JPH077268U - Auto focus device - Google Patents

Abstract

(57) [Abstract] [Purpose] Accurately detect an appropriate focus position by reducing erroneous judgments due to disturbances such as noise, camera shake, and subject movement. [Structure] In a focus voltage detection circuit, a high frequency component of a video signal is detected as a focus voltage. This focus voltage is A /
After D conversion, it is taken into the microcomputer. In the microcomputer, the magnitude of hysteresis x is obtained from the maximum value and the minimum value of the latest four fields of focus voltage. Then, hill climbing control is performed with the range of ± x as the dead zone. During the hill climbing, the degree of the gradient of the focus voltage between the four fields determines the magnitude of the hysteresis x, so that it is possible to reduce the local peak PN.
In the vicinity of the top PF of the focus voltage, the hysteresis gradually narrows and the proper top is detected.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an autofocus device suitable for, for example, a video camera, and more particularly to improvement of the autofocus device by a hill climbing servo system.

[0002]

[Prior art]

 NHK Technology Research, VO L17. There is "Television camera automatic focus adjustment by mountain climbing servo system" by Ishida et al. Disclosed in No.1 ('65), P21-37. Explaining this, the high frequency components included in the video signal of the captured image correspond to the degree of focus, and show the maximum value at the in-focus point. This is shown in FIG. 6, where the horizontal axis represents the lens position and the vertical axis represents the focus voltage that is the high frequency component. When the focus voltage becomes maximum, this is the proper apex (focus point) PF. Therefore, the focus adjustment (focusing) is performed by moving the focusing lens so that the focus voltage becomes maximum (arrow in the figure). (See FA).

By the way, in such a hill-climbing servo system, a fixed dead zone (hysteresis) is usually provided in determining whether the focus voltage increases or decreases, thereby preventing malfunction due to noise or the like. For example, as shown in the figure, assume that a local peak PN exists at an intermediate position due to noise or the like. Since this peak PN is not the maximum value of the focus voltage, it is desired to perform control so that it passes through this peak PN as indicated by arrow FA. Therefore, for example, a hysteresis indicated by h is set, and hill climbing is performed in this range regardless of the increase or decrease of the focus voltage.

[0004]

[Problems to be solved by the device]

 However, in the above conventional technique, if the hysteresis h is too large as shown in FIG. 7A, the overrun OR at the top of the focus voltage becomes large as shown by the arrow FB. Therefore, it takes time to reach the focus position. On the other hand, if the hysteresis h is small as shown in FIG. 6B, it is caught in the middle of the hill climbing as indicated by the arrow F C, and is easily affected by noise, camera shake, disturbance, and the like.

The present invention focuses on these points, and reduces the misjudgment due to disturbances such as noise, camera shake, and movement of the subject, and makes it possible to quickly detect an appropriate focus position. It is an object of the invention to provide an autofocus device.

[0006]

[Means for Solving the Problems]

 In order to achieve the above object, in an autofocus device that uses the high frequency component of a video signal and sets the hysteresis range to adjust the focus of the image pickup device by the hill climbing servo system, the degree of fluctuation of the high frequency component at multiple points in time. It is characterized by including a high-frequency component detecting means for detecting the above, and a hysteresis setting means for setting the above-mentioned hysteresis range in accordance with the degree of fluctuation of the high-frequency component detected thereby.

[0007]

[Action]

 According to the present invention, the range of hysteresis in the hill climbing servo control is set according to the degree of fluctuation of the high frequency component of the video signal at a plurality of time points. During mountain climbing, the variation of high frequency components is relatively large, so the hysteresis range is also set large. This will reduce the effect of local peaks due to noise. In addition, since the fluctuation of the high frequency component becomes smaller as it approaches the top, the range of hysteresis is also set smaller. This will reduce overruns.

[0008]

【Example】

 Hereinafter, an embodiment of an autofocus device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows the configuration of an autofocus device according to this embodiment. In the figure, a lens 12 for focus adjustment is provided on the light incident side of the image pickup device 10 such as a CCD. A video process circuit 14 is provided on the charge signal output side of the image sensor 10. The video signal is also connected so as to be output to the focus voltage detection circuit 16. A microcomputer 20 is connected to the output side of the focus voltage detection circuit 16 via an A / D converter 18, and its focus control output side is connected to a drive circuit 22.

Of the above-mentioned units, the lens 12 is movable by a motor 24, and the focus is adjusted by this. The video process circuit 14 includes well-known circuits such as a preamplifier, a color separation circuit, and a γ correction circuit, and outputs R (red), G (green), B (blue) or color difference video signals. It is supposed to be done. The focus voltage detection circuit 16 is for extracting the focus voltage which is a high frequency component from the input video signal, and is composed of a filter and a sample hold circuit.

The microcomputer 20 has a function of repeatedly performing the operation shown in FIG. 4 based on the focus point voltage data extracted by the focus voltage detection circuit 16. The focus control signal obtained by this is supplied to the drive circuit 22, and the drive circuit 22 drives the motor 24 based on the input control signal. The synchronization generation circuit 26 is a circuit for outputting a clock signal and a synchronization signal necessary for each section.

Next, a method for setting the hysteresis in the microcomputer 20 of this embodiment will be described with reference to FIG. For example, assume that the focus voltage of each field is changing as shown in FIG. In this embodiment, the focus voltage for four fields including the current field is used. That is, the focus voltage data of the oldest field is discarded when the focus voltage of the new field is obtained. Then, the difference x between the maximum value and the minimum value of the focus voltage for the latest four fields is set as the magnitude of hysteresis.

