JP3557222B2 - Automatic focusing device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an automatic focusing device, and more particularly, to an automatic focusing device that determines a focusing position of a lens based on contrast data representing the contrast of a subject image extracted from a video signal.
[0002]
[Prior art]
2. Description of the Related Art In recent years, it has become almost indispensable to incorporate an automatic focusing device into a camera or a video camera. With respect to video cameras such as stills and movies, a so-called imager that extracts contrast information from an image pickup signal of a subject taken in through an image sensor and performs focusing processing based on the information. What has a built-in AF automatic focusing device has become mainstream. This is because the device does not require a dedicated sensor for focus detection, which is advantageous in terms of cost and space.
[0003]
FIG. 5 is a main block configuration diagram of an electronic image pickup apparatus which is a video camera incorporating the above-described conventional imager AF automatic focusing apparatus. As shown in FIG. 1, the present apparatus mainly includes a focusing motor and a focusing actuator 7 composed of a motor driver, a focusing lens 1 of a focusing optical system driven by the actuator 7, An image sensor 2 for converting a captured subject image into an electric signal; a pre-processing circuit 3 for amplifying an image signal and a sample-and-hold process; and a video recording / reproducing system or a finder system (not shown) for converting an image signal. An imaging process circuit 4 for outputting a signal; and a detector for extracting contrast data as information for evaluating the degree of focusing, that is, a contrast value C from the imaging signal. A contrast information detector 5 composed of an integrating circuit, an A / D conversion circuit, etc., and a CPU, ROM, RAM, etc. And a means for detecting the in-focus position by taking in the contrast data, driving the lens 1 to the in-focus position, and further comprising a system controller 6 for controlling the entire apparatus. ing.
[0004]
In the present imaging apparatus configured as described above, first, subject light is captured via the imaging lens 1 and forms an image on the imaging surface of the image sensor 2 as a subject image. The output signal of the image sensor 2 is sampled and held in the pre-processing circuit 3 and is output to the imaging process circuit 4 and the contrast information detector 5 as an image signal. Then, the imaging signal is converted into a video signal by the imaging process circuit 4 and is output as a video signal to a recording / reproducing system or a finder system. On the other hand, in the contrast information detector 5, a high frequency component of the imaging signal is extracted as contrast data. Further, it is converted into a digital value, and is taken into the system controller 6 as a contrast value C. Then, the focus position is detected. Then, the system controller 6 moves the focusing lens 1 to the in-focus position via the focusing actuator 7.
[0005]
An example in which the hill-climbing method is applied as the focus position detection operation will be specifically described. First, when the subject is in a stationary state, as shown in FIG. 6, a focus position at which the contrast value reaches a peak is detected. The focusing lens 1 is moved from the direction of the in-focus position (infinity in-focus position) toward the closest in-focus position in a predetermined unit time in a hill-climbing operation in a predetermined unit time. Then, the sequential contrast values C0, C1, C1,... At each position of each elapsed time ti (i = 1, 2,...) Are fetched. Then, the transition from the rising process to the falling process of the contrast value change curve Y0 is regarded as exceeding the peak, and immediately thereafter, the lens is reversed and the peak position is detected. In the case of FIG. 6, it is determined that the peak position has been passed when the contrast value C5 is detected. Then, the lens drive position having the past maximum value C4 is determined as the in-focus position, and the focusing lens 1 is driven in the reverse direction to the in-focus position to complete the in-focus operation.
[0006]
As described above, when the subject is stationary, the change point Y0 of the contrast value does not change as shown in FIG. 6, so that the peak point at the desired position can be obtained quickly and accurately. However, when the subject is a moving object, the change curve Y of the contrast value during the focusing operation changes every moment. FIG. 7 is a diagram illustrating a change state of the contrast value C when a moving subject approaches the camera, that is, when the subject approaches the closest position from the ∞ position. = 0, 1, 2,...) Changes as Y0, Y1, Y2,. Therefore, the system controller 6 takes in the contrast values C0, C1, C2,... With a delay. Then, the contrast value C9 corresponding to the in-focus point is detected after the camera is already close to the closest position, and it takes a long time to focus.
[0007]
Further, when the speed of the moving object is higher, the characteristic curve of the contrast value changes quickly as shown by Y0 and Y1 as shown in FIG. 8, so that, for example, the characteristic value is later than the previously detected contrast value C0. In some cases, the detected contrast value C1 becomes smaller and the peak point cannot be detected.
