US 4,789,898 AGranted

Demand auto focus driven by scene information only

AssigneeHughes Aircraft Company

InventorsRobert Zwirn, Michael Thomas

Life of this patent

Estimating the term…

Loading patent…

Abstract

A demand auto focus system is driven by scene information only, In a scanned video system as the camera is brought into focus the high frequency content of the video signal will increase. The video signal is passed through a band-pass filter and then rectified in a conditional integrator to generate a control signal whose amplitude indicates to the degree of focus. The control signal is stored and later compared to a control signal derived from a subsequent scanning. Once a significant change in control signal levels is deteced a drive signal is sent to the focusing device. If after being driven the subsequent scene has less high frequency content, then a drive signal in the opposite polarity or direction is sent to the focusing device. In this manner the scene is toggled toward optimum focus. When rapid toggling occurs a number of times (three for example), control logic detects this condition which is symptomatic of hunting around optimum focus, and the bidirectional focusing mechanism drive is turned off until such time as the scene becomes so defocused as to reinitiate the focusing sequence.

Claims15

Dependent claims

A scene driven demand auto focus system for tuning a bidirectional focusing mechanism controlling the focus of a video image of a scene, said system comprising:

deriving means for receiving sequential video images of a scene and for deriving therefrom corresponding sequential indications of the high frequency content of the video images received;
comparing means receiving the derived indications for comparing the derived indication most recently derived with the derived indication previously derived and for generating a first drive signal if the derived indication previously derived is lower than the derived indication most recently derived by at least a certain amount and for generating a second drive signal if the derived indication previously derived is not lower than the derived indication most recently received by at least a certain amount;
means receiving the first and second drive signal for accelerating the bidirectional focusing mechanism whenever the first drive signal is received and for reversing the direction of travel, establishing a minimum velocity and accelerating the bidirectional focusing mechanism each time the second drive signal is received whereby the bidirectional focusing mechanism is toggled and driven in the direction indicated to increase the derived indication of the high frequency content the video images received which is the direction of increased focus;
and
demand means for detecting when the bidirectional focusing mechanism is being toggled back and forth in a manner symptomatic of hunting around optimum focus and for stopping the toggling when such occurs, said demand means including restart means for comparing the derived indication of high frequency content received as the toggling is stopped with subsequently derived indications of high frequency content and for restarting the toggling whenever a subsequently derived indication differs by more than a fixed amount.

2 more elements

A scene driven demand auto focusing system adapted to replace manual tuning of a bidirectional focusing mechanism controlling the focus of a video image of a scene, said system comprising:

deriving means for receiving sequential video images of a scene and for deriving therefrom corresponding sequential indications of the high frequency content of the video image received;
comparing means receiving the derived indications for comparing the derived indication most recently derived with the derived indication previously derived and for generating a first drive signal if the derived indication previously derived is lower than the derived indication most recently derived by at least a certain amount and for generating a second drive signal if the derived indication previously derived is not lower than the derived indication most recently received by at least a certain amount;
focusing means adapted to replace manual focusing of the bidirectional focusing mechanism, said focusing means receiving the first and the second drive signal for accelerating the bidirectional focusing mechanism whenever the first drive signal is received and for reversing the direction of travel, establishing a minimum velocity and accelerating the bidirectional focusing mechanism each time the second drive signal is received whereby the bidirectional focusing mechanism is toggled and driven in the direction indicated to increase the derived indication of the high frequency content of the video images received which is the direction of increased focus;
and
demand means for detecting when the bidirectional focusing mechanism is being toggled back and forth in a manner symptomatic of hunting around optimum focus and for stopping the toggling when such occurs, said demands means including restart means for comparing the derived indication of high frequency content received as the toggling is stopped with subsequently derived indications of high frequency content and for restarting the toggling whenever a subsequently derived indication differs by more than a fixed amount.

2 more elements

Dependencies are inferred from the claim text.