diff options
| author | Ico Doornekamp <libav@zevv.nl> | 2016-03-24 14:31:38 +0100 |
|---|---|---|
| committer | Michael Niedermayer <michael@niedermayer.cc> | 2016-04-28 03:47:13 +0200 |
| commit | e112096885c556e45be5f973a3cbb4cfb8bf48fe (patch) | |
| tree | af92e499bd97d12bae7625dc40bc3ceae73b2c0f | |
| parent | c6bb7659726728d9c523b168f08c8d04aec75433 (diff) | |
| download | ffmpeg-e112096885c556e45be5f973a3cbb4cfb8bf48fe.tar.gz | |
avformat/rtpdec_jpeg: fix low contrast image on low quality setting
Original mail and my own followup on ffmpeg-user earlier today:
I have a device sending out a MJPEG/RTP stream on a low quality setting.
Decoding and displaying the video with libavformat results in a washed
out, low contrast, greyish image. Playing the same stream with VLC results
in proper color representation.
Screenshots for comparison:
http://zevv.nl/div/libav/shot-ffplay.jpg
http://zevv.nl/div/libav/shot-vlc.jpg
A pcap capture of a few seconds of video and SDP file for playing the
stream are available at
http://zevv.nl/div/libav/mjpeg.pcap
http://zevv.nl/div/libav/mjpeg.sdp
I believe the problem might be in the calculation of the quantization
tables in the function create_default_qtables(), the attached patch
solves the issue for me.
The problem is that the argument 'q' is of the type uint8_t. According to the
JPEG standard, if 1 <= q <= 50, the scale factor 'S' should be 5000 / Q.
Because the create_default_qtables() reuses the variable 'q' to store the
result of this calculation, for small values of q < 19, q wil subsequently
overflow and give wrong results in the calculated quantization tables. The
patch below uses a new variable 'S' (same name as in RFC2435) with the proper
range to store the result of the division.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit e3e6a2cff4af9542455d416faec4584d5e823d5d)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
| -rw-r--r-- | libavformat/rtpdec_jpeg.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/libavformat/rtpdec_jpeg.c b/libavformat/rtpdec_jpeg.c index 6bf88f8c3a..32655cc5ef 100644 --- a/libavformat/rtpdec_jpeg.c +++ b/libavformat/rtpdec_jpeg.c @@ -193,16 +193,17 @@ static void create_default_qtables(uint8_t *qtables, uint8_t q) { int factor = q; int i; + uint16_t S; factor = av_clip(q, 1, 99); if (q < 50) - q = 5000 / factor; + S = 5000 / factor; else - q = 200 - factor * 2; + S = 200 - factor * 2; for (i = 0; i < 128; i++) { - int val = (default_quantizers[i] * q + 50) / 100; + int val = (default_quantizers[i] * S + 50) / 100; /* Limit the quantizers to 1 <= q <= 255. */ val = av_clip(val, 1, 255); |