JP2007286474A - Focus detector and photographing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detector capable of achieving improvement in focusing accuracy when a point light source exists. <P>SOLUTION: The focus detector, which calculates a focus evaluated value based on an imaging signal for each of a plurality of focus detection areas A1 to A5 respectively and calculates a focusing position based on the calculated focus evaluated value, is equipped with: a saturation decision means for deciding whether or not a saturation signal is included in the imaging signal for each of the focus detection areas A1 to A5; and a focusing position calculation means for calculating the focusing position based on the focus evaluated values of non-saturation focus detection areas A1, A2 and A5 decided as areas where the saturation signal is not included in the imaging signal by the saturation decision means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focus detection device and an imaging device including the focus detection device.

  2. Description of the Related Art A camera that captures a subject image using an image sensor such as a CCD and performs autofocus (AF) by a contrast method based on the image signal is known (see, for example, Patent Document 1).

JP 2004-246013 A

  However, if there is a high-brightness subject such as a point light source in the AF area, the imaging signal related to the high-brightness subject is saturated, the reliability of the focus evaluation value is lowered, and the focus position may not be detected correctly.

The invention of claim 1 is applied to a focus detection device that calculates a focus evaluation value based on an imaging signal for each of a plurality of focus detection areas, and calculates a focus position based on the calculated focus evaluation value. Saturation determination means for determining whether or not a saturation signal is included for each focus detection area, and based on the focus evaluation value of the non-saturation focus detection area determined by the saturation determination means that the saturation signal is not included And an in-focus position calculating means for calculating an in-focus position.
According to a second aspect of the present invention, in the focus detection device according to the first aspect, when the focus position calculation based on the focus evaluation value of the non-saturated focus detection region is impossible, the saturation determination means includes a saturation signal. The in-focus position is calculated based on the focus evaluation value of the saturated focus detection area determined to be.
According to a third aspect of the present invention, a camera includes the focus detection apparatus according to the first or second aspect.

  According to the present invention, since the focusing operation is performed based on the focus evaluation value in the non-saturated focus detection area, the focusing operation can be performed without being affected by the saturation signal having low reliability. It is possible to improve the focusing accuracy.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a photographing apparatus according to an embodiment of the present invention. FIG. 1 is a block diagram showing the main configuration of an autofocus (AF) electronic camera. The electronic camera includes a lens unit 1, an image sensor 2, an A / D converter 3, a memory 4, and an image processing circuit. 5, a control circuit 8, a CPU 14, a motor 12, and a focus control mechanism 13.

  The lens unit 1 includes a focus lens, and may be a single focal length (fixed focus) lens, or may be a variable focus such as a zoom lens or a step zoom lens. The focus lens is a lens that adjusts the focal position so that the subject light that has passed through the lens unit 1 forms an image on the imaging surface of the imaging device 2. By driving the focus control mechanism 13 with the motor 12, the focus lens moves forward and backward in the optical axis direction. The motor 12 is driven by a lens driving signal output from the CPU 14.

  The image sensor 2 is configured by, for example, a two-dimensional CCD image sensor. The imaging element 2 captures a subject image on the imaging surface and outputs an imaging signal corresponding to each pixel. The image signal output from the image sensor 2 has a different signal level depending on the intensity of light incident on each pixel. In this embodiment, a CCD image pickup device is used as the image pickup device 2, but a CMOS sensor, a CID, or the like may be used instead of the CCD. The control circuit 8 generates a timing signal for the image sensor 2 and sends it to the image sensor 2.

  The imaging signal output from the imaging device 2 is converted into a digital signal by the A / D converter 3 and then stored in the memory 4. The image processing circuit 5 performs compression processing on the image data stored in the memory 4 by a predetermined method (for example, JPEG), and stores the compressed image data in the external storage circuit 6. The image processing circuit 5 also performs decompression processing when the compressed data recorded in the external storage circuit 6 is read and decompressed. The external storage circuit 6 is configured by a data storage member such as a memory card, for example.

  The CPU 14 includes an AE / AWB circuit 7, a band pass filter 9, an integration circuit 10, an AF circuit 11, and a saturation determination unit 15. The AE / AWB circuit 7 performs known exposure calculation and white balance adjustment processing. The white balance adjustment process is performed on the image data stored in the memory 4.

