JP2017187743A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of reducing degradation of focusing accuracy or facilitating focusing under a circumstance subject to a high gain.SOLUTION: The imaging apparatus includes: imaging means that picks up an image focused on a light-receiving surface; gain means that applies a gain to the image output from the imaging means to electronically change brightness of the image; and focus signal generation means that extracts a signal of frequency bandwidth from the output from the gain means to generate a focus signal from the extracted signal. The focus signal generation means changes the frequency bandwidth of the signal which is used for generating the focus signal depending on the level of the gain.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an imaging apparatus.

  2. Description of the Related Art Conventionally, an autofocus function (hereinafter referred to as AF) is known as a function for performing focusing in an imaging apparatus. In this AF technique, various methods such as a phase difference method and a contrast method have been devised.

  For example, the contrast AF function uses a value generated based on the contrast of the high-frequency component extracted from the video signal as the AF evaluation value. In a state where the image is out of focus, the contrast of the high frequency component (that is, the AF evaluation value) is low, and the contrast of the high frequency component increases as the image is focused. Therefore, the focus can be adjusted by adjusting the focus position so that the AF evaluation value is maximized.

  In contrast to such a basic AF control method, Patent Document 1 generates a plurality of AF evaluation values having different frequency bands and matches signals having higher frequency components than the frequency band normally used at the time of focusing. In other words, a technique capable of improving the focusing accuracy by using the above is disclosed.

Japanese Patent No. 4641494

  When the subject is dark in the shooting environment, an automatic exposure adjustment function (AE) that applies a gain (hereinafter also referred to as “gain”) to the video signal to compensate for the darkness and maintains an appropriate exposure level. Is commonly used.

  As described above, when the process of multiplying the gain when dark is performed, noise is added to the video signal, so that the noise signal is superimposed on the high-frequency component used in the AF evaluation value. This noise has a greater influence on the video signal as the applied gain is higher (higher gain). Also, the noise signal resulting from applying gain has a greater influence on the high frequency component than on the low frequency component. Therefore, if the high frequency component is actively used as described in the above-mentioned Patent Document 1, it is easier to expand the noise component than the case where the high frequency component is not actively used, and the focusing accuracy may be lowered. , It may be difficult to focus.

  Therefore, an object of the present invention is to provide a technique that can reduce a decrease in focusing accuracy or easily perform focusing in an environment where a high gain such as a dark photographing condition is applied. It is to be.

  One aspect of an embodiment of an imaging measure according to the present invention is an imaging unit that captures an image formed on a light receiving surface, and an image indicated by the imaging signal by multiplying an imaging signal output from the imaging unit. Gain means capable of electronically changing the brightness of the signal, and a focus signal generation means for extracting a signal in a frequency band using the imaging signal output from the gain means, and generating a focus signal from the extracted signal; The focus signal generating means changes the frequency band of the signal used for generating the focus signal according to the height of the gain, according to another aspect of the present invention. This will be described in the form for carrying out.

  According to the present invention, it is possible to reduce a decrease in focusing accuracy under a shooting environment where a high gain is applied, and to easily perform focusing.

Configuration example of imaging apparatus according to this embodiment Example of AF evaluation value at low gain Example of AF evaluation value at high gain Flow of AF operation in embodiment 1 Graph showing an example of the relationship between AF evaluation value and contrast at low gain Graph showing an example of the relationship between AF evaluation value and contrast at high gain In-focus degree determination processing example in Embodiment 2 A graph showing the relationship between the focus position, F value, gain, and AF evaluation value in a low illumination environment Flow of AF operation in embodiment 3 Flow of focus direction discrimination operation in embodiment 3 Flow of AF operation in embodiment 4 Flow of AF operation in embodiment 5 AF operation flow for explaining the problem of the third embodiment AF operation example 1 AF operation example 2

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

[Embodiment 1]
The imaging apparatus of the present embodiment is an imaging apparatus that extracts a component in a certain frequency band from an imaging signal at the time of AF processing or in-focus determination, and uses an AF evaluation value generated using the extracted frequency component. The frequency component used for generating the AF evaluation value is changed according to the gain height. Since the influence of noise caused by applying gain to a video signal is more susceptible to high-frequency components than low-frequency components, an AF evaluation value is generated using a lower frequency signal than when it is low when the gain is high. Here, using a low frequency signal includes increasing the ratio of the low frequency signal. For example, when the AF evaluation value is generated by synthesizing the first frequency signal and the second frequency signal having a higher frequency than the first frequency signal, the ratio of the first frequency in the synthesized signal is increased. Including. Further, changing the frequency component includes changing the frequency itself of the component constituting the signal and changing the ratio of the component constituting the signal. Hereinafter, the present embodiment will be described more specifically.

  FIG. 1 shows a configuration example of an imaging apparatus according to the present embodiment. In FIG. 1, a lens group 101 is an optical system that condenses incident light from a subject and condenses it on an image sensor 105. The lens group 101 includes a focus lens that focuses on the subject, a zoom lens that adjusts the angle of view, and the like. The lens group 101 may be integrated with the imaging device, or the lens group 101 and the imaging device may be separated and the lens group 101 to be mounted may be interchangeable. In addition, the captured image may be a moving image or a still image.

  Light that has entered the camera through the lens group 101 passes through the optical filter 102, and the light amount is adjusted by the diaphragm 103 that adjusts the light amount incident on the image sensor 105. The type of the optical filter 102 is not particularly limited. For example, an infrared cut filter (IRCF) can be used.

  The video information whose light amount has been adjusted by the aperture 103 passes through the color filter 104 arranged in a predetermined order for each pixel on the light receiving surface of the image sensor 105 and is received by the image sensor 105.

  The image pickup element 105 is an image pickup means, picks up an image formed on the light receiving surface by the lens group 101, and outputs image information of a photographing target as an analog signal (image pickup signal).

  The brightness of the image indicated by the imaging signal output from the imaging element 105 is electronically adjusted (gain control) by a gain means (hereinafter also referred to as “AGC”) 106. The AGC 106 can multiply the image pickup signal output from the image pickup means by gain, and can electronically change the brightness of the image. The analog imaging signal output from the AGC 106 is converted into a digital signal by the A / D conversion unit 107.

