[Insight-users] Neighborhood Connected region growth algorithm description on ITK software guide

[Luis Ibanez]

Hi Quan,

Thanks for your detailed comments.


It seems that you are right, the effect of the NeighborhoodConnected
region growth algorithm is equivalent to a ConnectedThreshold followed
by only Erosion using a structuring element equal to the neighborhood
used in the region growth.

We will fix this comment on the Software Guide.



    Regards


       Luis



------------------
Quan Chen wrote:

> I believe that there is something wrong with the explanation of 
> Neighborhood Connected region growth algorithm (ITK Software Guide, Aug. 
> 21, 2003, page 319). 
>  
> The explanation says first "The NeighborhoodConnectedImageFilter, on the 
> other hand, will only accept a pixel if *all *its neighbors have 
> intensities that fit in the interval."
>  
> Then it claim "This filter is more resistant to the presence of noise in 
> the input image and may not require any initial filtering to smooth the 
> image."
>  
> 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.
>  
> Also, the manual said " The reason for considering the neighborhood 
> intensities instead of only the current pixel intensity is that isolated 
> pixels are less likely to be accepted in the region. This can be seen as 
> a preemptive mathematical morphology operation that is similar to using 
> the ConnectedThresholdImageFilter and then applying a combination of 
> erosion and dilation with a structuring element of the same radius used 
> for the neighborhood provided to the NeighborhoodConnected-ImageFilter."
>  
> 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.
>  
> So I believe either the explanation of the algorithm is incorrect, or 
> the implementation of the algorithm is incorrect.
> 
> 
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