Lossless compression scheme for color-indexed character images

摘要

Recently, in mobile environments, a variety of character images have been provided to mobile phones and PDAs. Most of character images are an indexed image with 256 index values, requiring a lossless compression due to the property of the indexed data. Encoded image data is delivered to user clients from a server of content providers. Mobile devices are usually equipped with low processing power compared with desktop devices so that the simplicity of decoding process as well as the satisfactory compression ratio of encoding process is required. Especially, the complexity of a decoder needs to be reduced for the fast view of images on the LCD monitor. Many lossless compression schemes have been proposed and adopted in practical fields. We propose an efficient compression scheme satisfying these requirements. The main difference distinguishing the conventional approaches and our proposed method is that ours is mainly interested in character image sequence, where each sequence is composed of twelve images. In experiments performed on many test sequences, we show that our proposed method produces a compression ratio of 3.32:1.