  The video signal processing unit 108 performs predetermined processing on the digital image pickup signal from the A / D conversion unit 107 and outputs a luminance signal and a color signal for each pixel. Each parameter to do is created. As parameters for camera control, for example, parameters used for aperture control, AF evaluation values that are frequency component values for focusing, parameters used for white balance control for adjusting color, etc. can give. In the present invention and this specification, an AF evaluation value signal may be referred to as a focus signal. Thus, since the video signal processing unit 108 generates a focus signal, it can also be referred to as a focus signal generation unit. It is possible to extract signals in a plurality of frequency bands from the imaging signal output from the imaging element 105 of the video signal processing unit 108 and gain-controlled by the AGC 106. For example, the video signal processing unit 108 can extract a signal in the first frequency band and a signal in the second frequency band that is a higher frequency band than the first frequency band. Here, the frequency band signal may be obtained by extracting a pinpoint frequency component signal. For example, a bandpass filter can be used to extract a signal in a specific frequency band.

  The video signal output unit 109 outputs the video signal created by the video signal processing unit 108 to the outside.

  The exposure control unit 110 calculates luminance information in the shooting screen from the luminance information output from the video signal processing unit 108, and controls the aperture 103 and the AGC 106 to adjust the shot image to a desired brightness. Further, the brightness can be adjusted by adjusting the storage time of the image sensor 105 by adjusting the shutter speed.

  The autofocus control (focusing operation) is performed using the high-frequency component value extracted from the video signal generated by the video signal processing unit 108 as an AF evaluation value. Specifically, this is performed by controlling the lens group 101 by the optical control unit 114 and adjusting the focus position so that the AF evaluation value becomes the maximum value. The optical control unit 114 is an optical control unit capable of driving and controlling a focus lens included in the lens group 101, and has an autofocus function.

  As described above, in this embodiment, when the gain is high, the AF evaluation value is generated using a signal in a lower frequency band than when the gain is low. The frequency band to be used may be changed steplessly or may be changed stepwise depending on the gain level. Stepwise includes two stages, for example, when a gain is a certain value (threshold) or more, a signal in the first frequency band is used, and when the gain is smaller than a certain value, the second frequency band is higher than the first frequency band. These signals may be used.

  The external setting means 115 is a generic name for setting means for performing camera settings, and is a means for performing so-called general camera operations such as focusing, brightness designation, and zoom magnification designation.

  The control setting unit 116 actually performs a control command for the camera sent from the external setting unit, and performs exposure control, lens control, and the like.

[Example 1]
In the present example, the first frequency band component and the second frequency band component that is a higher frequency band component than the first frequency band in the imaging apparatus according to the first embodiment described above are combined. An imaging apparatus that performs AF processing using the combined signal acquired in this way as an AF evaluation value will be described. In a high gain environment, the imaging apparatus according to the present exemplary embodiment acquires an AF evaluation value using a low frequency signal by increasing the proportion of the first frequency band component in the combined signal. Hereinafter, in the present embodiment, the component in the first frequency band is referred to as a low frequency component, and the component in the second frequency band is referred to as a high frequency component.

  2 and 3 schematically show examples of AF evaluation values of components in each frequency band at low gain and high gain. The horizontal axis represents the focus position, and the vertical axis represents the AF evaluation value corresponding to the focus signal. This figure shows the AF evaluation value signal (signal intensity of each frequency component) until the focus lens is moved from the point where it is out of focus to the point where it is out of focus. Are plotted). In this figure, the in-focus position, that is, the AF evaluation value signal is the highest.

  From FIG. 2, it can be seen that when the gain is low, a clean AF evaluation value is obtained with few noise components in each frequency band component.

  However, as shown in FIG. 3, when the gain is high, a noise component also affects the AF evaluation value, and the AF evaluation value itself is offset as a whole and the peak is crushed. In particular, the influence of the high-frequency AF evaluation value (solid line in FIGS. 2 and 3) that easily picks up noise components is significant. On the other hand, the low-frequency AF evaluation value (dotted line in FIGS. 2 and 3) has a characteristic that it is less susceptible to noise than a high-frequency component signal.

  When a high-frequency AF evaluation value is used at such a high gain, a signal buried in noise is used. As a result, there is a problem that blurring is lost or a peak of focus cannot be found.

  As described above, the characteristics of the high frequency component are advantageous for focusing, but are easily affected by noise. On the other hand, the low frequency component has a feature that it is disadvantageous for focusing, but is not easily affected by noise.

  Therefore, in this embodiment, the ratio of the frequency band used for generating the AF evaluation value is changed according to the gain height. As a result, focusing can be performed satisfactorily in both low gain and high gain environments.

  The synthesized signal described in FIG. 3 is a signal synthesized by mixing a high frequency component and a low frequency component. By using this mixed composite signal as an AF evaluation value, when a high frequency component is used as an AF evaluation value, a peak appears even in a high gain environment where the peak of the AF evaluation value did not appear much. , It is possible to reduce the accuracy degradation of the AF process.

  Furthermore, by adding not only the low frequency component but also the high frequency component, even if it is difficult to peak the evaluation value with only the low frequency component, the peak of the evaluation value stands near the peak position of the high frequency component. It is also possible to increase the accuracy of the focal position.

  On the other hand, when the gain is low, if it is used in a state where the ratio of low frequency components is large as shown in FIG. 2, a wide peak appears near the best focus position (also referred to as the in-focus position). is there. Therefore, the ratio of the high-frequency component in the synthesized signal is made larger at the time of low gain than at the time of high gain.

  Based on what has been described above, FIG. 4 shows an example of the basic operation of the AF function.

  First, in step S401, it is determined whether the focus lens remains in the same area a predetermined number of times. This determination is a determination that the best focus position is in that area when it remains within the same focus area. Since the determination of 401 does not pass at the beginning of the AF operation, the process proceeds to the next process.

  In step S402, it is determined whether or not the current shooting situation is in a high gain state. At the time of high gain, since the influence of noise appears on the video signal as described above, in this embodiment, the AF evaluation value signal generation method (ratio of each frequency component) used for focusing is based on the gain amount. change.

