JP2007174521A - Moving picture imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a moving picture from being disgraceful by stabilizing a focus during a composition change in moving picture imaging. <P>SOLUTION: When a change in composition is detected during moving picture imaging, focusing is prohibited in accordance with conditions. For example, when an object distance is long, a field depth is deep, so that even when focusing is prohibited, considerable out-of-focus does not result therefrom. Therefore, focusing is prohibited. When the object distance is short, on the other hand, since the field depth is shallow, focusing is not prohibited. When prohibiting a focal distance, a focusing lens may also be moved to an over focal distance position and fixed there. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a moving image photographing apparatus such as a video camera, and stabilizes focus during composition change.

  There are a video camera and a digital still camera with a video shooting function as a camera capable of shooting a video. In any camera, the AF (autofocus) operation is basically performed continuously during moving image shooting, and the AF follows the movement of the subject. There is a video camera (for example, Patent Document 1) that temporarily stops AF when camera shake is detected, but AF is always performed except when camera shake is detected.

JP-A-5-336426

  However, if you change the composition while shooting a movie, for example in panning, the perspective status of the subject in the screen changes, and AF tries to follow this, so the focus is constantly unstable during the composition change. May feel unsightly when watching videos.

The moving image shooting apparatus according to the present invention is composed of a focus adjustment unit that drives a focusing lens during moving image shooting to perform focus adjustment, a detection unit that detects whether or not the composition has been changed during moving image shooting, and a detection unit that has a composition. And control means for prohibiting focus adjustment when a change is detected.
When the focus adjustment is prohibited, the focusing lens is fixed at any position, but it may be fixed at the position when the composition change is started, or fixed at the hyperfocal distance position. Good. Further, the position where the focusing lens is fixed may be determined based on the position of the focusing lens when the composition change is started.
Judge whether or not focus adjustment is prohibited based on the distance to the subject, the focal length of the taking lens, or brightness information. If it is determined that focus adjustment is not prohibited, focus adjustment is prohibited even during composition change. You may make it not.
The presence or absence of composition change may be detected from the output of a sensor that detects camera shake.

  According to the present invention, the focus state during composition change can be stabilized, and unsightly can be eliminated.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram of a camera in the present embodiment. The camera can shoot movies, and may be a video camera or a digital still camera with a movie shooting function. Reference numeral 100 denotes a photographing lens including a focusing lens 1, an image blur correction lens 2, a zoom lens (not shown), and the like. A transmitted light beam of the photographing lens 100 is imaged on a light receiving surface of the image sensor 3. The image sensor 3 is a photoelectric conversion element that outputs an electrical image signal corresponding to the light intensity of the subject image formed on the light receiving surface, and the output image signal is processed in an analog manner by the analog signal processing unit 4. Is given.

  The image signal processed by the analog signal processing unit 4 is converted into a digital signal by the A / D converter 5 and then subjected to various digital image processing by the digital signal processing unit 6. The digitally processed image data is recorded on the external storage medium 15 via the recording / reproducing unit 12. The LCD 7 is a color liquid crystal monitor capable of displaying images, and can sequentially update and display images continuously captured on the screen. The series of photographing processing and display processing is controlled by the CPU 9.

  Further, the CPU 9 has an AF calculation unit, and performs contrast AF control (focus adjustment). Contrast AF is a method commonly used in video cameras, digital still cameras, etc., and pays attention to the fact that there is a correlation between the degree of blurring of the image and the contrast. Focusing is done by using what becomes. The magnitude of the contrast can be evaluated by the magnitude of the high frequency component of the image signal. For this reason, the AF calculation unit of the CPU 9 has a digital filter that extracts a high-frequency component in a predetermined band from an image signal obtained by imaging. Then, the absolute value of the high frequency component extracted by the digital filter is integrated and used as a focus evaluation value. In the shooting screen, AF areas are set in advance at one place or a plurality of places, and a focus evaluation value is calculated for each AF area.

  The focus evaluation value is an amount that changes in accordance with the contrast of the image, in other words, the focus adjustment state of the focusing lens 1, and becomes a maximum value (peak value) when the contrast becomes maximum after focusing. Therefore, by obtaining the lens position where the focus evaluation value reaches a peak and bringing the focusing lens 1 to that position, the subject in the AF area can be focused. Hereinafter, the operation of obtaining the lens position where the focus evaluation value reaches a peak and driving the focusing lens 1 is referred to as AF search.

  A hill-climbing method is known as an AF search method. In the hill-climbing method, the focus evaluation value is calculated for each predetermined sampling pitch while moving the focusing lens 1 by the focus motor 10, and the focus evaluation value is compared with the same evaluation value (memory value) at the previous sampling each time the calculation is performed. To do. If the current evaluation value is higher than the previous evaluation value, the peak is approaching, so sampling is continued while moving the focusing lens 1 in the same direction. If the current evaluation value is smaller than the previous evaluation value, the focus lens 1 is moved in the opposite direction because it is far from the peak. By repeating this operation, the focusing lens 1 can be finally brought to the peak position (the peak of the mountain).

