diff options
| author | Ico Doornekamp <libav@zevv.nl> | 2016-03-24 14:31:38 +0100 |
|---|---|---|
| committer | Michael Niedermayer <michael@niedermayer.cc> | 2017-08-23 13:15:16 +0200 |
| commit | 7f3a3c2010e499e9cfc489156f993688f16e295d (patch) | |
| tree | 405d637c6b31f2e56b3305f92fd5591ec31a134c | |
| parent | 18254765391fd4f94eeb18e6544cef415a7b0a5c (diff) | |
| download | ffmpeg-7f3a3c2010e499e9cfc489156f993688f16e295d.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 ccd80ad7e8..cefc00a370 100644 --- a/libavformat/rtpdec_jpeg.c +++ b/libavformat/rtpdec_jpeg.c @@ -207,16 +207,17 @@ 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); |