JP4819318B2 - Method and apparatus for automatic focusing of camera - Google Patents

Description

  The present invention relates to an automatic focus adjustment method and apparatus for a camera, and in particular, an automatic focus adjustment method for a camera that automatically adjusts the lens position of a focus lens so as to maximize the contrast of a subject (hereinafter referred to as “contrast AF”). And related to equipment

  Contrast AF, which is mainly used in digital cameras, etc., captures images while moving a focus lens that affects focus adjustment in the photographic optical system over the focus adjustment range, and extracts high-frequency components from the output image signal. An evaluation value for focusing is sequentially calculated, and the focus lens is moved to a position where the evaluation value is maximized (where the contrast is maximized) to be focused.

  However, the contrast AF has a problem that, for example, when the contrast is small because the subject is dark, the evaluation value for focusing obtained by moving the focus lens over the focus adjustment range becomes small as a whole.

Therefore, conventionally, a high-pass filter (HPF) for extracting a high-frequency component from an image signal, provided with a plurality of HPFs each having a different cutoff frequency, and when the aperture amount of the aperture mechanism is small (that is, when the subject is dark) ) Proposes an autofocus video camera in which an HPF having a low cut-off frequency is selected and thereby an evaluation value is increased (Patent Document 1).
JP 7-162731 A

  In contrast AF, when the subject is too dark or too bright and the contrast is low, the evaluation value obtained when the focus lens is moved over the focus adjustment range does not have a clear mountain shape. There is a problem that the lens position of the focus lens that maximizes the angle cannot be obtained accurately.

  Also, as described in Patent Document 1, when the subject is dark and an HPF having a low cut-off frequency is selected, and the evaluation value is increased by this, the evaluation value increases as a whole, but the focus lens moves. There is a problem that the evaluation value changes little with respect to the change in position, and in this case also, there is a problem in that the lens position of the focus lens that maximizes the evaluation value cannot be obtained accurately.

  The present invention has been made in view of such circumstances, and can improve the reliability of contrast AF when a subject is too dark or too bright, and can reduce the occurrence rate of a defocused image. An object is to provide an automatic focusing method and apparatus.

In order to achieve the above object, an automatic focusing method for a camera according to claim 1 comprises:
(a) moving the photographic lens over the focus adjustment range, and obtaining an image signal from the imaging means for imaging the subject each time the photographic lens moves by a predetermined amount, under a preset focus exposure condition Obtaining a captured image signal;
(b) calculating an evaluation value according to a contrast component of a subject based on an image signal acquired for each movement position of the photographing lens;
(c) determining whether the reliability of automatic focus adjustment is high or low based on the calculated evaluation value;
(d) If it is determined that the reliability of the automatic focus adjustment is low, the steps (a) and (b) are repeatedly executed after changing the setting of the exposure condition in the plus direction or the minus direction; ,
(e) When it is determined that the reliability of the automatic focus adjustment is high, a step of obtaining a movement position where the evaluation value reaches a peak based on the movement position of the photographing lens and the evaluation value calculated for each movement position When,
(f) viewing including the the steps of moving the photographing lens to the moving position obtained above,
A step of determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when it is determined that the reliability of the automatic focus adjustment is low; A step of moving the photographing lens to a preset lens position instead of the steps (e) and (f) when the maximum evaluation value is between a predetermined upper limit value and a lower limit value; It is characterized by having .

  That is, when it is determined that the reliability of the automatic focus adjustment is low based on the evaluation value calculated at the time of the AF search in the steps (a) and (b), the imaging means is not performed without performing the automatic focus adjustment. After changing the exposure condition setting in, AF search is performed again, and the exposure condition setting change is repeated until the reliability of automatic focus adjustment becomes high. Then, the automatic focus adjustment is performed based on the evaluation value when it is determined that the reliability of the automatic focus adjustment is high.

Here, the determination as to whether the reliability of the automatic focus adjustment is high or low is, for example, that the difference between the maximum value and the minimum value among the evaluation values calculated for each moving position of the photographing lens is equal to or greater than a predetermined threshold value. Depending on whether or not there is, it can be considered. This is because when the difference between the maximum value and the minimum value is greater than or equal to a predetermined threshold value, the mountain drawn by each evaluation value is clear and the peak position can be accurately obtained.
In addition, when the calculated maximum value of the evaluation value is between a predetermined upper limit value and a lower limit value, the exposure condition or the pixel mixing method is set appropriately. The reason for the low nature is not the brightness of the subject but the subject itself, like a wall, originally has a low contrast. Accordingly, in this case, since contrast AF cannot be performed, the lens is moved to a preset lens position.

