JP2007011199A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in which an automatic focusing device using an image signal greatly depends on a subject, so that a subject with a low contrast is smooth and flat in the peak of a signal indicating the degree of sharpness, and as a result, the detection of the peak is sometimes very difficult. <P>SOLUTION: When it is judged that focusing is impossible, a focus lens drive speed, focus evaluation signal noise level, focus determination level, or determination period are changed step by step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus including an electric zoom lens, an automatic focusing function, and an electric swivel head used for a TV conference system, a remote monitoring system, and the like.

  In a television camera, a subject image is exposed to an image sensor such as a CCD or a CMOS sensor for a desired time, and an image signal obtained therefrom is converted into a digital signal, subjected to predetermined processing such as YC processing, and the like. An image signal is obtained. In general, a method is known in which the sharpness of the screen is detected from the video signal of the subject image, and the focus lens position is controlled so as to maximize the screen sharpness. For the evaluation of the sharpness, a signal indicating the sharpness such as the intensity of the high frequency component obtained by BPF (band pass filter) to the video signal or the blur width of the video signal extracted by differentiation is used. When a normal subject is photographed, this is small when the subject is out of focus, increases as the subject comes into focus, and takes a local maximum when focused.

Therefore, when controlling the focus lens, when the sharpness is small, the focus lens is driven at a high speed in a large direction, reversed at a point where the increase is reduced, and driven at a low speed, and the focus lens is accurately stopped at the top of the mountain. This can be realized (FIG. 3A). This is a technique widely known as a hill-climbing autofocus system.
Japanese Patent Laid-Open No. 06-014245

  However, in the automatic focusing device using the video signal, the dependency of the subject is strong, and as shown in FIG. 3 (b), the sharpness signal mountain itself is gentle and has no undulation in the low contrast subject. It may be very difficult to detect the top, and there may be a problem such as hunting without finding a focal point.

  In addition, in a camera system used for surveillance purposes, there are many scenes where contrast is extremely low or nonexistent at night, such as continuous operation day and night, and AF operation (focusing) may be impossible.

  The present invention has been made paying attention to the above points, and by switching a plurality of focusing operations according to restart conditions, a smooth and reliable focusing operation can be realized, and a night shooting mode can be realized. An object of the present invention is to provide an imaging device capable of performing more appropriate switching by adding a focus determination level in addition to an illuminance level as a transition condition to (infrared cut filter removal, black and white photography, etc.). .

  The present invention has been made to solve the above-described problems, and is characterized by an imaging element that converts an optical signal imaged on an imaging surface into an electrical signal, and the imaging of the light of a subject image. A lens for guiding to the element, an imaging field angle changing means for driving the zoom lens to change the imaging field angle, and a focus evaluation signal extraction for extracting a focus evaluation signal corresponding to the sharpness from the video signal obtained from the imaging element Means, focus means for driving the focus lens using the focus evaluation means to obtain a focused state, and subject distance detecting means for detecting the distance to the subject using the positions of the zoom lens and the focus lens And an imaging light quantity detecting means for detecting the incident light quantity to the imaging device, and an imaging direction changing means for changing the imaging direction of the imaging part. If it is determined to be impossible, it has a function to change the focus lens drive speed, the noise level of the focus evaluation signal, the focus determination level, and the focus determination period step by step. Uses the brightness change, zoom operation, and panning / tilting operation in addition to contrast change for determination to perform restart, and has a function to switch multiple focusing operations according to restart conditions The imaging apparatus is characterized by the above.

Specifically, by changing the focusing speed, the focus detection threshold, etc. according to the amount of change in the exposure detection value and the number of autofocus huntings, the focus criteria can be relaxed. It achieves both the focal speed and accuracy.
1. The waiting time for shifting to the search mode is changed according to the degree of focus. The focus determination time is extended as the focus speed decreases at low illuminance and low contrast.
2. By appropriately switching the focusing speed, noise level, and focus detection threshold depending on the degree of hunting, both the focus speed and the low contrast focus are achieved.
3. Has multiple AF modes and switches according to the number of huntings.
4). The AF mode is switched according to the previous focus determination.
5. As a hunting counter reset condition, an angle of view movement such as switching from AF to MF, zooming operation, panning / tilting operation, etc. is added.
6). In addition to the illuminance level, the infrared cut filter is removed when the focus cannot be determined (shift to night mode).
It is characterized by.

