JP2621284B2 - Focus control circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contrast detection type focus control circuit used for auto focus of a video camera, for example.

SUMMARY OF THE INVENTION The present invention provides a focus control circuit for detecting a spectral component in a video signal and performing focus control, wherein a focus area is provided with a detection area larger than the focus area, and a video signal having a predetermined time interval within the detection area is provided. By comparing the signals and calculating the movement vector amount of the subject, it is determined whether or not the movement of the subject is due to camera shake based on the calculation result. In the case of camera shake, the focus lens is not moved so that the focus lens due to camera shake is obtained. Can be prevented from swinging.

[Related Art] The video camera's autofocus method includes a distance measurement method and a focus detection method when classified based on the principle of a focusing method. The distance measuring method measures the distance to a subject and controls the position of a lens in accordance with the distance. The focus detection method detects focus on an imaging surface and controls the position of a lens at a position where focus is achieved.

One of the focus detection methods is a contrast detection method. The contrast detection method performs focus control using the fact that the edge of a captured image becomes clearer as the lens approaches a focus position. The sharpening of the edge of the captured image corresponds to an increase in the high frequency component in the video signal.

FIG. 4 shows a conventional example of a contrast detection type autofocus circuit.

In FIG. 4, a focus lens 20 is displaced by a motor 21 and light from a subject is projected to an image sensor 22 via the focus lens 20. The image sensor 22 converts light from a subject into a video signal, and the video signal is passed through a signal processing system circuit 23 and an amplifier 24 to a band-pass filter (BP).
F) Output to 25. The band-pass filter 25 passes, for example, a component having a frequency of 200 KHz to 2 MHz.
The output of 25 is supplied to the detector 26. The detector 26 performs double-wave rectification on the input signal, and the output of the detector 26 is supplied to the A / D converter 27. The A / D converter 27 A / D converts only the signal corresponding to the focus area based on the focus area setting signal sent from the microcomputer 29, and supplies this digital signal to the integration circuit. The integration circuit 28 integrates the digital signal of the A / D converter 27, and the output of the integration circuit 28 is supplied to the microcomputer 29 as a focus evaluation value. Microcomputer
At 29, the position of the focus lens 20 at which the output of the integration circuit 28 is maximized is searched by, for example, an algorithm of hill-climbing control. Based on this, a motor drive command is given from the microcomputer 29 to the motor drive circuit 30, and the position of the focus lens 20 is controlled so that the focus evaluation value output from the integration circuit 28 is maximized.

[Problems to be Solved by the Invention] However, as shown in FIG. 2 (a), the target subject a was photographed in the focus area A. However, two points in FIG. The subject a may fall outside the focus area A as indicated by a chain line. In such a case, the microcomputer 29 controls the position of the focus lens 20 so as to automatically focus on an unintended subject in the focus area A. When the position due to camera shake is corrected and the subject a is photographed in the focus area A, the position of the focus lens 20 is controlled again. Oscillation of the focus lens 20 due to camera shake as described above is not only a wasteful operation, but also causes disadvantages such as delay of autofocus, promotion of wear of a driving part, and difficulty in viewing a screen.

Therefore, an object of the present invention is to provide a focus control circuit that prevents the focus lens from swinging due to camera shake.

[Means for Solving the Problems] To achieve the above object, a focus control circuit according to the present invention comprises: an imaging unit for converting an optical signal from a subject into a video signal; and a spectral component in the video signal in a focus area. A focus detection circuit for detecting a spectral component amount and calculating a focus position, wherein a detection area including the focus area is provided, and a detection area larger than the focus area is provided. A vector computing means for comparing data based on two video signals separated by a predetermined time interval to calculate a moving vector amount of the subject in the focus area, and a camera shake based on the moving vector amount calculated by the vector calculating means. A camera shake determining means for determining whether or not the camera shake There is the case it is determined that camera shake is obtained so as not to move the focus lens.

[Operation] The data in the detection area separated by a predetermined time interval is compared by the vector calculation means, the movement vector amount of the subject in the focus area is calculated, and the camera shake determination means determines whether or not the camera shake based on the calculation result. If it is determined that the camera shake, the focus lens is not moved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

1 to 3 show an embodiment of the present invention,
This embodiment shows a case where the focus control circuit of the present invention is applied to a video camera.