An automatic focusing method for a camera according to claim 2 comprises:
(a) A step of acquiring an image signal from an imaging means for imaging a subject every time the photographic lens is moved over a focus adjustment range and the photographic lens moves by a predetermined amount, and pixel mixing is performed by a preset pixel mixing method. Obtaining a processed image signal;
(b) calculating an evaluation value according to a contrast component of a subject based on an image signal acquired for each movement position of the photographing lens;
(c) determining whether the reliability of automatic focus adjustment is high or low based on the calculated evaluation value;
(d) If it is determined that the reliability of the automatic focus adjustment is low, after changing the setting of the pixel mixing method, repeatedly performing the steps (a) and (b);
(e) When it is determined that the reliability of the automatic focus adjustment is high, a step of obtaining a movement position where the evaluation value reaches a peak based on the movement position of the photographing lens and the evaluation value calculated for each movement position When,
(f) viewing including the the steps of moving the photographing lens to the moving position obtained above,
A step of determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when it is determined that the reliability of the automatic focus adjustment is low; A step of moving the photographing lens to a preset lens position instead of the steps (e) and (f) when the maximum evaluation value is between a predetermined upper limit value and a lower limit value; It is characterized by having .

  When it is determined that the reliability of the automatic focus adjustment is low, the invention according to claim 1 changes the setting of the exposure condition, whereas the invention according to claim 2 changes the setting of the pixel mixing method. This is different from the invention according to claim 1. As the pixel mixing method, there are two-pixel mixing, four-pixel mixing, and the like. As the evaluation value is lower, a pixel mixing method with a larger number of pixels to be mixed is set. In addition, the setting for acquiring an image signal of one pixel (in the case where pixels are not actually mixed) is also an aspect of setting of the pixel mixing method here.

The automatic focusing method of the camera according to claim 3 is:
(a) moving the photographic lens over the focus adjustment range, and obtaining an image signal from the imaging means for imaging the subject each time the photographic lens moves by a predetermined amount, under a preset focus exposure condition Acquiring an image signal that is imaged and pixel-mixed in a preset pixel-mixing method;
(b) calculating an evaluation value according to a contrast component of a subject based on an image signal acquired for each movement position of the photographing lens;
(c) determining whether the reliability of automatic focus adjustment is high or low based on the calculated evaluation value;
(d) If it is determined that the reliability of the automatic focus adjustment is low, after changing the setting of the exposure condition in the plus direction or the minus direction or changing the setting of the pixel mixing method, the steps (a) and a step of repeatedly executing (b);
(e) When it is determined that the reliability of the automatic focus adjustment is high, a step of obtaining a movement position where the evaluation value reaches a peak based on the movement position of the photographing lens and the evaluation value calculated for each movement position When,
(f) viewing including the the steps of moving the photographing lens to the moving position obtained above,
A step of determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when it is determined that the reliability of the automatic focus adjustment is low; A step of moving the photographing lens to a preset lens position instead of the steps (e) and (f) when the maximum evaluation value is between a predetermined upper limit value and a lower limit value; It is characterized by having .

  That is, when it is determined that the reliability of the automatic focus adjustment is low, the invention according to claim 3 performs the AF search again after changing the exposure condition setting or the pixel mixing method setting, and automatically Automatic focus adjustment is performed based on an evaluation value when it is determined that the reliability of focus adjustment is high.

  4. The camera automatic focusing method according to claim 3, wherein the step (d) first changes the setting of the exposure condition, and the change of the setting of the exposure condition is an upper limit or a lower limit. Then, after that, the setting of the pixel mixing method is changed.

  5. The automatic focusing method for a camera according to claim 3, wherein the step (d) first changes the setting of the pixel mixing method, and the change of the setting of the pixel mixing method is an upper limit. Alternatively, after reaching the lower limit, the setting of the exposure condition is changed.

  That is, in the invention according to claim 4, when it is determined that the reliability of the automatic focus adjustment is low, the exposure condition setting is changed first, and the reliability of the automatic focus adjustment is changed only by changing the exposure condition setting. If the value does not increase, then the AF search is performed by changing the setting of the pixel mixing method. On the contrary, in the invention according to claim 5, when it is determined that the reliability of the automatic focus adjustment is low, the setting of the pixel mixing method is changed first, and the automatic focus adjustment is performed only by changing the setting of the pixel mixing method. If the reliability of the camera does not become high, the AF search is performed by changing the exposure condition setting.

The invention according to claim 6 calculates the evaluation value according to the contrast component of the subject based on the image signal output from the imaging means each time the photographing lens is moved over the focus adjustment range and the photographing lens moves by a predetermined amount. Then, based on the movement position of the photographing lens and the evaluation value calculated for each movement position, a movement position where the evaluation value reaches a peak is obtained, and automatic focus adjustment of the camera that moves the photographing lens to the obtained movement position In the apparatus, when the reliability of the automatic focus adjustment is low by the determination means for determining whether the reliability of the automatic focus adjustment is high or low based on the evaluation value calculated for each moving position of the photographing lens, If determined, the setting of the exposure condition for focus when acquiring the image signal from the image pickup means is set in the plus direction from the preset exposure condition for focus. Is changed in the negative direction and / or the setting of the pixel mixing method is changed from a preset pixel mixing method, and when the determination unit determines that the reliability of the automatic focus adjustment is high, the current exposure condition and e Bei means for maintaining the pixel mixing method, and if it is determined that the reliability is low autofocusing by said discriminating means, the maximum value of the evaluation value described above is calculated and a predetermined upper limit value and the lower limit value Means for discriminating whether or not the lens is in between, and when the maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value, the photographing lens is set as a preset lens. And a means for moving to a position .

