EP O 1 79 291  B1                          ..     .
Description                                                       _    _ _
Field of the lnvention                        _
_    _        _ The invention relates to a method and an apparatus for processing bi-level._mage data which are
5  supplied from an image data supply means, such as an image scanner, before the supply of the b__-level
image data to a data compressor.
Prior An
NIKKEl ELECTRONICS November 3, 1915, pp. 3_3_ describes a pre-process of __mage data which is
Io  adaptable to a run-length coding. In the anicle, black __mage data and wh__te image data of a reference l__ne
and a coding line lcurrent PEL or scan line) are so re-arranged that the black image data, i.e. black b__ts. are
grouped.into a left half of a new l__ne and the wh__te image data, i.e. white bits, are grouped into a r__ght half of
the new line. The le_ half ìs called an A1 sequence and the r__ght half __s called the A2 sequence. And. a new,
unconvent__onal codìng scheme for adapting the A1 and A2 sequence is funher required.
15    Although the anicle relates to a pre-processing of b__-level image data, the detail of the process for the
re-arrangement of the __mage data of the an._cle differs essentially from that of the present invention.
UhA_ 229 768 relates to the pre-processing of binarv image data supplied from an image supplv
means in preparatìon for compression. The patent deals with a method for eliminating isolated spots in the
image data wh.ich are considered as noise. Funhermore, the patent teaches a smooth__ng process to avoid       .
2o. quantizing errors when scann__ng boundaries between black and wh__te areas. Transitions between black       '
and wh__te areas are detected and the distances between lefE end transitions or right end transitions._n
subsequent lines are changed to ach__eve smoothing by way of an al__gnment of trans__tions.
As the distances are not compared to ranges which have been predefined with the purpose to facilitate
the subsequent compression, the pre-process._ng scheme described in thís patent lacks flexibility, Although
z5  it allows a better representat._on of scanned._mage details of special shapes, it does not essentially and
generallv contribute to a facil._tated compression and to an essential reduct__on of compression data to be
transmitted,
It is, therefore, an object of the present __nvention to propose a method and an apparatus for pre-
processìng binary image data to allow an __mproved compress__on of such data.
3o    The method and the apparatus of the present invention are respectivelv defined in claims 1 and 7.
The improved compression according _o the present invention._s achieved by a selective processing of
d._stances of transìtions be_een black and white areas, in subsequent scanned l__nes. By putting the
distances ìn relation to the boundaries of a predetermined range the d._stances can be reduced in a flexible
way. For an appropr__ate choice ofthe boundaries ofthe range the compression coding scheme __s taken _into
35  consideration.
Br__ef Descr__ption of the Drawings
F._g. 1 shows an operat._onal flow chan of the pre-process in accordance with an embod__ment of the
present invent__on.
_o    Fig. 2 shows an example of the two-d_imens__onal coding scheme.
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