Image export: allow adding scalebar when scale are almost equal (1E-1…

…0 relative difference)

rsciio/image/_api.py

@@ -17,6 +17,7 @@
 # along with RosettaSciIO. If not, see <https://www.gnu.org/licenses/#GPL>.
 
 import logging
+import math
 import os
 from collections.abc import Iterable
 
@@ -167,10 +168,15 @@ def file_writer(
         # Sanity check of the axes
         # This plugin doesn't support non-uniform axes, we don't need to check
         # if the axes have a scale attribute
-        if axes[0]["scale"] != axes[1]["scale"] or axes[0]["units"] != axes[1]["units"]:
+        # Use 1E-10 precision to avoid error when scale are almost equal
+        if (
+            not math.isclose(axes[0]["scale"], axes[1]["scale"], rel_tol=1e-10)
+            or axes[0]["units"] != axes[1]["units"]
+        ):
             raise ValueError(
-                "Scale and units must be the same for each axes "
-                "to export images with a scale bar."
+                f"Scale ({axes[0]["scale"]} and {axes[1]["scale"]}) and "
+                f"units ({axes[0]["units"]} and {axes[1]["units"]}) must "
+                "be the same for each axes to export images with a scale bar."
             )
 
     if scalebar or output_size:

rsciio/tests/test_image.py

@@ -174,14 +174,31 @@ def test_export_scalebar_different_scale_units(tmp_path):
     s = hs.signals.Signal2D(np.arange(pixels**2).reshape((pixels, pixels)))
     s.axes_manager[0].scale = 2
 
-    filename = tmp_path / "test_export_size.jpg"
+    filename = tmp_path / "test_export_different_scale.jpg"
     with pytest.raises(ValueError):
         s.save(filename, scalebar=True)
 
     s = hs.signals.Signal2D(np.arange(pixels**2).reshape((pixels, pixels)))
     s.axes_manager[0].units = "nm"
 
-    filename = tmp_path / "test_export_size.jpg"
+    filename = tmp_path / "test_export_different_units.jpg"
+    with pytest.raises(ValueError):
+        s.save(filename, scalebar=True)
+
+
+def test_export_scalebar_different_scale_precision(tmp_path):
+    hs = pytest.importorskip("hyperspy.api", reason="hyperspy not installed")
+    pixels = 16
+    s = hs.signals.Signal2D(np.arange(pixels**2).reshape((pixels, pixels)))
+    s.axes_manager[0].scale = 1.9999999999
+    s.axes_manager[1].scale = 2.0
+    filename = tmp_path / "test_export_scale_1e-11_difference.jpg"
+    # pass with 1E-11 relative difference
+    s.save(filename, scalebar=True)
+
+    filename = tmp_path / "test_export_scale_1e-10_difference.jpg"
+    s.axes_manager[0].scale = 1.999999999
+    # fails with 1E-10 relative difference
     with pytest.raises(ValueError):
         s.save(filename, scalebar=True)