Improved lossless halftone image coding using a fast adaptive context template selection scheme

Applications such as printing on demand and personalized printing have arisen where lossless halftone image compression can be useful for increasing transmission speed and lowering storage costs. We present an improvement on the context modeling scheme by adapting the context template to the periodic structure of the halftone image. This is a non-trivial problem for which we propose a fast close-to-optimal context template selection scheme based on the calculation and sorting of the autocorrelation function on a part of the image. For evaluating our scheme, we have also investigated the compression performance of a suboptimal approach based on an incremental exhaustive search; this approach can be used in practice for decompression but not for compression because of timing requirements. We have experimented with classical halftones of different resolutions and sizes and screened under different angles.