Add viewer and label extraction tool for COSEM

[igorpisarev]

• Simple viewer for COSEM predictions.
• Label extraction tool activated by SPACE that saves thresholded & interpolated labels in the selected region of interest into Paintera-compatible format (for simplicity and efficiency, it's currently a single-scale dataset of primitive type uint64).

The label extraction dialog allows to select the size of the crop, threshold and scaling values, and what classes it is needed to export and where to save them. By default the position of the mouse cursor at the time of pressing SPACE is the center point of the region of interest.

The ViewCosem tool can be opened with:

n5-view-cosem \
  -i <path to n5 container with cosem predictions> \
  -r <path to raw data, can be either a multiscale group or a single dataset>

After the labels have been extracted, they can be opened as a Paintera project with the following command:

paintera \
  --add-n5-container=<path to n5 container with raw data> -d=/volumes/raw \
  --add-n5-container=<path to n5 container with extracted labels> --entire-container

@axtimwalde @neptunes5thmoon @d-v-b

[igorpisarev]

Added unique IDs for the prediction classes (according to the spreadsheet), so now Paintera would assign different colors to extracted label sources.