k) of the focus lens 22 is adjusted to the initial position F (A) is calculated and temporarily stored in the memory 41. Next, the current focus is obtained. It is determined whether or not the movement stage “k” of the lens 22 has reached the stage “B” corresponding to the limit position (step S114).

  If the stage “B” has not yet been reached (No determination in step S104), the moving stage “k” is raised by one stage (step S115), and the focus lens 22 is moved up by one stage. (Step S116), the process returns to step S112, and image capture in that state is executed. The processing from step S112 to step S116 is repeated until the movement stage of the focus lens 22 reaches the stage “B” corresponding to the limit position (Yes determination in step S114).

  When this stage “B” has been reached, from the stage “A” corresponding to the initial position to the stage “B” corresponding to this limit position, the memory 41 shown in FIG. The stage corresponding to the maximum covariance among the temporarily stored covariances is selected (step S117). Then, the focus lens 22 is moved to the position at the selected stage, that is, the focus position where the covariance is maximized (step S118), and the focus control shown in the flowchart of FIG. 3 ends. This step S118 corresponds to an example of a lens moving process according to the present invention. When the focus control ends, the process returns to the imaging process shown in the flowchart of FIG. 3, and the process following the focus control is executed.

  As described above, according to the digital camera 1 of the first embodiment, the focus control is performed based on the covariance having strong resistance to noise and point defects. An image can be taken.

  Next, a second embodiment of the present invention will be described.

  FIG. 7 is a block diagram showing a circuit configuration of a digital camera according to the second embodiment of the present invention.

  The digital camera 2 shown in FIG. 7 is that the parameter used for focus control is switched between covariance and dispersion according to the sensitivity determined by the exposure control circuit 40 in the first embodiment shown in FIG. Different from the digital camera 1 of FIG. Therefore, in the following description, attention is paid to the difference from the first embodiment, and redundant description is omitted. In FIG. 7, the same reference numerals as those in FIG. 2 are assigned to the same components as those shown in FIG. 2.

  The digital camera 2 shown in FIG. 7 performs covariance on the sensitivity acquisition circuit 51 that acquires the sensitivity determined by the exposure control circuit 40, and the calculation of parameters used for focus control according to the sensitivity acquired by the sensitivity acquisition circuit 51. An operation switching circuit 52 that switches between an operation by the operation circuit 37 and an operation by the distributed operation circuit 53, and a distributed operation circuit 53 that obtains the variance are provided. Here, the exposure control circuit 40 that determines the sensitivity of the digital camera 2 corresponds to an example of a sensitivity setting unit according to the present invention.

  In the digital camera 2, the AF detection circuit 54 performs focus control based on the covariance when the calculation switching circuit 52 switches to the calculation by the covariance calculation circuit 37, and performs the calculation by the distribution calculation circuit 53. When switched, focus control is performed based on dispersion. Here, the focus control based on the covariance corresponds to an example of the first mode according to the present invention, and the focus control based on the dispersion corresponds to an example of the second mode according to the present invention.

  The imaging sequence executed by the digital camera 2 of the second embodiment is the same as the imaging sequence shown in FIG. 3 executed by the digital camera 2 of the first embodiment, except for focus control. Therefore, the following description will focus on focus control executed by the digital camera 2.

  FIG. 8 is a flowchart showing the flow of focus control executed by the digital camera 2 shown in FIG.

  When the process starts, first, the sensitivity determined by the exposure control circuit 40 is acquired by the sensitivity acquisition circuit 51 (step S201). Then, it is determined whether or not the acquired sensitivity is higher than a predetermined threshold (step S202). When the sensitivity is higher than the threshold (Yes determination in step S202), focus control using covariance is executed (step S203). When the sensitivity is lower than the threshold (No determination in step S202), the variance is Focus control using is performed (step S204). Note that the focus control executed in step S203 is the same as the focus control represented by the flowchart of FIG. Further, since the focus control executed in step S204 is the same control except that the covariance in the focus control represented by the flowchart of FIG. 4 is replaced with the variance, the focus control executed in this step S204 is further controlled. Description is omitted.

