Autoinfer norm bounds.

Instead of special-casing lognorm to only autoscale from positive
values, perform autoscaling from values that map to finite transformed
values.  This ensures e.g. that make_norm_from_scale(LogitScale)
automatically does the right thing (autoscaling from values in [0, 1]).

This means that autoscale() and autoscale_None() are now slightly more
expensive (because the transform needs to be applied), so skip the call
to autoscale_None if not needed.  However, note that these should
typically only be called once per norm anyways, so hopefully this isn't
a bottleneck.

(Another idea would be to use `trf.inverse().transform([-np.inf,
np.inf])` as clipping bounds, but there are some tests using `x->x**2`
/ `x->sqrt(x)` as a test for FuncNorm, which 1. doesn't go all the way
to -inf, and 2. isn't even increasing for negative x's, so that idea
doesn't work.)

Author: anntzer

lib/matplotlib/colors.py

@@ -1229,7 +1229,8 @@ def __call__(self, value, clip=None):
 
         result, is_scalar = self.process_value(value)
 
-        self.autoscale_None(result)
+        if self.vmin is None or self.vmax is None:
+            self.autoscale_None(result)
         # Convert at least to float, without losing precision.
         (vmin,), _ = self.process_value(self.vmin)
         (vmax,), _ = self.process_value(self.vmax)
@@ -1520,7 +1521,8 @@ def __init__(self, *args, **kwargs):
 
         def __call__(self, value, clip=None):
             value, is_scalar = self.process_value(value)
-            self.autoscale_None(value)
+            if self.vmin is None or self.vmax is None:
+                self.autoscale_None(value)
             if self.vmin > self.vmax:
                 raise ValueError("vmin must be less or equal to vmax")
             if self.vmin == self.vmax:
@@ -1555,6 +1557,15 @@ def inverse(self, value):
                      .reshape(np.shape(value)))
             return value[0] if is_scalar else value
 
+        def autoscale(self, A):
+            # i.e. A[np.isfinite(...)], but also for non-array A's
+            in_trf_domain = np.extract(np.isfinite(self._trf.transform(A)), A)
+            return super().autoscale(in_trf_domain)
+
+        def autoscale_None(self, A):
+            in_trf_domain = np.extract(np.isfinite(self._trf.transform(A)), A)
+            return super().autoscale_None(in_trf_domain)
+
     Norm.__name__ = (f"{scale_cls.__name__}Norm" if base_norm_cls is Normalize
                      else base_norm_cls.__name__)
     Norm.__qualname__ = base_norm_cls.__qualname__
@@ -1603,14 +1614,6 @@ def forward(values: array-like) -> array-like
 class LogNorm(Normalize):
     """Normalize a given value to the 0-1 range on a log scale."""
 
-    def autoscale(self, A):
-        # docstring inherited.
-        super().autoscale(np.ma.array(A, mask=(A <= 0)))
-
-    def autoscale_None(self, A):
-        # docstring inherited.
-        super().autoscale_None(np.ma.array(A, mask=(A <= 0)))
-
 
 @make_norm_from_scale(
     scale.SymmetricalLogScale,