Patent US 5,481,095

A code reading pattern and an image pickup apparatus are provided for reading a symbol representing significant information, the symbol encoded by the pattern. The code reading pattern is formed by repeated markings of constant pitch on the surface of an object. The markings define area having at least one boundary, the at least one boundary defining an outline of the symbol. The apparatus includes a lighting system for illuminating the code reading pattern with parallel light, an imaging system for imaging light reflected from the pattern, a spatial frequency filtering system, located at the near back focal plane of the imaging system, for blocking regular reflected light and for transmiting diffracted light to project an image of the symbol, and a receiver for receiving the image.