  If not in the high gain state, an AF evaluation value signal is generated based on the synthesized signal obtained by synthesizing the low frequency component and the high frequency component at the first ratio (S403). On the other hand, if it is in the high gain state, an AF evaluation value signal is generated based on the synthesized signal obtained by synthesizing the low frequency component and the high frequency component at the second ratio (S404). Here, the first ratio is a ratio in which the ratio of the high-frequency component is larger than the second ratio. Therefore, in step S404, an AF evaluation value signal is generated so that the ratio of the low frequency component is larger than in step S403. At this time, the first ratio is preferably such that the high-frequency component ratio is equal to or greater than the low-frequency component ratio, and the second ratio is preferably such that the high-frequency component ratio is smaller than the low-frequency component ratio. Then, a focus search is performed using the AF evaluation value signal generated in steps S403 and S404 (S405). During the focus search, the focus position is driven by driving the focus lens, and the focus position information and the AF evaluation value at the focus position are sequentially acquired. During the focus search, the AF evaluation value being searched is always acquired, and it is determined whether or not the AF evaluation value acquired at that time is greater than the previously acquired AF evaluation value (S406). If the AF evaluation value increases during the focus search, it is considered that the best focus position is in the currently moving drive direction. Therefore, the focus lens included in the lens group is moved in the forward direction, the held AF evaluation value and focus position are updated to the current values, and are temporarily stored as the peak value and peak position of the AF evaluation value. (S408). On the other hand, if the AF evaluation value acquired this time becomes smaller than the previous AF evaluation value, it is determined that the subject has moved away from the best focus position. Therefore, the focus lens is moved in the direction opposite to the currently moving direction, and the AF evaluation value and the focus position that have been held so far are cleared as the driving direction is reversed (S407).

  Thereafter, the peak position of the AF evaluation value can be detected by returning to step S401 again and repeating steps S401 to S408. If it is determined in step S401 that the user has been in the same area a predetermined number of times, it is considered that there is an AF evaluation value peak in the AF evaluation values acquired so far. Then, the detection of the peak position of the AF evaluation value is terminated with the peak value and peak position of the AF evaluation value being held as the final peak value and peak position. Then, the focus position is stopped at the peak position, and a series of operations is completed (S409).

  Here, the case where the ratio of the frequency component used according to the gain is changed is described as an example. However, the same effect can be obtained not only by changing the ratio of frequency components but also by changing the frequency band to be used. In that case, it is desirable to lower the frequency band to be used as the gain increases, as in the case of changing the ratio as described above.

  Further, when the AF evaluation value is generated using a single frequency band, the frequency may be switched to a signal in a lower frequency band.

  Furthermore, when the focus position is stopped in the final AF operation shown in step S409 in FIG. 4, the peak position may be detected again, and the detected peak position may be set as the final peak position. When re-detecting the peak position, it is possible to use a signal having a higher frequency component compared to the focus search operation performed in step S405 or use an AF evaluation value signal having a high ratio of high frequency components. preferable. The reason for this is that, as shown in FIG. 2, the signal of the low frequency component is gentler in the vicinity of the peak position than that of the high frequency, so if only the low frequency signal is used, the signal is shifted from the best focus position. This is because focusing may stop.

  For this reason, in the rough adjustment (S402 to S408) for searching for the vicinity of the best focus position (near the focus position), the low-frequency component is taken in and the focus lens is led to the vicinity of the peak position. And, when detecting the focus position (focus stop position) when the focus position is finally stopped, a high-frequency component in which the peak of the AF evaluation value appears more in the coarsely adjusted area is performed. It is desirable to obtain each position by changing the frequency component to be used.

  On the other hand, when focusing is performed by incorporating a high frequency component in a high gain state, the peak may be buried in noise in the high frequency component. In this situation, if a signal in the same frequency band as the low gain state is used, or if the ratio of combining the high frequency component and the low frequency component is the same, the noise component becomes dominant and the focusing accuracy may decrease. .

  Therefore, even in the case where the peak position is detected again in step S409, it is preferable to use a low-frequency component matched to the gain as described above when the gain is high. Therefore, when the gain is not high, the AF evaluation value used in the final operation (S409) is acquired from the higher frequency signal than in the focus search (S405). In the case of high gain, the AF evaluation value is used during the focus search and the final operation. An AF evaluation value may be acquired from signals having the same frequency component. Further, even when the frequency component of the signal used in the final operation (S409) is higher than in the focus search (S405) in the case of high gain, the case where the gain is not high is higher than that in the case of high gain. It is preferable to increase the frequency component of the signal used during operation. In other words, also in step S409, it is preferable to change the frequency band used for generating the focus signal according to the gain. In this case, in the case of high gain, the same frequency signal as in S404 or a focus signal generated with a frequency ratio is used, while in other cases, a frequency signal or focus in a frequency band higher than S403 is used. The signal will be used. Therefore, the frequency band difference in step S409 is larger than the frequency band difference in steps S403 and 404.

  When the peak position is detected again in step S409, it is preferable to acquire AF evaluation values at a focus position interval finer than that during focus search, detect the peak position with high accuracy, and stop focusing. The detection of the peak position again in step 409 corresponds to the minute drive and the peak position acquisition process using the minute drive result of the third embodiment to be described later, and will be described in detail in the third embodiment.

  According to the present embodiment, since the AF operation can be performed while reducing the influence of noise even in a high gain environment, it is possible to reduce a decrease in focusing accuracy.

[Example 2]
In the present embodiment, a case will be described in which the degree of focus is determined from a captured image using the focus signal (AF evaluation value) generated by the focus signal generation unit.

  FIG. 5 is an example showing the relationship between the focus position and each evaluation value.

  In general, it is known that there is a correlation between the point where the contrast is highest and the focus position.

  When the subject is out of focus, the edge of the subject does not come out and there is no boundary line with the surrounding subject and the image is mixed with the surrounding image, so the image has no contrast. On the other hand, when the subject is in focus, the edge component of the subject appears clearly, so that the subject has a high contrast.

  As described above, if the AF evaluation value signal is output from the contrast state, it can be estimated whether or not the focus lens is in the vicinity of the in-focus position where the focus is achieved.

  For example, it is conceivable that a determination value indicating how much the AF evaluation value should be output in accordance with the contrast value is stored in advance as data, and if this determination criterion is exceeded, it is determined that the focus is in the vicinity.

  An example is shown in FIG. FIG. 5 shows values of each frequency component (high frequency component and low frequency component) which are the contrast value and the AF evaluation value. The peak position of the AF evaluation value of each frequency component indicates the best focus position. The contrast value is also the highest near the focus peak position, and the relationship between the focus position and contrast can be seen. If this degree of focus can be determined appropriately, the focus lens can be moved a lot in areas that are out of focus, and the focus lens can be moved finely in the vicinity of the focus to shorten the focusing time and improve focus performance. I can do it.

  In determining the degree of focus, it is possible to determine with high accuracy by using a high frequency component. That is, when a high frequency component signal is compared with a low frequency component signal, the higher the frequency component is, the lower the signal is when the focus is out of focus. There is a tendency to come. Therefore, since the peak of the evaluation value rises more steeply as a component in the high frequency band, it becomes easier to clearly determine whether the focus is out of focus or in focus.

  As shown in FIG. 5, the low frequency component has a gentler peak than the high frequency component, and the AF evaluation value of the high frequency component narrows down the focus area near the in-focus position more accurately. I understand that I can do things.

On the other hand, FIG. 6 shows a focus position and a state of each evaluation value in a state where a high gain is applied.
By applying gain to the luminance signal of the video to make it brighter when the video is dark, no peaks appear in the high frequency component signal as described in the first embodiment, and it is difficult to correctly determine the focus. Become.

  Further, since the high frequency component itself becomes high due to the influence of noise, the high frequency component signal is high from the noise signal even in a region where the contrast is not so high, and it is easy to erroneously determine that the signal is in focus.

  Therefore, in the present embodiment, the frequency component to be combined according to the gain with respect to the AF evaluation value signal which is a combined signal of a plurality of frequency bands for determining the degree of focus in consideration of the amount of noise superimposed according to the gain. It is proposed to change the ratio.

  By doing so, as described in the first embodiment, it is possible to reduce the influence of noise that is not good at high frequency components.

  As shown in FIG. 6, if the focus determination is performed using the low-frequency component with respect to the focus determination threshold set according to the contrast value (contrast in the figure), the high-frequency component is used. It is possible to improve the situation where the degree of focus could not be determined.

On the other hand, if the degree of focus determination is always performed using a low-frequency component, the region determined to be in-focus is increased as compared with the case where a high-frequency component is used, so that the determination accuracy becomes coarse.
In order to consider such characteristics, it is necessary to change the ratio of the low frequency component of the evaluation frequency in accordance with the gain.

  Based on what has been described above, FIG. 7 shows an example of a basic operation for determining the degree of focus. In step S701, it is determined whether the current shooting situation is in a high gain state.

  At the time of high gain, as described above, the influence of noise appears on the video signal. Therefore, here, the frequency signal used for determining the degree of focus is determined from the gain amount.

  If it is not in the high gain state, a synthesized signal containing many high frequency components (a signal obtained by synthesizing the low frequency component and the high frequency component at the first ratio) is synthesized to generate an AF evaluation value signal (S702). On the other hand, if the gain is high, a synthesized signal (a signal obtained by synthesizing the low frequency component and the high frequency component at the second ratio) is synthesized so that the ratio of the low frequency component is larger than that in step S702, and AF evaluation is performed. A value signal is generated (S703).

  Next, in step S704, a threshold value (referred to as an in-focus determination threshold value) for determining the in-focus level is acquired from the contrast of the video. A threshold value corresponding to a contrast value may be stored in advance, and a threshold value corresponding to a contrast value may be acquired as needed, or a correction value corresponding to a contrast value may be used with respect to a reference threshold value, The threshold value may be calculated using a calculation formula and a contrast value.

  Then, the current focus degree is determined by comparing the focus degree determination signal generated in steps S702 and 703 with the focus determination threshold value calculated in step S704 (S705).

  When the focus degree determination signal is smaller than the threshold value, it is determined that the focus is not in the vicinity of the in-focus position, and the in-focus position is determined (S706).

  On the other hand, when the focus degree determination signal is larger than the threshold value, it is determined that the subject is in the vicinity of the focus position.

  Here, the case where the ratio of the frequency component used according to the gain is changed is described as an example. Similar to the first embodiment, the same effect can be obtained not only by changing the frequency band ratio but also by changing the frequency band to be used. In that case, it is desirable to lower the frequency component used as the gain increases, as in the case of changing the ratio. Alternatively, a single frequency band may be used, and the frequency band may be switched to a signal in a lower frequency band.

  Furthermore, also in the threshold value used for the focus degree determination described in the present embodiment, as in the focus degree determination signal, the height of the gain at the time of determination, or the frequency to be used, and the ratio of the frequency to be used are It is desirable to set according to at least one of the conditions.

  In addition, when the absolute values of the frequency components themselves are different, it is desirable to normalize and use them or to normalize the focus determination threshold value itself according to the determination signal.

  By performing the processing as described above in this case, it is possible to perform a good focus determination even at a high gain.

[Embodiment 2]
In the present embodiment, the image pickup apparatus in which the gain changes during the AF operation, the stability determination unit that determines whether the gain is stable, the peak position using the determination result by the stability determination unit and the AF evaluation value An imaging apparatus provided with a peak position detection means for acquiring the will be described. In the imaging apparatus of the present embodiment, the optical control unit can perform focus adjustment by controlling the position of the focus lens so that the focus position approaches the peak position based on the detection result of the peak position detection unit. .

  When the gain applied to the video signal increases and the noise signal to be superimposed increases, the AF evaluation value tends to increase (see FIGS. 2 and 3). As a result, there may be a problem in the AF operation. For example, in the case of an imaging apparatus in which the gain can change during an AF operation, there may be a problem that the focus position when the gain is high is erroneously determined to be the in-focus position, resulting in blurring. Therefore, the peak position detection unit of the present embodiment detects the peak position using the AF evaluation value generated using the signal output from the AGC 106 after the gain is stabilized based on the determination result by the stability determination unit. Process. As a result, it is possible to reduce such problems and improve the focusing accuracy. Note that the determination by the stability determination means and the time lag due to A / D conversion or the like can be almost ignored. Therefore, in this embodiment, the video signal output from the A / D converter after determining that the gain is stable by the stability determination unit is regarded as the video signal output from the AGC after the gain is stabilized. Hereinafter, the present embodiment will be described more specifically.

  Since the configuration example of the imaging apparatus according to the present embodiment is the same as that illustrated in FIG. 1 described in the first embodiment, the description thereof is omitted, but unlike the first embodiment, the frequency used for generating the AF evaluation value according to the gain. Do not change the bandwidth. Therefore, since it is not necessary to acquire AF evaluation values from signals in a plurality of frequency bands, if the video signal processing unit 108 can extract a signal in one frequency band from the imaging signal, a signal in a plurality of frequency bands cannot be extracted. Also good. The AF flow in the imaging apparatus according to the present embodiment will be described in more detail in the following examples.

[Example 3]
In the present embodiment, a process for acquiring the peak position of the AF evaluation value after the gain is stabilized will be described more specifically.

  The relationship among the F value, gain, and AF evaluation value for each focus position in a low illuminance environment will be described with reference to FIGS. FIG. 8A illustrates the relationship between the F value and the gain for each focus position. In FIG. 8A, the F value 801 has a characteristic that the focus is higher toward the infinite side and lower toward the near side due to lens characteristics. Although the amount of light incident on the image sensor changes due to the change in the F value 801, the exposure is controlled by the AE function so as to maintain the brightness. In a low illumination environment, it is assumed that the aperture has already been opened and the shutter speed has been slowed down to the limit, so the gain 802 is controlled here. That is, the gain 802 becomes higher as the focus is infinite, and lower as the focus is closer. In this case, the gain value at the infinite end is Gain A, the gain value at the in-focus position is Gain B, and the gain value at the closest end is Gain C.

  FIG. 8B illustrates the relationship between the gain for each focus position and the AF evaluation value. FIG. 8B shows an AF evaluation value 803 when the gain value is fixed to Gain A, an AF evaluation value 804 when the gain value is fixed to Gain B, and an AF evaluation value 805 when the gain value is fixed to Gain C. . As the AF evaluation value increases, the noise signal is superimposed on the high-frequency component as the gain increases, and tends to increase. Therefore, at the same focus position, “Gain A AF evaluation value 803> Gain B AF evaluation value 804> Gain C AF evaluation value” 805 ". Reference numeral 806 denotes an example of the AF evaluation value when the gain varies due to the AE function. For example, the AF evaluation value when the focus is driven from the infinite end to the closest end gradually shifts from the AF evaluation value of Gain A to the AF evaluation values of Gain B and Gain C as indicated by reference numeral 806.

  Next, the problem to be solved by the present embodiment will be described in detail with reference to FIGS.

  FIG. 13 is a flowchart simply showing the AF operation. First, in step S1301, large search driving is performed. Here, the large search drive is a drive for obtaining an AF evaluation value at each focus position while driving the focus position largely and searching for a peak position of the AF evaluation value.

  Since the large search drive searches the peak position roughly at a high speed, the peak position here is rough. In step S1302, the peak position detected by the large search drive in step S1301 is driven at high speed, and then in step S1303, the peak position is detected to detect the peak position. In the minute drive, since the AF evaluation value at each focus position is acquired and the peak position of the AF evaluation value is detected while driving the focus position minutely, the accuracy is higher than the peak position acquired by the large search drive. The focus position is adjusted by regarding the peak position acquired in this step as the final peak position. In step S1304, the focus position is driven to the peak position detected by the minute driving in step S1303, and the AF operation is terminated. Note that it is preferable to generate an AF evaluation value using a high-frequency component at the time of minute driving than at the time of large search driving.

  An example of an AF operation failure caused by the above-described relationship between the gain and the AF evaluation value in the AF process will be described with reference to FIGS.

  The upper part of FIG. 14A shows the F value 1001 and the gain 1002 for each focus position, as in FIG. 8A. For the F value 1001 and the gain value 1002 at this time, the F value at the infinite end is F value A, the gain value is Gain A, the F value at the in-focus position is F value B, the gain value is Gain B, and the F value at the near end is The F value C and the gain value are GainC. Here, for the sake of detailed explanation, the scale is enlarged only near the in-focus position. The lower part of FIG. 14A shows an example of driving the focus position from steps S1301 to S1303 in FIG. First, let P0 be the focus position at the start of the AF operation. In step S1301, large search drive (arrow 1003) is performed from position P0 to position P1, and the peak position is roughly detected. Next, in step S1302, high-speed driving is performed up to position P2, which is the peak position detected by large search driving (arrow 1004). Thereafter, in step S1303, minute driving (arrow 1005) is performed from position P2 to position P3, and the peak position is detected.

  FIG. 14B shows transitions of the AF evaluation value 1006, the F value 1007, and the gain 1008 in the above-described focus operation example. Here, in the minute driving in step S1303, the AF evaluation value is higher at the position P2 which is the starting position of the minute driving than at the in-focus position. This is because the focus drive (arrow 1004) from the position P1 to the position P2 is high speed, and the gain follow-up is not in time, and a gain value higher than GainB is obtained at the position P2 that is originally GainB. . As a result, the peak position detected by the minute driving becomes the position P2, and it is assumed that there is a problem that the driving is not finally performed to the original in-focus position.

  Therefore, in this embodiment, in order to reduce erroneous detection of the peak position, the peak position is detected by minute driving using the AF evaluation value acquired after the gain is stabilized. However, even if the AF evaluation value is acquired by the micro drive before the gain is stabilized, the AF evaluation value may not be used for the detection of the peak position. A specific flow will be described later.

  Next, the driving direction at the time of driving the focus position will be described with reference to FIGS. As a method for determining the drive direction of the focus position, if the AF evaluation value is in the increasing direction, the focus position is approaching. Conversely, if the AF evaluation value is in the decreasing direction, the focus position is in the opposite direction. it is conceivable that. However, when the gain fluctuates, the focus drive direction may be wrong. FIGS. 15A and 15B show examples thereof.

  15A and 15B show an AF evaluation value 501 when the gain value is fixed to Gain A, and an AF evaluation value 502 when the gain value is fixed to Gain B. As described above, GainA> GainB. FIG. 15A shows the transition of the AF evaluation value when the focus position is driven one step from the position P10 under the condition that the gain is decreased from Gain A to Gain B. At this time, since the AF evaluation value decreases due to a decrease in gain even if the focus position is driven to P11 toward the focus position, the optical control unit 114 determines that the focus position has been driven to the side opposite to the focus position. Then, the driving direction is reversed. FIG. 15B shows the transition of the AF evaluation value when the focus is driven one step from the position P10 under the condition that the gain is increased from Gain B to Gain A. At this time, even if the focus position is driven to P12 that is opposite to the in-focus position, the AF evaluation value increases. Therefore, the optical control unit 114 determines that the focus position has been driven in the in-focus position direction, and is driven. Do not reverse direction. As described above, if the drive direction of the focus position cannot be correctly determined, the focus position may be searched while being driven in a direction opposite to the direction in which it should be driven. Therefore, it may take time to focus. is there.

  Therefore, in this embodiment, in order to reduce erroneous determination of the drive direction of the focus position, processing for changing the threshold value for reversing the focus drive direction is performed based on the gain and the amount of gain change. A specific flow will be described later.

  In the present embodiment, by performing the AF operation based on the above, it is possible to provide an imaging device capable of focusing quickly and accurately even in a low illumination environment where a lot of gain is required.

  The AF process of this embodiment will be described with reference to the flowcharts of FIGS.

  FIG. 9 is a flowchart showing the main process of the AF operation of this embodiment.

  In this embodiment, first, large search driving is performed in step S901, and peak position acquisition processing during large search driving is performed in step S902. The peak position acquisition process is a process for detecting a focus position (that is, a peak position) at which the AF evaluation value is maximum using the acquired AF evaluation value. For example, a plurality of focus positions and AF evaluation values based on video signals acquired at the focus positions are temporarily stored in association with each other, and the focus position associated with the highest AF evaluation value is selected from among them. It can be detected as a peak position. Further, as in the flow of the first embodiment, the peak position may be detected by updating the provisional AF evaluation value and the peak position.

  In step S903, the end of the large search drive is determined. As a determination method, for example, there is a method of terminating the large search drive when the degree of focus becomes a predetermined level or more. This is because the degree of focus (the degree of deviation between the focus position and the focus position) can be estimated if the AF evaluation value is obtained from the contrast state, so the AF evaluation value was acquired by a large search. This is a method using the fact that it is possible to guess whether or not there is an in-focus position near the position. However, in a low illumination environment where the gain increases and the noise increases, the estimation accuracy also deteriorates. Therefore, as in the first embodiment, a determination method may be considered in which the large search drive is terminated when the number of inversions in the driving direction becomes equal to or greater than a predetermined value, or the large search drive is terminated when a predetermined focus range is driven.

  When the large search driving is completed, the focus position is driven to the peak position acquired by the large search driving in step S904, and then the minute driving is performed in step S905. In subsequent step S906, it is determined whether or not the gain is stable by the stability determination means. Whether the gain is stable can be determined, for example, based on whether the fluctuation range of the gain within a predetermined time is within a predetermined range, whether a predetermined time has elapsed since the minute driving was started, or the like. In the case of using the former method, it is possible to determine whether or not the gain is fluctuating if the predetermined time is set as the gain acquisition cycle and the predetermined range is set as the minimum unit for determining whether or not the gain is changed.

  If the gain is stable, the peak position acquisition process is performed in step S907. If the gain is not stable, the peak position acquisition process is not performed. This is because, as described with reference to FIG. 14, if the peak position acquisition process is performed in a state where the gain is not stable, an erroneous peak position may be detected. Further, the AF evaluation value used in the peak position acquisition processing in step S907 is the AF evaluation value acquired after the gain is stabilized (FIG. 14B) (when the focus position becomes the in-focus position for the second time ( AF evaluation value obtained after the driving process has advanced to A).

  In step S908, the end of minute driving is determined. As the determination method, as in the large search drive end determination method, the degree of focus estimated from the AF evaluation value is used, the number of times of inversion of the drive direction is used, or the drive of the predetermined focus range is completed. For example, a method of making a determination can be considered.

  When the minute driving is finished, the focus position is driven to the peak position acquired by the minute driving in step S909, and the AF operation is finished.

  Even if the determination whether the gain is stable (S906) is performed before the minute driving (S905), the peak position can be detected using the AF evaluation value acquired after the gain is stabilized. . However, since the minute driving is started before the gain is stabilized, it can be used for detection of the peak position from the AF evaluation value acquired immediately after the gain is stabilized, so that the time required for the AF processing can be shortened. ,preferable.

FIG. 10 is a flow of direction determination processing performed by the optical control unit 114 during focus driving (S901, S905). First, in step S1001, the AF evaluation value and gain value before driving the focus position are held, and in step S1002, driving is performed one step. Thereafter, an AF evaluation value and a gain value after driving the focus position are acquired in step S1003, and a change amount before and after the focus position driving is calculated for each of the AF evaluation value and the gain value in step S1004. The amount of change is calculated from the difference. In step S1005, based on the amount of change in the gain value, a threshold value (hereinafter referred to as a direction reversal threshold value) used to determine whether to reverse the focus drive direction is changed. The threshold is set so that the threshold when the gain is increasing (the gain change amount is positive) is smaller than the threshold when the gain is decreasing (the gain change amount is negative). For example, the direction inversion threshold can be set to a value determined by the following equation.
Direction inversion threshold = predetermined value + (correction coefficient α × gain change amount)

  Even if the gain change amount is the same, the higher gain has a greater influence on the AF evaluation value. Therefore, it is preferable to increase the correction coefficient α as the gain value increases.

  Finally, in S1006, it is determined whether or not the change amount of the AF evaluation value is smaller than the corrected reversal threshold value. If it is smaller, the driving direction is reversed in step S1007, and the process ends. However, the change amount of the AF evaluation value is a value obtained by subtracting the AF evaluation value acquired this time from the previously acquired AF evaluation value, and the change amount becomes negative when the AF evaluation value is small. Further, the direction inversion threshold is a negative value, and when the change amount of the AF evaluation value is smaller than the direction inversion threshold, it indicates that the AF evaluation value is smaller than the absolute value of the direction inversion threshold. If the direction inversion threshold is a positive value, it may be determined whether or not the AF evaluation value is smaller than the direction inversion threshold.

