Autofocusing device for use in a video camera and an autofocusing method thereof

摘要

A method for autofocusing a video camera, adjusting the focus by defining the focus range in which the contrast signal is extracted, generating the control clock pulse having higher frequencies than the video signal during the occurrence period of horizontal and vertical synchronizing signals corresponding to the focus range, sampling the video signals obtained in the image pick-up elements by means of the control clock pulses, converting this sampled signal into digital signal, generating the digital differential signal which represents the difference between the values of one control clock pulse earlier one and current one, producing the digital weighted signal by transforming the digital differential signal by means of the nonlinear weight value, integrating the digital weighted signals for one or more fields or frames to obtain the focusing value, and moving the focusing lensd based on the focusing value to the location where the focusing value approximately reaches the maximum.