Improved layer processing for MRC compression of scanned documents

The Mixed Raster Content (MRC) document compression is a well documented standard. Its efficiency for representing sharp text and graphics over a background has been extensively presented. Scanned documents, however, are difficult to be dealt with because of soft transitions. In one of our previous works we presented a pre/post-processing algorithm for MRC compression of scanned images that sharpens the edges, before compression, and softens it again, after reconstruction. The present paper uses the same basic idea but describes three new features that improve, in a rate-distortion sense, the compression performance. First, the real bitrate is used to determine the pre/post-processing parameters. Second, the Mask layer and the edge sharpening/softening map have their quality improved and, third, layer resolution change has been explored. Experimental results show that the method not only provides higher subjective quality, but it can yield up to 2.5 dB gains in PSNR against single coder approaches, in the compression ranges of interest.