Abstract: Bit-mapped and compressed image data are converted one another through an intermediate image data or code form wherein each image is represented by a list of sublists, each sublist being itself a list of numerical values representing run lengths transistions from one type of picture element (pel) to a second and opposite type of picture element (pel) (e.g., a black pel and a white pel). Hence the intermediate code data structure according to the invention is termed a transition list or TL code or data structure. The data structure and coding rules are defined by rules relating to code type, code word length and code word interdependence. A specific conversion process specifies that the transition list be composed of sublists wherein each represents a scan line.

Abstract: An apparatus for selecting a reference line for image data compression including a plurality of mutually connected reference selector chips for selecting a reference scan line from vertical mode coding of image data. The reference selector chips select a reference scan line from a plurality of preceding scan lines in exclusive or combination of the image data of each candidate reference scan line with the image data from the input scan line. The candidate reference scan line that has the lowest number of dissimilar bits is selected as the reference scan line. Each candidate reference scan line has associated therewith a register having bit positions arranged from the highest order bit position to a lowest order bit position for storing a binary sum of the number of dissimilar bits. When the sums are compared, the binary value and successive bit positions are compared from the highest order bit position to the lowest order bit position.

Abstract: A method and apparatus for improving the performance of data compression processes, such as relative address coding, CCITT standard facsimile processes, and similar two-dimensional image coding processes, by block coding one or more of the vertical mode codes produced by these processes. The performance of data compression processes is improved by representing one or more sequences of vertical mode code words with a single block code word. A reference scan line is preferably selected from among a plurality of previous scan lines, for example, the immediately preceding ten scan lines, for two-dimensional image coding. The previous scan line which is most similar to the current scan line to be coded is selected as the reference scan line. The selected reference scan line is then fed with the current scan line to be coded to a two-dimensional data compression coding process so as to yield a first tier of data compression.

Abstract: A method and apparatus for selecting a reference scan line for two-dimensional image coding preferably compatible with known facsimile transmission equipment are disclosed. Selection of a reference scan line in accordance with the method and apparatus of the invention allows data compression for facsimile transmission so that the cost for use of the communication link is reduced. More than one previous scan line is considered as a candidate reference scan line. A reference scan line is selected from among a plurality of previous scan lines, for example, the immediately preceding ten scan lines. The preselected or adaptively selected scan line among the multiple prior scan lines, more particularly, the previous scan line which is most similar to the current scan line to be coded, is selected as the reference scan line. The reference scan line is then fed with the current scan line to be coded to a two-dimensional data compression coding process so as to yield optimum data compression.