JPH0352459A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To prevent the focusing position of a photographic image fluctuated and the image hard to observe by predicting the focusing position based on the change of amplitude of a high frequency component, and moving a photo graphic lens to a predicted focusing position. CONSTITUTION:A prediction arithmetic means 12 predicts the focusing position of the photographic image based on the amount of change of the amplitude of the high frequency component for the amount of travel of the photographic lens 2 supplied from a comparison means 10, and sets a prescribed range decided in advance centering the predicted focusing position. The prediction arithmetic means 12 sends a control signal so as to move the focusing position of the photographic image when the focusing position of the photographic image being photographed at present comes off the prescribed range. ln such a way, the fluctuation of the focusing position prevented occurring in the neighborhood of the focusing position in the focusing operation of the photographic image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focusing device for automatically focusing a captured image, which is used, for example, in a video camera.

[Prior Art] An automatic focusing device installed in, for example, a video camera is known, which performs a focusing operation on a photographed image using a signal sent from an image sensor that converts the photographed image into an electrical signal. This kind of automatic focusing device was developed by NHK Technical Research (7th edition in 1965).
Volume 1, serial number 86, P, 2 1-P. This method utilizes the so-called mountain-climbing servo method (hereinafter referred to as the "mountain-climbing method"), which was announced in 2003.

This hill-climbing method utilizes the fact that the amplitude of the Takagi frequency component (hereinafter referred to as high-frequency component) included in the signal sent out by the image sensor increases as the captured image is focused. I7 The amplitude of the high-frequency component This method determines that the point where is greatest is the focused position of the photographed image, and if the locus of the high frequency component is drawn, it will draw a parabolic shape as shown in FIG.

[The problem that the invention attempts to solve is: In this mountain climbing method, in order to determine the position where the vibration of high frequency components is greatest, the top of the parabola shown in Fig. 2,
In other words, the highest position of the high-frequency component can only be determined by measuring the high-frequency component at the focal point past the focal point, so the photographing lens always moves back and forth around the focal point to perform focusing operations. It will be carried out. Therefore, the photographed image obtained is always in a focused state and a state in which it is slightly out of focus repeatedly.

This does not have much of an effect on the focus of a still camera that captures images at the moment the camera stops moving, but in the case of a video camera that shoots continuously, the images become extremely difficult to see. .

The present invention has been made to solve these problems, and an object of the present invention is to provide an automatic focusing device in which the focus position does not change near the focus position during the focusing operation of a photographed image.

[Means for Solving the Problems] The present invention includes a focusing device that performs a focusing operation on a photographed image based on the amount of high frequency components extracted from a video signal obtained from a signal transmitted from an image sensor. In the automatic focusing device, a change amount calculation means calculates and sends out the amount of change in the high frequency component with respect to the amount of movement of the photographing lens, and a focus position of the photographed image is predicted based on information sent out by the change amount calculation means. At the same time, a predetermined range centered around the predicted in-focus position is set as an allowable area, and a control signal is sent to perform a focusing operation on the captured image when the focus of the captured image is at a focus position outside this allowable area. The present invention is characterized by comprising a predictive calculation means for sending data to the device.

[The effect prediction calculation means predicts the focal position of the photographed image based on the amount of change in the amplitude of the high frequency component with respect to the amount of movement of the photographic lens, which is supplied from the comparison means, and calculates the focus position within a predetermined range. The predicted focus position is set as the center. The predictive calculation means sends a control signal to move the focal position of the photographed image to the predicted focal position when the focal position of the photographed image currently being photographed is outside the predetermined range. Example] In FIG. 1 showing an embodiment of the automatic focusing device of the present invention, the photographing lens 2 is moved in the optical axis direction of the photographing lens 2 by an autofocus (AF) motor l, and the photographing lens 2 and the image sensor The distance to the imaging surface No. 3 is adjusted to perform a focusing operation of the photographed image. An image sensor 3 that converts a photographed image obtained through such a photographic lens 2 into an electric signal is connected to a signal processing circuit 4 that performs processing such as creating a video signal in the form of a television digital signal from the electric signal. Ru. The output side of the signal processing circuit 4 is connected to a camera circuit 7 that performs signal processing to visually display the video signal, and is also connected to a bandpass filter (BPF in the figure) that detects high frequency components from the video signal. ) 5 to the gate circuit 6. The gate circuit 6 is connected to the output side of an AF distance measuring frame circuit 8 which creates a distance range for performing automatic focusing operations from the video signal sent out by the camera circuit 7. The output side of the gate circuit 6 is supplied with the signal sent out from the camera circuit 7, and a sample hold (S in the figure) extracts and holds the high frequency component sent out from the gate circuit 6.
/H) is connected to circuit 9. The output side of the sample and hold circuit 9 is directly connected to the comparison circuit 10, and the high frequency component sent out by the sample and hold circuit 9 is
It is connected to the comparator circuit 10 via a one-field delay circuit 1l that delays the signal by one field. Therefore, the comparison circuit 10 is a circuit that compares the current high frequency component obtained from the photographed image and the high frequency component delayed by ■field, and sends out data for creating a hill climbing curve as shown in FIG. This is a circuit that does this. The output side of the comparator circuit 10 is connected to a prediction calculation circuit 12 that creates the above-mentioned hill-climbing curve based on the data sent out by the comparator circuit 10 and predicts the apex of the hill-climbing curve, the so-called in-focus point. The output side of the prediction calculation circuit 12 is connected to the AF motor 1.