  In this embodiment, it is determined whether or not the gain is stable regardless of the gain level. If the gain is not high, the influence of the gain change on the peak position detection is small. Therefore, when the gain is less than the threshold, step S906 may be skipped, or even if it is determined that the gain is not stable, the process may proceed to S907.

[Example 4]
This example is an example related to the second embodiment. The third embodiment uses the AF evaluation value acquired while the gain is stable (that is, after the gain is determined to be stable and before the gain is determined to be unstable). The peak position was detected. The present embodiment is different from the third embodiment in that once the gain is stabilized, the peak position is detected in minute driving without determining whether or not the current gain is stable.

  The main process of the AF operation of this embodiment will be described with reference to the flowchart of FIG. Note that description of the same components as those in the third embodiment is omitted.

  Steps S1101 to S1105 are the same as steps S901 to S905 of the first embodiment, and thus description thereof is omitted.

  In step S1106, the gain stabilization flag is checked. Here, the gain stabilization flag is a flag for determining whether or not the gain has been stabilized even once during minute driving. If the gain stability flag is ON, the process proceeds to step S1107, and a peak position acquisition process by fine driving is performed. On the other hand, if the gain stability flag is not ON (OFF), the process proceeds to step S1111 to determine whether the gain is stable (same as step S906 in the third embodiment). If stable, the process proceeds to step S1112 to turn on the gain stable flag.

  Steps S1108 and S1109 are the same as steps S908 and S909 of the third embodiment.

  Finally, in step S1110, the gain stabilization flag is turned off, and the AF operation ends.

  In the third embodiment, it is possible to reduce the erroneous determination of the peak position by performing the peak position acquisition process only when the gain is stable. However, when the gain is stabilized or it becomes unstable again, the peak position cannot be detected in the minute drive and the AF operation may not be completed. On the other hand, in this embodiment, once the gain is stabilized, even if the gain subsequently becomes an uneasy point, the peak position acquisition processing in the minute driving is performed, so that the AF operation does not end. Further, in the minute driving, since there is little possibility that the focus is greatly moved and the gain is changed, it is considered that it is difficult to erroneously determine the peak position once the gain is stabilized.

[Example 5]
In this example, an imaging apparatus according to both Embodiment 1 and Embodiment 2 will be described. By integrating the configurations of the first and second embodiments, the performance is further improved.

  Here, FIG. 12 shows a flowchart of the AF operation in the present embodiment, which will be described. Steps S1201 to S1208 are substantially the same as steps S401 to S408 of the first embodiment, and thus description of each step is omitted.

  Next, it is determined whether or not the gain for adjusting the brightness is stable. If it is determined that the gain is not stable, the process returns to step S1202 and the repeated flow is followed. As a result, there is a possibility that AF evaluation values for the same focus position and different gains may be acquired. However, AF evaluation values for each gain may be stored, or newly acquired AF The AF evaluation value acquired previously with the evaluation value may be rewritten. However, in any case, the AF evaluation value is preferably stored in association with the gain when the AF evaluation value is acquired.

  On the other hand, if the gain is stable, the process proceeds to step S1210, the peak position is updated, and the process returns to step S1201. Thereafter, if it is determined in step S1201 that the user has been in the same area a predetermined number of times, the process proceeds to step S1211, and the focus position is driven to the peak position acquired during the focus search so far to complete a series of operations. .

  In the present embodiment, as in the first embodiment, the case where the ratio of the frequency components to be used is changed according to the gain (steps S1202 to S1204) has been described, but not only the frequency ratio but also the frequency itself to be used is changed. The same effect can be obtained even if it is changed. In that case, it is desirable to lower the frequency component to be used as the gain increases, as in the case of changing the ratio described above. Even when the frequency itself is performed using a single frequency, the frequency may be switched to a signal in a lower frequency band.

  Further, similarly to step S411 of the first embodiment, also in step S1211, an AF evaluation value signal having a higher frequency component or a higher ratio of high frequency components than in the focus search operation performed in step S1205 is used. The peak position may be detected again. Further, the peak position may be redetected by performing finer focus driving than in the focus search. As described above, when the focus is re-detected in step S1211, this driving in step S1211 corresponds to the minute driving in the third and fourth embodiments (S905 to S909 in the third embodiment), and steps S1205 to S1210 are performed. This corresponds to the large search drive of the third and fourth embodiments. In this case, in the large search, the peak position is updated when the gain is stable, and the peak position is not updated when the gain is not stable. Thereby, compared with the case where step S1209 is not implemented, the focus detection accuracy at the time of large search can be improved. In addition, since the peak position of the minute drive is detected at least by the minute drive that is performed once the gain is stabilized, the detection accuracy of the peak position of the minute drive can be improved. On the other hand, steps S1205 to S1210 can be associated with minute driving. In this case, since it is determined whether or not the gain is stable (step S1209) at the time of peak detection at the time of micro driving, the detection accuracy of the peak position of micro driving can be improved. Further, it may be determined whether or not the gain is stable during both the large search and the minute drive. In that case, for example, step S1211 may be performed by performing steps S905 to S909 of the third embodiment.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

101 Lens Group 105 Image Sensor 106 AGC
108 video signal processing unit 110 exposure control unit 114 optical control unit

Claims (20)