  According to an eighth aspect of the present invention, in the camera automatic focus adjustment device according to the seventh aspect, when the determination means determines that the reliability of the automatic focus adjustment is low, the maximum value of the calculated evaluation value is predetermined. Means for determining whether or not the calculated upper limit value falls between a predetermined upper limit value and a lower limit value. And a means for moving the lens to a preset lens position.

  According to the present invention, when it is determined that the reliability of the contrast AF is low by the AF search, after changing the setting of the exposure condition in the imaging unit or the setting of the pixel mixing method, the AF is performed again. Since the search is performed, a good evaluation value can be obtained even when the subject is too dark or too bright. Thereby, the reliability of contrast AF can be improved, and the occurrence rate of a defocused image can be reduced.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a camera automatic focusing method and apparatus according to the present invention will be described in detail below with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an embodiment of a digital camera to which a camera automatic focus adjustment method according to the present invention is applied.

  The digital camera 10 records captured images on a memory card 54, and the operation of the entire camera is centrally controlled by a central processing unit (CPU) 40.

  The digital camera 10 is provided with an operation unit 38 including a shutter button and a mode dial for setting a shooting mode, a reproduction mode, and the like, and a signal corresponding to an operation on the operation unit 38 is input to the CPU 40.

Image light indicating a subject is imaged on a light receiving surface of an image sensor 16 such as a CCD image sensor or a CMOS image sensor through a photographing lens 12 and a diaphragm 14. The photographing lens 12 is driven by a lens driving unit 36 controlled by the CPU 40, and focus control and the like are performed. Diaphragm 14 is made of, for example, five diaphragm blades, driven by a diaphragm driver 34, which is controlled by the CPU 40, for example, is controlled diaphragm 5 stage 1A _V increments until the aperture value F2.8 ~F11.

  Further, the CPU 40 controls the diaphragm 14 via the diaphragm driving unit 34, and controls the charge accumulation time (shutter speed) in the image sensor 16, pixel mixing described later, and the like via the image sensor control unit 32. .

  The signal charge accumulated in the image sensor 16 is read out as a voltage signal corresponding to the signal charge based on a read signal applied from the image sensor control unit 32. The voltage signal read from the image sensor 16 is applied to the analog signal processing unit 18 where the R, G, and B signals for each pixel are sampled and held and then added to the A / D converter 20. It is done. The A / D converter 20 converts R, G, and B signals that are sequentially input into digital R, G, and B signals and outputs them to the image input controller 22.

  The digital signal processing unit 24 performs predetermined processing such as offset control, gain control processing including white balance correction and sensitivity correction, gamma correction processing, YC processing, etc., on the digital image signal input via the image input controller 22. Perform signal processing.

  The image data processed by the digital signal processing unit 24 is input to the VRAM 50. The VRAM 50 includes an A area and a B area each storing image data representing an image for one frame. In the VRAM 50, image data representing an image for one frame is rewritten alternately in the A area and the B area. Of the A area and B area of the VRAM 50, the written image data is read from an area other than the area where the image data is rewritten. The image data read from the VRAM 50 is encoded by the video encoder 28 and output to the liquid crystal monitor 30 provided on the back of the camera, whereby the subject image is displayed on the display screen of the liquid crystal monitor 30.

  Further, when the shutter button of the operation unit 38 is first pressed (half-pressed), the AE operation and the AF operation are started. That is, the image data output from the A / D converter 20 is taken into the AF detection unit 42 and the AE detection unit 44. The AF detection unit 42 uses image data (for example, a G signal in the center region (focus region) of the image sensor 16), and uses a high-pass filter (HPF) to generate a high-frequency component from a G signal continuous in a one-dimensional horizontal direction. A value (AF evaluation value) obtained by extracting and integrating the high frequency components is output to the CPU 40. The AE detection unit 44 integrates the G signals of the entire screen, or integrates the G signals with different weights in the central and peripheral portions of the screen, and outputs the integrated value to the CPU 40.

  Based on the AF evaluation value input from the AF detection unit 42, the CPU 40 moves the taking lens 12 to the lens position where the AF evaluation value is maximized via the lens driving unit 36, and the integration input from the AE detection unit 44. The brightness of the subject (shooting Ev value) is calculated from the value, and the aperture value of the aperture 14 and the electronic shutter (shutter speed) of the image sensor 16 are determined based on the shooting Ev value according to a predetermined program diagram. The aperture 14 is controlled via the aperture drive unit 34 based on the determined aperture value, and the charge accumulation time in the image sensor 16 is controlled via the image sensor control unit 32 based on the determined shutter speed.

