diff options
| author | Ico Doornekamp <libav@zevv.nl> | 2016-03-24 14:31:38 +0100 |
|---|---|---|
| committer | Martin Storsjö <martin@martin.st> | 2016-03-26 00:15:24 +0200 |
| commit | edf54887e2935a30f9d9a46dd806802c3c867c0e (patch) | |
| tree | 6966c30b43f4f130638df147f9eb5cca26de3114 /libavformat | |
| parent | 159323897f545e7405fb9db234e0ba123e174376 (diff) | |
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 <martin@martin.st>
Diffstat (limited to 'libavformat')
| -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 15324bf2ba..bc86b159de 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); |