Should be tackled as soon as T29206: [SEG] Implement a Qt model for LabelSets for MVC patterns is done.

I think the handling of multiple labels depends on each action and needs to be handled separately.

• Boolean Operations: I see a few options here
  • low effort: only allow for segmentations with one label. If there is more than one label, show a message that this is not possible
  • higher effort: completely rework the selection. Let the user select two specific labels (from the same or different segmentations) and work on these, either replacing the first label or adding a new label (or instance) to that segmentation
• Contour to Image & Surface to Image:
  • low effort: leave it as is, still works at the moment
  • higher effort: introduce the option to add the newly created segmentation as a new label / instance to an existing segmentation
• Image Masking:
  • low effort: leave it as is, still works at the moment (using all labels of a segmentation)
  • higher effort: introduce the option to select which labels/instances should be considered for masking
• Morphological Operations: Currently don't crash, but always use label 1
  • I think the most senseful solution would be to let the user select a specific label for the operation to work on. Multiple at the same time probably only get in each other's way and make it unnecessarily complicated.

Let's discuss how we want to approach each of these.

Discussion:

• Boolean Operations
  • chosen: high effort
  • Can be used so that the other functions can do everything
  • Work only on one image, select two labels
• Contour to Image & Surface to Image
  • chosen: low effort seems more senseful. The functionality can be achieved via other tools (e.g. boolean)
• Image Masking
  • chosen: low effort
• Morphological Operations
  • as proposed
  • Pick an image & pick a label
  • Include options like in picking tool, i.e. generate a new layer when doing an operation, lock labels (to make sure other labels are not overwritten e.g. for a dilution)
• Add a new tool: Transfer Label could be used to transfer a label from one image to another (if the same image is selected twice, it's just a rename)

For a lot of this, the operations have to be reworked to accomodate the new UI changes.