By default, don't change the figure face/edgecolor on savefig().

anntzer · anntzer · commit 57462b6477e7 · 2020-05-04T12:35:31.000+02:00
This seems to repeatedly confuse users.
diff --git a/doc/api/api_changes_3.3/behaviour.rst b/doc/api/api_changes_3.3/behaviour.rst
@@ -234,3 +234,10 @@ This also means there is a new keyword argument for `.axes.Axes.get_tightbbox`:
 bounding box using the rules above.  `.axis.Axis.get_tightbbox` gets an
 ``ignore_label`` keyword argument, which is *None* by default, but which can
 also be 'x' or 'y'. 
+
+:rc:`savefig.facecolor` and :rc:`savefig.edgecolor` now default to "auto"
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This newly allowed value for :rc:`savefig.facecolor` and :rc:`savefig.edgecolor`,
+as well as the *facecolor* and *edgecolor* parameters to `.Figure.savefig`, means
+"use whatever facecolor and edgecolor the figure current has".
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2008,11 +2008,13 @@ def print_figure(
         dpi : float, default: :rc:`savefig.dpi`
             The dots per inch to save the figure in.
 
-        facecolor : color, default: :rc:`savefig.facecolor`
-            The facecolor of the figure.
+        facecolor : color or 'auto', default: :rc:`savefig.facecolor`
+            The facecolor of the figure.  If 'auto', use the current figure
+            facecolor.
 
-        edgecolor : color, default: :rc:`savefig.edgecolor`
-            The edgecolor of the figure.
+        edgecolor : color or 'auto', default: :rc:`savefig.edgecolor`
+            The edgecolor of the figure.  If 'auto', use the current figure
+            edgecolor.
 
         orientation : {'landscape', 'portrait'}, default: 'portrait'
             Only currently applies to PostScript printing.
@@ -2068,21 +2070,23 @@ def print_figure(
         # but this should be fine.
         with cbook._setattr_cm(self, _is_saving=True, manager=None), \
                 cbook._setattr_cm(self.figure, dpi=dpi):
+            origfacecolor = self.figure.get_facecolor()
+            origedgecolor = self.figure.get_edgecolor()
 
             if facecolor is None:
                 facecolor = rcParams['savefig.facecolor']
+            if cbook._str_equal(facecolor, 'auto'):
+                facecolor = origfacecolor
             if edgecolor is None:
                 edgecolor = rcParams['savefig.edgecolor']
-
-            origfacecolor = self.figure.get_facecolor()
-            origedgecolor = self.figure.get_edgecolor()
+            if cbook._str_equal(edgecolor, 'auto'):
+                edgecolor = origedgecolor
 
             self.figure.set_facecolor(facecolor)
             self.figure.set_edgecolor(edgecolor)
 
             if bbox_inches is None:
                 bbox_inches = rcParams['savefig.bbox']
-
             if bbox_inches:
                 if bbox_inches == "tight":
                     renderer = _get_renderer(
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -2097,11 +2097,13 @@ def savefig(self, fname, *, transparent=None, **kwargs):
 
             This parameter is deprecated.
 
-        facecolor : color, default: :rc:`savefig.facecolor`
-            The facecolor of the figure.
+        facecolor : color or 'auto', default: :rc:`savefig.facecolor`
+            The facecolor of the figure.  If 'auto', use the current figure
+            facecolor.
 
-        edgecolor : color, default: :rc:`savefig.edgecolor`
-            The edgecolor of the figure.
+        edgecolor : color or 'auto', default: :rc:`savefig.edgecolor`
+            The edgecolor of the figure.  If 'auto', use the current figure
+            edgecolor.
 
         orientation : {'landscape', 'portrait'}
             Currently only supported by the postscript backend.
@@ -2172,9 +2174,6 @@ def savefig(self, fname, *, transparent=None, **kwargs):
                                              patch.get_edgecolor()))
                 patch.set_facecolor('none')
                 patch.set_edgecolor('none')
-        else:
-            kwargs.setdefault('facecolor', mpl.rcParams['savefig.facecolor'])
-            kwargs.setdefault('edgecolor', mpl.rcParams['savefig.edgecolor'])
 
         self.canvas.print_figure(fname, **kwargs)
 
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -1529,9 +1529,10 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
             pil_kwargs["pnginfo"] = pnginfo
         if format in ["jpg", "jpeg"]:
             format = "jpeg"  # Pillow doesn't recognize "jpg".
-            color = tuple(
-                int(x * 255)
-                for x in mcolors.to_rgb(mpl.rcParams["savefig.facecolor"]))
+            facecolor = mpl.rcParams["savefig.facecolor"]
+            if cbook._str_equal(facecolor, "auto"):
+                facecolor = mpl.rcParams["figure.facecolor"]
+            color = tuple(int(x * 255) for x in mcolors.to_rgb(facecolor))
             background = PIL.Image.new("RGB", pil_shape, color)
             background.paste(image, image)
             image = background
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -324,13 +324,13 @@ def validator(s):
 
 def validate_color_or_inherit(s):
     """Return a valid color arg."""
-    if s == 'inherit':
+    if cbook._str_equal(s, 'inherit'):
         return s
     return validate_color(s)
 
 
 def validate_color_or_auto(s):
-    if s == 'auto':
+    if cbook._str_equal(s, 'auto'):
         return s
     return validate_color(s)
 
@@ -1411,8 +1411,8 @@ def _convert_validator_spec(key, conv):
 
     ## Saving figure's properties
     'savefig.dpi':         ['figure', validate_dpi],  # DPI
-    'savefig.facecolor':   ['white', validate_color],
-    'savefig.edgecolor':   ['white', validate_color],
+    'savefig.facecolor':   ['auto', validate_color_or_auto],
+    'savefig.edgecolor':   ['auto', validate_color_or_auto],
     'savefig.orientation': ['portrait', ['landscape', 'portrait']],
     'savefig.jpeg_quality': [95, validate_int],
     # value checked by backend at runtime
diff --git a/matplotlibrc.template b/matplotlibrc.template
@@ -641,8 +641,8 @@
 ## e.g., you may want a higher resolution, or to make the figure
 ## background white
 #savefig.dpi:       figure      # figure dots per inch or 'figure'
-#savefig.facecolor: white       # figure facecolor when saving
-#savefig.edgecolor: white       # figure edgecolor when saving
+#savefig.facecolor: auto        # figure facecolor when saving
+#savefig.edgecolor: auto        # figure edgecolor when saving
 #savefig.format:    png         # {png, ps, pdf, svg}
 #savefig.bbox:      standard    # {tight, standard}
                                 # 'tight' is incompatible with pipe-based animation