In FIG. 1, the position of a focus lens 2 is changed by a motor 1, and an image of a subject a is formed on an image sensor 3 via the focus lens 2. The image sensor 3 converts light from the subject a into a video signal, and the output of the image sensor 3 is supplied to a signal processing circuit 4. The signal processing system circuit 4 creates a luminance signal by adding, for example, each of R, G, and B signals at a predetermined ratio, and sends this signal to the band-pass filter 6 and the A / D converter 7 via the amplifier 5. Can be The band-pass filter 6 serving as a spectrum detecting means is a filter that passes a component having a frequency of, for example, 200 KHz to 2 MHz. The band-pass filter 6 extracts all the spectral components other than the DC component and the noise component in the luminance signal. This bandpass filter 6
Is supplied to a detector 8, which rectifies the output of the band-pass filter 6 in both waves. Double-wave rectified detector 8
Is supplied to an A / D converter 9 and digitized by a sampling clock, and this digital signal is output to an integrating circuit 10. For example, a color subcarrier having a frequency fsc is used as the sampling clock. Integrator circuit 10
Integrates data which is a digital signal in the focus area A set by the focus area control circuit 15, and the integrated data is sent to the digital controller 13.

On the other hand, the A / D converter 7 digitizes the luminance signal from the amplifier 5 with a sampling clock, and sends the digitized luminance signal to the first memory 11. The data taken into the first memory 11 is transferred to the second memory 12, and the storage capacity of the first memory 11 and the second memory 12 has a capacity to store the data of the detection area B. The first memory 11 and the second memory 12 store
The reading is controlled by the digital controller 13, and the data in the detection area B is fetched into the first memory 11 at intervals of several frames, and the data already fetched into the first memory 11 is transferred to the second memory 12. By repeating this sequentially, the previous data B (x, y) is loaded into the second memory 12, and the subsequent data B '(x', y ') is loaded into the first memory 11. The detection area B includes a focus area A and is set to be larger than the focus area A, as shown in FIGS. 2 (a) and 2 (b). First
The output of the memory 11 and the output of the second memory 12 are output to the vector operation circuit 14 with the data of the corresponding addresses being synchronized. The vector operation circuit 14 includes the first memory 11 and the second
The position of the subject a in the first memory 11 in the focus area A is recognized in the second memory 12 based on the data sent from the memory 12 of the second memory 12, and the movement vector amount S of the subject a is calculated. I do. This calculation is performed in the detection area B of the second memory 12 as shown in the flowchart of FIG.
The data B (x, y) in the first memory 11 recognizes data substantially the same as the data A (x, y) in the focus area A in the data B (x, y). This recognition, for example,
As shown in FIG. 7A, the detection area B is divided into small blocks, and the sum of the digital values of the blocks of the second memory 12 and the first memory 11 is calculated to find a block having the same value. By doing. When the moving point of the subject a is recognized in this way, the subject a in the focus area A is recognized.
Is calculated. The vector operation circuit 14 calculates a movement vector amount (S _n , S _{n + 1} ,...) Every time the data in the first memory 11 and the second memory 12 is updated, and calculates the movement vector amount S (α, β) is output to the digital controller 13. The digital controller 13 determines from the output of the vector operation circuit 14 whether the movement of the subject a in the focus area A is caused by a camera shake or not.

This determination is performed, for example, as follows. In the case of camera shake, it is generally considered that the subject a reciprocates between two points in the detection area B. Now, the subject a is shown in FIG.
Suppose that it has moved as shown in FIG. 2 (b) → FIG. 2 (a).
The movement vector amount between FIG. 2A and FIG.
_{Assuming that n} (α _n , β _n ) and the amount of movement vector between FIG. 2B and FIG. 2A is S _{n + 1} (α _{n + 1} , β _{n + 1} ), For the moving direction, | β _n / α _n || β _{n + 1} / α _{n + 1} | For the moving distance, | α _n || α _{n + 1} |, | β _n | | Β _{n + 1} |.

Therefore, a certain threshold value is set, and || β _n / α _n | − | β _n−1 / α _n−1 || ≦ A... | Α _n | ≦ B, | β _n | ≦ C. If both conditions are satisfied, it is determined that the camera shake is occurring. When both of the conditions are not satisfied or when only one of the conditions is satisfied, the movement of the subject a is determined to be conscious.