When the subject is a moving body moving away from the camera, the characteristic curve of the contrast value moves in the ∞ direction as shown by Y0 and Y1 as shown in FIG. When the contrast C4 that is determined to have exceeded the peak among the detected contrast values C0, C1,... Is detected, the contrast value C3 which is the previous maximum value is adopted as the peak point corresponding value. . In this case, since the amount of change in the contrast value per unit time is larger than that in the case of a still subject, the possibility that the maximum contrast value C3 deviates from the true peak increases. That is, focusing accuracy is deteriorated.
[0008]
As a proposal that enables the focusing process on a moving object, the focusing device applied to the camera of Japanese Patent Application No. 3-147626 previously proposed by the present applicant is an imager. The present invention relates to an AF focusing device, and captures a contrast value corresponding to a peak position by forward rotation of a lens drive motor in a hill-climbing operation of the focusing process. Then, at the time when the contrast value is detected by the reverse drive of the lens drive motor, the video signal is transferred when the video signal is transferred.
[0009]
[Problems to be solved by the invention]
However, in the focusing device applied to the above-mentioned conventional example of Japanese Patent Application No. 3-147626, the driving speed of the focusing lens at the time of the hill-climbing operation is the same as that of the conventional one. Therefore, it is effective for a moving object having a relatively low speed, but has a problem similar to that of the conventional imager AF apparatus for a moving object having a high speed.
[0010]
The present invention has been made in order to solve the above-described problem, and performs a focus detection based on the data, by detecting a moving state of a subject, prior to a focusing operation. It is an object of the present invention to provide an automatic focusing device that enables a focusing operation with high accuracy to a subject and further shortens a focusing time itself.
[0011]
[Means for Solving the Problems]
According to the first automatic focusing apparatus of the present invention, the contrast data representing the amount of contrast of the subject image extracted from the video signal corresponding to the subject depends on a change occurring in response to driving of the focusing optical system. , an automatic focusing apparatus in which the contrast data is allowed to move the focusing optical system to the position shown substantial peak, first obtaining a plurality of contrast data relating to different times in a state of stopping the focusing optical system (1) means, second means for obtaining movement information representing the movement state of the subject based on the plurality of pieces of contrast data obtained by the first means, and focus adjustment operation according to the movement information obtained by the second means And third means for generating information for performing the following.
Further, the second automatic focusing device is the first automatic focusing device, wherein the movement information is information for determining whether the subject is in a state of approaching or away from a focused state. Wherein the information for performing the focus adjustment operation is a drive amount per unit time in the focus adjustment drive unit.
[0012]
[Action]
Prior to the focusing operation, based on the contrast data captured by the first means, the second means selects movement information indicating the movement state of the subject, and further performs a hill climbing operation based on the movement information. Then, sequential contrast data adapted to the moving state of the subject is obtained. Then, based on the obtained contrast data, the in-focus position is detected, and the in-focus drive is executed.
[0013]
【Example】
The present invention will be described below based on the illustrated embodiment.
The main configuration of the control unit of the electronic image pickup apparatus incorporating the automatic focusing apparatus according to the first embodiment of the present invention is the same as that of the conventional electronic image pickup apparatus shown in FIG. The apparatus is of the imager AF type.
However, first, the system controller 6 obtains, via the contrast detector 5, a plurality of contrast values, which are a plurality of pieces of contrast data at different times, via the contrast detector 5 while the focusing lens 1 serving as the focusing optical system is stopped. Means. Further, there is provided a second means for obtaining movement information indicating a moving state of the subject, for example, a moving speed, based on the plurality of contrast values obtained by the first means. Further, in accordance with the movement information obtained by the second means, a hill-climbing operation speed, that is, a value of the number of steps of a unit movement amount for moving the focusing lens 1 for one-time acquisition of a contrast value is selected. Third means for generating information for performing the focus adjustment operation.
