(minor) Simplify GroundedSAMInvocation._merge_masks(...).

Author: RyanJDick

invokeai/app/invocations/grounded_sam.py

@@ -74,7 +74,8 @@ def invoke(self, context: InvocationContext) -> ImageOutput:
 
             detections = self._filter_detections(detections)
             masks = [detection.mask for detection in detections]
-            combined_mask = self._merge_masks(masks)
+            # masks contains binary values of 0 or 1, so we merge them via max-reduce.
+            combined_mask = np.maximum.reduce(masks)
 
         # Map [0, 1] to [0, 255].
         mask_np = combined_mask * 255
@@ -188,10 +189,3 @@ def _filter_detections(self, detections: list[DetectionResult]) -> list[Detectio
             return [max(detections, key=lambda x: x.score)]
         else:
             raise ValueError(f"Invalid mask filter: {self.mask_filter}")
-
-    def _merge_masks(self, masks: list[npt.NDArray[np.uint8]]) -> npt.NDArray[np.uint8]:
-        """Merge multiple masks into a single mask."""
-        # Merge all masks together.
-        stacked_mask = np.stack(masks, axis=0)
-        combined_mask = np.max(stacked_mask, axis=0)
-        return combined_mask