An image pickup means for picking up an image formed on the light receiving surface; a gain means for multiplying an image pickup signal output from the image pickup means; and an electronic brightness change of the image indicated by the image pickup signal;
A focus signal generating unit that extracts a signal in a frequency band using the imaging signal output from the gain unit, and generates a focus signal from the extracted signal;
The image pickup apparatus, wherein the focus signal generation unit changes a frequency band of the signal used for generating the focus signal in accordance with the height of the gain.   The focus signal generation means extracts a signal in a first frequency band and a signal in a second frequency band that is a frequency band higher than the first frequency band from the output of the gain means, and the first frequency band The focus signal is generated from a synthesized signal obtained by synthesizing a signal in a frequency band and a signal in the second frequency band, and the signal in the first frequency band and the signal in the second frequency band occupied in the synthesized signal The imaging apparatus according to claim 1, wherein a frequency band of the signal used for generating the focus signal is changed by changing a ratio of the signal. Focusing determination means for determining the degree of focusing from the output of the focus signal;
The imaging apparatus according to claim 1, wherein the focus determination unit determines a focus degree from a contrast value obtained from the image and the focus signal. First peak position detecting means for detecting the peak of the focus signal and obtaining the vicinity of the in-focus position;
And a second peak position detecting means for detecting a focus signal peak by using the detection result of the first peak position detecting means and the focus signal to obtain a focus stop position. Item 4. The imaging device according to any one of Items 1 to 3.   The imaging apparatus according to claim 4, wherein the focus signal used for the second peak position detection unit is generated using a higher frequency than the focus signal used for the first peak position detection unit.   5. The imaging apparatus according to claim 4, wherein the same frequency component is used for the focus signal used for the first peak position detection means and the focus signal used for the second peak position detection means. The focus signal generation means extracts a signal of a first frequency band and a signal of a second frequency band that is a frequency band higher than the first frequency band from the output of the gain means, and the first frequency band Generating the focus signal from a synthesized signal obtained by synthesizing the signal of the frequency band and the signal of the second frequency band;
The synthesized signal used for generating the focus signal used by the first focusing means and the synthesized signal used for generating the focus signal used by the second focusing means, the signal in the first frequency band and the first signal The image pickup apparatus according to claim 4, wherein the ratio of the signal to the signal in the frequency band of 2 is the same.   The imaging apparatus according to claim 2, wherein the focus signal generation unit increases the ratio of the signal in the first frequency band that occupies the combined signal as the gain increases.   The imaging apparatus according to claim 1, wherein the focus signal generation unit lowers a frequency band used for generating the focus signal as the gain is higher. The focus signal generation means extracts a signal of a first frequency band and a signal of a second frequency band that is a frequency band higher than the first frequency band from the output of the gain means, and the first frequency band Generating the focus signal from a synthesized signal obtained by synthesizing the signal of the frequency band and the signal of the second frequency band;
Compared with the synthesized signal used for generating the focus signal used by the first focusing means, the synthesized signal used for generating the focus signal used by the second focusing means is the ratio of the signal in the second frequency band. The imaging device according to claim 1, wherein the imaging device is large. Peak position detection means for detecting a peak of the focus signal using the plurality of focus signals generated by the focus signal generation means;
Gain stability determining means for determining whether or not the gain is stable, and
The focus signal generation means generates a plurality of focus signals by generating the focus signal corresponding to each of a plurality of focus positions,
The peak position detection unit is generated using the imaging signal determined to be the imaging signal output from the gain unit after the gain is stabilized based on the determination result of the gain stability determination unit. The imaging apparatus according to claim 1, wherein a peak of the focus signal is detected using the focus signal. An image pickup means for picking up an image formed on the light receiving surface; a gain means for multiplying an image outputted from the image pickup means and changing the brightness of the image electronically;
A focus signal generating means for extracting a frequency band signal from the output of the gain means and generating a focus signal from the extracted signal;
Focusing determination means for determining the degree of focusing from the output of the focus signal;
The focus signal generating means changes the frequency band of the signal used for generating the focus signal in accordance with the height of the gain. An image pickup means for picking up an image formed on the light receiving surface; a gain means for multiplying an image pickup signal output from the image pickup means; and an electronic brightness change of the image indicated by the image pickup signal;
A gain stability determining means for determining whether or not the gain is stable;
A focus signal generating means for extracting a signal in a frequency band using the imaging signal output from the gain means, and generating a focus signal from the extracted signal;
Peak position detection means for detecting peak positions of the plurality of focus signals generated by the focus signal generation means;
Optical control means for controlling the focus position so that the focus position approaches the peak position based on the detection result by the peak position detection means,
The focus signal generation means generates a plurality of focus signals by generating the focus signal corresponding to each of a plurality of focus positions,
The peak position detection unit is generated using the imaging signal determined to be an imaging signal output from the gain unit after the gain is stabilized based on a determination result of the gain stability determination unit. An image pickup apparatus that detects a peak of the focus signal using the focus signal. The peak position detecting means includes
First peak position detecting means for detecting a first peak position;
Second peak position detecting means for detecting the second peak position,
The first peak position detection means detects the peak position of the focus signal using the focus signal acquired at a wider focus position interval than the second peak position detection means,
The second peak position detection means uses the focus signal generated using the imaging signal output from the gain means after the gain is stabilized by the gain stability determination means, and uses the focus signal generated from the gain signal. The image pickup apparatus according to claim 13, wherein the position is detected.   The focus signal used for the first peak position detection by the first peak position detection means is more than the focus signal used for the second peak position detection by the second peak position detection means. The imaging apparatus according to claim 14, wherein the imaging apparatus is a focus signal acquired by driving the focus position early.   The gain stability determination means is configured to detect the gain between the detection of the first peak position by the first peak position detection means and the detection of the second peak position by the second peak position detection means. The imaging apparatus according to claim 14, wherein it is determined whether or not the image is stable.   The peak position detecting means uses the focus signal generated using the imaging signal output from the gain means while the gain is determined to be stable by the gain stability determining means. The imaging apparatus according to claim 13, wherein a peak of the focus signal is detected.   18. The peak position detection unit detects the peak position when the gain is less than a threshold value, regardless of a result of the stability determination unit of the gain. The imaging device described in 1. An image pickup means for picking up an image formed on the light receiving surface; a gain means for multiplying an image pickup signal output from the image pickup means; and an electronic brightness change of the image indicated by the image pickup signal;
A gain stability determining means for determining whether or not the gain is stable;
A focus signal generating means for extracting a signal in a frequency band using the imaging signal from the gain means, and generating a focus signal from the extracted signal;
Peak position detection means for detecting peak positions of the plurality of focus signals generated by the focus signal generation means;
Optical control means for controlling the focus position so that the focus position approaches the peak position based on the detection result by the peak position detection means,
The optical control means reverses the driving direction of the focus position when the value of the focus signal becomes smaller than a threshold value,
The imaging apparatus, wherein the threshold value can be changed based on at least the amount of change in the gain.   The imaging apparatus according to claim 19, wherein a threshold value when the gain change amount is positive is smaller than a threshold value when the gain change amount is negative.