Data compression and reconstruction methods and apparatuses for a hard copy
device are provided. The data compression method of compressing source image data,
which is used for hard copying a bilevel screened image and stored in a memory
in units of bytes, for a hard copy device, includes the steps of transposing bytes
at each column to bytes at each row in the source image data; and entropy encoding
sequential chains, which include a current chain to be compressed and a chain or
chains succeeding the current chain, or the current chain depending on whether
a chain having the same value as that of the current chain exists in a dictionary
composed of previous chains compressed before, and determining the result of the
entropy encoding as the result of the compression. Neighboring bytes at each row
have neighboring memory addresses. The offset of neighboring bytes at each column
corresponds to the row width of the source image data. Start information containing
information on a chain which compression is performed on the source image data
starting from and header information are determined before the latter step and
included in the result of the compression, and each chain is composed of at least
two consecutive bytes at a row. Transposition is performed before entropy decoding
source image data, thereby improving the compression ratio, and the size of a template
can be arbitrarily controlled, thereby improving the compression speed.