[0014]
The focusing operation of the automatic focusing apparatus according to the present embodiment configured as described above will be described. First, prior to the hill-climbing operation, the focusing lens 1 is fixed and the contrast of the image sensor is controlled over two fields at different times. The two contrast values C0 and C1 are fetched via the information detector 5. However, the value C1 is a contrast value acquired at a later time. From these values, movement information indicating the movement state of the subject, that is, movement speed, is obtained. The number of fields may be two or more to obtain three or more contrast values. Also, the field to be acquired may be a continuous field or a discontinuous field. If there is no change in the two contrast values, it is determined that the subject is in a stationary state, and a focusing operation that is the same as the operation of the conventional automatic focusing device is performed.
[0015]
Also, as shown in FIG. 3, if the contrast value tends to decrease from C0 to C1, the subject approaches the imaging apparatus from the ∞ side on the assumption that the subject is a moving object and the lens initial position is the ∞ position. Judge that you are doing. In this case, the characteristic curves Y0, Y1,... Of the contrast value of the subject move with the lapse of time as shown in FIG. Then, in order to capture one contrast value during the hill-climbing operation, the unit movement amount for driving the focusing lens 1 within a predetermined unit time, for example, within one field period, is, for example, 1.5 times the normal, that is, 1. By setting five steps, the lens is moved quickly so as to follow the movement of the subject as much as possible. Thereafter, the lens 1 is moved 1.5 steps at a time to capture the contrast values C2, C3,..., And detect the contrast value C7 exceeding the peak at an earlier time. Then, the lens 1 is driven in the reverse direction until a contrast value obtained by multiplying the past maximum contrast value C6 by a predetermined coefficient is reached. However, the unit movement amount of the lens in the reverse rotation driving is smaller than usual by the unit movement amount at the time of the hill-climbing operation, and a more accurate peak position is detected. Thus, the focusing operation is completed.
[0016]
Further, if the contrast value tends to increase from C0 to C1 as shown in FIG. 4, it is determined that the subject is a moving object and is distant from the imaging device. In this case, the characteristic curves Y0, Y1,... Of the contrast value of the subject move with time as shown in FIG. Then, the unit movement amount for driving the focusing lens 1 to capture one contrast value during the hill-climbing operation is set to, for example, 0.5 times the normal, that is, 0.5 steps, and the contrast of the distant subject is set. The value is taken in as finely as possible to prevent a value shifted from the peak point from being detected as the maximum contrast value. After that, the lens 1 is moved by 0.5 steps to capture the contrast values C2, C3,... And detect the contrast value C5 exceeding the peak. Then, the lens 1 is driven to rotate in the reverse direction until a contrast value obtained by multiplying the past maximum contrast value C4 by a predetermined coefficient is reached. However, the unit movement amount of the lens in the reverse rotation drive is made to move more than usual, contrary to the unit movement amount in the hill-climbing operation, and a more accurate peak position is detected. Thus, the focusing operation is completed.
[0017]
Next, the focusing processing operation of the automatic focusing device of the present embodiment will be described in detail with reference to the flowcharts of FIGS. Here, a description will be given of a predetermined unit time used in the actual focusing process, for example, a set value of a lens unit moving amount driven during one field period. In order to capture one contrast value during a hill-climbing operation, the focusing lens 1 is moved. As a unit movement amount to be driven, a normal movement amount S, for example, one stage, a movement amount R that is longer than the normal movement amount S, for example, 1.5 stages as described above, and a normal movement amount S It is assumed that the movement amount T, which is a shorter distance, for example, three steps of 0.5 steps as described above is stored in the ROM of the system controller 6. In addition, the initial position of the lens is set to the ∞ position.
[0018]
When an instruction for focusing processing is issued, the processing of the routine in FIG. 1 is started. First, the number n of contrast value acquisitions is reset to 0 (step S1). Then, the focusing lens 1 is fixed at the initial position, and the contrast value in the first imaging field is taken as the value Cn (step S2). Subsequently, a contrast value of the imaging field after a predetermined time has elapsed is taken in as a value Cn + 1 (step S3). Note that the processing means in steps S2 and S3 correspond to the first means.
[0019]
In steps S4 and S5, the acquired contrast values Cn and Cn + 1 are compared. If the value Cn is larger, it is determined that the subject is a moving object and is approaching the imaging apparatus, and the movement of the lens is determined by the movement amount R, that is, 1. Set to 5 steps to allow the lens to move significantly. Then, the process proceeds to step S6. On the other hand, if the value Cn + 1 is larger, it is determined that the subject is a moving object and is away from the imaging device, and the peak point is not missed by the movement, so the unit movement amount of the lens is set to the movement amount T, that is, , 0.5 steps so that the lens can be finely moved. Then, the process jumps to step S15. If the values Cn and Cn + 1 are equal in the determinations in steps S4 and S5, it is determined that the subject is stationary, and the process jumps to step S23 shown in FIG. Then, the lens moving amount is set to the normal moving amount S, that is, one stage. The processing means in steps S4 and S5 correspond to the second means.
