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

anntzer · anntzer · commit ec90642badb4 · 2019-08-23T14:41:59.000+02:00
This seems to repeatedly confuse users.
diff --git a/doc/api/next_api_changes/2018-08-23-AL.rst b/doc/api/next_api_changes/2018-08-23-AL.rst
@@ -0,0 +1,6 @@
+: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
@@ -32,7 +32,7 @@
     The base class for the messaging area.
 """
 
-from contextlib import contextmanager
+from contextlib import contextmanager, ExitStack
 from enum import IntEnum
 import functools
 import importlib
@@ -2001,32 +2001,35 @@ def print_figure(self, filename, dpi=None, facecolor=None, edgecolor=None,
             can also be a file object on image backends
 
         orientation : {'landscape', 'portrait'}, optional
-            only currently applies to PostScript printing.
+            Only currently applies to PostScript printing.
 
         dpi : scalar, optional
-            the dots per inch to save the figure in; if None, use savefig.dpi
+            The dots per inch to save the figure in; if None, use
+            :rc:`savefig.dpi`.
 
-        facecolor : color or None, optional
-            the facecolor of the figure; if None, defaults to savefig.facecolor
+        facecolor : color or 'auto' or None, optional
+            The facecolor of the figure.  If 'auto', use the current figure
+            facecolor.  If None, use :rc:`savefig.facecolor`.
 
-        edgecolor : color or None, optional
-            the edgecolor of the figure; if None, defaults to savefig.edgecolor
+        edgecolor : color or 'auto' or None, optional
+            The edgecolor of the figure.  If 'auto', use the current figure
+            edgecolor.  If None, use :rc:`savefig.edgecolor`.
 
         format : str, optional
-            when set, forcibly set the file format to save to
+            When set, forcibly set the file format to save to.
 
         bbox_inches : str or `~matplotlib.transforms.Bbox`, optional
-            Bbox in inches. Only the given portion of the figure is
-            saved. If 'tight', try to figure out the tight bbox of
-            the figure. If None, use savefig.bbox
+            Bbox in inches. Only the given portion of the figure is saved. If
+            'tight', try to figure out the tight bbox of the figure. If None,
+            use :rc:`savefig.bbox`.
 
         pad_inches : scalar, optional
-            Amount of padding around the figure when bbox_inches is
-            'tight'. If None, use savefig.pad_inches
+            Amount of padding around the figure when bbox_inches is 'tight'. If
+            None, use :rc:`savefig.pad_inches`.
 
         bbox_extra_artists : list of `~matplotlib.artist.Artist`, optional
-            A list of extra artists that will be considered when the
-            tight bbox is calculated.
+            A list of extra artists that will be considered when the tight bbox
+            is calculated.
 
         """
         if format is None:
@@ -2050,27 +2053,29 @@ def print_figure(self, filename, dpi=None, facecolor=None, edgecolor=None,
         if dpi == 'figure':
             dpi = getattr(self.figure, '_original_dpi', self.figure.dpi)
 
-        # Remove the figure manager, if any, to avoid resizing the GUI widget.
-        # Some code (e.g. Figure.show) differentiates between having *no*
-        # manager and a *None* manager, which should be fixed at some point,
-        # but this should be fine.
-        with cbook._setattr_cm(self, _is_saving=True, manager=None), \
-                cbook._setattr_cm(self.figure, dpi=dpi):
-
+        with ExitStack() as stack:
+            # Remove the figure manager, if any, to avoid resizing the GUI
+            # widget.  Some code (e.g. Figure.show) differentiates between
+            # having *no* manager and a *None* manager, which should be fixed
+            # at some point, but this should be fine.
+            stack.enter_context(
+                cbook._setattr_cm(self, _is_saving=True, manager=None))
+            stack.enter_context(cbook._setattr_cm(self.figure, dpi=dpi))
             if facecolor is None:
                 facecolor = rcParams['savefig.facecolor']
+            if not cbook._str_equal(facecolor, 'auto'):
+                stack.callback(
+                    self.figure.set_facecolor, self.figure.get_facecolor())
+                self.figure.set_facecolor(facecolor)
             if edgecolor is None:
                 edgecolor = rcParams['savefig.edgecolor']
-
-            origfacecolor = self.figure.get_facecolor()
-            origedgecolor = self.figure.get_edgecolor()
-
-            self.figure.set_facecolor(facecolor)
-            self.figure.set_edgecolor(edgecolor)
+            if not cbook._str_equal(edgecolor, 'auto'):
+                stack.callback(
+                    self.figure.set_edgecolor, self.figure.get_edgecolor())
+                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(
@@ -2108,8 +2113,6 @@ def print_figure(self, filename, dpi=None, facecolor=None, edgecolor=None,
                 if bbox_inches and restore_bbox:
                     restore_bbox()
 