  The CPU 14 is connected to the control circuit 8 and the memory 4 and performs various calculations such as focus detection (AF), photometry (AE), white balance adjustment (AWB) of the electronic camera, and sequence control of the camera operation. Various operation signals are input to the CPU 14 from an operation member (not shown). The CPU 14 comprehensively manages focus detection control, exposure control, color balance control, and the like of the electronic camera according to operation signals input from the operation member.

  The band pass filter 9 is a filter that extracts a high frequency component from image data of an imaging region corresponding to a focus detection region (focus area) among image data before image processing stored in the memory 4. The image data after the filter processing by the bandpass filter 9 has a low frequency component, particularly a direct current component, removed compared to the image data before the filter processing. In the camera of the present embodiment, as shown in FIG. 2, a plurality of focus areas A1 to A5 are set in the object scene, and the bandpass filter 9 performs filter processing for each focus area.

  The integrating circuit 10 performs an integrating process based on the image data that has been filtered by the bandpass filter 9. The AF circuit 11 obtains a focus evaluation value based on the integrated value obtained by the integrating circuit 10. The saturation determination unit 15 reads the image data of each of the AF areas A1 to A5 from the memory 4 and determines whether or not the luminance signal is equal to or higher than the saturation level. In the present embodiment, the filter processing and integration processing by the bandpass filter 9 and the integration circuit 10 are processed by software by the CPU 14, but these functions may be realized by hardware.

  FIG. 3 is a diagram illustrating an example of the relationship between the position of the focus lens and the focus evaluation value. In FIG. 3, the horizontal axis is the position of the focus lens, and the vertical axis is the focus evaluation value. The lens position D1 where the focus evaluation value is maximized is the focus position of the focus lens with respect to the subject. By the way, as shown in FIG. 2, when a point light source L1 such as a light adorned with a tree is in the AF area, the output from the pixel capturing the point light source L1 may be saturated. In that case, the profile of the acquired focus evaluation value becomes a curve 41 shown in FIG.

  As shown by the curve 41, the focus evaluation value at the original focusing lens position D1 decreases, and the peak of the focus evaluation value appears at the lens positions before and after that. Therefore, when performing AF with the closest focus, if the close peak position D2 is closer to the main subject S1, the peak position D2 may be erroneously determined as the in-focus position. In the present embodiment, focus determination is performed using an algorithm that can avoid such a problem.

<Description of AF processing>
FIG. 5 is a flowchart showing an example of the AF operation in the present embodiment, and shows an AF process performed by the CPU 14. The process shown in FIG. 5 is started, for example, when a half-press operation signal is input to the CPU 14 from a release switch (not shown). In step # 1, data and flags necessary for AF processing are initialized. An example of the flag is a saturation flag indicating that the AF area is saturated.

  In step # 2, a search initial value for performing a focusing operation is set. The search initial value includes a search start position and a search end position of the focus lens, a lens moving speed during the search, and the like. Note that the movement time of the focus lens from the search start position to the search end position is determined by the movement speed. FIG. 6 is a diagram showing the lens position in the search operation, where the vertical axis represents the lens position and the horizontal axis represents time. The number of sampling points (black circles in the figure) in the search operation of FIG. 6 depends on the lens moving speed. If the lens moving speed is slowed down, the number of sampling points increases.

  Further, in the present embodiment, as shown in FIG. 6, the search start position is set at the nearest end and the search end position is set at the infinite (∞) end. Note that the search start position may be set to the infinite end and the search end position may be set to the close end, or may be set to an optimum value according to the lens position and the shooting mode at the start of the AF operation. In step # 3, the CPU 14 outputs a drive signal to the motor 12, and moves the focus lens (not shown) of the lens unit 1 to the search start position (closest end).

  Subsequent steps # 4 to # 7 show the processing of the search operation. In step # 4, the focus evaluation values of the AF areas A1 to A5 are calculated based on the image data stored in the memory 4. The calculated focus evaluation value is stored as an evaluation value history for each of the AF areas A1 to A5 in association with the lens position at the time of image data acquisition.

  In this embodiment, the image data once stored in the memory 4 is read into the CPU 14 and the evaluation value is calculated. However, the image data output from the A / D converter 3 is sequentially converted into a bandpass filter. The evaluation value may be calculated simultaneously with the data transfer. By adopting a configuration in which data is sequentially transferred to the band-pass filter 9, it is possible to reduce evaluation value calculation delay as compared with a case where data is temporarily stored in the memory 4.

