The filter strength i.e., the amount of filtering is computed
with the help of parmameter boundary strength (bS). The
boundary strength (bS) of the filter depends on the current
quantizer, macroblock type, motion vector, gradient of the
image samples across the boundary and other parameters as
shown in figure 3. The boundary strength is derived for each
edge between neighbouring 4 x 4 luminance blocks and for
each edge, bS parameter is assigned an integer value for 0 to
4. The rules for selecting integer value for bS parameter
boundary strength (bS) is illustrated in flow chart of figure
3. The bS values for filtering of chrominance block edges
are not calculated independently and same values calculated
for luminance edges are used. Application of these rules
results in strong filtering in the areas where there is
significant blocking distortion, such as boundary of intra
coded macroblock or a boundary between blocks that
contain coded coefficients.
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