updating convert_to modes. [docs]

Author: bigcat88

docs/image-modes.rst

@@ -51,11 +51,13 @@ When saving image from `Pillow` to `HEIF` format, next modes will be converted a
 Mode conversion
 ---------------
 
+.. note:: HEIF standard does not support 16 bit images, see :ref:`saving-16bit`
+
 For ``HeifImage`` some of these modes can be converted to each other using :py:meth:`~pillow_heif.HeifImage.convert_to` method:
 
     * ``BGRA;16``  -->  ``RGBA;10`` or ``RGBA;12``
     * ``BGR;16``  -->  ``RGB;10`` or ``RGB;12``
-    * ``RGBA;16``  -->  ``RGBA;10`` or ``RGBA;12``
+    * ``RGBA;16``  -->  ``RGBA;10``, ``RGBA;12`` or ``RGBA``
     * ``RGB;16``  -->  ``RGB;10`` or ``RGB;12``
     * ``L;16``  -->  ``L;10`` or ``L;12``
     * ``I;16``  -->  ``L;10`` or ``L;12``
@@ -68,13 +70,11 @@ For ``HeifImage`` some of these modes can be converted to each other using :py:m
     * ``BGR``  -->  ``RGB``
     * ``RGBA``  -->  ``BGRA``, ``RGBA;16`` or ``BGRA;16``
     * ``RGB``  -->  ``BGR``, ``RGB;16`` or ``BGR;16``
-    * ``BGRA;16`` <--> ``BGRa;16``
-    * ``BGRA;12`` <--> ``BGRa;12``
-    * ``BGRA;10`` <--> ``BGRa;10``
-    * ``BGRA`` <--> ``BGRa``
-    * ``RGBA;16`` <--> ``RGBa;16``
-    * ``RGBA;12`` <--> ``RGBa;12``
-    * ``RGBA;10`` <--> ``RGBa;10``
-    * ``RGBA`` <--> ``RGBa``
 
-.. note:: HEIF standard does not support 16 bit images, see :ref:`saving-16bit`
+Modes with premultiplied Alpha:
+    * ``BGRa;16``  -->  ``RGBa;10`` or ``RGBa;12``
+    * ``RGBa;16``  -->  ``RGBa;10``, ``RGBa;12`` or ``RGBa``
+    * ``RGBa;12``  -->  ``RGBa;16`` or ``BGRa;16``
+    * ``RGBa;10``  -->  ``RGBa;16`` or ``BGRa;16``
+    * ``BGRa``  -->  ``RGBa``
+    * ``RGBa`` --> ``RGB``, ``BGR``, ``RGBa;16`` or ``BGRa;16``