JP2009058720A - Focus detector and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detector capable of appropriately controlling the moving direction of a focus lens. <P>SOLUTION: The focus detector is equipped with: an integrating means 12 integrating a signal from an imaging device 2 picking up an image through a photographic lens 1; an acquiring means 12 successively acquiring focus evaluated value information showing relation between a lens position and an integrated value by the integrating means 12 while the focus lens of the photographic lens 1 is moving; a calculating means 12 calculating median for a predetermined number of focus evaluated values out of the focus evaluated value information; a detecting means 12 detecting the maximum value of the focus evaluated value information; and a deciding means 12 deciding whether or not the moving direction of the focus lens is reversed based on the maximum value and the median. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a camera focus detection apparatus.

  A camera focus detection method is known in which a subject image is picked up using an image pickup device such as a CCD image sensor, and an adjustment state of a focus position by a photographing lens is detected based on an image pickup signal output from the image pickup device (patent). Reference 1). In particular, the focus detection method called the hill-climbing method is such that the focus evaluation value indicating the sharpness (contrast) takes the maximum value while driving the focus lens forward and backward in the optical axis direction, that is, the data by the high frequency component of the imaging signal. The focus position is detected.

JP 2003-295040 A

  In the prior art, when an abnormal value is generated due to noise included in the imaging signal, there is a problem that it is not possible to appropriately control the moving direction of the focus lens performed by determining the peak of the “mountain” indicating the focus evaluation value. .

(1) The focus detection device according to the present invention is configured to integrate a signal from an image pickup element picked up through a photographing lens, and a relationship between the lens position and the integrated value obtained by the integrating device while the focus lens of the photographing lens is moving. Acquisition means for sequentially acquiring the focus evaluation value information to be shown, calculation means for calculating the median for a predetermined number of focus evaluation values in the focus evaluation value information, detection means for detecting the maximum value of the focus evaluation value information, and the maximum value And determining means for determining whether to reverse the moving direction of the focus lens based on the median.
(2) In the focus detection apparatus according to the first aspect, the calculating means can increase the predetermined number when the captured image changes.
(3) In the focus detection apparatus according to (1) or (2), when the median calculated for the most recent predetermined number of focus evaluation values does not decrease beyond the predetermined value from the previously calculated median, It is preferable to determine the maintenance of the moving direction of the lens.
(4) In the focus detection apparatus according to (3), the deciding means decreases the median calculated for the most recent predetermined number of focus evaluation values from the previously calculated median beyond a predetermined value, and the latest median It is preferable to determine the reversal of the moving direction of the focus lens when is smaller than a determination threshold smaller than the maximum value.
(5) A camera according to the present invention includes the focus detection device according to any one of claims 1 to 4.

  According to the present invention, the moving direction of the focus lens can be appropriately controlled.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining a main configuration of an autofocus (AF) electronic camera according to an embodiment of the present invention. In FIG. 1, an electronic camera includes a lens unit 1, an image sensor 2, an A / D converter 3, a memory 4, an image processing circuit 5, a control circuit 8, a CPU 12, a motor 13, and focus control. A mechanism 14 and an operation member 15 are provided.

  The lens unit 1 includes a focus lens (not shown). The focus lens is a lens that adjusts the focal position so that the subject luminous flux that has passed through the lens unit 1 forms an image on the imaging surface of the imaging device 2. When the motor 13 drives the focus control mechanism 14, the focus control mechanism 14 moves the focus lens back and forth in the optical axis direction. The motor 13 is driven by a lens driving signal output from the CPU 12.

  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. Note that the image sensor 2 may be configured using a MOS sensor, a CID, or the like 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 image pickup signal output from the image pickup 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 12 includes an AE / AWB circuit 7, a band pass filter (BPF) 9, an integration circuit 10, and an AF circuit 11. The CPU 12 is connected to the control circuit 8, the memory 4, and the like, and performs various calculations such as focus detection (AF), photometry (AE), white balance adjustment (AWB) of the electronic camera, and sequence control of camera operation. Various operation signals are input from the operation member 15 to the CPU 12. The CPU 12 comprehensively manages focus detection control, exposure control, and color balance control of the electronic camera in accordance with an operation signal input from the operation member 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 band pass filter 9 extracts a difference component from image data corresponding to a focus detection area (AF area) from image data before image processing stored in the memory 4 or extracts a high frequency component. Filter. The image data after the filter processing by the band pass filter 9 has a lower frequency component, particularly a direct current component, removed than the image data before the filter processing.

