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<DIV><FONT face=Arial size=2><SPAN class=431515222-07012005>I believe that there
is something wrong with the explanation of Neighborhood Connected region growth
algorithm (ITK Software Guide, Aug. 21, 2003, page 319).
</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=431515222-07012005></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT face=Arial size=2>The
explanation says first "</FONT><FONT face=Arial><FONT size=2>The
NeighborhoodConnectedImageFilter, on the other hand, will only accept a pixel if
</FONT><B><FONT size=2>all </FONT></B><FONT size=2>its </FONT></FONT><FONT
size=2><FONT face=Arial>neighbors have intensities that fit in the
interval.<SPAN
class=431515222-07012005>"</SPAN></FONT></FONT></SPAN></FONT></DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=2><FONT
face=Arial><SPAN
class=431515222-07012005></SPAN></FONT></FONT></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT face=Arial size=2>Then it claim "</FONT><FONT
face=Arial size=2>This filter is more resistant to the presence of noise in the
input image and may not require any </FONT><FONT size=2><FONT face=Arial>initial
filtering to smooth the image.<SPAN
class=431515222-07012005>"</SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=2><FONT face=Arial><SPAN
class=431515222-07012005></SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=2><FONT face=Arial><SPAN
class=431515222-07012005>This is wrong. If there are a noise point which
the value exceed the pre-defined intensity interval, the old connected threshold
region growth algorithm only exclude that point from the region, whereas the
neighborhood connected region growth algorithm will exclude all points in the
neighbor of that noise point. Therefore, the noise will have a much bigger
impact on the neighborhood connected region growth algorithm than connected
threshold region growth method. For the connected threshold region growth
method, you could do a dilation and erosion at last stage to solve the noise
problem.</SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=2><FONT face=Arial><SPAN
class=431515222-07012005></SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=+0><SPAN class=431515222-07012005><FONT
face=Arial size=2>Also, the manual said " </FONT><FONT face=Arial size=2>The
reason for considering the neighborhood intensities instead of only the current
pixel intensity </FONT><FONT face=Arial size=2>is that isolated pixels are less
likely to be accepted in the region. This can be seen as a </FONT><FONT
face=Arial size=2>preemptive mathematical morphology operation that is similar
to using the ConnectedThresholdImageFilter </FONT><FONT face=Arial size=2>and
then applying a combination of erosion and dilation with a structuring element
</FONT><FONT face=Arial size=2>of the same radius used for the neighborhood
provided to the NeighborhoodConnected-</FONT><FONT size=2><FONT
face=Arial>ImageFilter.<SPAN
class=431515222-07012005>"</SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></SPAN></FONT></DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=+0><SPAN class=431515222-07012005><FONT
size=2><FONT face=Arial><SPAN
class=431515222-07012005></SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=+0><SPAN class=431515222-07012005><FONT
size=2><FONT face=Arial><SPAN class=431515222-07012005>This is also wrong, as my
last point, the noise in neighborhood connected region growth method will
affect all its neighbors, therefore, this method will similar to using
the ConnectedThresholdImageFilter and then applying ONLY the erosion operation
(and choose only the region connected to the seed). This is also evident
when you compare Fig. 9.1 to Fig.
9.2.</SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></SPAN></FONT></DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=+0><SPAN class=431515222-07012005><FONT
size=2><FONT face=Arial><SPAN
class=431515222-07012005></SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=431515222-07012005><FONT size=+0><SPAN
class=431515222-07012005><FONT size=+0><SPAN class=431515222-07012005><FONT
size=2><FONT face=Arial><SPAN class=431515222-07012005>So I believe either the
explanation of the algorithm is incorrect, or the implementation of the
algorithm is
incorrect.</SPAN></FONT></FONT></SPAN></FONT></SPAN></FONT></SPAN></FONT></DIV></FONT></DIV></BODY></HTML>