Refer to quantization method docs in Image.quantize()

All quantization methods are already documented in a dedicated
section. Don't duplicate that information in the documentation
of Image.quantize(). Link to the existing section.

docs/reference/Image.rst

@@ -479,6 +479,8 @@ Used to specify the pallete to use for the :meth:`~Image.convert` method.
 .. data:: WEB
 .. data:: ADAPTIVE
 
+.. _quantization-methods:
+
 Quantization methods
 ^^^^^^^^^^^^^^^^^^^^
 
@@ -486,11 +488,11 @@ Used to specify the quantization method to use for the :meth:`~Image.quantize` m
 
 .. data:: MEDIANCUT
 
-    Median cut
+    Median cut. RGBA not supported.
 
 .. data:: MAXCOVERAGE
 
-    Maximum coverage
+    Maximum coverage. RGBA not supported.
 
 .. data:: FASTOCTREE
 

src/PIL/Image.py

@@ -1054,9 +1054,8 @@ class Image:
 
         :param colors: The desired number of colors, <= 256
         :param method: :data:`MEDIANCUT` (default),
-                       :data:`MAXCOVERAGE`,
-                       :data:`FASTOCTREE` (default for RGBA images),
-                       :data:`LIBIMAGEQUANT`.
+                       :data:`FASTOCTREE` (default for "RGBA" mode).
+                       See :ref:`quantization-methods` for all available methods.
         :param kmeans: Integer
         :param palette: Quantize to the palette of given
                         :py:class:`PIL.Image.Image`.