  Here, the calculation for obtaining the covariance is a calculation for the RG two-color signal component as shown in the above equation (2), and only for the R signal component in the above equation (1). Compared to the calculation of variance, it takes time and effort. Therefore, in the present embodiment, only when the sensitivity of imaging is higher than a predetermined threshold, the noise level included in the image signal obtained by imaging is increased, and the accuracy of focus control based on dispersion may be reduced. Focus control based on covariance is executed. As a result, according to the digital camera 2 of the second embodiment, it is possible to efficiently perform imaging in a highly accurate in-focus state similar to the first embodiment.

  Next, a third embodiment of the present invention will be described.

  FIG. 9 is a block diagram showing a circuit configuration of a digital camera according to the third embodiment of the present invention.

  The digital camera 3 shown in FIG. 9 is the same as the second embodiment in that the parameter used for focus control is switched between covariance and variance. It differs from the second embodiment in that it is performed according to the number of point defects. Therefore, in the following, an explanation will be given focusing on the differences from the second embodiment, and duplicate explanation will be omitted. In FIG. 9, the same reference numerals as those in FIG. 7 are given to components equivalent to the components shown in FIG. 7.

  Here, the replaceable CCD 55 is mounted on the digital camera 3 shown in FIG. The CCD 55 has a ROM 55a, and the ROM 55a stores the number of point defects obtained by inspection at the time of shipment of the CCD 55. Further, the digital camera 3 includes a point defect number acquisition circuit 56 for acquiring the number of point defects stored in the ROM 55a. Here, the ROM 55a corresponds to an example of a “memory storing the number of point defects” according to the present invention, and the point defect number acquisition circuit 56 corresponds to an example of a point defect number acquisition unit according to the present invention. In this digital camera 3, the calculation switching circuit 57 calculates the parameters used for focus control according to the number of point defects acquired by the point defect number acquisition circuit 56, and the calculation by the covariance calculation circuit 37. Switching between calculation by the calculation circuit 53 is performed.

  FIG. 10 is a flowchart showing the flow of focus control executed by the digital camera 3 shown in FIG.

  When the process starts, first, the number of point defects of the CCD 55 is acquired by the point defect number acquisition circuit 56 from the ROM 55a of the CCD 55 currently mounted on the digital camera 3 (step S301). Then, it is determined whether or not the acquired number of point defects is greater than a predetermined threshold (step S302). When the number of point defects is larger than the threshold (Yes determination in step S302), focus control using covariance is executed (step S303), and when the number of point defects is smaller than the threshold (No in step S302). Determination) and focus control using dispersion is executed (step S304). Note that redundant description of the focus control executed in steps S303 and S304 is omitted.

  In the present embodiment, focus control based on covariance is executed only when the number of point defects of the mounted CCD 55 is greater than a predetermined threshold and the accuracy of focus control based on variance may be reduced. As a result, according to the digital camera 3 of the third embodiment, it is possible to efficiently execute imaging in a highly accurate in-focus state similar to the first embodiment.

  Next, a fourth embodiment of the present invention will be described.

  FIG. 11 is a block diagram showing a circuit configuration of a digital camera according to the fourth embodiment of the present invention.

  The digital camera 4 shown in FIG. 11 is the same as the second embodiment and the third embodiment described above in that the parameter used for focus control is switched between covariance and dispersion. This embodiment is different from these embodiments in that it is performed according to the temperature. Therefore, in the following description, attention is paid to the differences from the second embodiment and the third embodiment, and duplicate descriptions are omitted. In FIG. 11, the same reference numerals as those in FIG. 7 are assigned to the same components as those shown in FIG. 7.

