Segmentation ID Metadata

I think this is a somewhat fix for the Segmentation ID.
Without line 50 in post_processing "Null" gets passed through to the metadata.

The addition in utils just checks if the item has the attribute segmentation_id and adds it to the metadata info dictionary

kubric/post_processing.py

@@ -47,6 +47,7 @@ def adjust_segmentation_idxs(
       new_segmentation[segmentation == i] = asset.segmentation_id
     elif asset in new_assets_list:
       new_segmentation[segmentation == i] = new_assets_list.index(asset) + 1
+      asset.segmentation_id = i
     else:
       new_segmentation[segmentation == i] = ignored_label
   return new_segmentation

kubric/utils.py

@@ -163,6 +163,8 @@ def get_instance_info(scene, assets_subset=None):
     info = copy.copy(instance.metadata)
     if hasattr(instance, "asset_id"):
       info["asset_id"] = instance.asset_id
+    if hasattr(instance, "segmentation_id"):
+        info["segmentation_id"] = instance.segmentation_id
     info["positions"] = instance.get_values_over_time("position")
     info["quaternions"] = instance.get_values_over_time("quaternion")
     info["velocities"] = instance.get_values_over_time("velocity")