Remove algorithm identification from background class

src/highdicom/seg/sop.py

@@ -1444,6 +1444,15 @@ def _add_segment_descriptions(
             # descriptions having a positive value can remain in place.
             bg_description.SegmentNumber = 0
 
+            # Remove the algorithm identification sequence, since it is not
+            # actually required (highdicom is stricter than the standard here)
+            # and doesn't make sense for a background class
+            if bg_algo_id is not None:
+                delattr(
+                    bg_description,
+                    'SegmentationAlgorithmIdentificationSequence'
+                )
+
             self.SegmentSequence = [
                 bg_description,
                 *segment_descriptions

tests/test_seg.py

@@ -1724,6 +1724,19 @@ def test_construction_8(self):
         assert not hasattr(instance, 'ExtendedOffsetTable')
         assert not hasattr(instance, 'ExtendedOffsetTableLengths')
 
+        # Segment descriptions include background
+        assert (
+            len(instance.SegmentSequence) ==
+            len(self._segment_descriptions) + 1
+        )
+
+        # Background segment has no algorithm identification
+        bg_desc = instance.SegmentSequence[0]
+        assert not hasattr(
+            bg_desc,
+            'SegmentationAlgorithmIdentificationSequence'
+        )
+
     def test_construction_9(self):
         # A label with a palette color LUT
         instance = Segmentation(