[0020]
In steps S6 and S7, the focusing lens 1 is rotated forward by 1.5 steps, which is the moving amount R, and the contrast value obtained therefrom is taken in as a value Cn + 2. Further, in step S8, the value Cn + 1 is compared with the value Cn + 2, and if the value Cn + 2 is larger, it is determined that the contrast value is increasing, and the number n of times of capturing is incremented (step S9). It returns to S6. Then, the normal rotation drive of the lens 1 based on the movement amount R is continued. On the other hand, if the value Cn + 1 is larger, it is determined that the contrast value has exceeded the peak, and the process proceeds to step S10.
[0021]
In step S10, a value obtained by multiplying the past maximum value Cn + 1 by a predetermined coefficient k2 is set as a peak identification reference contrast value CM. Subsequently, the lens 1 is driven to rotate in the reverse direction by a unit movement amount. The unit movement amount is a movement amount T, which is a small amount opposite to the movement amount R during the hill-climbing operation, that is, 0.5 steps (step S11). . Then, the acquired contrast value is set to a value CL and compared with the value CM. If the value CM is larger, it is determined that the value has not yet returned to the peak point (steps S12 and S13). Then, the process returns to step S11 to continue the reverse rotation movement of the lens 1. If it is determined in step S13 that the value CL has increased, it is determined that the value has returned to the peak point, the process proceeds to step S14, the driving of the lens 1 is stopped, and the focusing operation ends.
[0022]
If it is determined in step S4 that the value Cn + 1 is larger, the process proceeds to step S15. In this case, the focusing lens 1 is rotated forward by 0.5 steps, which is the moving amount T, and the contrast value obtained there is obtained. As a value Cn + 2 (step S16). Further, in step S17, the value Cn + 1 is compared with the value Cn + 2, and if the value Cn + 2 is larger, it is determined that the contrast value is increasing, and the number of times of capturing n is incremented (step S18). It returns to S15. Then, the normal rotation drive of the lens 1 based on the movement amount T is continued. On the other hand, if the value Cn + 1 is larger, it is determined that the contrast value has exceeded the peak, and the process proceeds to step S19.
[0023]
In step S19, a value obtained by multiplying the past maximum contrast value Cn + 1 by a predetermined coefficient k3 is set as a peak identification reference contrast value CM. Subsequently, the lens 1 is driven to rotate in the reverse direction by a unit movement amount. The unit movement amount is a large movement amount R, which is the reverse of the movement amount T during the hill-climbing operation, that is, 1.5 steps (step S20). . Then, the acquired contrast value is set to a value CL and compared with the value CM. If the value CM is larger, it is assumed that the value has not returned to the peak point yet (steps S21 and S22). Then, the process returns to step S20 to continue the reverse rotation movement of the lens 1. Also, if CL is larger in the determination in step S22, it is determined that it has returned to the peak point, and the flow jumps to step S14 to stop driving the lens 1 and terminate the focusing operation.
[0024]
If the value Cn is equal to the value Cn + 1 in the determination in step S4, the process proceeds from step S23 to step S30 shown in FIG. 2, but this process is a focusing process for a normal still subject. Action. The difference from the processing in steps S6 to S13 or steps S15 to S22 is that in steps S23 and S28, the unit movement amount during forward rotation drive or reverse rotation drive of the lens 1 is different. The normal movement amount S, that is, a point that is set to one stage, and that a coefficient k1 different from the above is used as a coefficient for obtaining the peak identification reference contrast value CM in step S27. . Other processes are the same. The processing after step S6, the processing after step S15, and the processing after step S23 are processing by the third means.
[0025]
In the above-described embodiment, the lens moving amount is stored in the ROM as a fixed value. However, as a modified example, the lens moving speed may be changed depending on the shooting speed of the automatic focusing device such as the subject speed, the aperture, and the brightness. May be set finely and controlled. The lens moving speed is obtained by calculation, calculation by a lookup table method, fuzzy calculation, or the like.