  The digital camera 4 shown in FIG. 11 includes a temperature detection circuit 58 that acquires the temperature of the CCD 24. Here, the temperature detection circuit 58 corresponds to an example of a temperature detection unit according to the present invention. In the digital camera 3, the calculation switching circuit 59 calculates the parameters used for focus control according to the temperature detected by the temperature detection circuit 58 by the calculation by the covariance calculation circuit 37 and the distribution calculation circuit 53. Switch between operations.

  FIG. 12 is a flowchart showing the flow of focus control executed by the digital camera 4 shown in FIG.

  When the process starts, the temperature detection circuit 58 first determines whether or not a predetermined time has elapsed since the digital camera 4 was started based on the time measured by the timer 36 shown in FIG. 11 (step S401). ) When a predetermined time has elapsed since the start (Yes determination in step S401), the temperature of the CCD 24 is detected (step S402). Then, it is determined whether or not the detected temperature is higher than a predetermined threshold (step S403).

  When the detected temperature is higher than the threshold value (Yes determination in step S403), focus control using covariance is executed (step S404), and a predetermined time has not elapsed since the start (step S404). If the detected temperature is lower than a predetermined threshold (No determination in step S403), focus control using dispersion is executed (step S405). Note that redundant description of the focus control executed in steps S404 and S405 is omitted.

  In the present embodiment, after a predetermined time has elapsed since the start, the temperature of the CCD 55 is higher than a predetermined threshold, and a point defect in the CCD 24 becomes obvious, causing a point-like flaw in an image captured for focus control, and the influence of the flaw. The focus control based on the covariance is executed only when there is a risk that the accuracy of the focus control based on the variance may be reduced. As a result, according to the digital camera 4 of the fourth embodiment, it is possible to efficiently perform imaging in the in-focus state as in the first embodiment.

  In the above, a digital camera has been exemplified as an embodiment of the present invention. However, the present invention is not limited to this, and the embodiment of the present invention can be used for, for example, a mobile phone having a camera function or a video shooting. It may be a video camera or the like.

  Further, in the above, as an example of the lens moving unit referred to in the present invention, the focus lens is moved from a predetermined initial position to a limit position, and a position where the covariance is maximized is found. However, the lens moving unit referred to in the present invention is not limited to this. For example, the focus lens is moved in a direction in which the covariance increases, and the focus lens is at a position where the change of the covariance is maximized. It may be a thing that stops the movement of.

It is an external appearance perspective view common to each digital camera which is each 1st to 4th embodiment of this invention. It is a block diagram which shows the circuit structure of the digital camera which is 1st Embodiment of this invention. 3 is a flowchart showing an imaging sequence executed by the digital camera 1 shown in FIG. It is a flowchart showing the flow of focus control. It is a figure which shows typically the influence which dispersion | distribution and covariance each receive from a point defect. It is a figure which shows typically the influence which the relationship between the position of the focus lens 22, and each of dispersion | distribution and covariance receives from noise or a point defect. It is a block diagram which shows the circuit structure of the digital camera which is 2nd Embodiment of this invention. It is a flowchart showing the flow of the focus control performed with the digital camera 2 shown in FIG. It is a block diagram which shows the circuit structure of the digital camera which is 3rd Embodiment of this invention. 10 is a flowchart showing a flow of focus control executed by the digital camera 3 shown in FIG. 9. It is a block diagram which shows the circuit structure of the digital camera which is 4th Embodiment of this invention. 12 is a flowchart showing a flow of focus control executed by the digital camera 4 shown in FIG.

