Lossless Compression of Maps, Charts, and Graphs via Color Separation

Abstract

In this paper, we present a fast lossless compression scheme for digital map images, and chart and graph images in the raster image format. This work contains two main contributions. The first is centered around the creation of a codebook that is based on symbol entropy. The second contribution is the introduction of a new row-column reduction coding algorithm. This scheme determines the number of different colors in the given image and creates a separate bi-level data layer for each color i.e., one for the color and the second is for the background. Then, the bi-level layers are individually compressed using the proposed method, which is based on symbol-entropy in conjunction with our row-column reduction coding algorithm. Our experimental results show that our lossless compression scheme scored a compression equal to 0.035 bpp on average for map images and 0.03 bpp on average for charts and graphs. These results are better than most reported results in the literature. Moreover, our scheme is simple and fast.