support gray16 pixel format in tiff

[dericed]

Summary of the bug:

I would like to use a 16 bit gray pixel format in tiff. I see gray8 but if I want 16 bit I need to use an rgb64 pixel format (which is a bit larger than necessary). Here's a command that attempted to create a 16 bit gray tiff image (ffmpeg uses rgb64le).

How to reproduce:

ffmpeg started on 2012-07-05 at 14:27:23
Report written to "ffmpeg-20120705-142723.log"
Command line:
ffmpeg -report -f lavfi -i testsrc -vframes 1 -pix_fmt gray16be 16bit_gray16le.tiff
ffmpeg version 0.11.1.git Copyright (c) 2000-2012 the FFmpeg developers
  built on Jul  5 2012 11:22:03 with gcc 4.2.1 (Apple Inc. build 5666) (dot 3)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --enable-libfreetype --cc=/usr/bin/gcc-4.2 --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-librtmp --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libxvid --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libass --enable-libvo-aacenc
  libavutil      51. 64.100 / 51. 64.100
  libavcodec     54. 33.100 / 54. 33.100
  libavformat    54. 15.100 / 54. 15.100
  libavdevice    54.  1.100 / 54.  1.100
  libavfilter     3.  0.101 /  3.  0.101
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[Parsed_testsrc_0 @ 0x7ff0c1418440] size:320x240 rate:25/1 duration:-1.000000 sar:1/1
[out @ 0x7ff0c1418960] No opaque field provided
[lavfi @ 0x7ff0c184e200] All info found
[lavfi @ 0x7ff0c184e200] Estimating duration from bitrate, this may be inaccurate
Input #0, lavfi, from 'testsrc':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0, 1, 1/25: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 320x240 [SAR 1:1 DAR 4:3], 25 tbr, 25 tbn, 25 tbc
[buffer @ 0x7ff0c1419ce0] Setting entry with key 'video_size' to value '320x240'
[buffer @ 0x7ff0c1419ce0] Setting entry with key 'pix_fmt' to value '2'
[buffer @ 0x7ff0c1419ce0] Setting entry with key 'time_base' to value '1/25'
[buffer @ 0x7ff0c1419ce0] Setting entry with key 'pixel_aspect' to value '1/1'
[buffer @ 0x7ff0c1419ce0] Setting entry with key 'sws_param' to value 'flags=2'
[buffer @ 0x7ff0c1419ce0] Setting entry with key 'frame_rate' to value '25/1'
[graph 0 input from stream 0:0 @ 0x7ff0c1419820] w:320 h:240 pixfmt:rgb24 tb:1/25 fr:25/1 sar:1/1 sws_param:flags=2
[output stream 0:0 @ 0x7ff0c141a020] No opaque field provided
Incompatible pixel format 'gray16be' for codec 'tiff', auto-selecting format 'rgb48le'
[format @ 0x7ff0c141a1a0] auto-inserting filter 'auto-inserted scaler 0' between the filter 'Parsed_null_0' and the filter 'format'
[auto-inserted scaler 0 @ 0x7ff0c141a660] w:320 h:240 fmt:rgb24 sar:1/1 -> w:320 h:240 fmt:rgb48le sar:1/1 flags:0x4
Output #0, image2, to '16bit_gray16le.tiff':
  Metadata:
    encoder         : Lavf54.15.100
    Stream #0:0, 0, 1/90000: Video: tiff, rgb48le, 320x240 [SAR 1:1 DAR 4:3], q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> tiff)
Press [q] to stop, [?] for help
No more output streams to write to, finishing.
frame=    1 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.04 bitrate=   0.0kbits/s    
video:399kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.000000%

[richardpl]

should be fixed.