Next, using the x thus determined, the range of ± x is set as the range of hysteresis, that is, the dead zone. This state is shown in FIG. 3, and the range of ± x indicated by P2 and P3, which is x away from the center P1, is set as the hysteresis range.

Next, the operation of the present embodiment as described above will be described with reference to the flowchart of FIG. 4 and the graph of FIG. The image pickup device 10 picks up an input image and outputs a charge signal to the video process circuit 14. In the video process circuit 14, desired processing such as amplification and color separation is performed on the input signal, and a video signal is output. This video signal is supplied to a video tape or a display device as needed.

In the present embodiment, this video signal is also supplied to the focus voltage detection circuit 16, where the high frequency component thereof is detected as the focus voltage. The detected focus voltage is converted into a digital signal by the A / D converter 18 and taken into the microcomputer 20. As described above, the microcomputer 20 stores the latest four field focus voltages in its memory (FIG. 4, step S1). Next, the magnitude of hysteresis x is obtained from the maximum value and the minimum value (step S2). Then, in the range of ± x, hill climbing control is performed on the assumption that the focus voltage has not changed. That is, a control signal to the effect that the mountain is climbed up to the maximum value of the focus voltage is output to the drive circuit 22 (step S3).

In the drive circuit 22, the motor 24 is driven based on the control signal input from the microcomputer 20, and the focus lens 12 is moved. Such an operation is repeatedly executed until the proper summit is detected (step S4). Such operation will be described in detail with reference to FIG. First, since the focus position is gradually approached during the hill climbing, the focus voltage gradually rises with each new field, as shown by points Q1 to Q4 in FIG. Therefore, the degree of inclination of the focus voltage between the four fields determines the magnitude of the hysteresis x. Therefore, even if there is a local peak PN due to noise or the like during the mountain climbing, the mountain climbing is performed within the range of ± x, so that the goodness due to the peak PN is reduced.

Next, when the focus voltage approaches the in-focus position and the focus voltage is near the apex, the curve of the focus voltage is rounded, so that the focus voltage changes as shown by points Q5 to Q8 in FIG. The change gradually becomes smaller. For this reason, the hysteresis x gradually decreases with each new field. Since mountain climbing is performed in this range, an appropriate turn-around point, that is, an appropriate summit can be detected.

As described above, according to the present embodiment, the hysteresis range is wide corresponding to the change of the focus voltage, that is, when the change of the focus voltage is large, the hysteresis range is wide when the change of the focus voltage is small. Since it is set to be narrow, erroneous judgments and overruns due to disturbances such as noise, camera shake, and movement of the subject are well reduced, and a proper focus position is quickly detected.

<Other Embodiments> The present invention is not limited to the above embodiments, and includes, for example, the following ones. (1) An upper limit and a lower limit may be set for the value of the hysteresis x obtained in the above embodiment. This has the effect that the sensitivity for detecting the proper peak can be kept constant. Further, in the above-mentioned embodiment, the hysteresis value is obtained from the focus voltage for four fields, but it may be appropriately set if necessary, and an appropriate calculation may be combined. For example, the hysteresis x may be 1/2 of the difference between the maximum value and the minimum value of the focus voltage for 8 fields.

(2) In the above-described embodiment, the focus voltage is obtained from the high frequency component of the video signal. However, the focus voltage is obtained from each of the appropriate bands of 2 or more, and the hysteresis voltage is used to synthesize the focus voltage. Focus control may be performed as desired. For example, the average of the hysteresis values obtained for the focus voltage in each band is used.

[0020]

[Effect of device]

 As described above, according to the autofocus device of the present invention, the hysteresis range is set according to the degree of fluctuation of the high frequency component contained in the video signal, so that noise, camera shake, movement of the subject This has the effect of reducing erroneous determinations due to disturbances such as the above, suppressing overruns, and being able to quickly detect an appropriate focus position.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an autofocus device according to the present invention.

FIG. 2 is an explanatory diagram showing how the focusing voltage changes with time.

FIG. 3 is an explanatory diagram showing how hysteresis is set in the embodiment.

FIG. 4 is a flowchart showing the operation of the embodiment.

FIG. 5 is an explanatory diagram showing the operation of the embodiment.

FIG. 6 is an explanatory diagram showing a basic operation of a hill climbing servo system.

FIG. 7 is an explanatory diagram showing an inconvenience of hill climbing control according to a conventional technique.

[Explanation of symbols]

Reference numeral 10 ... Imaging element, 12 ... Focusing lens, 14 ... Video process circuit, 16 ... Focus voltage detection circuit (high frequency component detection means), 18 ... A / D converter, 20 ... Microcomputer (hysteresis setting means), 22 ... Drive circuit, 24 ... Motor, 26 ... Synchronous generation circuit, FA, FB,
FC ... Arrow indicating climbing, PF ... Focusing peak, P
N ... local peaks, Q1 to Q8 ... points indicating fields, h, x ... magnitude of hysteresis.

Claims (1)

[Scope of utility model registration request] 1. An autofocus device that uses a high-frequency component of a video signal to set a hysteresis range to adjust the focus of an image pickup device by a hill-climbing servo system. An autofocus device comprising: a component detection unit; and a hysteresis setting unit that sets the hysteresis range in accordance with the degree of variation of the high-frequency component detected by the component detection unit.