Bar code reader for decoding a four state bar code

Abstract

A bar code reader which is suitable for decoding a four-state bar code such as a Postnet bar code and which is designed to extract a bar code correctly from a background in a captured image. The bar code reader includes a binary coding circuit transforming a captured image into a binary image, an image storage storing therein the binary image, a shrinking circuit shrinking each pattern in the binary image by k pixels, a vertical expansion circuit expanding each pattern in the image outputted from the shrinking circuit vertically by m pixel, an edge detector detecting a contour of each pattern in the image outputted from the vertical expansion circuit to produce an image containing an edge of each pattern, a horizontal expansion circuit expanding each pattern in the image outputted from the edge detector horizontally by n pixel, a horizontal contraction circuit contracting each pattern in the image outputted from the horizontal expansion circuit horizontally by n an identification circuit labeling patterns in the image outputted from the horizontal contraction circuit to identify the patterns, and a decoder. The identification circuit specifies a bar code area based on shape characteristics of the patterns. The decoder selects data on the image stored in the image storage which belongs in the bar code area specified by the identification circuit to decode the bar code.