PATTERN RECOGNITION CIRCUIT FOR RELIABLY DISTINGUISHING BETWEEN DIFFERENT PORTIONS OF A DIASCOPE PATTERN DURING VIDEO CAMERA SETUP

摘要

ABSTRACT OF THE DISCLOSUREA pattern recognition circuit integral with acheckerboard diascope pattern used for spatial and shadingerror measurement and correction, performs detection in thetime domain. A locator time window is provided to positivelylocate and distinguish white-to-black transitions of coarselocators selectively placed within the diascope pattern from,for example, checker white-to-black transitions, or fromwhite-to-grey transitions, even under adverse scanning condi-tions. The circuit includes narrow time windows for identifyingspecific valid locator transitions, to thereby preventtriggering due to checker transitions, short noise pulses, etc.During one field interval, each locator is scanned a numberof lines, but only the middle line scan is used to describethe locator coordinates, i.e., is used to generate a locatorstrobe output for latching the coarse locator positions into asystem memory for subsequent comparison with the diascopepattern to determine the coarse scan errors. Checker tran-sitions are indicated via a checkers valid output which remainsin a high logic state as long as checkers are being scanned.-2-