matplotlib · dstansby · Jul 26, 2023 · Jul 21, 2023 · Jul 26, 2023 · Jul 26, 2023
diff --git a/docs/changelog.rst b/docs/changelog.rst
@@ -1,5 +1,16 @@
 Changelog
 =========
+1.0.2
+-----
+Bug fixes
+~~~~~~~~~
+- A full dataset is no longer read into memory when using ``HistogramWidget``.
+  Only the current slice is loaded.
+
+Changes
+~~~~~~~
+- Histogram bin limits are now caclualted from the slice being histogrammed, and
+  not the whole dataset. This is as a result of the above bug fix.

 1.0.1
 -----

diff --git a/src/napari_matplotlib/histogram.py b/src/napari_matplotlib/histogram.py
@@ -33,14 +33,19 @@ def draw(self) -> None:
        Clear the axes and histogram the currently selected layer/slice.
        """
        layer = self.layers[0]
-        bins = np.linspace(np.min(layer.data), np.max(layer.data), 100)

        if layer.data.ndim - layer.rgb == 3:
            # 3D data, can be single channel or RGB
            data = layer.data[self.current_z]
            self.axes.set_title(f"z={self.current_z}")
        else:
            data = layer.data
+        # Read data into memory if it's a dask array
+        data = np.asarray(data)
+
+        # Important to calculate bins after slicing 3D data, to avoid reading
+        # whole cube into memory.
+        bins = np.linspace(np.min(data), np.max(data), 100)

        if layer.rgb:
            # Histogram RGB channels independently