[Insight-users] Sparse vs Dense ChanAndVeseLevelSetImageFilter

[Sgouritsa, Eleni]

Hello Kishore,

I have some questions on the sparse and dense chan&vese level set filters.

1. I would expect getting the same segmentation result for a given volume using sparse and dense filters with the same parameters. However the result using the sparse filter is "bigger" (the level set evolved more) and non-smooth compared with the one using the dense. Is this acceptable?

2. Debugging the sparse filter code in the place where is the CalculateUpdateValue function, we compute for the level set update:
ValueType new_value = old_value + dt * change;
In this place the old value is always 0 in the first iteration and 1e-06 in the next iterations. Is this correct? I would expect as old_values positive and negative values near zero depending on the distance from the zero level set.
I tried increasing the number of layers used in the narrow band, but it is still the same.

3. Could it be possible in the future to have this function 
virtual ValueType CalculateUpdateValue (const IndexType &, const TimeStepType &dt, const ValueType &value, const ValueType &change)
in the protected members of the dense filter as it is in the sparse right now?
( Currently, for the dense filter this calculation is embedded in the ApplyUpdate function )

Thank you very much,
Eleni
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