  When the AE operation and the AF operation are completed and the shutter button is pressed in the second stage (full press), the image data for one frame output from the A / D converter 20 in response to the press is input to the image. The data is input to the memory (SDRAM) 48 from the controller 22 and temporarily stored.

  The image data is read from the memory 48, and predetermined signal processing including luminance data and color difference data generation processing (YC processing) is performed in the digital signal processing unit 24. The YC-processed image data (YC data) is read from the digital signal processing unit 24 and stored in the memory 48 again. Subsequently, the YC data is output to the compression / decompression processing unit 26, and a predetermined compression process such as JPEG (joint photographic experts group) is executed. The compressed YC data is output and stored again in the memory 48, and then read out by the media controller 52 and recorded in the memory card 54.

  Next, an automatic focus adjustment method of the digital camera 10 having the above configuration will be described.

[First Embodiment]
FIG. 2 is a flowchart showing a first embodiment of the automatic focusing method for a camera according to the present invention.

  In FIG. 2, when the shutter button of the operation unit 38 is half-pressed, the CPU 40 first performs AE control for focus (step S10). That is, the Ev value is calculated from the integrated value input from the AE detection unit 44, and the charge accumulation time (focus exposure) in the diaphragm 14 and the image sensor 16 is controlled based on this Ev value. In the focus AE control, in order to obtain more high-frequency signals, in general, the focus exposure is often over-exposure controlled than the photographic exposure.

  Subsequently, the CPU 40 performs an AF search (step S12).

  As shown in FIG. 3, in the AF search, the photographing lens 12 is moved over the focus adjustment range from the close range to infinity, and an AF evaluation value calculated every time the photographing lens 12 moves by a predetermined amount is taken from the AF detection unit 42. .

  Next, it is determined whether the AF reliability is high or low based on the AF evaluation value captured as described above (step S14). For this determination, for example, the difference between the maximum value top and the minimum value min of the captured AF evaluation values is obtained, and if this difference (top-min) is less than a predetermined threshold th, the reliability of AF is Determined to be low.

  FIG. 4 is a graph showing AF evaluation values captured during AF search. As shown in FIG. 4A, when the difference between the maximum value top and the minimum value min of the AF evaluation value is large, a peak of the AF evaluation value can be clearly drawn, and this AF evaluation value is the maximum. It is possible to accurately determine the lens position (that is, the auto focus position). Therefore, in this case, it can be said that the reliability of AF is high.

  On the other hand, in the case of the AF evaluation value shown in FIG. 4B, the AF evaluation value is generally small, and it is difficult to determine the focal position by AF. Such AF evaluation value characteristics are often seen when the subject is dark.

  Further, in the case of the AF evaluation value shown in FIG. 4C, the AF evaluation value is large overall, the AF evaluation value reaches a peak state, and it is still difficult to determine the focal position by AF. Such AF evaluation value characteristics are often seen when the subject is bright.

  Returning to FIG. 2, if it is determined in step S14 that the AF reliability is high, the process proceeds to step S16, where the autofocus position is determined. This automatic focus position is determined by calculating the lens position of the taking lens 12 that maximizes the AF evaluation value based on the AF evaluation value acquired by the AF search as shown in FIG. Then, automatic focus adjustment is performed by moving the photographing lens to the determined automatic focus position (focusing operation).

  On the other hand, if it is determined in step S14 that the AF reliability is low, it is determined whether or not the maximum AF value of the AF evaluation value is less than a predetermined lower limit value th-min (step S18). If it is determined that the maximum AF evaluation value top is less than the lower limit value th-min, it is then determined whether or not the current focus exposure is the upper limit (focus exposure at the darkest) (step S20).

  If the current focus exposure is not the upper limit, the current focus exposure is corrected in the positive direction (for example, overexposure correction by +1 EV) (step S22), and the process returns to step S12.

  On the other hand, if it is determined in step S20 that the current focus exposure is the upper limit, the process proceeds to step S24, where the photographing lens 12 is set to a preset lens position (fixed focal position when contrast AF is impossible). ).

  If it is determined in step S18 that the maximum value top of the AF evaluation value is greater than the lower limit value th-min, then the maximum value top of the AF evaluation value is greater than the predetermined upper limit value th-max. It is determined whether or not it is larger (step S26). If it is determined that the maximum AF value of the AF evaluation value is larger than the upper limit value th-max, it is subsequently determined whether or not the current focus exposure is the lower limit (focus exposure at the brightest) (step S28). ).

  If the current focus exposure is not the lower limit, the current focus exposure is subjected to exposure correction in the negative direction (for example, under exposure correction by -1 EV) (step S30), and the process returns to step S12.

  On the other hand, if it is determined in step S28 that the current focus exposure is the lower limit, the process proceeds to step S24, where the photographing lens 12 is moved to a preset lens position.

  If it is determined that the AF reliability is low as described above, the focus exposure (exposure conditions during AF search) is changed and the AF search is performed again, so the subject is too dark or too bright. However, a good evaluation value can be obtained, and the reliability of contrast AF can be improved.

