A note on transitions

We want to record occupancy in various bands. In general we need to consider seven (7) situations:

(1)     (2)  (3)             (4)
\       /   \           /   \           /
__\_____/_____\_________/_____\_________/______ Upper Limit
  \   /       \       /       \       /
  /   \        \-->--/         \--<--/     /-----\
v     ^                                  /       \(7)
\      \                                 \       /
  \      \      /--<--\      /-->--\       \-----/
____\______\____/_______\____/_______\_________ Lower Limit
  \      \  /         \  /         \
          (5)          (6)

We know that following "next" pointers around an outline keeps the black area on the LEFT. We only need be concerned with situations 1,2,3,5 and 7. 4 and 6 can be ignored as they represent small incursions into a large black region which will be recorded elsewhere. Situations 3 and 5 define enclosed areas bounded by the upper and lower limits respectively. Situation 1 is open to the right, awaiting a closure by a situation 2 which is open to the right. Situation 7 is entirely enclosed within the band.

The situations are refered to as region types and are determined by find_region_type.

An empty region type is used to denote entry to an adjacent band and return to the original band at the same x location.

See blkocc.cpp

Todo:

None of the functions in blkocc.cpp seem to be called during standard processing of an image - are they only for development?

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