Region is a set of pixels such that its subset of interior pixels 
is non-empty. A full region has more than four pixels, its contour 
is a simple path, and its interior pixel subset is d-connected. 
PIXEL CONNECTIVITY MAP 
Many picture processing algorithms depend on locally searching the 
image by means of a 3 x 3 neighborhood of pixels. Significant 
processing efficiency can be achieved by means of a data structure 
that we call a pixel connectivity map. The notion of encoding a 
3x3 neighborhood of a pixel in a compact 8-bit code was introduced 
by Sobel (1978). The motivation for its use was to alleviate the 
computational burden of accessing the neighbors of pixels. It 
reduces the problem of accessing and testing the eight neighbors of 
a pixel by accessing a single byte. Sobel proposed that a simple 
hardware encoder be utilized to assemble the pixel connectivity map 
in one pass through the bilevel image array. The map consists of an 
8-bit field in which each bit corresponds to the neighbor numbering 
convention presented in definition "Neighbor". For example, the 
neighborhood of pixel P is represented as: 
B7 
B6 
B5 B4 
B3 
B2 
B1 
BO 
0 
0 
1 
0 
1 
1 
0 
1 
PIXEL CONNECTIVITY MAP FOR PIXEL P 
The pixel connectivity map for a segmented and labeled image may be 
achieved in a single scan through the data. 
By interrogating the pixel connectivity map via bit mask templates, 
it is possible to determine many necessary characteristics of a 
connected component including: contour pixels, interior pixels, 
component endpoints, local minima and maxima points, and component 
junctions. Knowing these characteristics can enhance many raster 
manipulation algorithms. Before illustrating these enhancements, let 
us briefly examine how these characteristics can be determined. 
PROPERTIES OF THE PIXEL CONNECTIVITY MAP 
Since the 
component 
of pixels 
operation 
a contour 
member of 
pixel may 
4, and 6). 
subsets of contour pixels and interior pixels of a connected 
are mutually exclusive, it is possible to categorize the set 
for a connected component by applying a simple logical 
on the set's pixel connectivity map array. For example, 
pixel possesses at least one d-neighbor that is not a 
the property set. The pixel connectivity map for a contour 
be tested for at least one d-bit being equal to 0 (Bits 0, 2,