  Further, the AF search in step S12 in FIG. 2 is not limited to a search method that always performs the same AF search (AF search having the same search range and search step) as shown in FIG. 3, but a rough search as shown in FIG. It is also possible to apply a search method that combines an advanced search and a detailed search.

  That is, in FIG. 5, it is determined whether or not the search counter is 0 during AF search (step S40). If the search counter is 0, rough search is executed (step S42). It is assumed that the search counter is given 0 as an initial value before the start of AF search.

  In the rough search, the search step of the photographing lens 12 to be moved over the focus adjustment range from the closest to infinity is roughened, and an AF evaluation value is acquired for each search step.

  When the rough search ends, the search counter is incremented by 1 (step S44), and the process returns to step S40.

  When the search counter becomes 1 after the rough search, the process proceeds from step S40 to step S46. In step S46, the search range of the detailed search is determined from the result of the rough search in step S42. That is, a predetermined range centering on the lens position where the maximum value of the AF evaluation values obtained by the rough search is obtained is determined as the search range of the detailed search.

  Subsequently, a detailed search is performed on the determined search range. That is, in the detailed search, the determined search range is searched with finer search steps than in the rough search, and an AF evaluation value is acquired for each search step.

  By combining the rough search and the detailed search as described above, it is possible to shorten the time of the AF search. Further, the reliability of AF may be determined from the result of rough search, and the detailed search may be performed only when the reliability is high.

[Second Embodiment]
FIG. 6 is a flowchart showing the second embodiment of the automatic focusing method for a camera according to the present invention. In FIG. 6, the same reference numerals are given to the portions common to the first embodiment shown in FIG. 2, and detailed description thereof will be omitted.

  The second embodiment shown in FIG. 6 is different from the first embodiment shown in FIG. 2 mainly in the contents of the AF search.

  That is, in the first embodiment shown in FIG. 2, the AF search in step S12 is performed only for the detailed search (without the rough search), or the detailed search is performed after the rough search as shown in FIG. However, as shown in FIG. 7, the AF search in step S12 ′ shown in FIG. 6 is either a rough search or a detailed search within the search range limited by the rough search result in one step S12 ′. Only do. When any search is completed, the search counter is incremented by 1 (step S44 '). In the AF search shown in FIG. 7, the same reference numerals are given to the portions common to the AF search processing shown in FIG. 5, and the detailed description thereof is omitted.

  In FIG. 6, in step S14, it is determined whether the AF reliability is high or low based on the AF evaluation value acquired in the AF search in step S12 ′. Based on this, it is determined whether the AF reliability is high or low. When the focus exposure is corrected because the AF reliability is low, and then AF search is performed again in step S12 ', this AF search is performed only in the detailed search within the search range limited by the rough search result.

  If it is determined in step S14 in FIG. 6 that the AF reliability is high, it is determined whether or not the search counter is 1 (step S50). When the search counter = 1, only the rough search is performed in the AF search in step S12 ′. In this case, a detailed search within the search range limited by the rough search result is performed (step S52). ), The process proceeds to step S16. On the other hand, if the search counter is not 1, the detailed search has already been performed in the AF search in step S12 ', and the detailed search is omitted, and the process proceeds to step S16.

[Third Embodiment]
FIG. 8 is a flowchart showing a third embodiment of the automatic focusing method for a camera according to the present invention. In FIG. 8, the same reference numerals are given to the portions common to the first embodiment shown in FIG. 2, and the detailed description thereof is omitted.

  In the first embodiment, when it is determined that the AF reliability is low and the maximum AF evaluation value top is out of a predetermined range (top <th-min, top> th-max), the focus exposure is performed. However, the second embodiment is different in that the pixel mixing method is changed without correcting the focus exposure in the above case.

  Here, the pixel mixing method applied to the third embodiment will be described.

  FIGS. 9A and 9B are diagrams showing a pixel mixing method. FIG. 9A shows G two-pixel mixing, and FIG. 9B shows G four-pixel mixing.

  In the pixel mixing method, the image signals of a plurality of pixels of the same color (G pixels in this embodiment) adjacent in the vertical direction of the image sensor 16 are mixed, and thereby, the signal level is higher than the image signal of one pixel. This is a process for obtaining a large image signal. The larger the number of pixels mixed, the larger the image signal can be generated.

  If it is determined in step S18 in FIG. 8 that the maximum AF top value of the AF evaluation value is less than the lower limit value th-min, the current number of pixel mixtures is the upper limit (of the number of mixtures that can be mixed by the digital camera 10). It is determined whether it is the maximum) (step S100).

  If the current number of mixtures is not the upper limit, the number of mixtures is increased so that the number of mixtures is the next larger than the current number of mixtures (step S110), and the process returns to step S12.

  Now, in the case where there are three types of pixel mixing methods of G one pixel, G two pixel mixing, and G four pixel mixing, when the current pixel mixing method is two pixel mixing, the four pixel mixing method is set. In this embodiment, one pixel of G (in the case where pixels are not actually mixed) is also one mode of setting of the pixel mixing method here.