When the movement of the subject a is determined to be a camera shake, a motor drive command is not given to the motor drive circuit 16, and when it is determined that the movement is not a camera shake, a motor drive command is given to the motor drive circuit 16. When a motor drive command is given, the motor drive circuit 16 outputs a motor drive signal to the motor 1 so that the motor 1 is driven. The rotation of the motor 1 is picked up by a frequency generator (FG) 17 and the frequency generator (FG) 17
Is sent to the digital controller 13 and feedback-controlled. The digital controller 13 searches for the position of the focus lens 2 at which the output of the integration circuit 10 becomes maximum by the algorithm of the hill-climbing control.

 Hereinafter, the operation of the above configuration will be described.

As shown in FIG. 2A, when the target subject a is captured in the focus area A of the image frame C, the image sensor 3
Converts the light from the subject a into a video signal. This video signal is supplied to a band pass filter 6, a detector 8 and an A / D
The data is converted into predetermined data via the converter 9 and the data in the focus area A is integrated by the integration circuit 10. The integrated data is sent to the digital controller 13, and the digital controller 13 controls the position of the focus lens 2 by using the hill-climbing control algorithm so that the integrated value becomes maximum.

On the other hand, a flowchart shown in FIG. 3 is executed to determine whether or not there is a camera shake. That is, the video signal data in the detection area B in the state shown in FIG.
It is taken in. A few frames after this state, the subject a moves as shown in FIG. 2 (b), and the video signal data of the detection area B in this state is fetched into the first memory 11, and at the same time, it is first stored in the first memory 11. The fetched video signal data is transferred to the second memory 12. This is sequentially repeated, and the previous data B (x, x,
y) is stored in the first memory 11 as data B '(x',
y ′) are fetched, and each time these data are updated, both data are output to the vector operation circuit 14. The vector calculation circuit 14 sequentially calculates the movement vector amount S (α, β) of the subject a in the focus area A, and supplies the calculation result to the digital controller 13.

When the digital controller 13 determines that the movement of the subject a is intentional, it issues a motor drive command to the motor drive circuit 16 and focuses on a new subject a in the focus area A by the above-described control. Subject a
When it is determined that the movement is caused by camera shake, no motor drive command is issued to the motor drive circuit 16 and the focus lens 2 is not displaced by camera shake.

In this embodiment, two memories 11 and 12 are used to simultaneously obtain data based on video signals separated by a predetermined time interval in the detection area B. However, one memory may be used. May be obtained. In this embodiment, the movement of the subject a is calculated using the video signal. However, the movement of the subject a can be calculated using the output of the detector 8.

[Effects of the Invention] As described above, according to the present invention, in a focus control circuit that detects a spectral component in a video signal and performs focus control, a detection area larger than the focus area is provided. A video signal at predetermined time intervals is compared to calculate a moving vector amount of the subject, and it is determined whether or not the moving of the subject is due to camera shake based on a result of the calculation. In the case of camera shake, the focus lens is not moved. Therefore, it is possible to prevent defects such as delay of autofocus, wear of a driving part, and difficulty in viewing a screen, which are caused by swinging of the focus lens due to camera shake.

[Brief description of the drawings]

1 to 3 show an embodiment of the present invention. FIG. 1 is a block diagram of a focus control circuit, and FIG. 2 (a) and FIG.
FIG. 3B is a diagram for explaining the movement of the subject due to camera shake, FIG. 3 is a flowchart for explaining whether or not the camera shake, and FIG. 4 is a block diagram of a focus control circuit showing a conventional example. 3... Image sensor (imaging means), 6... Band-pass filter (spectrum detecting means), 13... Digital controller (camera shake determining means), 14... Vector calculating circuit (vector calculating means), a. A: Focus area, B: Detection area.

Claims (1)

(57) [Claims] An image pickup means for converting an optical signal from a subject into a video signal, and a spectrum detection means for detecting a spectral component in the video signal in a focus area, wherein a focus is detected by detecting an amount of the spectral component. A focus control circuit for calculating a position, including a focus area, and providing a detection area larger than the focus area, comparing data based on two video signals separated by a predetermined time interval within the detection area, and A vector calculating means for calculating a moving vector amount of the subject in the focus area; and a camera shake determining means for determining whether or not the camera shake based on the moving vector amount calculated by the vector calculating means. Not to move the focus lens when it is determined that A focus control circuit.