Segmentation exported to model file and imported does not preserve transparency

[lassoan (Andras Lasso)]

I think this post will answer this question:

How can I export a brain tumor 3d model with brains opacity?

OBJ is an export format for segmentation (for exchanging data with other software), not a saving format (for saving data to be reloaded later). If you want to save the segmentation to disk without losing any information then save it as a .seg.nrrd (if labelmap is the master representation) or .seg.vtm (if closed surface is the master representation). Slicer’s OBJ reader only reads the .obj file (mesh geometry and material IDs) and not the .mat file (that contains the colors and opacities).