  Similarly, if it is determined in step S26 that the maximum AF evaluation value top is larger than the upper limit value th-max, whether or not the current mixture number of pixel mixtures is the lower limit (in this embodiment, one pixel). Is determined (step S120).

  If the current mixture number is not the lower limit, the mixture number is decreased so that the mixture number is the next smaller than the current mixture number (step S130), and the process returns to step S12.

  Now, in the case where there are three types of pixel mixing methods of G one pixel, G two pixel mixing, and G four pixel mixing, when the current pixel mixing method is two pixel mixing, the four pixel mixing method is set.

  When it is determined that the reliability of AF is low as described above, the number of pixel mixture is changed and the AF search is performed again. Therefore, even if the subject is too dark or too bright, the signal level is appropriate. An image signal can be taken in, whereby a good evaluation value can be obtained.

[Fourth Embodiment]
FIG. 10 is a flowchart showing a fourth embodiment of the automatic focusing method for a camera according to the present invention. In FIG. 10, parts common to the third embodiment shown in FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The fourth embodiment shown in FIG. 10 differs from the third embodiment shown in FIG. 8 mainly in the content of the AF search in step S12 ′. The AF search shown in FIG. 7 is performed as the AF search in step S12 ′.

  In step S14, it is determined whether the AF reliability is high or low based on the AF evaluation value captured in the AF search in step S12 ′. However, the AF performance is determined based on the AF evaluation value captured in the first rough search. Determine whether the reliability is high or low. When the number of pixel mixtures is increased / decreased because AF reliability is low, and then AF search is performed again in step S12 ′, this AF search is performed only in the detailed search within the search range limited by the rough search result. .

  If it is determined in step S14 in FIG. 10 that the AF reliability is high, it is determined whether or not the search counter is 1 (step S150). When the search counter = 1, only the rough search is performed in the AF search in step S12 ′. In this case, a detailed search within the search range limited by the rough search result is performed (step S152). ), The process proceeds to step S16. On the other hand, if the search counter is not 1, the detailed search has already been performed in the AF search in step S12 ', and the detailed search is omitted, and the process proceeds to step S16.

[Fifth Embodiment]
FIG. 11 is a flowchart showing a fifth embodiment of the automatic focusing method for a camera according to the present invention. In FIG. 11, the same reference numerals are given to the portions common to the first and third embodiments shown in FIGS. 2 and 8, and the detailed description thereof is omitted.

  In the fifth embodiment shown in FIG. 11, it is determined that the reliability of AF is low, and the maximum AF evaluation value top is outside a predetermined range (top <th-min, top> th-max). In the same manner as in the first embodiment, first, the focus exposure is corrected, and then the AF search is performed again. If the AF reliability cannot be obtained only by the correction of the focus exposure, the third search is performed thereafter. It is different from the first and third embodiments in that the pixel mixing method is changed as in the embodiment.

  That is, if it is determined in step S20 ′ in FIG. 11 that the current focus exposure is the upper limit, the photographing lens 12 is not immediately moved to the fixed focus position as in the first embodiment. In step S100, it is determined whether the number of pixels to be mixed is the upper limit. If the current number of mixtures is not the upper limit, the number of mixtures is increased so that the number of mixtures is larger than the current number of mixtures (step S110), and AF search is performed again (step S12). In the AF search in step S112, the same processing as the AF search in step S12 is performed.

  Similarly, when it is determined in step S28 ′ in FIG. 11 that the current focus exposure is the lower limit, the photographing lens 12 is not immediately moved to the fixed focal position as in the first embodiment. The process proceeds to step S120, where it is determined whether or not the number of pixels to be mixed is a lower limit. If the current mixture number is not the lower limit, the mixture number is decreased so that the mixture number is the next smaller than the current mixture number (step S130), and AF search is performed again (step S112).

  Next, it is determined whether the AF reliability is high or low based on the AF evaluation value captured in step S112 (step S114). This determination is similar to the determination in step S14, in which the difference between the maximum value top and the minimum value min of the captured AF evaluation values is obtained, and this difference (top-min) is less than a predetermined threshold th. Determines that the reliability of AF is low.

  If it is determined in step S114 that the AF reliability is low, it is then determined whether or not the maximum AF evaluation value top is less than a predetermined lower limit th-min (step S116). When it is determined that the maximum value top of the AF evaluation value is less than the lower limit value th-min, the process returns to step S100, where it is determined whether the number of pixels to be mixed is the upper limit.

  On the other hand, when it is determined in step S116 that the maximum value top of the AF evaluation value is larger than the lower limit value th-min, the maximum value top of the AF evaluation value is subsequently larger than a predetermined upper limit value th-max. Whether or not (step S118). If it is determined that the maximum AF value of the AF evaluation value is larger than the upper limit value th-max, the process returns to step S120, where it is determined whether the number of pixels to be mixed is the lower limit.