[0026]
Further, the above embodiment is an example of application to a system in which the initial position is set to the ∞ position for the sake of explanation, and the direction in which the subject exists can always be limited to one direction on the closest side. In this case, it is possible to omit an initial trial for determining a hill-climbing direction used in a general system in which an arbitrary lens position is set as an initial position. However, the same applies to the case where the present invention is applied to the system in which the initial trial is performed. In the present embodiment, focusing on the first step of hill climbing, if the contrast value is C2 <C1, the lens is moved in the reverse direction. Drive. When the contrast value satisfies C2> C1, the lens is directly rotated as it is. The driving speed at this time is set by using the contrast values C0 and C1 as in the case of the present embodiment.
[0027]
As described above, before the focusing operation, the automatic focusing apparatus of the present embodiment acquires contrast values of different fields with the lens position fixed, thereby determining whether the subject is a moving object, It is determined whether the subject is moving toward or away from the apparatus. Then, since the unit movement amount of the lens at the time of the hill-climbing operation for focus detection is set based on the discrimination result, the hill-climbing operation according to the moving state of the object approaching or moving away is set. It is possible to do. Therefore, the focus position can be detected more accurately for the moving object, and the focus position can be detected more quickly. Imaging is possible. Further, it is less likely that focus detection cannot be performed due to a moving object.
The gist of the present invention can be applied not only to a video camera but also to a camera using a silver halide film.
[0028]
【The invention's effect】
As described above, the automatic focusing apparatus of the present invention detects the moving state of the subject at the beginning of the focusing operation, and performs driving for focus detection based on the data. Focusing operation with high accuracy is possible even for a moving subject, and further, there are many remarkable effects such as a faster focusing time itself.
[Brief description of the drawings]
FIG. 1 is a flowchart of a focusing processing operation of an automatic focusing device according to a first embodiment of the present invention.
FIG. 2 is a flowchart divided and shown in the flowchart of FIG. 1;
FIG. 3 is a diagram showing a change in an acquired contrast value with respect to lens movement when focusing on a subject approaching the device during a focus detection operation of the automatic focusing device of FIG. 1;
FIG. 4 is a diagram showing a change in an acquired contrast value with respect to lens movement when focusing on a subject moving away from the device during a focus detection operation of the automatic focusing device in FIG. 1;
FIG. 5 is a main block configuration diagram of an image pickup apparatus including a conventional imager AF automatic focusing apparatus.
FIG. 6 is a diagram showing a change in an acquired contrast value with respect to lens movement when focusing on a still subject during a focus detection operation of the automatic focusing device in FIG. 5;
FIG. 7 is a diagram showing a change in an acquired contrast value with respect to lens movement when focusing on a subject approaching the device during a focus detection operation of the automatic focusing device in FIG. 5;
FIG. 8 is a diagram showing a change in an acquired contrast value with respect to lens movement in a case where focusing on a subject approaching the device becomes impossible during a focus detection operation of the automatic focusing device in FIG. 5;
FIG. 9 is a diagram showing a change in an acquired contrast value with respect to lens movement when focusing on a subject moving away from the device during the focus detection operation of the automatic focusing device of FIG. 5;
[Explanation of symbols]
1. Focusing lens (focusing optical system)
C, Cn, Cn + 1, Cn + 2 ... contrast value (contrast data)
Step S2, Step S3 ... Step S4 by the first means, Step S5 ... Steps S6 to S13, Steps S15 to S22, Steps S23 to S30 by the second means ... Processing by the third means

Claims (2)

Contrast data representing the amount of contrast of the subject image extracted from the video signal corresponding to the subject is located at a position where the contrast data substantially shows a peak , depending on a change occurring in response to driving of the focusing optical system. An automatic focusing device for moving the focusing optical system,
First means for obtaining a plurality of pieces of contrast data at different times while the focusing optical system is stopped;
A second means for obtaining movement information representing a moving state of the subject based on the plurality of pieces of contrast data by the first means;
A third means for generating information for performing a focus adjustment operation according to the movement information by the second means;
An automatic focusing device comprising: The movement information is information for determining whether the subject is in a state of approaching a focused state or in a state of moving away. The automatic focusing device according to claim 1, wherein the driving amount is a driving amount per unit time.

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