ffmpeg | branch: master | Ico Doornekamp <li...@zevv.nl> | Thu Mar 24 14:31:38 2016 +0100| [edf54887e2935a30f9d9a46dd806802c3c867c0e] | committer: Martin Storsjö
rtpdec_jpeg: fix low contrast image on low quality setting 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. Instead, use a new variable 'S' (same name as in RFC2435) with the proper range to store the result of the division. Signed-off-by: Martin Storsjö <mar...@martin.st> > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=edf54887e2935a30f9d9a46dd806802c3c867c0e --- libavformat/rtpdec_jpeg.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/libavformat/rtpdec_jpeg.c b/libavformat/rtpdec_jpeg.c index 15324bf..bc86b15 100644 --- a/libavformat/rtpdec_jpeg.c +++ b/libavformat/rtpdec_jpeg.c @@ -186,16 +186,17 @@ 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); _______________________________________________ ffmpeg-cvslog mailing list ffmpeg-cvslog@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-cvslog