  FIG. 2 is a diagram showing the relationship between the focusing lens position and the focus evaluation value, and shows an example having three AF areas (A1, A2, A3). In each area, the in-focus state is the best at the lens positions R1, R2, and R3 at the top of the mountain. Eventually, the focusing lens 1 is driven to one of these three lens positions. For example, in the case of a close-priority algorithm (focus on the closest subject), in this example, R1 is set. The focal lens 1 is driven. On the other hand, it is possible for the photographer to select one of the areas in advance, and in this case, the focusing lens 1 is driven to the peak position of the selected area.

  In addition, the camera according to this embodiment includes an optical camera shake correction device. In the optical camera shake correction, camera shake caused by camera shake or the like is detected by a shake detection sensor 11 (FIG. 1) such as a gyro, and the image shake correction lens 2 is driven in a direction orthogonal to the optical axis based on the detection result. By doing so, image blur is corrected. Two shake detection sensors 11 are provided, one of which detects angular shake in the yaw direction of the camera and the other in the pitch direction.

  The image blur correction unit 8 in FIG. 1 includes a drive source (for example, a voice coil motor) of the image blur correction lens 2 and a lens position detection device that detects the position of the image blur correction lens 2. Two drive sources and two lens position detection devices are also provided corresponding to the yaw direction and the pitch direction.

  The CPU 9 calculates the drive amount and drive direction of the image blur correction lens 2 based on the outputs of the blur detection sensor 11 and the lens position detection device, sends a lens drive signal based on the calculation result to the correction lens drive source, and causes image blur. The correction lens 2 is driven in two directions orthogonal to the optical axis. As a result, the shake of the image formed on the image sensor 3 is reduced, and the image is stabilized.

  In addition to the above-described image blur correction, for example, the image pickup device is driven in a direction orthogonal to the optical axis based on the output of the shake detection sensor, or the image is corrected based on the output. There is also.

Next, AF control during moving image shooting will be described.
FIG. 3 shows the behavior of the focusing lens 1 when the composition is changed, and shows an example in which the subject distance changes to the close side at the time T1 due to the composition change. In a general camera, when the composition is changed during moving image shooting in the continuous AF mode, the focusing lens tries to follow the change in the subject distance as shown in FIG. P1 is an in-focus position at the initial subject distance, P2 is an in-focus position at the changed subject distance, and the lens is in the P1 position and focused on the subject before the composition change.

  It is ideal to drive the focusing lens 1 quickly and linearly from P1 to P2 in accordance with the composition change (subject distance change). However, in the above-described contrast AF, the subject distance changes due to the change in the focus evaluation value. Although it can be perceived, it cannot be immediately understood how much it has changed in which direction. Therefore, the focusing lens 1 is driven in any direction, and the target position of the focusing lens 1 is searched based on the change state of the focus evaluation value. In some cases, it may be necessary to return the focusing lens 1 to infinity once as shown in the figure and then start an AF search again. Finally, the target position P2 is found and the focusing lens 1 is brought to that position. Until (time T2), the focusing lens 1 may be in a stray state as illustrated.

  When the focusing lens 1 strays, the focus becomes extremely unstable between T1 and T2, for example, it is largely blurred at first, gradually approaches the in-focus state, but passes through the in-focus state, then moves in the opposite direction, and finally comes into focus. There are many things to do. In moving image shooting, a period in which the focus is unstable is recorded as a video, which makes it very unsightly when the moving image is viewed later. During this time, the focus driving sound is constantly generated and recorded, so that the user feels uncomfortable with the sound.

  In order to solve the above problem, in the present embodiment, the AF search is prohibited according to the condition during composition change in moving image shooting. The prohibition of AF search means that the focusing lens 1 is fixed at any position and the AF search is not restarted.

  In general, in moving image shooting, when changing the composition when the subject distance is relatively long, for example, an object that shakes the camera sideways or moves far away to shoot the entire surroundings (distant view) in a scenic area There are many cases where panning is taken. In either case, the subject to be focused on is relatively far away, so if you focus the subject once before changing the composition, it will always be within the depth of field even if the subject distance changes during the composition change. If this is the case, even if the AF search is prohibited during the composition change, there will be no out of focus.

Here, whether or not the composition is being changed can be determined from the output of the shake detection sensor 11 described above.
FIG. 4 shows the output (camera shake signal) of the blur detection sensor 11 during shooting. This is an output example when shooting a still subject, that is, when the composition is constant, and the period of camera shake is a few Hz and the angular velocity is a slight vibration of several degrees per second. On the other hand, FIG. 5B shows an output example at the time of photographing accompanying composition change such as panning, and the camera shake signal increases from the start to the end of composition change. Although the figure shows an example, it has been found that, in general, the camera shake signal becomes large during the composition change.

