| 摘要 |
<p>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 detected 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.</p> |
