The initial image
is the overlay of two complementary masks
and
. This overlay evolves according to two rules
and
. The result
of evolving
by the first rule
is masked by multiplication with bitmap mask
. The result
of evolving
by the second rule
is masked by multiplication with the inverted bitmask
which is taken to be
. The sum of the results
and
gives the next image
.
The rule numbers
and
specify two of the 1024 totalistic 9-neighbor two-color cellular automaton rules.
In this Demonstration mask
and its negative
can display (1) the selected rule numbers, (2) a number which gives the number of the current step, (3) static random patterns, or (4) a new random pattern for each step.
Note that the sums of the masked automaton results are always positive. Differences of those intermediary masked results can give negative values. However, taking the absolute value makes negative results of differences acceptable for the next step of evolution by the binary automaton rules
and
.
