[Insight-users] LabelMap related issues

[cagatay bilgin]

I've been using LabelMap related filters and had a
few issues with them. These issues could stem from my
lack of knowledge about the design of these filters but I thought
it is good to have them on the list so that someone else could benefit
from or maybe some sort of cleanup can be performed on them.

1) LabelObject::SetLabel method has no
effect as the labels are stored in the LabelMap. If one
wants to change the labels, they need to go through the
ChangeLabelMapFilter or RelabelLabelMapFilter.

This function is just confusing as you can not properly
change the label, but it gives you the impression
that the label is changed. Either LabelObject::SetLabel
should do the expected behavior and change the label,
or this method should be dropped or renamed or return
something to warn you.

2) Assuming that I have a labelobject that I created somehow...
When I want to add this labelobject to a labelmap, there
are two functions available.
LabelMap::AddLabelObject
LabelMap::PushLabelObject

PushLabelObject searches for an unused label(largest label+1),
whereas AddLabelObject does not. If the label of the object at
hand clashes with another one in the labelmap, AddLabelObject
does not warn you, and just overwrites whatever was there.
PushLabelObject on the other hand looks for an unused label,
and changes the label of the object with whatever is available.

It is nice to have these two different options but these should be
explicitly stated somewhere. I would also suggest to propagate
the return value (pair<iter,bool>) of the STL map's insert, instead
of having just void.

3) All the features are accessed by GetProperty methods,
e.g. GetBoundingBox, GetPhysicalSize etc except
the size. It took me a while to realize that the function
was not GetSize but just Size. I would expect to have
GetSize instead of Size.

4) There are multiple ways of converting the label map
to an image but as far as I can see no direct support of
converting "a" label object to its corresponding image

i) I need to create a new empty label map,
ii) call copyInformation or SetRegions with the
bounding box of the object depending on the
type of image I am interested
iii) add the labelobject to the labelmap
iv) and then use labelmaptolabelimage filter.

I guess a GetImage function could be provided.

5) If for some reason, possibly due to a not well thought design of mine,
I call BinaryImagetoShapeLabelMap with int type,
the InputforegroundValue is set to -1 and
the OutputBackgroundValue is set to 0 by the filter by default.
I would expect the default InputForegroundValue to be
+max int or 1 or 255, but not -1.

6) In BinaryImagetoShapeLabelMap
there is SetInputForegroundValue to modify the foreground but
there is no SetInputBackgroundValue. Likewise, SetOutputBackgroundValue
exists, but SetOutputForegroundValue does not exists.
I would expect the missing functions to be available unless
there is good reason to not to.

7) The return type for RemoveLabel, RemoveLabelObject in
LabelMap class are void. STL map tells how many
objects are removed with the corresponding function prototype.
This information can be provided to the caller.

Kind Regards,
Cagatay
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