Update cached log data in ImageItem.set_data()

plotpy/items/image/base.py

@@ -340,6 +340,15 @@ def get_r_values(self, i0, i1, j0, j1, flag_circle=False):
         """
         return self.get_x_values(i0, i1)
 
+    def _recompute_log_data(self) -> None:
+        """Refresh the cached log10 data from the current ``self.data``.
+
+        Used both when toggling the Z-axis log scale on and when the underlying
+        data is replaced (e.g. via :meth:`set_data`) while the log scale is
+        already active.
+        """
+        self._log_data = np.array(np.log10(self.data.clip(1)), dtype=np.float64)
+
     def set_data(
         self, data: np.ndarray, lut_range: tuple[float, float] | None = None
     ) -> None:
@@ -353,9 +362,15 @@ def set_data(
         self.histogram_cache = None
         self.update_bounds()
         self.update_border()
+        # Refresh the cached log10 data when log scale is active, otherwise the
+        # display would keep using the previous (now stale) log data.
+        if self.get_zaxis_log_state():
+            self._recompute_log_data()
         if not self.param.keep_lut_range:
             if lut_range is not None:
                 _min, _max = lut_range
+            elif self.get_zaxis_log_state():
+                _min, _max = get_nan_range(self._log_data)
             else:
                 _min, _max = get_nan_range(data)
             self.set_lut_range((_min, _max))
@@ -574,7 +589,7 @@ def set_zaxis_log_state(self, state: bool) -> None:
         if state:
             self._lin_lut_range = self.get_lut_range()
             if self._log_data is None:
-                self._log_data = np.array(np.log10(self.data.clip(1)), dtype=np.float64)
+                self._recompute_log_data()
             self.set_lut_range(get_nan_range(self._log_data))
             dtype = self._log_data.dtype
         else:

plotpy/tests/unit/test_image_log_set_data.py

@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -*-
+#
+# Licensed under the terms of the BSD 3-Clause
+# (see plotpy/LICENSE for details)
+
+"""Regression tests for cached log10 data refresh in ``ImageItem.set_data``.
+
+When the Z-axis is in logarithmic scale, ``ImageItem`` keeps a cached
+``_log_data`` array. Prior to the fix, calling ``set_data`` did not refresh
+that cache, so the displayed image kept reflecting the previous values until
+the user toggled the log scale off and on again.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+from guidata.qthelpers import qt_app_context
+
+from plotpy.builder import make
+
+
+def _make_item(data: np.ndarray):
+    """Return an ``ImageItem`` ready for log-scale tests."""
+    return make.image(data, interpolation="nearest")
+
+
+def test_set_data_refreshes_log_data_when_log_scale_enabled() -> None:
+    """``set_data`` must recompute ``_log_data`` when log scale is active."""
+    with qt_app_context(exec_loop=False):
+        first = np.array([[1.0, 10.0], [100.0, 1000.0]])
+        item = _make_item(first)
+        item.set_zaxis_log_state(True)
+        np.testing.assert_array_almost_equal(item._log_data, np.log10(first.clip(1)))
+
+        second = np.array([[10.0, 100.0], [1000.0, 10000.0]])
+        item.set_data(second)
+
+        # The cache must reflect the new data, not the previous one.
+        np.testing.assert_array_almost_equal(item._log_data, np.log10(second.clip(1)))
+        # And the LUT range must be derived from the refreshed log data.
+        lut_min, lut_max = item.get_lut_range()
+        assert lut_min == np.log10(second.clip(1)).min()
+        assert lut_max == np.log10(second.clip(1)).max()
+
+
+def test_set_data_keeps_lut_range_in_log_mode() -> None:
+    """``keep_lut_range`` must be honored even when log scale is active."""
+    with qt_app_context(exec_loop=False):
+        first = np.array([[1.0, 10.0], [100.0, 1000.0]])
+        item = _make_item(first)
+        item.set_zaxis_log_state(True)
+        item.set_lut_range((0.5, 2.5))
+        item.param.keep_lut_range = True
+
+        second = np.array([[10.0, 100.0], [1000.0, 10000.0]])
+        item.set_data(second)
+
+        # Cache must still be refreshed (display correctness)…
+        np.testing.assert_array_almost_equal(item._log_data, np.log10(second.clip(1)))
+        # …but the LUT range must remain frozen as requested by the user.
+        assert item.get_lut_range() == (0.5, 2.5)
+
+
+def test_set_data_does_not_create_log_data_when_log_scale_disabled() -> None:
+    """When log scale is off, ``set_data`` must not create ``_log_data``."""
+    with qt_app_context(exec_loop=False):
+        item = _make_item(np.array([[1.0, 2.0], [3.0, 4.0]]))
+        assert item._log_data is None
+        item.set_data(np.array([[5.0, 6.0], [7.0, 8.0]]))
+        assert item._log_data is None