The coefficients of a chamfer mask are, to within a multiplicative scale
factor making it possible to give them an integer value, approximations
of the Euclidian distances separating the pixels covered by the mask,
from the pixel under analysis placed at the center of the mask. As there
are at least two possible integer values for each coefficient, the over-
and the under-approximation, one is rapidly faced with a considerable
number of possible combinations. The method proposed allows progressive
selection of the possible integer values, firstly at the level of each
coefficient by virtue of an axis error rate criterion, then at the level
of the coefficients considered by binomials by virtue of a sector error
rate criterion, which considerably reduces the number of combinations to
be analyzed to arrive at an optimal combination from the point of view of
the error rate obtained in the distance estimations.