  The integrating circuit 10 integrates the image data filtered by the band pass filter 9. In the integration process, the absolute values of the image data are integrated in order to integrate the differences due to the high frequency components.

  The AF circuit 11 obtains a focus evaluation value (contrast value) using the integrated value obtained by the integrating circuit 10. FIG. 2 is a diagram illustrating an example of the relationship between the position of a focus lens (not shown) in the photographing lens 1 and the focus evaluation value. In FIG. 2, the horizontal axis represents the position of the focus lens, and the vertical axis represents the focus evaluation value. A lens position D1 corresponding to the peak of the focus evaluation value curve L21 is the focus position of the focus lens with respect to the main subject.

  The AF circuit 11 (CPU 12) of this embodiment moves the focus lens in a direction in which the focus evaluation value increases, and repeats a reversal drive operation that reverses the movement direction of the focus lens when the focus evaluation value changes from increase to decrease. The peak of the focus evaluation value “mountain” is obtained. FIG. 3 is a diagram illustrating an example of the movement of the focus lens and the change in the focus evaluation value. In FIG. 3, the upper waveform is a curve L32 representing the focus evaluation value, and the lower waveform is a curve L31 representing the movement of the focus lens. In both the upper and lower stages, the horizontal axis represents time, the upper vertical axis represents the magnitude of the focus evaluation value, and the lower vertical axis represents the position of the focus lens.

  For example, the AF circuit 11 starts moving the focus lens from the ∞ (infinity) end toward the close end at time t0. When the focus lens passes the in-focus position at time t1, the focus evaluation value starts to decrease. The AF circuit 11 temporarily stops the movement of the focus lens at time t2, and starts moving from the closest end toward the ∞ end at time t3.

  The AF circuit 11 obtains the peak of the focus evaluation value “mountain” while repeating the same inversion driving operation (time t3 to t6), and moves the focus lens to the lens position P31 corresponding to the peak to obtain a focused state. (Time t7).

  The AF process performed by the CPU 12 of the AF electronic camera will be described with reference to the flowcharts of FIGS. The process shown in FIG. 4 is started when, for example, a half-press operation signal is input to the CPU 12 from a release switch constituting the operation member 15. In step S1 of FIG. 4, the CPU 12 initializes flags necessary for the process and proceeds to step S2.

  In step S2, the CPU 12 determines an AF area and proceeds to step S3. The AF area is determined in accordance with, for example, an operation signal from an AF area selection switch that constitutes the operation member 15. In step S3, the CPU 12 determines the number of data used for median calculation described later, and proceeds to step S4.

The CPU 12 normally sets the number of data at the time of median calculation to three, but if any of the conditions listed below is met, the number of data is changed to a larger number (for example, five).
[1] When the subject includes a flicker light source (one whose brightness changes periodically) [2] When the subject brightness is a predetermined value (for example, Lv5) or less [3] The photographing magnification is a predetermined value (for example, 1) / 5 times) or more [4] When the subject is moving

  In order to perform the condition determination, the CPU 12 acquires luminance information by integrating raw image data that has not been filtered. When the luminance information changes periodically, it is determined that the flicker light source is included in the shooting screen. Further, the sum of luminance information (Bv) and sensitivity information (Sv) corresponds to Lv.

  In step S4, the CPU 12 acquires the integrated value (focus evaluation value) by the integrating circuit 10, and proceeds to step S5. In step S5, the CPU 12 calculates focus lens position information and proceeds to step S6. The position of the focus lens is calculated by inputting information indicating the lens position from the focus control mechanism 14, for example.

