[ITK-users] Region of two labelObjects

[Gaetan Lehmann]

Hi Pol,

2015-03-30 23:02 GMT+02:00 Pol Monsó Purtí <lluna.nova at gmail.com>:

>
> Hello all,
>
> I have two label objects, how can I merge the two BoundingBoxes together
> so I know the necessary size of the image? (other than creating it myself
> by searching max/min of each dimension)
>
> How come LabelMap doesn't resize automatically when objects are added? It
> could.
>

The LabelMap class was designed to work as much as possible as the Image
class, that does not have this kind of behavior, and to avoid as much as
possible the costly operations.

So while I don't think this should be done automatically, we should have
some methods or filters to make this easy to do.

There are a few filters to manipulate the regions of a LabelMap, but none
of them does exactly what you need:

* PadLabelMapFilter that can enlarge the LabelMap region, but not based on
its content
* CropLabelMapFilter that can shrink the LabelMap region, but not based on
its content
* RegionFromReferenceLabelMapFilter that makes the LabelMap region match
the region of a reference input image
* AutoCropLabelMapFilter that reduce the region covered by a label map
based on its content, but can't enlarge it

In my opinion, we should have a ComputeBoundingBox() method in LabelMap
that compute the region covered by all the label objects - the code can be
moved from AutoCropLabelMapFilter. We could then do

  labelMap->AddLabelObject(labelObject1);
  labelMap->AddLabelObject(labelObject2);
  labelMap->SetRegions(labelMap->ComputeBoundingBox());

to update the region.

Would you agree to implement such a method for the LabelMap class?

Optionally, we could also think to a filter to do that in a pipeline.

Regards,

Gaëtan
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