  The blur detection by the blur detection sensor 11 is performed at a cycle of about 1 kHz. On the other hand, the focus evaluation value calculation during the AF search is as low as about 30 Hz in accordance with the frame rate (generally 30 frames / second) of moving image recording. Can be detected with sufficient accuracy. In this way, since the presence or absence of composition change can be detected by the blur detection sensor 11 used for image blur correction, it is not necessary to newly provide a composition change detection means.

  FIG. 5A is a diagram showing the waveform and the lens behavior of FIG. 5B on the same time axis. The solid line L1 shows the behavior in this embodiment, and the broken line L2 shows the behavior in the conventional camera. In the present embodiment, since the focusing lens 1 is fixed during the composition change, the focus is stable, no focus driving sound is generated, and the user feels unsightly or uncomfortable when watching the video later. There is nothing.

  By the way, when the subject distance is long as described above, even if AF search is prohibited during the composition change, there is no significant defocusing. However, when the subject distance is short, the depth of field is shallow, so when changing the composition If the AF search is prohibited, there is a possibility that the subject is so large that it cannot be distinguished. In this case, it is better to follow the subject as soon as possible even if the AF becomes a stray state. Therefore, when the subject distance is short, the AF search is performed as usual even if the composition is being changed.

  The subject distance threshold th that determines whether or not to prohibit AF search may be a constant value, but is preferably determined in consideration of the focal length of the photographing lens (zoom state) and the luminance of the subject. For example, when the subject is dark, the out-of-focus state is not so noticeable (however, AF strays are conspicuous even when it is dark), so AF search is prohibited even if the subject distance is short to some extent. Further, since the depth of field becomes shallow when the focal length is long, AF search is not prohibited even if the subject distance is long to some extent.

  Further, the focusing lens 1 is fixed by prohibiting the AF search, but the fixing position may be a position at the start of composition change, or the focusing lens 1 is fixed after the focusing lens 1 is moved to a predetermined position. May be. For example, when the composition change is started after the focusing lens 1 is focused on a certain subject, the focusing lens 1 may be fixed at the initial focusing position. That is, when the AF search is prohibited when the subject distance is long, the subject after the composition change at the initial lens position is likely to be within the depth of field.

  On the other hand, during AF search, that is, when the composition change is started before the focusing lens 1 is still focused on the subject, the depth of field is increased by fixing the focusing lens 1 at the position when the composition change is started. May deviate. In particular, when the target position of the focusing lens 1 is not yet known in the AF search, the focusing lens 1 may be in a position far from the focusing position. Therefore, in this case, it is desirable to fix the focusing lens 1 after driving it to the hyperfocal distance position (pan focus position). The hyperfocal distance is a distance that is uniquely obtained from the focal length of the lens and the aperture value. By placing the focusing lens 1 at this distance position, the depth of field is increased on both the far side and the near side. Can prevent large blurring.

  However, even during the AF search, if the target position of the focusing lens 1 is already known, it is desirable to drive and fix the focusing lens 1 to the target position.

FIG. 6 shows an example of a processing procedure for realizing the AF control described above.
This program is periodically called and executed by the CPU 9 during moving image shooting. In step S1, the output of the shake detection sensor 11 is read to determine whether or not the composition is being changed. If the composition is not being changed, the AF prohibition flag is set to 0 in step S11, and an AF search is executed in step S12. In this case, since the AF search is not prohibited, the focus follows the movement when the subject moves.

  If it is determined in step S1 that the composition is being changed, an AF prohibition flag is determined in step S2. When the AF prohibition flag is 1 (when AF search is already prohibited), the process proceeds to step S8, and when it is not 1, it is determined whether or not the AF search is being performed in step S3. If composition change is started with the focusing lens 1 in the in-focus position, step S3 is denied, the focusing flag is set to 1 in step S7, and the process proceeds to step S8.

  On the other hand, when the composition change is started in a state where the in-focus state is not reached, step S3 is affirmed, and it is determined in step S4 whether or not the in-focus target position (position where the in-focus lens 1 should be driven) has already been determined. judge. When the in-focus state has not been reached but the in-focus target position is already known, the in-focus flag is set to 1 in step S5, the in-focus lens 1 is moved to the target position, and the process proceeds to step S8. When the in-focus target position is not yet known, the in-focus flag is set to 0 in step S6, the in-focus lens 1 is stopped at the current position, and the process proceeds to step S8.

