Adaptive Block/Location Coding of Facsimile Signals Using Subsampling and Interpolation for Pre- and Postprocessing

In this paper, an information lossy preprocessing technique using subsampling is described. Notches and pinholes in the original image are first removed using a set of masks, after which single element runs are doubled to preserve connectivity. The image is then subsampled by taking alternate picture elements (pels) horizontally and vertically. Enlargement of the subsampled image is carried out at the receiver where replication, bilinear, and cubic B-spline interpolation techniques are investigated. The edges of the interpolated images are "smoothed out" by a set of restoration masks, producing a visually acceptable result. A formal subjective experiment is also conducted to determine the order of subjective preference of the resulting restored images. Finally, adaptive block/ location coding (ABLC), with respect to a numerical measure of complexity, is used to code the subsampled image. Compression ratios achieved for the CCITT documents range from 13.31:1 to 63.77:1, a reduction, on average, by about 40 percent when one-dimensional run-length coding using the modified Huffman code (MHC) is applied to the subsampled image and by about 73 percent when MHC is applied to the original data.