Two-dimensional Bar Code Encoding And Decoding Principle And Applied Research

This paper covers the characteristics and basic principles of the design of two-dimensional bar code and detailed examples of its application, including an encoding method for both English and Chinese characters. Two-dimensional bar code possesses the capability of error-correcting which one-dimensional bar code doesn't. So, besides a brief introduction of Reed-Solomon error-correcting code (RS code), this paper also gives a thorough analysis of RS code's application in two-dimensional bar code PDF417, giving detailed error-correcting principles in GF(929). Meanwhile, a looking-up database method used for yielding PDF47 error correcting codes has been developed, which makes it easier and more accurate to compute the coefficients of the generating polynomial and results of syndrome polynomials. The efficiency of PDF417 error-correcting function is therefore highly improved. As for the decoding process, this paper describes a solution based on whole bar code picking up by CCD vision system, and computer processing to detect the edges of the barcodes. An algorithm is also designed here based on PDF417 two-dimensional barcodes' structure. It first proposes a filter to eliminate noise, then deals with vertical scratches and those points that do not comply with the bar codes' boundary characteristics by a point-search strategy. Later, during process of restoring the bar coded pictures, the contaminations will not be restored due to that fact that their seeds for restoration have been cleaned beforehand. Experiments have proved that this algorithm can effectively eliminate the negative smooth of the bar code caused by filtering. The restored pictures will then be decoded by an improved edge-detecting projection method which can lead to efficiency and accuracy of the decoding process while demanding a lower error correcting level.