[Insight-users] Incremental Updates

[Ron Inbar]

Hi Luis,

> Could you describe more details about the filter you
> have in mind?

Yes.  I was thinking about using a frame-grabber to incrementally build a
volume from acquired video frames, and I'd like to see the results of the
segmentation on the fly.  To be more specific, I want to segment
intra-vascular ultrasound (IVUS) images of a coronary artery.

I saw that VTK has a class called vtkVideoSource (with several
hardware-specific subclasses) that is supposed to do just that, but I didn't
exactly understand how it fits into the pipeline framework.

> I'm assuming that by 'adding' you mean something
> like concatenating image regions, not cumulating
> values in the same initialy defined image region.

Yes, exactly.

> This can be done at the application level by using
> events and observers, but cannot be done using the
> current built-in pipeline mechanisms.

I'm aware of that, and I don't see any particular problem with implementing
it at the application level.

What I'm concerned about is efficiency: I don't want to process the existing
data over and over again as new data are concatenated to the region;
instead, I would like each filter to use the data in its current
BufferedRegion as it computes the new, larger output.  The problem with this
requirement, as far as I see, is that generally when a filter is asked to
update its output it has no knowledge about the nature of the change in its
input; it can't tell, for example, whether it was re-wired to a new source
altogether, or whether new data were simply concatenated to the existing
data, as is the case in my application.  That's why I said I'm willing to
write my own filters: I could make these filters take a "hint" from the
application programmer, telling them that the input was just extended.  If
they don't receive this hint, they would just re-compute everything from
scratch, but if they do, they will try to avoid redundant re-computation.

If you can think of a way to achieve the same effect using existing ITK
components, it would be of great assistance.

Sincerely,

Ron


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