fix: Lock contrast after first FOV during live acquisition

ndviewer_light/core.py

@@ -1484,6 +1484,7 @@ def __init__(self, dataset_path: str = ""):
         self._plane_cache = MemoryBoundedLRUCache(PLANE_CACHE_MAX_MEMORY_BYTES)
         self._updating_sliders: bool = False  # Prevent recursive updates
         self._acquisition_active: bool = False  # True during live acquisition
+        self._auto_contrast_done: bool = False  # Lock contrast after first FOV
         self._time_play_timer: Optional[QTimer] = None  # Timer for T slider animation
         self._fov_play_timer: Optional[QTimer] = None  # Timer for FOV slider animation
         self._load_debounce_timer: Optional[QTimer] = (
@@ -1781,6 +1782,7 @@ def start_acquisition(
         self._current_time_idx = 0
         self._max_time_idx = 0
         self._acquisition_active = True
+        self._auto_contrast_done = False
 
         # Update sliders
         self._updating_sliders = True
@@ -2187,6 +2189,41 @@ def _update_ndv_data(self, data):
             # Fallback: full rebuild (shouldn't happen often)
             self._set_ndv_data(xarr)
 
+        # After the first FOV is displayed, schedule locking contrast limits
+        # so subsequent FOVs don't re-autoscale.
+        if not self._auto_contrast_done:
+            self._auto_contrast_done = True  # Prevent redundant scheduling
+            QTimer.singleShot(500, self._lock_contrast_limits)
+
+    def _lock_contrast_limits(self, _retries: int = 3):
+        """Lock current contrast limits so subsequent FOVs don't re-autoscale.
+
+        Reads the auto-computed clims from each channel and switches them
+        to manual mode with the same values.  Retries if clims aren't
+        computed yet (data may still be loading).
+        """
+        if not self.ndv_viewer:
+            return
+        try:
+            from ndv.models._lut_model import ClimsManual
+
+            display = self.ndv_viewer._data_model.display
+            all_locked = True
+            for key, lut_model in display.luts.items():
+                cached = lut_model.clims.cached_clims
+                if cached is not None:
+                    lut_model.clims = ClimsManual(min=cached[0], max=cached[1])
+                else:
+                    all_locked = False
+            if all_locked:
+                logger.info("Contrast limits locked after first FOV")
+            elif _retries > 0:
+                QTimer.singleShot(500, lambda: self._lock_contrast_limits(_retries - 1))
+            else:
+                logger.warning("Could not lock contrast limits: clims not yet computed")
+        except (ImportError, AttributeError) as e:
+            logger.warning("Could not lock contrast limits: %s", e)
+
     def end_acquisition(self):
         """Mark acquisition as ended.