diff --git a/probeflow/gui/dialogs/image_viewer_chrome_mixin.py b/probeflow/gui/dialogs/image_viewer_chrome_mixin.py
index e0398d1..e3df784 100644
--- a/probeflow/gui/dialogs/image_viewer_chrome_mixin.py
+++ b/probeflow/gui/dialogs/image_viewer_chrome_mixin.py
@@ -241,7 +241,7 @@ def _build_viewer_menu_bar(self) -> None:
         processing_menu.addSeparator()
         self._add_combo_menu(
             processing_menu, "Align rows", self._processing_panel._align_combo,
-            ["None", "Median", "Mean"],
+            ["None", "Median", "Mean", "Linear"],
         )
         self._add_combo_menu(
             processing_menu, "Bad line correction", self._processing_panel._bad_lines_combo,
diff --git a/probeflow/gui/processing.py b/probeflow/gui/processing.py
index b0f2d9a..9dbd438 100644
--- a/probeflow/gui/processing.py
+++ b/probeflow/gui/processing.py
@@ -129,10 +129,11 @@ def _col_lbl(text: str, target):
         line_lbl.setAlignment(Qt.AlignCenter)
         lay.addWidget(line_lbl)
 
-        self._align_combo = _combo_row("Align rows:", ["None", "Median", "Mean"])
+        self._align_combo = _combo_row("Align rows:", ["None", "Median", "Mean", "Linear"])
         self._align_combo.setToolTip(
             "Level each scan line by subtracting its median or mean, removing "
-            "row-to-row offsets and slow tilt along the slow-scan direction."
+            "row-to-row offsets and slow tilt along the slow-scan direction. "
+            "'Linear' also fits and removes a straight slope within each row."
         )
 
         self._bad_lines_combo = _combo_row(
@@ -340,7 +341,7 @@ def _col_lbl(text: str, target):
         lay.addWidget(self._filter_section)
 
     def state(self) -> dict:
-        align_map = {0: None, 1: "median", 2: "mean"}
+        align_map = {0: None, 1: "median", 2: "mean", 3: "linear"}
         bad_map = {0: None, 1: "step", 2: "mad"}
         cfg = {
             "align_rows": align_map[self._align_combo.currentIndex()],
@@ -382,7 +383,7 @@ def set_state(self, state: dict | None) -> None:
         state = state or {}
         old_block = self._align_combo.blockSignals(True)
         self._align_combo.setCurrentIndex(
-            {None: 0, "median": 1, "mean": 2}.get(state.get("align_rows"), 0))
+            {None: 0, "median": 1, "mean": 2, "linear": 3}.get(state.get("align_rows"), 0))
         self._align_combo.blockSignals(old_block)
         self._bad_lines_combo.setCurrentIndex(
             {None: 0, "step": 1, "step_segments": 1,
diff --git a/tests/test_gui_processing_panel.py b/tests/test_gui_processing_panel.py
index 8f446ae..91a92dd 100644
--- a/tests/test_gui_processing_panel.py
+++ b/tests/test_gui_processing_panel.py
@@ -145,6 +145,20 @@ def test_browse_quick_panel_emits_only_thumbnail_corrections(qapp):
     assert panel.state() == {"align_rows": "median", "remove_bad_lines": None}
 
 
+def test_align_rows_exposes_linear_option(qapp):
+    # The backend align_rows supports median/mean/linear; the GUI must offer all
+    # three so the documented 'linear' option is actually reachable.
+    from probeflow.gui import ProcessingControlPanel
+
+    panel = ProcessingControlPanel("viewer_full")
+    items = [panel._align_combo.itemText(i) for i in range(panel._align_combo.count())]
+    assert items == ["None", "Median", "Mean", "Linear"]
+
+    panel.set_state({"align_rows": "linear"})
+    assert panel._align_combo.currentIndex() == 3
+    assert panel.state()["align_rows"] == "linear"
+
+
 def test_viewer_full_panel_round_trips_standard_processing_state(qapp):
     from PySide6.QtWidgets import QCheckBox, QLabel, QPushButton
     from probeflow.gui import ProcessingControlPanel