-                self.figure.set_facecolor(origfacecolor)
-                self.figure.set_edgecolor(origedgecolor)
                 self.figure.set_canvas(self)
             return result
 
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -587,8 +587,10 @@ def print_jpg(self, filename_or_obj, *args, dryrun=False,
             # The image is "pasted" onto a white background image to safely
             # handle any transparency
             image = Image.fromarray(np.asarray(self.buffer_rgba()))
-            rgba = mcolors.to_rgba(rcParams['savefig.facecolor'])
-            color = tuple([int(x * 255) for x in rgba[:3]])
+            facecolor = rcParams["savefig.facecolor"]
+            if cbook._str_equal(facecolor, "auto"):
+                facecolor = self.figure.get_facecolor()
+            color = tuple(int(x * 255) for x in mcolors.to_rgb(facecolor))
             background = Image.new('RGB', image.size, color)
             background.paste(image, image)
             if pil_kwargs is None:
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -2116,13 +2116,13 @@ def savefig(self, fname, *, transparent=None, **kwargs):
             progressive JPEG file. Applicable only if *format* is jpg or
             jpeg, ignored otherwise. Is *False* by default.
 
-        facecolor : color or None, optional
-            The facecolor of the figure; if *None*, defaults to
-            :rc:`savefig.facecolor`.
+        facecolor : color or 'auto' or None, optional
+            The facecolor of the figure.  If 'auto', use the current figure
+            facecolor.  If None, use :rc:`savefig.facecolor`.
 
-        edgecolor : color or None, optional
-            The edgecolor of the figure; if *None*, defaults to
-            :rc:`savefig.edgecolor`
+        edgecolor : color or 'auto' or None, optional
+            The edgecolor of the figure.  If 'auto', use the current figure
+            edgecolor.  If None, use :rc:`savefig.edgecolor`.
 
         orientation : {'landscape', 'portrait'}
             Currently only supported by the postscript backend.
@@ -2197,9 +2197,6 @@ def savefig(self, fname, *, transparent=None, **kwargs):
                                              patch.get_edgecolor()))
                 patch.set_facecolor('none')
                 patch.set_edgecolor('none')
-        else:
-            kwargs.setdefault('facecolor', rcParams['savefig.facecolor'])
-            kwargs.setdefault('edgecolor', rcParams['savefig.edgecolor'])
 
         if frameon:
             original_frameon = self.patch.get_visible()
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -1525,9 +1525,10 @@ 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(rcParams["savefig.facecolor"]))
+                facecolor = rcParams["savefig.facecolor"]
+                if cbook._str_equal(facecolor, "auto"):
+                    facecolor = rcParams["figure.facecolor"]
+                color = tuple(int(x * 255) for x in mcolors.to_rgb(facecolor))
                 background = Image.new("RGB", pil_shape, color)
                 background.paste(image, image)
                 image = background
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -297,13 +297,13 @@ 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)
 
@@ -1325,8 +1325,8 @@ def _validate_linestyle(ls):
 
     ## 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.frameon':     [True, validate_bool],
     'savefig.orientation': ['portrait', validate_orientation],
     'savefig.jpeg_quality': [95, validate_int],
diff --git a/matplotlibrc.template b/matplotlibrc.template
@@ -638,8 +638,8 @@
 ## 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
