Method and apparatus for detecting mark from image data

摘要

An apparatus for detecting from first image data mark image data corresponding to a mark and having a first length in a first direction and a second length in a second direction perpendicular to the first direction in unit of pixels. The apparatus includes a differentiating processor, an adding processor and a controller. The differentiating processor executes differential operations for the first image data in response to first and second differential operation commands from the controller to obtain second and third image data and executes the differential operations for fourth image data in response to third and fourth differential operation commands from the controller to obtain fifth and sixth image data. The adding processor adds the second and third image data shifted by 1/2 the first length in opposite directions in response to the addition command from the controller to obtain the fourth image data and adds the fifth and sixth image data shifted by 1/2 the second length in opposite directions in response to the addition command from the controller to obtain seventh image data. The controller detects a center position of the mark from the seventh image data.