  In step # 5, saturation determination based on the image data stored in the memory 4 is performed for each of the AF areas A1 to A5. The saturation determination unit 15 obtains a luminance signal in the AF area and determines whether or not the maximum value of the luminance signal is equal to or higher than a preset saturation level. If it is determined that the saturation level is exceeded, a saturation flag is set. As the saturation level, for example, when the luminance signal is AD-converted with 12 bits, the signal level 3800 may be set as the saturation level.

  The saturation determination level is set to an optimum value depending on the characteristics of the image sensor 2. For example, when the image sensor 2 is a CCD, there may be a case where a transfer method in which the output addition method of each pixel is different can be set. When the saturation charge amount varies depending on the transfer method, the saturation determination level also varies. In such a case, the saturation level may be individually determined according to the transfer method.

  In step # 6, the focus lens is moved at the moving speed set in step # 2. In step # 7, it is determined whether or not the lens position of the focus lens has reached the search end position set in step # 2. If it is determined that the lens has reached, the process proceeds to step # 8, and is determined not to have been reached. Returning to step # 4, the search operation is continued.

  In step # 8, a saturated area is determined. That is, for each of the AF areas A1 to A5, it is determined whether a saturation flag is set, and the AF area where the saturation flag is set is determined as a saturation area. For example, in the example shown in FIG. 2, the AF areas A3 and A4 including the point light source L1 are determined as the saturation areas.

  Since the above-described processing of step # 5 for setting the saturation flag is performed at each sampling point during the search operation, in the case of the present embodiment, the maximum value of the luminance signal in any one of the plurality of samplings. If it is determined that the level is equal to or higher than the saturation level, the AF area is determined to be a saturated area. If the maximum value of the luminance signal is equal to or higher than the saturation level even once during the search operation, instead of determining as the saturated area, it is determined as the saturated area when the number of times exceeding the saturation level is equal to or greater than the predetermined number. May be.

  In Step # 9, based on the evaluation value history for each AF area acquired in Step # 4, the in-focus positions PosIF Area [A1] to PosIF Area [A5] of the AF areas A1 to A5 are calculated. In step # 10, based on the determination of the saturated area in step # 8, it is composed of one priority group composed of AF areas A1, A2, and A5 that are not saturated areas, and AF areas A3 and A4 determined as saturated areas. Into two priority groups.

  In step # 11, the final in-focus position PosInfocus is calculated according to the grouping in step # 10. FIG. 7 is a flowchart showing the detailed process of step # 11. In determining the final focus position PosInfocus, the priority 1 group has a higher priority than the priority 2 group. In step # 101, it is checked whether or not the focus position can be detected for all the AF areas A1, A2, and A5 included in the priority group 1, and it is determined whether or not all the AF areas cannot be detected. . For example, when the peak value of the focus evaluation value of the AF area is smaller than a threshold that can be regarded as in-focus, or the difference between the maximum value and the minimum value of the focus evaluation value is smaller than a predetermined value, the AF area is detected. Impossible.

  If it is determined in step # 101 that all cannot be detected, the process proceeds to step # 103. If the in-focus position can be detected in any AF area included in the priority group 1, the process proceeds to step # 102. When the process proceeds to step # 102, the closest focus position among the focus positions of the AF areas A1, A2, and A5 is set as the final focus position PosInfocus.

  On the other hand, if it is determined in step # 101 that it is all undetectable and the process proceeds to step # 103, it is impossible to detect the in-focus position for all AF areas A3 and A4 included in the priority 2 group in step # 103. It is determined whether or not all AF areas are undetectable. Since the AF areas A3 and A4 included in the priority 2 group include the point light source L1, peaks may occur on both sides of the original in-focus position as shown in FIG. In such a case, the undetectable determination as described above is performed for the higher peak (lens position D2).

  If it is determined in step # 103 that all cannot be detected, the process proceeds to step # 105, and if the in-focus position can be detected in any of the AF areas A3 and A4 included in the priority 2 group, the process proceeds to step # 104. In step # 104, the closest focus position among the focus positions where the AF areas A3 and A4 of the priority two groups can be detected is set as the final focus position PosInfocus. In this case, the focus position of each AF area may be calculated by the same method as that for the priority 1 group, or as described in the patent application (Japanese Patent Application Laid-Open No. 2004-246013) filed by the present inventor. The focus position may be calculated by a method that takes into account the saturation signal.

  Here, an outline of the method for calculating the in-focus position in the AF areas A3 and A4 including the point light source L1 and where the saturation signal exists will be described. For the AF area where the saturation signal exists, the second evaluation value AFv2 obtained by integrating the image pickup signal that does not pass through the bandpass filter 9 is used together with the focus evaluation value (here, the focus evaluation value AFv1) described above. Using this, the focus position for each AF area is calculated.