[Sixth Embodiment]
FIG. 12 is a flowchart showing a sixth embodiment of the automatic focusing method for a camera according to the present invention. In FIG. 12, parts common to the fifth embodiment shown in FIG. 11 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The sixth embodiment shown in FIG. 12 differs from the fifth embodiment shown in FIG. 11 mainly in the contents of the AF search in steps S12 ′ and S112 ′. The AF search shown in FIG. 7 is performed as the AF search in steps S12 ′ and 112 ′.

  If it is determined in step S14 or step S114 in FIG. 12 that the AF reliability is high, it is determined whether or not the search counter is 1 (step S150). When the search counter = 1, only the rough search is performed in the AF search. In this case, a detailed search within the search range limited by the rough search result is performed (step S152), and the process proceeds to step S16. To do. On the other hand, if the search counter is not 1, the detailed search has already been performed in the AF search of step S12 'or step S112', so the detailed search is omitted and the process proceeds to step S16.

[Seventh Embodiment]
FIG. 13 is a flowchart showing a seventh embodiment of the camera automatic focusing method according to the present invention. In FIG. 13, the same reference numerals are given to the portions common to the fifth embodiment shown in FIG. 11, and the detailed description thereof is omitted.

  In the seventh embodiment shown in FIG. 13, contrary to the fifth embodiment shown in FIG. 11, it is determined that the reliability of AF is low, and the maximum value top of the AF evaluation value is within a predetermined range. In the case of outside (top <th-min, top> th-max), first, after performing the AF search again after changing the pixel mixing method, AF reliability cannot be obtained only by changing this pixel mixing method This is different from the fifth embodiment in that the focus exposure is subsequently changed (that is, the order of the change of the focus exposure and the change of the pixel mixing method is reversed).

  That is, if it is determined in step S100 'in FIG. 13 that the current pixel mixture number is the upper limit, the process proceeds to step S20, where it is determined whether the focus exposure is the upper limit. Similarly, if it is determined in step S120 'that the current pixel mixture number is the lower limit, the process proceeds to step S28, where it is determined whether the focus exposure is the lower limit.

[Eighth Embodiment]
FIG. 14 is a flowchart showing an eighth embodiment of the automatic focusing method for a camera according to the present invention. In FIG. 14, parts that are the same as those in the seventh embodiment shown in FIG. 13 are given the same reference numerals, and detailed descriptions thereof are omitted.

  The eighth embodiment shown in FIG. 14 differs from the seventh embodiment shown in FIG. 13 mainly in the contents of AF search in steps S12 'and S112'. The AF search shown in FIG. 7 is performed as the AF search in steps S12 ′ and 112 ′.

  If it is determined in step S14 or step S114 in FIG. 14 that the AF reliability is high, it is determined whether or not the search counter is 1 (step S150). When the search counter = 1, only the rough search is performed in the AF search. In this case, a detailed search within the search range limited by the rough search result is performed (step S152), and the process proceeds to step S16. To do. On the other hand, if the search counter is not 1, the detailed search has already been performed in the AF search of step S12 'or step S112', so the detailed search is omitted and the process proceeds to step S16.

FIG. 1 is a block diagram showing an embodiment of a digital camera to which a camera automatic focus adjustment method according to the present invention is applied. FIG. 2 is a flowchart showing a first embodiment of the automatic focusing method for a camera according to the present invention. FIG. 3 is a diagram used for explaining the AF search. FIG. 4 is a graph showing AF evaluation values captured during AF search. FIG. 5 is a flowchart showing another example of the AF search in FIG. FIG. 6 is a flowchart showing the second embodiment of the automatic focusing method for a camera according to the present invention. FIG. 7 is a flowchart showing the AF search in FIG. FIG. 8 is a flowchart showing a third embodiment of the automatic focusing method for a camera according to the present invention. FIG. 9 is a diagram used for explaining the pixel mixing method. FIG. 10 is a flowchart showing a fourth embodiment of the automatic focusing method for a camera according to the present invention. FIG. 11 is a flowchart showing a fifth embodiment of the automatic focusing method for a camera according to the present invention. FIG. 12 is a flowchart showing a sixth embodiment of the automatic focusing method for a camera according to the present invention. FIG. 13 is a flowchart showing a seventh embodiment of the camera automatic focusing method according to the present invention. FIG. 14 is a flowchart showing an eighth embodiment of the automatic focusing method for a camera according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Digital camera, 12 ... Shooting lens, 14 ... Aperture, 16 ... Image sensor, 24 ... Digital signal processing part, 32 ... Image sensor control part, 34 ... Aperture drive part, 36 ... Lens drive part, 38 ... Operation part, 40 ... CPU, 42 ... AF detector, 44 ... AE detector, 48 ... memory

Claims (6)

