Iterative pre- and post-processing for MRC layers of scanned documents

Abstract

The mixed raster content (MRC) document compression standard (ITU T.44) specifies a multi-layer multi-resolution representation of a compound document. The model is very efficient for representing sharp text and graphics onto a background. However, since the mask layer is binary, it is difficult to deal with scanned data and soft edges. The edge transitions do not fully belong to the foreground neither to the background, and cause some "halo" to the object edges using the MRC model. This paper presents an algorithm that builds an edge sharpening map and iteratively parameterizes the original edge "softness" at the encoder. The generated map and the "softness" parameters are, then, used to reconstruct the original soft edges at the decoder. Experimental results are presented, showing that the method can yield 1.5 dB gains in PSNR, in the compression ranges of interest.