[Insight-users] About Examples/Segmentation/FastMarchingImageFIlter.cxx

[Luis Ibanez]

Hi Diaoxianfen,

The output of the FastMarching image filter is a Time-Crossing map.

It tells you who long it took to the zero-set to get to each pixel.

Time is represented in artificial units in that time-crossing map.
Keep in mind that what LevelSet filters do is to compute the evolution
of a system dominated by Partial Differential Equations that are a
function of time. Time is simulated by incremental steps, and the
state of the system is updated iteratively. In this context, each
iteration corresponds to a discrete step in time.

When you analyze the output of the FastMarching level set image filter,
in order to see the extent of the zero-set at a given instant you must
select a time in that time-crossing map. That selection is done in the
SoftwareGuide example with a thresholding filter.


So, to answer you question: yes the timeThreshold parameter is both
things. It is a time-value in the time-crossing map, and it is an
intensity in the output image of the FastMarching filter... because
the output of this filter is the time-crossing map itself.



  Regards,



      Luis



---------------------
diaoxianfen wrote:

> In this exmaple,itk::BinaryThresholdImageFilter is used.I think this 
> class is used to cast the pixel value to 1 or 255.The method 
> SetLowerThreshold(...),SetUpperThreshold(...)are used to set the range 
> to distinguish the foreground from background.But there are
> sentence as follows:
> typedef itk::BinaryThresholdImageFilter< InternalImageType,
>                         OutputImageType    >    ThresholdingFilterType;
>   ThresholdingFilterType::Pointer thresholder = 
> ThresholdingFilterType::New();
>  
>   //const InternalPixelType  timeThreshold = TimeThreshold;
>   thresholder->SetLowerThreshold(0.0);
>   thresholder->SetUpperThreshold(timeThreshold)
>  
> In the ItkSoftwareGuide.pdf page 367/565,the sentence is as follows.
> The upper threshold passed to the BinaryThresholdImageFilter will define 
> the time snapshot that we are taking from the time-crossing map.
> Does the "timeThreshold" parameter have the time means?Or it should be a 
> value among the pixel value of the image?
> 
> 
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