A bit resolution-extension method is provided. The bit
resolution-extension method includes acquiring the shortest distance from
a central pixel to a positive contour and the shortest distance from the
central pixel to a negative contour in a filtering region which scans the
positive contour comprising large pixels of a fixed value and the
negative contour comprising small pixels of a fixed value, based on a
value of the central pixel, generating an extension bit of the central
pixel by interpolating the shortest distance from the central pixel to
the positive contour and the shortest distance from the central pixel to
the negative contour, and adding the extension bit as a lower bit of the
central pixel.