Change pcolor and contourf default antialiasing to False; closes 3151847.

efiring · efiring · commit 5114b14121fc · 2011-01-16T01:00:37.000Z
To avoid misplaced boundaries and artifacts with alpha &lt; 1, we do not
stroke the pcolor and contourf patch boundaries by default; but without
that stroking, antialiasing produces boundary artifacts that tend to
be visually disturbing.  Therefore we sacrifice antialiasing for these
patches.

svn path=/branches/v1_0_maint/; revision=8920
diff --git a/lib/matplotlib/axes.py b/lib/matplotlib/axes.py
@@ -6921,14 +6921,14 @@ def pcolor(self, *args, **kwargs):
 
         %(PolyCollection)s
 
-        Note: the default *antialiaseds* is taken from
+        Note: the default *antialiaseds* is False if the default
+        *edgecolors*="none" is used.  This eliminates artificial lines
+        at patch boundaries, and works regardless of the value of
+        alpha.  If *edgecolors* is not "none", then the default
+        *antialiaseds* is taken from
         rcParams['patch.antialiased'], which defaults to *True*.
-        In some cases, particularly if *alpha* is 1,
-        you may be able to reduce rendering artifacts (light or
-        dark patch boundaries) by setting it to *False*.  An
-        alternative it to set *edgecolors* to 'face'.  Unfortunately,
-        there seems to be no single combination of parameters that
-        eliminates artifacts under all conditions.
+        Stroking the edges may be preferred if *alpha* is 1, but
+        will cause artifacts otherwise.
 
         """
 
@@ -6977,21 +6977,28 @@ def pcolor(self, *args, **kwargs):
 
         C = compress(ravelmask, ma.filled(C[0:Ny-1,0:Nx-1]).ravel())
 
+        linewidths = (0.25,)
+        if 'linewidth' in kwargs:
+            kwargs['linewidths'] = kwargs.pop('linewidth')
+        kwargs.setdefault('linewidths', linewidths)
+
         if shading == 'faceted':
             edgecolors = 'k',
         else:
             edgecolors = 'none'
-        linewidths = (0.25,)
-        # Not sure if we want to have the following, or just trap
-        # invalid kwargs and raise an exception.
         if 'edgecolor' in kwargs:
             kwargs['edgecolors'] = kwargs.pop('edgecolor')
-        if 'linewidth' in kwargs:
-            kwargs['linewidths'] = kwargs.pop('linewidth')
+        ec = kwargs.setdefault('edgecolors', edgecolors)
+
+        # aa setting will default via collections to patch.antialiased
+        # unless the boundary is not stroked, in which case the
+        # default will be False; with unstroked boundaries, aa
+        # makes artifacts that are often disturbing.
         if 'antialiased' in kwargs:
             kwargs['antialiaseds'] = kwargs.pop('antialiased')
-        kwargs.setdefault('edgecolors', edgecolors)
-        kwargs.setdefault('linewidths', linewidths)
+        if 'antialiaseds' not in kwargs and ec.lower() == "none":
+                kwargs['antialiaseds'] = False
+
 
         collection = mcoll.PolyCollection(verts, **kwargs)
 
diff --git a/lib/matplotlib/contour.py b/lib/matplotlib/contour.py
@@ -662,7 +662,14 @@ def __init__(self, ax, *args, **kwargs):
         self.colors = kwargs.get('colors', None)
         norm = kwargs.get('norm', None)
         self.extend = kwargs.get('extend', 'neither')
-        self.antialiased = kwargs.get('antialiased', True)
+        self.antialiased = kwargs.get('antialiased', None)
+        if self.antialiased is None and self.filled:
+            self.antialiased = False # eliminate artifacts; we are not
+                                     # stroking the boundaries.
+            # The default for line contours will be taken from
+            # the LineCollection default, which uses the
+            # rcParams['lines.antialiased']
+
         self.nchunk = kwargs.get('nchunk', 0)
         self.locator = kwargs.get('locator', None)
         if (isinstance(norm, colors.LogNorm)
@@ -734,11 +741,15 @@ def __init__(self, ax, *args, **kwargs):
             tlinewidths = self._process_linewidths()
             self.tlinewidths = tlinewidths
             tlinestyles = self._process_linestyles()
+            aa = self.antialiased
+            if aa is not None:
+                aa = (self.antialiased,)
             for level, width, lstyle, segs in \
                     zip(self.levels, tlinewidths, tlinestyles, self.allsegs):
                 # Default zorder taken from LineCollection
                 zorder = kwargs.get('zorder', 2)
                 col = collections.LineCollection(segs,
+                                     antialiaseds = aa,
                                      linewidths = width,
                                      linestyle = lstyle,
                                      alpha=self.alpha,
@@ -1358,6 +1369,10 @@ def _initialize_x_y(self, z):
             Override axis units by specifying an instance of a
             :class:`matplotlib.units.ConversionInterface`.
 
+          *antialiased*: [ True | False ]
+            enable antialiasing, overriding the defaults.  For
+            filled contours, the default is True.  For line contours,
+            it is taken from rcParams['lines.antialiased'].
 
         contour-only keyword arguments:
 
@@ -1385,9 +1400,6 @@ def _initialize_x_y(self, z):
 
         contourf-only keyword arguments:
 
-          *antialiased*: [ True | False ]
-            enable antialiasing
-
           *nchunk*: [ 0 | integer ]
             If 0, no subdivision of the domain. Specify a positive integer to
             divide the domain into subdomains of roughly *nchunk* by *nchunk*
