Merge pull request #7904 from radarhere/releasenotes

Added release notes for #7872, #7882 and #7891

docs/releasenotes/10.3.0.rst

@@ -61,10 +61,24 @@ Deprecated                                    Use instead
 API Changes
 ===========
 
-TODO
-^^^^
+Added alpha_quality argument when saving WebP images
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-TODO
+When saving WebP images, an ``alpha_quality`` argument can be passed to the encoder. It
+is an integer value between 0 to 100, where values other than 100 will provide lossy
+compression.
+
+Negative kmeans error
+^^^^^^^^^^^^^^^^^^^^^
+
+When calling :py:meth:`~PIL.Image.Image.quantize`, a negative ``kmeans`` will now
+raise a :py:exc:`ValueError`, unless a palette is supplied to make the value redundant.
+
+Negative P1-P3 PPM value error
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If a P1-P3 PPM image contains a negative value, a :py:exc:`ValueError` will now be
+raised.
 
 API Additions
 =============