AUTOMATIC METHOD OF OPTICALLY SCANNING A TWO-DIMENSIONAL SCENE LINE-BY-LINE AND OF ELECTRONICALLY INSPECTING PATTERNS THEREIN BY "SHAPE-TRACKING"

A two-dimensional pattern made up of primary and secondary shapes having different levels of contrast, e.g. a printed circuit card, is visually inspected by means of a line-by-line scan, e.g. using a beam of light. A data structure or "file" is built up representative of the current scan line and is compared with a similar file representative of the accumulated scan history so far. The accumulated history file is then updated, the next line is scanned, and the sequence repeats. Allowable changes in shape between scan lines can be coded in the form of multiple-entry digital tables. Non-allowable changes cause alarms to be generated. Allowable changes can easily be altered by downloading a new set of tables, thereby enabling the method to be readily adapted to inspecting different types of object. The method is suitable for implementation by hard-wired logic for high-speed real-time operation.