  According to the present invention, the focus lens drive speed, the noise level of the focus evaluation signal, the focus determination level, and the determination period are changed stepwise in accordance with the in-focus inability determination. In the start determination, in addition to the contrast change, brightness change, zoom operation, panning / tilting operation are used, and by switching a plurality of focusing operations according to the restart condition, smooth, and A reliable focus operation can be realized.

  In addition to the illuminance level, as a condition for shifting to the night shooting mode (infrared cut filter removal, black and white shooting, etc.), more appropriate switching can be performed by adding a focus determination level.

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

(First embodiment)
FIG. 1 is a block diagram showing the main configuration of the camera system according to the first embodiment of the present invention. In FIG. 1, 101 is a fixed front lens constituting the first group lens, and 102 is the second group. A zoom lens constituting the lens performs a zoom operation via a stepping motor 117. Reference numeral 103 denotes an iris (aperture), 104 denotes a fixed third group lens, and 105 denotes a focus lens, which perform focus adjustment via a stepping motor 119.

  Reference numeral 106 denotes an image sensor such as a CCD or CMOS sensor, 120 denotes a synchronization signal generation circuit (Timing Generator), 107 denotes an automatic gain control circuit (CDS / AGC), 108 denotes an A / D conversion circuit, 109 denotes a signal processing circuit, and 110 denotes D / A conversion circuit, 111 is a memory, 112 is a temperature detection circuit, 113 is a microcomputer (controller), 114 is an electric swivel head that can perform panning and tilting operations at arbitrary angles as shown in FIG. Is a processing circuit for detecting an evaluation value of AE / AWB, and 116 is a processing circuit for detecting an evaluation value of AF.

  In the above configuration, the light of the subject image is formed on the image pickup surface of the image pickup element 106 by the lens and converted into an electric signal. Here, when the iris 104 is fully opened and the luminance signal level (the amount of light received by the image sensor 106) does not reach a predetermined value, the AGC circuit 107 performs signal amplification in accordance with the brightness of the subject. The A / D conversion circuit 108 converts the signal into a digital signal. Thereafter, the video signal is appropriately processed in accordance with a video signal standard such as color separation, white balance, and gamma correction in the signal processing circuit 109, and then the video signal in an appropriate format is output in the D / A conversion circuit 110. Converted to output.

  The AF evaluation value detection processing circuit 116 indicates a gate circuit for gating a video signal corresponding to a predetermined distance measurement frame set in the imaging surface from the video signal, and shows a sharpness necessary for performing focus detection. It is configured by a BPF or the like for extracting a high frequency component as an evaluation value. Further, the sharpness (focus evaluation) signal detected by the AF evaluation value detection processing circuit 116 is supplied to a controller 113 that controls the entire system such as AF, AE, and AWB.

  FIG. 2 is an example of a pan, tilt and zoom (PTZ) camera. Reference numeral 201 denotes a main body, 202 denotes a panning angle of view movement direction, 203 denotes a tilting angle of view movement direction, and 204 denotes a camera server.

  The operation setting at the next AF restart is performed according to the brightness at the time of focusing stop, the contrast value, the brightness change amount at the AF restart, and the contrast change amount. For example, the start mode is changed in the search mode or the minute drive mode.

  Next, the basic operation of the automatic focus detection of the present invention will be described using the flowchart of FIG.

  Here, in the case of a general subject that does not generate hunting before focusing, the normal AF mode is used (step 403). However, when the contrast is relatively low, the focus determination level is switched according to the number of times of hunting or according to the contrast peak value at the time of focus signal evaluation (step 402).

  In accordance with the number of times of hunting, the noise threshold level is changed (step 405), the search mode switching level is changed (step 406), and the focus determination level is changed (407), and then focus detection is performed (step 408).

  If focusing is impossible even when the low contrast AF mode 1 is performed (step 401), the low contrast AF mode 2 is entered.

