Add an rcparam for image.interpolation_stage.

Author: anntzer

doc/users/next_whats_new/interpolation_stage_rc.rst

@@ -0,0 +1,4 @@
+``image.interpolation_stage`` rcParam
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This new rcParam controls whether image interpolation occurs in "data" space or
+in "rgba" space.

lib/matplotlib/image.py

@@ -789,10 +789,9 @@ def set_interpolation_stage(self, s):
         ----------
         s : {'data', 'rgba'} or None
             Whether to apply up/downsampling interpolation in data or RGBA
-            space.
+            space.  If None, use :rc:`image.interpolation_stage`.
         """
-        if s is None:
-            s = "data"  # placeholder for maybe having rcParam
+        s = mpl._val_or_rc(s, 'image.interpolation_stage')
         _api.check_in_list(['data', 'rgba'], s=s)
         self._interpolation_stage = s
         self.stale = True

lib/matplotlib/mpl-data/matplotlibrc

@@ -603,6 +603,7 @@
 ## ***************************************************************************
 #image.aspect:          equal        # {equal, auto} or a number
 #image.interpolation:   antialiased  # see help(imshow) for options
+#image.interpolation_stage: data     # see help(imshow) for options
 #image.cmap:            viridis      # A colormap name (plasma, magma, etc.)
 #image.lut:             256          # the size of the colormap lookup table
 #image.origin:          upper        # {lower, upper}

lib/matplotlib/rcsetup.py

@@ -1051,12 +1051,13 @@ def _convert_validator_spec(key, conv):
                                 "bb", "frak", "scr", "regular"],
     "mathtext.fallback":       _validate_mathtext_fallback,
 
-    "image.aspect":          validate_aspect,  # equal, auto, a number
-    "image.interpolation":   validate_string,
-    "image.cmap":            _validate_cmap,  # gray, jet, etc.
-    "image.lut":             validate_int,  # lookup table
-    "image.origin":          ["upper", "lower"],
-    "image.resample":        validate_bool,
+    "image.aspect":              validate_aspect,  # equal, auto, a number
+    "image.interpolation":       validate_string,
+    "image.interpolation_stage": ["data", "rgba"],
+    "image.cmap":                _validate_cmap,  # gray, jet, etc.
+    "image.lut":                 validate_int,  # lookup table
+    "image.origin":              ["upper", "lower"],
+    "image.resample":            validate_bool,
     # Specify whether vector graphics backends will combine all images on a
     # set of Axes into a single composite image
     "image.composite_image": validate_bool,

lib/matplotlib/tests/test_image.py

@@ -1462,6 +1462,15 @@ def test_rgba_antialias():
                   cmap=cmap, vmin=-1.2, vmax=1.2)
 
 
+def test_rc_interpolation_stage():
+    for val in ["data", "rgba"]:
+        with mpl.rc_context({"image.interpolation_stage": val}):
+            assert plt.imshow([[1, 2]]).get_interpolation_stage() == val
+    for val in ["DATA", "foo", None]:
+        with pytest.raises(ValueError):
+            mpl.rcParams["image.interpolation_stage"] = val
+
+
 # We check for the warning with a draw() in the test, but we also need to
 # filter the warning as it is emitted by the figure test decorator
 @pytest.mark.filterwarnings(r'ignore:Data with more than .* '