Some small corrections.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84090 b8fc166d-592f-0410-95f2-cb63ce0dd405
More tests for subchroma image.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84091 b8fc166d-592f-0410-95f2-cb63ce0dd405