  In step S6, the CPU 12 updates the history data and proceeds to step S7. Specifically, the focus evaluation value history data HisFVal [n] and the lens position information history data HisLPave [n] are stored in the AF circuit 11 in association with each other. n represents the order of acquisition, and 0, 1, 2,...

  In step S7, the CPU 12 performs median calculation. The CPU 12 calculates the median (median value) of the latest three (corresponding to the number of data determined in step S3) among the focus evaluation value history data HisFVal [n], and uses the AF circuit as median history data HisFValMedian [n]. 11 and proceed to step S8.

  In step S8, the CPU 12 calculates the maximum value FValMax from the focus evaluation value history data HisFVal [n], and proceeds to step S9. In step S9, the CPU 12 calculates the amount of movement of the focus lens and proceeds to step S10. Details of calculation of the driving amount of the focus lens will be described later.

  In step S10, the CPU 12 performs in-focus stop determination. The CPU 12 makes an affirmative determination in step S10 and proceeds to step S11 when the focus evaluation value “peak” exceeds the peak of the predetermined number of times (that is, the reversal driving operation is repeated a predetermined number of times). If the CPU 12 has not exceeded the peak of the “peak” of the focus evaluation value a predetermined number of times, the CPU 12 makes a negative determination in step S10 and returns to step S4. The process returns to step S4 when the focus lens inversion driving operation is repeated.

  In step S11, the CPU 12 calculates a focus position FocusPos of the focus lens by performing a three-point interpolation operation using three history data including the maximum value FValMax among the focus evaluation value history data HisFVal [n]. To do. The CPU 12 moves the focus lens to the in-focus position FocusPos and proceeds to step S12.

  In step S12, the CPU 12 prepares for restart and proceeds to step S13. Specifically, an integrated value (focus evaluation value) by the integrating circuit 10 is acquired after the focus lens is moved to the in-focus position FocusPos. The CPU 12 further stores the acquired focus evaluation value in the AF circuit 11 as FValRestart. Further, the CPU 12 stores the luminance information at this time in the AF circuit 11 as the restart determination luminance value BVRestart. Luminance information is obtained by integrating raw image data that has not been filtered as described above.

  In step S13, the CPU 12 acquires the integrated value (focus evaluation value) by the integrating circuit 10, and proceeds to step S14. Note that the luminance information at this time is also acquired. In step S14, the CPU 12 calculates position information of the focus lens and proceeds to step S15.

  In step S15, the CPU 12 updates the history data and proceeds to step S16. Specifically, the focus evaluation value history data HisFVal [n] and the lens position information history data HisLPave [n] are stored in the AF circuit 11 in association with each other. n represents the order of acquisition, and 0, 1, 2, ... from the most recent one.

  In step S16, the CPU 12 performs median calculation. The CPU 12 calculates the median (median value) of the latest three (corresponding to the number of data determined in step S3) among the focus evaluation value history data HisFVal [n], and uses the AF circuit as median history data HisFValMedian [n]. 11 and proceed to step S17.

  In step S17, the CPU 12 calculates the maximum value FValMax from the focus evaluation value history data HisFVal [n], and proceeds to step S18. In step S18, the CPU 12 performs a restart determination. If any of the following conditions is met, the CPU 12 makes a positive determination in step S18 and returns to step S2. If none of the following conditions is satisfied, the CPU 12 makes a negative determination in step S18 and returns to step S13.

[1] When the maximum value FValMax acquired in step S13 changes by a predetermined value or more with respect to the focus evaluation value FValRestart [2] The luminance information acquired in step S13 is predetermined for the restart determination luminance value BVRestart. [3] When a predetermined time has elapsed after the focus determination (step S10) [4] When a zoom operation signal is input from the operation member 15

  Details of the focus lens drive amount calculation will be described with reference to the flowchart of FIG. In step S1001 of FIG. 5, the CPU 12 determines whether or not the median of the focus evaluation value has decreased by a predetermined value or more compared to the median calculated last time. If the latest median history data HisFValMedian [n] has decreased beyond the predetermined value from the previous calculated value, the CPU 12 makes an affirmative decision in step S1001 and proceeds to step S1003. When the decrease amount from the previous calculated value of the latest median history data HisFValMedian [n] is less than the predetermined value, the CPU 12 makes a negative determination in step S1001 if it has increased from the previous calculated value, and proceeds to step S1002. .

