consistent with the allocation currently done for PIX_FMT_GRAY8
pictures.

No significant slow-downs have been measured.

See the thread:
Subject: [FFmpeg-devel] [PATCH] Is gray8 a paletted format?
Date: Sun, 15 Nov 2009 23:36:03 +0100

Originally committed as revision 22191 to svn://svn.ffmpeg.org/ffmpeg/trunk