Abstract: A hand-held optical reader for reading 2D bar code symbols. The reader includes an illuminating system for illuminating the symbol and an optical system for focusing an image thereof on a 2D image sensor. The image sensor is of the type which allows its imaging parameters, such as exposure, to be controlled by external circuitry. The reader also includes an image sensor processor which sets and changes the imaging parameters used by the image sensor as necessary to meet predetermined image quality criteria and to reduce the time necessary to complete a read operation.

Abstract: A two dimensional (2D) matrix symbology for use with bar code and other optical readers. A finder structure includes a center square and a plurality of nested squares having centers that approximately coincide with the center square. A symbol descriptor located adjacent to the finder structure encodes data indicating the size of the symbol and the length of the message encoded therein. A reference grid extends throughout the symbol to facilitate the location of individual data elements with respect to the finder structure thereof. The data structure of the symbol is filled with data blocks which are organized into layers which surround the finder structure. Data encoded in the data blocks may be read sequentially within layers and between layers. The symbology is a versatile symbology in that the number of check data blocks is user selectable to provide the desired level of error correction.