  In step S1002, the CPU 12 maintains the current moving direction of the focus lens, ends the process of FIG. 5, and returns to FIG. Maintaining the moving direction of the focus lens corresponds to the case where the focus lens is moved in the direction in which the focus evaluation value increases, as illustrated in FIG. FIG. 6A is a diagram for explaining the correspondence between the movement of the focus lens and the flowchart of FIG.

  In step S1003, the CPU 12 determines whether or not the focus evaluation value exceeds the peak due to the focus lens movement. If any of the following conditions is met, the CPU 12 makes a positive determination in step S1003 and proceeds to step S1005. If none of the following conditions is satisfied, the CPU 12 makes a negative determination in step S1003 and proceeds to step S1004.

[1] When the median history data HisFValMedian [n] of the focus evaluation value is decreased by a predetermined value or more with respect to the maximum value FValMax [2] The focus evaluation value acquired at the start of driving of the focus lens after restart is When different from the maximum value FValMax

  In step S1004, the CPU 12 reverses the current moving direction of the focus lens, ends the process of FIG. 5, and returns to FIG. Reversing the moving direction of the focus lens corresponds to the case where the focus evaluation value is decreased due to the movement of the focus lens after the restart as illustrated in FIG. 6B. FIG. 6B is a diagram for explaining the correspondence between the movement of the focus lens and the flowchart of FIG.

  In step S1005, the CPU 12 calculates the lens movement amount (drive amount) to the peak position (corresponding in-focus position) based on the focus evaluation value history data HisFVal [n], and ends the processing of FIG. Returning to FIG. Whether the focus evaluation value history curve exceeds the peak is determined when the focus evaluation value is changed from increasing to decreasing, as illustrated in FIG. 6C. FIG. 6C is a diagram for explaining the correspondence between the movement of the focus lens and the flowchart of FIG.

  The effect of this embodiment is demonstrated with reference to FIG. FIG. 7 exemplifies the movement of the focus lens and the change in the focus evaluation value, particularly in the vicinity where the focus evaluation value changes from increasing to decreasing. In FIG. 7, the upper waveform is an ideal curve L61 representing the focus evaluation value, and the lower waveform is a curve LM61 representing the movement of the focus lens. In both the upper and lower stages, the horizontal axis represents time, the upper vertical axis represents the magnitude of the focus evaluation value, and the lower vertical axis represents the position of the focus lens.

  The determination threshold value V61 corresponds to the maximum focus evaluation value FValMax. The determination threshold value V62 corresponds to a determination threshold value (a value that is lower than the maximum value FValMax by a predetermined value Δh) used for peak crossing determination. The CPU 12 starts moving the focus lens at time t61 and obtains focus evaluation values FV201, FV202,..., FV208, FV209 at predetermined intervals. In the example of FIG. 7, noise is superimposed on the image data at time t62 before time t63 when the maximum focus evaluation value FValMax is acquired. Thereby, the focus evaluation value FV204 acquired at time t62 temporarily decreases, becomes smaller than the focus evaluation values FV202 and FV201 acquired before time t62, and is greatly different from the ideal curve L61.

(1) The median of the three most recent values (corresponding to the number of data determined in step S3) of the focus evaluation value history data HisFVal [n] is calculated, and this median calculated value is decreased from the previous median calculated value. When the width is less than the predetermined value (including the case where the width is increased from the previous median calculation value), the movement direction (drive direction) of the focus lens is maintained. Thereby, for example, it is possible to prevent erroneous determination that the focus evaluation value history is reduced by one abnormal value (VF204) among the focus evaluation values VF202, VF203, and VF204. By using the median, it is possible to improve the accuracy of determining the decrease in the focus evaluation value history and to appropriately control the moving direction of the focus lens, compared to the case of using the moving average.