  In step 8S, the current zoom state (focal length), luminance information, and current focus lens position R are acquired. The zoom state and the focusing lens position may be read from a predetermined encoder, and the luminance information may be read from the output of the AE photometric sensor. In step S9, a subject distance threshold th that determines whether or not to prohibit AF search is obtained based on the zoom state and the luminance information. For the reasons described above, the longer the focal length, the longer the th, and the lower the luminance, the shorter the th. For example, a table in which the threshold value th is associated with the zoom state and the luminance information may be stored in the memory, and the corresponding th may be extracted from the table.

  In step S10, the detected current focusing lens position R is compared with a threshold value th. If it is determined that R <th, since the depth of field is shallow, the process proceeds to step S11 to perform AF search even during composition change. On the other hand, as described above, it is highly possible that R ≧ th is determined when the entire surrounding scene is photographed at a scenic spot or when an object moving far away is photographed. In this case, the process proceeds to step S13. . In step S13, the AF prohibition flag is determined. If it is already 1, the process returns. If it is not 1, it is set to 1 in step S14 and the process proceeds to step S15.

  In step S15, a focus flag is determined in order to determine at which position the focusing lens 1 is fixed. If the in-focus flag is 0, even the in-focus target position is not yet determined during the AF search, so the focus lens 1 is driven and fixed to the hyperfocal distance position (pan focus position) in step S16, and the return. To do. As a result, AF strays can be prevented while minimizing defocusing.

  On the other hand, if the focus flag is determined to be 1 in step S15, since the focus lens 1 is already at the target position (original focus position), the focus lens 1 is fixed at the current position in step S17. To return. Also in this case, the stray lens 1 can be prevented from straying while minimizing defocusing.

  In the above description, the object distance, the focal distance, and the luminance are taken into account when determining whether or not AF is prohibited. However, the determination may be made based on only one of these information. For example, AF may be prohibited when the focal length is greater than or equal to a predetermined value, and may be permitted at other times, or AF may be prohibited when the brightness of the subject is less than or equal to a predetermined value, and otherwise You may make it permit. Alternatively, the AF search may be prohibited unconditionally during composition change without considering the above conditions.

  In addition, the AF search status is taken into account when determining the lens fixing position when the AF search is prohibited, but this is not taken into account, and it is unconditionally fixed to a predetermined value (for example, the position at the start of composition change or the hyperfocal distance position). May be.

The block diagram of the camera in one Embodiment of this invention. The figure which shows the relationship between the lens position and contrast evaluation value in contrast AF. The figure which shows the behavior of a focusing lens when a to-be-photographed object distance changes in contrast AF. It is a wave form diagram which shows the output of a shake detection sensor, and shows a wave when composition is constant. The figure which shows the output waveform of the blur detection sensor when a composition is changed, and the behavior of the focusing lens in the related art and the embodiment on the same time axis. The flowchart which shows AF control in embodiment.

Explanation of symbols

1 Focusing lens 9 CPU
10 Focus motor 11 Shake detection sensor

Claims (9)

Focus adjustment means for adjusting the focus by driving the focusing lens during video recording,
Detection means for detecting whether or not the composition has changed during video recording;
And a control means for prohibiting the focus adjustment when the detection means detects a change in composition.   2. The moving image photographing apparatus according to claim 1, wherein when the focus adjustment is prohibited, the control unit fixes the focusing lens at a position when composition change is started.   The moving image photographing apparatus according to claim 1, wherein the control unit drives and fixes a focusing lens at a predetermined position when the focus adjustment is prohibited.   The moving image photographing apparatus according to claim 3, wherein the predetermined position is a hyperfocal distance position.   The said control means determines the position which fixes a focusing lens based on the position of a focusing lens when composition change is started, when prohibiting the said focus adjustment. Movie shooting device.   The image forming apparatus further includes a determination unit that determines whether or not the focus adjustment is prohibited based on a distance to a subject. When the determination unit determines that the focus adjustment is not prohibited, the focus is adjusted even when the composition is being changed. The moving image photographing apparatus according to claim 1, wherein adjustment is not prohibited.   The image forming apparatus further includes a determination unit that determines whether or not the focus adjustment is prohibited based on a focal length of the photographing lens, and the control unit determines that the focus adjustment is not prohibited when the determination unit determines that the focus adjustment is not prohibited. The moving image photographing apparatus according to claim 1, wherein focus adjustment is not prohibited.   The image forming apparatus further includes a determination unit that determines whether or not the focus adjustment is prohibited based on luminance of the subject, and when the determination unit determines that the focus adjustment is not prohibited, the focus adjustment is performed even when the composition is being changed. The moving image photographing apparatus according to claim 1, wherein the moving image photographing apparatus is not prohibited.   The moving image photographing apparatus according to claim 1, wherein the detection unit detects presence or absence of the composition change from an output of a sensor that detects camera shake.

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