Film positioning system using dual perforation sensors

摘要

A method and apparatus for controlling the positioning of a filmstrip in a film scanning gate using signal states derived from a pair of spaced film sprocket holes or perforation ("perf") sensors on either side of the film scanning gate in conjunction with line scan counts and filmstrip drive, stepper motor half-step counts. The filmstrip is advanced by the stepper motor in a pre-scan operation through the film scanning gate for line scanning the image frames at a low resolution and advanced in the reverse direction back into the film scanning gate for high resolution scanning in a main-scan operation. A line scan array of line scan counts and half-step counts as well as first and second perf arrays of half-step counts and perf sensor states are generated in the pre-scan operation. Image frame borders are located in the pre-scan operation as border line scan counts and correlated in the line scan array to the half step counts to go to in the main-scan. During main-scan, the filmstrip image frames are positioned in the scanning gate by reverse drive of the stepper motor in a coarse and fine alignment process employing the half step counts to go to and the state transitions in the first and second perf arrays. Filmstrip jams, slips and perforation defects are detected from perf state durations in the perf arrays in relation to the associate half-step counts.