(2) The median of the latest three (corresponding to the number of data determined in step S3) of the focus evaluation value history data HisFVal [n] is calculated, and the peak is exceeded when this median calculated value is smaller than the determination threshold value V62. Judgment was made. As a result, as in the case of (1) above, even when an abnormal value is included in any of the focus evaluation values VF207, VF208, and VF209, for example, it is erroneously determined that the peak of the focus evaluation value history curve has been exceeded. This can be prevented and the moving direction of the focus lens can be appropriately controlled.

(3) In step S3, the number of data at the time of median calculation is normally three, and when any of the above four conditions is met, the number of data at the time of median calculation is changed to a larger number. Even if an abnormal value occurs in a part of the focus evaluation value history by increasing the number of data in a situation where the image is likely to change (the focus evaluation value is likely to vary), it is erroneously determined that the focus evaluation value history has decreased. It is possible to prevent erroneous determination of exceeding the peak of the focus evaluation value history curve.

(Modification 1)
In the description of step S3, in order to determine the number of data at the time of median calculation, four cases are exemplified as situations in which an image is likely to change (focal evaluation values tend to vary). In addition to the above four determination conditions, the following four examples may be further included.
[5] When the shooting sensitivity is higher than the predetermined sensitivity [6] When the image stabilization mechanism is turned off [7] When set to the night scene shooting mode [8] When set to the macro shooting mode

(Modification 2)
The number of data used for median calculation is not limited to three or five as described above, and may be seven or nine as long as it is an odd number. By increasing the number of data, it is possible to cope with a case where a plurality of abnormal values may occur.

(Modification 3)
The example of starting the movement of the focus lens from the infinity (infinity) end toward the near end during AF processing has been described, but conversely, the movement of the focus lens from the nearest end toward the infinity may be started. Good.

(Modification 4)
In the description of step S2, the example in which the AF area is determined according to the operation signal from the AF area selection switch has been described, but the CPU 12 may be configured to automatically select from a plurality of AF areas.

(Modification 5)
You may apply this invention not only to an electronic camera but to the focus detection apparatus of a silver salt camera. In this case, an imaging element for focus detection may be provided separately from the photosensitive member for photographing.

  The above description is merely an example, and is not limited to the configuration of the above embodiment.

It is a block diagram explaining the principal part structure of AF electronic camera by one embodiment of this invention. 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 explaining an example of a motion of a focus lens, and a change of a focus evaluation value. It is a flowchart explaining AF processing. It is a flowchart explaining the drive amount calculation of a focus lens. FIG. 6 is a diagram illustrating a correspondence relationship between movement of the focus lens and FIG. 5. It is a figure which illustrates the movement of a focus lens, and the change of a focus evaluation value in the vicinity where a focus evaluation value changes from increase to decrease.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lens unit 2 ... Image pick-up element 9 ... Band pass filter 10 ... Integration circuit 11 ... AF circuit 12 ... CPU

Claims (5)

Integrating means for integrating the signals from the image sensor imaged through the taking lens;
Acquisition means for sequentially acquiring focus evaluation value information indicating a relationship between the lens position and the integrated value by the integrating means while the focus lens of the photographing lens is moving;
Calculating means for calculating a median for a predetermined number of focus evaluation values in the focus evaluation value information;
Detecting means for detecting a maximum value of the focus evaluation value information;
A focus detection apparatus comprising: a determination unit configured to determine whether to reverse the moving direction of the focus lens based on the maximum value and the median. The focus detection apparatus according to claim 1,
The focus detection apparatus characterized in that the calculation means increases the predetermined number when the captured image changes. The focus detection apparatus according to claim 1 or 2,
The determining unit determines to maintain the moving direction of the focus lens when the median calculated for the most recent predetermined number of focus evaluation values does not decrease beyond a predetermined value from the previously calculated median. Focus detection device. The focus detection apparatus according to claim 3,
The determining means is configured such that the median calculated for the most recent predetermined number of focus evaluation values decreases from a previously calculated median beyond a predetermined value, and the most recent median is smaller than a determination threshold smaller than the maximum value. In this case, the focus detection apparatus determines reversal of the moving direction of the focus lens.   A camera comprising the focus detection device according to any one of claims 1 to 4.

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