refactor nodes into standalone file

backend/nodes/threshold_mask.py

@@ -0,0 +1,61 @@
+from __future__ import annotations
+import numpy as np
+from backend.node_registry import register_node
+from backend.data_types import DataField, encode_preview
+from backend.nodes.helpers import _mask_overlay
+
+
+@register_node(display_name="Threshold Mask")
+class ThresholdMask:
+    _CUSTOM_PREVIEW = True
+
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+                "method": (["otsu", "absolute", "relative"],),
+                "threshold": ("FLOAT", {"default": 0.0, "min": -1e9, "max": 1e9, "step": 0.001}),
+                "direction": (["above", "below"],),
+            }
+        }
+
+    RETURN_TYPES = ("IMAGE",)
+    RETURN_NAMES = ("mask",)
+    FUNCTION = "process"
+
+    DESCRIPTION = (
+        "Create a binary mask by thresholding data. "
+        "Otsu automatically finds the optimal threshold. "
+        "Equivalent to Gwyddion's threshold and otsu_threshold modules."
+    )
+
+    _broadcast_fn = None
+    _current_node_id: str = ""
+
+    def process(self, field: DataField, method: str, threshold: float, direction: str) -> tuple:
+        data = field.data
+
+        if method == "otsu":
+            from skimage.filters import threshold_otsu
+            t = threshold_otsu(data)
+        elif method == "absolute":
+            t = float(threshold)
+        elif method == "relative":
+            dmin, dmax = data.min(), data.max()
+            t = dmin + float(threshold) * (dmax - dmin)
+        else:
+            raise ValueError(f"Unknown threshold method: {method}")
+
+        if direction == "above":
+            mask = (data >= t).astype(np.uint8) * 255
+        else:
+            mask = (data < t).astype(np.uint8) * 255
+
+        if ThresholdMask._broadcast_fn is not None:
+            overlay = _mask_overlay(field, mask)
+            ThresholdMask._broadcast_fn(
+                ThresholdMask._current_node_id, encode_preview(overlay),
+            )
+
+        return (mask,)