MNT: move creating interal ScalarMappable to where it is used

tacaswell · tacaswell · commit 80b7c57d65a1 · 2020-10-06T21:59:22.000-04:00
This make it clearer that we only need this in one of the code paths
and avoids creating the un-used ScalarMappable in the png savefig code
path.
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -1553,8 +1553,6 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
     else:
         # Don't bother creating an image; this avoids rounding errors on the
         # size when dividing and then multiplying by dpi.
-        sm = cm.ScalarMappable(cmap=cmap)
-        sm.set_clim(vmin, vmax)
         if origin is None:
             origin = mpl.rcParams["image.origin"]
         if origin == "lower":
@@ -1567,6 +1565,8 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
             # as is, saving a few operations.
             rgba = arr
         else:
+            sm = cm.ScalarMappable(cmap=cmap)
+            sm.set_clim(vmin, vmax)
             rgba = sm.to_rgba(arr, bytes=True)
         if pil_kwargs is None:
             pil_kwargs = {}