(a) moving the photographic lens over the focus adjustment range, and obtaining an image signal from the imaging means for imaging the subject each time the photographic lens moves by a predetermined amount, under a preset focus exposure condition Obtaining a captured image signal;
(b) calculating an evaluation value according to a contrast component of a subject based on an image signal acquired for each movement position of the photographing lens;
(c) determining whether the reliability of automatic focus adjustment is high or low based on the calculated evaluation value;
(d) If it is determined that the reliability of the automatic focus adjustment is low, the steps (a) and (b) are repeatedly executed after changing the setting of the exposure condition in the plus direction or the minus direction; ,
(e) When it is determined that the reliability of the automatic focus adjustment is high, a step of obtaining a movement position where the evaluation value reaches a peak based on the movement position of the photographing lens and the evaluation value calculated for each movement position When,
(f) moving the taking lens to the determined moving position;
Including
A step of determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when it is determined that the reliability of the automatic focus adjustment is low; A step of moving the photographing lens to a preset lens position instead of the steps (e) and (f) when the maximum evaluation value is between a predetermined upper limit value and a lower limit value; When an automatic focusing method features and to Luke camera to have a. (a) A step of acquiring an image signal from an imaging means for imaging a subject every time the photographic lens is moved over a focus adjustment range and the photographic lens moves by a predetermined amount, and pixel mixing is performed by a preset pixel mixing method. Obtaining a processed image signal;
(b) calculating an evaluation value according to a contrast component of a subject based on an image signal acquired for each movement position of the photographing lens;
(c) determining whether the reliability of automatic focus adjustment is high or low based on the calculated evaluation value;
(d) If it is determined that the reliability of the automatic focus adjustment is low, after changing the setting of the pixel mixing method, repeatedly performing the steps (a) and (b);
(e) When it is determined that the reliability of the automatic focus adjustment is high, a step of obtaining a movement position where the evaluation value reaches a peak based on the movement position of the photographing lens and the evaluation value calculated for each movement position When,
(f) moving the taking lens to the determined moving position;
Including
A step of determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when it is determined that the reliability of the automatic focus adjustment is low; A step of moving the photographing lens to a preset lens position instead of the steps (e) and (f) when the maximum evaluation value is between a predetermined upper limit value and a lower limit value; When an automatic focusing method features and to Luke camera to have a. (a) moving the photographic lens over the focus adjustment range, and obtaining an image signal from the imaging means for imaging the subject each time the photographic lens moves by a predetermined amount, under a preset focus exposure condition Acquiring an image signal that is imaged and pixel-mixed in a preset pixel-mixing method;
(b) calculating an evaluation value according to a contrast component of a subject based on an image signal acquired for each movement position of the photographing lens;
(c) determining whether the reliability of automatic focus adjustment is high or low based on the calculated evaluation value;
(d) If it is determined that the reliability of the automatic focus adjustment is low, after changing the setting of the exposure condition in the plus direction or the minus direction or changing the setting of the pixel mixing method, the steps (a) and a step of repeatedly executing (b);
(e) When it is determined that the reliability of the automatic focus adjustment is high, a step of obtaining a movement position where the evaluation value reaches a peak based on the movement position of the photographing lens and the evaluation value calculated for each movement position When,
(f) moving the taking lens to the determined moving position;
Including
A step of determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when it is determined that the reliability of the automatic focus adjustment is low; A step of moving the photographing lens to a preset lens position instead of the steps (e) and (f) when the maximum evaluation value is between a predetermined upper limit value and a lower limit value; When an automatic focusing method features and to Luke camera to have a.   In the step (d), the setting of the exposure condition is changed first, and when the change of the setting of the exposure condition reaches an upper limit or a lower limit, the setting of the pixel mixing method is changed thereafter. Item 4. A method of automatically focusing a camera according to Item 3.   The step (d) first changes the setting of the pixel mixing method, and when the change of the setting of the pixel mixing method reaches an upper limit or a lower limit, thereafter, the setting of the exposure condition is changed. The method for automatically focusing a camera according to claim 3. The photographic lens is moved over the focus adjustment range, and an evaluation value corresponding to the contrast component of the subject is calculated based on the image signal output from the imaging means every time the photographic lens moves by a predetermined amount, and the moving position of the photographic lens And the evaluation value calculated for each movement position to determine the movement position at which the evaluation value reaches a peak, and in the automatic focus adjustment device of the camera that moves the photographing lens to the obtained movement position,
Based on the evaluation value calculated for each moving position of the photographing lens, it is determined that the reliability of the automatic focus adjustment is high or low, and the determination means determines that the reliability of the automatic focus adjustment is low. And setting the exposure condition for focus when acquiring the image signal from the imaging means to change from the preset focus exposure condition to the plus direction or the minus direction and / or setting the pixel mixing method. And changing from a preset pixel mixing method, and when the determining means determines that the reliability of the automatic focus adjustment is high, means for maintaining the current exposure condition and the pixel mixing method,
Means for determining whether or not a maximum value of the calculated evaluation value is between a predetermined upper limit value and a lower limit value when the determination means determines that the reliability of automatic focus adjustment is low; And a means for moving the photographic lens to a preset lens position when the calculated maximum value of the evaluation value is between a predetermined upper limit value and a lower limit value. autofocus system of to Luke camera.

Images