Pattern recognition circuit for reliably distinguishing between different portions of a diascope pattern during video camera setup

摘要

A pattern recognition circuit integral with a checkerboard diascope pattern used for spatial and shading error measurement and correction, performs detection in the time domain. A locator time window is provided to positively locate and distinguish white-to-black transitions of coarse locators selectively placed within the diascope pattern from, for example, checker white-to-black transitions, or from white-to-grey transitions, even under adverse scanning conditions. The circuit includes narrow time windows for identifying specific valid locator transitions, to thereby prevent triggering due to checker transitions, short noise pulses, etc. During one field interval, each locator is scanned a number of lines, but only the middle line scan is used to describe the locator coordinates, i. e., is used to generate a locator strobe output for latching the coarse locator positions into a system memory for subsequent comparison with the diascope pattern to determine the coarse scan errors. Checker transitions are indicated via a checkers valid output which remains in a high logic state as long as checkers are being scanned.