一种优化的Freeman链码及其在工程图纸绘制中的应用

An Optimized Freeman Chain Coding Method and Its Application to Engineering Drawing Plotting

提出一种适合于线状结构二值图象的最优化Ｆｒｅｅｍａｎ链码，并讨论其在绘图仪图纸绘制中的应用。与传统的Ｆｒｅｍａｎ链码相比，本文的方法是基于数字化点阵图象的无失真编码。根据图象中直线段长度的统计特性选择码长，以使编码压缩率为最高。理论分析和实验结果证明，本方法优于已有的方法并易于工程图纸的图象存储和在绘图仪上的输出。

In this paper, we present an optimized Freeman chain coding method for bi level line structured images and discuss its application in the storage and automatic plotting of engineering drawings. Compared with the traditional Freeman chain coding that uses single ring or multi ring image quantizers, the proposed method is based on already quantized dot matrix digital images, and is a lossless coding method. We select the code length according to the statistics of the length of straight line segment in the image and thus minimize the average number of bits needed to encode the segment. Theoretical rate analysis and several experimental results show that the proposed method achieves lower bit rate than the existing one and can be easily applied to the storage and plotting of engineering drawings.