Merge pull request matplotlib#21391 from anntzer/jpegbkg

Reuse imsave()'s background-blending code in FigureCanvasAgg.print_jpeg.

Author: greglucas

lib/matplotlib/backends/backend_agg.py

@@ -560,13 +560,11 @@ def print_to_buffer(self):
 
     @_api.delete_parameter("3.5", "args")
     def print_jpg(self, filename_or_obj, *args, pil_kwargs=None):
-        # Remove transparency by alpha-blending on an assumed white background.
-        r, g, b, a = mcolors.to_rgba(self.figure.get_facecolor())
-        try:
-            self.figure.set_facecolor(a * np.array([r, g, b]) + 1 - a)
+        # savefig() has already applied savefig.facecolor; we now set it to
+        # white to make imsave() blend semi-transparent figures against an
+        # assumed white background.
+        with mpl.rc_context({"savefig.facecolor": "white"}):
             self._print_pil(filename_or_obj, "jpeg", pil_kwargs)
-        finally:
-            self.figure.set_facecolor((r, g, b, a))
 
     print_jpeg = print_jpg