Explanation of symbols

1, 2, 3, 4 Digital camera 11 Imaging lens 12 Zoom lens barrel 13 Flash light emitting device 14 Optical viewfinder objective window 15 Power switch 16 Release button 21 Zoom lens 22 Focus lens 23 Iris 24, 55 CCD
25 Reading Circuit 26 Image Input Controller 27 Image Signal Processing Circuit 28 Compression Processing Circuit 29 Video Encoder 30 LCD
31 CPU
32, 33, 34 Motor driver 36 Timer 37 Covariance calculation circuit 38, 54 AF detection circuit 39 AE & AWB detection circuit 40 Exposure control circuit 41 Memory 42 Media controller 43 Switch group 44 Power supply circuit 45 Battery 50 Bus line 51 Sensitivity acquisition circuit 52, 57, 59 Operation switching circuit 53 Distributed operation circuit 55a ROM
56 point defect number acquisition circuit 58 temperature detection circuit 100 recording medium

Claims (5)

An optical system that allows subject light to pass therethrough and forms an image by the action of one or more lenses;
Represents an image composed of a plurality of pixels in which the color of the subject light imaged through the optical system is represented by a combination of a plurality of signal components corresponding to each of a plurality of predetermined colors for each of the plurality of pixels. An imaging unit for generating an image signal;
A covariance calculating unit that calculates covariance using a predetermined two signal components of the plurality of signal components for a plurality of pixels constituting an image represented by an image signal generated by the imaging unit;
An image pickup apparatus comprising: a lens moving unit that moves the lens in a direction in which the covariance increases along the optical axis of the optical system. A sensitivity setting unit for setting the sensitivity when the imaging apparatus captures an image;
A dispersion calculating unit that calculates a dispersion using a predetermined one of the plurality of types of signal components for the plurality of pixels;
The lens moving unit moves the lens along the optical axis of the optical system in a direction in which the covariance increases, and the lens moves along the optical axis of the optical system. A second mode for moving in a direction in which dispersion increases, and when the sensitivity set by the sensitivity setting unit exceeds a predetermined sensitivity, the lens is moved in the first mode, and the sensitivity setting unit The imaging apparatus according to claim 1, wherein when the acquired sensitivity is equal to or lower than a predetermined sensitivity, the lens is moved in the second mode. The image pickup unit is configured such that a replaceable image sensor is mounted together with a memory in which the number of point defects of the image sensor is stored, and the image signal is generated using the image sensor.
A point defect number acquisition unit for acquiring the number of point defects stored in the memory; and a variance for calculating a variance using a predetermined one of the plurality of types of signal components for the plurality of pixels A calculation unit,
The lens moving unit moves the lens along the optical axis of the optical system in a direction in which the covariance increases, and the lens moves along the optical axis of the optical system. A second mode that moves in a direction in which the dispersion increases, and when the number of point defects acquired by the point defect number acquisition unit exceeds a predetermined number, the lens is moved in the first mode, The imaging apparatus according to claim 1, wherein the lens is moved in the second mode when the number of point defects acquired by the point defect number acquisition unit is a predetermined number or less. A temperature detection unit for directly or indirectly detecting the temperature of the imaging unit;
A dispersion calculating unit that calculates a dispersion using a predetermined one of the plurality of types of signal components for the plurality of pixels;
The lens moving unit moves the lens along the optical axis of the optical system in a direction in which the covariance increases, and the lens moves along the optical axis of the optical system. A second mode for moving in a direction in which the dispersion increases, and when the temperature detected by the temperature detector exceeds a predetermined temperature, the lens is moved in the first mode, and the temperature detector The imaging apparatus according to claim 1, wherein when the detected temperature is equal to or lower than a predetermined temperature, the lens is moved in the second mode. In an imaging method executed by an imaging device that captures an image of subject light,
A plurality of signals corresponding to a plurality of predetermined colors for each of a plurality of pixels, and the colors of the subject light formed through an optical system that passes through the subject light and forms an image by the action of one or more lenses. An imaging process for generating an image signal representing an image composed of the plurality of pixels expressed by a combination of components;
A covariance calculation process for calculating covariance using a predetermined two signal components of the plurality of signal components for a plurality of pixels constituting an image represented by the image signal generated in the imaging process;
An imaging method comprising: a lens moving process for moving the lens in a direction in which the covariance increases along the optical axis of the optical system.

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