  As shown in FIG. 3A, when the sharpness signal (focus evaluation signal) is steep, if the noise threshold level is set to Nthreshold1 and the search mode switching level is set to Sthreshold1, driving up to the noise threshold is performed at high speed. Then, it is possible to gradually decelerate to the search mode switching level, reverse at a point where the increase and decrease are switched, and drive at a low speed to stop the focus lens at the top of the mountain with high accuracy. , (C), a predetermined sharpness signal level cannot be obtained, and hunting occurs. Next, assuming that the noise threshold level is set to Nthreshold2 and the search mode switching level is set to Sthreshold3, in-focus determination is possible in FIGS. 3B and 3C, but what is the period during which the focus is driven at high speed? Even the signal is shortened, and as a result, it takes time to focus.

  Normally, normalization processing of a sharpness signal (focus evaluation signal) is performed so as to be able to cope with a certain threshold level. However, normalization may fail depending on the subject under low illumination.

  Originally, the focus lens drive speed is changed according to the sharpness signal. However, when driven at a high speed, the focus lens position point that can be acquired from the captured image becomes rough, resulting in a sharpness signal of threshold 1 or higher. It is also conceivable that the vehicle passes without being obtained.

  Therefore, by changing the noise threshold level from Nthreshold1 to Nthreshold1, the search mode switching level from Sthrhold1 to Threshold2 to Threshold3, and the focus speed from Fspeed1 to Fspeed2 to Fspeed2 according to the number of times of hunting, the sharpness detection peak signal is detected. Can be done systematically.

  Next, in order to suppress the number of times of hunting as much as possible, it is also effective to switch the noise threshold level, the search mode switching level, and the focus speed in accordance with the maximum and minimum values of the sharpness signal when reversing the focus drive.

  In addition, when the focus speed is lowered, it takes time to detect the peak of the sharpness signal, so the determination period is extended.

  When configured in this way, depending on the number of times of hunting, a high-contrast subject can be focused more quickly, and even a low-contrast subject can reach the in-focus vicinity quickly, and the time to focus can be reduced. It becomes.

  Next, the operation of this system from the focus stop state under low illuminance and low contrast or the AF restart from the stop state due to the inability to focus will be described with reference to the flowchart of FIG.

  In the low illumination / low contrast AF stop state (step 501), if the incident light amount (brightness) change of the image sensor 106 is not less than a predetermined value, the process proceeds to step 509, and if not, the process proceeds to step 504.

  For example, the luminance change is detected by calculating an appropriate time interval from the assumed luminance change, comparing it with the luminance history in the memory, and clearing the hunting counter if it exceeds the predetermined value (step 509), and restarting AF (Step 510), the AF stop flag due to low illuminance is canceled. In addition, the hunting counter is cleared (step 509) when the angle of view is changed, such as panning / tilting (step 504), zooming (step 505), and AF restart is performed (step 510). Release.

  In the case of a stop state due to the inability to focus (step 502), it is conceivable that the focus position is greatly deviated, and in that state, a change in luminance and a large change in contrast cannot be expected. Therefore, the restart determination luminance level (step 507) and the contrast level (step 508) are input low and set so that AF restart occurs with a small change.

  In other words, if a significant change in brightness or contrast is observed, changes in the situation, such as illumination projection or the subject entering the screen, can be considered, so restarting in the normal AF mode is sufficient. However, when the luminance change and the contrast change are small, restarting in the low contrast AF mode is appropriate. These are very effective for restarting AF after stopping when focusing is impossible during non-illumination.

  In the low contrast AF mode 2, for example, the BPF characteristics are switched to those that emphasize low contrast, and the maximum position in the focus evaluation signal collected during the search operation is extracted and set before and after the focus drive restriction range. This is a mode in which a minute contrast can be detected, for example, a sharpness signal (focus evaluation product number) is evaluated and a peak value is detected while the focus lens is moved at a predetermined feed amount.

  Due to the inability to focus on AF, if the hunting is repeated, the mechanical mechanism such as a motor is accelerated, and if stopped at an out-of-focus position, the amount of change in brightness and sharpness (focus evaluation value) becomes extremely small. Since it may lead to erroneous AF restart timing, it is very important to focus on the optimal point.

  These determinations may be performed independently as shown in the flowchart of FIG. 5, but in actual application, when multiple conditions are met, change depending on the applicable model, conditions, environment, etc. Become.

(Second Embodiment)
FIG. 1 is a block diagram showing the main configuration of a camera system according to a second embodiment of the present invention. In FIG. 1, 101 is a fixed front lens constituting the first group lens, and 102 is the second group. A zoom lens constituting the lens performs a zoom operation via a stepping motor 117. Reference numeral 103 denotes an iris (aperture), 104 denotes a fixed third group lens, and 105 denotes a focus lens, which perform focus adjustment via a stepping motor 119.

  Reference numeral 106 denotes an image sensor such as a CCD or CMOS sensor, 120 denotes a synchronization signal generation circuit (Timing Generator), 107 denotes an automatic gain control circuit (CDS / AGC), 108 denotes an A / D conversion circuit, 109 denotes a signal processing circuit, 110 denotes D / A conversion circuit, 111 is a memory, 112 is a temperature detection circuit, 113 is a microcomputer (controller), 114 is an electric swivel head that can perform panning and tilting operations at arbitrary angles, as shown in FIG. Is a processing circuit for detecting an AE / AWB evaluation value, and 116 is a processing circuit for detecting an AF evaluation value (sharpness).

  In the above configuration, the light of the subject image is formed on the imaging surface of the imaging element 106 by the lens group and converted into an electrical signal. Here, when the iris 104 is fully open and the luminance signal level (the amount of light received by the image sensor 106) does not reach a predetermined value, the AGC circuit 107 performs signal amplification according to the brightness of the subject, and thereafter The A / D conversion circuit 108 converts the digital signal. The video signal converted into the digital signal is appropriately processed in accordance with a video signal standard such as color separation, white balance, and gamma correction in the signal processing circuit 109, and then is appropriately processed in the D / A conversion circuit 110. It is converted into a format video signal and output.

  Here, the AF evaluation value detection processing circuit 116 is a gate circuit that gates a video signal corresponding to a predetermined distance measuring frame set in the imaging surface from the video signal, and a sharpness necessary for performing focus detection. BPF for extracting a high frequency component as an evaluation value indicating Further, the sharpness (focus evaluation) signal detected by the AF evaluation value detection processing circuit 116 is supplied to a controller 113 that controls the entire system such as AF, AE, and AWB.

  For example, when monitoring at a parking lot, when taking a picture at night, light such as a headlight enters when a car enters and leaves, which hinders mode switching determination.

  In view of this, there can be considered a means for inserting an infrared cut filter based on the detection of an increase in the luminance average value with reference to a point in time when there is no moving object by dynamic detection and the luminance average value is the lowest for several minutes.

  Next, the basic operation of the night mode transition of the present invention will be described using the flowchart of FIG.

  First, the amount of incident light (brightness) of the image sensor 106 is evaluated, and if it is equal to or smaller than a predetermined value, the process proceeds to step 601 and if it is equal to or larger than the predetermined value, the process ends. Next, the contrast signal is evaluated. If it is equal to or smaller than the predetermined value, the process proceeds to step 602, and if it is equal to or larger than the predetermined value, the process is terminated. Transition to night mode (removal of infrared cut filter, black and white mode) is made in luminance and contrast determination (step 603). After the transition, in order to perform a suitable AF operation, the characteristic switching of the sharpness signal (focus evaluation signal) detection BPF (step 604) and the AF mode switching (step 605) are performed.

  Next, the basic operation in the case of performing the night mode transition with the AF inability to focus and the low illumination determination will be described with reference to the flowchart of FIG.

  First, the amount of incident light (brightness) of the image sensor 106 is evaluated. If it is equal to or smaller than a predetermined value, the process proceeds to step 701, and if it is equal to or larger than the predetermined value, the process ends. Next, it is evaluated whether or not the focus is determined in the low illumination AF mode. If the focus is not stopped, the process proceeds to step 702, and if it is, the process is terminated. Based on the brightness and focus determination, the mode shifts to the night mode (removal of the infrared cut filter, monochrome mode) (step 703). After the transition, in order to perform a suitable AF operation, the characteristic switching of the sharpness signal (focus evaluation signal) calculation BPF (step 704) and the AF mode switching (step 705) are performed.

  In AF mode 2, for example, the BPF characteristic is switched to one that emphasizes low contrast, and the sharpness is evaluated and the peak value is detected while the focus lens is moved at the minimum feed amount within the focus limit range. In this mode, a minute change in contrast can be detected.

  Next, a basic operation for returning from the night mode will be described with reference to the flowchart of FIG.

  In the night mode (step 801), the amount of change in luminance per unit time is evaluated. If the amount of change is less than or equal to the predetermined amount, the process proceeds to step 802. If the amount of change is greater than or equal to the predetermined value, the headlight or flashlight of the car It is excluded because it is large. Next, the average value of the luminance signal is obtained (step 803). The minimum average value among the luminance average values is obtained (step 804). The minimum average value among the luminance average values is compared with the current luminance signal average value (step 805). If a difference of a predetermined value or more has occurred, the night mode is canceled (step 806).

  The detection method as described above is very effective because it can be used even when it is not linked to external infrared illumination in the night mode.

Block diagram for explaining a first embodiment of the present invention External view of pan, tilt and zoom camera for explaining the present invention Diagram for explaining autofocus sharpness (evaluation signal) Flowchart for explaining the first embodiment of the present invention. Flowchart for explaining the first embodiment of the present invention. Flowchart for explaining the first embodiment of the present invention. Flowchart for explaining a second embodiment of the present invention. Flowchart for explaining a second embodiment of the present invention.

Explanation of symbols

101 Front lens 102 Zoom lens 103 Iris (aperture)
104 Fixed third group lens 105 Focus lens 106 Image sensor 107 Automatic gain control circuit (CDS / AGC)
108 A / D conversion circuit 109 Signal processing circuit 110 D / A conversion circuit 111 Memory 112 Temperature detection circuit 113 Microcomputer (controller)
114 electric swivel head 115 processing circuit 116 processing circuit 117 stepping motor 119 stepping motor 120 synchronization signal generation circuit (Timing Generator)
201 Body 202 Panning angle of view movement direction 203 Tilting angle of view movement direction 204 Camera server

Claims (6)

  An image sensor that converts an optical signal formed on the imaging surface into an electrical signal, a lens that guides light of the subject image to the image sensor, and a zoom lens that changes the image angle of view by driving the zoom lens A focus evaluation signal extracting means for extracting a focus evaluation signal corresponding to the sharpness from the video signal obtained from the image sensor, and driving the focus lens in accordance with the output of the focus evaluation signal extracting means for focusing. A focusing unit that obtains a state; and an incident light amount detection unit that detects an incident light amount to the image sensor. If it is determined that focusing cannot be performed, the focus lens driving speed and focus evaluation signal noise are gradually increased. An imaging apparatus having a function of changing a level, a focus determination level, or a determination period.   The imaging apparatus according to claim 1, wherein a predetermined time and the number of inversions of the focus drive direction are used as the in-focus inability determination unit.   3. The imaging apparatus according to claim 2, further comprising means for changing the predetermined determination time in accordance with a focus drive speed.   In addition to the change in contrast, in addition to the change in contrast, the incident direction changing unit has an imaging direction changing unit that can change the imaging direction of the imaging unit, and in addition to the change in contrast, the incident light amount detecting unit and the imaging field angle changing unit 2. The imaging apparatus according to claim 1, wherein the focusing operation is restarted according to the output and the imaging direction changing means output.   5. A function of switching a plurality of focus detection operations and restarting the focusing means according to the incident light amount detection means, the output of the imaging field angle change means, and the output of the imaging direction change means. The imaging device described.   An imaging element that converts an optical signal formed on the imaging surface into an electrical signal, a lens that guides light of a subject image to the imaging element, and an imaging field angle changing unit that drives the zoom lens to change the imaging field angle And an infrared component removing unit that is detachably disposed in the imaging optical path to the imaging device and blocks infrared light in the optical signal, and focus evaluation according to sharpness from the video signal obtained from the imaging device Using focus evaluation signal extraction means for extracting a signal, focusing means for driving a focus lens in accordance with the output of the focus evaluation signal extraction means to obtain a focused state, position information on the zoom lens and the focus lens An object distance detecting means for detecting the distance to the object, an incident light quantity detecting means for detecting the incident light quantity to the image sensor, and a moving object detecting means for detecting the movement of the object. Has the door, imaging apparatus characterized by having a function of removing or inserting a the infrared component removing means according to the output of the said focus evaluation signal extracting means and the incident light quantity detecting means and the animal body detecting means.

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