EP0279424A2
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EP
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Automatic focusing circuit for automatically matching focus in response to video signal
Assignee: Sanyo Electric Co Ltd
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Filing: 1988-02-17
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Granted: —
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Expires: 2008-02-17
Abstract
Abstract In an automatic focusing circuit of a video camera, an automatic focusing operation is performed by a focus evaluating value produced in response to a video signal obtained in an image sensing circuit (4). A focusing motor control circuit (14) controls rotation of a focusing motor (3) so that a focusing lens (1) is once fixed in the position where the focus evaluating value takes the maximum value. Then, a control circuit (14) resumes the automatic focusing operation after a lapse of a second time period when it is determined that the focus evaluating value was decreased to a predetermined level during a first time period and maintained the level over the second time period, and does not resume the automatic focusing operation when it is determined that the focus evaluating value did not maintain the level. On the other hand, the control circuit (14) resumes the automatic focusing operation after a lapse of the first time period when it is determined that the time period more than the first time period is required until the focus evaluating value attains the predetermined level.
Inventors
- 👤 Hirotsugu Murashima
- 👤 Satoru Maeda
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 23:39
CPC Classifications
H; H04; H04N; H04N23/00; H04N23/60; H04N23/67; H04N23/673
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
409 words
An automatic focusing circuit for automatically matching the focus relative to an object in response to a video signal obtained from image sensing means having a focusing lens and an image sensor, comprising: relative position changing means (2, 3) for changing the relative position in the direction of an optical axis of said focusing lens relative to said image sensor, focus evaluating value detecting means (5) for detecting a level of a high frequency component of the video signal obtained from said image sensing means every constant time period, converting the level into either a focus evaluating value which takes the maximum value in the in-focus position or a focus evaluating value which takes the minimum value in the in-focus position and sequentially supplying the same, control means (10, 11, 12, 13, 14, 15, 16) responsive to the focus evaluating value supplied from said focus evaluating value detecting means for controlling said relative position changing means such that the relative position of said focusing lens is once fixed in the position where said focus evaluating value takes the maximum value or the minimum value, and object change detecting means (50) responsive to the change of the focus evaluating value supplied from said focus evaluating value detecting means for detecting the change of said object after the relative position of said focusing lens is fixed by said control means, said object change detecting means comprising first memory means (17) for holding as a reference value said focus evaluating value at the time point when the relative position of said focusing lens is fixed by said control means, first detecting means (61) for determining that the focus evaluating value supplied from said focus evaluating value detecting means is decreased to a predetermined level with respect to the reference value held in said first memory means within a predetermined first time period, second detecting means (60) for determining that the focus evaluating value supplied from said focus evaluating value detecting means remains at a level less than said predetermined level over a predetermined second time period which is longer than said first time period after the focus evaluating value is decreased to said predetermined level within said first time period, and means (25) for supplying outputs of said first and second detecting means to said control means, said control means being responsive to outputs of said first and second detecting means for resuming control of the relative position of said focusing lens.
Claim 2
Dependent Claim
89 words
An automatic focusing circuit according to claim 1, wherein said focus evaluating value detecting means converts a video signal corresponding to a predetermined sampling area into a focus evaluating value every said constant time period, said first time period being a time period expected to be required until an object other than said object has entered a field of view corresponding to said sampling area, and said second time period being a time period expected to be required until the other object has passed through said field of view.
Claim 3
Dependent Claim
84 words
An automatic focusing circuit according to claim 2, wherein said control means resumes control of the relative position of said focusing lens after a lapse of said second time period when the output of said first detecting means shows that said focus evaluating value is decreased to said predetermined level within said first time period and then, the output of said second detecting means shows that said focus evaluating value remains at a level less than said predetermined level over said second time period.
Claim 4
Dependent Claim
80 words
An automatic focusing circuit according to claim 2, wherein said control means does not resume control of the relative position of said focusing lens when the output of said first detecting means shows that said focus evaluating value is decreased to said predetermined level within said first time period and then, the output of said second detecting means shows that said focus evaluating value does not remain at a level less than said predetermined level over said second time period.
Claim 5
Dependent Claim
62 words
An automatic focusing circuit according to claim 2, wherein said control means resumes control of the relative position of said focusing lens after a lapse of said first time period when the output of said first detecting means shows that the time period more than said first time period is required until said focus evaluating value is decreased to said predetermined level.
Claim 6
Dependent Claim
114 words
An automatic focusing circuit according to claim 2, wherein said first detecting means comprises first comparing means (19) having a relative first threshold value associated with said reference value held in said first memory means and a second threshold value which is larger than the first threshold value and generating a first signal when the difference between said reference value and the focus evaluating value outputted from said focus evaluating value detecting means is between said first and second threshold values, delay means (23) for outputting a second signal obtained by delaying said first signal by said first time period, and first AND means (24) for ANDing said first signal and said second signal.
Claim 7
Dependent Claim
111 words
An automatic focusing circuit according to claim 2, wherein said second detecting means comprises second comparing means (18) having said first threshold value and generating a third signal when the difference between said reference value and the focus evaluating value supplied from said focus evaluating value detecting means exceeds said first threshold value, means (20) for generating a fourth signal having duration which is equal to said second time period in synchronization with the third signal generated from said second comparing means, means (21) for generating a fifth signal in synchronization with termination of said fourth signal, and second AND means (22) for ANDing said third signal and said fifth signal.
Claim 8
Dependent Claim
39 words
An automatic focusing circuit according to claim 2, wherein means for supplying the outputs of said first and second detecting means to said control means comprises OR means (25) for ORing outputs of said first and second AND means.
Claim 9
Dependent Claim
133 words
An automatic focusing circuit according to claim 2, wherein said focus evaluating value detecting means comprises synchronizing signal separating means (5a) for separating a vertical synchronizing signal and a horizontal synchronizing signal from said video signal, gate means (5b, 5c) for passing every said constant time period said video signal within said sampling area set in response to said vertical synchronizing signal and said horizontal synchronizing signal separated from said vertical synchronizing signal separating means, filtering means (5d) for extracting a level of a high-frequency component of a video signal which passed through said gate means, integrating means (5f) for integrating the level of the high-frequency component of the video signal extracted by said filtering means, and analog/digital converting means (5g) for converting an output of said integrating means into a digital output.
References Cited (Backward Citations)
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