The operation of the automatic focusing device configured in this manner will be described below.

A captured image obtained through the photographic lens 1 is converted into an electrical signal by the image sensor 3, and converted into a television signal by the signal processing circuit 4. This television signal is transmitted to the camera circuit 7
The image is processed so that an operator or the like can visually confirm the photographed image, and is also supplied to a bandpass filter 5 to extract a high frequency component, and the extracted high frequency component is sent to a gate circuit 6.

In the gate circuit 6, the high frequency component is transferred to the AF distance measuring frame circuit 8.
With the signal supplied from the camera, a fraction of only the range where automatic focusing is performed is extracted and sent to the sample and hold circuit 9. The sample and hold circuit 9 performs sampling and holding of the sampled high frequency components based on the signal sent out by the camera circuit 7, and the high frequency components sent out from the sample and hold circuit 9 are sent to the comparator circuit 10. At , the high frequency component delayed by one field by the one field delay circuit 1 l is compared with the high frequency component that is not delayed, and the comparison result is sent to the prediction calculation circuit 12 .

In the prediction calculation circuit 12, based on the compared high frequency components supplied for each field from the comparison circuit 10,
The relationship between the high frequency components of the photographed image and the focal position of the photographed image is approximately found. That is, in the prior art, the position where the amplitude of the high-frequency component is the largest is searched based on the amount of high-frequency component at each predetermined time point, but in the automatic focusing device of this embodiment, the photographing lens 2 supplied from the comparison circuit 10 A parabolic function as shown in FIG. 2 is approximately determined based on the amount of change in the amplitude of the high frequency component with respect to the amount of movement. For example, if the approximation is to a biconvex parabola as shown in FIG. Considering that there are factors, the prediction calculation circuit 12 approximately calculates the function of the parabola by using an approximation processing method such as least squares calculation based on the measured value data supplied from the comparison circuit 1O three times or more. demand. Furthermore, the prediction calculation circuit 12 calculates the position where the differential coefficient of the obtained function becomes zero, that is, the in-focus position. When the pre-focus position is determined in this way,
The prediction calculation circuit 12 sets a preset allowable range centered on the predicted focus position. If the current focus position of the photographed image is outside the above-mentioned allowable range, the prediction calculation circuit 12 sends a control signal to the AF motor 1 to move the photographing lens 2 to the above-mentioned predicted focus position. Note that the above-mentioned allowable range refers to a shift in the focal position of a captured image within a range where the shift in focus of the captured image cannot be visually recognized.

As described above, according to the automatic focusing device of this embodiment, the photographic lens 2 is moved to the predicted focal position in one go at the time when the predicted focal position of the captured image is determined, so that the automatic focusing device in this embodiment is not focused as in the conventional example. The photographing lens does not move back and forth around the position, so that the photographed image does not become difficult to see. Further, after the predicted focus position is calculated, the photographic lens 2 is moved to the focus position in one step, thereby reducing the time required to adjust the focus position. Furthermore, even after the focus position has been determined as described in Section 2, data continues to be sent from the comparator circuit 10 to the prediction calculation circuit 12, and if the focus position of the captured image falls outside the above-mentioned tolerance range. By not moving the camera I/lens 2 until the tolerance is exceeded, and then re-entering the focusing operation once the tolerance has been exceeded, unnecessary focusing operations can be omitted, and furthermore, the difficulty in viewing the photographed image can be eliminated. be able to.

[Effects of the Invention] As detailed above, according to the present invention, instead of determining the in-focus position while moving the photographic lens based on the magnitude of the amplitude of the high frequency component extracted from the video signal, Predicting the in-focus position based on changes in the amplitude of high-frequency components 17 By moving the photographing lens in one go to the predicted in-focus position, the in-focus position of the photographed image does not change and the photographed image becomes difficult to see. There isn't.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the structure of one embodiment of the automatic focusing device of the present invention, and FIG. 2 is a diagram showing the relationship between focal length and high frequency components. 1... AF motor, 2... Photography lens, 10...
Comparison circuit, 12... Prediction calculation circuit.

Claims (1)

[Claims] (1) In an automatic focusing device equipped with a focusing device that performs a focusing operation on a photographed image based on the amount of high frequency components extracted from a video signal obtained from a signal transmitted from an image sensor, movement of a photographing lens is performed. a change amount calculation means for calculating and sending out the amount of change in the high frequency component with respect to the amount of change; a predetermined range set as a permissible range, and a predictive calculation means for sending a control signal to a focusing device to perform a focusing operation on the photographed image when the photographed image is focused at a focal position outside the permissible range. An automatic focusing device characterized by: