ashok@atrp.mit.edu (Ashok C. Popat) (07/04/90)
Archive-name: arith-coding/03-Jul-90 Original-posting-by: ashok@atrp.mit.edu (Ashok C. Popat) Original-subject: Compression of multi-bit images Archive-site: cod.nosc.mil [128.49.16.5] Archive-directory: /pub Reposted-by: emv@math.lsa.umich.edu (Edward Vielmetti) In article <1990Jun7.114905.1714@athena.mit.edu> ashok@atrp.mit.edu (Ashok C. Popat) writes: >In article <SPENCER.90Jun4170821@spline.eecs.umich.edu> spencer@eecs.umich.edu (Spencer W. Thomas) writes: >>Lossless methods: >> >>Simple Huffman (adaptive or otherwise (the Unix 'pack' program) may do >>well if the pixel intensity (consider R,G,B values separately) >>histogram is not flat, even on scanned images. Arithmetic coding will >>do better, but is harder to do. > >Among arithmetic codes, those designed for a two-letter source >alphabet have received the most attention (for example, the Q-coder >has been talked about a lot recently). Although it is possible to >encode an arbitrary source with a binary arithmetic code, it is not >the right thing to do for a bunch of reasons. The right thing to do >in most cases is to use an arithmetic code that handles a multi-letter >source alphabet directly. The basic principles of such a code are >simple but the details are a little complicated. I describe the >details of a suitable arithmetic code in chapt. 3 of my SM thesis, >which I'll make available in (Postscript form) via anonymous ftp >somewhere if enough people are interested. Let me >(ashok@atrp.mit.edu) know if you're interested. The thesis and some C code to do arithmetic coding is now available for anonymous ftp on cod.nosc.mil (internet number = ?) in /pub under arith_coding.tar.Z. Thanks much to herman@marlin.nosc.mil for kindly putting it there. Ashok Chhabedia Popat Swiss Federal Institute of Technology, Lausanne