  The evaluation value AFv2 is acquired and stored at the same timing as the focus evaluation value AFv1 during the search operation process described above. A curve 42 in FIG. 4 shows a profile of the evaluation value AFv2, and has a minimum at the in-focus position D1. Further, a difference Δ = AFv2−AFv1 between the evaluation value AFv2 and the focus evaluation value AFv1 is obtained for each sampling point, and the maximum value is selected from these differences Δ and set as Δmax. Then, a difference between the maximum value Δmax and each difference Δ is set as an evaluation value AFv3 (= Δmax−Δ). Since the lens position at which the evaluation value AFv3 is maximum coincides with the focus position D1, the lens position (focus position) at which the evaluation value AFv3 is maximum is calculated for each AF area A3, A4. Then, among these focusing positions, the closest focusing position is set as the final focusing position PosInfocus.

  Alternatively, the AF areas A3 and A4 where the saturation signal exists may be regarded as one area, and the closest focus position may be obtained. The difference Δ in this case is calculated as Δ = ΣAFv2−ΣAFv1. Σ is summed with respect to the evaluation value of the AF area A3 and the evaluation value of the AF area A4.

  On the other hand, if it is determined in step # 103 that all cannot be detected and the process proceeds to step # 105, a predetermined position determined in advance is set as the final focus position PosInfocus in step # 105. The predetermined position may be changed according to the zoom position and the brightness, and is selected, for example, as a subject distance of about 2 m.

  Returning to FIG. 5, in step # 12, the motor 12 is driven to move the focus lens to the final focusing position PosInfocus calculated in step # 11, and the focusing operation process shown in FIG. 5 is ended.

The embodiment described above has the following operational effects.
(1) It is determined for each focus detection region A1 to A5 whether or not a saturation signal is included in the imaging signal, and the focus of the unsaturated focus detection regions A1, A2, and A5 determined as not including the saturation signal. Based on the evaluation value, the focusing operation was performed. That is, the focus position is calculated for each of the focus detection areas A1, A2, and A5, and the closest focus position among them is set as the final focus position PosInfocus. Therefore, the focus position is affected by a low-reliability saturation signal. The focusing operation can be performed without any problem, and the focusing accuracy can be improved.
(2) When the focus position calculation based on the focus evaluation values of the non-saturated focus detection areas A1, A2, and A5 is impossible, the saturated focus detection area A3 that is determined to contain a saturation signal. , A based on the focus evaluation value of A, the in-focus position is calculated, so that it is possible to avoid the occurrence of the in-focus situation as much as possible.

  In the above-described embodiment, the camera has been described as an example. However, the present invention is not limited to the camera and can be applied to various photographing apparatuses. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

It is a figure explaining the camera which concerns on one embodiment of this invention. It is a figure which shows the relationship between AF area A1-A5 on a screen, main to-be-photographed object S1, and point light source L1. It is a figure which shows an example of the relationship between the position of a focus lens, and a focus evaluation value. It is a figure which shows focus evaluation value AFv1 and evaluation value AFv2 in case there exists a saturation signal. It is a flowchart which shows an example of AF operation | movement in this Embodiment. It is a figure which shows the lens position in search operation | movement. It is a flowchart which shows the detailed operation | movement of step # 11 of FIG.

Explanation of symbols

  1: Lens unit, 2: Image sensor, 3: A / D converter, 4: Memory, 9: Band pass filter, 10: Integration circuit, 11: AF circuit, 14: CPU, 15: Saturation determination unit, A1 to A1 A5: AF area, L1: Point light source

Claims (3)

In a focus detection device that calculates a focus evaluation value based on an imaging signal for each of a plurality of focus detection regions, and calculates a focus position based on the calculated focus evaluation value.
Saturation determination means for determining for each focus detection region whether or not a saturation signal is included in the imaging signal;
A focus position calculating means for calculating a focus position based on a focus evaluation value of a non-saturated focus detection area determined by the saturation determination means as not containing a saturation signal. Detection device. The focus detection apparatus according to claim 1,
The in-focus position calculation means is a saturated focus that is determined by the saturation determination means to include a saturation signal when the in-focus position calculation based on the focus evaluation value of the non-saturation focus detection area is impossible. A focus detection apparatus that calculates a focus position based on a focus evaluation value of a detection area.   An imaging apparatus comprising the focus detection apparatus according to claim 1.

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